The Research Of Degradation Mechanism Of Ecologically-friendly P(3HB-co-4HB) And Its Application For The Preparation Of Porous Scaffolds

Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)],is a new type of biological polymer in the family of poly(β-hydroxybutyrate), and it can be produced in microbial body by controlling C/N ratio in medium. In natural environment, P(3HB-co-4HB) can be degraded absolutely, and its degradation products are carbon dioxide and water. The synthesis material of P(3HB-co-4HB) are environmentally friendly, therefore it is considered as the best alternative to traditional plastic products. At present, most of research on P(3HB-co-4HB) mainly focus on material modification, by this way the defects of P(3HB-co-4HB)(such as brittleness and hard) can be overcame up to a point. By changing the 4-hydroxybutyrate(4HB)monomer proportion in P(3HB-co-4HB) copolymer, the physical and chemical properties of P(3HB-co-4HB) can be controlled, and then expand the application range of the polymer. However, there is almost no research on biodegradable characterics for P(3HB-co-4HB). The degradation property of P(3HB-co-4HB) in natural environment has not been evaluated, and research on microbial species and distribution with P(3HB-co-4HB)-degrading ablility have not been reported.Researches on the enzymatic mechanism of P(3HB-co-4HB) have also not been reported nowadays. Researchers generally believe that the enzymatic hydrolysis of P(3HB-co-4HB) is similar to PHB. PHB can be degraded by PHB depolymerase, and the enzymatic mechanism has been found in the past. It is not sure whether two kinds of enzymatic degradation are completely consistent. And then 4HB monomer in P(3HB-co-4HB) copolymer is how to influence its degradation.With the wide spread application of P(3HB-co-4HB) copolymer in biomedical and packaging field, we need to know the degradation ability of P(3HB-co-4HB) innatural environment, and explore the influencing factors of enzyme degradation on P(3HB-co-4HB). Finally the biodegradation mechanism of P(3HB-co-4HB) would be analysed. The results and significance of this study is summarized as follows:1. Evaluation of P(3HB-co-4HB) degradability in natural ecological environmentP(3HB-co-4HB) films can be degraded in natural environment. After 50 days of degradation in natural soil, the weight loss rate of P(3HB-co-4HB) film increased to21.94%. The degradation property of P(3HB-co-4HB) in soil or water from different ecological source exists obvious differences. Flower soil shows the best degradation ability in three experimental soil, and Southern Lake shows the best degradation ability in three experimental water. In the same ecological environment, the degradation ability of P(3HB-co-4HB) is better than that of the degradation of PHB.When 4HB monomer content in copolymer is 12mol%, the degradation ability of P(3HB-co-4HB) is best. Under different ecological environmental conditions, the species and quantities of microbes is the root cause of polymer degradation. The more the number of microorganisms in forest soil, the faster the rate of degradation of P(3HB-co-4HB) is.2. Various factors influencing the enzymatic degradation of P(3HB-co-4HB)and its enzymatic mechanismOptimize degradation conditions of the P34 HBase DSGZ: 50℃, phosphate buffer(pH 8.0), 0.4mg/mL of enzyme concentration. Blending with certain proportion of polylactic acid or adding a certain amount of CaCO3 into enzymatic reaction mixture, would improve the enzymatic degradation rate of P(3HB-co-4HB). The preparation procedure, crystallinity, and 4HB composition of the P(3HB-co-4HB)copolymer showed evident effect on degradation behavior. P34 HBase DSGZ has a obvious degradable selectivity to Polyhydroxyalkanoates. P(3HB-co-4HB) of enzyme degradation products are determined to be hydroxybutyric acid monomer and hydroxy butyric acid dimers, and this hydroxybutyric acid monomers are found to include3-hydroxy butyric acid and 4-hydroxy butyric acid by nuclear magnetic resonance(NMR).3. Porous PLA materials were acquired through selective enzymatic methodBecause of good biocompatibility and biodegradation of the polylactic acid(PLA), the porous PLA material prepared by selective enzyme degradation can be applied in tissue engineering or oil/water separation field. Changing the P(3HB-co-4HB) compositions of polymer blends or the degradation time, can effectively control porosity and porous structure of the PLA porous scaffolds. The porosity PLA scaffolds reached to 80%, the average pore diameter was up to 80μm,and the connectivity of the porous structure was well. Porous PLA materials showed good mechanical properties and certain hydrophobic properties.4. The application value of porous PLA material in tissue engineering fieldThe preparation, modification, and biocompatibility of porous PLA scaffolds for tissue engineering were studied. The in-vitro degradation results demonstrated that the PLA scaffolds could be degraded completely into harmless products in SBF solution at a slow degradation rate, and the weight loss of the scaffolds could achieve 80%after 8-month in-vitro degradation. Meanwhile, the PLA scaffolds showed the largest swelling value of 157.4% after immersion in the SBF solution for 14 days. On the other hand, MEF cell and Human pulmonary epithelial cell viabilities were determined by the combination of the scanning electron microscopy(SEM) and the3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide(MTT) test, and the results showed that the PLA scaffolds were beneficial to the attachment and growth of the cells with good viability which implied the potential application of the PLA as a scaffold for tissue regeneration. Porous PLA scaffolds modified by poly-L-lysine(PLL) showed a better hydrophilcity and biocompatibility.5. Porous PLAs material has the potential of oil/water separationPreparation and characterization of biodegradable porous poly(lactic acid)oil/water separating materials by selective enzymatic starch in blends. Porousmaterials showed high hydrophobicity and porosity(80%). It is a new attempt to use biodegradable materials with special wettability to solve the problems during separating oils from oil/water mixtures. The porous PLA materials could be reused in oil/water separating for many times.