Abstract
The use of thermoplastic composites based on poly(lactic) acid and phosphate glass fibres over metallic alloys for clinical restorative treatment is highly beneficial due to their biocompatibility and biodegradability. However, difficulties in achieving a thorough melt impregnation at high fibre contents while limiting polymer degradation is one of the main issues encountered during their manufacture. This paper reports for the first time on the effects of pressure cycling on the mechanical properties of compression moulded polylactic acid-phosphate glass fibre composites. The strength of the composites consolidated under pressure cycling were at least 30% higher than those in which conventional static pressure was used. The marked disparity was attributed to the influence of pressure cycling on the fibre preform permeability, the melt viscosity and the capillary pressure, leading to improved fibre wet-out with respect to static pressure. Implementation of a cyclic pressure appeared to promote the occurrence of transcrystallinity in the polymer matrix as suggested by DSC traces. The fibre content influenced PLA thermal degradation since the matrix molecular weight decreased as the fibre content increased on account of the moisture adsorbed by the glass surface. However, this extent of degradation did not impair the matrix mechanical performance in the composites.
Highlights
Bone atrophy due to stress shielding associated with metallic fixation devices can result in secondary surgery for removal of these implants to prevent long term complications
This paper reports on the effects of a dynamic compression moulding variant for the production of high volume fraction laminate bioresorbable composites aiming to: i) limit the PLA matrix thermal degradation, ii) minimise void content and iii) significantly improve composite mechanical properties through the optimisation of the pressure scheme applied
The absence of air bubbles in the regions adjacent to the top and bottom surfaces of the fibre mats (Fig. 5) and the overall low void contents calculated for both pressure profiles indicated that the initial application of cyclic pressure managed to successfully eliminate large pockets of entrapped air and vapour possibly stemming from moisture adsorbed during mould loading
Summary
Bone atrophy due to stress shielding associated with metallic fixation devices can result in secondary surgery for removal of these implants to prevent long term complications. Current research efforts have been focused on the development of novel fully bioresorbable devices capable of eliciting beneficial host responses postimplantation [1,2,3]. Long-fibre composites fabricated from biodegradable materials, such as polylactic acid ‘PLA’ and phosphate-based glass fibres ‘PGF’ can be engineered to initially match (and even surpass) bone mechanical properties and gradually transfer the load to the healing tissue upon degradation. The controlled release of phosphate glasses degradation by-products could stimulate the fracture healing mechanism following in situ degradation [4,5]. Amongst the factors that regulate the loading response of composite materials, the fibre content and the adhesion between the matrix and the reinforcement play a critical role [6,7]. From Darcy's law [7], it follows that the higher the viscosity of the polymer melt and the thicker the porous medium, i.e. the higher the fibre volume fraction, the more difficult would be for a given fluid to fully percolate through the interstices of the fibre network
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