Nano-to-Submicron Hydroxyapatite Coatings for Magnesium-based Bioresorbable Implants - Deposition, Characterization, Degradation, Mechanical Properties, and Cytocompatibility.

Magnesium (Mg) and its alloys have shown attractive biocompatibility and mechanical strength for medical applications, but low corrosion resistance of Mg in physiological environment limits its broad clinical translation. Hydroxyapatite (HA) nanoparticles (nHA) are promising coating materials for decreasing degradation rates and prolonging mechanical strength of Mg-based implants while enhancing bone healing due to their osteoconductivity and osteoinductivity. Conformal HA coatings with nano-to-submicron structures, namely nHA and mHA coatings, were deposited successfully on Mg plates and rods using a transonic particle acceleration (TPA) process under two different conditions, characterized, and investigated for their effects on Mg degradation in vitro. The nHA and mHA coatings enhanced corrosion resistance of Mg and retained 86-90% of ultimate compressive strength after in vitro immersion in rSBF for 6 weeks, much greater than non-coated Mg that only retained 66% of strength. Mg-based rods with or without coatings showed slower degradation than the respective Mg-based plates in rSBF after 6 weeks, likely because of the greater surface-to-volume ratio of Mg plates than Mg rods. This indicates that Mg-based plate and screw devices may undergo different degradation even when they have the same coatings and are implanted at the same or similar anatomical locations. Therefore, in addition to locations of implantation, the geometry, dimension, surface area, volume, and mass of Mg-based implants and devices should be carefully considered in their design and processing to ensure that they not only provide adequate structural and mechanical stability for bone fixation, but also support the functions of bone cells, as clinically required for craniomaxillofacial (CMF) and orthopedic implants. When the nHA and mHA coated Mg and non-coated Mg plates were cultured with bone marrow derived mesenchymal stem cells (BMSCs) using the in vitro direct culture method, greater cell adhesion densities were observed under indirect contact conditions than that under direct contact conditions for the nHA and mHA coated Mg. In comparison with non-coated Mg, the nHA and mHA coated Mg reduced BMSC adhesion densities directly on the surface, but increased the average BMSC adhesion densities under indirect contact. Further long-term studies in vitro and in vivo are necessary to elucidate the effects of nHA and mHA coatings on cell functions and tissue healing

Magnesium-Based Bioresorbable Medical Implants: Improvement to Standardization

Medical implants are devices that are often placed inside the human body to provide support to organs and tissues. Magnesium (Mg) shows great potentials as bioresorbable medical implants. Specifically, Mg is cytocompatible with many human cells in vitro and in vivo. Mg naturally degrades in the human body, which eliminates the secondary removal procedure of the implant. The primary degradation product, Mg ions, is an essential element which participates in over 300 enzymatic metabolisms. As a light metal, Mg possesses an adequate mechanical strength, even for the load-bearing condition in orthopedic device applications.We conducted concentration-dependent tests of Mg degradation products, i.e., Mg ions, OH- ions, MgO and Mg(OH)2, with representative cell models. For human urothelial cells, pH of 8.6 showed cytotoxicity, and Mg ions of 10 mM showed a decrease in cell proliferation rate. We investigated three major strategies to improve Mg, that is, surface coating, alloying and composite. A bioactive, protective surface coating will control degradation rate, and possibly induce a positive tissue response to Mg. Alloying of Mg with other metal elements can potentially result in alloys with improved corrosion resistance and mechanical strength. Sintering Mg powders with calcium phosphates could result in Mg composite with lower degradation rate.In an attempt to establish the consensus standard of the testing Mg-based implant, we design three different in vitro culture methodologies to mimic different in vivo cell-biomaterial interactions. Direct culture is suitable in vitro method when it is important to evaluate direct cell attachment on the biomaterial surfaces. Direct exposure culture isdesirable in vitro method for investigating the response of well-established cells in the body with newly implanted biomaterials. Exposure culture method is appropriate for evaluating cell-biomaterial interactions in the same environment, where they are not in direct contact. Due to the continuous degradation of Mg, cells that were direct contact or indirect contact with Mg substrates, both responded differently to different culture methodologies. A loading apparatus that we designed indicated that Mg under load had a significantly faster degradation rate. Thus, future evaluation of Mg should also take specific loads of different applications into account

Nanostructured calcium phosphate coatings on magnesium alloys: characterization and cytocompatibility with mesenchymal stem cells

This article reports the deposition and characterization of nanostructured calcium phosphate (nCaP) on magnesium-yttrium alloy substrates and their cytocompatibility with bone marrow derived mesenchymal stem cells (BMSCs). The nCaP coatings were deposited on magnesium and magnesium-yttrium alloy substrates using proprietary transonic particle acceleration process for the dual purposes of modulating substrate degradation and BMSC adhesion. Surface morphology and feature size were analyzed using scanning electron microscopy and quantitative image analysis tools. Surface elemental compositions and phases were analyzed using energy dispersive X-ray spectroscopy and X-ray diffraction, respectively. The deposited nCaP coatings showed a homogeneous particulate surface with the dominant feature size of 200-500 nm in the long axis and 100-300 nm in the short axis, and a Ca/P atomic ratio of 1.5-1.6. Hydroxyapatite was the major phase identified in the nCaP coatings. The modulatory effects of nCaP coatings on the sample degradation and BMSC behaviors were dependent on the substrate composition and surface conditions. The direct culture of BMSCs in vitro indicated that multiple factors, including surface composition and topography, and the degradation-induced changes in media composition, influenced cell adhesion directly on the sample surface, and indirect adhesion surrounding the sample in the same culture. The alkaline pH, the indicator of Mg degradation, played a role in BMSC adhesion and morphology, but not the sole factor. Additional studies are necessary to elucidate BMSC responses to each contributing factor

Comparative transcriptome reveal the potential adaptive evolutionary genes in Andrias davidianus

Abstract To search the evidence of molecular evolution mechanism for aquatic and cave habitat in Andrias davidianus, the evolution analysis was carried out among several species transcriptome data. The transcriptome data of Notophthalmus viridescens, Xenopus tropicalis, Cynops pyrrhogaster, Hynobius chinensis and A. davidianus were obtained from the Genbank and reassembled except Xenopus tropicalis. The BLAST search of transcriptome data obtained 1244 single-copy orthologous genes among five species. A phylogenetic tree showed A. davidianus to have the closest relationship to H. chinensis. Fourteen positively selected genes were detected in A. davidianus and N. vridescens group and fifteen in A. davidianus and H. chinensis group. Five genes were shared in the both groups which involved in the immune system, suggesting that A. davidianus adaptation to an aquatic and cave environment required rapid evolution of the immune system compared to N. viridescens and H. chinensis

Regulatory mechanism of LncRNAs in gonadal differentiation of hermaphroditic fish, Monopterus albus

Abstract Background Monopterus albus is a hermaphroditic fish with sex reversal from ovaries to testes via the ovotestes in the process of gonadal development, but the molecular mechanism of the sex reversal was unknown. Methods We produced transcriptomes containing mRNAs and lncRNAs in the crucial stages of the gonad, including the ovary, ovotestis and testis. The expression of the crucial lncRNAs and their target genes was detected using qRT‒PCR and in situ hybridization. The methylation level and activity of the lncRNA promoter were analysed by applying bisulfite sequencing PCR and dual-luciferase reporter assays, respectively. Results This effort revealed that gonadal development was a dynamic expression change. Regulatory networks of lncRNAs and their target genes were constructed through integrated analysis of lncRNA and mRNA data. The expression and DNA methylation of the lncRNAs MSTRG.38036 and MSTRG.12998 and their target genes Psmβ8 and Ptk2β were detected in developing gonads and sex reversal gonads. The results showed that lncRNAs and their target genes exhibited consistent expression profiles and that the DNA methylation levels were negatively regulated lncRNA expression. Furthermore, we found that Ptk2β probably regulates cyp19a1 expression via the Ptk2β/EGFR/STAT3 pathway to reprogram sex differentiation. Conclusions This study provides novel insight from lncRNA to explore the potential molecular mechanism by which DNA methylation regulates lncRNA expression to facilitate target gene transcription to reprogram sex differentiation in M. albus, which will also enrich the sex differentiation mechanism of teleosts

Additional file 2: of Comparative transcriptome reveal the potential adaptive evolutionary genes in Andrias davidianus

Table S1. Orthologs gene under positive selection among species. (DOCX 18 kb

Additional file 1: of Comparative transcriptome reveal the potential adaptive evolutionary genes in Andrias davidianus

Figure S1. Phylogenetic tree of selected species based on 1244 single-copy orthologous genes. (TIFF 212 kb