| BackgroundDefects of the chest wall always occur as a result of excision of neoplasm (primary and recurrent), infection and trauma. In the process of chest wall resection and reconstruction, the most important thing is to close the extensive chest wall defect. The types of materials can be classified into autogenous, heterogenous and prosthetic materials. In recent years the role of prosthetic materials in the reconstruction of a thoracic defect has earned interest for providing better stability, shortening and simplifying surgical procedures. Many artificial materials used for repairing chest wall defects nowadays have several drawbacks. With the development of biomaterial and biomedical engineering, the synthetic degradable biomaterials are becoming the hot point of reconstructive surgery. Many experiments and clinical research have proved that degradable biomaterials have better biocompatibility and degradation cycle time, and can induce the regeneration of cell and tissue. We are collaborating with Shanghai Jiaotong University to design and prepare prosthetic degradable biomaterials used for repairing chest wall defects. We have dong some prophase study of degradable biomaterials used for chest wall defect.Objective1. Study the biological and physiochemical properties of macromolecule biomaterials, Prepare the artificial reparation biomaterials by composed forming skills2. Evaluate comprehensively the biocompatibility and biological safety of the reparation biomaterial in vitro and in vivo in accordance with ISO and GB/T of China.3. Study the variation of the mechanical and chemical properties and the tissue reaction of the materials in the process of degradation by biodegradation test in vitro and vivo.4. Cultivate and induction BMSCs based in tissue engineering princip and methods. Prepare the biomaterial as bracket, observe the changing of BMSCs, explore the feasibility about this biomaterials to be reparation material for chest wall defect. Methods1. The design and preparation of reparation biomaterial: Polycaprolactone(PCL) has excellent biocompatible and biodegradable properties, slow biodegradation. Besides. Silk fiber also has good mechanical properties. Reinforced silk fiber and PCL composite were prepared by means of melt blending and modeling. We study the the mechanical properties and microstructure of PCL composite, and select fiber reinforced PCL composite with the optimal fiber content.2. The biological evaluation of reparation biomaterial: The biocompatibility and biological safety of the reparation biomaterial were evaluated comprehensively according to ISO10993-l:1992 and GB/T16886.1-1997. The cytotoxicity test, acute systemic toxicity test, hemolysis test, pyrogen test, skin hypersusceptibility test and genetic toxicity test were all conducted.3. The biodegradation test in vitro and vivo of reparation biomaterial: Through biodegradation test in vitro, observe the variation of PH value in degradation fluid, water intake rate, weight loss rate of materials in the process of degradation. Through biodegradation test in vivo, investigate the variation of bio-absorbable rate,the hyper-structure and the tissue reaction of the implanted materials in the absorbable process in body.4. Cultivate and induction of BMSCs, empirical study of the biomaterial bracket with cells: Bone marrow mesenchymal stem cells were cultured in DMEM medium and conditional medium(containing Dex,VitC and Na/β-glycerophosphate).The osteoblastic differentiation, proliferation and osteogenetic phenotype were observed by phase contrast microscope .The cells were examined by ALP histochemistry stain, Von-kossa and Alizarin-Red stain. Then we seeded the cells in the biomaterial bracket. After several days of the cells continuous cultivateion, scanning electron microscope (SEM), cell proliferation, ALP were detected.Results1. Silk fiber reinforced PCL composite increased the flexile and tensile strength. The reinforcement was more obvious than in pure PCL material because of fiber. The speed of degradation were elevate by porous structure(DA=200-30μm).The new biomaterial was better than traditional materials in several properties.2. There were no obvious morphological changes of cultured cells attachment on the surface of the composite materials, and the growth and proliferation of the cultured cells could not be inhibited by the tested biomaterials. The extract liquid of the biomaterials were testified no cytotoxicity. Furthermore, the biomaterials were found no acute systemic toxicity and no hemolytic reaction. The skin hypersusceptibility test showed negative. The composites have fine biocompatibility and may be safe for clinical use of reparation of chest wall defect.3. Biodegradation test in vitro showed that the water intake rate, weight loss rate and mechanical properties of silk fiber reinforced PCL composites was quicker than those of pure PCL. The speed of biodegradation in vivo was faster than in vitro. There was neither hyperplasia or necrosis nor other rejection reactions after fiber reinforced PCL composite and pure PCL were implanted.4. BMSCs were able to grow with normal morpha and vigor. The results of stain reaction were positive in inducing group(including ALP histochemistry stain, Vonkossa and Alizarin-Red stain),and negative in control group. BMSCs could grow with normal morphon and vigor after them atached to the material with creeping morphon. Cell proliferation and alkaline phosphatase activity were increase gradually in induced group.ConclusionBased on current results, we conclude that artificial reparation material of chest wall defect made from degradable silk fiber reinforced PCL biomaterials are characterized by excellent biocompatibility, fine degradability and optimal mechanical properties. They can provide effective support to chest walls and facilitating cell growing as well as tissue regeneration and new bone formation. In a word, this biomaterial is the prospective biomaterial in clinical use for reparation and reconstruction of chest wall defcects.
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