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The vasculature is an essential component of the circulatory system that plays a vital role in the development, homeostasis, and disease of various organs in the human body. The ability to emulate the architecture and transport function of blood vessels in the integrated context of their associated organs represents an important requirement for studying a wide range of physiological processes. Traditional in vitro models of the vasculature, however, largely fail to offer such capabilities. Here we combine microfluidic three-dimensional (3D) cell culture with the principle of vasculogenic self-assembly to engineer perfusable 3D microvascular beds in vitro. Our system is created in a micropatterned hydrogel construct housed in an elastomeric microdevice that enables coculture of primary human vascular endothelial cells and fibroblasts to achieve de novo formation, anastomosis, and controlled perfusion of 3D vascular networks. An open-top chamber design adopted in this hybrid platform also makes it possible to integrate the microengineered 3D vasculature with other cell types to recapitulate organ-specific cellular heterogeneity and structural organization of vascularized human tissues. Using these capabilities, we developed stem cell-derived microphysiological models of vascularized human adipose tissue and the blood-retinal barrier. Our approach was also leveraged to construct a 3D organotypic model of vascularized human lung adenocarcinoma as a high-content drug screening platform to simulate intravascular delivery, tumor-killing effects, and vascular toxicity of a clinical chemotherapeutic agent. Furthermore, we demonstrated the potential of our platform for applications in nanomedicine by creating microengineered models of vascular inflammation to evaluate a nanoengineered drug delivery system based on active targeting liposomal nanocarriers. These results represent a significant improvement in our ability to model the complexity of native human tissues and may provide a basis for developing predictive preclinical models for biopharmaceutical applications.

Purpose: To compare the physical and biological characteristics of commercial gamma-irradiated corneas with those of fresh human corneas and to determine suitability for transplantation. Methods: The physical properties of gamma-irradiated and fresh corneas were evaluated with respect to light transmittance, hydration (swelling ratio), elastic modulus (compressive modulus by the indentation method), matrix organization (differential scanning calorimetry), and morphology (light and transmission electron microscopy). The biological properties of the gamma-irradiated cornea, including residual cell content and cellular biocompatibility, were evaluated by quantifying DNA content and measuring the proliferation rate of human corneal epithelial cells, respectively. Results: The hydration, light transmittance, elastic modulus, and proliferation rate of human corneal epithelial cells were not significantly different between fresh and gamma-irradiated corneas. However, differences were observed in tissue morphology, DNA content, and thermal properties. The density of collagen fibrils of the gamma-irradiated corneal sample (160.6 6 33.2 fibrils/mm 2 ) was significantly lower than that of the fresh corneal sample (310.0 6 44.7 fibrils/mm 2 ). Additionally, in the gamma-irradiated corneas, cell fragments—but not viable cells—were observed, supported by lower DNA content of the gamma-irradiated cornea (1.0 6 0.1 mg/mg) than in fresh corneas (1.9 mg/mg). Moreover, the denaturation temperature of gamma-irradiated corneas (61.8 6 1.1 °C) was significantly lower than that of fresh corneas (66.1 6 1.9 °C). Conclusions: Despite structural changes due to irradiation, the physical and biological properties of the gamma-irradiated cornea remain similar to the fresh cornea. These factors, combined with a decreased risk of rejection and longer shelf life, make the gammairradiated tissue a viable and clinically desired option in various ophthalmic procedures.

The main functions of the conjunctiva, an essential part of the ocular surface, are to maintain the equilibrium of the tear film and to protect the eye. Upon injuries, the prerequisite to successful ocular surface repair is conjunctival reconstruction. Tissue engineering techniques, including transplantation of autografts, amniotic membranes and numerous synthetic/natural materials, have been developed. However, none of these strategies is completely satisfactory due to lack of goblet cell repopulation, poor mechanical properties or non-standardized preparation procedure. Here, we cultured conjunctival epithelial cells on vitrified collagen membranes and developed a tissue equivalent for repairing damaged conjunctiva. Optimized vitrified collagen has superior mechanical and optical properties to previous biomaterials for ocular surface application, and its unique fibrillar structure significantly benefited conjunctival epithelial cell growth and the phenotypic development in vitro. In a rabbit model, vitrified collagen greatly promoted conjunctival regeneration with rapid re-epithelization, sufficient repopulation of goblet cells and minimized fibrosis and wound contracture, proved by gene expression analyses and histological staining. In conclusion, we have demonstrated the potential suitability of utilizing vitrified collagen-based tissue equivalent in ocular surface reconstruction.

This study was performed to evaluate the potential of a chondroitin sulfate-polyethylene glycol (CS-PEG) adhesive and collagen-based membrane (collagen vitrigel, CV) combination as a method to treat penetrating ocular injuries on the battlefield and to improve this method with two technologies: an antibiotic releasing CS-PEG adhesive and a corneal shaped CV. Burst testing using porcine cadaveric eyes, high-performance liquid chromatography, the Kirby-Bauer bacterial inhibition test, and CV implantations on the live and cadaveric rabbit eyes were performed. The ocular burst test showed CS-PEG adhesive could successfully repair 5-mm to 6-mm length wounds in the corneal and corneoscleral regions but would require CS-PEG + CV to treat larger wounds similar to those seen on the battlefield. In addition, high performance liquid chromatography and the Kirby-Bauer bacterial inhibition test presented evidence suggesting the vancomycin incorporated CS-PEG could inhibit Staphylococcus infection for 9 days. Furthermore, the curved CV showed an advantage by matching the corneal contour without any wrinkle formation. Although this pilot study showed a limited range of possible applications, we demonstrated that the combination of CS-PEG adhesive + CV is a promising method and the 2 technologies improve their applicability to the special demands of the battlefield.

Replacement of autogenous or allograft bones by artificial graft materials represents a growing area of interest in current bone repair strategies. Bioactive ceramics in particulate form, such as Bioglass® (BG) 45S5, stimulate bone mineralization comparable to autologous bone grafts, but have potential issues of particle migration and inflammation. The aim of this study was to employ a chondroitin sulfate- (CS-) based bioadhesive to improve integration of the bioglass (NovaBone® Putty) to prevent particle migration and promote bone regeneration. This BG-CS composite can encapsulate bone marrow (BM) to form a mechanically stable construct, BG-CS-BM. Rheological characterization confirmed the formation of CS-BM hydrogel by reacting the CS-based bioadhesive with the BM. Compared to the bioglass, the BG-CS-BM composite demonstrated a superior capacity to maintain construct integrity under both aqueous and turbulent environments in vitro. After implantation for 4 weeks in a critical-size distal femoral bone defect in a rabbit model, there was significantly greater bone growth in BG-CS-BM as compared to bioglass-only and the empty control. Unlike BG-CS-BM, BG-CS recruited BM in situ from the bone defect. BG-CS demonstrated a similar effect in bone formation but at a comparatively slower rate than BG-CS-BM over 6-weeks' implantation. © 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 103A: 235–242, 2015.

Hyaluronic acid (HA) solutions effectively lubricate the ocular surface and are used for the relief of dry eye related symptoms. However, HA undergoes rapid clearance due to limited adhesion, which necessitates frequent instillation. Conversely, highly viscous artificial tear formulations with HA blur vision and interfere with blinking. Here, we developed an HA-eye drop formulation that selectively binds and retains HA for extended periods of time on the ocular surface. We synthesized a heterobifunctional polymer-peptide system with one end binding HA while the other end binding either sialic acid-containing glycosylated transmembrane molecules on the ocular surface epithelium, or type I collagen molecule within the tissue matrix. HA solution was mixed with the polymer-peptide system and tested on both ex vivo and in vivo models to determine its ability to prolong HA retention. Furthermore, rabbit ocular surface tissues treated with binding peptides and HA solutions demonstrated superior lubrication with reduced kinetic friction coefficients compared to tissues treated with conventional HA solution. The results suggest that binding peptide-based solution can keep the ocular surface enriched with HA for prolonged times as well as keep it lubricated. Therefore, this system can be further developed into a more effective treatment for dry eye patients than a standard HA eye drop. Statement of Significance Eye drop formulations containing HA are widely used to lubricate the ocular surface and relieve dry eye related symptoms, however its low residence time remains a challenge. We designed a polymer-peptide system for the targeted delivery of HA to the ocular surface using sialic acid or type I collagen as anchors for HA immobilization. The addition of the polymer-peptide system to HA eye drop exhibited a reduced friction coefficient, and it can keep the ocular surface enriched with HA for prolonged time. This system can be further developed into a more effective treatment for dry eye than a standard HA eye drop.

Cellular metabolic activity, especially mitochondrial metabolism, plays a vital role in regulating cell proliferation and differentiation. Metabolism could therefore be an important factor to consider when using engineering technologies to stimulate tissue development and repair. The small metabolite carnitine and its derivative acetylcarnitine affect the activities of several pathways in mitochondrial metabolism, but their influence on cell differentiation has not yet been thoroughly studied. To elucidate the effects of these two small molecules on mesenchymal tissue engineering, we used adult stem cells as a platform in both monolayer and 3D hydrogel culture systems. We investigated the impact of these two small molecules on the differentiation of adult stem cells and analysed gene expression, cell proliferation and extracellular matrix deposition. We found that the molecules reduced adipogenesis but stimulated osteogenesis and chondrogenesis in both culture systems. Our results suggest that carnitine and acetylcarnitine could affect the differentiation rate of adult stem cells by regulating mitochondrial metabolism. The effects of these two small molecules give rise to the possibility of employing such metabolites in tissue-engineering systems to enhance cell differentiation and tissue development.

Bone substitutes can be designed to replicate physiological structure and function by creating a microenvironment that supports crosstalk between bone and immune cells found in the native tissue, specifically osteoblasts and osteoclasts. Human induced pluripotent stem cells (hiPSC) represent a powerful tool for bone regeneration because they are a source of patient-specific cells that can differentiate into all specialized cell types residing in bone. We show that osteoblasts and osteoclasts can be differentiated from hiPSC-mesenchymal stem cells and macrophages when co-cultured on hydroxyapatite-coated poly(lactic-co-glycolic acid)/poly(L-lactic acid) (HA–PLGA/PLLA) scaffolds. Both cell types seeded on the PLGA/PLLA especially with 5% w/v HA recapitulated the tissue remodeling process of human bone via coupling signals coordinating osteoblast and osteoclast activity and finely tuned expression of inflammatory molecules, resulting in accelerated in vitro bone formation. Following subcutaneous implantation in rodents, co-cultured hiPSC-MSC/-macrophage on such scaffolds showed mature bone-like tissue formation. These findings suggest the importance of coupling matrix remodeling through osteoblastic matrix deposition and osteoclastic tissue resorption and immunomodulation for tissue development.

Replacement of autogenous or allograft bones by artificial graft materials represents a growing area of interest in current bone repair strategies. Bioactive ceramics in particulate form, such as Bioglass (BG) 45S5, stimulate bone mineralization comparable to autologous bone grafts, but have potential issues of particle migration and inflammation. The aim of this study was to employ a chondroitin sulfate- (CS-) based bioadhesive to improve integration of the bioglass (NovaBone Putty) to prevent particle migration and promote bone regeneration. This BG-CS composite can encapsulate bone marrow (BM) to form a mechanically stable construct, BG-CS-BM. Rheological characterization confirmed the formation of CS-BM hydrogel by reacting the CS-based bioadhesive with the BM. Compared to the bioglass, the BG-CS-BM composite demonstrated a superior capacity to maintain construct integrity under both aqueous and turbulent environments in vitro. After implantation for 4 weeks in a critical-size distal femoral bone defect in a rabbit model, there was significantly greater bone growth in BG-CS-BM as compared to bioglass-only and the empty control. Unlike BG-CS-BM, BG-CS recruited BM in situ from the bone defect. BG-CS demonstrated a similar effect in bone formation but at a comparatively slower rate than BG-CS-BM over 6-weeks' implantation.

Cellular metabolic activity, especially mitochondrial metabolism, plays a vital role in regulating cell proliferation and differentiation. Metabolism could therefore be an important factor to consider when using engineering technologies to stimulate tissue development and repair. The small metabolite carnitine and its derivative acetylcarnitine affect the activities of several pathways in mitochondrial metabolism, but their influence on cell differentiation has not yet been thoroughly studied. To elucidate the effects of these two small molecules on mesenchymal tissue engineering, we used adult stem cells as a platform in both monolayer and 3D hydrogel culture systems. We investigated the impact of these two small molecules on the differentiation of adult stem cells and analysed gene expression, cell proliferation and extracellular matrix deposition. We found that the molecules reduced adipogenesis but stimulated osteogenesis and chondrogenesis in both culture systems. Our results suggest that carnitine and acetylcarnitine could affect the differentiation rate of adult stem cells by regulating mitochondrial metabolism. The effects of these two small molecules give rise to the possibility of employing such metabolites in tissue-engineering systems to enhance cell differentiation and tissue development.

Tissue adhesives can bind together damaged tissues and serve as tools to deliver and localize therapeutics to facilitate regeneration. One emerging therapeutic trend in orthopedics is the use of intraoperative biologics (IOB), such as bone marrow (BM) and platelet-rich plasma (PRP), to stimulate healing. Here, we introduce the application of the biomaterial chondroitin sulfate succinimidyl succinate (CS-NHS) to deliver IOB in a hydrogel adhesive. We demonstrate the biomaterial's ability to bind various tissue types and its cellular biocompatibility with encapsulated human mesenchymal stem cells (hMSCs). Further, we examine in detail the CS-NHS adhesive combined with BM aspirate for use in bone applications. hMSCs were encapsulated in CS-BM and cultured for 5 weeks in osteogenic medium. Quantitative RT-PCR demonstrated osteogenesis via upregulation of the osteogenic transcription factor Runx2 and bone markers alkaline phosphatase and osteocalcin. Significant deposition of calcium and osteocalcin was detected using biochemical, histological, and immunohistochemical techniques. Shear testing demonstrated that the CS-BM adhesive exhibited an adhesive strength approximately an order of magnitude stronger than fibrin glue and approaching that of a cyanoacrylate adhesive. These results indicate that CS-NHS is a promising delivery tool for IOB in orthopedic applications requiring a strong, degradable, and biocompatible adhesive that supports bone growth. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31: 392–400, 2013

The aim of this study is to demonstrate the effect of extracellular calcium ion (Ca2+) and inorganic phosphate (Pi) concentrations on the growth and differentiation of bone-marrow-derived mesenchymal stem cells (MSCs), which is essential to understand the interaction between calcium phosphate ceramic (CPC) scaffolds and seeded cells during the construction of tissue-engineered bones. MSCs were separated from rabbits and cultured in media with different concentrations of Ca2+ and Pi supplements. Their proliferation, apoptosis, mineralization and osteogenic differentiation were determined by the MTT assay, TUNEL assay, Vonkossa stain and RT-PCR examination. A two-way ANOVA calculation with comparisons of estimated marginal means by LSD was used for statistical analysis. Results showed that the optimal extracellular Ca2+ and Pi concentrations for the cells to proliferate and differentiate were 1.8 mM and 0.09 mM, respectively, which are the concentrations supplied in many commonly used culture media such as DMEM and alpha-MEM. Cell proliferation and differentiation decreased significantly with greater or lower concentrations of the Pi supplement. Greater Pi concentrations also led to significant cell apoptosis. Greater Ca2+ concentrations did not change cell proliferation but significantly inhibited cell differentiation. In addition, greater Ca2+ concentrations could significantly enhance cell mineralization. In conclusion, extracellular Ca2+ and Pi significantly influence the growth and osteogenic differentiation of MSCs. It is important to take the cellular effect of Ca2+ and Pi into consideration when designing or constructing scaffolds for bone tissue engineering with CPC.

The ocular surface is a component of the anterior segment of the eye and is covered by the tear film. Together, they protect the vital external components of the eye from the environment. Injuries, surgical trauma, and autoimmune diseases can damage this system, and in severe cases, tissue engineering strategies are necessary to ensure proper wound healing and recovery. Dry eye is another major concern and a complicated disease affecting the ocular surface. More effective and innovative therapies are required for better outcomes in treating dry eye. This review focuses on the regenerative medicine of the conjunctiva, which is an essential part of the ocular surface system. Features and advances of different types of biomolecular materials, and autologous and allogeneic tissue grafts are summarized and compared. Specifically, vitrigel, a collagen membrane and novel material for use on the ocular surface, offers significant advantages over other biomaterials. This review also discusses a breakthrough microfluidic technology, “organ-on-a-chip” and its potential application in investigating new therapies for dry eye.

Repair and reconstruction of the cornea has historically relied on synthetic materials or tissue transplantation. However, the future holds promise for treatments using smart biomaterials and stem cells that direct tissue repair and regeneration to ultimately create new ocular structures that are indistinguishable from the original native tissue. The cornea is a remarkable engineering structure. By understanding the physical structure of the tissue and the resulting impact of the structure on biological function, we can design novel materials for a number of ophthalmic clinical applications. Furthermore, by extending this structure-function approach to characterizing corneal disease processes, new therapies can be engineered.