gms | German Medical Science

Objectives/Interrogation: A new chemical adhesive for bone repair based on the thiol-ene coupling (TEC) chemistry was developed. The adhesive is inspired by dental resin composites and self-etch primers. Fracture fixation is achieved by building a patch over the fracture constituted by a primer solution followed by layers of the adhesive with imbedded hydroxyapatite and polyethylene terephthalate (PET) fiber meshes. The layers of the patch are cured by using tissue-friendly high-intensity light. The result is a FRAP (Fiber Reinforced Adhesive Patch) and provides a fixation that can be custom made for every fracture. The objective of the study was to examine biomechanical properties, safety and influence on fracture healing and inflammation of the FRAP.

Methods: Adhesion strength to bone was tested biomechanically in vitro on processed wet bovine bone regarding shear bond strength and compared to commercially available dental adhesives. The rigidity of the FRAP was compared to crossed 1,2 mm K-wires and AO Compact hand 1,5 plates in two fracture patterns, transverse and oblique, on pig metatarsals using 1000 cyclic loads of 10-70 N in a three point bending set up. In vivo studies were performed on a rat femur fracture model investigating adhesion to bone, effect on bone healing and inflammation. A safety evaluation (ISO 10993-1:2009) on FRAP leachables was also carried out.

Results and Conclusions: Shear bond strength in vivo was 55% higher than commercially available acrylate dental adhesive, 9.0 MPa vs 5.8MPa. In comparison between K-wire and plate fixation on pig metatarsal fractures in cyclic loading there was no detectable difference of the fixation between metal plate and FRAP, whereas K-wires showed considerable movement and displacement. Histology studies from in vivo samples on rat revealed no inflammation, and no negative effect on bone healing. Initial adhesion strength and adhesion after 5 weeks in vivo revealed that FRAP had maintained 60% bond strength. No cytotoxicity nor genotoxicity was detected in safety evaluation and neither skin irritation nor inflammation were seen.

The FRAP has promising properties and has potential to become a new versatile technique for osteosynthesis for phalangeal fractures. The fixation material is strong, adheres well to bone, does not cause inflammation and is benign to tissues. Further development to human use is under way.