A Statistical Approach to the Effect of Sol-Gel Process Variables on the Physical Properties of Polymer [PLLA]-Silica Hy
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A Statistical Approach to the Effect of Sol-Gel Process Variables on the Physical Properties of Polymer [PLLA]-Silica Hybrid Materials for Use as Biomaterials Carole C. Perry*1, David Eglin1, Saad A.M. Ali2, Sandra Downes2 Department of Physics and Chemistry, Nottingham Trent University, Nottingham NG11 8FU, UK. 2 Smith & Nephew Group Research Centre, York Science Park, Heslington, York YO10-5DF, UK. 1
ABSTRACT Hybrid poly(L-lactic acid)-silica materials for potential use in orthopaedic applications have been prepared by a sol-gel method using an experimental design approach to investigate the effect of synthesis variables separately and together on the physical form of the organic polymer. The five factors investigated were the molar ratios of tetraethyl orthosilicate (TEOS)/Poly(Llactic acid) (PLLA), Toluene/PLLA, EtOH/TEOS, Water/TEOS and HCl (catalyst)/TEOS. All other synthesis conditions were kept constant. X-Ray powder diffraction (Statton’s graphical method) and differential scanning calorimetry were used to assess the extent of polymer crystallinity in the hybrid materials. In accordance with other studies, increasing the molar ratio of TEOS/PLLA lead to increasing incorporation of the organic polymer into the silica network. Increase of the toluene/PLLA molar ratio lead to an increase in the crystallinity of the polymer phase. As our studies investigated the effect of synthesis variables simultaneously it was possible to identify, for the first time, that interactions between specific reactants are important in the development of the two structural components of this hybrid system. The most important of these was the TEOS/PLLA*H2O/TEOS interaction that may indicate that silica species from hydrolysed TEOS interact with the PLLA phase possibly via hydrogen bonding and leads to the lowering of the crystalline order of the polymer The results from this study give useful information on the ability of the organic polymer and the silica phase to form interpenetrating networks, an important requirement for the generation of a potential hybrid polyester-silica biomaterial for orthopaedic applications.
INTRODUCTION Poly(L-lactic acid) (PLLA), polyglycolic acid (PGA) and poly(ε-caprolactone) (PCL) are biocompatible and resorbable poly(α-hydroxyacids). They represent an important growing class of materials in the field of medicine. Use of PLLA in particular has been reported for replacement bone grafts [1], tissue regeneration [2], scaffolding for bone and cartilage [3] and drug delivery systems [4]. PLLA is an attractive material because it is biocompatible and resorbable through natural pathways [5]. Its mechanical properties can be tailored through its synthesis and very high molecular weight PLLA has been prepared for load bearing devices [6]. Enhanced PLLA composites have been extensively studied [7]. Materials have been made from blending or copolymerisation of PLLA with other polymers [8] such as PCL-PLLA [9] and a PGA-PLLA [10] copolymer has been used as a surgical suture since the1970’s [11]. The control of
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