Ho, S.M.; (2006) Injectable biodegradable poly(ester-co-ether) methacrylate monomers for bone tissue engineering and drug delivery applications. Doctoral thesis , University of London.

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Abstract

The aim of this project was to produce strong, fast photocuring polymer adhesives and composites for biomedical applications that degrade and can release drugs at a controllable rate after set. Five ABA triblock poly(lactide-co-propylene glycol-co- lactide)s with 7, 17 or 34 propylene glycol and 2, 4 or 8 lactic acid units in each B and A block respectively, end capped with methacrylate groups, were prepared. Using FTIR, Raman and NMR, the relative lactide, polypropylene glycol and methacrylate levels in the monomer were proved controllable and as expected from reactant ratios. Polymerisation rates upon blue light exposure for 60, 120 or 240 s using 0.5, 1 or 2 wt% initiators were determined. The shortest monomer with 0.5 wt% initiator achieved 96 % conversion by 120 s after start of 60 s illumination, forming a semi-rigid polymer that in water degraded almost linearly with time with 19 wt% material loss over 14 weeks. Raising initiator concentration reduced polymerisation rate on the lower surface of samples. Increasing the number of lactic acid units in each A block from 2 to 8 enhanced water sorption and increased average total mass loss in 14 weeks to 60 wt% but degradation rate decreased with time. Monomers produced with longer polypropylene glycol B blocks required longer periods of light exposure for full cure and the final more flexible polymers exhibited slower non-linear degradation. Drug release was controlled by varying monomer composition and drug loading level. With hydrophobic ketoprofen, release was more enhanced from rapid-eroding, high water-absorbing polymers. Release of the more water-soluble chlorhexidine diacetate and prednisolone were affected more by polymer swelling and drug diffusion rates through the polymer. Two highly soluble phosphate glasses (67 wt%) were added to one monomer producing composites without losing the rapid set capacity of the polymer. Within a few days in water the glass was leached out providing a means to generate a porous structure. Replacement of phosphate glass with p-tricalcium phosphate and monocalcium phosphate monohydrate filler increased the composite modulus by an order of magnitude upon water sorption, buffered the acidic polymer degradation products and raised the polymer erosion rate significantly. Through further investigations, these polymers and composites should potentially provide a new range of injectable biodegradable slow drug-releasing adhesive materials for various applications in bone tissue engineering and drug delivery.

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