Ⅰ Study On The Mechanism Of Crystallization Of CaCO₃ Mediated By Polyacrylic Acid And Its Sodium Salt And Preparation Of The Composite Ⅱ Preliminary Study On Polypropylene Mesh Modified By Regenerated Silk Fibroin And Its Application

The biomaterials,such as shell of mullosc are well-known for their outstanding mechanical propertites,which have been popular field of material science.Shell of mullosc is constituted of calcium carbonate and organic matrix,and the organic matrix is assembled from chitin and silk-fibroin-like protein.With the control of some biological macromolecules such as acidic proteins,calcium carbonate in shell of mollusc exists as calcite,aragonite and amorphous calcium carbonate,etc.The layered structure of nacre in shell of mullosc is formed from brick and motar,the brick is flat crystal of aragonite,the thickness of which is less than 1.0μm.The aragonite crystals show a well defined preferred orientation,which are separated by a 50-100 nm thick interlayer of organic biomacromolecules.The fine structure of nacre in shell of mollusk results in the unique properties and become a nice example for designing of the high mechanical hybrid biomaterials.It is very important for us to study on the forming process of flat aragonite layer in the nacre of mullosc shell and the mediated functions in the crystallization of calcium carbonate associated with the organic matrix and acidic proteins,in order to biomimetic synthese of the high mechanical hybrid composite on the basis of mimicking the structure and forming process of nacre.The hybrid composite of calcium carbonate/regenerated silk fibroin was prepared successfully in supersaturated solution of calcium carbonated with polyacrylic acid (Mw 2000,as PAA 2kDa below) as crystallization mediator and regenerated silk fibroin membrane as organic matrix.It revealed that with control of the concertration of PAA 2kDa in the range of 5-200μg/ml,the continuous flat and smooth film of calcium carbonate is formed on the surface of regernated silk fibroin membrane, which is composed of calcite within the concentration of PAA 2kDa above 20μg/ml. The continuous flat and smooth film of aragonite on the surface of regenerated silk fibroin membrane could be synthesized with the mediated function of 20μg/ml PAA 2kDa and concentrated solution of Mg²⁺ ions(Mg²⁺/Ca²⁺=6/1),which resembles to the layer of aragonite crystal in the nacre of mollusc shell.Poly(acrylic acid) or its sodium salt with different Mw is added into the supersaturated solution of calcium carbonate as substitute of acidic proteins to study their mediated functions in the crystallization of calcium carbonate.It is concluded that:(1) The crystallization of calcium carbonate is prohibited by lower Mw PAA, such as PAA 2kDa.The distorted crystals of calcium carbonate were obtained with the concentration of PAA 2kDa above 100μg/ml.(2) The formation of calcium carbonate hybrid micro-spheres the diameter of which is about 0.1-3.0μm can be induced by the medium Mw sodium polyacrylate(such as PAAs 5.1kDa,PAAs 8kDa and PAAs 15kDa).The inorganic mineral in the hybrid micro-spheres existed as aragonite under the control of sodium polyacrylate with high concentration.(3) The hybrid micro-spheres of amorphous calcium carbonate were formed under the control of high Mw sodium polyacrylate(such as PAAs 100kDa),the diameter of which is in the range of 0.4-1.5μm.The crystallization of calcium carbonate in the hybrid micro-spheres is inhibited entirely by PAAs 100kDa with high concentration(above 100μg/ml).Dynamic light scatter and XRD investigations of the mechanics of formation of hybrid micro-spheres of calcium carbonate revealed that the hybrid micro-spheres are formed from aggregation of amorphous calcium carbonate particles with diameter of 400-600 nm.The difference of inhibiting the amorphous calcium carbonate from crystallization under sodium sodium polyacrylate with different Mw resulted in the formation of amorphous calcium carbonate or aragonite hybrid micro-spheres. The inguinal incisional hernias occur in 5 to 20%of patitents after abdominal surgery.The introduction of tension-free incisional hernias repair by laparoscopic technology has reduced the recurrence rate from up to 50%to less than 5%.Due to its good mechanical properties,polypropylene mesh has been proved to be a suitable prosthetic material in hernias repair.However,it can induce the serious adhesion between polypropylene mesh and bowel,omentum or the other viscera,which results in severe complications,such as bowel erosion,intestinal obstruction and enterocutaneous fistulas,etc.In the disseration,the surface of PP mesh was treated by plasma at low temperature to improve its hydrophilicity and then coated in the solution of regenerated silk fibroin.The primary animal test revealed that the adhesion between polypropylene mesh and omentum,bowel and the other viscera in the abdominal wall repair of Wistar rat is significantly decreased with polypropylene mesh modified by regenerated silk fibroin.The dual-side polypropylene mesh of maximizing peritoneal in -growth on one side while mimizing visceral adhesion on the other side modified by regenerated silk fibroin can be fabricated by treating polypropylene mesh with plasma and coating on one side,which can be used in the inguinal incisional hernias repair.