Heparin‐Conjugated Poly(Lactic‐Co‐Glycolic Acid) Nanospheres Enhance Large‐Wound Healing by Delivering Growth Factors in Platelet‐Rich Plasma

Platelet‐rich plasma (PRP) contains many growth factors that are involved in tissue regeneration processes. For successful tissue regeneration, protein growth factors require a delivery vehicle for long‐term and sustained release to a defect site in order to maintain their bioactivity. Previously, we showed that heparin‐conjugated poly(lactic‐co‐glycolic acid) nanospheres (HCPNs) can provide long‐term delivery of growth factors with affinity for heparin. In this study, we hypothesize that treatment of a skin wound with a mixture of PRP and HCPNs would provide long‐term delivery of several growth factors contained in PRP to promote the skin wound healing process with preservation of bioactivity. The release of platelet‐derived growth factor‐BB (PDGF‐BB), contained in PRP, from HCPN with fibrin gel (FG) showed a prolonged release period versus a PRP mixture with FG alone (FG‐PRP). Also, growth factors released from PRP with HCPN and FG showed sustained human dermal fibroblast growth for 12 days. Full‐thickness skin wound treatment in mice with FG‐HCPN‐PRP resulted in much faster wound closure as well as dermal and epidermal regeneration at day 9 compared with treatment with FG‐HCPN or FG‐PRP. The enhanced wound healing using FG‐HCPN‐PRP may be due to the prolonged release not only of PDGF‐BB but also of other growth factors in the PRP. The delivered growth factors accelerated angiogenesis at the wound site.     

Bilaminar Device of Poly(Lactic‐co‐Glycolic Acid)/Collagen Cultured With Adipose‐Derived Stem Cells for Dermal Regeneration

Several materials are commercially available as substitutes for skin. However, new strategies are needed to improve the treatment of skin wounds. In this study, we developed and characterized a new device consisting of poly(lactic‐co‐glycolic acid) (PLGA) and collagen associated with mesenchymal stem cells derived from human adipose tissue. To develop the bilaminar device, we initially obtained a membrane of PLGA by dissolving the copolymer in chloroform and then produced a collagen type I scaffold by freeze‐drying. The materials were characterized physically by gel permeation chromatography, scanning electron microscopy, and mass loss. Biological activity was assessed by cell proliferation assay. A preliminary study in vivo was performed with a pig model in which tissue regeneration was assessed macroscopically and histologically, the commercial device Integra being used as a control. The PLGA/collagen bilaminar material was porous, hydrolytically degradable, and compatible with skin growth. The polymer complex allowed cell adhesion and proliferation, making it a potentially useful cell carrier. In addition, the transparency of the material allowed monitoring of the lesion when the dressings were changed. Xenogeneic mesenchymal cells cultured on the device (PLGA/collagen/ASC) showed a reduced granulomatous reaction to bovine collagen, down‐regulation of α‐SMA, enhancement in the number of neoformed blood vessels, and collagen organization as compared with normal skin; the device was superior to other materials tested (PLGA/collagen and Integra) in its ability to stimulate the formation of new cutaneous tissue.     

Effects of Nano‐hydroxyapatite/Poly(DL‐lactic‐co‐glycolic acid) Microsphere‐Based Composite Scaffolds on Repair of Bone Defects: Evaluating the Role of Nano‐hydroxyapatite Content

The aim of the current study was to prepare microsphere‐based composite scaffolds made of nano‐hydroxyapatite (nHA)/poly (DL‐lactic‐co‐glycolic acid) (PLGA) at different ratios and evaluate the effects of nHA on the characteristics of scaffolds for tissue engineering application. First, microsphere‐based composite scaffolds made of two ratios of nHA/PLGA (nHA/PLGA = 20/80 and nHA/PLGA = 50/50) were prepared. Then, the effects of nHA on the wettability, mechanical strength, and degradation of scaffolds were investigated. Second, the biocompatibility and osteoinductivity were evaluated and compared by co‐culture of scaffolds with bone marrow stromal stem cells (BMSCs). The results showed that the adhesion, proliferation, and osteogenic differentiation of BMSCs with nHA/PLGA (50/50) were better than those with nHA/PLGA (20/80). Finally, we implanted the scaffolds into femur bone defects in a rabbit model, then the capacity of guiding bone regeneration as well as the in vivo degradation were observed by micro‐CT and histological examinations. After 4 weeks' implantation, there was no significant difference on the repair of bone defects. However, after 8 and 12 weeks' implantation, the nHA/PLGA (20/80) exhibited better bone formation than nHA/PLGA (50/50). These results suggested that a proper concentration of nHA in the nHA/PLGA composite should be taken into account when the composite scaffolds were prepared, which plays an important role in the biocompatibility, degradation rate and osteoconductivity.     

Effects of Pulsatile Bioreactor Culture on Vascular Smooth Muscle Cells Seeded on Electrospun Poly (lactide‐co‐ε‐caprolactone) Scaffold

Electrospun nanofibrous scaffolds have several advantages, such as an extremely high surface‐to‐volume ratio, tunable porosity, and malleability to conform over a wide variety of sizes and shapes. However, there are limitations to culturing the cells on the scaffold, including the inability of the cells to infiltrate because of the scaffold's nano‐sized pores. To overcome the limitations, we developed a controlled pulsatile bioreactor that produces static and dynamic flow, which improves transfer of such nutrients and oxygen, and a tubular‐shaped vascular graft using cell matrix engineering. Electrospun scaffolds were seeded with smooth muscle cells (SMCs), cultured under dynamic or static conditions for 14 days, and analyzed. Mechanical examination revealed higher burst strength in the vascular grafts cultured under dynamic conditions than under static conditions. Also, immunohistology stain for alpa smooth muscle actin showed the difference of SMC distribution and existence on the scaffold between the static and dynamic culture conditions. The higher proliferation rate of SMCs in dynamic culture rather than static culture could be explained by the design of the bioreactor which mimics the physical environment such as media flow and pressure through the lumen of the construct. This supports regulation of collagen and leads to a significant increase in tensile strength of the engineered tissues. These results showed that the SMCs/electrospinning poly (lactide‐co‐ε‐caprolactone) scaffold constructs formed tubular‐shaped vascular grafts and could be useful in vascular tissue engineering.