Reinforced bioresorbable implants for craniomaxillofacial osteosynthesis in pigs

Abstract

Our aim was to design a new bioresorbable fixation device for craniomaxillofacial surgery based on reinforcement of fibres between 2 different polymers. The final device, the 2.8 mm polyglycolide fibre-reinforced-poly-l-lactide screw (PGA FR-PLLA; PLLA/PGA: 70%:30%), was evaluated for its mechanical properties and compared with a commercial resorbable device that was not reinforced with fibre. To model clinical conditions, a unilateral sagittal split ramus osteotomy fixation model in pigs was then used to compare the clinical effectiveness of the resorbable screw with that of a titanium screw in vivo, followed by 3-dimensional reconstructive imaging and histological analysis. Finally, an ex vivo biomechanical test was completed to investigate the immediate fixation stability of the newly designed screws. The PGA FR-PLLA screw resulted in clinical healing that was comparable to that of the titanium screw and was mechanically superior to the commercial device, indicating that the newly-developed screws have a potential clinical application.

Introduction

Optimal healing of fractures and osteotomies in the craniomaxillofacial region generally requires the use of rigid internal fixation with titanium systems. However, there are many drawbacks to these non-degradable metallic alloys, such as interference with imaging, shielding from stress, limitations of use in children, and the presence of a foreign body with the possibility of infection.¹

Bioresorbable screws are selectively used clinically to address these drawbacks. These are commonly made of the biocompatible materials poly-(d,l)-lactic acid, poly-(l)-lactic acid (PLLA), or copolymers of polylactic acid (PLA) and polyglycolic acid (PGA).2, 3 These biodegradable materials have been approved by the Federal Drug Administration in the US, and do not cause appreciable inflammatory or toxic reactions in humans.⁴ However, the main consideration for bioresorbable products is in sustaining appropriate rigidity throughout the healing process, as degradation begins at the time of implantation, which leads to less mechanical stability.1, 5

Reinforcement of screws by material modification is possible through self-reinforcement, which uses oriented reinforcing elements such as fibres within the screw matrix that are made of the same material. This allows the development of devices with ultra-high mechanical strength and different degradation properties.³ The aim of this study was to develop and evaluate a new fibre-reinforced, composite screw that incorporates unidirectional PGA fibres with a PLLA matrix through the injection-moulding manufacturing technique. In contrast to traditional self-reinforced screws, this new heterogeneous polymer reinforcement technique may provide new mechanical variables that are suitable for clinical use.