A reproducible, high throughput method for fabricating fibrin gels

Structure, Properties and Degradation of Self-Assembled Fibrinogen Nanofiber Scaffolds

Self-assembled fibrinogen nanofibers are promising candidates for skin tissue engineering due to their biocompatibility and ability to mimic the native blood clot architecture. Here, we studied the structure-property relationship and degradation of rehydrated fibrinogen nanofibers prepared by salt-induced self-assembly, focusing on the effect of scaffold layering, cross-linking time and freeze-drying. Optimal fiber stability was achieved with cross-linking by formaldehyde (FA) vapor, while treatment with liquid aldehydes, genipin, EDC, and transglutaminase failed to preserve the nanofibrous architecture upon rehydration. Scaffold layering did not significantly influence the mechanical properties but changed the scaffold architecture, with bulk fiber scaffolds being more compact than layered scaffolds. Freeze-drying maintained the mechanical properties and interconnected pore network with average pore diameters around 20 μm, which will enhance the storage stability of self-assembled fibrinogen scaffolds. Varying cross-linking times altered the scaffold mechanics without affecting the swelling behavior, indicating that scaffold hydration can be controlled independently of the mechanical characteristics. Cross-linking times of 240 min increased scaffold stiffness and decreased elongation, while 30 min resulted in mechanical properties similar to native skin. Cross-linking for 120 min was found to reduce scaffold degradation by various enzymes in comparison to 60 min. Overall, after 35 days of incubation, plasmin and a combination of urokinase and plasminogen exhibited the strongest degradative effect, with nanofibers being more susceptible to enzymatic degradation than planar fibrinogen due to their higher specific surface area. Based on these results, self-assembled fibrinogen fiber scaffolds show great potential for future applications in soft tissue engineering that require controlled structure-function relationships and degradation characteristics.

Histotripsy Bubble Dynamics in Elastic, Anisotropic Tissue-Mimicking Phantoms

Elastic, anisotropic tissue such as tendon has proven resistant to mechanical fractionation by histotripsy, a subset of focused ultrasound that uses the creation, oscillation and collapse of cavitation bubbles to fractionate tissue. Our objective was to fabricate an optically transparent hydrogel that mimics tendon for evaluation of histotripsy bubble dynamics. Ex vivo bovine deep digital flexor tendons were obtained (n = 4), and varying formulations of polyacrylamide (PA), collagen and fibrin hydrogels (n = 3 each) were fabricated. Axial sound speeds were measured at 1 MHz for calculation of anisotropy. All samples were treated with a 1.5-MHz focused ultrasound transducer with 10-ms pulses repeated at 1 Hz (p+ = 127 MPa, p- = 35 MPa); treatments were monitored with passive cavitation imaging and high-speed photography. Dehydrated fibrin gels were found to be the most similar to tendon in cavitation emission energy (fibrin = 0.69 ± 0.24, tendon = 0.64 ± 0.19 [× 1010 V2]) and anisotropy (fibrin = 3.16 ± 1.12, tendon = 19.4). Bubble cloud area in dehydrated fibrin (0.79 ± 0.14 mm2) was significantly smaller than most other tested hydrogels. Finally, anisotropy was found to have moderately strong linear relationships with cavitation energy and bubble cloud size (r = -0.65 and -0.80, respectively). Dehydrated fibrin shows potential as a repeatable, transparent, tissue-mimicking hydrogel for evaluation of histotripsy bubble dynamics in elastic, anisotropic tissues.

A Multifunctional 3D Bioprinting System for Construction of Complex Tissue Structure Scaffolds: Design and Application

Three-dimensional (3D) bioprinting offers a potentially powerful new approach to reverse engineering human pathophysiology to address the problem of developing more biomimetic experimental systems. Human tissues and organs are multiscale and multi-material structures. The greatest challenge for organ printing is the complexity of the structural elements, from the shape of the macroscopic structure to the details of the nanostructure. A highly bionic tissue-organ model requires the use of multiple printing processes. Some printers with multiple nozzles and multiple processes are currently reported. However, the bulk volume, which is inconvenient to move, and the high cost of these printing systems limits the expansion of their applications. Scientists urgently need a multifunctional miniaturized 3D bioprinter. In this study, a portable multifunctional 3D bioprinting system was built based on a modular design and a custom written operating application. Using this platform, constructs with detailed surface structures, hollow structures, and multiscale complex tissue analogs were successfully printed using commercial polymers and a series of hydrogel-based inks. With further development, this portable, modular, low-cost, and easy-to-use Bluetooth-enabled 3D printer promises exciting opportunities for resource-constrained application scenarios, not only in biomedical engineering but also in the education field, and may be used in space experiments.

A Minireview of Microfluidic Scaffold Materials in Tissue Engineering

In 2020, nearly 107,000 people in the U.S needed a lifesaving organ transplant, but due to a limited number of donors, only ∼35% of them have actually received it. Thus, successful bio-manufacturing of artificial tissues and organs is central to satisfying the ever-growing demand for transplants. However, despite decades of tremendous investments in regenerative medicine research and development conventional scaffold technologies have failed to yield viable tissues and organs. Luckily, microfluidic scaffolds hold the promise of overcoming the major challenges associated with generating complex 3D cultures: 1) cell death due to poor metabolite distribution/clearing of waste in thick cultures; 2) sacrificial analysis due to inability to sample the culture non-invasively; 3) product variability due to lack of control over the cell action post-seeding, and 4) adoption barriers associated with having to learn a different culturing protocol for each new product. Namely, their active pore networks provide the ability to perform automated fluid and cell manipulations (e.g., seeding, feeding, probing, clearing waste, delivering drugs, etc.) at targeted locations in-situ. However, challenges remain in developing a biomaterial that would have the appropriate characteristics for such scaffolds. Specifically, it should ideally be: 1) biocompatible-to support cell attachment and growth, 2) biodegradable-to give way to newly formed tissue, 3) flexible-to create microfluidic valves, 4) photo-crosslinkable-to manufacture using light-based 3D printing and 5) transparent-for optical microscopy validation. To that end, this minireview summarizes the latest progress of the biomaterial design, and of the corresponding fabrication method development, for making the microfluidic scaffolds.

Self-assembled fibrinogen nanofibers support fibroblast adhesion and prevent E. coli infiltration

Fibrinogen nanofibers hold great potential for wound healing applications since they mimic the native blood clot architecture and offer important binding sites to support fibroblast adhesion and migration. Recently, we introduced a new method of salt-induced self-assembly to prepare nanofibrous fibrinogen scaffolds. Here, we present our results on the mechanical properties of these scaffolds and their interaction with 3T3 fibroblasts and E. coli bacteria, which we used as model systems for wound healing. Hydrated, nanofibrous fibrinogen scaffolds showed a Young's modulus of 1.3 MPa, which is close to the range of native fibrin. 3T3 fibroblasts adhered and proliferated well on nanofibrous and planar fibrinogen up to 72 h with a less pronounced actin cytoskeleton on nanofibers in comparison to planar fibrinogen. Fibroblasts on nanofibers were smaller with many short filopodia while larger cells with few long filopodia were found on planar fibrinogen. Live cell tracking revealed higher migration velocities on nanofibers in comparison to planar fibrinogen. The growth of E. coli bacteria on nanofibrous fibrinogen was significantly reduced as compared to agar controls with no bacteria migrating through the nanofibers. In summary, we conclude that self-assembled fibrinogen nanofibers could become highly attractive as future scaffolds for wound healing applications.

Towards Mimicking the Fetal Liver Niche: The Influence of Elasticity and Oxygen Tension on Hematopoietic Stem/Progenitor Cells Cultured in 3D Fibrin Hydrogels

Hematopoietic stem/progenitor cells (HSPCs) are responsible for the generation of blood cells throughout life. It is believed that, in addition to soluble cytokines and niche cells, biophysical cues like elasticity and oxygen tension are responsible for the orchestration of stem cell fate. Although several studies have examined the effects of bone marrow (BM) niche elasticity on HSPC behavior, no study has yet investigated the effects of the elasticity of other niche sites like the fetal liver (FL), where HSPCs expand more extensively. In this study, we evaluated the effect of matrix stiffness values similar to those of the FL on BM-derived HSPC expansion. We first characterized the elastic modulus of murine FL tissue at embryonic day E14.5. Fibrin hydrogels with similar stiffness values as the FL (soft hydrogels) were compared with stiffer fibrin hydrogels (hard hydrogels) and with suspension culture. We evaluated the expansion of total nucleated cells (TNCs), Lin⁻/cKit⁺ cells, HSPCs (Lin⁻/Sca⁺/cKit⁺ (LSK) cells), and hematopoietic stem cells (HSCs: LSK- Signaling Lymphocyte Activated Molecule (LSK-SLAM) cells) when cultured in 5% O₂ (hypoxia) or in normoxia. After 10 days, there was a significant expansion of TNCs and LSK cells in all culture conditions at both levels of oxygen tension. LSK cells expanded more in suspension culture than in both fibrin hydrogels, whereas TNCs expanded more in suspension culture and in soft hydrogels than in hard hydrogels, particularly in normoxia. The number of LSK-SLAM cells was maintained in suspension culture and in the soft hydrogels but not in the hard hydrogels. Our results indicate that both suspension culture and fibrin hydrogels allow for the expansion of HSPCs and more differentiated progeny whereas stiff environments may compromise LSK-SLAM cell expansion. This suggests that further research using softer hydrogels with stiffness values closer to the FL niche is warranted.

Short Term Results of Fibrin Gel Obtained from Cord Blood Units: A Preliminary in Vitro Study

BACKGROUND

Recent findings have shown that the fibrin gel derived from cord blood units (CBUs) play a significant role in wound healing and tissue regeneration. The aim of this study was to standardize the fibrin gel production process in order to allow for its regular use.

METHODS

CBUs (n = 200) were assigned to 4 groups according to their initial volume. Then, a two-stage centrifugation protocol was applied in order to obtain platelet rich plasma (PRP). The concentration of platelets (PLTs), white blood cells (WBCs) and red blood cells (RBCs) were determined prior to and after the production process. In addition, targeted proteomic analysis using multiple reaction monitoring was performed. Finally, an appropriate volume of calcium gluconate was used in PRP for the production of fibrin gel.

RESULTS

The results of this study showed that high volume CBUs were characterized by greater recovery rates, concentration and number of PLTs compared to the low volume CBUs. Proteomic analysis revealed the presence of key proteins for regenerative medicine. Fibrin gel was successfully produced from CBUs of all groups.

CONCLUSION

In this study, low volume CBUs could be an alternative source for the production of fibrin gel, which can be used in multiple regenerative medicine approaches.

Plasma-based fast-gelling biohybrid gels for biomedical applications

Blood based biomaterials are widely researched and used in different biomedical applications including cell therapy, drug delivery, sealants etc. due to their biocompatibility and biodegradability. Blood derived gels are successfully used in clinical studies due to the presence of fibrinogen and several platelet growth factors. In spite of their wide applications, it is challenging to use blood-based biomaterials due to their low mechanical stability, poor adhesive property and contamination risk. In this study, we used porcine plasma to form gel in presence of biodegradable synthetic crosslinkers. Mechanical strength of this plasma gel could be tailored by altering the amount of crosslinkers for any desired biomedical applications. These plasma gels, formed by the synthetic crosslinkers, were utilized as a drug delivery platform for wound healing due to their low cytotoxicity. A model drug release study with these plasma gels indicated slow and sustained release of the drugs.

Physical Properties of Implanted Porous Bioscaffolds Regulate Skin Repair: Focusing on Mechanical and Structural Features

Porous bioscaffolds are applied to facilitate skin repair since the early 1990s, but a perfect regeneration outcome has yet to be achieved. Until now, most efforts have focused on modulating the chemical properties of bioscaffolds, while physical properties are traditionally overlooked. Recent advances in mechanobiology and mechanotherapy have highlighted the importance of biomaterials' physical properties in the regulation of cellular behaviors and regenerative processes. In skin repair, the mechanical and structural features of porous bioscaffolds are two major physical properties that determine therapeutic efficacy. Here, first an overview of natural skin repair with an emphasis on the major biophysically sensitive cell types involved in this multistage process is provided, followed by an introduction of the four roles of bioscaffolds as skin implants. Then, how the mechanical and structural features of bioscaffolds influence these four roles is discussed. The mechanical and structural features of porous bioscaffolds should be tailored to balance the acceleration of wound closure and functional improvements of the repaired skin. This study emphasizes that decoupling and precise control of the mechanical and structural features of bioscaffolds are significant aspects that should be considered in future biomaterial optimization, which can build a foundation to ultimately achieve perfect skin regeneration outcomes.

Engineering fibrin hydrogels to promote the wound healing potential of mesenchymal stem cell spheroids

Mesenchymal stem cells (MSCs) secrete endogenous factors such as vascular endothelial growth factor (VEGF) and prostaglandin E2 (PGE2) that promote angiogenesis, modulate the inflammatory microenvironment, and stimulate wound repair, and MSC spheroids secrete more trophic factors than dissociated, individual MSCs. Compared to injection of cells alone, transplantation of MSCs in a biomaterial can enhance their wound healing potential by localizing cells at the defect site and upregulating trophic factor secretion. To capitalize on the therapeutic potential of spheroids, we engineered a fibrin gel delivery vehicle to simultaneously enhance the proangiogenic and anti-inflammatory potential of entrapped human MSC spheroids. We used multifactorial statistical analysis to determine the interaction between four input variables derived from fibrin gel synthesis on four output variables (gel stiffness, gel contraction, and secretion of VEGF and PGE2). Manipulation of the four input variables tuned fibrin gel biophysical properties to promote the simultaneous secretion of VEGF and PGE2 by entrapped MSC spheroids while maintaining overall gel integrity. MSC spheroids in stiffer gels secreted the most VEGF, while PGE2 secretion was highest in more compliant gels. Simultaneous VEGF and PGE2 secretion was greatest using hydrogels with intermediate mechanical properties, as small increases in stiffness increased VEGF secretion while maintaining PGE2 secretion by entrapped spheroids. The fibrin gel formulation predicted to simultaneously increase VEGF and PGE2 secretion stimulated endothelial cell proliferation, enhanced macrophage polarization, and promoted angiogenesis when used to treat a wounded three-dimensional human skin equivalent. These data demonstrate that a statistical approach is an effective strategy to formulate fibrin gel formulations that enhance the wound healing potential of human MSCs.

STATEMENT OF SIGNIFICANCE

Mesenchymal stem cells (MSCs) are under investigation for wound healing applications due to their secretion of bioactive factors that enhance granulation tissue formation, blood vessel ingrowth, and reduce inflammation. However, the effectiveness of cell-based therapies is reduced due to poor engraftment and high rates of cell death when transplanted into harsh environments characteristic of large wounds. Compared to dissociated cells, MSCs exhibit increased overall function when aggregated into three-dimensional spheroids, and transplantation of cells using biomaterials is one strategy for guiding cell function in the defect site. The present study demonstrates that the biophysical properties of fibrin hydrogels, designed for use as a cell carrier, can be engineered to dictate the secretion of bioactive factors by entrapped MSC spheroids. This strategy enables MSCs to contribute to wound healing by synergistically promoting neovascularization and modulating the inflammatory milieu.

Mesenchymal Stem Cell Spheroids Retain Osteogenic Phenotype Through α2β1 Signaling

The induction of mesenchymal stem cells (MSCs) toward the osteoblastic lineage using osteogenic supplements prior to implantation is one approach under examination to enhance their bone-forming potential. Spheroids formed from induced cells exhibited improved retention of osteogenic markers as a function of integrin binding to cell-secreted extracellular matrix (ECM). These results demonstrate the capacity of spheroidal culture to sustain the mineral-producing phenotype of MSCs, thus enhancing their contribution toward bone formation and repair.

The induction of mesenchymal stem cells (MSCs) toward the osteoblastic lineage using osteogenic supplements prior to implantation is one approach under examination to enhance their bone-forming potential. MSCs rapidly lose their induced phenotype upon removal of the soluble stimuli; however, their bone-forming potential can be sustained when provided with continued instruction via extracellular matrix (ECM) cues. In comparison with dissociated cells, MSC spheroids exhibit improved survival and secretion of trophic factors while maintaining their osteogenic potential. We hypothesized that entrapment of MSC spheroids formed from osteogenically induced cells would exhibit better preservation of their bone-forming potential than would dissociated cells from monolayer culture. Spheroids exhibited comparable osteogenic potential and increased proangiogenic potential with or without osteogenic preconditioning versus monolayer-cultured MSCs. Spheroids were then entrapped in collagen hydrogels, and the osteogenic stimulus was removed. In comparison with entrapped dissociated MSCs, spheroids exhibited significantly increased markers of osteogenic differentiation. The capacity of MSC spheroids to retain their osteogenic phenotype upon withdrawal of inductive cues was mediated by α₂β₁ integrin binding to cell-secreted ECM. These results demonstrate the capacity of spheroidal culture to sustain the mineral-producing phenotype of MSCs, thus enhancing their contribution toward bone formation and repair.

Significance

Despite the promise of mesenchymal stem cells (MSCs) for cell-based therapies for tissue repair and regeneration, there is little evidence that transplanted MSCs directly contribute to new bone formation, suggesting that induced cells rapidly lose their osteogenic phenotype or undergo apoptosis. In comparison with dissociated cells, MSC spheroids exhibit increased trophic factor secretion and improved cell survival. The loss of phenotype represents a significant clinical challenge for cell therapies, yet there is no evidence for whether MSC spheroids retain their osteogenic phenotype upon entrapment in a clinically relevant biomaterial. These findings demonstrate that MSC spheroids retain their osteogenic phenotype better than do dissociated MSCs, and this is due to integrin engagement with the cell-secreted extracellular matrix. These data provide evidence for a novel approach for potentiating the use of MSCs in bone repair.

Hydrogel biophysical properties instruct coculture-mediated osteogenic potential

Cell-based approaches for bone formation require instructional cues from the surrounding environment. As an alternative to pharmacological strategies or transplanting single cell populations, one approach is to coimplant populations that can establish a new vasculature and differentiate to bone-forming osteoblasts. Mesenchymal stem/stromal cells (MSCs) possess osteogenic potential and produce numerous angiogenic growth factors. Endothelial colony-forming cells (ECFCs) are a subpopulation of endothelial progenitor cells capable of vasculogenesis in vivo and may provide endogenous cues to support MSC function. We investigated the contribution of the carrier biophysical properties to instruct entrapped human MSCs and ECFCs to simultaneously promote their osteogenic and proangiogenic potential. Compared with gels containing MSCs alone, fibrin gels engineered with increased compressive stiffness simultaneously increased the osteogenic and proangiogenic potential of entrapped cocultured cells. ECFCs produced bone morphogenetic protein-2 (BMP-2), a potent osteoinductive molecule, and increases in BMP-2 secretion correlated with gel stiffness. Coculture of MSCs with ECFCs transduced to knockdown BMP-2 production abrogated the osteogenic response to levels observed with MSCs alone. These results demonstrate that physical properties of engineered hydrogels modulate the function of cocultured cells in the absence of inductive cues, thus increasing the translational potential of coimplantation to speed bone formation and repair.

Implantation of fibrin gel on mouse lung to study lung-specific angiogenesis

Recent significant advances in stem cell research and bioengineering techniques have made great progress in utilizing biomaterials to regenerate and repair damage in simple tissues in the orthopedic and periodontal fields. However, attempts to regenerate the structures and functions of more complex three-dimensional (3D) organs such as lungs have not been very successful because the biological processes of organ regeneration have not been well explored. It is becoming clear that angiogenesis, the formation of new blood vessels, plays key roles in organ regeneration. Newly formed vasculatures not only deliver oxygen, nutrients and various cell components that are required for organ regeneration but also provide instructive signals to the regenerating local tissues. Therefore, to successfully regenerate lungs in an adult, it is necessary to recapitulate the lung-specific microenvironments in which angiogenesis drives regeneration of local lung tissues. Although conventional in vivo angiogenesis assays, such as subcutaneous implantation of extracellular matrix (ECM)-rich hydrogels (e.g., fibrin or collagen gels or Matrigel - ECM protein mixture secreted by Engelbreth-Holm-Swarm mouse sarcoma cells), are extensively utilized to explore the general mechanisms of angiogenesis, lung-specific angiogenesis has not been well characterized because methods for orthotopic implantation of biomaterials in the lung have not been well established. The goal of this protocol is to introduce a unique method to implant fibrin gel on the lung surface of living adult mouse, allowing for the successful recapitulation of host lung-derived angiogenesis inside the gel. This approach enables researchers to explore the mechanisms by which the lung-specific microenvironment controls angiogenesis and alveolar regeneration in both normal and pathological conditions. Since implanted biomaterials release and supply physical and chemical signals to adjacent lung tissues, implantation of these biomaterials on diseased lung can potentially normalize the adjacent diseased tissues, enabling researchers to develop new therapeutic approaches for various types of lung diseases.

Engineered Fibrin Gels for Parallel Stimulation of Mesenchymal Stem Cell Proangiogenic and Osteogenic Potential

Mesenchymal stem/stromal cells (MSCs) are under examination for use in cell therapies to repair bone defects resulting from trauma or disease. MSCs secrete proangiogenic cues and can be induced to differentiate into bone-forming osteoblasts, yet there is limited evidence that these events can be achieved in parallel. Manipulation of the cell delivery vehicle properties represents a candidate approach for directing MSC function in bone healing. We hypothesized that the biophysical properties of a fibrin gel could simultaneously regulate the proangiogenic and osteogenic potential of entrapped MSCs. Fibrin gels were formed by supplementation with NaCl (1.2, 2.3, and 3.9% w/v) to modulate gel biophysical properties without altering protein concentrations. MSCs entrapped in 1.2% w/v NaCl gels were the most proangiogenic in vitro, yet cells in 3.9% w/v gels exhibited the greatest osteogenic response. Compared to the other groups, MSCs entrapped in 2.3% w/v gels provided the best balance between proangiogenic potential, osteogenic potential, and gel contractility. The contribution of MSCs to bone repair was then examined when deployed in 2.3% w/v NaCl gels and implanted into an irradiated orthotopic bone defect. Compared to acellular gels after 3 weeks of implantation, defects treated with MSC-loaded fibrin gels exhibited significant increases in vessel density, early osteogenesis, superior morphology, and increased cellularity of repair tissue. Defects treated with MSC-loaded gels exhibited increased bone formation after 12 weeks compared to blank gels. These results confirm that fibrin gel properties can be modulated to simultaneously promote both the proangiogenic and osteogenic potential of MSCs, and fibrin gels modified by supplementation with NaCl are promising carriers for MSCs to stimulate bone repair in vivo.

Human mesenchymal stem cell spheroids in fibrin hydrogels exhibit improved cell survival and potential for bone healing

Mesenchymal stem cells (MSCs) have great therapeutic potential for the repair of nonhealing bone defects, because of their proliferative capacity, multilineage potential, trophic factor secretion and lack of immunogenicity. However, a major challenge to the translation of cell-based therapies into clinical practice is ensuring their survival and function upon implantation into the defect site. We hypothesize that forming MSCs into more physiologic three-dimensional spheroids, rather than employing dissociated cells from two-dimensional monolayer culture, will enhance their survival when exposed to a harsh microenvironment but maintain their osteogenic potential. MSC spheroids were formed by using the hanging drop method with increasing cell numbers. Compared with larger spheroids, the smallest spheroids, which contained 15,000 cells, exhibited increased metabolic activity, reduced apoptosis and the most uniform distribution of proliferating cells. Spheroids were then entrapped in fibrin gels and cultured in serum-free medium and 1 % oxygen. Compared with identical numbers of dissociated MSCs in fibrin gels, spheroids exhibited significantly reduced apoptosis and secreted up to 100-fold more vascular endothelial growth factor. Moreover, fibrin gels containing spheroids and those containing an equivalent number of dissociated cells exhibited similar expression levels of early and late markers of osteogenic differentiation. Thus, MSC spheroids exhibit greater resistance to apoptosis and enhanced proangiogenic potential while maintaining similar osteogenic potential to dissociated MSCs entrapped in a clinically relevant biomaterial, supporting the use of MSC spheroids in cell-based approaches to bone repair.

Lysophosphatidic acid enhances stromal cell-directed angiogenesis

Ischemic diseases such as peripheral vascular disease (PVD) affect more than 15% of the general population and in severe cases result in ulcers, necrosis, and limb loss. While the therapeutic delivery of growth factors to promote angiogenesis has been widely investigated, large-scale implementation is limited by strategies to effectively deliver costly recombinant proteins. Multipotent adipose-derived stromal cells (ASC) and progenitor cells from other tissue compartments secrete bioactive concentrations of angiogenic molecules, making cell-based strategies for in situ delivery of angiogenic cytokines an exciting alternative to the use of recombinant proteins. Here, we show that the phospholipid lysophosphatidic acid (LPA) synergistically improves the proangiogenic effects of ASC in ischemia. We found that LPA upregulates angiogenic growth factor production by ASC under two- and three-dimensional in vitro models of serum deprivation and hypoxia (SD/H), and that these factors significantly enhance endothelial cell migration. The concurrent delivery of LPA and ASC in fibrin gels significantly improves vascularization in a murine critical hindlimb ischemia model compared to LPA or ASC alone, thus exhibiting the translational potential of this method. Furthermore, these results are achieved using an inexpensive lipid molecule, which is orders-of-magnitude less costly than recombinant growth factors that are under investigation for similar use. Our results demonstrate a novel strategy for enhancing cell-based strategies for therapeutic angiogenesis, with significant applications for treating ischemic diseases.

Assembly of discrete collagen-chitosan microenvironments into multiphase tissue constructs

Modular assembly of protein-polysaccharide microenvironments into 3D macroscale tissue constructs is reported. Rapid and simple centrifugation and vacuum molding methods are used to create cohesive multiphase constructs with prescribed geometries. Human fibroblasts are shown to survive in the microenvironments and in the macroscale constructs. Control of the spatial organization in engineered tissues is a key to recreating the complex tissue architectures needed for regenerative therapies.