Integrated molecular design of melt-processable bioresorbable engineering nanocomposites for healthcare (BENcH)

Abstract

Event Abstract Back to Event Integrated molecular design of melt-processable bioresorbable engineering nanocomposites for healthcare (BENcH) Andrew J. Parsons1*, Kirsty Walton1, Fredric Hild1, Alexander Ilchev1, Miquel Gimeno-Fabra1, Magdalena M. Tomczynska1, Michael Ward1, Alessia Canciani1, Gabriel Y. Choong1, Davide S. De Focatiis1*, Edward H. Lester1*, David M. Grant1* and Derek J. Irvine1* 1 The University of Nottingham, Faculty of Engineering, United Kingdom Introduction: The aim of the BENcH project is to develop novel, integrated methodologies for the design and scalable manufacture of next generation resorbable polymer nanocomposites. The long term objectives are the production of highly tailored health-care materials in applications ranging from bone fracture fixation to drug delivery. Novel plate-shaped hydroxyapatite (HA) nanoparticles have been simultaneously formed and coated with specifically designed molecular dispersants using a hydrothermal process, to produce a feedstock for compounding with medical grade polylactic acid (PLA). The end-products are formed using traditional plastics processing techniques and their properties investigated both post-moulding and during degradation. Close contact with industrial partners has ensured that all the processes in use are commercially scalable and a demonstrator product is under development. Materials and Methods: Ring-opening polymerisation has produced a series of low molecular weight dispersant/coupling agents. These have functional head groups linking to the surface of the HA nanoparticles and PLA chain structure tails to interact with bulk PLA[1]. Dispersants are applied to the surface of the nanoparticles during a one-step hydrothermal synthesis process to produce coated feedstock[2], processed using a micro-compounder and compression- or injection-moulded to form nanocomposite components[3][4]. Extensive characterisation of both the feedstocks and the compounded products was undertaken in terms of thermal, physical, mechanical, imaging and rheological studies[5][6]. Results and Discussion: The synthetic dispersants have been key to achieving not only improved dispersion of the nanoparticles in the polymer (fig. 1) but also to enhance the interaction of the polymer with the particles. Experimental data shows that the addition of nanoplates by themselves, or together with an uncoated dispersant, provide only limited improvements to material characteristics. Figure 1. TEM images showing dispersion of 2.5 w% uncoated HA platelets (top) and 2.5 wt% equivalent of dispersant coated HA platelets (bottom) in HA/PLA nanocomposites The addition of coated nanoHA increases the viscosity during compounding, suggesting that energy is being dissipated in nanoparticle dispersion. A custom micro-mechanical test rig has allowed measurement of increases in modulus and yield strength (creep resistance) in the nanocomposites. Dramatic effects have also been observed on the rate of water uptake with nanoparticles , allowing an added element of control to the degradation. Rheological studies have monitored molecular weight changes during processing as well as the effect of nanoparticles on material structure. Imaging techniques such as TEM and microCT have contributed to a greater understanding of the dispersion and of the process of degradation in PLA materials. Conclusion: The BENcH project has been successful in producing HA platelet/medical grade PLA nanocomposite materials. This was achieved through the use of bespoke dispersant materials in commercially applicable processes. The nanocomposites display desirable characteristics for a resorbable medical device and a prototype is in development. This work was supported by grant EP/J017272/1 from the UK Engineering and Physical Sciences Research Council; The authors would also like to acknowledge the valuable input of TESco Associates, Inc., Evonik Industries, ThermoFisher Scientific and Promethean Particles