Electrospun Screw Augment Membrane:A Study In Biomechanical And Biocompatibility

Objective: Screw loosening following fracture fixation or spinal arthrodesis remains a problem in orthopaedics.Screws loosen for many reasons including infection,non-union,poor bone quality,screw repositioning or screw replacement for length changes.Few solutions exist for hardware fixation failures caused by screw replacement,repositioning and intrinsic bone factors such as bone density.In this study,we researched the reason to explain how the screws will be loose,and we developed screw augmentation membranes using electrospinning and absorbable materials and determined if the immediate and long-term stability of bone screws could be improved without negatively affecting fracture healing.Methods: The simulation of operation was on the rigid polyurethane(ASTM-F 1893),we chose the self-tapping screw to screw into and out from the specimen,then screwed into it again.We have tested the axial pullout force of the two conditions,researched the reason for screw loosening via observing the changes of morphology of trajectory.Polyethylene glycol 4000(PEG),Poly-?-hydroxybutyrate(PHB)and graphene oxide(GO)(concentration of GO: 0.5,1,1.5,2,and 2.5 mg/ml)were used to prepare membranes(designated: P,P-P,P-P-G0.5,P-P-G1,P-P-G1.5,P-P-G2,and P-P-G2.5)by electrospinning.The microstructure,mechanical properties and cellular compatibility of the membranes were characterized.The values of axial pullout forces(APFs)of bone screws with membranes(membrane-screws,MS)and without membranes(normal-screws,NS)were compared in two scenarios: a partially loose model(PL)and a completely loose model(CL),setting screws under non-loose condition as control group.Following this,the optimal membrane was selected for treating rabbits with incomplete intertrochanteric fractures and a simulated CL trajectory.Results: The trajectory would be fit with the screw thread when the screw first insert the specimen.The tissue at the screw head has been cut more,which would be aggravated for screw replacement,and the self-tapping screw tip could damage the thread trace in original trajectory,then the screws will be loose,the APF has reduced 17%(P<0.05).The P-P-G1 membrane exhibited strong hydrophilicity,good cellular compatibility,sufficient roughness,large elastic modulus and low strain.In vitro,the APF of the MS group was higher than that of the NS in the PL(P<0.05)and CL(P<0.0005)groups.In vivo,for the CL condition,the immediate APF of the MS was significantly stronger than that of the NS-CL(P<0.0005).By 4 weeks,there were no significant differences between the APFs of the MS-CL and Control groups,which were stronger than that of NS-CL group(P<0.0001).Imaging showed that all groups healed completely.Hematoxylin and eosin staining showed that the fractured zone healed without obvious inflammatory reactions.Conclusions: The replacement of screws has potential to lead screw loose.The biocompatible P-P-G screw membrane worked well to prevent screw loosening without negative effects.Biospun screw augmentation membranes hold promise in preventing internal fixation failure induced by screw loosening.