Effects Of Chemical Treatment On Degradation And Biocompatibility Of Silk

Silk,which is made of silkworm or silkworm larvae producing natural silk fiber,is called mulberry silk and tussah silk.The silk refers to the home of silk in this article.During the process,the retral sericterium secretion of silkworm larvae produced silk fibroin(sf),and middle sericterium of it produced sericin protein(sericin).Silk fibroin is mixed sericin with middle silkgland,out of the body and form cocoon silk.Without being treated,the silk sericin is called silk.On the contrary,it is called soft silk.Silk is a kind of natural material with good biocompatibility,and it has been widely used in the field of biomedical research and practice.Surgical suture is a typical example of the application of silk in the field of biomedicine.According to the properties of degradation,biological tissue engineering materials can be divided into two kinds.One is that the material does not being degradated within the animal body,such as teflon artificial blood vessels,metal materials for bone and the materials for dental USES.The other is to completely degradation materials in animals.in the process of using this kind of material,people hope that with the tissue regeneration,the material is degradated step by step,and finally is completely metabolized,which requires the degradation rate of this kind of material to match that of tissue regeneration.Research shows that the degradation rate of silk is very slow in the body,and it limits the silk to applicate in tissue engineering.Therefore,this study attempts to explore the in vitro of silk chemical treatment if promoting them to degrade in the body.Tissue engineering material needs certain mechanical properties.However,due to the differences in usage,there is discrepancy during the requirement of mechanical properties.Artificial blood vessels need good toughness and elasticity,bone fixation materials need a better hardness,and artificial neural requires lowly for mechanical properties,that is good to tolerate nerve transplant operation.The process of chemical treatment in vitro,the aim of this study is part of the degradation of silk at the same time it can maintain the status of fiber and certain mechanical properties.Studies have shown that the degradation of silk fiber is random in the body.When silk is transplanted into animals,the number of silk fiber will reduce.At the same time,some of the silk fiber morphology and diameter have no significant change,and we suspect that it is inflammation mediated cell phagocytosis.The cell phagocytosis function at the same time with tissue fibrosis.This study intends to examine the silk in the process of rat subcutaneous preparetions inflammation factors and the expression of collagen.The home of silk as the main material in this paper,it has been boiled in 1% Na2CO3 solution for 30 min then get soft silk after sericin off.Then we modulate 0.05 mo L/L,0.1 moL/L,0.5 moL/L of NaOH,NaHCO3,HCl,H3PO4,CH3 COOH,CaCl2 solution and saturated limewater to treat soft silk.We can get material at 1,2,3,and 4 weeks,testing mechanical properties,weighing weightlessness rate of calculation,testing the protein content and pH in the solution;Scanning electron microscopy,observing the surface morphology.Heeling-in the rat subcutaneous,based on paraffin section,observating H.E staining and frozen section immunofluorescence staining;the situation is about RT-PCR detection of inflammation and collagen related genes.It reflects the concentration effect in the process of vitro degradation of silk in7 kinds of chemical substances.The degradation by chemical treatment of silk in vitro from strong to weak in order of sodium hydroxide> saturated lime water> hydrochloric acid> acetic acid> sodium bicarbonate> phosphoric acid solution> calcium chloride.The results of scanning electron microscopy showed that the filament diameter of each experimental group was reduced compared with the diameter of monofilament before treatment,but the degree of reduction was different.The degree of fiber diameter is reduced from large to small in order of saturated lime water> sodium hydroxide> acetic acid> hydrochloric acid> sodium bicarbonate and calcium chloride.The results of mechanical tests show that the mechanical strength of silk fibers is significantly reduced with the increase of chemical treatment concentration.The degree of reduction is acetic acid> sodium bicarbonate> calcium chloride> sodium hydroxide> hydrochloric acid> phosphoric acid> saturated lime water.With the extension of time,the hardness of silk fiber increases.Order from large to small is calcium chloride> acetic acid> sodium bicarbonate> hydrochloric acid> phosphoric acid> saturated lime water> sodium hydroxide.Silk elasticity varies with the processing time.Order of silk elasticity from large to small is acetic acid> sodium bicarbonate> calcium chloride> hydrochloric acid> phosphoric acid> saturated lime water> sodium hydroxide.Observation of tissue section staining showed that each group had a different degree of degradation of the silk,after subcutaneous implantation of silk after chemical treatment.Based on the number of silk remaining in the unit area,it was speculated that the phagocytosis of cells on silk was in the order of weak and strong,followed by the control group,the phosphate treatment group,the hydrochloric acid treatment group,the acetic acid treatment group,the lime water treatment group,the sodium hydroxide treatment group,the calcium chloride treatment group and the sodium bicarbonate treatment group.Based on the average area of the cross section of the residual silk,the order of the degradation of the silk was as follows: hydrochloric acid treatment group,phosphate treatment group,acetic acid treatment group,sodium bicarbonate treatment group,calcium chloride treatment group,sodium hydroxide treatment group,lime water treatment group and control group.RT-PCR showed that different chemical treatments had different effects on the biocompatibility of silk materials.The order of decreasing the biocompatibility of silk was as follows: phosphoric acid treatment group,hydrochloric acid treatment group,acetic acid treatment group,lime water treatment group,sodium hydroxide treatment group,calcium chloride treatment group and sodium bicarbonate treatment group.Therefore,the effects of seven kinds of chemical substances on the morphological structure,mechanical properties,degradation properties and biocompatibility of silk were significant.They have accelerated the rate of degradation of silk in the body,and maintain the fibrous morphology of silk and a certain mechanical properties.The effect is from excellent to inferior order: sodium hydroxide,hydrochloric acid,sodium bicarbonate,saturated lime water,acetic acid,calcium chloride,phosphoric acid.