Development of a mouldable and resorbable bone filler

The purpose of this study was to develop a resorbable, mouldable bone filler that can be used to repair damaged bone. Work was focused on the use of the resorbable polymer poly DL lactide (PDLLA). The ideal formulation was to be hand mouldable and thus the initial step was to carry out a plasticization study on the polymer. Differential Scanning Calorimetry (DSC), Dynamic Mechanical Thermal Analysis (DMTA) and tensile testing were conducted on plasticized PDLLA to indicate the effect citrate ester plasticizers had on the production of a mouldable PDLLA compound. Blending PDLLA with different citrate esters resulted in sample compositions which were malleable and flexible, with increasing plasticizer content having an increase effect on the hand mouldable characteristics. This was followed by an investigation into improving the load bearing properties of the plasticized PDLLA, and so an examination into chemically crosslinking the polymer was carried out, initiated by the use of heat, gamma radiation and UV irradiation. The resultant structures were analysed in a series of swelling studies with the most promising crosslinked compositions then analysed by DMTA and tensile testing. Crosslinking was found not to be a viable approach to harden the polylactide filler as not only were high temperatures needed for crosslinking initiation which would cause cellular necrosis, there was also a reduction in the mechanical and physical integrity of the polymer worsening its load bearing properties. An alternative method of producing a polylactide based bone filler was also explored. By combining polylactide particles with the liquid monomer cyanoacrylate, a hand mouldable and putty-like compound was created. With the onset of polymerization of the monomer, the material then hardened. The composition was modified with the addition of plasticizers and a hydroxyapatite (HA) filler. Initial water absorption and tensile testing conducted found that the addition of the plasticizer and the HA decreased the mechanical properties. A study into optimising the compounds composition was then carried out, and a new source of HA was added to the compositions which helped to increase mechanical properties. The new material composition was found to be injectable with setting rates which could be altered. Aging the polymer compound in PBS for 8 weeks did not alter the resultant tensile properties of the compound by a noticeable degree. A tensile modulus of 1.3 GPa, a tensile strength of 40MPa, a fracture toughness of 2.5MPa m- 1/2, a flexural modulus of 1.7GPa, and a flexural strength of 37MPa were the highest mechanical results achieved. Some of important mechanical properties are lower then those found in human cortical bone, however the results are higher than many commercially available bone substitutes. With further modification of compositions, the mechanical properties could be further increased producing a material fulfilling requirements for a bone graft substitute which is currently not commercially available.