Patent Description:
Additive manufacturing (also known as "<NUM>-D printing") has been proposed for various biological applications. Significant attention is for the improvement of preclinical models, where scientists in pharmaceutical development and clinical research are looking towards bioprinting technologies, to provide new in vitro tissue models with physiological relevant cell compositions, material properties and complex micro-structures. Bioprinting technology possesses the capability of precise positioning of biomaterials and living cells to reconstruct complex structures, with the goal of generating repeatable models of both diseased and healthy tissue. Bioprinting offers opportunities to integrate patient-specific cell sources into tissue models, further improving the biological relevance of in vitro screening.

<CIT> discloses tissue-like structures being assembled using a microfluidic print head via cell deposition onto patterned substrates.

<NPL> discloses a bioprinter that can be used to print multilayered 3D cell-laden hydrogel structures of tissue.

<NPL> discloses layer-by-layer assembly using inkjet printing of single cells and proteins.

<NPL> discloses multilayer cell films on a surface.

One aspect of the invention provides a method of generating three-dimensional biological structures. The method includes: (a) depositing a first layer of a suspension over a substrate, the suspension including a liquid and a plurality of cells; (b) allowing the plurality of cells to attach to the substrate and form a first layer of attached cells; (c) depositing a cell-attachment agent over the first layer of attached cells; and (d) depositing a second layer of the suspension over the cell-attachment agent.

This aspect of the invention can have a variety of embodiments. The method can further include (b') culturing the plurality of cells in the first layer for a period of time in order to establish or increase the amount of, one or more selected from the group consisting of: cell-cell interactions, cell-cell attachments, cell-substrate interactions, cell-substrate attachments, cell mass, and cell quantity. The period of time can include one or more ranges of time selected from the group consisting of: from about <NUM> minutes to about <NUM> minutes, from about <NUM> minutes to about <NUM> minutes, from about <NUM> hour to about <NUM> hours, form about <NUM> hours to about <NUM> day, from about <NUM> day to about <NUM> days, from about <NUM> days to about <NUM> week, from about <NUM> week to about <NUM> weeks, from about <NUM> weeks to about <NUM> weeks, and from about <NUM> weeks to about <NUM> weeks.

The method can further include: (e) repeating steps (b)-(d) until a biological structure having a predefined thickness is generated. The predefined thickness can be selected from the group consisting of: about <NUM>, between about <NUM> and about <NUM>, between about <NUM> and about <NUM>, between about <NUM> and about <NUM>, between about <NUM> and about <NUM>, between about <NUM> and about <NUM>, between about <NUM> and about <NUM>, between about <NUM> and <NUM>, and between about <NUM> and <NUM>.

The method further includes: (e) repeating steps (a)-(c) at a new location on the substrate.

The suspension can be deposited using a flow-confinement device. The cell-attachment agent can be applied globally or in a pattern. The suspension can be applied globally or in a pattern.

The suspension can include a single cell type or a plurality of cell types.

The substrate can be selected from the group consisting of: tissue and organ.

The method can further include: (f) depositing a cell blocking agent over the second layer of the suspension. The cell-blocking agent can be selected from the group consisting of: polyethylene glycol (PEG), block copolymers, bovine serum albumin (BSA), surfactant, casein, polytetrafluoroethylene (PTFE), silanes, particulate solutions, nanoparticles, metal nanoparticles, gold nanoparticles, silver nanoparticles, aluminum nanoparticles, titanium nanoparticles, and polymeric microspheres.

The cell-attachment agent can be selected from the group consisting of: adhesion proteins, cell-attachment proteins, cell-adhesion biomolecules, cell-adhesion molecules, polylysine, laminin, fibronectin, vitronectin, extracellular matrix (ECM), actin, integrin, perlecan, desmin, poly glycans, fibulin, elastin, tropoelastin, cadherin, gelatin, concanavalin, collagen, lipid structures, lipid nanotubes, lipid vesicles, lipid droplets, growth serum, fetal bovine serum, calf serum, horse serum, nucleic acids, DNA strands, RNA strands, cationic solutions, calcium solutions, magnesium solutions, and zinc solutions.

The substrate can be selected from the group consisting of: cell-attachment agent, plastic, glass, silicon, paper, cotton, biomaterial, lipid films, gel, aerogel, hydrogel, polymer matrix, metals, metal oxides, semipermeable membranes, permeable membranes, polysaccharides, starch, collagen, cellulose, gelatin, biological scaffolds, biological tissue, decellularized tissue, non-biological tissue, and biological cells.

The substrate can have a planar, uneven, structured, or patterned topology.

The substrate can include adjacent sections of different substrate materials.

For a fuller understanding of the nature and desired objects of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawing figures wherein like reference characters denote corresponding parts throughout the several views.

The instant invention is most clearly understood with reference to the following definitions.

As used herein, the singular form "a," "an," and "the" include plural references unless the context clearly dictates otherwise.

Unless specifically stated or obvious from context, as used herein, the term "about" is understood as within a range of normal tolerance in the art, for example within <NUM> standard deviations of the mean. "About" can be understood as within <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, or <NUM>% of the stated value. Unless otherwise clear from context, all numerical values provided herein are modified by the term about.

As used herein, the term "attachment" can refer to both physical, chemical, biological ionic, and electrostatic interactions, such as steric, covalent, ionic and hydrogen bonds, between cells and a substrate, surface or other cells. Attachment can be formed on the order of a minute for some cells. Other cells (e.g., neurons) may attach over weeks. Exemplary time ranges for allowing for attachment may include: from about <NUM> second to about <NUM> seconds, from about <NUM> seconds to about <NUM> seconds, from about <NUM> seconds to about <NUM> seconds, from about <NUM> minute to about <NUM> minutes, from about <NUM> minutes to about <NUM> minutes, from about <NUM> minutes to about <NUM> minutes, from about <NUM> hour to about <NUM> hours, form about <NUM> hours to about <NUM> day, from about <NUM> day to about <NUM> days, from about <NUM> days to about <NUM> week, from about <NUM> week to about <NUM> weeks, from about <NUM> weeks to about <NUM> weeks, and from about <NUM> weeks to about <NUM> weeks, from about <NUM> weeks to about <NUM> weeks, and so on.

As used in the specification and claims, the terms "comprises," "comprising," "containing," "having," and the like can have the meaning ascribed to them in U. patent law and can mean "includes," "including," and the like.

Unless specifically stated or obvious from context, the term "or," as used herein, is understood to be inclusive.

Unless specifically stated or obvious from context, the term "recirculation" can have the meaning of a fluid flow path exiting the device and returning to the same device.

Ranges provided herein are understood to be shorthand for all of the values within the range. For example, a range of <NUM> to <NUM> is understood to include any number, combination of numbers, or sub-range from the group consisting <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> (as well as fractions thereof unless the context clearly dictates otherwise).

Aspects of the invention provide systems and methods for the controlled deposition of biological cells or cell constituents onto surfaces, including but not limited to the additive manufacturing of small-to-large cellular networks, tissues, organs, and other biological structures. In particular, embodiments of the invention can be used to create histologically complex cell structures in 2D and 3D.

In some embodiments of the invention, the fluid dispenser includes a nozzle or other device that ejects a fluid. For example, embodiments of the invention can be applied to existing additive manufacturing (also known as "<NUM>-D printing") devices, e.g., by incorporating the systems and methods described herein alongside existing additive manufacturing printheads that apply materials such as polymers, e.g., biocompatible polymers, for the production of organs-on-a-chip.

Referring now to <FIG>, in some embodiments, the printing systems and methods utilize a flow-confinement device <NUM> and a controller <NUM> configured to generate a confined liquid volume outside of the flow-confinement device <NUM> where the confined liquid volume can be modulated by said controller <NUM> to include modulated and non-confined flow modes, as well as zero-flow modes, and where the controller <NUM> can be used to switch between any flow modes in arbitrary sequence, for arbitrary periods of time.

Some embodiments of the invention utilize fluid flows or recirculating fluid flows, generated at the tip of a flow-confinement device <NUM>, to achieve high resolution printing (e.g., with respect to both the lateral and axial position of the cells, deposition spot size for cell groupings, layer thicknesses, quantities of cells deposited, types of cells deposited, and the like). Although embodiments of the invention provide single-cell-deposition capabilities, embodiments of the invention can also deposit multiple cells at a time. For example, and without being bound by theory, Applicant believes that embodiments of the invention can reliably deposit layers having a thickness of less than two cells (e.g., less than about <NUM>, less than about <NUM>, less than about <NUM>, less than about <NUM>, less than about <NUM>, less than about <NUM>, less than about <NUM>, less than about <NUM>, less than about <NUM>, less than about <NUM>, and the like).

As depicted most clearly in <FIG>, flow-confinement device <NUM> can include one or more channels of which some channels are configured as outlet channels, through which liquid leaves the device <NUM> into an open volume and some channels are inlet channels, through which liquid is withdrawn from the open volume into the device. In some embodiments, outlet channels and inlet channels are different channels. In some embodiments same channel can be intermittently switched to be outlet channel and an inlet channel, e.g., as further described in <CIT>.

Controller <NUM> can be configured to control the liquid flow such that all liquid leaving from the device is returning eventually back into the device when in recirculatory mode. Outflow can reach a limited maximal distance from the outlet channel before returning into the inlet channel. This distance defines the size of the confined liquid volume. Therefore, the liquid outflow can reach a substrate (e.g., cell dish in <FIG>) or a surface, if it is positioned closer than the critical dimension of the confined liquid volume. In some embodiments, the outflow can reach the substrate, such that the flow-confinement device <NUM> does not have a direct contact with the substrate. The tip of the flow-confinement device <NUM> can, in some non-limiting applications, be in contact with the substrate.

In various embodiments, the device can reliably deposit single cells, and or groups of cells, with a lateral resolution on the order of a single cell (e.g., less than about <NUM>, less than about <NUM>, less than about <NUM>, less than about <NUM>, less than about <NUM>, less than about <NUM>, and the like).

Exemplary devices and methods for generating confined fluid flows are described in <CIT>; <CIT>; and <CIT>.

Still referring to <FIG>, the recirculating fluid flow-confinement device <NUM> can be readily positioned relative to an object of interest using either a manual positioning system, or through the implementation of an electronically controlled positioning device <NUM>. The positioning system may include hydraulic, mechanical, or electrical (e.g., stepper or servo motor) micromanipulators. These actuators can be arranged in one, two, three, four or greater directions.

The electronically controlled position of both the printhead and the substrate can be achieved through on-demand control, e.g., through the use of a joystick, gamepad controller, scroll wheel, a touch screen and combinations thereof, and/or through the use of a computationally determined path. These paths can for example, be derived from a simple coordinate system, a design file, such as. stl (STereoLithography) CAD files, and/or through a relative feedback response, e.g., adapting to the changing position of cell propagation.

In some embodiments, methods of cell deposition may be carried out under the control of a preprogrammed flow controller. In various embodiments, the system may further comprise a cell concentration measuring device for measuring cell deposition. In various embodiments, the preprogrammed flow controller may be programmed to assess whether a predefined number of cells are correctly located on the substrate. The feature of various embodiments by which parameters of the method are adjusted based on information collected over the course of the method is termed "feedback".

In various embodiments, the system may further comprise a device or method for measuring a cell property, such as a method for measuring protein expression, gene expression, metabolic markers, cell-cell interactions, ions, or other biological, physical or chemical properties of one or several cells in the various flow modes, including recirculatory flow.

The concentration of particles/cell in the flow can be determined from either the initial concentration as it entered the microfluidic device and/or monitoring within the dispenser or on the substrate, e.g., conductivity, impedance, fluorescence, phase retardation and the like.

Coverage can be assessed through a variety of techniques and devices. By way of non-limiting example, coverage may be assessed by optical assessment, particle tracking, by measuring conductivity and/or impedance, by ultrasound and/or by optical phase retardation measurements. A person of skill in the art will appreciate that different techniques for measuring coverage are more or less appropriate based on circumstances including, for example, the cell type and the type of liquid or liquids used.

In one embodiment, optical assessment can be performed using a digital camera (e.g., a charge-coupled device (CCD) or complementary metal oxide semiconductor (CMOS) image sensor), which can optionally be associated with various optics such as microscope, a light source, and the like. Suitable imaging modalities such as reflection, absorption, phase retardation, polarization, fluorescence, phosphorescence, and the like. Image processing can be performed on the captured image and examined to determine if the current coverage state is acceptable (e.g., in view of a. stl source file). Various patterns can place the same or similar cells adjacent to each other, place different cells adjacent to each other, place cells adjacent to non-cellular materials such as polymeric scaffolds, and the like.

In another embodiment, suspended particles are tracked, e.g., after exiting from the microfluidic printhead. For example, sperm tracking technology such as described in <CIT> can be applied to track a plurality of moving suspended particles. The fluid flow can be modified or paused in order to facilitate desired placement of the suspended particle(s).

In another embodiment, conductivity and/or impedance can be utilized to assess coverage. For example, two or more electrodes can be positioned in the deposition chamber, at least one of which should be adjacent to the microfluidic printhead, and current can be applied between the electrodes. Without being bound by theory, Applicant believes that resistance will increase in measurements during recirculating fluid flow as cells are deposited. Likewise and without being bound by theory, Applicant believes that the presence of deposited cells after cessation of the recirculating fluid flow will result in decreased impedance. Result-indicative conductivity and/or impedance values can be determined experimentally for particular embodiments, stored in computer-readable media, and referenced in a particular embodiment.

In still another embodiment, acoustic waves (e.g., ultrasound waves) can be utilized to detect the presence and position of a recirculating fluid flow and/or a deposited particle.

In yet another embodiment, deposited particle position and/or surface coverage may be determined by optical phase retardation measurements. Any source of polarized light and as well as any technique for phase detection, such as digital holographic microscopy (DHM) may be employed.

As used herein, the term "substrate" refers to the area or the object in or on which cells are deposited. The term "substrate" is to be construed broadly as the methods of the invention may be applied to a wide variety of different substrates. By way of non-limiting example, the substrate may be a surface, such as glass or plastic, which may or may not be functionalized. The substrate may be a volume element, such as a contained fluid or a gel. The substrate may also be cells of the same type or different from those deposited. In embodiments in which the substrate is a cell or cells, the cells may be suspended in a solution, attached to a surface or another object, or part of tissue, either in culture or from a living organism including a human.

The substrate can, among other materials, be composed of: a cell-attachment agent, plastic, glass, silicon, paper, cotton, biomaterial, lipid films, gel, aerogel, hydrogel, polymer matrix, metals, metal oxides, semipermeable membranes, permeable membranes, polysaccharides, starch, cellulose, gelatin, biological scaffolds, biological tissue, non-biological tissue, biological cells, or a composite material of any of the preceding list.

Exemplary plastic types include, but are not limited to, polycarbonate, polystyrene, polyethylene terephthalate, high-density polyethylene, low-density polyethylene, polyvinyl chloride, polypropylene, polystyrene, polylactide, polyacetal, poly dimethyl siloxane, acrylic, acrylonitrile butadiene, nylon, and the like.

The suspensions dispensed by the printhead can include a variety of solvents including aqueous solvents. The viscosity of the suspension can be configured so that the suspension remains in a desired location for sufficient time for cell attachment and/or growth. In some embodiments, the solvent is a dilute gel.

The dispensed suspensions can include a variety of biological materials such as cells, cell fragments, vesicles, subcellular organelles, particles, and the like.

Cell suspensions may be prepared using standard techniques, as understood in the art. For example, mammalian cells may be suspended in a solution of about <NUM>×<NUM><NUM> cells/mL to about <NUM>×<NUM><NUM> cells/mL. The cell suspension solution may be combined with a PEG (e.g., mol wt <NUM>). In some embodiments, the cell suspension solutions may have a final concentration of about <NUM>/ml.

In some embodiments, each layer includes a single cell type. In other embodiments, a plurality of cell types are provided in the same suspension. In still other embodiments, a plurality of suspensions, each containing a single cell type are applied adjacent to each other within a single layer. In yet another embodiment, the cell types vary from layer-to-layer.

The cell attachment agent (CAA) can be delivered globally (over the whole sample surface), locally (within a defined region of the sample) and/or directly patterned (over the whole sample or locally, where the region is defined by the path of the fluidic printhead).

CAA types include, but are not limited to adhesion proteins, cell-attachment proteins, cell-adhesion biomolecules, cell-adhesion molecules and further include, but are not limited to: polylysine (e.g., poly-L-lysine (PLL)), laminin, fibronectin, vitronectin, extracellur matrix (ECM) (e.g., available under the GELTREX® mark from Life Technologies Corporation of Carlsbad, California), actin, integrin, perlecan, desmin, poly glycans, fibulin, elastin, tropoelastin, cadherin, , gelatin, concanavalin, collagen, organic and inorganic gels, lipid structures (e.g., nanotubes, vesicles, droplets, and the like), growth serum (e.g., fetal bovine serum, calf serum, horse serum, and the like), nucleic acids (e.g., DNA and/or RNA strands), cationic solutions (containing, e.g., calcium, magnesium, zinc, and the like), or a composite solution comprised of any of the preceding list.

The CAA may be prepared as a working solution for pretreating one or more substrates. The CAA working solution for pretreating may include one or more of PLL, poly-D-lysine (PDL), ECM, and a buffer including for example sodium borate buffer. In certain embodiments, the working solution for pretreating includes: <NUM>/mL poly-L-lysine (PLL) and <NUM>µg/mL extracellular matrix (protein concentration <NUM>-<NUM>µg/mL, GELTREX®, Gibco), prepared using <NUM> sodium borate buffer. The working solution for pretreating may be prepared a time interval before use, including immediately prior to use.

The CAA may be prepared as a working solution for direct printing, further known as CAA-dp. The CAA-dp may be of the same composition as CAA or be of a composition including one or more of PLL, PDL, serum (e.g., fetal bovine serum), and buffer (e.g., phosphate-buffered saline buffer). In certain embodiments, the working solution for direct printing includes: <NUM>/mL poly-L-lysine (PLL) and <NUM>% FBS, prepared in a <NUM>× phosphate-buffered saline (PBS) buffer. The working solution for direct printing may be prepared a time interval before use, including immediately prior to use.

CAA may additionally include envrinmentally responsive compounds, such as Poly(N-isopropylacrylamide (PNIPAAm) for thermal responsivity or Rose Bengal or riboflavin for photoactive linkers.

In a similar manner to CAA, cell-blocking agent (CBA) can be applied globally over a substrate, locally, or patterned using the fluidic printhead. The CBA can prevent attachment between adjacent cells and/or act as a placeholder. In some embodiments, the CBA is a dissolvable substance. For example, a CBA such as PEG can be deposited as a scaffold to establish a lumen while cells are deposited around the lumen to form a vessel.

CBA types include, but are not limited to, polyethylene glycol (PEG), block copolymers, bovine serum albumin (BSA), surfactants (e.g., PLUORONIC™ surfactants available from ThermoFisher Scientific of Waltham, Massachusetts), casein, polytetrafluoroethylene (PTFE) (e.g., TELLON® available from The Chemours Company of Wilmington, Delaware), silanes, particulate solutions (e.g., including nanoparticles (e.g., metal nanoparticles such as gold, silver, aluminium, titanium, and the like), polymeric microspheres, and the like), or a composite solution comprised of any of the preceding list.

Embodiments of the invention can be applied to add material to living organisms. In such embodiments, the organism can be considered the substrate. Such embodiments can be used for a variety of therapeutic and/or cosmetic applications including regenerative medicine, tissue grafting, plastic surgery, orthopedics, and the like.

Embodiments of the invention utilizing a soft printhead are particularly advantageous in such embodiments, especially when applied to delicate tissues such as the eye and the ear.

Such an in-situ-generated graft can be bound to the organism through various techniques including the use of cross-linking as discussed herein.

In-situ-generated grafts can also be used for research purposes. For example, cancer cells can be printed within an organism (e.g., in a predefined and consistent pattern across multiple organisms) for experimental animal research.

The references to methods of treatment above, under heading "Additions to Living Organisms", are to be interpreted as references to the compounds, pharmaceutical compositions and medicaments of the present invention for use in a method for treatment of the human (or animal) body by therapy (or for diagnosis).

The invention is further described in detail by reference to the following experimental examples. These examples are provided for purposes of illustration only, and are not intended to be limiting unless otherwise specified. Thus, the invention should in no way be construed as being limited to the following examples, but rather, should be construed to encompass any and all variations which become evident as a result of the teaching provided herein.

In order to prepare an exemplary three-dimensional skin model, the following materials were prepared and used according to the following methods.

HaCaT cells were maintained and grown in complete Dulbecco's Modified eagle's Medium (DMEM, Gibco) supplemented with <NUM>% fetal bovine serum (FBS, Gibco), at <NUM> and <NUM>% CO<NUM>. Cells used as experimental controls were sub-cultured when they attained a confluency of approximately <NUM>%, preventing the cells from differentiating. To mimic psoriasis-affected cells, a separate culture of HaCaT cells were prepared and allowed to differentiate, by growing the culture for <NUM>-<NUM> additional days, once a <NUM>% confluency had been achieved.

To induce the psoriasis-like protein expression, differentiated HaCaT cells were exposed to a combination of inflammatory cytokines IL-1α (<NUM> ng/ml, Peprotech) and TNF-α (<NUM> ng/ml, Peprotech) for <NUM> hrs prior the bioprinting process.

Undifferentiated and differentiated psoriasis-like (cytokine-treated) HaCaT cells were used for bioprinting a skin model with the BIOPIXLAR® platform. The skin model was formed by printing stripes of psoriasis-like ("diseased") and undifferentiated ("healthy") cells side-by-side. The printing process was performed on CAA-precoated IBIDI® dishes. After printing, the cells were allowed to grow and proliferate in full growth media (DMEM +<NUM>% FBS) at <NUM>, <NUM>% CO<NUM> for <NUM> hrs.

In general, the following protocol was utilized for printing the skin model as described herein.

** If a localized area is to be treated for printing instead of the global substrate, the CAA-dp can be locally applied by exposing the surface to the CAA-dp solution using the printhead. This localized patterning does not require a complete change of the substrate immersion medium.

To verify the applicability of the bioprinted skin model, the effect of all-trans retinoic acid (RA) (Sigma), a drug used for many skin disorders, was compared against a control. Four hours post-printing, RA was introduced to the full growth media to a final concentration of <NUM>. The model was then allowed to grow for <NUM> hrs. The control model was treated with equal amounts of the RA solvent.

Claim 1:
A method of generating three-dimensional biological structures, the method comprising:
(a) depositing, using a flow-confinement device, a first layer of a suspension in a pattern over a substrate, the suspension comprising a liquid and a plurality of cells;
(b) allowing the plurality of cells to attach to the substrate and form a first layer of attached cells;
(b') culturing the plurality of cells in the first layer for a period of time of between about <NUM> minutes and about <NUM> weeks, in order to establish or increase the amount of one or more selected from the group consisting of: cell-cell interactions, cell-cell attachments, cell mass, and cell quantity, the culturing resulting in a tissue-like structure;
(c) depositing a cell-attachment agent over the first layer of attached cells;
(d) depositing, using a flow-confinement device, a second layer of the suspension in a pattern over the cell-attachment agent; and
(e) repeating steps (b)-(d) until a biological structure having a predefined thickness is generated,
where steps a)-d) are not performed on the human or animal body.