Unveiling the role of hydroxyapatite and hydroxyapatite/silver composite in osteoblast-like cell mineralization: An exploration through their viscoelastic properties

Mechanical properties are becoming fundamental for advancing the comprehension of cellular processes. This study addresses the relationship between viscoelastic properties and the cellular mineralization process. Osteoblast-like cells treated with an osteogenic medium were employed for this purpose. Additionally, the study explores the impact of hydroxyapatite (HA) and hydroxyapatite/silver (HA/Ag) composite on this process. AFM relaxation experiments were conducted to extract viscoelastic parameters using the Fractional Zener (FZ) and Fractional Kelvin (FK) models. Our findings revealed that the main phases of mineralization are associated with alterations in the viscoelastic properties of osteoblast-like cells. Furthermore, HA and HA/Ag treatments significantly influenced changes in the viscoelastic properties of these cells. In particular, the HA/Ag treatment demonstrated a marked enhancement in cell fluidity, suggesting a possible role of silver in accelerating the mineralization process. Moreover, the study underscores the independence observed between fluidity and stiffness, indicating that modifications in one parameter may not necessarily correspond to changes in the other. These findings shed light on the factors involved in the cellular mineralization process and emphasize the importance of using viscoelastic properties to discern the impact of treatments on cells.

Using a two-step method of surface mechanical attrition treatment and calcium ion implantation to promote the osteogenic activity of mesenchymal stem cells as well as biomineralization on a β-titanium surface

Combination of the SMAT technique and Ca-ion implantation produced a β-titanium alloy with a bioactive surface layer, which was proved to effectively promote the osteogenic activity of MSCs and Ca–P mineral deposition in vitro.

Anodic formation and biomedical properties of hafnium-oxide nanofilms

Hafnium dioxide (HfO₂) is attracting attention for bio-related applications due to its good cytocompatibility, high density, and resistance to corrosion and mechanical damage. Here we synthesize two types of hafnium-oxide thin films on substrates via self-organized electrochemical anodization: (1) an array of hierarchically structured nanorods anchored to a thin oxide layer and (2) a microscopically flat oxide film. The nanostructured film is composed of a unique mixture of HfO₂, suboxide Hf₂O₃, and oxide-hydroxide compound HfO₂·nH₂O whereas the flat film is mainly HfO₂. In vitro interaction of the two films with MG-63 osteoblast-like cells and Gram-negative E. coli bacteria is studied for the first time to assess the potential of the films for biomedical application. Both films reveal good cytocompatibility and affinity for proteins, represented by fibronectin and especially albumin, which is absorbed in a nine times larger amount. The morphology and specific surface chemistry of the nanostructured film cause a two-fold enhanced antibacterial effect, better cell attachment, significantly improved proliferation of cells, five-fold rise in the cellular Young's modulus, slightly stronger production of reactive oxygen species, and formation of cell clusters. Compared with the flat film, the nanostructured one features the weakening of AFM-measured adhesion force at the cell/surface interface, probably caused by partially lifting the nanorods from the substrate due to the strong contact with cells. The present findings deepen the understanding of biological processes at the living cell/metal-oxide interface, underlying the role of surface chemistry and the impact of nanostructuring at the nanoscale.

Osteoimmunomodulation, osseointegration, and in vivo mechanical integrity of pure Mg coated with HA nanorod/pore-sealed MgO bilayer

Fast degradation of Mg-based implants results in the loss of mechanical integrity and poor osseointegration. Herein, a bilayer-structured coating (termed as HAT), comprising an outer layer of hydroxyapatite (HA) nanorods and an inner layer of pores-sealed MgO with HA/Mg(OH)2, was formed on Mg using plasma electrolytic oxidation and hydrothermal treatment. Osteoimmunomodulation, osseointegration, mechanical integrity, and bone-implant interfacial structure evolution of the HAT-coated Mg were investigated by implantation in rabbit femora, together with Mg coated with plasma electrolytic oxidized porous MgO (termed as PEO0) and bare Mg. As compared to PEO0-coated and bare Mg, HAT-coated Mg greatly downregulated pro-inflammatory TNF-α and IL-1β, upregulated anti-inflammatory IL-10, and suppressed osteoclastogenesis, modulating the surrounding microenvironment toward favoring the recruitment of osteogenetic cells. Moreover, HAT-coated Mg accelerated bone sialoprotein and osteopontin secretion of osteogenetic cells and their mineralization to form a cement line matrix. It also promoted the differentiation of osteogenetic cells, secretion of collagen overlying on the cement line matrix, inducing an earlier and more pronounced bone matrix formation. The cement line matrix wrapped the HA nanorods and filled the interrod spaces of the HAT coating, forming strong interdigitation at the bone-coating interface, and therefore, yielding enhanced osseointegration by means of contact osteogenesis. Due to the considerably reduced corrosion of Mg by the pores-sealed bilayer structure of HAT coating, HAT-coated Mg maintained the mechanical integrity for a longer duration than PEO0-coated and bare Mg. It is clarified that the degradation of MgO and HA, rather than delamination, was the vanishing mode of PEO0 and HAT coatings during long-term implantation, avoiding osteolysis induced by the delamination-generated particles.

In vitro corrosion behavior and biocompatibility of nanostructured Ti6Al4V

Ti6Al4V (TC4) alloy has long been used as a bone interfacing implant material in dentistry and orthopedics due to its excellent biocompatibility and mechanical properties. The performance of TC4 can be further tailored by altering its grain structures. In this study, by means of sliding friction treatment (SFT), a nano-grained (NG) surface layer with an average grain size of ≤100 nm on the topmost surface was successfully generated on coarse-grained (CG) TC4 alloy sheet. It was shown that the NG surface possessed notably enhanced corrosion resistance in physiological solution compared to the CG surface, due to the formation of thicker and denser passive film facilitated by surface nanocrystallization. Additionally, the NG surface with stronger hydrophilicity favorably altered the absorption of anchoring proteins such as fibronectin (Fn) and vitronectin (Vn) that can mediate subsequent osteoblast functions. The in vitro results indicated that the NG surface exhibited remarkable enhancement in osteoblast adherence, spreading and proliferation, and obviously accelerated the osteoblast differentiation as compared to CG surface. Moreover, the NG surface also demonstrated good hemocompatibility. These findings suggest that SFT can endure bio-metals with advanced multifunctional properties for biomedical applications.

Anti-infection silver nanoparticle immobilized biomaterials facilitated by argon plasma grafting technology

Many research groups have attained slow, persistent, continuous release of silver ions through careful experimental design using existing methods. Such methods effectively kill planktonic bacteria and therefore prevent surface adhesion of pathogens. However, the resultant modified coatings cannot provide long-term antibacterial efficacy due to sustained anti-microbial release. In this study, the anti-infection activity of AgNP immobilized biomaterials was evaluated, facilitated by argon plasma grafting technology and activated by bacterial colonization. The modified materials generated in this study showed excellent specificity and were active against both Gram-positive and Gram-negative biofilm forming bacteria, including methicillin-resistant Staphylococcus aureus, Staphylococcus epidermidis, and Escherichia coli. The anti-infection biomaterials developed in this study demonstrate several attractive advantages in comparison to traditional anti-bacterial surfaces loaded with antibiotics or other types of antibacterial agents and include (1) broad spectrum of activity against antibiotic resistant bacteria, (2) the unlikelihood of bacterial resistance, (3) specificity, (4) biocompatibility, and (5) stability.

Mineral-substituted hydroxyapatite reinforced poly(raffinose-citric acid)–polyethylene glycol nanocomposite enhances osteogenic differentiation and induces ectopic bone formation

Progress of biomimetic mineral-substituted hydroxyapatite reinforced poly(raffinose-citric acid)–polyethylene glycol–poly(raffinose-citric acid) for prospective ectopic bone formation.

Silver-nanoparticles-modified biomaterial surface resistant to staphylococcus: new insight into the antimicrobial action of silver

Titanium implants are widely used clinically, but postoperative implant infection remains a potential severe complication. The purpose of this study was to investigate the antibacterial activity of nano-silver(Ag)-functionalized Ti surfaces against epidemic Staphylococcus from the perspective of the regulation of biofilm-related genes and based on a bacteria-cell co-culture study. To achieve this goal, two representative epidemic Staphylococcus strains, Staphylococcus epidermidis (S. epidermidis, RP62A) and Staphylococcus aureus (S. aureus, USA 300), were used, and it was found that an Ag-nanoparticle-modified Ti surface could regulate the expression levels of biofilm-related genes (icaA and icaR for S. epidermidis; fnbA and fnbB for S. aureus) to inhibit bacterial adhesion and biofilm formation. Moreover, a novel bacteria-fibroblast co-culture study revealed that the incorporation of Ag nanoparticles on such a surface can help mammalian cells to survive, adhere and spread more successfully than Staphylococcus. Therefore, the modified surface was demonstrated to possess a good anti-infective capability against both sessile bacteria and planktonic bacteria through synergy between the effects of Ag nanoparticles and ion release. This work provides new insight into the antimicrobial action and mechanism of Ag-nanoparticle-functionalized Ti surfaces with bacteria-killing and cell-assisting capabilities and paves the way towards better satisfying the clinical needs.

The dual function of Cu-doped TiO2 coatings on titanium for application in percutaneous implants

To endow percutaneous implants with improved skin integration and antibacterial activity, microporous TiO₂ coatings doped with different doses of Cu²⁺ (0-1.93 wt%) were directly fabricated on Ti via micro-arc oxidation (MAO). The structures of coatings were investigated; the adhesion, proliferation, phenotype, differentiation and extracellular collagen secretion of fibroblasts, as well as the response of Staphylococcus aureus (S. aureus), were also investigated. The obtained results show that microporous TiO₂ coatings all consist of antase and rutile, and incorporation of Cu²⁺ almost does not alter the phase component, surface roughness and topography of coating. Cu²⁺ facilitates the fibroblasts to switch to fibrotic phenotype and differentiate to myofibroblasts by enhancing the production of intracellular specific protein contents (connective tissue growth factor (CTGF) and alpha smooth muscle action (α-SMA)). Compared to Ti, the adhesion and proliferation of fibroblasts can be significantly enhanced on the TiO₂ coating with 0.67 wt% Cu, while greatly inhibited with 1.93 wt% Cu. The difference should be due to the compromise between the positive effectiveness and the cytotoxicity of Cu²⁺. Cu²⁺-doped TiO₂ coatings show good antibacterial properties, including contact-killing and release-killing of S. aureus, and these properties are positively related to the dose of Cu²⁺ in the coatings.

Antibacterial Surface Design of Titanium-Based Biomaterials for Enhanced Bacteria-Killing and Cell-Assisting Functions Against Periprosthetic Joint Infection

Periprosthetic joint infection (PJI) is one of the formidable and recalcitrant complications after orthopedic surgery, and inhibiting biofilm formation on the implant surface is considered crucial to prophylaxis of PJI. However, it has recently been demonstrated that free-floating biofilm-like aggregates in the local body fluid and bacterial colonization on the implant and peri-implant tissues can coexist and are involved in the pathogenesis of PJI. An effective surface with both contact-killing and release-killing antimicrobial capabilities can potentially abate these concerns and minimize PJI caused by adherent/planktonic bacteria. Herein, Ag nanoparticles (NPs) are embedded in titania (TiO2) nanotubes by anodic oxidation and plasma immersion ion implantation (PIII) to form a contact-killing surface. Vancomycin is then incorporated into the nanotubes by vacuum extraction and lyophilization to produce the release-killing effect. A novel clinical PJI model system involving both in vitro and in vivo use of methicillin-resistant Staphylococcus aureus (MRSA) ST239 is established to systematically evaluate the antibacterial properties of the hybrid surface against planktonic and sessile bacteria. The vancomycin-loaded and Ag-implanted TiO2 nanotubular surface exhibits excellent antimicrobial and antibiofilm effects against planktonic/adherent bacteria without appreciable silver ion release. The fibroblasts/bacteria cocultures reveal that the surface can help fibroblasts to combat bacteria. We first utilize the nanoarchitecture of implant surface as a bridge between the inorganic bactericide (Ag NPs) and organic antibacterial agent (vancomycin) to achieve total victory in the battle of PJI. The combination of contact-killing and release-killing together with cell-assisting function also provides a novel and effective strategy to mitigate bacterial infection and biofilm formation on biomaterials and has large potential in orthopedic applications.

Multifunctional coatings to simultaneously promote osseointegration and prevent infection of orthopaedic implants

The two leading causes of failure for joint arthroplasty prostheses are aseptic loosening and periprosthetic joint infection. With the number of primary and revision joint replacement surgeries on the rise, strategies to mitigate these failure modes have become increasingly important. Much of the recent work in this field has focused on the design of coatings either to prevent infection while ignoring bone mineralization or vice versa, to promote osseointegration while ignoring microbial susceptibility. However, both coating functions are required to achieve long-term success of the implant; therefore, these two modalities must be evaluated in parallel during the development of new orthopaedic coating strategies. In this review, we discuss recent progress and future directions for the design of multifunctional orthopaedic coatings that can inhibit microbial cells while still promoting osseointegration.

Formation mechanism and cytocompatibility of nano-shaped calcium silicate hydrate/calcium titanium silicate/TiO2 composite coatings on titanium

Compared with as-MAOed TiO₂, the triple-layered coating (HT2h) comprised of an outer layer of nanoleaf Ca₃Si₆O₁₅(H₂O)₇, a middle layer of nanograined Ca(Si_1.9Ti_0.1)O₅ and an inner layer of microporous TiO₂ can significantly improve the behaviors of osteoblasts.

Hydroxyapatite coatings with oriented nanoplate arrays: synthesis, formation mechanism and cytocompatibility

A novel strategy has been developed to fabricate hydroxyapatite coatings with oriented nanoplate arrays for implants of human hard tissues.