Study on Application of Thermo- Sensitive Hydrogels Based on Biomaterials

Abstract

In chapter 2, We herein examined the bone formation from rat muscle-derived stem cells (rMDSCs) using an injectable in situ-forming chitosan gel in vivo. The rMDSCs were easily isolated from rat muscle tissue. The osteogenic factors caused differentiation of rMDSCs toward the osteogenic lineage. The rMDSCs survived well on the scaffold created by the in vitro and in vivo in situ-forming chitosan gel, indicating that in situ gel-forming chitosan was a suitable substrate for the attachment and proliferation of rMDSCs. Bone formation was observed only in chitosan gel containing both rMDSCs and osteogenic factors. Subcutaneous implantation of the in situ-forming chitosan gel demonstrated that rMDSCs-containing chitosan gel induced much lower host tissue responses than did the chitosan gel alone, probably due to the immunosuppression of the transplanted rMDSCs. In chapter 3, The sol-to-gel transition occurring at around body temperature makes the MPEG-PCL diblock copolymer an ideal candidate material for use as an injectable in situ?-forming gel containing human adipose tissue?-derived stem cells (hADSCs). The sol can be prepared at room temperature, and the gel forms at body temperature. Solutions of the copolymer containing hADSCs and osteogenic factors injected into rats formed gel scaffolds at the injection sites. The gels thus formed showed the interconnective pore structure required to support growth, proliferation, and differentiation of hADSCs. Bromodeoxyuridine-labeled hADSCs were confirmed to be present in gels formed in vivo. Bone formation was observed only in gel implants containing both hADSCs and osteogenic factors. Subcutaneous implantation of the in situ?-forming gel scaffold demonstrated that hADSCs embedded in the gel stimulated much lower host tissue responses than did the gel alone, probably because of the unique immunomodulatory properties of hADSCs. In conclusion, our data on hADSCs embedded in an in situ gel scaffold suggest that this formulation may provide numerous benefits as a noninvasive alternative for tissueengineered bone formation. In chapter 4, We herein formulated and characterized an in situ-forming gel consisting of sodium carboxymethylcellulose (CMC) and poly(ethyleneimine) (PEI), and examined its use as an in vivo scaffold for rat bone marrow stem cells (rBMSCs). The electrostatic interaction and temperaturedependence between CMC anionic and PEI cationic were confirmed by the changes of zeta potential, size and viscosity of CMC solutions with 0-30 wt% PEI. CMC/PEI solution gave electrostatically crosslinked gel with a three-dimensional network structure. The CMC solution containing 10 wt% PEI transformed to a gel at temperatures greater than 35oC, and chosen for subcutaneous injection into rats. The CMC/PEI (90/10) gel with pore structure acted as a suitable biocompatible substrate for the in vitro and in vivo attachment and proliferation of rBMSCs. As CMC/PEI (90/10) solution with and without rBMSCs was injected into Fisher rats, it became a gel in the subcutaneous dorsum of a rat and maintained their shape even after 28 days in vivo. The injected rBMSCs survived in the CMC gel for 28 days. Injection of CMC/PEI gel alone induced macrophage accumulation in the host tissue and at the edge of the gel, whereas injection of CMC/PEI gel containing rBMSCs was associated with decreased macrophage accumulation, indicating immunosuppression by the transplanted rBMSCs. Our results collectively show that CMC/PEI gel could serve as an in situ-forming gel scaffold for entrapped rBMSCs in vivo.