Study On The Preparation, Biocompatibility And Biological Stability Of The Red Clay/Polyurethane Composite

Polyurethane (PU) has been widely used in the biomedical field owing to good mechanical properties and biocompatibility. The demand of PU medical products including artificial heart, artificial blood vessels, medical films, elastic bandages, medical catheters, and so on is increasing year by year. However, as a long-term implantation materials, the mechanical properties, biocompatibility and biological stability of PU are still unable to meet the requirements yet. The degradation of PU productions in vivo limits its applications. Therefore, to improve the mechanical properties, biocompatibility and bio-stability of PU, was meaningful and significant.In this paper, the mineral clay - red clay which widely exists in the South China region was introduced to improve the properties of PU. Due to its chemical and physical characteristics, it is supposed to be an efficacy modification. After being purified and dispersed, a super-concentrated system of micro-nano-red clay was got. And then, this micro-nano-red clay was added into the PU solution by a certain percentage of solvent to make different red clay/PU composites.Laser diffractometer and transmission electron microscopy (TEM) were introduced to investigate particle size and micro-structure of red clay. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to analyze the surface properties of different red clay/PU composites. Electronic universal testing machine was applied to measure the mechanical properties of this composite. The hemolytic rate, clotting time test, cytotoxicity test and direct contact method was introduced to evaluate the biocompatibility of them. The H₂O₂/CoCl₂ system together with papain degradation solution was published to simulate the degradation of PU in vivo. To find out the difference of surface morphology, molecular structure and mechanical properties before and after degradation, SEM, infrared spectrometer (FTIR) and the electronic universal testing machine were introduced. The results as below:1. The original red clay presented a structure of stacked-radiation type. The average particle size of original red clay was 1609nm. After purification and dispersion, the average particle size of red clay was reduced to 227.8nm. The largest number of purificatory red clay was in 48nm components, 17nm size of particles could be observed under TEM. Red clay particles uniformly dispersed in the matrix, and possess good interface interaction between the PU. Compared with pure PU, the surface roughness of 5wt% red clay content of PU composite was reduced, which is from 14.23nm to 9.626nm. The results indicate that red clay is conducive in reducing the surface adsorption of small molecules in blood components and improving the blood compatibility of PU.2. When the red clay content lower than 10wt%, the tensile strength and elongation at break of red clay/PU composite increasing with the increase of content of red clay. Tensile strength and elongation at break of pure PU were 37.67MPa and 610.6%. Especially, 5wt% red clay content of PU composite reached the peak which is 673.10% and 42.62MPa. There are 13% and 10% growth comparing with pure PU. Over the peak that the red clay content is 10wt%, the tensile strength and elongation at break of red clay / PU composite start to fall.3. Level of cytotoxicity of pure PU was 1. Various contents of the red clay/PU composite were 0, which indicates the cell toxicity is on low level or none. Hemolytic rates of red clay/PU composite were lower than pure PU, less than 5% of international standards. Especially, hemolytic rate of 3wt% red clay content of PU composite was the lowest which was 0.31%. Base on these results, the red clay/PU composite is supposed to be an efficacy modification in improving the biocompatibility of PU.4. After accelerate oxidative degradation and enzymatic degradation, cracks and holes could be observed on the surface of red clay/PU composite, however, the surface of pure PU almost delaminating. FTIR showed that free radical oxidation makes the ether bond of soft segments of pure PU depredates to carboxylic acid and alcohol. In the red clay/PU composite, any displacement of C=O and the C-O absorption peak of ester bond couldn't be found, which indicated the red clay/PU composite didn't depredate or depredate slightly. After accelerate oxidative degradation, the tensile strength of the composite didn't reduce, on the contrary, there was a little rise; After the enzyme degradation, the tensile strength was slightly declined but the decreasing amplitude was smaller than pure PU. All mentioned above indicate that composites with better bio-stability would be acquired by adding red clay into PU.In a word, red clay/PU composite not only improve the mechanical properties but also get better biocompatibility and biological stability than matrix, which has shown strengths and great potential in preparation of new modified PU medical products.