Enhancement of antimicrobial properties by metals doping in nano-crystalline hydroxyapatite for efficient biomedical applications

A review on hydroxyapatite fabrication: from powders to additive manufactured scaffolds

Hydroxyapatite (HA), the main inorganic bone component, is the most widely researched bioceramic for bone repair. This paper presents a comprehensive review of recent advancements in HA synthesis methods and their integration into additive manufacturing (AM) processes. Synthesis methodologies discussed include wet, dry, and biomimetic routes, emphasizing their impact on tailoring the physicochemical properties of HA for biomedical applications. The incorporation of dopants and additives during synthesis is explored for optimizing the mechanical, biological, and osteogenic characteristics of HA-based materials. Moreover, the evolution of AM technologies from conventional 3D printing to advanced 4D and 5D printing is detailed, covering material selection, process parameters, and post-processing strategies vital for fabricating intricate, patient-specific scaffolds, implants, and drug delivery systems utilizing HA. The review underscores the importance of achieving precise control over microstructure and porosity to mimic native tissue architectures accurately. Furthermore, emerging applications of HA-based constructs in tissue engineering, regenerative medicine, drug delivery, and orthopedic implants are discussed, highlighting their potential to address critical clinical needs. Despite the glimmer of hope provided by the advent and progress of such AM capabilities, several aspects need to be addressed to develop efficient HA-based bone substitutes, which are explored in detail in this review.

Enhanced antimicrobial efficacy of hydroxyapatite-based composites for healthcare applications

Hydroxyapatite (HAp) and hydroxyapatite-based materials show promising potential in the healthcare sector due to their distinctive properties such as biocompatibility, antimicrobial efficacy, non-toxicity, and robust mechanical characteristics. This makes HAp materials play an important role in hindering infection spreading in healthcare provider institutions. This study assesses the antimicrobial efficacy of the developed hydroxyapatite-based composites incorporating copper, zinc, and silver nanoparticles. The synthesized HAp and its modified composite variants (Cu/HAp, Zn/HAp, and Ag/HAp) with varying ratios ranging from 0 to 15% (wt) were characterized using XRD, XPS, SEM, and TEM analyses. Furthermore, the antibacterial and antifungal properties of the synthesized HAp and HAp-based composites were evaluated. The antibacterial effectiveness of the HAp and its composites was evaluated using a modified disc diffusion test, where the resulting inhibition zones on the agar surface were observed. All the HAp and HAp-based composites (HAp, Cu/HAp, Zn/HAp, and Ag/HAp materials) elicited in the formation of inhibitory zones. The most substantial inhibition values were observed for the 5% Ag/HAp formulation, with values of 19.7 and 13.8, against E. coli and S. aureus, respectively. The 5% Ag/HAp concentration may strike an ideal balance, providing high antimicrobial activity without adverse effects on biocompatibility or material stability. These findings underscore the recommendation of the proposed HAp-based composites for infection control measures through their application on medical instruments, textiles, healthcare personnel attire, and patient garments.

Biocompatibility and Osteogenic Activity of Samarium-Doped Hydroxyapatite-Biomimetic Nanoceramics for Bone Regeneration Applications

In this study, we report on the development of hydroxyapatite (HAp) and samarium-doped hydroxyapatite (SmHAp) nanoparticles using a cost-effective method and their biological effects on a bone-derived cell line MC3T3-E1. The physicochemical and biological features of HAp and SmHAp nanoparticles are explored. The X-ray diffraction (XRD) studies revealed that no additional peaks were observed after the integration of samarium (Sm) ions into the HAp structure. Valuable information regarding the molecular structure and morphological features of nanoparticles were obtained by using Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The elemental composition obtained by using energy-dispersive X-ray spectroscopy (EDS) confirmed the presence of the HAp constituent elements, Ca, O, and P, as well as the presence and uniform distribution of Sm3+ ions. Both HAp and SmHAp nanoparticles demonstrated biocompatibility at concentrations below 25 μg/mL and 50 μg/mL, respectively, for up to 72 h of exposure. Cell membrane integrity was preserved following treatment with concentrations up to 100 μg/mL HAp and 400 μg/mL SmHAp, confirming the role of Sm3+ ions in enhancing the cytocompatibility of HAp. Furthermore, our findings reveal a positive, albeit limited, effect of SmHAp nanoparticles on the actin dynamics, osteogenesis, and cell migration compared to HAp nanoparticles. Importantly, the biological results highlight the potential role of Sm3+ ions in maintaining cellular balance by mitigating disruptions in Ca2+ homeostasis induced by HAp nanoparticles. Therefore, our study represents a significant contribution to the safety assessment of both HAp and SmHAp nanoparticles for biomedical applications focused on bone regeneration.

Thermal spray processes influencing surface chemistry and in-vitro hemocompatibility of hydroxyapatite-based orthopedic implants

Orthopedic implants made from titanium are a popular choice in the medical field because of their remarkable strength-to-weight ratio. Nevertheless, they may not interact well with human blood, resulting in thrombosis and hemolysis. In fact, non-hemocompatibility is believed to be responsible for about 31 % of medical device failures in the US alone, requiring painful and expensive revision surgery. To address this issue, bioactive hydroxyapatite coatings are applied to Ti-6Al-4V implants using thermal spray techniques. However, the temperature used during thermal processing impacts the coating's surface properties, affecting the mechanical and biological properties. Furthermore, the effectiveness of HA coatings on titanium for orthopedic applications has not been validated by biocompatibility tests, particularly hemocompatibility. In this study, we aimed to investigate the relative efficacy of three thermal spray processes of different temperature ranges: Atmospheric plasma spray (APS) (high temperature), Flame spray (FS) (moderate temperature), and High-Velocity Oxy-Fuel spray (HVOF) (low temperature), and study their impact on coating's surface properties, affecting blood components and implant's strength. The crystallinity of the HA coating increased by 32 % with a decrease in the operating temperature (APS < FS < HVOF). HVOF coating exhibited a ~ 34 % and ~ 120 % improvement in adhesion strength and ~ 31 % and 59 % increment in hardness compared to APS and FS coating, respectively, attributed to its low porosity, low coating thickness (~55 μm), and high degree of crystallinity. The HVOF coating showcased a significant increase in non-hemolytic behavior, with hemolysis rates ~8 and ~ 11 times lower than APS and FS coatings, respectively, owing to its smooth texture and high degree of crystallinity (p < 0.05). Furthermore, the HVOF coating exhibited minimal blood clotting based on the whole blood clotting assay, again confirmed by PT and aPTT assays showing delayed clotting time, indicating its non-thrombogenic behavior. The number of platelets adhered to the three coatings showed no significant difference compared to Ti-6Al-4V. APS and FS coatings showed low platelet activation, unlike HVOF coating and titanium, which revealed round platelets, similar to the negative control. Neither titanium nor HA coatings exhibited antibacterial properties, which may be due to their high affinity for organic substances, which promotes bacterial adhesion and replication. Among the three thermal processes, HVOF coating displayed good apatite growth, non-hemolytic, and non-thrombogenicity with no platelet activation owing to its low processing temperature, high degree of crystallinity (89.7 %), hydrophilicity, smooth (~4 μm) and dense (~97 %) microstructural properties. The results demonstrated that the HVOF-HA coating presented in this work meets the hemocompatible requirements and shows promise for prospective application as an orthopedic implant. Furthermore, this study has the potential to significantly reduce the use of animals in in-vivo research and improve their welfare while also cutting costs.

Iron and Magnesium Co-substituted Hydroxyapatite Nanoparticles in Orthodontic Composite: A Preliminary Assessment

Aim The study aims to characterize Fe and Mg co-substituted hydroxyapatite nanoparticles (FeMgHAPn) and assess the antimicrobial properties of FeMgHAPn-incorporated orthodontic composite. Materials and methods FeMgHAPn was synthesized using the sol-gel method, and the prepared nanoparticle powder was characterized using Fourier Transform Infrared Spectroscopy (FTIR), energy-dispersive X-ray analysis (EDX)) and scanning electron microscopic (SEM) analysis. The FeMgHAPn was incorporated into a commercially available orthodontic composite in two concentrations (40 and 20 μL), and the structure was examined using SEM. The FeMgHAPn-incorporated composite was tested for its antimicrobial efficacy against Streptococcus mutans, Staphylococcus aureus, and Escherichia coli using the agar-well diffusion method. The zones of inhibition (ZOI) were measured in millimeters (mm). Results The characterization of the FeMgHAPn indicated the successful formation of the nanoparticle without any impurities or byproducts. The high concentration (40 μL) of FeMgHAPn-incorporated orthodontic composite showed the maximum ZOI against all three microbes, followed by the low concentration (20 μL) and the control group. Conclusion The FeMgHAPn-incorporated orthodontic composite showed promising antimicrobial activity against caries-causing S. mutans, S. aureus, and E. coli.