Oscillating cell culture bioreactor

Abstract

Methods and devices for cell or tissue culture are provided. One aspect provides a bioreactor having a gas permeable, closed-loop chamber for cell or tissue culture, and an oscillating means for moving the gas permeable, closed-loop chamber bidirectionally along an axis horizontal to an axis normal to the closed-loop chamber to force convection of cells and fluid in the gas permeable, closed-loop chamber. The bioreactor optionally includes a tissue engineering scaffold, an inlet means, an outlet means, and integrated sensors. Another aspect provides a bioreactor having a plurality of gas permeable, closed-loop chambers for cell or tissue culture. Methods of culturing cells and producing tissue constructs are also provided.

Description

FIELD OF THE INVENTION

The present invention generally relates to methods and devices for cell or tissue culture and cell or tissue culture bioreactor systems.

BACKGROUND OF THE INVENTION

Tissue-engineering holds the promise of repairing or replacing failing organs to treat illness or improve and extend life expectancy. One of the principle methods behind tissue engineering involves growth of the relevant three-dimensional (3D) organ or tissue starting from dissociated cells and 3D porous matrices, known as scaffolds. The cells attach and colonize the scaffold to produce tissue constructs (Langer, R., Vacanti, J. P. (1993) Tissue engineering. Science 260: 920-926). Bioreactors are an important tool for successful clinical implementation of tissue-engineering and regenerative medicine strategies, as bioreactors are able to reliably reproduce physiological conditions in vitro. Improved bioreactors are needed to improve engineered tissue construct size, structure, mechanical properties, cellularity, and molecular composition to more closely resemble functional native tissues, and to maintain viability of harvested cells prior to their actual transplantation

One major challenge in tissue engineering that can be met by using a bioreactor is cell attachment to a 3D porous scaffold, herein referred to as ‘cell seeding’. To create an autologous implant starting from a biopsy of limited size and cells of limited expansion potential, the harvested cells should be seeded onto scaffolds with the highest possible efficiency. A spatially uniform distribution of cells throughout a 3D scaffold should provide the basis for homogeneous tissue generation, but it is challenging to disperse viable cells throughout 3D scaffolds having complex and diverse architectures.

A commonly used method of cell seeding is to add concentrated cells to a scaffold in a petri dish, but this ‘static seeding’ method is associated with low efficiency and spatially non-uniform cell distributions. Alternatively, cells can either be added to a magnetically stirred spinner flask in which scaffolds are threaded on needles and hence fixed in place or perfused through a cartridge in which a scaffold is fixed in place. However, previously developed cell seeding devices were associated with low efficiency and spatially non-uniform cell distributions.

Subsequent to cell seeding, sufficient transport of gases, nutrients and other molecules during the culture of large tissue constructs has been a primary obstacle in the field of tissue engineering. A cell culture device should provide high rates of gas exchange (for cell types with high oxygen requirements), relatively low working volumes (for cell types that require media supplementation with costly growth factors) and controllable levels of hydrodynamic shear (for cell types that are shear-sensitive).

A related challenge in the field of regenerative medicine that can be met by using a bioreactor is to maintain the viability of harvested cells prior to the time of their actual transplantation. Harvested cells typically die or lose their specialized phenotype (de-differentiate) when cultured in conventional petri dishes or spinner flasks. Moreover, shear stress, which is absent in petri dishes and present at high levels in spinner flasks, is required to support the oxygen and nutrient transport requirements of metabolically active cells, but high levels of shear stress can induce programmed cell death (apoptosis) and/or de-differentiation.

Current cell culture bioreactors suffer from several drawbacks. For example, typical cell culture bioreactor devices require two distinct system components: one to provide gas exchange and another to provide perfusion. The requirement for two separate components renders the devices bulky and cumbersome. Additionally, existing bioreactor devices work in two distinct phases: one device is required for the cell seeding phase and a second device is required for the cell culture phase. Lastly, the majority of the existing bioreactor devices developed for cell seeding and culture are of limited use in a commercial setting, due to complexity of the required components, e.g. multi-channel peristaltic pumps, bi-directional syringe pumps or vacuum pumps combined with multiple sensors and solenoid valves.

Therefore, it is an objective of the invention to provide an integrated cell culture bioreactor suitable for cell seeding and cell culture for the production of tissue engineered constructs.

It is a further objective of the invention to provide methods for producing tissue constructs using a single, integrated bioreactor for cell seeding and cell culture.

It is a further objective of the invention to provide a cell culture bioreactor that combines effective mass transport of gases, nutrients, and regulatory molecules in the context of a single, integrated and commercially applicable device.

It is a further objective of the invention to provide a method and cell culture apparatus that can provide sufficient transport of gases, nutrients and other molecules during the culture of tissue constructs greater than 200 μm one dimension.

It is still another objective of the invention to provide an integrated cell culture bioreactor suitable for maintaining the viability of harvested cells prior to the time of their actual transplantation.

SUMMARY OF THE INVENTION

Methods and devices for cell or tissue culture on support matrices are provided which use a bioreactor having a gas permeable, closed-loop chamber for cell or tissue culture, and an oscillating means for moving the gas permeable, closed-loop chamber bidirectionally along an axis horizontal to an axis normal to the closed-loop chamber to force convection of cells and fluid within the gas permeable, closed-loop chamber. The bioreactor optionally includes inlet and outlet means. The bioreactor may include a plurality of gas permeable, closed-loop chambers for cell or tissue culture. This compact, integrated bioreactor provides high efficiency, spatially uniform seeding of cells throughout 3D porous scaffolds and produces tissue constructs through the combination of effective mass transport of gases, nutrients, and growth factors in the context of a commercially applicable device. The bioreactor can also provide a low, controllable level of shear stress to meet the metabolic requirements of shear-sensitive cells without compromising their viability.

The methods of producing a tissue construct include the steps of obtaining a tissue biopsy from a patient, expanding cells of the biopsy in vitro, and culturing the cells in the bioreactors containing a scaffold to produce a tissue construct. In one embodiment, “perfusion seeding and culture”, the method of producing a tissue construct involves inoculating a cells and culture media into a gas permeable, closed loop chamber containing a porous three dimensional (“3D”) scaffold, oscillating this chamber bidirectionally along an axis horizontal to an axis normal to the closed-loop chamber to force convection of the cell suspension through the scaffold, and culturing the cell-scaffold composition under physiologic conditions to produce a tissue construct.

In another embodiment, “perfusion culture after seeding”, the method of producing a tissue construct includes the steps of loading a cell-hydrogel composition and culture media into a gas permeable, closed-loop chamber, sealing the gas permeable, closed-loop chamber, oscillating it bidirectionally along an axis horizontal to an axis normal to the closed-loop chamber to force convection of the culture media, and culturing the cell-hydrogel composition under physiological conditions to produce a tissue construct. In another embodiment, the method of producing a tissue construct includes the steps of loading a cell-hydrogel composition in combination with a 3D porous scaffold and culture media into a gas permeable, closed-loop chamber, sealing the gas permeable, closed-loop chamber, oscillating it bidirectionally along an axis horizontal to an axis normal to the closed-loop chamber to force convection of the culture media, and culturing the cell-hydrogel-scaffold composition under physiological conditions to produce a tissue construct.

Another embodiment, “culture of adherent cells or cells in suspension” provides a method of maintaining cell viability and includes the steps of inoculating cells and culture media into a closed-loop chamber not containing a scaffold, and oscillating the gas permeable, closed-loop chamber bidirectionally along an axis horizontal to an axis normal to the closed-loop chamber to force convection of the cells and culture media to maintain cell viability.

Still another embodiment provides a bioreactor system that is an integrated, system. In another embodiment, the bioreactor system includes modules for ease of scale-up and automation.

Another embodiment provides methods of treatment using tissue constructs produced according to the disclosed methods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front, cross-sectional view of one embodiment of the disclosed cell culture bioreactor.

FIG. 2 is a side, perspective view of a diagram of another embodiment of the bioreactor.

FIGS. 3A and 3B are graphs demonstrating efficacy of perfusion seeding and culture in the oscillating perfused bioreactor. FIG. 3A is a graph of DNA (μg/construct) of 4-day constructs and FIG. 3B is the cross-sectional thicknesses (mm/construct) of 14-day constructs, comparing results after seeding chondrocytes onto 3-dimensional scaffolds in the oscillating perfused bioreactor (“OPB”), static culture (“ST”), or spinner flask culture (“SF”). Data are Avg.±SD of 3-4 measurements; * significant difference between OPB and ST; ** significant difference due to seeding and culture method.

FIGS. 4A-4G are graphs comparing cell viability and tissue regeneration after 8 days of static (ST) or oscillating perfused bioreactor (OPB) culture of cardiomyocytes entrapped within porous 3D scaffolds using Matrigel, in control (CTL) or JOF supplemented (+IGF) media. FIG. 4A, cell viability (MTT assay), FIG. 4B, apoptosis (TUNELpositive cells, %); FIGS. 4C and 4D, cardiac troponin-I and connexin-43, respectively (cardiac marker proteins, % native heart); FIG. 4E, total protein (mg/construct); FIG. 4F, contractile amplitude (% area change); FIG. 4G, excitation threshold (volts). Data are Avg.±SEM of 3-6 measurements for A-E or 12-28 measurements for F-G; * significantly different from ST CTL; † significantly different from ST+IGF; ‡ significantly different from OPB CTL.

FIG. 5. is a graph of lactate/glucose ratio, an index of culture aerobicity during static (ST) or oscillating perfused bioreactor (OPB) culture of cardiomyocytes entrapped within 3D porous scaffolds using three different gels (Matrigel, self assembling peptide gel and fibrin gel), demonstrating that the bioreactor provides more aerobic culture conditions than static culture. Data are average±SD of duplicative measurements; * significant difference due to the culture method.

FIG. 6 is a graph demonstrating that the bioreactor promotes maintenance of cell viability, plotting percent cell viability over time for cardiomyocytes cultured in suspension in the oscillating perfused bioreactor (OPB), spinner flasks (SF), or orbitally mixed flasks (MF). Data are the average±SD of n+3 measurements.

DETAILED DESCRIPTION OF THE INVENTION

I. Cell Culture Bioreactors

One embodiment of an oscillatory cell culture bioreactor system provides flow of cell suspensions and/or culture media directly through a porous 3D scaffold (during cell seeding) and a 3D construct (during subsequent cultivation) within a gas-permeable closed-loop tube. The bioreactor is designed to exploit the principles of gas transport and mass transport during the processes of cell culture and cell seeding of 3D scaffolds and in vitro culture of 3D tissue engineered constructs. The bioreactor can also be used with cells in the absence of a scaffold, e.g., to maintain the viability of dissociated cells in suspension. In certain embodiments, the bioreactor is simple, modular, and flexible, and the component parts are easy to assemble, operate and inexpensive. Chamber volume can be very low, but can also be easily scaled up for commercial uses. The bioreactors are well suited to work with different biological specimens (including in particular cells with high oxygen requirement and/or shear sensitivity), different scaffold structures and dimensions, and combinations thereof.

Bioreactors based on the disclosed design should increase the efficacy of mass transport. Since the bioreactors can be used without any set-up modification to move from the seeding to the culturing phase, these bioreactors are expected to increase reliability, reduce the risk of contamination, reduce sample loss, and reduce costs.

A. Closed-Loop Chamber

FIG. 1 shows a representative bioreactor that includes a closed-loop chamber (10) which contains the cells to be cultured or the tissue construct to be cultured. In one embodiment of the disclosed method and apparatus, relatively small and inexpensive silicone rubber closed-loop chambers may be used to grow prokaryotic or eukaryotic, preferably mammalian cells with growth kinetics and final saturation densities that are similar to or higher than those observed using conventional culture systems. The silicone rubber closed-loop chambers may produce cell and tissue growth rates higher than the growth rates obtained using conventional methods of cell culture including static, mixed, and magnetically stirred flasks.

The closed-loop chamber (10) is formed at least in part from a gas permeable material, preferably a highly gas permeable material, to allow efficient gas exchange during the cell seeding/culturing process. Efficient gas exchange by a gas permeable material is defined as that required to maintain equilibrated in the cell culture medium within the closed-loop chamber dissolved gas concentrations that are physiological for the cells cultured therein (e.g., for heart cells, dissolved oxygen preferred >75 mm Hg, more preferred >80 mm Hg, most preferred, >85 mm Hg. Suitable gas permeable materials include, but are not limited to, gas-permeable materials including hydrophobic polymer materials such as silicone and polydimethylsiloxane (“PDMS”). Silicone rubber and other suitable gas permeable polymers provide means for the facile transport of oxygen and/or other gases into or away from a culture. Silicone rubber has a relatively high permeability to O₂ and CO₂ when compared to other known polymers. For example, the permeability (in [cm³][cm]/[cm²][S][cm Hg]×10¹³) of silicone rubber to O₂ and CO₂ is 367 and 2430, respectively. In comparison, the permeability of polystyrene film is 2.0 and 7.9, respectively. The permeability of polyethylene is comparable to polystyrene. Thus, silicone rubber has over 100 times the O₂ permeability of polystyrene, polyethylene, or virtually any other polymer. Furthermore, in addition to being permeable to oxygen, carbon dioxide, nitrogen, and other low molecular weight gases, silicone rubber may also be permeable to other volatile molecules, such as ethylene oxide (ETO). Therefore, permeability of silicone rubber and other suitable polymers to unwanted reagents such as ETO may allow their non-invasive removal in some embodiments.

The closed-loop chamber can be partially or completely formed of optically translucent or clear material. The closed-loop chamber (10) has a holder (11) for securing a scaffold (32), which may be a hydrogel and/or fibrous, sponge-like, mesh, non-woven mesh, woven fabric, foam, decellularized tissue or capillary with or without additional support or another form. Within the holder (11), the scaffold (32) may be secured directly to the wall of the closed-loop chamber (10) or placed within a means for retaining the scaffold (32) such as a porous bag or frame secured to the wall of the closed-loop chamber (10). The motion (15) forces the fluid and cells and gases through the entire thickness of the scaffold. In a preferred embodiment, scaffold (32) is more than 200 micrometers in diameter, so that the fluids must transport nutrients and gases over a distance greater than 200 micrometers. This is significant because nutrients and gases normally do not diffuse more than a distance of 100 micrometers within a tissue, and, absent vascular flow, the cells die or fail to attach and proliferate at the farther distances from the exterior surfaces of the scaffold or tissue construct.

One embodiment provides one or more toroidal closed-loop chamber(s) (20) as shown in FIG. 2. The toroidal closed-loop chamber is formed, for example, by fusing the ends of a tube, preferably a silicone rubber tube or other gas permeable material. N in FIG. 2 indicates the normal axis.

In one embodiment, a fluid (12), with or without cells, is added to closed-loop chamber (10 or 20) such that all or most of the air is displaced (i.e., with or without an enclosed air bubble (14)). Typically, the fluid is conventional cell culture fluid containing nutrients and growth factors sufficient to culture cells or tissue constructs. Other types of fluids include, but are not limited to, growth media containing regulatory molecules such as paracrine factors, micro or nanoparticles, quantum dots, or other agents for regulating, detecting and/or monitoring cellular activity or chemical species.

The gas permeable, closed-loop chambers can be of any size or dimension. A single bioreactor system can contain multiple chambers that have different capacities. The chambers can be partially or completely filled with fluid. In certain embodiments, the interior surfaces of the close-loop chambers are coated with material to promote or prevent cell attachment such as the silicone-based spray-coating SIGMACOTE™.

In other embodiments, the closed-loop chamber optionally includes a chamber occlusion system, for example a roller like that used to propel fluid in a standard peristaltic pump.

Another embodiment provides closed-loop chambers configured with an outlet to be used with/without a 10-μm pore cut-off membrane to sample media without/with cells.

Referring to FIG. 2, another embodiment provides an oscillating cell culture bioreactor system within housing (22). Housing (22) provides a controlled environment for cell or tissue culture, for example a humidified 37° C., 5% CO₂ incubator. The conditions of the controlled environment can be adjusted to optimize the culture conditions for different cells or tissue types.

One or more closed-loop chambers (20) are removably attached to shaft (16). Shaft (16) is attached to motor (17) that provides an oscillatory movement to the closed-loop chambers (20). Arrow (15) indicates one embodiment of the direction of the applied oscillating movement. Movement of the closed-loop chamber (20) induces relative motion of the closed-loop/scaffold/construct with respect to the fluid (12). In the case where the fluid is a cell suspension, cells will come into contact with the scaffold and eventually adhere to the scaffold. The fluid containing the cells can partially or completely penetrate the porous scaffold. Gas exchange (i.e., of oxygen and carbon dioxide) occurs from the environment through gas permeable walls of closed-loop chamber (20) and into the fluid (12) as required for preserving viability of metabolically active cells or tissue constructs. Controller (19) controls motor (17) to provide adjustable levels of oscillating motion to closed-loop chamber (20) and thereby achieve mass transport while also controlling the level of fluid dynamic shear occurring inside closed-loop chamber (20) for example, to preserve viability of shear-sensitive cells and also enhance their differentiation.

The oscillatory cell culture bioreactor can be easily custom-modified to match specific fluids and biological specimens for different tissue engineering applications with respect to the chamber (i.e., section, material, capacity, filling, gas permeability, optical transparency, presence and location of inlets (24)/outlets (26), sensors (25), and actuators (30), the scaffold (32) (i.e., material, structure, geometry and orientation), the type of motion (i.e., rotational, non-oscillatory, oscillatory) and its characteristics (i.e., speed, arc of oscillatory motion) and the types of fluid flow (i.e., laminar, turbulent, non-turbulent). It will be appreciated that the inlets (24) or outlets (26) can be positioned anywhere along closed-loop chamber (10 or 20), For example, outlet (26) can be positioned on the lower half of closed-loop chamber (10 or 20) similar to inlet (24).

In one embodiment of the oscillatory cell culture bioreactor, a toroidal chamber (20) was constituted by silicone tubing within which a scaffold holder (11) was molded from poly(dimethyl siloxane)(PDMS). In certain embodiments, the scaffold holder (11) is optically clear to permit visual inspection of the scaffold/tissue construct. Scaffold holder (11) can be configured to receive a scaffold (32) for culturing tissue constructs and can be formed from a variety of materials and include sensors (28) or actuators (30) suitable for the type of cell or tissue construct to be cultured.

Oscillatory motion was achieved by an electrical motor (17) turning shaft (16) where the inversion of the turning direction (15) (i.e., oscillation) was obtained and controlled by either eccentric cam rotation or a simple control circuit with micro-switches (36). The oscillatory motion can create laminar, non-turbulent motion or turbulent motion depending on the speed and angle of motion. Up to sixteen individual closed-loop toroidal chambers (20), each containing a single scaffold (32), were attached to a single shaft (16) via discs of appropriate diameter and moved in unison with the shaft. It will be appreciated that the number of closed-loop chambers can be varied, for example, from 1 to 24, preferably 5 to 16, more preferably 8-16. Oscillatory motion of the chamber forced convection of the cell suspension and culture media directly through the scaffold (32). Convective flow can be achieved either by trapping a small air bubble (14) at the top of the closed-loop chamber (20) or by using a minimally occlusive roller (not shown) to compress the tubing at the top of closed-loop chamber (20). The bioreactor system is operably connected to power supply (38).

Scale-up of the disclosed system can be easily achieved for this modular system, e.g., by stacking chambers on a single shaft of an oscillatory base; chambers with different characteristics can be stacked on the same shaft.

In one embodiment, the bioreactor system provides sixteen individual cell culture chambers, allowing one or more cell types from one or more different patients and/or culture conditions to be separately cultured within a single culturing routine, as may be required for autologous cell therapies for different patients (i.e., cells from different patients must be individually cultured, to avoid cross contamination). For example, one closed-loop chamber can be culturing cardiac mesenchymal cells, whereas another closed-loop chamber attached to the same device as shown in FIG. 2 can be culturing skeletal muscle cells from the same patient or from another patient.

In one embodiment controller (19) is a processor, for example a conventional computer. Controller (19) can be programmed to monitor culture conditions for example via input from sensors (28) and automatically vary conditions such as temperature, humidity, pH, concentrations of dissolved O₂ and CO₂, and oscillating movement including speed, arc rotation, and direction. Controller (19) is operably connected to motor (17) and power supply (38). Sensors (28) can be designed to monitor temperature, humidity, pH, concentrations of dissolved O₂ and CO₂, glucose, etc. The controller can be communicatively linked to each individual closed-loop chamber to adjust each chamber independently. Alternatively, the controller can be communicatively linked to each closed-loop chamber so that the conditions of all of the closed-loop chambers are altered uniformly.

B. Scaffold Materials

The gas permeable, closed-loop chamber can contain one or more scaffolds. The scaffold can be made of synthetic and natural polymers capable of forming a three dimensional, porous platform. Preferred polymers are biodegradable. Suitable synthetic polymers include, but are not limited to aliphatic polyesters such as polyglycolic acid (PGA), polylactic acid (PLLA), their copolymers (e.g., PLGA), polyp-dioxanone), copolymers of trimethylene carbonate and glycolide, poly(3-hydroxybutyrate), poly(3-hydroxyvalerate), poly-ε-caprolactone (PCL), poly(valcrolactone), poly(tartronic acid), poly(β-malonic acid), poly(propylene fumarates), polyanhydrides, polyorthoesters, polyurethanes diiscoyanates such as lysine diisocyanate (LDI) (2,6-diisocyanatohexanoate) and other aliphatic diisocyanates like hexamethylene diisocyanate (HDI), polyphosphazenes (P. A. Gunatillake and Raju Adhikari (2003) Eur. Cells Mater. 5:1-16), polyhydroxyalkanoates, poly(glycerol-sebacate), and xylitol-based polymers (J. P. Bruggeman et al. (Adv Mater, 2008).

In other embodiments, the polymers can be biodegradable, shape-memory polymers (A. Lendlein and R. Langer (2002) Science 296(5573):1673-1676. Additional polymers for use in the disclosed methods and devices can be found in R. A. Pethric et al. (eds) Polymer Yearbook 16, Overseas Publishers Assoc. Singapore (1999) and S. K. Mallapragada and B. Narasimhan (eds) Handbook of Biodegradable Polymeric Materials and Their Applications, American Scientific Publishers (2005), and R. Lanza, R. Langer, and J. Vacanti (eds) Principles of Tissue Engineering, 3^rd Edition (2007).

Natural polymers include but are not limited to protein or carbohydrate polymers such as collagen or gelatin and naturally occurring polymers made by recombinant DNA technology. In other embodiments, the scaffold can be formed using ceramic composites such as hydroxyapatite, tricalcium phosphate or metal meshes and foams.

One embodiment provides scaffolds formed from live or decellularized tissues, as in H. C. Ott et al., Nature Medicine (2008), and naturally occurring or semi-synthetic materials such as hyaluronan benzyl ester, HYAFF-11® (Fidia Advanced Biopolymers). Additional suitable scaffolds are those as described in U.S. Pat. No. 5,770,417 to Langer et al. and U.S. Pat. No. 6,962,814 to Mitchell et al.

One embodiment includes scaffolds having paracrine factors such as growth factors, cytokines, morphogens, cell signaling agents, nucleic acid fragments or combinations thereof releasably attached or associated with the scaffold matrix. The paracrine agents can be controllably released from the scaffold by the application of a releasing agent. The degree of release can be further controlled by the time and amount of releasing agent applied. Representative releasing agents are chemical agents or peptide agents, for example an enzyme such as an esterase. In other embodiments, the bioactive factor freely diffuses out of the scaffold. In still other embodiments, the bioactive factors are attached to the scaffold to form a gradient. Gradients of paracrine factors can be used to help direct the formation of specific tissues. Suitable growth factors include, but are not limited to, epidermal growth factor (EGF), fibroblast growth factor (FGF), hepatocyte growth factor (HOF), platelet-derived growth factor (PDGF), vascular endothelial cell growth factor (VEGF), and insulin-like growth factor (IGF). A morphogen is a substance governing the pattern of tissue development and, in particular, the positions of the various specialized cell types within a tissue. Some growth factors are also morphogens. Morphogens include bone morphogenic proteins (BMP), decapentaplegic/transforming growth factor beta, hedgehog/sonic hedgehog, wingless/Wnt, epidermal growth factor, and fibroblast growth factor, and biologically active fragments thereof.

Scaffolds or matrices can be produced using known techniques, including, but not limited to, laser microablation, free form fabrication, phase-change jet printing, 3D Plotter, Fused Deposition Modeling (FDM), Stereolithography (SLA), Three Dimensional Printing (3DP), freeze drying, solution casting, emulsion freeze drying, melt molding, phase separation, fiber meshes/fiber bonding, gas foaming, and solvent-casting particulate-leaching or a combination thereof (P. A. Gunatillake and R. Adhikari (2003) Eur. Cells Mater. 5:1-16)(S. J. Hollister (2005) Nature Materials 4: 518-524), The size and shape of the scaffold can be varied to optimize culture of specific cells and tissue constructs.

C. Cells

Suitable cells for use in the disclosed methods and apparatus include prokaryotic and eukaryotic cells, preferably mammalian cells. Representative cells include mammalian, preferably human, cells, embryonic or adult stem cells; pluripotent or totipotent cells obtained from placenta, cord blood, adipose tissue, neural tissue, muscle tissue, cardiac tissue, parenchymal tissues, epidermal tissue, or bone marrow;, or somatic cells optionally corresponding to a tissue or organ to be treated. The cells can be derived from mesoderm, endoderm, or ectoderm. Representative cells include mesenchymal cells, especially fibroblasts, interstitial cells, endothelial cells, smooth or skeletal muscle cells, heart cells, myocytes (muscle cells), chrondocytes, adipocytes, fibromyoblasts, and ectodermal cells, including ductile and skin cells, hepatocytes, Islet cells, cells present in the intestine and other parenchymal cells, osteoblasts and other cells forming bone or cartilage, bone marrow cells and blood cells. Cells genetically engineered to avoid the need for immunosuppression in a host receiving the tissue construct may also be used.

A population of cells to be cultured can be a single type of cell, cells from a single type of tissue (for example a population of cardiac cells), or a combination of different types of cells (for example endothelial cells in combination with cardiac myocytes). The cells can be autologous, heterologous, allogenic, xenogenic, or a combination thereof.

Suitable cells also include recombinant cells that express one or more heterologous nucleic acids. The heterologous nucleic acid can express a protein involved in wound healing or tissue regeneration, for example an extracellular matrix protein, matrix metalloprotease or GAG synthase, or a fusion protein thereof. Alternatively, the cell can be genetically engineered to secrete paracrine factors including, but not limited to growth factors such as fibroblast growth factor, hepatocyte growth factor, platelet-derived growth factor, vascular endothelial cell growth factor, and insulin-like growth factor, bone morphogenic proteins and combinations thereof. The cells can also be engineered to express inhibitors of complement or inflammation, such as CD46 or CD59. Methods and protocols for producing recombinant cells are known in the art.

In some embodiments, cells are obtained by biopsy and dissociated using standard techniques, such as digestion with a collagenase, trypsin or other protease solution. Cells can be easily obtained through a biopsy anywhere in the body, for example, skeletal muscle biopsies can be obtained easily from the arm, forearm, or lower extremities, smooth muscle can be obtained from the area adjacent the subcutaneous tissue throughout the body, and bone marrow can be obtained from the iliac crest. The biopsy can be readily obtained with the use of a biopsy needle, a rapid action needle which makes the procedure extremely simple and almost painless. Cells may also be procured from, for example, cardiac tissue, blood vessels, blood, such as umbilical cord blood or adult blood, valves and discarded tissues, such as placenta and tissue obtained during orthopaedic, reconstructive, aesthetic or cosmetic surgical procedures.

For example, the dermal layer of a skin biopsy can be digested with collagenase or other proteases. After the digestion of the dermal fragments, mesenchymal cells can be harvested following centrifugation and expanded in cell culture media. Alternatively, dermal fibroblasts or adventitial fibroblasts may be used. Fibroblasts are easily available, and they are the primary collagen secreting cells in connective tissues. Dermal fibroblasts are typically harvested from normal adult skin specimens removed during reductive breast surgery, or from neonatal foreskin.

The cells, which may or may not be immobilized on or entrapped in hydrogels, microcarriers or particles including for example nanoparticles, can be introduced into the cell culture media (fluid) within the bioreactor.

II. Applications of the Bioreactors

The oscillating cell culture bioreactor can be used to culture cell populations, i.e., to maintain their viability or expand their quantity, and/or to produce tissue constructs from a suspension of cells or tissue sampled from one or more patients. The cells or tissue constructs produced using the disclosed methods and devices can be used to treat wounds, repair, restore, or replace damaged or diseased tissues or organs in a patient, for example a human. Additionally, the tissue constructs can be used in transplant procedures to replace tissues or organs or parts thereof in a patient in need of such treatment, including use of the cells within the tissue construct as sources of proteins or other products expressed by the cells, or by genes incorporated into the cells by genetic engineering. Particular embodiments provide methods for producing cardiac tissue, cartilage, bone, muscle, and skin tissue. The tissue constructs can have single or multiple layers and can be formed of the same type of cells or multiple types of cells.

The bioreactor system is useful for the mass production of cell-based, tissue engineered constructs for the repair of damaged or defective tissues, according to the tissue engineering approach wherein cells obtained by biopsy are expanded in vitro, cultured on a 3D biomaterial scaffold, and then implanted as an autograft. Accordingly, one embodiment provides a method including the steps of obtaining a sample of cells from a patient, preferably a human, expanding the sample of cells in vitro and/or culturing the cells in the bioreactor system to produce a tissue construct, and implanting the tissue construct in the same or another patient. Methods of surgical implantation are known in the art, and one of ordinary skill in the art of tissue engineering and/or medicine could readily implant the produced tissue construct into a patient.

The bioreactor devices can, be used for cell culture in at least three configurations: (1) for perfusion seeding and culture, i.e., by addition of a cell suspension into a closed chamber containing a scaffold fixed within a holder, (2) for perfusion culture after cell seeding, i.e., by addition of a previously cell seeded construct or by addition of a cell-hydrogel mix directly onto a scaffold, within a holder prior to closing and operating the chamber, and (3) for maintaining the viability of adherent cells or cells in suspension culture, i.e., by adding cell suspensions to a chamber that does not contain any biomaterial scaffold. In the first configuration, significant increases in construct cellularity, thickness, and staining for extracellular matrix demonstrated enhanced cartilage tissue regeneration in the oscillatory cell culture bioreactor.

In the second configuration, significant increases in cardiomyocyte viability, differentiation, and contractility demonstrated enhanced cardiac tissue regeneration in the oscillatory cell culture bioreactor. In the third configuration, suspended heart cells remained viable for 8 days in vitro.

A. Perfusion Seeding and Culture

One embodiment provides a method for producing a tissue construct in which a cell suspension is added into a gas permeable, closed-loop chamber optionally containing a scaffold removably attached to a holder. The method includes introduction of a cell suspension into the closed-loop system by simple injection using a syringe, for example, into a receiving means or inlet. Injection significantly reduces the risk of contamination and facilitates subsequent selective addition/sampling of products (for example, cells, paracrine factors or media). Media, paracrine factors, and pharmacological agents, as well as any other fluid or suspension, can be added through the inlet. Excess media can be drained though the outlet.

The method includes oscillating the closed-loop chamber to force convection of the cell suspension and culture media through the scaffold for example by trapping a small air bubble at the top of the closed-loop chamber or by using a minimally occlusive roller to compress the tubing at the top of closed-loop chamber. The closed-loop chamber can be oscillated by rotating the chamber about the axis parallel to shaft. The angle of rotation is typically less than 360°, preferably less than 300°, more preferably less than 240°, or most preferably 180° in one direction followed by a substantially equivalent rotation in the opposite direction. The speed of the oscillating motion can be adjusted, alone or in combination, with the angle of rotation sufficient to force convection of the cell suspension and culture media through scaffold. Forcing the cells through the scaffold is the “seeding” step of this method. As the cells are moved through the scaffold, a number of the cells will attach to the scaffold and begin to form a tissue construct. Additional cells can attach to the scaffold and to cells attached to the scaffold to form tissue.

The method further provides convective flow of the media through the construct during its culture in the closed-loop chamber. Covective flow of media through the construct is the “perfusion culture” step of this method.

The method further provides gas exchange to the media within the closed-loop chamber during both the seeding and perfusion culture steps. Typically, the closed-loop chamber is maintained in a controlled environment so that gas exchange occurs through the gas permeable walls of the closed-loop chamber. In particular, oxygen passes from the controlled environment into the closed-loop chamber in amounts sufficient to thoroughly saturate the fluid within which the growing tissue construct is immersed. In certain embodiments, the growing tissue construct is sufficiently oxygenated to produce tissue constructs having at least one dimension greater than 200 μm.

B. Perfusion Culture after Cell Seeding

Another embodiment provides a method for producing a tissue construct by oscillating a closed-loop chamber containing a previously cell seeded construct or a scaffold to which a cell-hydrogel mixture has been added. The scaffold is typically removably attached to a holder, and the holder is fixed to the closed-loop chamber. The cell-hydrogel suspension can then be entrapped within a porous scaffold by pipetting the suspension directly onto the scaffold prior to closing the toroidal chamber to localize cell delivery to the scaffold. In one embodiment, the holder is injection molded to fit into the toroidal chamber prior to closure. The toroidal chamber can be closed using conventional methods, for example, by an adhesive, thermal fusion, a clip or press-fit.

Representative hydrogels include, but are not limited to, MATRIGEL™. MATRIGEL™ is the trade name for a gelatinous protein mixture secreted by mouse tumor cells and marketed by BD Biosciences. Other suitable hydrogels are fibrin, collagen, and self-assembling peptides, such as PURAMATRIX™ marketed by 3DM™. Other suitable hydrogels are those formed from poly(hyaluronic acid), poly(sodium alginate), poly(N-isopropyl acrylamide), and poly(anhydride), poly(ethylene glycol), or combinations thereof. In certain embodiments, the hydrogels are biodegradable.

C. Culture of Adherent Cells or Cells in Suspension

Another embodiment provides cells or other biological specimens cultured in a closed-loop chamber without a scaffold, in order to maintain the viability of these cells in prolonged culture. In this method, the cells are added to the closed-loop chamber, eventually adequately coated to induce/prevent cell attachment, containing cell culture media. Typically, the cells are added by injection into the closed-loop chamber through an inlet. The closed-loop chamber is oscillated as described above to provide convection flow of the culture medium and, if necessary, to force the convection of cells off of the bottom of the chamber and maintain the cells in suspension.

D. Methods of Treatment

The cells and tissue constructs produced according the disclosed methods can be used to treat a variety of pathologies. For example, the tissue constructs can be used to treat a wound or damaged tissue of a patient. The damaged tissue can be the result of trauma, genetic defect, surgical procedure, myocardial infarction, atherosclerosis, inflammation, auto immune disease, aneurysm or congenital birth defect. In certain embodiments, the tissue constructs can be used in cosmetic procedures. In a preferred embodiment, the tissue constructs can be used to augment, fortify or support a patient's tissues.

The tissue constructs produced according to the methods disclosed herein can also be used as grafts and transplants in patients in need thereof. The tissue constructs can be formed autologous, allogenic, or xenogenic. For example, the tissue constructs can be used to treat burn victims or patients with cartilage defects by replacing damaged skin or damaged or missing cartilage in a joint.

In still another embodiment, the tissue constructs can be used to replace part or all of a defective organ for example, the heart, skin, liver, kidney, pancreas, eye, or component of the nervous system.

The methods and compositions described herein will be further understood by reference to the following non-limiting examples.

EXAMPLES

Example 1

Perfusion Seeding and Culture

Materials and Methods:

Cells harvested from bovine calf cartilage were cultured on 3D non-woven fibrous scaffolds by perfusion seeding and culture in the oscillating perfused bioreactor (OPB). The two control groups were otherwise identical constructs seeded and cultured either in spinner flasks (SF) and static petri dishes (ST). The DNA content of constructs sampled on day 4 was quantified to provide an index of cell seeding efficiency. Cross-sectional thickness of constructs sampled on day 14 was quantified to provide an index of construct growth. Cell morphology and extracelluar matrix deposition in 14-day constructs were assessed by safranin-O staining for glycosaminoglycans (GAG).

Results and Discussion:

The DNA content of 4-day constructs from the OPB group was significantly higher than the ST group, indicating that the OPB enhanced cell seeding efficiency (FIG. 3A). Cross-sectional thickness of 14-day constructs was significantly affected by the method of seeding and culture, and was highest in the OPB group, indicating the bioreactor enhanced the growth of engineered cartilage (FIG. 3B). The 14-day constructs from the ST group resembled immature cartilage consisting of small round cells and low intensity matrix staining for GAG, a key extracellular matrix component of articular cartilage, whereas those from the OPB group resembled more mature cartilage consisting of round-to-oval chondrocytes in lacunar spaces and intense, spatially homogenous matrix staining for GAG. The 14-day constructs from the SF group exhibited non-homogenous cell and tissue morphologies. Increased cellularity, thickness, and intensity of staining for glycosaminoglycans suggests that perfusion seeding and culture in the oscillating perfused bioreactor enhanced cartilage tissue regeneration.

Example 2

Perfusion Culture after Seeding

Materials and Methods:

Cells harvested from neonatal rat hearts were seeded on 3D porous solid scaffolds by entrapment in MATRIGEL® and then cultured for 8-days statically (ST) or in the oscillating perfused bioreactor (OPB) in either control (CTL) or IGF-supplemented (+IGF) media, Cell viability was quantified by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. Apoptosis was quantified by the terminal deoxynucleotidyl tranferase (TdT)-mediated dUTP nick end labeling (TUNEL) assay. Amounts of cardiac troponin-I (Tn-I) and connexin-43 were assessed by Western blot, and total protein content was quantified by a commercial kit. Contractile amplitude was assessed as percent area change during a contractile cycle by computer based image analysis. Excitation threshold (ET) was assessed by placing constructs between a pair of electrodes to which pacing stimuli were applied at 1 Hz; the voltage at which each impulse was followed by a contractile tissue response defined as the ET. Cell morphology was evaluated by immunohistochemical staining for cardiac Tn-I.

Results and Discussion:

Cell viability was significantly increased by the OPB and by IGF (FIG. 4A), and apoptosis was significantly reduced by the OPB and by IGF (FIG. 4B). Two markers of cardiomyocyte differentiation (cardiac Tn-I and connexin-43) were significantly increased by the OPB (FIG. 4 C-D); these markers were also increased by IGF but not significantly. Total protein content was significantly increased by the OPB (FIG. 4E). Contractile amplitude was significantly increased by the OPB and by IGF (FIG. 4F), and excitation threshold was significantly reduced by the OPB and by IGF (FIG. 4G). Spontaneous, synchronous contractility was readily observed in 8-day constructs cultured in the OPB (OPB CTL, OPB+IGF), but not in constructs cultured statically (ST CTL, ST+IGF). In ST CTL and ST+IGF groups, the cells appeared rounded and expressed low levels of cardiac Tn-I, whereas in the OPB CTL and OPB+IGF groups the cells were elongated and exhibited centrally positioned elongated nuclei and characteristic cross-striations as are characteristic of native heart tissue. Significant improvements in all quantified constructs properties (Table 1) in association with enhanced cell elongation, suggests that perfusion culture in the OPB enhanced cardiomyocyte viability, differentiation, contractility, and hence the regeneration of myocardial tissue. These results were published by Cheng, M. Y., Moretti, M., Engelmayr, G. C., Freed, L. E., (2007) Circulation 116: II-591).

TABLE 1
Individual and interactive effects of experimental parameters on cardiac construct properties.
	Culture Vessel		Interactive
	Static	Static	Bioreactor	Bioreactor	Individual	Individual	effect of
	Culture Medium	effect of	effect Of	Bioreactor
8-day construct property	CTL	IGF	CTL	IGF	Bioreactor	IGF	and IGF
TUNEL positive cells (%, a″3)	53.8 ± 5.6	23.8 ± 1.9*	14.1 ± 1.3*	3.83 ± 0.6*†	P < 0.01	P < 0.01	P < 0.01
MIT (OD units/construct″5)	0.24 ± 0.005	0.34 ± 0.014*	0.61 ± 0.0019*†	0.68 ± 0.022*†‡	P < 0.01	P < 0.01	NS
Cardiac Tropoain-1	1.7 ± 1.7	6.4 ± 2.5	31 ± 4.02*†	40 ± 6.4*†	P < 0.01	NS	NS
(% of native, a″3)
Coaaxxin-13 (% of native, a″3)	18 ± 6.48	31 ± 7.04	39 ± 23	42 ± 4.04*	P < 0.05	NS	NS
Total Protein (mg/construct, a″5)	0.79 ± 0.02	0.84 ± 0.04	1.16 ± 0.08*†	1.29 ± 0.09*†	P < 0.01	NS	NS
Contractile Amplitude	1.14 ± 0.05	1.96 ± 0.09*	3.93 ± 0.17*†	4.701 ± 0.12*†‡	P < 0.01	P < 0.01	NS
(% area change, n″12)
Excitation Threshold	1.26 ± 0.08	0.97 ± 0.02*	0.82 ± 0.05*	0.57 ± 0.03*†‡	P < 0.01	P < 0.01	NS
(volts, a″12)
Construct wet weight (mg, a″5)	42.6 ± 1.6	43.8 ± 1.9	51.4 ± 4.8	50.6 ± 3.8	P < 0.05	NS	NS
DNA (μg/construct a″5)	11.4 ± 1.56	12.7 ± 0.94	13.8 ± 1.32	14.7 ± 0.7	NS	NS	NS
Abbreviations: CTL = control medium; IGF = medium supplemented with insulin-like growth factor I; TUNEL = terminal deoxynucleotidyl transferase; Biotin-
2-deoxyuridine 5-triphosphate nick end labeling; MTT = 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetraxolium bromide DNA = deoxyribonucleic acid; NS = not statistically significant. Data represent the mean ± SEM of n = 3 to 12 independent samples.
*Significantly different (p < 0.05 by Tukey test) from corresponding constructs in the static CTL group.
†Significantly different (p < 0.05 by Tukey test) from corresponding constructs in the static + IGF group.
‡Significantly different (p < 0.05 by Tukey test) from corresponding constructs in the bioreactor CTL group.

Example 3

Perfusion Culture after Seeding

Materials and Methods.

Cells harvested from neonatal rat hearts were seeded on 3D porous solid scaffolds by entrapment in one of three different hydrogels (i.e. MATRIGEL®, a self-assembling peptide gel, PURAMATRIX®, and fibrin gel) and then cultured for 8 days either statically (ST) or in the oscillatory perfused bioreactor (OPB). To provide an index of culture aerobicity, the molar ratio of lactate produced to glucose consumed (Lac/Glu ratio) was calculated, wherein values of 1.0 and 2.0 indicate purely aerobic and purely anaerobic metabolism, respectively.

Result and Discussion.

The Lac/Glu ratio was significantly lower for bioreactor than static cultures of cells (cardiomyocytes) entrapped within 3D porous scaffolds using three different hydrogels (FIG. 5). This result supports the use of the OPE for maintaining aerobicity during culture of large tissue constructs

Example 4

Maintenance of Cell Viability prior to Transplantation

Materials and Methods:

Cells harvested from neonatal rat hearts were cultured in suspension in either the oscillating perfused bioreactor (OPB), spinner flasks (SF), or orbitally mixed flasks (MF). Aliquots of these cell suspensions were sampled at days 0, 2, 4, 6, 8 and cell viability was quantified by trypan blue exclusion.

Result and Discussion:

Cell viability was better maintained in the OPB than either the SF or MF groups, and by culture day 8, the OPB yielded approximately 50% higher cell viability than either SF or MF (FIG. 6). This result shows the use of the OPB for maintaining cell viability prior to transplantation.

Claims

1. A bioreactor comprising one or more gas permeable, closed-loop chambers which can contain fluid and gases and a tissue engineering scaffold for cell or tissue culture;a tissue engineering scaffold or tissue engineering matrix secured directly to the wall of the closed-loop chamber or placed within a means for retaining the scaffold which is secured directly to the wall of closed-loop chamber so that fluid, cells and gases are forced through the entire thickness of the scaffold; andan oscillator and controller for moving the gas permeable, closed-loop chamber bidirectionally along an axis horizontal to an axis normal to the closed-loop chamber to force cells and fluid within the gas permeable, closed-loop chamber by convective flow through the secured tissue engineering scaffold.

2. The bioreactor of claim 1, wherein the gas permeable, closed-loop chamber is toroidal.

3. The bioreactor of claim 1, further comprising a plurality of gas permeable, closed-loop chambers.

4. The bioreactor of claim 1, further comprising a housing for providing controlled environmental conditions.

5. The bioreactor of claim 4, comprising means for maintaining humidity, means for regulating temperature at about 35-37° C., and means for controlling gases to about 21% oxygen and between about 5-10% CO2.

6. The bioreactor of claim 4, wherein the housing oxygenates and buffers the pH of a fluid in the gas permeable, closed-loop chamber.

7. The bioreactor of claim 1, wherein the gas permeable, close-looped chamber comprises a gas-permeable polymer.

8. The bioreactor of claim 7, wherein the gas-permeable polymer is silicone rubber.

9. The bioreactor of claim 7 wherein the polymer is translucent or transparent.

10. The bioreactor of claim 1, further comprising therein cells on the scaffold or tissue engineering matrix.

11. The bioreactor of claim 10 wherein the cells are mammalian cells selected from the group consisting of cardiac cells, mesenchymal cells, fibroblasts, interstitial cells, neural cells, endothelial cells, smooth or skeletal muscle cells, myocytes, chrondocytes, adipocytes, fibromyoblasts, ectodermal cells, ductile and skin cells, hepatocytes, Islet cells, cells present in the intestine, parenchymal cells, osteoblasts, bone marrow cells, blood cells, and stem cells.

12. The bioreactor of claim 1, further comprising a hydrogel in combination with the scaffold or matrix.

13. The bioreactor of claim 1 wherein the scaffold is a hydrogel.

14. The bioreactor of claim 1 comprising cells to be cultured to form cardiac tissue, cartilage, bone, muscle or skin tissue.

15. The bioreactor of claim 1 wherein convective flow is achieved by trapping a bubble at the top of the closed-loop chamber or using a partially occlusive roller which compresses tubing at the top of the closed-loop chamber.

16. A method for culturing cells comprising culturing the cells in a bioreactor comprisingone or more gas permeable, closed-loop chambers which can contain fluid and gases and a tissue engineering scaffold for cell or tissue culture;a tissue engineering scaffold or tissue engineering matrix secured directly to the wall of the closed-loop chamber or placed within a means for retaining the scaffold which is secured directly to the wall of the closed-loop chamber so that fluid, cells and gases are forced through the entire thickness of the scaffold; andan oscillator and controller for moving the gas permeable, closed-loop chamber bidirectionally along an axis horizontal to an axis normal to the closed-loop chamber to force cells and fluid within the gas permeable, closed-loop chamber by convective flow through the secured tissue engineering scaffold.

17. The method of claim 16 for producing a scaffold or tissue engineering matrix comprising placing a scaffold or tissue engineering matrix and culture media in the gas permeable, closed-loop chamber;sealing the gas permeable, closed-loop chamber;oscillating the gas permeable, closed-loop chamber bidirectionally along an axis horizontal to an axis normal to the closed-loop chamber to force convection of the culture media and cells through the scaffold; andculturing the cells in the bioreactor.

18. The method of claim 17, wherein the cells are selected from the group consisting of cardiac cells, mesenchymal cells, fibroblasts, interstitial cells, neural cells, endothelial cells, smooth or skeletal muscle cells, myocytes, chrondocytes, adipocytes, fibromyoblasts, ectodermal cells, ductile and skin cells, hepatocytes, Islet cells, cells present in the intestine, parenchymal cells, osteoblasts, bone marrow cells, blood cells, and stem cells.

19. The method of claim 16 wherein convective flow is achieved by trapping a bubble at the top of the closed-loop chamber or using a partially occlusive roller which compresses tubing at the top of the closed-loop chamber.