Surface Modification Of Nano-Apatite Particles Influncing On The Properties Of Polymeric Composites

Great attention is paid to nano-apatite/polymer composite biomaterials for bone repair, as a result of an increasing number of patients suffered from bone defects in clinic practice. It is of vital importance to improve properties such as mechanical characteristics and biological property of apatite/polymer biocomposites. Some special effects brought by apatite nano-particles are introduced to composite biomaterials by imitating chemical composition and structure of organic bone and expected to explore new applications in bone repair. However, nano-apatite (n-HA) particles tend to become bigger aggregates, and thus the aggregates of n-HA particles can not be equably dispersed in polymer matrix in fabricating functional composites and interfacial bonding strength between aggregate and polymer matrix is lessened, which result in weakening mechanical and biological properties of biocomposites. Surface modifications in physical, chemical or engineering ways have been suggested to weaken the aggregates of n-HA particles, therefore, it is necessary to innovate traditional ways in surface modifications to weak aggregates of n-HA particles and improve compositive properties nano-apatite/polymer composites.This dissertation stresses two hands about surface modification of n-HA partices and effects of physical or chemical modification on improving properties of polymeric composite biomaterials. On the one hand, it focused on inpact of physical adsorption modification of surface coating agents with n-HA particles in mechnical strength, elongation rate,hydrophile and cell compatibility of n-HA/poly (D,L-lactide) (PDLLA) composite biomaterials. On the other hand, it emphasized influence of chemical reaction modification of silane coupling agents to n-HA particles on mechnical strength, elasticity modulus, hydrophile, bioactivity and cell compatibility of n-HA/poly (ε-polycaprolacton) (PCL) composites.Polyethylene Glycol (PEG) was firstly selected to coat n-HA and micro-sized apatite(m-HA) particles to understand effects of PEG on surface modification of different size HA. Results showed that with scale of HA rising, Hydrogen bonding between two molecules of PEG and HA would change stronger, and therefore bonding strength between them was weaker than between m-HA and PEG. in aqueous slurry. Secondly, PEG was coated on the surface of n-HA particles by two physical adsorption technical routes to discuss the formation of HA nano-crystals. Results showed that morphology of the HA particles exhibited acicular shape and the same size as without coating HA. PEG appeared on the surface of HA crystals and crystallization of HA particles sintered up to 800℃was not evidently different by two methods. PEG as a medium reagent could inhibit their growth in some directions, and reduced size of HA crystals. However, HA crystals in the second route were not influenced by the modifier.Three kinds of surface coating agents like Polyethylene glycol (PEG), poly (propyl oxide)-poly (ethyl oxide)-co-poly(propyl oxide)(Pluronic F127) and poly(D, L-lactide)-co-poly (ethylene glycol) (PELA) were firstly employed to modify the surfaces of n-HA particles, respectively, and then modified n-HA/PDLL A composites were prepared by combining solvent-blend with hot-pressing method. The results showed that PEG-modified n-HA/PDLLA composite displayed 1242.93 % ultrahigh elongation rate.Mechanism of ultrahigh elongation rate of modified n-HA/PDLLA composite was firstly suggested.The linear structure of molecular chain of PDLLA polymer matrix was changed into cross-linked one by interaction with molecules of the modifiers and nano-apatite, and this cross-liked structure of PDLLA molecular chain led to the high elastic and plastic deformation.On the other hand,3-Methylacryloxy propyl-trimethoxy silane (KH560),γ-Methacryloxy propyltrimethoxy silane (KH570) and N-(β-aminoethyl)-γ-aminopropyltrimethoxy silane (KH792) were emloyed to modi- fy the surfaces of n-HA particles, respect-ively, and then the silane modified n-HA/ PCL composites were prepared by combining solvent dispersion, melting-blend and hot-pressing methods. Results showed that three silane coupling agents successfully graft to the surfaces of HA nano-particles. Crystalline temperatures of KH560, KH570 and KH792 modified n-HA/PCL composites were heightened. Measurements of mechanical properties proved that ultimate tensile strength of the silane modified composite was higher than one of the contrastive group.Three silane modifications improve interfacial quality between nano-fillers and PCL polymers. In addition, n-HA particles present uniformly and de-agglomerative dispersion in PCL composites, which resulted from our fabrication technique. Two major factors discussed above lead to an enhanced mechanical properties of PCL matrix composite biomaterials.Hydrophile, Alamar Blue and ALP activity of PEG, PELA and F127 modified n-HA/ PDLLA composites were carefully examined. Results showed that good hydrophile was found on three kinds of PEG polymer modified n-HA/PDLLA composite biomaterials and it suggested that PEG modification of n-HA had positive effects on enhancing hydrophile of PDLL-matrix composites. Besides, PEG surface modification of n-HA particles could elevate values of Alamar Blue and ALP activity and this hinted that PEG modification promoted cell compatibility of n-HA/PDLLA composite with cancer of bone.Hydrophile, bioactivity, Alamar Blue and ALP activity of the KH560,KH570 and KH792 modified n-HA/PCL composite were carefully mearsured. Results showed that three silane modified n-HA/PCL composites was bioactive materials, through there are longer time to induced like-bone apatite on the surfaces of the silane modified composites. Besides, contents of three kinds of the silane coating agents had the important effects on hydrophile of modified composites. For examples, 2% contents of KH560 in the modified materials were propitious to improve hydrophile, while 5% contents of KH79 were prone to counterwork hydrophile. On the whole, three kinds of of the silane coating agents baffled to improve the cell compatibility of n-HA/PCL composite with cancer of bone.