The Antimicrobial Efficacy of Hypoxia Mimicking Cobalt Oxide Doped Phosphate-Based Glasses against Clinically Relevant Gram Positive, Gram Negative Bacteria and a Fungal Strain

A Metal‐Ion‐Incorporated Mussel‐Inspired Poly(Vinyl Alcohol)‐Based Polymer Coating Offers Improved Antibacterial Activity and Cellular Mechanoresponse Manipulation

Cobalt (Co^II) ions have been an attractive candidate for the biomedical modification of orthopedic implants for decades. However, limited research has been performed into how immobilized Co^II ions affect the physical properties of implant devices and how these changes regulate cellular behavior. In this study we modified biocompatible poly(vinyl alcohol) with terpyridine and catechol groups (PVA‐TP‐CA) to create a stable surface coating in which bioactive metal ions could be anchored, endowing the coating with improved broad‐spectrum antibacterial activity against Escherichia coli and Staphylococcus aureus, as well as enhanced surface stiffness and cellular mechanoresponse manipulation. Strengthened by the addition of these metal ions, the coating elicited enhanced mechanosensing from adjacent cells, facilitating cell adhesion, spreading, proliferation, and osteogenic differentiation on the surface coating. This dual‐functional PVA‐TP‐CA/Co surface coating offers a promising approach for improving clinical implantation outcomes.

Co-exchanged montmorillonite: a potential antibacterial agent with good antibacterial activity and cytocompatibility

As a biocompatible material with rich resources and economic benefits, montmorillonite (MMT) has been widely used in the antibacterial field as a drug carrier and toxin adsorbent. In addition, the distinctive structure of MMT provides a possibility to tune its property in a wide range through ion-exchange. In this study, Co-montmorillonite (CoMMT) was prepared by the ion-exchanging method in a Co(NO₃)₂ solution and its antibacterial activity and cytocompatibility were investigated. The results showed that Co was introduced into MMT successfully and led to an increase in the interlayer spacing of MMT. Also, CoMMT showed a morphology of irregular aggregates consisting of stacked and intertwined lamellae with a uniform cobalt distribution. Besides, CoMMT had better dispersity and higher specific surface area than unmodified MMT. The antibacterial test results showed that CoMMT had good antibacterial activity against S. aureus and E. coli when the CoMMT concentration was higher than 0.2 mg mL^-1 and 0.4 mg mL^-1, respectively. The possible antibacterial mechanism of CoMMT was speculated and verified by a combination of SEM and EDS results. In addition, CoMMT showed no obvious cytotoxicity to MC3TC-E1 at the observed antibacterial concentration. These findings demonstrated that CoMMT with good biocompatibility and antibacterial activity could be used as a novel antibacterial agent for tissue engineering.

Synergistic Antimicrobial Metal Oxide-Doped Phosphate Glasses; a Potential Strategy to Reduce Antimicrobial Resistance and Host Cell Toxicity

The emergence of antimicrobial resistant strains bacteria and a decline in the discovery of new antibiotics has led to the idea of combining various antimicrobials to treat resistant strains and/or polymicrobial infections. Metal oxide-doped glasses have been extensively investigated for their antimicrobial potential; however to date, most experiments have focused on single metal species in isolation. The present study investigates the antimicrobial potential of sodium calcium phosphates (P₂O₅)₅₀(Na₂O)₂₀(CaO)_30-X(MO)_X, where M is cobalt, copper, or zinc as single species. In addition, this work studied the effect of co-doping glasses containing two different metal ions (Co + Cu, Co + Zn, and Cu + Zn). The antimicrobial efficacy of all glasses was tested against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacterial strains, as well as a fungal strain (Candida albicans). Minimum inhibitory and bactericidal concentrations and time kill/synergy assays were used to assess the antimicrobial activity. An enhanced antimicrobial effect, at 5 mg/mL concentration, was exhibited by cobalt, copper, and zinc oxide glasses alone and in combinations. A synergistic antimicrobial effect was observed by Cu + Co and Cu + Zn against E. coli and Cu + Zn against S. aureus.

Multifarious applications of bioactive glasses in soft tissue engineering

Tissue engineering (TE), a new paradigm in regenerative medicine, repairs and restores the diseased or damaged tissues and eliminates drawbacks associated with autografts and allografts. In this context, many biomaterials have been developed for regenerating tissues and are considered revolutionary in TE due to their flexibility, biocompatibility, and biodegradability. One such well-documented biomaterial is bioactive glasses (BGs), known for their osteoconductive and osteogenic potential and their abundant orthopedic and dental clinical applications. However, in the last few decades, the soft tissue regenerative potential of BGs has demonstrated great promise. Therefore, this review comprehensively covers the biological application of BGs in the repair and regeneration of tissues outside the skeleton system. BGs promote neovascularization, which is crucial to encourage host tissue integration with the implanted construct, making them suitable biomaterial scaffolds for TE. Moreover, they heal acute and chronic wounds and also have been reported to restore the injured superficial intestinal mucosa, aiding in gastroduodenal regeneration. In addition, BGs promote regeneration of the tissues with minimal renewal capacity like the heart and lungs. Besides, the peripheral nerve and musculoskeletal reparative properties of BGs are also reported. These results show promising soft tissue regenerative potential of BGs under preclinical settings without posing significant adverse effects. Albeit, there is limited bench-to-bedside clinical translation of elucidative research on BGs as they require rigorous pharmacological evaluations using standardized animal models for assessing biomolecular downstream pathways.

Biodeterioration of Glass-Based Historical Building Materials: An Overview of the Heritage Literature from the 21st Century

The main goal of this work was to review the 21st century literature (2000 to 2021) regarding the biological colonisation and biodeterioration of glass-based historical building materials, particularly stained glass and glazed tiles. One of the main objectives of this work was to list and systematize the glass-colonising microorganisms identified on stained glass and glazed tiles. Biodiversity data indicate that fungi and bacteria are the main colonisers of stained-glass windows. Glazed tiles are mainly colonised by microalgae and cyanobacteria. Several studies have identified microorganisms on stained glass, but fewer studies have been published concerning glazed tiles. The analysis of colonised samples is a vital mechanism to understand biodeterioration, particularly for identifying the colonising organisms and deterioration patterns on real samples. However, the complexity of the analysis of materials with high biodiversity makes it very hard to determine which microorganism is responsible for the biodeteriogenic action. The authors compared deterioration patterns described in case studies with laboratory-based colonisation experiments, showing that many deterioration patterns and corrosion products are similar. A working group should develop guidelines or standards for laboratory experiments on fungi, bacteria, cyanobacteria, and algae on stained glass and glazed tiles.

Bioactive glasses and electrospun composites that release cobalt to stimulate the HIF pathway for wound healing applications

BACKGROUND

Bioactive glasses are traditionally associated with bonding to bone through a hydroxycarbonate apatite (HCA) surface layer but the release of active ions is more important for bone regeneration. They are now being used to deliver ions for soft tissue applications, particularly wound healing. Cobalt is known to simulate hypoxia and provoke angiogenesis. The aim here was to develop new bioactive glass compositions designed to be scaffold materials to locally deliver pro-angiogenic cobalt ions, at a controlled rate, without forming an HCA layer, for wound healing applications.

METHODS

New melt-derived bioactive glass compositions were designed that had the same network connectivity (mean number of bridging covalent bonds between silica tetrahedra), and therefore similar biodegradation rate, as the original 45S5 Bioglass. The amount of magnesium and cobalt in the glass was varied, with the aim of reducing or removing calcium and phosphate from the compositions. Electrospun poly(ε-caprolactone)/bioactive glass composites were also produced. Glasses were tested for ion release in dissolution studies and their influence on Hypoxia-Inducible Factor 1-alpha (HIF-1α) and expression of Vascular Endothelial Growth Factor (VEGF) from fibroblast cells was investigated.

RESULTS

Dissolution tests showed the silica rich layer differed depending on the amount of MgO in the glass, which influenced the delivery of cobalt. The electrospun composites delivered a more sustained ion release relative to glass particles alone. Exposing fibroblasts to conditioned media from these composites did not cause a detrimental effect on metabolic activity but glasses containing cobalt did stabilise HIF-1α and provoked a significantly higher expression of VEGF (not seen in Co-free controls).

CONCLUSIONS

The composite fibres containing new bioactive glass compositions delivered cobalt ions at a sustained rate, which could be mediated by the magnesium content of the glass. The dissolution products stabilised HIF-1α and provoked a significantly higher expression of VEGF, suggesting the composites activated the HIF pathway to stimulate angiogenesis.

The antimicrobial efficacy of zinc doped phosphate-based glass for treating catheter associated urinary tract infections

In this study, a series of phosphate-based glasses; (P₂O₅)₅₀(Na₂O)₂₀(CaO)_30-x (ZnO)_x were prepared with increasing concentration of zinc oxide to determine the antimicrobial effect against clinically relevant microorganisms. The addition of 1 and 3 mol% zinc oxide decreased glass degradation however a higher dissolution rate was observed for 5 and 10 mol% ZnO. The antimicrobial results showed a concentration dependent effect on the viability of microorganisms. When in direct contact zinc doped glasses showed a complete kill, within 24 h, against Escherichia coli and a significant (p < 0.01) kill was observed against Staphylococcus aureus however the effect of dissolution products was not seen until 48 h. Furthermore, the cytotoxic studies showed no toxic effects on the viability of uroepithelial cells. This study has shown that zinc doped phosphate-based glasses can potentially be used to prevent/treat catheter associated urinary tract infections.

Antibacterial silver-doped phosphate-based glasses prepared by coacervation

Herein we report synthesis, characterization and antimicrobial activity of bioresorbable silver-doped polyphosphate glasses, produced via the coacervation method.