Poly(lactide-co-glycolide) microspheres and hydrogel delivery systems for soft tissue and cartilage tissue engineering applications

摘要

Polymeric microspheres have been widely investigated as delivery systems and are clinically used today. We examined the use of poly(lactide-co-glycolide) (PLGA) microspheres in delivery systems for soft tissue engineering, chemotherapeutic delivery, and cartilage tissue engineering. Soft tissue defects due to trauma or tumor removal remain a clinical challenge. We examined the use of PLGA microspheres and adipose derived stem cells (ASCs) to fill in soft tissue defects. We first demonstrated the use of PLGA microspheres to increase ASC proliferation and survival by encapsulating fibroblast growth factor-2 (FGF-2). The released FGF-2 increased ASC proliferation and survival in vitro. Addition of the FGF-2 microspheres in an in vivo study resulted in an increase in angiogenesis. We then examined the ability of released adipogenic factors to induce the differentiation of ASCs into mature adipocytes. Oil red O staining and Western blots confirmed that adipogenesis was induced by the released factors. The second goal was to examine a delivery system to reduce the risk of local recurrence in breast cancer patients following a lumpectomy. Breast cancer lumps are commonly treated by tumor removal (lumpectomy) followed by radiation or chemotherapy, and both have adverse side effects. PLGA microspheres encapsulating doxorubicin were embedded with a natural scaffold, gelatin, to locally deliver chemotherapy and maintain the breast contour. Our results demonstrated a more controlled release from microspheres embedded within gelatin compared to microspheres alone. Released doxorubicin killed tumor cells in vitro. The implantation of the scaffolds in vivo resulted in tumor ablation. Local and systemic toxicity were not observed even though a dose 60 times the normal dose was given. Our next objective was to analyze the release of TGF-beta1 (TGF-) from PLGA microspheres incorporated into a synthetic hydrogel, poly(ethylene glycol) (PEG)-genipin for cartilage repair. The release of TGF-was dependent upon the genipin concentration of the hydrogel. The released TGF- was bioactive, as demonstrated by the inhibition of mink lung cell proliferation. The final goal was to develop and characterize a hydrogel based on PEG-genipin to gel in situ. As such, we examined genipin and multi-branched aminated PEG. Gelation time was affected by pretreating genipin. Exposure of the genipin aqueous solution to air and oxygen decreased the gelation time. PEG structure also had an effect on gelation time. The gelation time was reduced by utilizing 4-arm PEG and increasing the temperature from 25oC to 37oC. The results of this thesis demonstrate the efficacy of PLGA microspheres embedded in hydrogels for use as delivery systems for soft tissue and cartilage tissue engineering. The delivery systems can be modified to tailor delivery rates, deliver multiple drugs/growth factors, tailor degradation, and promote tissue growth.