Long-term clinical study and multiscale analysis of in vivo biodegradation mechanism of Mg alloy.

There has been a tremendous amount of research in the past decade to optimize the mechanical properties and degradation behavior of the biodegradable Mg alloy for orthopedic implant. Despite the feasibility of degrading implant, the lack of fundamental understanding about biocompatibility and underlying bone formation mechanism is currently limiting the use in clinical applications. Herein, we report the result of long-term clinical study and systematic investigation of bone formation mechanism of the biodegradable Mg-5wt%Ca-1wt%Zn alloy implant through simultaneous observation of changes in element composition and crystallinity within degrading interface at hierarchical levels. Controlled degradation of Mg-5wt%Ca-1wt%Zn alloy results in the formation of biomimicking calcification matrix at the degrading interface to initiate the bone formation process. This process facilitates early bone healing and allows the complete replacement of biodegradable Mg implant by the new bone within 1 y of implantation, as demonstrated in 53 cases of successful long-term clinical study.

Atmospheric scanning electron microscopy and its applications for biological specimens.

Scanning electron microscopy in ambient conditions (Air-SEM) was developed recently and has been used mainly for industrial applications. We assessed the potential application of Air-SEM for the analysis of biological tissues by using rat brain, kidney, human tooth, and bone. Hard tissues prepared by grinding and frozen sections were observed. Basic cytoarchitecture of bone and tooth was identified in the without heavy metal staining. Kidney tissue prepared using routine SEM methodology yielded images comparable to those of field emission (FE)-SEM. Sharpness was lower than that of FE-SEM, but foot process of podocytes was observed at high magnification. Air-SEM observation of semithin sections of kidney samples revealed glomerular basement membrane and podocyte processes, as seen using conventional SEM. Neuronal structures of soma, dendrites, axons, and synapses were clearly observed by Air-SEM with STEM detector and were comparable to conventional transmission electron microscopy images. Correlative light and electron microscopy observation of zebrafish embryos based on fluorescence microscopy and Air-SEM indicated the potential for a correlative approach. However, the image quality should be improved before becoming routine use in biomedical research.

Induction of Angiogenesis by Matrigel Coating of VEGF-Loaded PEG/PCL-Based Hydrogel Scaffolds for hBMSC Transplantation.

hBMSCs are multipotent cells that are useful for tissue regeneration to treat degenerative diseases and others for their differentiation ability into chondrocytes, osteoblasts, adipocytes, hepatocytes and neuronal cells. In this study, biodegradable elastic hydrogels consisting of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic poly(ε-caprolactone) (PCL) scaffolds were evaluated for tissue engineering because of its biocompatibility and the ability to control the release of bioactive peptides. The primary cultured cells from human bone marrow are confirmed as hBMSC by immunohistochemical analysis. Mesenchymal stem cell markers (collagen type I, fibronectin, CD54, integrin1ß, and Hu protein) were shown to be positive, while hematopoietic stem cell markers (CD14 and CD45) were shown to be negative. Three different hydrogel scaffolds with different block compositions (PEG:PCL=6:14 and 14:6 by weight) were fabricated using the salt leaching method. The hBMSCs were expanded, seeded on the scaffolds, and cultured up to 8 days under static conditions in Iscove's Modified Dulbecco's Media (IMDM). The growth of MSCs cultured on the hydrogel with PEG/PCL= 6/14 was faster than that of the others. In addition, the morphology of MSCs seemed to be normal and no cytotoxicity was found. The coating of the vascular endothelial growth factor (VEGF) containing scaffold with Matrigel slowed down the release of VEGF in vitro and promoted the angiogenesis when transplanted into BALB/c nude mice. These results suggest that hBMSCs can be supported by a biode gradable hydrogel scaffold for effective cell growth, and enhance the angiogenesis by Matrigel coating.

In vivo corrosion mechanism by elemental interdiffusion of biodegradable Mg-Ca alloy.

We elucidated the in vivo corrosion mechanism of the biodegradable alloy Mg-10 wt % Ca in rat femoral condyle through transmission electron microscope observations assisted by focused ion beam technique. The alloy consists of a primary Mg phase and a three-dimensional lamellar network of Mg and Mg(2)Ca. We found that the Mg(2)Ca is rapidly corroded by interdiffusion of Ca and O, leading to a structural change from lamellar network to nanocrystalline MgO. In contrast to the fast corrosion rate of the lamellar structure, the primary Mg phase slowly changes into nanocrystalline MgO through surface corrosion by O supplied along the lamellar networks. The rapid interdiffusion induces an inhomogeneous Ca distribution and interestingly leads to the formation of a transient CaO phase, which acts as a selective leaching path for Ca. In addition, the outgoing Ca with P from body fluids forms needle-type calcium phosphates similar to hydroxyl apatite at interior and surface of the implant, providing an active biological environment for bone mineralization.