Antimicrobial activity of bioactive glass S53P4 against representative microorganisms causing osteomyelitis - Real-time assessment by isothermal microcalorimetry

Initial therapeutic evidence of a borosilicate bioactive glass (BSG) and Fe3O4 magnetic nanoparticle scaffold on implant-associated Staphylococcal aureus bone infection

Implant-associated Staphylococcus aureus (S. aureus) osteomyelitis is a severe challenge in orthopedics. While antibiotic-loaded bone cement is a standardized therapeutic approach for S. aureus osteomyelitis, it falls short in eradicating Staphylococcus abscess communities (SACs) and bacteria within osteocyte-lacuna canalicular network (OLCN) and repairing bone defects. To address limitations, we developed a borosilicate bioactive glass (BSG) combined with ferroferric oxide (Fe3O4) magnetic scaffold to enhance antibacterial efficacy and bone repair capabilities. We conducted comprehensive assessments of the osteoinductive, immunomodulatory, antibacterial properties, and thermal response of this scaffold, with or without an alternating magnetic field (AMF). Utilizing a well-established implant-related S. aureus tibial infection rabbit model, we evaluated its antibacterial performance in vivo. RNA transcriptome sequencing demonstrated that BSG + 5%Fe3O4 enhanced the immune response to bacteria and promoted osteogenic differentiation and mineralization of MSCs. Notably, BSG + 5%Fe3O4 upregulated gene expression of NOD-like receptor and TNF pathway in MSCs, alongside increased the expression of osteogenic factors (RUNX2, ALP and OCN) in vitro. Flow cytometry on macrophage exhibited a polarization effect towards M2, accompanied by upregulation of anti-inflammatory genes (TGF-β1 and IL-1Ra) and downregulation of pro-inflammatory genes (IL-6 and IL-1β) among macrophages. In vivo CT imaging revealed the absence of osteolysis and periosteal response in rabbits treated with BSG + 5%Fe3O4 + AMF at 42 days. Histological analysis indicated complete controls of SACs and bacteria within OLCN by day 42, along with new bone formation, signifying effective control of S. aureus osteomyelitis. Further investigations will focus on the in vivo biosafety and biological mechanism of this scaffold within infectious microenvironment.

Efficacy of different bioactive glass S53P4 formulations in biofilm eradication and the impact of pH and osmotic pressure

AIM

The challenging properties of biofilm-associated infections and the rise of multidrug-resistant bacteria are prompting the exploration of alternative treatment options. This study investigates the efficacy of different bioactive glass (BAG) formulations - alone or combined with vancomycin - to eradicate biofilm. Further, we study the influence of BAG on pH and osmotic pressure as important factors limiting bacterial growth.

METHOD

Different BAG S53P4 formulations were used for this study, including (a) powder (<45 μm), (b) granules (500-800 µm), (c) a cone-shaped scaffold and (d) two putty formulations containing granules with no powder (putty A) or with additional powder (putty B) bound together by a synthetic binder. Inert glass beads (1.0-1.3 mm) were included as control. All formulations were tested in a concentration of 1750 mg/ml in Müller-Hinton-Broth against methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant Staphylococcus epidermidis (MRSE). Vancomycin was tested at the minimum-inhibitory concentration for each strain. Changes in pH and osmolality over time were assessed at 0 h, 24 h, 72 h and 168 h.

RESULTS

All tested BAG formulations showed antibiofilm activity against MRSA and MRSE. Powder and putty B were the most effective formulations suppressing biofilm leading to its complete eradication after up to 168 h of co-incubation, followed by granules, scaffold and putty A. In general, MRSE appeared to be more susceptible to bioactive glass compared to MRSA. The addition of vancomycin had no substantial impact on biofilm eradication. We observed a positive correlation between a higher pH and higher antibiofilm activity.

CONCLUSIONS

BAG S53P4 has demonstrated efficient biofilm antibiofilm activity against MRSA and MRSE, especially in powder-containing formulations, resulting in complete eradication of biofilm. Our data indicate neither remarkable increase nor decrease in antimicrobial efficacy with addition of vancomycin. Moreover, high pH appears to have a direct antimicrobial impact; the role of high osmolality needs further investigation.

β-TCP/S53P4 Scaffolds Obtained by Gel Casting: Synthesis, Properties, and Biomedical Applications

The objective of this study was to investigate the osteogenic and antimicrobial effect of bioactive glass S53P4 incorporated into β-tricalcium phosphate (β-TCP) scaffolds in vitro and the bone neoformation in vivo. β-TCP and β-TCP/S53P4 scaffolds were prepared by the gel casting method. Samples were morphologically and physically characterized through X-ray diffraction (XRD) and scanning electron microscope (SEM). In vitro tests were performed using MG63 cells. American Type Culture Collection reference strains were used to determine the scaffold's antimicrobial potential. Defects were created in the tibia of New Zealand rabbits and filled with experimental scaffolds. The incorporation of S53P4 bioglass promotes significant changes in the crystalline phases formed and in the morphology of the surface of the scaffolds. The β-TCP/S53P4 scaffolds did not demonstrate an in vitro cytotoxic effect, presented similar alkaline phosphatase activity, and induced a significantly higher protein amount when compared to β-TCP. The expression of Itg β1 in the β-TCP scaffold was higher than in the β-TCP/S53P4, and there was higher expression of Col-1 in the β-TCP/S53P4 group. Higher bone formation and antimicrobial activity were observed in the β-TCP/S53P4 group. The results confirm the osteogenic capacity of β-TCP ceramics and suggest that, after bioactive glass S53P4 incorporation, it can prevent microbial infections, demonstrating to be an excellent biomaterial for application in bone tissue engineering.

Analytical methods for assessing antimicrobial activity of nanomaterials in complex media: advances, challenges, and perspectives

Assessing the antimicrobial activity of engineered nanomaterials (ENMs), especially in realistic scenarios, is of great significance for both basic research and applications. Multiple analytical methods are available for analysis via off-line or on-line measurements. Real-world samples are often complex with inorganic and organic components, which complicates the measurements of microbial viability and/or metabolic activity. This article highlights the recent advances achieved in analytical methods including typical applications and specifics regarding their accuracy, cost, efficiency, and user-friendliness. Methodological drawbacks, technique gaps, and future perspectives are also discussed. This review aims to help researchers select suitable methods for gaining insight into antimicrobial activities of targeted ENMs in artificial and natural complex matrices.

Evaluation of the effectiveness of bioactive glass fillers against Candida albicans adhesion to PMMA denture base materials: An in vitro study

Background

Dentures with antimicrobial properties are desirable for preventing Candida albicans adhesion. This study was to assess the effectiveness of bioactive glass (BAG) on C. albicans adhesion, surface roughness, and hardness of denture base materials.

Methods

Heat-polymerized (HP) and autopolymerized (AP) acrylic resins were used to fabricate 240 disk specimens (120/material, 60/C. albicans, 60/surface roughness and hardness). Specimens were divided into five groups (n = 10) based on the BAG concentration: 0.5, 1.5, 3, 5, and 7.5 wt% of the acrylic powder, with a control group comprised of unmodified specimens. Direct culture method was used to assess C. albicans adhesion. A profilometer and Vickers hardness test were used to measure surface roughness and hardness respectively. Analysis of variance (ANOVA) and post hoc Tukey's test were used for data analysis (α = 0.05).

Results

BAG addition significantly decreased the C. albicans count when compared with the control group (P < 0.001) for both HP and AP. Regarding surface roughness, there was no change in the HP acrylic resins (P > 0.05), while the AP acrylic resins exhibited significantly higher surface roughness with BAG addition (P < 0.001). The hardness of the HP and AP acrylic resins were significantly higher with the addition of BAG (P < 0.001).

Conclusions

The addition of BAG to HP and AP acrylic resins effectively decreases C. albicans adhesion. The roughness of AP acrylic resins increases with the addition of BAG, while the hardness of both HP and AP acrylic resins increase with the addition of BAG.

Perimeter and carvacrol-loading regulate angiogenesis and biofilm growth in 3D printed PLA scaffolds

Carvacrol is a natural low-cost compound derived from oregano which presents anti-bacterial properties against both Gram-positive and Gram-negative bacteria. In this work, carvacrol-loaded PLA scaffolds were fabricated by 3D printing as platforms to support bone tissue regeneration while preventing biofilm development. Scaffolds were printed with or without a perimeter (lateral wall) mimicking the cortical structure of bone tissue to further evaluate if the lateral interconnectivity could affect the biological or antimicrobial properties of the scaffolds. Carvacrol incorporation was performed by loading either the PLA filament prior to 3D printing or the already printed PLA scaffold. The loading method determined carvacrol localization in the scaffolds and its release profile. Biphasic profiles were recorded in all cases, but scaffolds loaded post-printed released carvacrol much faster, with 50-80% released in the first day, compared to those containing carvacrol in PLA filament before printing which sustained the release for several weeks. The presence or absence of the perimeter did not affect the release rate, but total amount released. Tissue integration and vascularization of carvacrol-loaded scaffolds were evaluated in a chorioallantoic membrane model (CAM) using a novel quantitative micro-computed tomography (micro-CT) analysis approach. The obtained results confirmed the CAM tissue ingrowth and new vessel formation within the porous structure of the scaffolds after 7 days of incubation, without leading to hemorrhagic or cytotoxic effects. The absence of lateral wall facilitated lateral integration of the scaffolds in the host tissue, although increased the anisotropy of the mechanical properties. Scaffolds loaded with carvacrol post-printing showed antibiofilm activity against Staphylococcus aureus and Pseudomonas aeruginosa as observed in a decrease in CFU counting after biofilm detachment, changes in metabolic heat measured by calorimetry, and increased contact killing efficiency. In summary, this work demonstrated the feasibility of tuning carvacrol release rate and the amount released from PLA scaffolds to achieve antibiofilm protection without altering angiogenesis, which was mostly dependent on the perimeter density of the scaffolds.

Mastoid obliteration and external auditory canal reconstruction using 3D printed bioactive glass S53P4 /polycaprolactone scaffold loaded with bone morphogenetic protein-2: A simulation clinical study in rabbits

INTRODUCTION

The lack of good prosthetic materials and objective standards has limited the promotion of mastoid obliteration and external auditory canal reconstruction, and the quality of the surgery varies. In this study, bioactive glass S53P4 (S53P4), the most popular artificial prosthetic material, was modified and combined with polycaprolactone (PCL) and bone morphogenetic protein-2 (BMP-2) to produce an individualized biological scaffold using 3D printing technology to explore a better material and method for mastoid obliteration and external auditory canal reconstruction.

METHODS

3D-printed S53P4/PCL scaffolds were fabricated from 3D reconstruction data of bone defect areas in New Zealand rabbits simulating "Canal Wall Down Mastoidectomy". The water absorption, swelling rate, porosity, and Young's modulus of the scaffold were measured, and the morphology and pore size of the scaffold were observed using scanning electron microscopy. The cytotoxicity of the S53P4/PCL scaffolds was detected using the CCK8 assay, and the in vitro antibacterial activity of the S53P4/PCL scaffolds was detected using the inhibition circle method. The BMP-2-loaded S53P4/PCL scaffolds were prepared using the drop-in lyophilization method and implanted into animal models. The biocompatibility, osteogenic activity, and external auditory canal repair of the scaffolds were observed using endoscopy, micro-CT, and histological examination.

RESULTS

The S53P4/PCL scaffold was highly compatible with the defective area of the animal model, and its physicochemical properties met the requirements of bone tissue engineering. In vitro experiments showed that the S53P4/PCL scaffold was non-cytotoxic and exhibited better antibacterial activity than the same volume of the S53P4 powder. In vivo experiments showed that the S53P4/PCL scaffold had good biocompatibility and osteogenic activity, and could effectively repair bone defects and reconstruct the normal morphology of the external auditory canal in animal models. Furthermore, its osteogenic activity and repair ability were significantly improved after loading with BMP-2.

CONCLUSIONS

The 3D printed S53P4/PCL scaffold has great potential for clinical mastoid obliteration and external auditory canal reconstruction.

New and Efficient Bioactive Glass Compositions for Controlling Endodontic Pathogens

Endodontic treatment aims to conserve teeth through removing infected tissue, disinfecting, and filling/sealing the root canal. One of the most important treatment steps is the removal of microorganisms to avoid reinfection and consequent tooth loss. Due to increased resistance to intracanal medications, new alternative procedures are needed. Thus, an intracanal medication is suggested using three bioactive glass (BG) compositions (BG1, BG2, and BG3) produced by the sol–gel method, with different molar contents of bactericidal oxides. The BGs were morphologically and physically characterized. Their ability to inhibit the growth of two oral pathogens responsible for the failure of endodontic treatments (E. faecalis and C. albicans) was also studied. The results suggest that BG2 and BG3 can inhibit the growth of E. faecalis after 48 h of incubation, and all BG samples have a significant effect on C. albicans survival.

Efficacy of Experimental Mouth Rinses on Caries-Related Biofilms in vitro

This study assessed the efficacy of tin and Polyethylenglycol (PEG-3) tallow aminopropylamine in different concentrations on Streptococcus mutans (S. mutans) biofilms to establish a new screening process for different antimicrobial agents and to gain more information on the antibacterial effects of these agents on cariogenic biofilms. Isothermal microcalorimetry (IMC) was used to determine differences in two growth parameters: lag time and growth rate; additionally, reduction in active biofilms was calculated. Experimental mouth rinses with 400 and 800 ppm tin derived from stannous fluoride (SnF₂) revealed results (43.4 and 49.9% active biofilm reduction, respectively) similar to meridol mouth rinse (400 ppm tin combined with 1,567 ppm PEG-3 tallow aminopropylamine; 55.3% active biofilm reduction) (p > 0.05), while no growth of S. mutans biofilms was detected during 72 h for samples treated with an experimental rinse containing 1,600 ppm tin (100% active biofilm reduction). Only the highest concentration (12,536 ppm) of rinses containing PEG-3 tallow aminopropylamine derived from amine fluoride (AmF) revealed comparable results to meridol (57.5% reduction in active biofilm). Lower concentrations of PEG-3 tallow aminopropylamine showed reductions of 16.9% for 3,134 ppm and 33.5% for 6,268 ppm. Maximum growth rate was significantly lower for all the samples containing SnF₂ than for the samples containing control biofilms (p < 0.05); no differences were found between the control and all the PEG-3 tallow aminopropylamine (p > 0.05). The growth parameters showed high reproducibility rates within the treated groups of biofilms and for the controls; thus, the screening method provided reliable results.

Cognizing the crystallization aspects of NaCaPO4 concomitant 53S bioactive-structures and their imprints in in vitro bio-mineralization

Compositional and bio-physico-chemical characteristic features of bioactive glasses are of great importance in biomedical field.