The effectiveness of stem cell therapies has been hampered by cell death and limited control over fate. These problems can be partially circumvented by using macroporous biomaterials that improve the survival of transplanted stem cells and provide molecular cues to direct cell phenotype. Stem cell behaviour can also be controlled in vitro by manipulating the elasticity of both porous and non-porous materials, yet translation to therapeutic processes in vivo remains elusive. Here, by developing injectable, void-forming hydrogels that decouple pore formation from elasticity, we show that mesenchymal stem cell (MSC) osteogenesis in vitro, and cell deployment in vitro and in vivo, can be controlled by modifying, respectively, the hydrogel’s elastic modulus or its chemistry. When the hydrogels were used to transplant MSCs, the hydrogel’s elasticity regulated bone regeneration, with optimal bone formation at 60 kPa. Our findings show that biophysical cues can be harnessed to direct therapeutic stem cell behaviours in situ.

We tested the potential of a new technology developed in our laboratory to create new hyaline cartilage for re surfacing distal femoral joint surfaces of New Zealand White rabbits that had been surgically denuded of ar ticular cartilage. We removed hyaline cartilage from the patellar groove of the distal femurs in 24 rabbits. Chon drocytes isolated from the excised cartilage of 12 of these rabbits (experimentals) were seeded onto syn thetic biocompatible, biodegradable polymers com posed of polyglycolic acid. The cells were labeled in vitro with a thymidine analog, BrdU (5-bromo-2' deoxyuridine). After 1 week in vitro, the cell-polymer structures were implanted onto the denuded surfaces of 12 defects made in the hyaline cartilage of the con tralateral knees of the experimental animals. Twelve control animals received either no implants or implants not containing cells on similar surgical defects. After 7 weeks, we found evidence of new cartilage growth in 11 of the 12 experimental animals and virtually no new car tilage formation in any of the animals in either control group. Immunohistochemical analysis demonstrated the presence of BrdU-labeled chondrocytes in repre sentative specimens.

Current treatment modalities for soft tissue augmentation which use autologous grafting and commercially available fillers present a number of challenges and limitations, such as donor site morbidity and volume loss over time. Adipose tissue engineering technology may provide an attractive alternative. This study investigated the feasibility of a degradable alginate hydrogel system with commercially available cryopreserved human adipose stem cells (hADSCs) to engineer adipose tissue. hADSCs were differentiated into adipogenic cells, and encapsulated in alginate hydrogels made susceptible to hydrolysis by partial periodate oxidation of the polymer chains. Cell laden gels were subcutaneously injected into the chest wall of male nude mice, and a cell suspension without alginate served as control. After 10 weeks, specimens were harvested and analyzed morphologically, histologically, and with immunoblotting of tissue extractions. Newly generated tissues were semitransparent and soft in all experimental mice, grossly resembling adipose tissue. Analysis using confocal live imaging, immunohistochemisty and western blot analysis revealed that the newly generated tissue was adipose tissue. This study demonstrates that degradable, injectable alginate hydrogels provide a suitable delivery vehicle for preconditioned cryopreserved hADSCs to engineer adipose tissue.

Background Partial or complete necrosis of a skin flap is a common problem. Polydeoxyribonucleotide (PDRN) can be extracted from trout sperm and used as a tissue repair agent. The aim of this study was to investigate whether PDRN could improve the survival of random pattern skin flaps in rats. Methods Twenty-two male Sprague-Dawley rats were randomly divided into two groups: the PDRN treatment group (n=11) and the control group (n=11). Caudally pedicled random pattern skin flaps were elevated on their dorsal skin and resutured. The treatment group received daily intraperitoneal administration of PDRN (8 mg/kg/day), and the control group received fluid vehicle (NaCl 0.9%, 8 mg/kg/day) from day 0 to day 6. On day 7, the flap survival was evaluated and the harvested tissue surrounding the demarcation line of the necrotic area was stained with H&E, anti-rat vascular endothelial cell growth factor (VEGF) antibody, and PECAM-1/CD31 antibody. Results The average necrotic area of the flap in the PDRN group was significantly smaller when compared with that of the control group. Histologic and immunohistochemical evaluation showed that granulation thickness score and VEGF-positive staining cells were marked higher in the PDRN group than in the control group. PECAM-1/CD31-positive microvascular densities were significantly higher in the PDRN group when compared with the control group. Conclusions This study confirms that PDRN improves the survival of random pattern skin flaps in rats. These results may represent a new therapeutic approach to enhancing flap viability and achieving faster wound repair.