Polylactide - carbon nanotubes nanocomposites as membranes for guided nerve regeneration (GNR)

New generation of membrane materials can play role in regeneration process in living organism e.g. creation of optimal conditions for regeneration of bone tissue (GBR/GTR technique) or defected peripheral nerve (GNR technique). However, biodegradable polymeric materials which are now widely used in GNR technique (PLA, PCL, collagen) does not have satisfactory mechanical properties such as strength (RM) or Young's modulus (E) because it is difficult to control their porosity [1,2]. Materials suitable for nerve regeneration should exhibit electrical properties which stimulate the regeneration [3]. The main idea of the guided nerve regeneration is utilisation of a membrane separating two tissues i.e. defected nerve tissue and connective tissue. Inside the defected nerve tissue surrounded by the membrane should be present factors influencing the regeneration process such as: ECM protein, nervotrofic factors. On the other hand, the membrane should act as a barrier for fibroblast cells inflowing into the defected area. The work presents results of investigations on porous nanocomposite materials basing on bioresorbable aliphatic polyesters i.e. poly-(L/DL)-lactide and carbon nanotubes (CNT). All materials i.e. nanocomposite foils and porous materials were prepared using synthetic co-polymer of L/DL-lactide with L/DL ratio of 80/20 from Purac®. The polymer had the FDA attestation confirming its biocompability. As the nanofillers, two types of CNTs produced by Nanostructured and Amorphous Materials (Inc. Huston, USA) were used: MWCNTs (multi-wall carbon nanotubes; diameter 10-30 nm and length 1-2 μm) and SWCNTs (single-wall carbon nanotubes; diameter 0.7-2 nm and length 15-30 μm). Nanocomposite membrane materials (PLDLA/0.5% wt. MWCNTs and PLDLA/0.5% wt. SWCNTs) were prepared using combined methods: phase inversion and freeze-drying. Porous microstructure of the nanocomposites was investigated using SEM/EDS. It was found, that the presence of the CNT influenced shape, size (5-50 μm) and distribution of pores in the material (total porosity of PLDLA/ MWCNTs was about ~65% and PLDLA/S WCNTs was about ~35%). The nanoadditives increased mechanical properties of the membrane materials. For example addtition of the SWCNTs increased the membrane strength (RM) form 16 to 24 MPa. Physicochemical properties of the materials surface were investigated by means of wettability and surface energy measurements. It was shown that dispersion part of surface free energy decreased when SWCNTs were used as additives (from 4.5 mm/mJ PLDLA membrane to 0.7 mm/mJ PLDLA/SWCNTs), while in the case of the MWCNTs addition dispersion part of surface energy increased from 4.5 mm/mJ to 6.9 mm/mJ. Such PLDLA-based materials modified with CNTs (MWCNTs, SWCNTs) may be an attractive support for adhering cells. SWCNTs were more suitable nanoad- ditives for PLDLA-matrix membranes than MWCNTs, because such membranes were stronger, hydrophilic and much more bioactive.