WO2018193454A1

WO2018193454A1 - Microfluidic head for laser induced forward transfer

Info

Publication number: WO2018193454A1
Application number: PCT/IL2018/050440
Authority: WO
Inventors: Aryeh Batt; Amos Eitan; Ariel EISENBACH
Original assignee: Precise Bio Inc.; Precise Bio 3D Ltd
Priority date: 2017-04-19
Filing date: 2018-04-18
Publication date: 2018-10-25

Abstract

Methods and systems for Laser-Induced Forward Transfer are disclosed in which a microfluidic chip is used as the printing head. The head comprises a transparent upper layer, a middle layer comprising an ink channel, and a lower layer region that comprises an orifice that is in fluid contact with the ink channel. When a pulse of energy is applied to ink flowing through the ink channel, typically irradiation by the output of a pulsed laser,, a transient pressure increase is generated that forces ink out of the orifice and onto a receiving substrate.

Description

MICROFLUIDIC HEAD FOR LASER INDUCED FORWARD TRANSFER

REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from U.S. Provisional Pat. Appl. No. 62/487,018, filed 19 April 2017, which is incorporated by reference in its entirety.

FIELD OF THE INVENTION

[0002] This invention relates in general to means and methods for Laser Induced Forward Transfer (LIFT). It relates in particular to a microfluidic head for LIFT.

BACKGROUND OF THE INVENTION

[0003] Laser Induced Forward Transfer (LIFT) is a printing process, particularly for 3-D printing, that is useful for printing of rigid, highly viscous, or sensitive materials. While LIFT can provide a resolution that is higher than other printing methods, LIFT methods currently known in the art are of limited efficiency in some uses (particularly for bio-printing) because they tend to require a long preliminary preparation process and complex system design. A general review of the state of the art can be found in the article "Laser Direct-Write Techniques for Printing of Complex Materials" (Arnold, C.B.; Serra, P.; Pique, A. MRS Bull. 32, 2007, 23-31), which is hereby incorporated by reference in its entirety.

[0004] The standard LIFT process known in the art is illustrated schematically in FIG. 1. A typical LIFT system 10 comprises a block 100 that delivers material to a receiving substrate 150 upon activation by the output 110 of a pulsed laser (the laser itself is not shown in the figure). Block 100 is suspended in the air near the receiving substrate. Block 100 comprises a substrate 120 that is made of a material that is transparent at the wavelength of the laser output. Substrate 120 is coated with an intermediate layer 130 that is made from a material, typically a metal or polymer, that absorbs strongly at the wavelength of the laser output. A third layer 140 comprising the material to be deposited on the receiving substrate (hereinafter referred to as "ink") coats the intermediate layer, facing the receiving substrate as shown in the illustration. The laser is typically focused on the intermediate layer so that each pulse will deliver its energy to a small spot at the interface between transparent substrate 120 and the intermediate layer.

[0005] When the laser is activated, the light pulse delivers energy to a spot on the intermediate layer, creating a bubble of vapor 135. When the bubble of vapor collapses, it generates a transient high pressure in the direction of the ink layer 140, thereby forming a jet of ink 145, which is deposited on a region 155 of the receiving substrate. The relative positions of block 100, laser output 110, and receiving substrate 150 are then adjusted such that each successive laser pulse irradiate fresh intermediate layer, and deposits the ink on a different region of the receiving substrate if so desired. If the ink itself absorbs sufficiently strongly at the wavelength of the laser output, then the ink layer can be coated directly onto the transparent substrate without any need for the intermediate layer.

[0006] U.S. Pat. No. 9446618, which is hereby incorporated by reference in its entirety, discloses an improved LIFT system and method. In this "Renewable LIFT" system 20, schematically illustrated in FIG. 2, instead of separate ink and intermediate layers, the system utilizes liquid or gel ink 240 contained in a reservoir 260 that has an orifice 265 facing the receiving substrate 250. Inlet 270 allows a constant flow of ink into the reservoir. In Renewable LIFT, laser output 240 is focused via transparent substrate 220 directly into the ink. Vapor bubble 235 is formed within the reservoir and upon collapse produces a pressure spike that forces a jet of ink 245 through the orifice and onto the receiving substrate at location 255. Reservoir inlet 270 permits refilling of the reservoir, or alternatively, a constant flow of ink into and through the reservoir.

[0007] While Renewable LIFT allows high throughput and resolution of 10 μιη or even less, it also suffers from some drawbacks. Because of mixing, diffusion, and variable flow stability, it is not possible to include an intermediate layer in Renewable LIFT systems. Moreover, precise control of the level of the meniscus of the ink layer is difficult, and the meniscus geometry can vary over time due to such factors as the humidity, atmospheric pressure, etc.

[0008] Thus, there remains a long-felt yet unmet need for a LIFT method and system that can overcome these limitations of currently known LIFT systems while maintaining high throughput and high resolution, and that comprises relatively inexpensive components.

SUMMARY OF THE INVENTION

[0009] The system disclosed herein is designed to meet this long-felt need. Instead of an arrangement that includes components such as block 100 or reservoir 260, the inventive system and method uses an integrated microfluidic chip (MFC) that controls and stabilizes the flow of ink. The MFC comprises a material that is substantially transparent at the laser output wavelength to transmit the laser fluence to the ink; at least one channel embedded in the chip through which the ink flows, and a small orifice through which droplets of ink are ejected to the receiving substrate. The shallow channel decreases the Reynolds number of the flow, thereby maintaining the ink thickness and velocity in front of the orifice by suppressing turbulence within the flow.

[0010] It is therefore an object of the present invention to disclose a Laser-Induced Forward Transfer (LIFT) printing head (300), wherein said LIFT printing head comprises a microfluidic chip (MFC), said MFC comprising three regions: an upper region (320); a middle region (330) comprising at least one ink channel (3300), said ink channel comprising an inlet (3301) and an outlet (3302); and, a bottom region (340), said bottom region comprising an orifice (365) in fluid connection with said ink channel.

[0011] It is a further object of this invention to disclose such a LIFT printing head, wherein said orifice opens to a side of said MFC intersected by a line connecting said three regions.

[0012] It is a further object of this invention to disclose such a LIFT printing head, wherein said orifice opens to a side of said MFC not intersected by a line connecting said three regions.

[0013] It is a further object of this invention to disclose a LIFT printing head as defined in any of the above, wherein said at least one ink channel is characterized by a height of between about 20 μιη and about 1 mm and a width of between about 50 μιη and about 3 mm.

[0014] It is a further object of this invention to disclose a LIFT printing head as defined in any of the above, wherein said inlet and said outlet are configured to connect to standard connectors.

[0015] It is a further object of this invention to disclose a LIFT printing head as defined in any of the above, wherein said inlet is configured to connect to one type of connector and said outlet is configured to connect to a different type of connector.

[0016] It is a further object of this invention to disclose a LIFT printing head as defined in any of the above, wherein said inlet and said outlet have different areas. In some embodiment of the invention, said inlet and said outlet have similar shapes. In other embodiments of the invention, said inlet and said outlet have different shapes.

[0017] It is a further object of this invention to disclose a LIFT printing head as defined in any of the above, wherein said MFC is constructed of material selected from the group consisting of PMMA, COC, glass, metal, and ceramic. In some preferred embodiments of the invention, said MFC is constructed of a rigid polymer with glass embedded in said upper region.

[0018] It is a further object of this invention to disclose a Laser-Induced Forward Transfer (LIFT) printing system, comprising: an energy source; a receiving substrate (350); and, at least one printing head (300) disposed between said energy source and said receiving substrate such that ink within said printing head is irradiated by energy output of said energy source and a jet of ink produced by said printing head following its irradiation by said energy output will exit said printing head toward said receiving substrate; wherein said printing head comprises a microfluidic chip (MFC), said MFC comprising three regions: an upper region (320) substantially transparent to energy output of said energy source; a middle region (330) comprising at least one ink channel (3300), said ink channel comprising an inlet (3301) and an outlet (3302); and, a bottom region (340), said bottom region comprising an orifice (365) in fluid connection with said ink channel.

[0019] It is a further object of this invention to disclose such a system, wherein said system is configured such that a line collinear with said output of said energy source passes through said orifice.

[0020] It is a further object of this invention to disclose such a system, wherein said orifice opens to a side of said MFC not intersected by a line connecting said three regions.

[0021] It is a further object of this invention to disclose a LIFT printing system as defined in any of the above, wherein said energy source comprises at least one laser providing pulsed output (310). In some preferred embodiments of the invention, the system comprises focusing means configured to focus said laser output to a spot characterized by a radius of between about 1 μιη and about 1 mm.

[0022] In some preferred embodiments of the invention in which said energy source comprises at least one laser providing pulsed output, said system comprises ink, and said laser is configured to provide output at a wavelength at which said ink absorbs and of sufficient energy such that upon irradiation by said output, said ink is at least partially evaporated.

[0023] In some preferred embodiments of the invention in which said energy source comprises at least one laser providing pulsed output, said system comprises ink, and said laser is configured to provide output at a wavelength at which said ink absorbs and of sufficient energy such that upon irradiation by said output, said ink is at least partially ablated.

[0024] In some preferred embodiments of the invention in which said energy source comprises at least one laser providing pulsed output, said system comprises ink and is characterized by an ink-air interface at said orifice, wherein said laser is configured to provide output at a wavelength at which said ink absorbs and of sufficient energy such that upon irradiation by said output, a pressure wave is propagated through said ink, resulting in a deformation of said ink-air interface.

[0025] In some preferred embodiments of the invention in which said energy source comprises at least one laser providing pulsed output, said system comprises ink dissolved in a solvent, wherein said laser is configured to provide output at a wavelength at which said solvent absorbs and of sufficient energy such that upon irradiation by said output, said solvent is at least partially evaporated.

[0026] In some preferred embodiments of the invention in which said energy source comprises at least one laser providing pulsed output, said system comprises ink, and said laser is configured to provide output of sufficient energy such that upon irradiation by said output, said ink is at least partially evaporated due to non-linear interactions with said output.

[0027] In some preferred embodiments of the invention in which said energy source comprises at least one laser providing pulsed output, said system comprises ink and an additive mixed with said ink, and said laser is configured to provide output at a wavelength at which said additive absorbs and of sufficient energy such that upon irradiation by said output, said solvent is at least partially evaporated. In some preferred embodiments of the invention, said additive is a dye or pigment. In some preferred embodiments of the invention, said additive is dissolved in said ink. In some preferred embodiments of the invention, said additive is suspended in said ink. In some other particularly preferred embodiments of the invention, said additive is selected from the group consisting of food coloring additives, anthocyanin pigments, hemoglobin, β-carotene, melanin, metallic compounds, organometallic compounds, organic compounds, metallic nanoparticles, organometallic nanoparticles, and organic nanoparticles.

[0028] In some preferred embodiments of the invention in which said energy source comprises at least one laser providing pulsed output, said system comprises focusing means for focusing said pulsed output to a predetermined location. In some particularly preferred embodiments, said predetermined location is selected from the group consisting of: an interface between said at least one ink channel and said upper region; and, within said ink channel.

[0029] It is a further object of this invention to disclose a LIFT printing system as defined in any of the above, comprising at least one optical fiber disposed so as to transmit said pulsed output from said laser to said printing head. In some preferred embodiments of the invention, said optical fiber is inserted into said MFC and immersed in said ink. In some other preferred embodiments of the invention, said optical fiber is kept outside of the MFC, and said system comprises collimating and focusing means configured to collimate light emitted from said optical fiber to refocus said light into said MFC. In some preferred embodiments of the invention, the system comprises focuser embedded at an end of said optical fiber and configured to focus light emitted from said end of said optical fiber to a predetermined location. In some preferred embodiments of the invention, the system comprises scanning means and/or alignment means configured to direct light emitted from said end of said optical fiber to a predetermined location. In some particularly preferred embodiments of the invention, said scanning means and/or alignment means are selected from the group consisting of GALVO and MEMS.

[0030] In some preferred embodiments of the invention in which the system comprises an optical fiber, said optical fiber is selected from the group consisting of hollow-core optical fibers and photonic-crystal fibers (PCFs).

[0031] It is a further object of this invention to disclose a LIFT printing system as defined in any of the above, wherein said orifice opens to a side of said MFC intersected by a line connecting said three regions.

[0032] It is a further object of this invention to disclose a LIFT printing system as defined in any of the above, wherein said orifice opens to a side of said MFC not intersected by a line connecting said three regions.

[0033] It is a further object of this invention to disclose a LIFT printing system as defined in any of the above, wherein said at least one ink channel is characterized by a height of between about 20 μιη and about 1 mm and a width of between about 50 μιη and about 3 mm.

[0034] It is a further object of this invention to disclose a LIFT printing system as defined in any of the above, wherein said inlet and said outlet are configured to connect to standard connectors. [0035] It is a further object of this invention to disclose a LIFT printing system as defined in any of the above, wherein said inlet is configured to connect to one type of connector and said outlet is configured to connect to a different type of connector.

[0036] It is a further object of this invention to disclose a LIFT printing system as defined in any of the above, wherein said inlet and said outlet have different areas. In some preferred embodiments of the printing system, said inlet and said outlet have similar shapes. In some other preferred embodiments of the printing system, said inlet and said outlet have different shapes.

[0037] It is a further object of this invention to disclose a LIFT printing system as defined in any of the above, wherein said MFC is constructed of material selected from the group consisting of PMMA, COC, glass, metal, and ceramic. In some preferred embodiments of the printing system, wherein said MFC is constructed of a rigid polymer with glass embedded in said upper region.

[0038] It is a further object of this invention to disclose a LIFT printing system as defined in any of the above, comprising pumping means for pumping ink through said ink channel.

[0039] It is a further object of this invention to disclose a LIFT printing system as defined in any of the above, comprising a reservoir in fluid connection with said inlet.

[0040] It is a further object of this invention to disclose a LIFT printing system as defined in any of the above, comprising a reservoir in fluid connection with said inlet and with said outlet.

[0041] It is a further object of this invention to disclose a LIFT printing system as defined in any of the above, wherein at least one of said head and said receiving substrate is mounted on an XYZ stage having a precision of +1 μιη or better in each direction.

[0042] It is a further object of this invention to disclose a LIFT printing system as defined in any of the above, comprising n printing heads, n > 1. In some preferred embodiments of the invention, said energy source is configured to irradiate each of said n printing heads sequentially. In some preferred embodiments of the invention, said energy source comprises n energy sources, each of which is configured to irradiate one of said n printing heads.

[0043] It is a further object of this invention to disclose a LIFT printing system as defined in any of the above, wherein said head is located above said receiving substrate. [0044] It is a further object of this invention to disclose a LIFT printing system as defined in any of the above, wherein said head is located below said receiving substrate.

[0045] It is a further object of this invention to disclose a LIFT printing system as defined in any of the above, wherein said head is located alongside said receiving substrate.

[0046] It is a further object of this invention to disclose a LIFT printing system as defined in any of the above, wherein said system is in a location characterized by an environment, said system comprising environmental control means configured to control at least one environmental parameter of said environment. In some preferred embodiments of the system, said at least one environmental parameter is selected from the group consisting of temperature, humidity, C0₂ concentration, and 0₂ concentration.

[0047] It is a further object of this invention to disclose a LIFT printing system as defined in any of the above, wherein said MFC is separated from said receiving substrate by a distance of between about 50 μιη and about 5 mm.

[0048] It is a further object of this invention to disclose a method for Laser-Induced Forward Transfer (LIFT) printing, wherein said method comprises:

[0049] flowing ink through at least one ink channel (3300) passing through a printing head (300) comprising a microfluidic chip (MFC), said MFC characterized by three generally vertically disposed regions:

[0050] an upper region (320);

[0051] a middle region (330) comprising said at least one ink channel (3300), said ink channel comprising an inlet (3301) and an outlet (3302); and,

[0052] a bottom region (340), said bottom region comprising an orifice (365) in fluid connection with said ink channel;

[0053] irradiating said ink with output (310) of an energy source, said output having sufficient energy at a location at which said ink is irradiated to cause ink to be ejected from said orifice; and,

[0054] receiving said ink forced out of said orifice on at least one predetermined location on a receiving substrate (350).

[0055] It is a further object of this invention to disclose such a method, wherein said step of irradiating said ink comprises irradiating said ink with output of said energy source sufficient to at least partially evaporate said ink at a location at which said output intersects said flow of said ink, said location at a position along said ink channel opposite to said orifice such that upon collapse of a vapor bubble formed upon said irradiation, a transient pressure increase is created, thereby forcing ink out of said orifice.

[0056] It is a further object of this invention to disclose the method as defined in any of the above, wherein said step of irradiating said ink comprises irradiating said ink with output of said energy source sufficient to generate a pressure wave that propagates within said ink, resulting in a deformation of an ink-air interface at said orifice and thereby forcing ink out of said orifice.

[0057] It is a further object of this invention to disclose the method as defined in any of the above, wherein said step of flowing ink comprises flowing said ink at a flow rate of between about 0.1 mm s^"1 and about 1 m s^"1.

[0058] It is a further object of this invention to disclose the method as defined in any of the above, wherein said step of flowing ink comprises flowing said ink at a volumetric flow rate of less than 0.01 μL· s^"1.

[0059] It is a further object of this invention to disclose the method as defined in any of the above, wherein said upper region is substantially transparent to said energy output.

[0060] It is a further object of this invention to disclose the method as defined in any of the above, wherein said step of irradiating comprises irradiating with output of a pulsed laser.

[0061] It is a further object of this invention to disclose the method as defined in any of the above, wherein said step of irradiating comprises irradiating by light characterized as comprising a wavelength at which said ink absorbs.

[0062] It is a further object of this invention to disclose the method as defined in any of the above, comprising dissolving said ink in a solvent, wherein said step of irradiating comprises irradiating by light characterized as comprising a wavelength at which said solvent absorbs.

[0063] It is a further object of this invention to disclose the method as defined in any of the above, said step of irradiating comprises irradiating with sufficient energy such that said ink is at least partially evaporated due to non-linear interactions with said output.

[0064] It is a further object of this invention to disclose the method as defined in any of the above, comprising mixing an additive with said ink, wherein said step of irradiating comprises irradiating at a wavelength at which said additive absorbs. In some preferred embodiments of the method, said step of mixing an additive with said ink comprises mixing an additive selected from the group consisting of dyes and pigments to said ink. In some particularly preferred embodiments of the method, said additive is selected from the group consisting of food coloring additives, anthocyanin pigments, hemoglobin, β-carotene, melanin, metallic compounds, organometallic compounds, organic compounds, metallic nanoparticles, organometallic nanoparticles, and organic nanoparticles.

[0065] It is a further object of this invention to disclose the method as defined in any of the above, comprising focusing said output at a location selected from the group consisting of: an interface between said at least one ink channel and said upper region; and, within said ink channel. In some preferred embodiments of the invention, said step of focusing comprises focusing said output to a spot characterized by a radius of between about 1 μιη and about 1 mm.

[0066] It is a further object of this invention to disclose the method as defined in any of the above, wherein said step of irradiating comprises transmitting said pulsed output from said laser to said printing head by means of an optical fiber. In some preferred embodiments of the method, said optical fiber is inserted into said MFC and immersed in said ink. In some other preferred embodiments of the invention, said optical fiber is kept outside of the MFC, said method comprising collimating and focusing light emitted from said optical fiber. In some preferred embodiments of the method, it comprises focusing light emitted from said end of said optical fiber to a predetermined location by means of a focuser embedded at an end of said optical fiber from which light is emitted. In some preferred embodiments of the method, it comprises aligning light emitted from said end of said optical fiber to a predetermined location by use of scanning means and/or alignment means. In some particularly preferred embodiments of the method, said scanning means and/or alignment means is selected from the group consisting of GALVO and MEMS. In some preferred embodiments of the method, said optical fiber is selected from the group consisting of hollow-core optical fibers and photonic-crystal fibers (PCFs).

[0067] It is a further object of this invention to disclose the method as defined in any of the above, wherein said orifice opens to a side of said MFC intersected by a line connecting said three regions. [0068] It is a further object of this invention to disclose the method as defined in any of the above, wherein said orifice opens to a side of said MFC not intersected by a line connecting said three regions.

[0069] It is a further object of this invention to disclose the method as defined in any of the above, wherein said step of flowing ink through at said least one ink channel comprises flowing ink through at least one ink channel characterized by a height of between about 20 μηι and about 1 mm and a width of between about 50 μιη and about 3 mm.

[0070] It is a further object of this invention to disclose the method as defined in any of the above, wherein said inlet and said outlet are configured to connect to standard connectors.

[0071] It is a further object of this invention to disclose the method as defined in any of the above, wherein said inlet is configured to connect to one type of connector and said outlet is configured to connect to a different type of connector.

[0072] It is a further object of this invention to disclose the method as defined in any of the above, wherein said inlet and said outlet have different areas. In some embodiments of the method, said inlet and said outlet have similar shapes. In some other embodiments of the method, said inlet and said outlet have different shapes.

[0073] It is a further object of this invention to disclose the method as defined in any of the above, wherein said MFC is constructed of material selected from the group consisting of PMMA, COC, glass, metal, and ceramic. In some preferred embodiments of the method, said MFC is constructed of a rigid polymer with glass embedded in said upper region.

[0074] It is a further object of this invention to disclose the method as defined in any of the above, comprising pumping ink through said ink channel.

[0075] It is a further object of this invention to disclose the method as defined in any of the above, wherein said step of flowing ink comprises flowing ink withdrawn from a reservoir in fluid contact with said inlet.

[0076] It is a further object of this invention to disclose the method as defined in any of the above, comprising recirculating said ink via a reservoir in fluid connection with said inlet and with said outlet.

[0077] It is a further object of this invention to disclose the method as defined in any of the above, comprising positioning at least one of said head and said receiving substrate on an XYZ stage having a precision of +1 μιη or better in each direction. [0078] It is a further object of this invention to disclose the method as defined in any of the above, wherein said step of flowing comprises flowing said ink through channels in n printing heads, n > 1, and said step of irradiating comprises irradiating ink in each of said n printing heads. In some preferred embodiments of the method, said step of irradiating comprises irradiating each of said n printing heads sequentially. In some other preferred embodiments of the method, said step of irradiating comprises irradiating with the output of n energy sources, each of which is configured to irradiate one of said n printing heads.

[0079] It is a further object of this invention to disclose the method as defined in any of the above, wherein said printing head is located above said receiving substrate.

[0080] It is a further object of this invention to disclose the method as defined in any of the above, wherein said printing head is located below said receiving substrate.

[0081] It is a further object of this invention to disclose the method as defined in any of the above, wherein said printing head is located alongside said receiving substrate.

[0082] It is a further object of this invention to disclose the method as defined in any of the above, comprising changing at least one parameter during said LIFT printing, said at least one parameter selected from the group consisting of: distance between said printing head and said receiving substrate; and, orientation of printing head relative to said receiving substrate. In some embodiments of the invention, said step of changing at least one parameter comprises changing said at least one parameter continuously. In some other embodiments of the invention, said step of changing at least one parameter comprises: changing said at least one parameter by a predetermined amount; holding said at least one parameter constant for a predetermined time; and, repeating the previous two steps until said LIFT printing is complete.

[0083] It is a further object of this invention to disclose the method as defined in any of the above, wherein said system is in a location characterized by an environment, said method comprising controlling at least one environmental parameter of said environment. In some preferred embodiments of the invention, said step of controlling at least one environmental parameter comprises controlling at least one environmental parameter selected from the group consisting of temperature, humidity, C0₂ concentration, and 0₂ concentration.

[0084] It is a further object of this invention to disclose the method as defined in any of the above, wherein said step of irradiating is performed repeatedly at a repetition rate of between 100 Hz and 100 kHz. BRIEF DESCRIPTION OF THE DRAWINGS

[0085] The invention will now be described with reference to the drawings, wherein:

[0086] FIG. 1 illustrates schematically the principles of LIFT as known in the art;

[0087] FIG. 2 illustrates schematically a second type of LIFT system known in the art;

[0088] FIG. 3 illustrates schematically a typical embodiment of a LIFT system of the present invention that incorporates a microfluidic chip as a LIFT head, with FIG. 3A showing a schematic cross-sectional view and FIG. 3B showing a schematic three-dimensional view illustrating the flow of ink through the microfluidic chip; and,

[0089] FIGs. 4A and 4B illustrate schematically two views of an embodiment of a microfluidic chip LIFT head of the present invention in which the irradiation of the ink within the ink channel is not coplanar with the direction of the ink jet expelled from the chip.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0090] In the following description, various aspects of the invention will be described. For the purposes of explanation, specific details are set forth in order to provide a thorough understanding of the invention. It will be apparent to one skilled in the art that there are other embodiments of the invention that differ in details without affecting the essential nature thereof. In some cases, for clarity or conciseness, individual elements of the invention (system components or method steps) are discussed separately. Nonetheless, any combination of individual elements disclosed herein that is not self-contradictory is considered by the inventors to be within the scope of the invention.

[0091] As used herein, the abbreviation "LIFT" stands for "Laser Induced Forward Transfer."

[0092] As used herein, the abbreviation "MFC" stands for "microfluidic chip."

[0093] As used herein, the term "ink" refers to any substance that is deposited from the MFC head onto a receiving substrate.

[0094] As used herein, with reference to LIFT printing, the term "ink jet" refers to ink expelled from a LIFT device to be deposited on a substrate. The "jet" may comprise a stream of ink or one or more droplets.

[0095] As used herein, with reference to numerical quantities the term "about" refers to a value within a range of + 25% of the nominal quantity. [0096] In the following description of the LIFT system of the present invention, for simplicity, embodiments of the system and method are described in which the output of a pulsed laser is used as the energy source for creating the jet of ink that is sent to the receiving substrate. Since the general principle of LIFT involves the use of an energy pulse that creates the conditions that lead to the pressure transient rather than an energy pulse emanating specifically from a laser, any method for creating an energy pulse sufficiently strong to cause the creation of an ink jet via forward transfer of energy is considered by the inventors to be within the scope of the invention. Non-limiting examples of other energy sources that can be used in the present invention include electric arcs and flashlamps.

[0097] In addition, in the following description of the geometry of the MFC print head, the terms "upper," "middle," and "lower" are used to describe three regions into which the MFC is divided. The terms do not necessarily refer to the absolute physical locations of the regions in space, but rather are used for simplicity and convenience to describe the general construction of the MFC. In this context, the term "upper" refers to that region of the MFC through which energy is transferred from an energy source to ink located in an ink channel inside the MFC; the term "lower" refers to that region of the MFC that contains an orifice from which ink is expelled from the MFC head towards a receiving substrate; and the term "middle" refers to that region of the MFC that contains a channel through which ink flows during the LIFT process. While in some embodiments of the invention, the regions are disposed generally vertically one above the other, the terms are not to be construed to limit the construction of the MFC to any specific arrangement of the three regions.

[0098] It is within the scope of the invention to disclose a LIFT printing head that is incorporated into an MFC, as well to disclose a LIFT system in which the LIFT printing head is an MFC. The MFC can be made of any appropriate rigid material. Non-limiting examples of typical materials of construction include polymers such as PMMA and COC as well as materials such as glass, metal, ceramic, etc. In some embodiments of the invention, the MFC is made of a polymer such as PMMA, and glass is embedded in the upper region of the MFC, described in detail below, in order to prevent damage to the chip by the high temperatures and pressures that are developed during the LIFT process.

[0099] Reference is now made to FIG. 3, which presents a schematic diagram of a typical embodiment 30 of a LIFT system of the present invention. The system comprises an MFC 300 which serves as the LIFT head, and a receiving substrate 350. The MFC comprises three regions: a relatively thick upper region 320, which is typically a few mm thick; a relatively thin middle region 330 that comprises at least one ink channel 3300, each ink channel having an inlet 3301 for introducing a flow of ink into the ink channel and an outlet 3302 from which the flow of ink exits the ink channel; and a relatively thin bottom region 340 that includes an orifice 365 facing the receiving substrate. In the embodiment of the invention illustrated in FIG. 3, orifice 365 is at the bottom of the MFC. In other embodiments of the invention (not illustrated in the figure), orifice 365 is placed at the side of the MFC rather than at the bottom.

[0100] In some embodiments of the invention, the different regions are separate physical layers. In other embodiments of the invention, the MFC is constructed as a single block comprising the three regions, for example, by using a 3D printer, sintering, or deep laser ablation. Any method known in the art may be used to construct the MFC. In the discussion that follows, for clarity, the different regions are described as independent entities. Embodiments that include transition zones between the regions in which the physical properties are intermediate between those of the regions themselves are considered by the inventors to be within the scope of the invention, as are embodiments in which the "regions" are merely conceptual and represent areas or volumes of the chip in which the various stages of the LIFT process occur.

[0101] The upper region is substantially transparent at the wavelength of the laser output. That is, enough light passes through the upper region such that the light impinging on the ink retains enough energy such that absorption of the energy by the ink is sufficient to produce an ink jet that exits the orifice. In some embodiments of the invention, the MFC is constructed such that sufficient energy will impinge on the ink to sufficient evaporate enough ink to produce a vapor bubble that will, upon collapse, provide a pressure transient sufficiently great to force ink out of the orifice in the direction of the receiving substrate. In other embodiments of the invention, the MFC is constructed such that absorption of the energy is sufficient to create a pressure wave that propagates through the ink, thereby resulting in a deformation of the ink-air interface at the orifice and subsequent expulsion of ink from the orifice, creating an ink jet. In yet other embodiments of the invention, sufficient energy passes through the upper region to cause ablation of the ink, thereby expelling ink from the orifice and creating an ink jet.

[0102] The sizes of the channels are optimized for the particular material being used. In typical embodiments of the invention, the height of the channel is between 20 μιη and 1 mm, and the width is between 50 μιη and 3 mm. As a general rule, a smaller channel height will result in smaller droplets being ejected as the ink jet, and will require less energy per pulse than a taller channel would need. On the other hand, if the ink is highly viscous, a channel having smaller dimensions will result in a larger pressure drop across the channel, especially in the cases of highly viscous inks flowing through the MFC at a high velocity, which can lead to clogging of the ink in the channel.

[0103] In some embodiments of the invention, the inlet and outlet have different areas. As non-limiting examples, the inlet and outlet can have similar shapes but different sizes; or the inlet and outlet can have different shapes. In some embodiments of the invention in which the inlet and outlet have different areas, the dimensions of the ink channel vary from the inlet to the outlet, in order to provide better pressure control at the orifices.

[0104] In typical embodiments of the invention, connections between channel inlets and outlets and external tubes are made by standard microfluidic connectors. Embodiments in which the inlet and outlet are configured to connect to different types of connectors are considered by the inventor to be within the scope of the invention. The external tubes provide a fluid connection between the MFC and at least one pump that creates the flow of ink through the channel. Non-limiting examples of the types of pumps that can be used with the MFC head disclosed herein include peristaltic, pressure, and syringe pumps. The required flow rate of the ink will depend on the required refresh rate, which depends inter alia on the droplet sizes in the ink jet and the desired printing rate. In typical embodiments of the invention, the flow rate through the channel is between 0.1 mm s^"1 and 1 m s^"1.

[0105] The flow rate can be governed by either volumetric flow rate control or by pressure difference control. In preferred embodiments of the invention, volumetric flow rate control is used, as the inventors have found that the liquid level and surface shape at the orifice is best maintained when volumetric flow rate control is used. In some preferred embodiments of the invention, the volumetric flow rate through the channel is less than 0.01 μL· s^"1. In some embodiments of the invention, the stability of the liquid level at the orifice is maintained by having the suction at the exit be greater than the pressure at the inlet. In other non-limiting embodiments of the invention, the liquid level and surface shape at the orifice are monitored by a closed feedback loop; by measuring the pressure inside the MFC, at the inlet, or at the outlet; or by measuring the shape of the meniscus formed by the ink at the orifice.

[0106] In the embodiment of the invention illustrated schematically in FIG. 3, the three regions of the MFC are shown as being substantially vertically disposed, with the middle region atop the bottom region and the upper region atop the middle region. Embodiments of the MFC printing head and of the LIFT system of the present invention in which the three regions are not vertically disposed are considered the by inventors to be within the scope of the invention. Reference is now made to FIG. 4, which presents bottom (FIG. 4A) and side (FIG. 4B) views of one such embodiment. In the embodiment shown in FIG. 4, laser output 310 is not coplanar with ink channel 3300, but is rather at an angle (in preferred embodiments, perpendicular) to the plane of the ink channel. Orifice 365 is in this embodiment is coplanar with the ink channel. In the embodiment illustrated in the figure, lower region 340 is perpendicular to upper region 320 and middle region 330. In the embodiment shown, the "lower region" is actually more of a conceptual region than a separate physical layer. The ink jet 345 exits from a side of the MFC that is adjacent to the side through which the laser beam enters the MFC. It is known in the art that the ink jet formed during the LIFT process does not necessarily have to propagate in the same direction as the laser beam; see, for example, "Laser- Generated Liquid Microjets: Correlation between Bubble Dynamics and Liquid Ejection" (Patrascioiu, A.; Fernandez-Pradas, J. M.; Palla- Papavlu, A.; Morenza, J. L.; Serra, P. Microfluid Nanofluid 16, 2014, 55), and "Time- Resolved Imaging of the Laser Forward Transfer of Liquids" (Duocastella, M.; Fernandez- Pradas, J. M.; Morenza, J. L.; Serra, P. J. Appl. Phys. 106, 2009, 084907), both of which are hereby incorporated by reference in their entirety.

[0107] In the embodiment of the MFC illustrated in FIG. 4, the inlet and outlet of the ink channel are located on the side of the MFC through which the laser beam enters, i.e. they pass through upper region 320. Alternative geometries such as those in which the inlet and outlet are located on one or more of the sides of the MFC perpendicular to the side through which the laser beam passes are considered by the inventors to be within the scope of the invention.

[0108] Non-limiting examples of additional optional components that can be included in the LIFT system disclosed herein include an air trap, pressure sensors, pressure regulators, valves, and temperature control apparatus.

[0109] The orifice can be of any shape or size appropriate to the desired output of the LIFT system. As non-limiting examples, shape and size of the orifice can be chosen for purposes such as controlling the LIFT process; stabilizing the flow through the MFC; controlling the shape of the meniscus at the orifice; and preventing unwanted ejection of liquid from or introduction of air bubbles into the MFC. In typical embodiments of the invention, the orifice will have either a round or a square shape. In some non-limiting embodiments of the invention, the orifice may have either a trapezoidal or an elliptical shape. In some other non- limiting embodiments of the invention, the orifice has non-uniform boundaries. The diameter of the orifice typically ranges from 100 μιη to 1 mm, depending on the viscosity and flow rate of the ink.

[0110] In some embodiments of the invention, the orifice is coated or subject to or other surface treatment that will alter the contact angle of the ink droplets being formed. The coating or surface treatment may be of any appropriate type known in the art, and prepared by any appropriate method known in the art.

[0111] In a typical LIFT process using this system, laser output 310 is focused on the ink channel opposite the orifice and directed to the ink channel via the upper region. The laser light is at least partially absorbed by ink in the channel, which then evaporates, forming a bubble of vapor that, upon collapse, causes the transient pressure increase that creates ink jet 345 that passes through orifice 365 toward the receiving substrate, where it is deposited (355). In contrast to normal LIFT processes, however, in the instant invention, fresh sample is brought before the laser by the aforementioned flow of ink through the ink channel rather than by movement of the LIFT head or laser.

[0112] In preferred embodiments of the invention, the channel or channels in the MFC are prepared by ablating a layer in the desired shape according to any process known in the art. A bottom layer is then used to seal the channels.

[0113] As shown in FIGs. 3 and 4, the MFC LIFT head herein disclosed does not incorporate an intermediate layer as is found in standard LIFT. Rather, the energy used to produce the vapor bubble is focused on the material within the ink channel. Thus, in preferred embodiments of the invention, in which the energy source is a pulsed laser, the ink comprises a material that absorbs light at the output wavelength of the laser. The wavelength, polarization, and mode distribution of the laser light are restricted only by the requirement that the absorption coefficient for absorption of the laser output by the ink must be sufficiently high that a single laser pulse is sufficient to at least partially evaporate the ink that absorbs the light in order to create the vapor bubble and eventually the ink jet that exits the MFC via the orifice. In preferred embodiments of the invention, the absorption coefficient of the ink at the laser wavelength is at least 1000 cm^"1.

[0114] The system of the present invention can readily be adapted for use in cases in which the ink itself does not absorb strongly at the laser output wavelength, however. Such adaptations are considered by the inventors to be within the scope of the invention disclosed herein. Non-limiting examples of embodiments that incorporate such adaptations include:

[0115] 1. The ink is dissolved or suspended within a solvent, and laser has an output wavelength that is strongly absorbed by the solvent. As a non-limiting example, if the ink is present as an aqueous solution, a laser with output at a wavelength near a strong absorption band of water (e.g. ~ 3 μηι, near the strongly absorbing H₂0 symmetric O-H stretch) can be used.

[0116] 2. In other embodiments, the power of the laser output is sufficiently high that nonlinear absorption effects such as multiphoton absorption take place; in these embodiments, a power density of about 10 11 W cm -^"2 or greater is required.

[0117] 3. In yet other embodiments, an additive that absorbs strongly at the laser output wavelength is added to the ink, for example, as a suspension or solution. In some embodiments, the additive is a pigment or dye. Non-limiting examples of materials suitable for use as additives include food coloring additives (e.g. those that are derived from naturally occurring anthocyanin pigments), biological materials that strongly absorb light (e.g. hemoglobin, β-carotene, melanin, etc.), or metallic, organometallic, or organic compounds or nanoparticles. Since for many dyestuffs, the absorption spectrum is pH-dependent, a buffer solution may be added to the ink in order to stabilize the pH at a value appropriate for absorption of the laser output by the second component.

[0118] For the printing of living cells, a liquid or gel medium is used that has mechanical, biological, and optical properties appropriate to the specific application for which the system is being used. Commercially available bio-inks can be used with the invention herein disclosed. Non-limiting examples of such bio-inks include inks made from materials such as collagen, gelatin, alginate, gellan gum, polyethylene glycol, and hyaluronic acid. Most of these bio-inks are hydrogels comprising an aqueous solution of polymer and cross-linker.

These bio-inks tend to have dynamic viscosities (μ) of between 10 3 and 3 x 105 mPa^»s at low shear rates. At higher flow rates, these gels tend to show shear thinning behavior having an approximately power-law relation with flow behavior index n = 0 (i.e. μ = Κτ^"1, where τ is the shear rate and K is a constant). The viscosity may be selected to have a value that is appropriate to the particular application or specific biological tissue to which the LIFT printing is being applied. [0119] The system and method herein disclosed, in which the head lacks an intermediate layer, are thus useful for applications that include inter alia organ-on-a-chip, micro-organs, and biological research.

[0120] In preferred embodiments of the invention, the laser pulse duration is < 10 ns. The use of lasers that produce picosecond or femtosecond pulses are within the scope of the invention. In preferred embodiments of the invention, the laser fluence at the focus is greater than 0.2 J cm^"2

[0121] In typical embodiments of the invention, the laser light travels through free space, directed as needed by beam steering and focusing elements known in the art such as mirrors, simple lenses, MEMS, GALVO, and microscope objectives. In typical embodiments, the laser output is focused to a spot size having a radius of between 1 μιη and 1 mm. The spot size will depend on the particular application, as the size of the droplets of ink exiting the head is directly related to the laser spot size.

[0122] While embodiments of the invention in which the laser light travels to the MFC via free space are considered by the inventors to be within the scope of the invention, in some preferred embodiments of the invention, the laser energy is transferred to the ink via an optical fiber. Because of the high laser pulse energies used in the LIFT process, in preferred embodiments of the invention in which optical fibers are used to transfer the laser energy to the LIFT head, hollow-core optical fibers or photonic-crystal fibers (PCFs) are used. In some embodiments of the invention, the fiber is inserted into the MFC and immersed in the ink. In some preferred embodiments of the invention in which optical fibers are used to transfer the laser energy to the LIFT head and in which the optical fiber is kept outside of the MFC, collimation of the light at the end of the fiber is done by embedding a focuser at the end of the fiber. Any appropriate type of focuser known in the art can be used. In some embodiments of the invention a scanner or other alignment means is used in addition to the focusing elements.

[0123] In some embodiments of the invention, the system comprises a plurality of MFC LIFT printing heads. These embodiments are particularly useful for cases in which different inks are to be applied to the substrate or if a high printing rate is desired. In cases in which inks of different materials are used, the different MFC heads can be designed with different dimensions or architectures optimized for the properties of the ink. As a non-limiting example, the diameters of the ink channels can be set to optimize the flow for materials of different viscosities.

[0124] In the embodiments in which multiple printing heads are used, separate lasers can be used for each printing head, or a single laser can be used and its output divided among the heads either physically, for example by using beamsplitters or a plurality of optical fibers, or temporally by alternating the head to which the laser light is sent. As a non-limiting example, in a system with 5 printing heads for which a 10 kHz printing rate is desired, a laser firing at a 50 kHz repetition rate can be used with successive pulses directed to successive heads, or a single laser firing at a 10 kHz repetition rate in which the output is divided physically among the printing heads can be used instead.

[0125] In the embodiments of the invention illustrated schematically in FIGs. 3 and 4, the MFC LIFT head is located above the receiving substrate. Because gravitational effects are not very significant on the length scale of the LIFT process disclosed herein, the MFC LIFT head may be placed in any convenient orientation relative to the receiving substrate, and all possible orientations of the MFC LIFT head relative to the receiving substrate, including but not limited to cases in which the ink jet is expelled horizontally or in which the MFC LIFT head is located below the receiving substrate are considered by the inventors to be within the scope of the invention. In some embodiments of the invention, the MFC LIFT head changes its orientation relative to the receiving substrate during the LIFT printing process. Non- limiting examples of parameters that can be changed during the LIFT printing process include the distance between the MFC and the receiving substrate and the orientation of the MFC relative to the receiving substrate (relative angle and/or relative position). The changes in orientation can be continuous, or the head can be moved to a particular orientation relative to the substrate, held in place for a predetermined length of time, and then moved to the next position. The changes in orientation that are within the scope of the invention include embodiments in which the LIFT head makes one or more complete circuits around the receiving substrate during the LIFT printing process.

[0126] LIFT systems that incorporate the MFC LIFT head described above are also within the scope of the invention. In typical LIFT systems of the present invention, the position and orientation of at least one of the MFC or the receiving substrate are controlled by placing the component on an XYZ stage, preferably electrically actuated and preferably having a precision of +1 μιη or better in each direction. XYZ stages having these capabilities are well- known in the art. The MFC LIFT head is typically placed so that the orifice is between 50 μιη and 5 mm from the receiving substrate. One of ordinary skill in the art will appreciate that the exact distance between the orifice and the receiving substrate will depend on parameters of the specific application, for example, the specific properties of the ink used and the droplet size and shape required by the application.

[0127] In some embodiments of the invention, the LIFT system additionally includes a source of ultraviolet light placed to irradiate the receiving substrate and thereby stimulating the secondary gelation or curing of the ink after it has been deposited on the receiving substrate. The irradiation of the receiving substrate by UV light may be performed continuously during printing, at the end of the process, or, particularly in 3D printing applications, after each layer of ink has been deposited on the receiving substrate.

[0128] The printing rate is limited primarily by the laser repetition rate, the maximum flow rate of the ink, and the surface re-initialization time. Thus printing rates even of 1 MHz or more are possible in principle with the LIFT system disclosed herein, as is printing of a single drop of ink. In practice, the upper limit on the printing rate is generally set by the viscosity of the ink. LIFT systems that incorporate the MFC head disclosed herein typically have printing rates of -10 kHz.

[0129] Particularly for biological applications such as printing of biological solutions and the use of cell-based bio-inks, the system additionally includes apparatus for controlling the environment, preferably apparatus that can control at least the temperature, humidity, and C0₂ and 0₂ levels. Typical printing temperatures for biological applications are between 4 °C and 37 °C. Any appropriate type of environmental control system known in the art may be used. In addition, in biological applications, the system is preferably placed in a sterile hood that comprises air-flow control, and in preferred embodiments of the system as used in biological applications, the printing head is sterilized prior to use and most preferably during use as well as needed to prevent contamination.

Claims

CLAIMS We claim:

1. A Laser-Induced Forward Transfer (LIFT) printing head (300), wherein said LIFT printing head comprises a microfluidic chip (MFC), said MFC comprising three regions:

an upper region (320);

a middle region (330) comprising at least one ink channel (3300), said ink channel comprising an inlet (3301) and an outlet (3302); and,

a bottom region (340), said bottom region comprising an orifice (365) in fluid connection with said ink channel.

2. The LIFT printing head according to claim 1, wherein said orifice opens to a side of said MFC intersected by a line connecting said three regions.

3. The LIFT printing head according to claim 1, wherein said orifice opens to a side of said MFC not intersected by a line connecting said three regions.

4. The LIFT printing head according to claim 1, wherein said at least one ink channel is characterized by a height of between 20 μιη and 1 mm and a width of between 50 μιη and 3 mm.

5. The LIFT printing head according to claim 1, wherein said inlet and said outlet have different areas.

6. The LIFT printing head according to claim 1, wherein said MFC is constructed of material selected from the group consisting of PMMA, COC, glass, metal, and ceramic.

7. A Laser-Induced Forward Transfer (LIFT) printing system, comprising:

an energy source;

a receiving substrate (350); and,

at least one printing head (300) disposed between said energy source and said receiving substrate such that ink within said printing head is irradiated by energy output of said energy source and a jet of ink produced by said printing head following its irradiation by said energy output will exit said printing head toward said receiving substrate;

wherein said printing head comprises a microfluidic chip (MFC), said MFC comprising three regions:

an upper region (320) substantially transparent to energy output of said energy source; a middle region (330) comprising at least one ink channel (3300), said ink channel comprising an inlet (3301) and an outlet (3302); and,

8. The LIFT printing system according to claim 7, wherein said orifice opens to a side of said MFC intersected by a line connecting said three regions.

9. The LIFT printing system according to claim 7, wherein said orifice opens to a side of said MFC not intersected by a line connecting said three regions.

10. The LIFT printing system according to claim 7, wherein said system is configured such that a line collinear with said output of said energy source passes through said orifice.

11. The LIFT printing system according to claim 7, wherein said energy source comprises at least one laser providing pulsed output (310).

12. The LIFT printing system according to claim 11, comprising focusing means configured to focus said laser output to a spot characterized by a radius of between about 1 μιη and about 1 mm.

13. The LIFT printing system according to claim 11, comprising ink and characterized by at least one characteristic selected from the group consisting of:

said laser is configured to produce output at a wavelength at which said ink absorbs and of sufficient energy such that upon irradiation by said output, said ink is at least partially evaporated;

said laser is configured to provide output at a wavelength at which said ink absorbs and of sufficient energy such that upon irradiation by said output, said ink is at least partially ablated;

said LIFT printing system is characterized by an ink-air interface at said orifice, and said laser is configured to provide output at a wavelength at which said ink absorbs and of sufficient energy such that upon irradiation by said output, a pressure wave is propagated through said ink, resulting in a deformation of said ink-air interface; said LIFT printing system comprises ink dissolved in a solvent, and said laser is configured to provide output at a wavelength at which said solvent absorbs and of sufficient energy such that upon irradiation by said output, said solvent is at least partially evaporated; said laser is configured to provide output of sufficient energy such that upon irradiation by said output, said ink is at least partially evaporated due to non-linear interactions with said output; and,

said LIFT printing system comprises ink and an additive mixed with said ink, and said laser is configured to provide output at a wavelength at which said additive absorbs and of sufficient energy such that upon irradiation by said output, said solvent is at least partially evaporated.

14. The LIFT printing system according to claim 13, wherein said LIFT printing system comprises ink and an additive mixed with said ink, and at least one of the following is true: said additive is a dye or pigment;

said additive is dissolved in said ink;

said additive is suspended in said ink; and,

said additive is selected from the group consisting of food coloring additives, anthocyanin pigments, hemoglobin, β-carotene, melanin, metallic compounds, organometallic compounds, organic compounds, metallic nanoparticles, organometallic nanoparticles, and organic nanoparticles.

15. The LIFT printing system according to claim 11, comprising focusing means for focusing said pulsed output to a predetermined location selected from the group consisting of:

an interface between said at least one ink channel and said upper region; and, within said ink channel.

16. The LIFT printing system according to claim 11, comprising at least one optical fiber disposed so as to transmit said pulsed output from said laser to said printing head.

17. The LIFT printing system according to claim 7, wherein said at least one ink channel is characterized by a height of between about 20 μιη and about 1 mm and a width of between about 50 μηι and about 3 mm.

18. The LIFT printing system according to claim 7, wherein said MFC is constructed of material selected from the group consisting of PMMA, COC, glass, metal, and ceramic.

19. The LIFT printing system according to claim 7, comprising pumping means for pumping ink through said ink channel.

20. The LIFT printing system according to claim 7, comprising a reservoir, said reservoir making a fluid connection selected from the group consisting of:

said reservoir in fluid connection with said inlet; and, said reservoir in fluid connection with said inlet and with said outlet.

21. The LIFT printing system according to claim 7, comprising n printing heads, n > 1.

22. The LIFT printing system according to claim 21, wherein said energy source is configured to irradiate each of said n printing heads sequentially.

23. The LIFT printing system according to claim 21, comprising n energy sources, each of which is configured to irradiate one of said n printing heads.

24. The LIFT system according to claim 7, wherein said system is in a location characterized by an environment, and said system comprises environmental control means configured to control at least one environmental parameter of said environment.

25. The LIFT system according to claim 24, wherein said at least one environmental parameter is selected from the group consisting of temperature, humidity, C0₂ concentration, and 0₂ concentration.

26. The LIFT system according to claim 7, wherein said MFC is separated from said receiving substrate by a distance of between 50 μιη and 5 mm.

27. A method for Laser-Induced Forward Transfer (LIFT) printing, wherein said method comprises:

flowing ink through at least one ink channel (3300) passing through a printing head (300) comprising a microfluidic chip (MFC), said MFC characterized by three regions:

an upper region (320);

a middle region (330) comprising said at least one ink channel (3300), said ink channel comprising an inlet (3301) and an outlet (3302); and, a bottom region (340), said bottom region comprising an orifice (365) in fluid connection with said ink channel;

irradiating said ink with output (310) of an energy source, said output having sufficient energy at a location at which said ink is irradiated to cause ink to be ejected from said orifice; and,

receiving said ink forced out of said orifice on at least one predetermined location on a receiving substrate (350).

28. The method according to claim 27, wherein said orifice opens to a side of said MFC intersected by a line connecting said three regions.

29. The method according to claim 27, wherein said orifice opens to a side of said MFC not intersected by a line connecting said three regions.

30. The method according to claim 27, wherein said step of irradiating said ink comprises at least one selected from the following:

irradiating said ink with output of said energy source sufficient to at least partially evaporate said ink at a location at which said output intersects said flow of said ink, said location at a position along said ink channel opposite to said orifice such that upon collapse of a vapor bubble formed upon said irradiation, a transient pressure increase is created, thereby forcing ink out of said orifice; and,

irradiating said ink with output of said energy source sufficient to generate a pressure wave that propagates within said ink, resulting in a deformation of an ink-air interface at said orifice and thereby forcing ink out of said orifice.

31. The method according to claim 27, wherein said step of flowing ink comprises flowing said ink at a flow rate selected from the group consisting of:

a flow rate of between about 0.1 mm s^"1 and about 1 m s^"1; and,

a volumetric flow rate of less than 0.01 μL· s^"1.

32. The method according to claim 27, wherein said step of irradiating comprises irradiating with output of a pulsed laser.

33. The method according to claim 27, wherein said step of irradiating comprises at least one of the following:

irradiating by light comprising a wavelength at which said ink absorbs;

dissolving said ink in a solvent and, irradiating by light comprising a wavelength at which said solvent absorbs;

irradiating with sufficient energy such that said ink is at least partially evaporated due to non-linear interactions with said output; and,

mixing an additive with said ink and irradiating at a wavelength at which said additive absorbs.

34. The method according to claim 33, wherein said step of irradiating comprises mixing an additive with said ink, and said additive is selected from the group consisting of dyes and pigments.

35. The method according to claim 27, comprising focusing said output at a location selected from the group consisting of:

36. The method according to claim 35, wherein said step of focusing comprises focusing said output to a spot characterized by a radius of between 1 μιη and 1 mm.

37. The method according to claim 27, wherein said step of irradiating comprises transmitting said pulsed output from said laser to said printing head by means of an optical fiber.

38. The method according to claim 27, wherein said step of flowing ink through at said least one ink channel comprises flowing ink through at least one ink channel characterized by a height of between 20 μιη and 1 mm and a width of between 50 μιη and 3 mm.

39. The method according to claim 27, wherein said MFC is constructed of material selected from the group consisting of PMMA, COC, glass, metal, and ceramic.

40. The method according to claim 27, comprising pumping ink through said ink channel.

41. The method according to claim 27, wherein said step of flowing ink comprises flowing ink withdrawn from a reservoir in fluid contact with said inlet.

42. The method according to claim 27, comprising recirculating said ink via a reservoir in fluid connection with said inlet and with said outlet.

43. The method according to claim 27, wherein said step of flowing comprises flowing said ink through channels in n printing heads, n > 1, and said step of irradiating comprises irradiating ink in each of said n printing heads.

44. The method according to claim 43, wherein said step of irradiating comprises irradiating each of said n printing heads sequentially.

45. The method according to claim 43, wherein said step of irradiating comprises irradiating with the output of n energy sources, each of which is configured to irradiate one of said n printing heads.

46. The method according to claim 27, comprising changing at least one parameter during said LIFT printing, said at least one parameter selected from the group consisting of:

distance between said printing head and said receiving substrate; and,

orientation of printing head relative to said receiving substrate.

47. The method according to claim 46, wherein said step of changing at least one parameter comprises changing said at least one parameter continuously.

48. The method according to claim 46, wherein said step of changing at least one parameter comprises:

changing said at least one parameter by a predetermined amount;

holding said at least one parameter constant for a predetermined time; and,

repeating the previous two steps until said LIFT printing is complete.

49. The method according to claim 27, wherein said system is in a location characterized by an environment, said method comprising controlling at least one environmental parameter of said environment.

50. The method according to claim 49, wherein said step of controlling at least one environmental parameter comprises controlling at least one environmental parameter selected from the group consisting of temperature, humidity, C0₂ concentration, and 0₂ concentration.

51. The method according to claim 27, wherein said step of irradiating is performed repeatedly at a repetition rate of between 100 Hz and 100 kHz.