ABSTRACT

1. Processability of novel resorbable and biocompatible PLLA/Mg composites CENIM S.C. Cifuentes a,b, F.A. López a, R. Benavente b, J. L. González-Carrasco a,c a. National Center for Metallurgical Research (CENIM-CSIC), Madrid, Spain b. Institute of Polymer Science and Technology (ICTP-CSIC) Madrid, Spain c. Biomedical Research Networking center in Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), Spain e-mail: sccifuentesc@cenim.csic.es , flopez@cenim.csic.es, rbenavente@ictp.csic.es , jlg@cenim.csic.es ABSTRACT The development of PLLA/Mg composites responds to the need of overcoming the lack of bioactivity and low mechanical properties of current bioresorbable biomaterials for medical applications. Their manufacturing will likely require a high temperature step to mould the material by using a compression, extrusion or injection process. Given that previous works have established that metal hydroxides/oxides reduce the thermal stability of PLLA, in order to move forward the PLLA/Mg composite processing and design, the study of the effects of pure Mg particles on PLLA thermal stability and melting behaviour, as well as its effect on the mechanical properties becomes an ineludible goal. Materials: A poly-L-lactic acid matrix is reinforced with Mg particles of 50 um. The PLLAXMg composites are compounded by extrusion and moulded by compression. Characterization: The effect on the melting behaviour and thermal stability of Mg on PLLA is studied by DSC and TGA, respectively. The mechanical studies are performed under compression tests on an universal machine. PROCESSING PLLA Granules + Mg powder Extrudedsolid 0.2 %Mg Screw Die + PLLA 0.5 %Mg 1 %Mg f=12mm h= 2 mm Compression Moulding T melt=190ºC P= 20 - 30 bar Mg Compounding by Extrusion RESULTS Melting behaviour Thermal stability PLDA 1 m PLDA02Mg 1 mm Fig. 4. Thermal degradation rate Fig. 2. Thermogravimetric curves Fig. 3. Isothermal thermogravimetric curves Fig. 1. DSC diagrams Fig. 2 shows that Mg accelerates the thermal degradation of PLLA without compromising the temperature window required for commercial processing (extrusion, injection) (~ <200ºC). Figs. 3 and 4 make more evident the effect of Mg on the thermal degradation of PLLA as, in isothermic conditions, PLLA thermal degradation rate has an exponential growth as the Mg content increases. 1 mm 1 mm Mg has a mild effect on the cold crystallization and melting temperatures. They are shifted towards lower values as Mg content increases. A content of 7% of Mg has a more evident effect on the melting peak, where the material starts to melt near 150ºC. Mechanical properties PLDA1Mg 1 mm Fig. 5 shows the effect of Mg on the mechanical properties under compression. There are the reinforcement effect as well as the thermal degradation effect. Mg improves the mechanical properties of the composite when the reinforcement effect is greater than the thermal degradation effect, this occurs until 5% of Mg content. When the material has a 7% of Mg the mechanical properties drop dramatically due to the higger effect of thermal degradation CONCLUSIONS • Mg does not compromise the processability of the material when proper parameters for reinforcement are selected. • There is a specific volume fraction of Mg where the highest mechanical properties are achieved. • PLLA/Mg composites with improved mechanical properties can be manufactured by plastic s processing technologies. Special thanks to: Project MAT2012-37736-C05-01, Spanish National Research Council - CSIC and European Social Fund (Fondo Social Europeo) for JAE-I3P Grant. CIBER-BBN is supported by the Ministerio de Salud Carlos III BIBLIOGRAPHY [1] S. C Cifuentes, E. Frutos, J.L. González Carrasco, M. Muñoz, M. Multigner, J. Chao, R. Benavente, M. Lieblich. Materials Letters 74, 239-242 (2012)