• Osteoinduction of 3D printed particulate and short-fibre reinforced composites produced using PLLA and apatite-wollastonite

      Melo, P.; Ferreira, A-M.; Waldron, K.; Swift, Thomas; Gentile, P.; Magallanes, M.; Marshall, M.; Dalgarno, K. (2019-11)
      Composites have clinical application for their ability to mimic the hierarchical structure of human tissues. In tissue engineering applications the use of degradable biopolymer matrices reinforced by bioactive ceramics is seen as a viable process to increase osteoconductivity and accelerate tissue regeneration, and technologies such as additive manufacturing provide the design freedom needed to create patient-specific implants with complex shapes and controlled porous structures. In this study a medical grade poly(l-lactide) (PLLA) was used as matrix while apatite-wollastonite (AW) was used as reinforcement (5 wt% loading). Premade rods of composite were pelletized and processed to create a filament with an average diameter of 1.6 mm, using a twin-screw extruder. The resultant filament was 3D printed into three types of porous woodpile samples: PLLA, PLLA reinforced with AW particles, and PLLA with short AW fibres. None of the samples degraded in phosphate buffered solution over a period of 8 weeks, and an average effective modulus of 0.8 GPa, 1 GPa and 1.5 GPa was obtained for the polymer, particle and fibre composites, respectively. Composite samples immersed in simulated body fluid exhibited bioactivity, producing a surface apatite layer. Furthermore, cell viability and differentiation were demonstrated for human mesenchymal stromal cells for all sample types, with mineralisation detected solely for biocomposites. It is concluded that both composites have potential for use in critical size bone defects, with the AW fibre composite showing greater levels of ion release, stimulating more rapid cell proliferation and greater levels of mineralisation.
    • Short phosphate glass fiber - PLLA composite to promote bone mineralization

      Melo, P.; Tarrant, E.; Swift, Thomas; Townshend, A.; German, M.; Ferreira, A-M.; Gentile, P.; Dalgarno, K. (Elsevier, 2019-11)
      The clinical application of composites seeks to exploit the mechanical and chemical properties of materials which make up the composite, and in researching polymer composites for biomedical applications the aim is usually to enhance the bioactivity of the polymer, while maintaining the mechanical properties. To that end, in this study medical grade Poly(L-lactic) acid (PLLA) has been reinforced with short phosphate-based glass fibers (PGF). The materials were initially mixed by melting PLLA granules with the short fibers, before being extruded to form a homogenous filament, which was pelletized and used as feedstock for compression moulding. As made the composite materials had a bending strength of 51 MPa ± 5, and over the course of eight weeks in PBS the average strength of the composite material was in the range 20–50 MPa. Human mesenchymal stromal cells were cultured on the surfaces of scaffolds, and the metabolic activity, alkaline phosphatase production and mineralization monitored over a three week period. The short fiber filler made no significant difference to cell proliferation or differentiation, but had a clear and immediate osteoinductive effect, promoting mineralization by cells at the material surface. It is concluded that the PLLA/PGF composite material offers a material with both the mechanical and biological properties for potential application to bone implants and fixation, particularly where an osteoinductive effect would be valuable.