Biomimetic Calcium Phosphate Coatings for Bioactivation of Titanium Implant Surfaces: Methodological Approach and In Vitro Evaluation of Biocompatibility

Surface Functionalization of Titanium-Based Implants with a Nanohydroxyapatite Layer and Its Impact on Osteoblasts: A Systematic Review

This study aims to evaluate the influence of a nanohydroxyapatite layer applied to the surface of titanium or titanium alloy implants on the intricate process of osseointegration and its effect on osteoblast cell lines, compared to uncoated implants. Additionally, the investigation scrutinizes various modifications of the coating and their consequential effects on bone and cell line biocompatibility. On the specific date of November 2023, an exhaustive electronic search was conducted in esteemed databases such as PubMed, Web of Science, and Scopus, utilizing the meticulously chosen keywords ((titanium) AND ((osteoblasts) and hydroxyapatite)). Methodologically, the systematic review meticulously adhered to the PRISMA protocol. Initially, a total of 1739 studies underwent scrutiny, with the elimination of 741 duplicate records. A further 972 articles were excluded on account of their incongruence with the predefined subjects. The ultimate compilation embraced 26 studies, with a predominant focus on the effects of nanohydroxyapatite coating in isolation. However, a subset of nine papers delved into the nuanced realm of its modifiers, encompassing materials such as chitosan, collagen, silver particles, or gelatine. Across many of the selected studies, the application of nanohydroxyapatite coating exhibited a proclivity to enhance the osseointegration process. The modifications thereof showcased a positive influence on cell lines, manifesting in increased cellular spread or the attenuation of bacterial activity. In clinical applications, this augmentation potentially translates into heightened implant stability, thereby amplifying the overall procedural success rate. This, in turn, renders nanohydroxyapatite-coated implants a viable and potentially advantageous option in clinical scenarios where non-modified implants may not suffice.

Enhanced antimicrobial properties and bioactivity of 3D-printed titanium scaffolds by multilayer bioceramic coating for large bone defects

The restoration of large bone defects caused by trauma, tumor resection, or infection is a major clinical problem in orthopedics and dentistry because postoperative infections, corrosion, and limited osteointegration of metal implants can lead to loosening of the implant. The aim of this study was to improve the surface properties of a 3D-printed (electron beam melting) Ti6Al4V-based macroporous scaffold by multilayer coating with bioactive silicate glasses (BAGs) and hydroxyapatite doped with a silver (AgHAP) or AgHAP additionally sonochemically modified with ZnO (ZnO-AgHAP). The coated scaffolds AgHAP_BAGs_Ti and ZnO-AgHAP_BAGs_Ti enhanced cytocompatibility in L929 and MRC5 cell lines and expressed bioactivity in simulated body fluid. A lower release of vanadium ions in coated samples compared to bare Ti scaffold indicates decreased dissolution of Ti alloy in coated samples. The coated samples reduced growth ofEscherichia coliandStaphylococcus aureusfor 4-6 orders of magnitude. Therefore, the 3D-printed Ti-based scaffolds coated with BAGs and (ZnO-)AgHAP have great potential for application as a multifunctional implant with antibacterial properties for the restoration of defects in load-bearing bones.

Bioglass and Vitamin D3 Coatings for Titanium Implants: Osseointegration and Corrosion Protection

The use of MAPLE synthesized thin films based on BG and VD3 for improving the osseointegration and corrosion protection of Ti-like implant surfaces is reported. The distribution of chemical elements and functional groups was shown by FTIR spectrometry; the stoichiometry and chemical functional integrity of thin films after MAPLE deposition was preserved, optimal results being revealed especially for the BG+VD3_025 samples. The morphology and topography were examined by SEM and AFM, and revealed surfaces with many irregularities, favoring a good adhesion of cells. The thin films' cytotoxicity and biocompatibility were evaluated in vitro at the morphological, biochemical, and molecular level. Following incubation with HDF cells, BG57+VD3_ 025 thin films showed the best degree of biocompatibility, as illustrated by the viability assay values. According to the LDH investigation, all tested samples had higher values compared to the unstimulated cells. The evaluation of cell morphology was performed by fluorescence microscopy following cultivation of HDF cells on the obtained thin films. The cultivation of HDF's on the thin films did not induce major cellular changes. Cells cultured on the BG57+VD3_025 sample had similar morphology to that of unstimulated control cells. The inflammatory profile of human cells cultured on thin films obtained by MAPLE was analyzed by the ELISA technique. It was observed that the thin films did not change the pro- and anti-inflammatory profile of the HDF cells, the IL-6 and IL-10 levels being similar to those of the control sample. The wettability of the MAPLE thin films was investigated by the sessile drop method. A contact angle of 54.65° was measured for the sample coated with BG57+VD3_025. Electrochemical impedance spectroscopy gave a valuable insight into the electrochemical reactions occurring on the surface.

Bio-Activation of HA/β-TCP Porous Scaffolds by High-Pressure CO2 Surface Remodeling: A Novel "Coating-from" Approach

Biphasic macroporous Hydroxyapatite/β-Tricalcium Phosphate (HA/β-TCP) scaffolds (BCPs) are widely used for bone repair. However, the high-temperature HA and β-TCP phases exhibit limited bioactivity (low solubility of HA, restricted surface area, low ion release). Strategies were developed to coat such BCPs with biomimetic apatite to enhance bioactivity. However, this can be associated with poor adhesion, and metastable solutions may prove difficult to handle at the industrial scale. Alternative strategies are thus desirable to generate a highly bioactive surface on commercial BCPs. In this work, we developed an innovative "coating from" approach for BCP surface remodeling via hydrothermal treatment under supercritical CO₂, used as a reversible pH modifier and with industrial scalability. Based on a set of complementary tools including FEG-SEM, solid state NMR and ion exchange tests, we demonstrate the remodeling of macroporous BCP surface with the occurrence of dissolution-reprecipitation phenomena involving biomimetic CaP phases. The newly precipitated compounds are identified as bone-like nanocrystalline apatite and octacalcium phosphate (OCP), both known for their high bioactivity character, favoring bone healing. We also explored the effects of key process parameters, and showed the possibility to dope the remodeled BCPs with antibacterial Cu²⁺ ions to convey additional functionality to the scaffolds, which was confirmed by in vitro tests. This new process could enhance the bioactivity of commercial BCP scaffolds via a simple and biocompatible approach.

Extrusion-Based Bioprinted Boron Nitride Nanotubes Reinforced Alginate Scaffolds: Mechanical, Printability and Cell Viability Evaluation

Alginate (Alg) hydrogels are commonly used as bioinks in 3D bioprinting. However, one of the significant drawbacks of using Alg hydrogels is their unstable mechanical properties. In this study, a novel hydrogel-based ink composed of Alg reinforced with functionalised boron nitride nanotubes (f-BNNTs) was developed and systematic quantitative characterisation was conducted to validate its printability, physiochemical properties and biocompatibility. The printability, contact angle and mechanical test results indicated good structural stability of the scaffolds. The thermal stability of the scaffolds increased with the incorporation of f-BNNTs into Alg. Human embryonic kidney cells (HEK 293T) were seeded on the scaffolds and the cell viability was recorded for 24, 48 and 72 h. Quantitative studies showed a slight effect on toxicity with a higher concentration of BNNTs in scaffolds. The results suggest that the 3D printable f-BNNTs reinforced Alg could be used as bioink for tissue engineering applications with further studies on biocompatibility.

Bioactive Coatings Loaded with Osteogenic Protein for Metallic Implants

Osteoconductive and osteoinductive coatings represent attractive and tunable strategies towards the enhanced biomechanics and osseointegration of metallic implants, providing accurate local modulation of bone-to-implant interface. Composite materials based on polylactide (PLA) and hydroxyapatite (HAp) are proved beneficial substrates for the modulation of bone cells' development, being suitable mechanical supports for the repair and regeneration of bone tissue. Moreover, the addition of osteogenic proteins represents the next step towards the fabrication of advanced biomaterials for hard tissue engineering applications, as their regulatory mechanisms beneficially contribute to the new bone formation. In this respect, laser-processed composites, based on PLA, Hap, and bone morphogenetic protein 4(BMP4), are herein proposed as bioactive coatings for metallic implants. The nanostructured coatings proved superior ability to promote the adhesion, viability, and proliferation of osteoprogenitor cells, without affecting their normal development and further sustaining the osteogenic differentiation of the cells. Our results are complementary to previous studies regarding the successful use of chemically BMP-modified biomaterials in orthopedic and orthodontic applications.