Biodegradation behaviors of magnesium(Mg)-based alloy nails in autologous bone grafts: In vivo study in rabbit skulls.

OBJECTIVE: In this study, autologous bone grafts using bone-fixing nails made of magnesium-zinc-calcium ternary alloys were performed using rabbit skulls. MATERIAL AND METHODS: Two types of nails for bone fixation were prepared: 2.5 mm width, 3 mm length and 2.5 mm width, 2 mm length. A disk-shaped bone with a diameter of 5 mm was resected from the parietal bone and fixed with a 3 mm long nail. As a control group, a 2 mm long nail was driven into the existing bone. The rabbits were sacrificed at 1, 4, 12, and 24 weeks after surgery. The resected samples were observed with micro X-ray CT, and embedded in methyl methacrylate to prepare non-decalcified specimens. The in vivo localization of elements was examined using energy-dispersive X-ray spectroscopy (EDS). RESULTS: Micro X-ray CT images of samples showed volume reduction due to degradation in both the bone graft and control groups. No significant difference in the amount of degradation between the two groups was observed, however characteristic degradation processes were observed in each group. The samples stained with alizarin red S showed amorphous areas around the nails, which were considered as corrosion products and contacted directly with the newly formed bones. EDS analysis showed that corrosion products were mainly composed of magnesium and oxygen at an early stage, while calcium and phosphorus were detected on the surface layer during the long-term observation. CONCLUSIONS: The degradation speed of the magnesium alloy nails varied depending on the shapes of the nails and surrounding tissue conditions. A calcium phosphate layer was formed on the surface of magnesium alloy nails, suggesting that the degradation rate of the nail was slow.

In vivo behaviors of highly flexible paper consisting of ultralong hydroxyapatite nanowires.

This study was conducted in order to investigate biological compatibility of a thin and flexible hydroxyapatite (HAP) paper which consists of ultralong hydroxyapatite nanowires. Circular-shaped cranial bone defects with a diameter of 8.8 mm were prepared to expose the dura maters in Wistar rats. The similar-sized, circular-shaped HAP paper was placed at the bottom of the bone defects. After 2, 4, and 8 weeks, the rats were sacrificed, and the experimental sections were examined by micro-CT scanning and histological observation. The HAP paper covered with fibrous tissues showed no inflammatory cell infiltration, and their thicknesses decreased over time. Tartrate-resistant acid phosphatase-positive osteoclast-like cells were induced around the edges of the HAP paper along with the exfoliation of the HAP paper. The newly-formed bones were observed in the bone-defected areas, either with a direct contact with the HAP paper or through thin fibrous tissues. The HAP paper-induced osteoblast differentiation was confirmed since the alkaline phosphatase activities were detected on the surfaces of the HAP paper. These results indicated that the HAP paper may induce osteogenesis without causing any harmful effects. The highly flexible HAP paper can contribute to further development of bone regenerative therapy.

Osteogenic response under the periosteum by magnesium implantation in rat tibia.

This study was designed to examine osteoconductive effects of Mg in rats tibia. The animals were sacrificed after 1, 2, and 8 weeks. The elemental analysis was performed using SEM/EDX at week 1. Following X-ray micrography at weeks 2 and 8, samples were embedded in paraffin. The expression of osteocalcin was observed by immunohistochemical staining. The element concentrations of fibrous capsules around the specimens were also measured by ICP-MS. The concentrations of Ca and P on the surface of the Mg specimen increased in SEM/EDX. The tissue specimen showed new bone formation on the bone surface near the implanted area. The concentrations of Mg, Ca, and P were high in the fibrous capsules surrounding Mg. Implantation induced differentiation of osteoblasts, and this process was considered to be associated with new bone formation. Induction of cell differentiation may be influenced by corrosion products in addition to corroding magnesium.

In vitro and in vivo analysis of the biodegradable behavior of a magnesium alloy for biomedical applications.

The present study was designed to investigate the biodegradation behavior of Mg alloy plates in the maxillofacial region. For in vitro analysis, the plates were immersed in saline solution and simulated body fluid. For in vivo, the plates were implanted into the tibia, head, back, abdominal cavity, and femur and assessed at 1, 2, and 4 weeks after implantation. After implantation, the plate volumes and the formed insoluble salt were measured via micro-computed tomography. SEM/EDX analysis of the insoluble salt and histological analysis of the surrounding tissues were performed. The volume loss of plates in the in vitro groups was higher than that in the in vivo groups. The volume loss was fastest in the abdomen, followed by the head, back, tibia, and femur. There were no statistically significant differences in the insoluble salt volume of the all implanted sites. The corrosion of the Mg alloy will be affected to the surrounding tissue responses. The material for the plate should be selected based on the characteristic that Mg alloys are decomposed relatively easily in the maxillofacial region.

Initial organ distribution and biological safety of Mg2+ released from a Mg alloy implant.

Magnesium (Mg) alloys are considered promising materials for biodegradable medical devices; however, the initial effects and distribution of released Mg2+ ions following implantation are unclear. This is addressed in the present study, using two types of Mg alloys implanted into rats. An in vitro immersion test was first carried out to quantify Mg2+ ions released from the alloys at early stages. Based on these data, we performed an in vivo experiment in which large amounts of alloys were subcutaneously implanted into the backs of rats for 1, 5, 10, and 25 h. Mg2+ accumulation in organs was measured by inductively coupled plasma mass spectrometry. In vivo, blood and urine Mg2+ concentrations were higher in rats receiving the implants than in controls after 1 h; however, the levels were within clinically accepted guidelines. The Mg2+ concentration in bone was significantly higher in the 25 h implanted group than in the other groups. Our results suggest that homeostasis is maintained by urinary excretion and bone accumulation of released Mg2+ ions in response to sudden changes in Mg2+ ion concentration in the body fluid in a large number of Mg alloy implants at the early stages.

In vivo corrosion behaviour of magnesium alloy in association with surrounding tissue response in rats.

Biodegradable magnesium (Mg) alloys are the most promising candidates for osteosynthesis devices. However, their in vivo corrosion behaviour has not been fully elucidated. The aim of this study was to clarify the influence of the physiological environment surrounding Mg alloys on their corrosion behaviour. A Mg-1.0Al alloy with a fine-grained structure was formed into plates using titanium (Ti) as a control. These plates were implanted into the subperiosteum in the head, subcutaneous tissue of the back, and in the muscle of the femur of rats for 1, 2 and 4 weeks. The volumes of the remaining Mg alloy and of the insoluble salt deposition and gas cavities around the Mg alloy were determined by microtomography, and the volume losses were calculated. Then, the tissue response around the plates in each implantation site was examined histopathologically, and its relation to the respective volume loss was analyzed. These analyses determined that the Mg alloy was corroded fastest in the head, at an intermediate level in the back, and slowest in the femur. The insoluble salt deposition at the Mg alloy surface had no influence on the volume loss. Gas cavities formed around the Mg alloy at all implantation sites and decreased after 4 weeks. Histopathological examination revealed that the Mg alloy exhibited good biocompatibility, as was seen with Ti. In addition, vascularized fibrous capsules formed around the plates and became mature with time. Notably, the volume loss in the different anatomical locations correlated with capsule thickness. Together, our results suggest that, to facilitate the successful clinical application of Mg alloys, it will be necessary to further comprehend their interactions with specific in vivo environments.

Pressure controlled clamp using shape memory alloy for minimal vessel invasion in blood flow occlusion.

PURPOSE: Vessel damage after clamping may affect the success of surgical operations. A new pressure controlled clamp (SMA clamp) was designed using super elastic property of shape memory alloy (SMA) to realize atraumatic vessel occlusion. The ability and biological effect of the SMA clamp to control pressure was investigated in vivo. METHODS: The loading-displacement curves of the SMA clamps (experimental group) and conventional clamp (control group) by occlusion of pig carotid arteries were evaluated using a clamping-pressure analyzing system. To investigate macroscopically and histologically the vessel damage of the SMA and conventional clamps, pig carotid arteries were stained with Evan's blue and its histological sections were stained with Elastica Massion after clamping for fifteen minutes. RESULTS: Constant value was shown in the loading-displacement curve of SMA clamp. In the control group, damaged area stained with Evan's blue in the vessel wall showed enlargement with the pressure increasing. Less areas in experimental groups are observed than that in the control group. Histological section in the experimental group showed no obvious except a slight compressive damage in the tunica intima. In the control group, vessel wall showed irreversible damages. CONCLUSIONS: This experiment indicated that the SMA clamp, which has a unique mechanical property, can be used without vessels damage. This pressure controlled clamp can be a selection in clinical apparatus to improve surgical safety.

New internalized distraction device for craniofacial plastic surgery using Ni-free, Ti-based shape memory alloy.

This study was undertaken to examine effects and biocompatibility of a new internalized distraction device made from newly developed Ti-Nb-Al shape memory alloy (SMA). Crania of Wistar rats were expanded using a U-shaped wire of this SMA set on each cranium in an experimental group. At 2 or 4 weeks after operation, the rats were killed; width measurements and three-dimensional observations of crania were conducted using soft x-ray and microfocus x-ray computed tomography photography. After photography, histologic sections were made and stained with hematoxylin and eosin. No pathologic change in the experimental duration was observed macroscopically or histologically. Significantly increased size was found for the rat crania in the experimental group compared with the control group. Results demonstrated the feasibility and biocompatibility of internalized distraction osteogenesis using Ni-free, Ti-based SMA in craniofacial plastic surgery for craniofacial deformities.

MPC polymer regulates fibrous tissue formation by modulating cell adhesion to the biomaterial surface.

The aim of this study was to analyze the effects of 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer on fibrous tissue formation and cell adhesion plaque (CAP)-forming reactions. Silastic elastomer (SE) plates coated (experimental group) and uncoated (control group) with MPC polymer were prepared for in vivo and in vitro experiments. For the in vivo animal experiments, SE plates were implanted subcutaneously in the rat dorsal region. At 4, 8, and 12 weeks, thicknesses of the fibrous tissue capsules in the experimental group were lower than in the control group. Likewise, the amount of collagen in the experimental group was lower than that of the control group. For the in vitro cell culture experiments, KMST-6 fibroblast cells in the experimental group demonstrated enhanced cell migration, accompanied with a weaker expression of vinculin and a larger amount of filopodia. Furthermore, weaker expressions of paxillin, talin, and ROCK1, but stronger expression of cofilin, were observed in the experimental group. Taken together, these results suggested that MPC polymer regulated fibrous tissue formation by modulating cell adhesion through changes in local CAPs and downstream signaling.