Antimicrobial activity of ion-substituted calcium phosphates: A systematic review

Assessment of Quality in Antimicrobial Calcium Phosphate Research (AQUACAP): A Systematic Review

The effectiveness of antimicrobial ion-substituted calcium phosphate biomaterials has been investigated in numerous studies, but reporting guidelines and quality checklists are missing. A novel quality checklist was created for assessing reporting and methodological quality by experts of relevant disciplines. The checklist consisted of 20 items for reporting quality (maximum score 32) and 11 for methodological quality (maximum score 18). The checklist was subsequently implemented to assess the reporting and methodological quality of 58 studies in this field. Possible associations between study quality, year of publication and citations were investigated, and items for improvement were identified. Main items for improvement in reporting quality (average score 18/32) were reporting variability and statistics of data, reporting rationales for study design and the clinical relevance of the outcomes. Methodological quality (average score 11/18) could be improved by including positive control groups, using clinically relevant material formulations and including tests of the material toxicity. No association was found between study quality and year of publication. Methodological quality was associated with a higher number of annual citations. This study identifies key areas for improvement of reporting and methodological quality in the field of ion-substituted antimicrobial calcium phosphates. With these findings, the quality of future studies on antimicrobial CaP materials can be improved. The new quality checklist can also be used to improve study design for future research and enables better comparison between study outcomes.

Calcium phosphate-based anti-infective bone cements: recent trends and future perspectives

Bone infection remains a challenging condition to fully eradicate due to its intricate nature. Traditional treatment strategies, involving long-term and high-dose systemic antibiotic administration, often encounter difficulties in achieving therapeutic drug concentrations locally and may lead to antibiotic resistance. Bone cement, serving as a local drug delivery matrix, has emerged as an effective anti-infective approach validated in clinical settings. Calcium phosphate cements (CPCs) have garnered widespread attention and application in the local management of bone infections due to their injectable properties, biocompatibility, and degradability. The interconnected porous structure of calcium phosphate particles, not only promotes osteoconductivity and osteoinductivity, but also serves as an ideal carrier for antibacterial agents. Various antimicrobial agents, including polymeric compounds, antibiotics, antimicrobial peptides, therapeutic inorganic ions (TIIs) (and their nanoparticles), graphene, and iodine, have been integrated into CPC matrices in numerous studies aimed at treating bone infections in diverse applications such as defect filling, preparation of metal implant surface coatings, and coating of implant surfaces. Additionally, for bone defects and nonunions resulting from chronic bone infections, the utilization of calcium phosphate-calcium sulfate composite multifunctional cement loaded with antibacterial agents serves to efficiently deal with infection, stimulate new bone formation, and attain an optimal degradation rate of the bone cement matrix. This review briefly delves into various antibacterial strategies based on calcium phosphate cement for the prevention and treatment of bone infections, while also discussing the application of calcium phosphate-calcium sulfate composites in the development of multifunctional bone cement against bone infections.

Bone formation and bioresorption of silver-doped β-tricalcium phosphate in rabbit bone defects

Implant-associated infections pose a significant challenge in orthopedic surgery but may be prevented using biomaterials containing antimicrobial agents such as Ag ions. This study examines the effects of Ag doping on bone metabolism following the implantation of β-tricalcium phosphate (β-TCP) doped with 0, 1, 3, and 5 at% Ag with 75% porosity. Additionally, the antimicrobial activity of Ag-doped β-TCP was evaluated against Staphylococcus aureus and Escherichia coli using shake flask tests, revealing increased antimicrobial activity with higher Ag concentrations. Cylindrical bone defects (diameter 4 mm; depth 10 mm) were introduced in the lateral femoral condyles of rabbits and treated with Ag-doped β-TCP. The rabbits were euthanized at 2-, 4-, 8-, and 12-weeks post-operation (n = 6/time point). Specimens were decalcified for histological examination using optical and scanning electron microscopy (SEM). Bone formation, residual material, and tartrate-resistant acid phosphatase (TRAP)-positive cell counts were quantified, with statistical significance assessed using one-way ANOVA (p < 0.05). Bone formation increased over time up to 12 weeks but was lower with higher Ag concentrations. Residual material decreased, while TRAP-positive cells peaked at 2 weeks and gradually declined thereafter. SEM revealed Ag accumulation in the bone marrow outside the newly formed bone. Ag doping inhibited material resorption more than osteogenesis. Bone metabolism in the defect area was delayed as Ag concentration increased, likely due to reduced osteoclast activity. This study highlights the dual effect of Ag-doped β-TCP on bone metabolism and implant-associated infections. While Ag incorporation enhanced antimicrobial potential, higher concentrations delayed bone metabolism. Optimizing Ag content is crucial to balancing infection control with effective bone regeneration, guiding the development of advanced orthopedic implants.

3D printing of strontium-enriched biphasic calcium phosphate scaffolds for bone regeneration

Calcium phosphate (CaP) scaffolds doping with therapeutic ions are one of the focuses of recent bone tissue engineering research. Among the therapeutic ions, strontium stands out for its role in bone remodeling. This work reports a simple method to produce Sr-doped 3D-printed CaP scaffolds, using Sr-doping to induce partial phase transformation from β-tricalcium phosphate (β-TCP) to hydroxyapatite (HA), resulting in a doped biphasic calcium phosphate (BCP) scaffold. Strontium carbonate (SrCO3) was incorporated in the formulation of the 3D-printing ink, studying β-TCP:SrO mass ratios of 100:0, 95:5, and 90:10 (named as β-TCP, β-TCP/5-Sr, and β-TCP/10-Sr, respectively). Adding SrCO3 in the 3D-printing ink led to a slight increase in viscosity but did not affect its printability, resulting in scaffolds with a high printing fidelity compared to the computational design. Interestingly, Sr was incorporated into the lattice structure of the scaffolds, forming hydroxyapatite (HA). No residual SrO or SrCO3 were observed in the XRD patterns of any composition, and HA was the majority phase of the β-TCP/10-Sr scaffolds. The addition of Sr increased the compression strength of the scaffolds, with both β-TCP/5-Sr and β-TCP/10-Sr performing better than the β-TCP. Overall, β-TCP/5-Sr presented higher mineralized nodules and mechanical strength, while β-TCP scaffolds presented superior cell viability. The incorporation of SrCO3 in the ink formulation is a viable method to obtain Sr-BCP scaffolds. Thus, this approach could be explored with other CaP scaffolds aiming to optimize their performance and the addition of alternative therapeutic ions.

Antimicrobial and Cell-Friendly Properties of Cobalt and Nickel-Doped Tricalcium Phosphate Ceramics

β-Tricalcium phosphate (β-TCP) is widely used as bone implant material. It has been observed that doping the β-TCP structure with certain cations can help in combating bacteria and pathogenic microorganisms. Previous literature investigations have focused on tricalcium phosphate structures with silver, copper, zinc, and iron cations. However, there are limited studies available on the biological properties of β-TCP containing nickel and cobalt ions. In this work, Ca10.5-xNix(PO4)7 and Ca10.5-xCox(PO4)7 solid solutions with the β-Ca3(PO4)2 structure were synthesized by a high-temperature solid-state reaction. Structural studies revealed the β-TCP structure becomes saturated at 9.5 mol/% for Co2+ or Ni2+ ions. Beyond this saturation point, Ni2+ and Co2+ ions form impurity phases after complete occupying of the octahedral M5 site. The incorporation of these ions into the β-TCP crystal structure delays the phase transition to the α-TCP phase and stabilizes the structure as the temperature increases. Biocompatibility tests conducted on adipose tissue-derived mesenchymal stem cells (aMSC) using the (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) (MTT) assay showed that all prepared samples did not exhibit cytotoxic effects. Furthermore, there was no inhibition of cell differentiation into the osteogenic lineage. Antibacterial properties were studied on the C. albicans fungus and on E. coli, E. faecalis, S. aureus, and P. aeruginosa bacteria strains. The Ni- and Co-doped β-TCP series exhibited varying degrees of bacterial growth inhibition depending on the doping ion concentration and the specific bacteria strain or fungus. The combination of antibacterial activity and cell-friendly properties makes these phosphates promising candidates for anti-infection bone substitute materials.

Development and Characterization of Electrospun Composites Built on Polycaprolactone and Cerium-Containing Phases

The current study reports on the fabrication of composite scaffolds based on polycaprolactone (PCL) and cerium (Ce)-containing powders, followed by their characterization from compositional, structural, morphological, optical and biological points of view. First, CeO2, Ce-doped calcium phosphates and Ce-substituted bioglass were synthesized by wet-chemistry methods (precipitation/coprecipitation and sol-gel) and subsequently loaded on PCL fibres processed by electrospinning. The powders were proven to be nanometric or micrometric, while the investigation of their phase composition showed that Ce was present as a dopant within the crystal lattice of the obtained calcium phosphates or as crystalline domains inside the glassy matrix. The best bioactivity was attained in the case of Ce-containing bioglass, while the most pronounced antibacterial effect was visible for Ce-doped calcium phosphates calcined at a lower temperature. The scaffolds were composed of either dimensionally homogeneous fibres or mixtures of fibres with a wide size distribution and beads of different shapes. In most cases, the increase in polymer concentration in the precursor solution ensured the achievement of more ordered fibre mats. The immersion in SBF for 28 days triggered an incipient degradation of PCL, evidenced mostly through cracks and gaps. In terms of biological properties, the composite scaffolds displayed a very good biocompatibility when tested with human osteoblast cells, with a superior response for the samples consisting of the polymer and Ce-doped calcium phosphates.