Phosphate conversion coating reduces the degradation rate and suppresses side effects of metallic magnesium implants in an animal model

Development and Future Trends of Protective Strategies for Magnesium Alloy Vascular Stents

Magnesium alloy stents have been extensively studied in the field of biodegradable metal stents due to their exceptional biocompatibility, biodegradability and excellent biomechanical properties. Nevertheless, the specific in vivo service environment causes magnesium alloy stents to degrade rapidly and fail to provide sufficient support for a certain time. Compared to previous reviews, this paper focuses on presenting an overview of the development history, the key issues, mechanistic analysis, traditional protection strategies and new directions and protection strategies for magnesium alloy stents. Alloying, optimizing stent design and preparing coatings have improved the corrosion resistance of magnesium alloy stents. Based on the corrosion mechanism of magnesium alloy stents, as well as their deformation during use and environmental characteristics, we present some novel strategies aimed at reducing the degradation rate of magnesium alloys and enhancing the comprehensive performance of magnesium alloy stents. These strategies include adapting coatings for the deformation of the stents, preparing rapid endothelialization coatings to enhance the service environment of the stents, and constructing coatings with self-healing functions. It is hoped that this review can help readers understand the development of magnesium alloy cardiovascular stents and solve the problems related to magnesium alloy stents in clinical applications at the early implantation stage.

Effect of titanium implants along with silver ions and tetracycline on type I interferon-beta expression during implant-related infections in co-culture and mouse model

Type I interferon-beta (IFN-β) is a crucial component of innate and adaptive immune systems inside the host. The formation of bacterial biofilms on medical implants can lead to inflammatory diseases and implant failure. Biofilms elicit IFN-β production inside the host that, in turn, restrict bacterial growth. Biofilms pose strong antibiotic resistance, whereas surface modification of medical implants with antibacterial agents may demonstrate strong antimicrobial effects. Most of the previous investigations were focused on determining the antibacterial activities of implant surfaces modified with antibacterial agents. The present study, for the first time, measured antibacterial activities and IFN-β expression of titanium surfaces along with silver or tetracycline inside co-culture and mouse models. A periodontal pathogen: Aggregatibacter actinomycetemcomitans reported to induce strong inflammation, was used for infection. Silver and tetracycline were added to the titanium surface using the heat evaporation method. Macrophages showed reduced compatibility on titanium surfaces with silver, and IFN-β expression inside cultured cells significantly decreased. Macrophages showed compatibility on implant surfaces with tetracycline, but IFN-β production significantly decreased inside seeded cells. The decrease in IFN-β production inside macrophages cultured on implant surfaces with silver and tetracycline was not related to the downregulation of Ifn-β gene. Bacterial infection significantly upregulated mRNA expression levels of Isg15, Mx1, Mx2, Irf-3, Irf-7, Tlr-2, Tnf-α, Cxcl-1, and Il-6 genes. Notably, mRNA expression levels of Mx1, Irf7, Tlr2, Tnf-α, Cxcl1, and Il-6 genes inside macrophages significantly downregulated on implant surfaces with silver or tetracycline. Titanium with tetracycline showed higher antibacterial activities than silver. The in vivo evaluation of IFN-β expression around implants was measured inside transgenic mice constitutive for IFN-β expression. Of note, the non-invasive in vivo imaging revealed a significant decrease in IFN-β expression around subcutaneous implants with silver compared to titanium and titanium with tetracycline in sterile or infected situations. The histology of peri-implant tissue interfaces around infected implants with silver showed a thick interface with a significantly higher accumulation of inflammatory cells. Titanium implants with silver and tetracycline remained antibacterial in mice. Findings from this study unequivocally indicate that implant surfaces with silver decrease IFN-β expression, a crucial component of host immunity.

3D gel-printed porous magnesium scaffold coated with dibasic calcium phosphate dihydrate for bone repair in vivo

Background

/Objective: The treatment of bone defect has always been a difficult problem in orthopedic clinic. The search for alternative biodegradable implants is a hot topic. The development of biodegradable magnesium scaffolds for the treatment of bone defects has long been a goal of the public.

Methods

In this study, we proposed a porous magnesium scaffold prepared by 3D gel printing and surface modification with an additional calcium phosphate coating and use of its strength, degradability and slow degradation rate in a bone graft substitute material. The porous magnesium granular scaffold was prepared by 3D gel printing technology and modified by DCPD (Dibasic Calcium Phosphate Dihydrate) coating. The biocompatibility, degradation rate, and osteogenic ability of the scaffold were evaluated in vitro and in vivo.

Results

The biocompatibility, in vivo degradation and bone defect healing response of the implants were investigated. Porous magnesium scaffolds were successfully prepared, and the strength of sintered scaffolds reached 5.38 ​MPa. The degradation rates of scaffolds were significantly reduced after coating with DCPD. The cell compatibility evaluation showed that DCPD-coated Mg scaffold was suitable for cell proliferation. In vivo biosafety monitoring showed that scaffold implantation did not cause an increase in Mg ion concentration in vivo, and no toxic damage was detected in the liver or kidney. Micro-CT and pathological results showed that a large amount of new bone was formed at 6 weeks. At 12 weeks, approximately 52% of the scaffold volume remained. At 24 weeks, osteogenesis, which was stimulated by some residual scaffold, still can be observed. In summary, this study suggests that 3D gel-printed DCPD-coated porous magnesium scaffolds have great potential as bone graft alternatives.

Conclusion

In summary, this study suggests that 3D gel-printed DCPD-coated porous magnesium scaffolds have great potential as bone graft alternatives.

The Translational potential of this article

The translational potential of this article is to make use of the advantages of 3D gel printing technology with higher efficiency and lower cost compared with SLM and SLS technologies, and use pure magnesium powder as raw material to prepare degradable porous magnesium metal scaffolds, opening up a new technical route for the preparation of degradable porous magnesium scaffolds which are made for bone defect regeneration in the future.

Bacterial-Specific Induction of Inflammatory Cytokines Significantly Decreases upon Dual Species Infections of Implant Materials with Periodontal Pathogens in a Mouse Model

Cytokine profiles are often perturbed after infections of medical implants. With a non-invasive in vivo imaging system, we report in a mouse model that interferon expression after infection of subcutaneous implants with Streptococcus oralis, Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, and Treponema denticola (alone or as a combination) was species-specific, persisted longer in the presence of implants, and notably decreased upon dual species infections. This type I interferon expression disappeared within two weeks; however, histology of implant–tissue interface indicated high recruitment of immune cells even after three weeks. This was suggestive that biomaterial-associated infections could have prolonged effects, including the systemic stimulation of inflammatory cytokines. The present study investigated the systemic impact of this chronic peri-implant inflammation on the systemic expression of inflammatory cytokines (23) using a multiplex assay. Initially, the cytokine measurement in murine fibroblasts exposed to periodontal pathogens remained limited to the expression of five cytokines, namely, IL-6, G-CSF, CXCL-1/KC, MCP-1 (MCAF), and IL-12 (p40). The systemic determination of cytokines in mice increased to 19 cytokines (IL-1α, IL-2, IL-3, IL-5, IL-6, IL-9, IL-12 (p40), IL-12 (p70), IL-13, IL-17A, CCL-11/Eotaxin, G-CSF, IFN-γ, CXCL1/KC, MCP-1 (MCAF), MIP-1α/CCL3, MIP-1β/CCL4, CCL5/RANTES, and TNF-α). Systemic induction of cytokines was species-specific in the mouse model. The cytokine induction from infected implants differed significantly from sole tissue infections and sterile implants. Notably, systemic cytokine induction decreased after infections with dual species compared to single species infections. These findings describe the systemic effect of chronic peri-implant inflammation on the systemic induction of inflammatory cytokines, and this effect was strongly correlated to the type and composition of initial infection. Systemic modulations in cytokine expression upon dual species infections exhibit an exciting pattern that might explain the complications associated with biomaterial-related infection in patients. Moreover, these findings validate the requirement of multispecies infections for pre-clinical studies involving animal models.

Evidence for inoculum size and gas interfaces as critical factors in bacterial biofilm formation on magnesium implants in an animal model

Infections of medical implants caused by bacterial biofilms are a major clinical problem. Bacterial colonization is predicted to be prevented by alkaline magnesium surfaces. However, in experimental animal studies, magnesium implants prolonged infections. The reason for this peculiarity likely lies within the ‒still largely hypothetical‒ mechanism by which infection arises. Investigating subcutaneous magnesium implants infected with bioluminescent Pseudomonas aeruginosa via in vivo imaging, we found that the rate of implant infections was critically dependent on a surprisingly high quantity of injected bacteria. At high inocula, bacteria were antibiotic-refractory immediately after infection. High cell densities are known to limit nutrient availability, restricting proliferation and trigger quorum sensing which could both contribute to the rapid initial resistance. We propose that gas bubbles such as those formed during magnesium corrosion, can then act as interfaces that support biofilm formation and permit long-term survival. This model could provide an explanation for the apparent ineffectiveness of innovative contact-dependent bactericidal implant surfaces in patients. In addition, the model points toward air bubbles in tissue, either by inclusion during surgery or by spontaneous gas bubble formation later on, could constitute a key risk factor for clinical implant infections.

Influence of surface modifications on the degradation of standard-sized magnesium plates and healing of mandibular osteotomies in miniature pigs

Biodegradable magnesium alloys are suitable osteosynthesis materials. Despite the alloy composition, surface modifications appear to have an influence on the degradation process and biocompatibility. The aim of this study was to investigate the impact of hydrogenation and fluoridation of the surface in a mandibular osteotomy model. Standard-sized plates and screws were implanted in an osteotomy at the mandibular angle in nine miniature pigs. The plates and screws were harvested together with the adjacent tissues at 8 weeks after surgery and were investigated by micro-computed tomography and histological analysis. The bone healing of the osteotomy was undisturbed, independent of the surface properties. The adjacent bone tissue showed new bone formation at the implant surface; however, formation of some lacunae could be observed. The corrosion was between 9.8% and 11.6% (fluoridated<hydrogenated<non-modified) in histological specimens, while radiologically neither the volume nor the density of the osteosynthesis material was reduced in any treatment group. The soft tissues exhibited full biocompatibility with every surface property. In summary, surface modification by hydrogenation and fluoridation did not significantly influence bone healing, biocompatibility, or corrosion kinetics of the magnesium osteosynthesis at the mandibular angle.

Fabrication, in vitro and in vivo studies of bilayer composite membrane for periodontal guided tissue regeneration

Development of a guided occlusive biodegradable membrane with controlled morphology in order to restrict the ingrowth of epithelial cells is still a challenge in dental tissue engineering. A bilayer membrane with a non-porous upper layer (polyurethane) and porous lower layer (polycaprolactone and bioactive glass composite) with thermoelastic properties to sustain surgery treatment was developed by lyophilization. Morphology, porosity, and layers attachment were controlled by using the multi-solvent system. In vitro and in vivo biocompatibility, cell attachment, and cell proliferation were analyzed by immunohistochemistry and histology. The cell proliferation rate and cell attachment results showed good biocompatibility of both surfaces, though cell metabolic activity was better on the polycaprolactone-bioactive glass surface. Furthermore, the cells were viable, adhered, and proliferated well on the lower porous bioactive surface, while non-porous polyurethane surface demonstrated low cell attachment, which was deliberately designed and a pre-requisite for guided tissue regeneration/guided bone regeneration membranes. In addition, in vivo studies performed in a rat model for six weeks revealed good compatibility of membranes. Histological analysis (staining with hematoxylin and eosin) indicated no signs of inflammation or accumulation of host immune cells. These results suggested that the fabricated biocompatible bilayer membrane has the potential for use in periodontal tissue regeneration.