Xiaobing Jin

Nanofibrous hollow microspheres self-assembled from star-shaped polymers as injectable cell carriers for knee repair

Biomaterials play pivotal roles in engineering tissue regeneration and repair. To regenerate irregular shaped defects, injectable cell carriers are desirable. Here, we report the development of self-assembled nanofibrous hollow microspheres from star-shaped biodegradable polymers as an injectable cell carrier for tissue regeneration. The nanofibrous hollow microspheres were shown to efficiently accommodate cells and enhance cartilage regeneration over control microspheres. The nanofibrous hollow microspheres also supported a significantly larger amount and higher quality cartilage regeneration over the chondrocytes alone group in an ectopic implantation model. In a critical-size rabbit osteochondral defect repair model, the nanofibrous hollow microspheres/chondrocytes group achieved substantially better cartilage repair and integration compared to the chondrocytes alone group that simulates the clinically available autologous chondrocyte implantation (ACI) procedure. These results indicate that the nanofibrous hollow microspheres are an excellent cell carrier for cartilage regeneration and are worthy of further investigation towards the aimed clinical application.

Rapid Self-Integrating, Injectable Hydrogel for Tissue Complex Regeneration

A novel rapid self-integrating, injectable, and bioerodible hydrogel is developed for bone-cartilage tissue complex regeneration. The hydrogels are able to self-integrate to form various structures, as can be seen after dying some hydrogel disks pink with rodamine. This hydrogel is demonstrated to engineer cartilage-bone complex.

Calcium phosphate deposition rate, structure and osteoconductivity on electrospun poly(l-lactic acid) matrix using electrodeposition or simulated body fluid incubation

Mineralized nanofibrous scaffolds have been proposed as promising scaffolds for bone regeneration due to their ability to mimic both nanoscale architecture and chemical composition of natural bone extracellular matrix. In this study, a novel electrodeposition method was compared with an extensively explored simulated body fluid (SBF) incubation method in terms of the deposition rate, chemical composition and morphology of calcium phosphate formed on electrospun fibrous thin matrices with a fiber diameter in the range ~200-1400 nm prepared using 6, 8, 10 and 12 wt.% poly(l-lactic acid) (PLLA) solutions in a mixture of dichloromethane and acetone (2:1 in volume). The effects of the surface modification using the two mineralization techniques on osteoblastic cell (MC3T3-E1) proliferation and differentiation were also examined. It was found that electrodeposition was two to three orders of magnitude faster than the SBF method in mineralizing the fibrous matrices, reducing the mineralization time from ~2 weeks to 1h to achieve the same amounts of mineralization. The mineralization rate also varied with the fiber diameter but in opposite directions between the two mineralization methods. As a general trend, the increase of fiber diameter resulted in a faster mineralization rate for the electrodeposition method but a slower mineralization rate for the SBF incubation method. Using the electrodeposition method, one can control the chemical composition and morphology of the calcium phosphate by varying the electric deposition potential and electrolyte temperature to tune the mixture of dicalcium phosphate dihydrate and hydroxyapatite (HAp). Using the SBF method, one can only obtain a low crystallinity HAp. The mineralized electrospun PLLA fibrous matrices from either method similarly facilitate the proliferation and osteogenic differentiation of preosteoblastic MC3T3-E1 cells as compared to neat PLLA matrices. Therefore, the electrodeposition method can be utilized as a fast and versatile technique to fabricate mineralized nanofibrous scaffolds for bone tissue engineering.

Development of channeled nanofibrous scaffolds for oriented tissue engineering

A tissue-engineering scaffold resembling the structure of the natural extracellular matrix can often facilitate tissue regeneration. Nerve and tendon are oriented micro-scale tissue bundles. In this study, a method combining injection molding and thermally induced phase separation techniques is developed to create single- and multiple-channeled nanofibrous poly(L-lactic acid) scaffolds. The overall shape, the number and spatial arrangement of channels, the channel wall matrix architecture, the porosity and mechanical properties of the scaffolds are all tunable. The porous NF channel wall matrix provides an excellent microenvironment for protein adsorption and the attachment of PC12 neuronal cells and tendon fibroblast cells, showing potential for neural and tendon tissue regeneration.

Nanofibrous spongy microspheres for the delivery of hypoxia-primed human dental pulp stem cells to regenerate vascularized dental pulp.

UNLABELLED Dental pulp infection and necrosis are widespread diseases. Conventional endodontic treatments result in a devitalized and weakened tooth. In this work, we synthesized novel star-shaped polymer to self-assemble into unique nanofibrous spongy microspheres (NF-SMS), which were used to carry human dental pulp stem cells (hDPSCs) into the pulp cavity to regenerate living dental pulp tissues. It was found that NF-SMS significantly enhanced hDPSCs attachment, proliferation, odontogenic differentiation and angiogenesis, as compared to control cell carriers. Additionally, NF-SMS promoted vascular endothelial growth factor (VEGF) expression of hDPSCs in a 3D hypoxic culture. Hypoxia-primed hDPSCs/NF-SMS complexes were injected into the cleaned pulp cavities of rabbit molars for subcutaneous implantation in mice. After 4 weeks, the hypoxia group significantly enhanced angiogenesis inside the pulp chamber and promoted the formation of ondontoblast-like cells lining along the dentin-pulp interface, as compared to the control groups (hDPSCs alone group, NF-SMS alone group, and hDPSCs/NF-SMS group pre-cultured under normoxic conditions). Furthermore, in an in situ dental pulp repair model in rats, hypoxia-primed hDPSCs/NF-SMS were injected to fully fill the pulp cavity and regenerate pulp-like tissues with a rich vasculature and a histological structure similar to the native pulp. STATEMENT OF SIGNIFICANCE Vascularization is key to the regeneration of many vital tissues. However, it is challenging to create a suitable microenvironment for stem cells to regenerate vascularized tissue structure. This manuscript reports a novel star-shaped block copolymer that self-assembles into unique nanofibrous spongy microspheres, which as an injectable scaffold recapitulate the cell-cell and cell-matrix interactions in development. Using a clinically-relevant surgical procedure and a hypoxic treatment, the nanofibrous spongy microspheres were used to deliver stem cells and successfully regenerate dental pulp with a rich vasculature and a complex histologic structure similar to that of the native dental pulp. The novel microspheres can likely be used to regenerate many other vascularized tissues.

Nanofibrous Spongy Microspheres Enhance Odontogenic Differentiation of Human Dental Pulp Stem Cells

Dentin regeneration is challenging due to its complicated anatomical structure and the shortage of odontoblasts. In this study, a novel injectable cell carrier, nanofibrous spongy microspheres (NF-SMS), is developed for dentin regeneration. Biodegradable and biocompatible poly(l-lactic acid)-block-poly(l-lysine) are synthesized and fabricated into NF-SMS using self-assembly and thermally induced phase separation techniques. It is hypothesized that NF-SMS with interconnected pores and nanofibers can enhance the proliferation and odontogenic differentiation of human dental pulp stem cells (hDPSCs), compared to nanofibrous microspheres (NF-MS) without pore structure and conventional solid microspheres (S-MS) with neither nanofibers nor pore structure. During the first 9 d in culture, hDPSCs proliferate significantly faster on NF-SMS than on NF-MS or S-MS (p < 0.05). Following in vitro odontogenic induction, all the examined odontogenic genes (alkaline phosphatase content, osteocalcin, bone sialoprotein, collagen 1, dentin sialophosphoprotein (DSPP)), calcium content, and DSPP protein content are found significantly higher in the NF-SMS group than in the control groups. Furthermore, 6 weeks after subcutaneous injection of hDPSCs and microspheres into nude mice, histological analysis shows that NF-SMS support superior dentin-like tissue formation compared to NF-MS or S-MS. Taken together, NF-SMS have great potential as an injectable cell carrier for dentin regeneration.

Local pulsatile PTH delivery regenerates bone defects via enhanced bone remodeling in a cell-free scaffold

Parathyroid hormone (PTH) is currently the only FDA-approved anabolic drug to treat osteoporosis, and is systemically administered through daily injections. A new local pulsatile PTH delivery device was developed from biodegradable polymers to expand the application of PTH from systemic treatment to spatially controlled local bone defect regeneration in this work. This is the first time that local pulsatile PTH delivery has been demonstrated to promote bone regeneration via enhanced bone remodeling. The biodegradable delivery device was designed to locally deliver PTH in a preprogrammed pulsatile manner. The PTH delivery was utilized to facilitate the regeneration of a bone defect spatially defined with a cell-free biomimetic nanofibrous (NF) scaffold. The local pulsatile PTH delivery (daily pulse for 21 days) not only promoted the regeneration of a critical-sized bone defect with negligible systemic side effects in a mouse model, but also advantageously achieved higher quality regenerated bone than the standard systemic PTH injection. These results demonstrate a promising and novel pulsatile PTH delivery device for spatially defined local bone regeneration.

Pore size directs bone marrow stromal cell fate and tissue regeneration in nanofibrous macroporous scaffolds by mediating vascularization

In the U.S., 30% of adults suffer joint pain, most commonly in the knee, which severely limits mobility and is often attributed to injury of cartilage and underlying bone in the joint. Current treatment methods such as microfracture result in less resilient fibrocartilage with eventual failure; autografting can cause donor site morbidity and poor integration. To overcome drawbacks in treatment, tissue engineers can design cell-instructive biomimetic scaffolds using biocompatible materials as alternate therapies for osteochondral defects. Nanofibrous poly (l-lactic acid) (PLLA) scaffolds of uniform, spherical, interconnected and well-defined pore sizes that are fabricated using a thermally-induced phase separation and sugar porogen template method create an extracellular matrix-like environment which facilitates cell adhesion and proliferation. Herein we report that chondrogenesis and endochondral ossification of rabbit and human bone marrow stromal cells (BMSCs) can be controlled by scaffold pore architecture, particularly pore size. Small-pore scaffolds support enhanced chondrogenic differentiation in vitro and cartilage formation in vivo compared to large-pore scaffolds. Endochondral ossification is prevented in scaffolds with very small pore sizes; pore interconnectivity is critical to promote capillary ingrowth for mature bone formation. These results provide a novel strategy to control tissue regenerative processes by tunable architecture of macroporous nanofibrous scaffolds. STATEMENT OF SIGNIFICANCE: Progress in understanding the relationship between cell fate and architectural features of tissue engineering scaffolds is critical for engineering physiologically functional tissues. Sugar porogen template scaffolds have uniform, spherical, highly interconnected macropores. Tunable pore-size guides the fate of bone marrow stromal cells (BMSCs) towards chondrogenesis and endochondral ossification, and is a critical design parameter to mediate neotissue vascularization. Preventing vascularization favors a chondrogenic cell fate while allowing vascularization results in endochondral ossification and mineralized bone formation. These results provide a novel strategy to control tissue regenerative processes by tunable architecture of macroporous nanofibrous scaffolds.