BIOACTIVITY OF BIORESORBABLE OSTEOSYNTHETIC DEVICES MADE OF HYDROXYAPATITE/ POLY-DL-LACTIDE COMPOSITES: AN EXPERIMENTAL STUDY

Aim. To investigate the bioactivity of the self- designed biodegradable osteosynthetic devices made of resorbable hydroxyapatite microparticles/ poly- DL- lactide (HA/PDLLA) composites. Method. Forty- three rabbits with a transverse transcondylar osteotomy of the distal femur were fixed intramedullary by a HA/PDLLA rod, the duration of follow- up were 3， 6， 12, 24 and 36 weeks. Histological, scanning electron microscopic (SEM), energy dispersive X- ray (EDX) and biomechanical analyses were done. Results. Active new bone formation and direct bone- bonding were seen at the bone- implant interface. Generous apatite crystals deposited and grew on the surface of the composites at 3～ 6 weeks postoperation. The interfacial shear strength increased significantly. Conclusion. Through the incorporating of resorbable HA microparticles, specific bone- bonding and active osteogenic capacity is introduced. This kind of bioactivity, together with other properties such as sufficient mechanical strength, enhanced biocompatibility and radiopacity, which are intrinsically unobtainable in totally resorbable polymer/polymer systems, make the HA/PDLLA composites become a desirable material for the internal fixation of cancellous bone.

Biodegradation of Absorbable Hydroxyapatite/Poly-DL-lactide Composites in Different Environment

To develop a new generation of absorbable fracture fixation devices with enhanced biocompatibility, the biodegradation mechanism and its influence on the cellular response at the tissue/implant interface of hydroxyapatite/ poly DL lactide (HA/PDLLA) composites were investigated in vitro and in vivo.HA/PDLLA rods were immersed in phosphate buffered saline,or implanted in muscle and bony tissue for 52 weeks.Scanning electron microscopic and histological studies were done.The degradation rate was the slowest in vitro,slower in muscle tissue and fast in bone.In vitro, the composites degraded heterogeneously and a hollow structure was formed.In bone,the limited clearing capacity leads to the accumulation of oligomeric debris,which contribute totally to the autocatalytic effect.So,the fastest degradation and intense tissue response were seen.In muscle tissue,oligomeric debris migrated into vicinal fibers over a long distance from the original implant cavity and the tissue reactions were,however, quite moderate.For the same size organic/inorganic composite,the environment where it was placed is the major factor in determining its biodegradation process and cellular reaction.In living tissue,factors such as cells,enzymes and mechanical stress have an obvious influence on the biodegradation and biological process at the tissue/implant interface.The biocompatibility of the HA/PDLLA composites is enhanced with the incorporating of the resorbable HA microparticles.

Intrathoracic Migration of a Steinman Pin after Glenohumeral Fixation—The Journey Continues

We report the case of a 71-year-old woman, who was treated for intrathoracic migration of a Steinman pin, after glenohumeral fixation of an instable dislocation. A thoracotomy was necessary to retrieve the pin. We believe this case can be a reminder of the risks of transarticular fixation around the shoulder. A review of the literature shows very little information regarding glenohumeral pinning.

In Vivo Investigation of Zr-Based Bulk Metallic Glasses Sub-Periosteally Implanted on the Bone Surface

Bulk metallic glasses (BMG) show higher strength and lower Young’s modulus than SUS 316L stainless steel and Ti-6Al-4V alloys. This study aimed to investigate the reaction of Zr-based BMG sub-periosteally implanted on the surface of the rat femur, thereby evaluate the possibility of the BMG as biomaterials for osteosynthetic devices. Zr65Al7.5Ni10Cu17.5 BMG ribbons with 10 mm length, 2 mm width and 0.5 mm thickness were implanted sub-periosteally on the femur surface in three male Wistar rats for 6 weeks. Systemic effects were evaluated by measuring Cu and Ni levels in the blood, and local effects were evaluated by the histological observation of the surrounding soft tissues in contact with the BMG. The reaction of the surface of the BMG was examined with scanning electron microscopy. No increase of Cu and Ni levels in the blood was recognized. In the scanning electron microscopy observation, spherical deposits which were considered as sodium chloride crystals were observed. Neither breakage nor pitting corrosion was noted. BMG will be a promising metallic biomaterial for osteosynthetic device that must be removed.