Roxane Bonithon

Large bone defect repair remains challenging. Bioactive glass (BG) particles are established to promote bone regeneration, but amorphous scaffold production requires alternative compositions. The 13-93 composition (mol%: 54.6 SiO₂, 22.1 CaO, 6.0 Na₂O, 7.7 MgO, 7.9 K₂O, 1.7 P₂O₅) has been additively manufactured into large porous scaffolds but not evaluated in vivo in a clinically relevant defect. Here, 13-93 BG and geometrically matched titanium (Ti) scaffolds (Ø8 mm × 12 mm) were implanted into ovine femoral-condyle critical-size defects with unrestricted ambulation and evaluated at six and twelve weeks. Correlative multimodal microscopy integrating microcomputed tomography, backscattered electron microscopy, energy-dispersive spectroscopy (EDS) and histomorphometry quantified bone formation, scaffold degradation, osseointegration and their coupling. By twelve weeks, bone volume fraction reached 55.3 ± 6.6% in 13-93 BG versus 12.1 ± 2.1% in Ti (p < 0.0001). 13-93 BG scaffold volume fraction fell from 47.7% at implantation to 13.4 ± 8.1% by six weeks, then stabilised, whereas Ti was unchanged. Histological osseointegration of 13-93 BG increased from 50.9 ± 4.6% to 72.6 ± 5.6% between six and twelve weeks, exceeding Ti at both timepoints (34.4 ± 14.6% and 24.7 ± 11.0%; p < 0.05, p < 0.001). EDS showed depletion of glass-phase elements (Si, K, Na, Mg) and enrichment of Ca and P, both strongly correlated with bone volume fraction (Ca, P: r = 0.89; glass-phase: r = -0.71 to -0.88; all p ≤ 0.001). These 13-93 BG scaffolds supported bone regeneration in a large-animal critical-size defect, with degradation and bone formation quantitatively coupled.

Chitosan–hydroxyapatite (CS–HA) composite coatings offer a multifunctional surface modification to improve titanium implant performance, combining hydroxyapatite’s osteoconductivity with chitosan’s biocompatibility and antimicrobial properties. This review examines recent in vitro and in vivo studies, noting consistent enhancements in osteoblast adhesion, alkaline phosphatase activity, apatite formation, and bone–implant contact. Incorporation of silver, strontium, or graphene oxide can further boost antibacterial and osteogenic effects. However, variability in coating preparation, substrate treatment, and testing protocols limits reproducibility and clinical extrapolation. Standardised methodologies and extended in vivo validation are essential to advance CS–HA coatings toward reliable dental and orthopaedic applications.

Dental implants have become common for restoring function and aesthetics after edentulism, with titanium (Ti) remaining the most widely used material due to its excellent mechanical properties and biocompatibility. Despite their clinical success, long-term performance is strongly influenced by surface characteristics, which regulate osseointegration and susceptibility to bacterial colonisation. Consequently, surface modification approaches have become critical strategies to enhance implant stability, bioactivity and longevity. This review critically evaluates conventional, advanced, and hybrid surface modification strategies. Subtractive methods, such as sandblasting and acid etching, increase microroughness (Ra 1.5–3 μm), enhancing osteoblast attachment and differentiation, but may promote bacterial adhesion and surface contamination. Combined treatments like SLA and SLActive generate hierarchical micro–nano topographies, improving protein adsorption, early-stage osteoblast proliferation (up to 2-fold), and clinical stability. Laser ablation and photofunctionalisation further modulate surface chemistry and wettability, accelerating osseointegration and epithelial cell adhesion. Coating approaches, including layer-by-layer self-assembly, nanospray drying, plasma spraying, and piezoelectric nanocomposites, introduce antimicrobial activity (>95% reduction in Escherichia coli or Staphylococcus aureus) and enhanced osteogenic differentiation with mechanical stability, with adhesion values reaching 49 MPa. Hybrid techniques such as sol–gel, hydrothermal, and anodisation provide controlled topography, chemical composition, and bioactivity, promoting early bone-to-implant contact (BIC increase of 10%–25%) in preclinical models. Notwithstanding promising in vitro and in vivo outcomes, variability in processing parameters and limited standardisation restrict large-scale clinical translation. Overall, contemporary Ti surface engineering emphasises a synergistic balance of topography, chemistry, wettability, and hierarchical structuring to optimise biological performance for dental implant applications.

Resorbable magnesium (Mg) alloys are attractive for orthopaedic and cardiovascular implants but can degrade rapidly in physiological electrolytes, and combined corrosion–mechanical loading may trigger premature failure. Electrochemical oxidation (ECO) coatings can reduce corrosion by forming a ceramic-like surface enriched with fluoride and phosphate species, yet their brittleness raises concerns regarding integrity under concurrent corrosion and loading. Here, we investigate how ECO coating thickness influences corrosion behaviour and mechanical response under physiologically relevant conditions. AZ31 and X0 alloys were coated with 5 µm and 15 µm ECO layers and tested under static and cyclic three-point bending in Hank’s balanced salt solution (HBSS). Three-point bending fatigue tests revealed that cracks in the alloy initiate at the tensile surface and are associated with coating defects such as pits and cracks in the coating, or localised Ca–P deposits. Under non-corroded conditions and after 1-week of corrosion, uncoated alloy rods generally demonstrated higher fatigue resistance and delayed crack initiation compared to coated counterparts. However, after 3 weeks, only the coated rods sustained any mechanical loading, with 15 µm coatings displaying longer fatigue life, attributed to in-situ Mg(OH)₂ deposition that sealed coating defects. Static sustained loading highlighted the role of ECO coatings in stress corrosion cracking (SCC): and while all coatings reduced crack initiation under elastic loading, only 15 µm coatings suppressed through-thickness propagation under plastic stresses. Overall, ECO coatings mitigate but do not eliminate corrosion–mechanical interactions, and their protective effect depends on thickness, defect morphology, and the mechanical and chemical environments.

Biodegradable magnesium (Mg) alloys are promising for various biomedical applications but their susceptibility to corrosion poses significant challenges. This study systematically examines the microstructural integrity and failure mechanisms of electrochemically deposited phosphate- and fluorine-rich coatings on AZ31 Mg alloy subjected to three-point bending (3 PB) in both non-corrosive and physiological (HBSS) environments. High-resolution digital image correlation (HR-DIC) combined with scanning electron microscopy (SEM) enables in situ visualization and quantitative analysis of crack initiation, evolution, and propagation within the coatings. Our findings reveal that thinner (5 µm) coatings are prone to forming dense networks of fine cracks, while thicker (15 µm) coatings display fewer but wider cracks, with both morphologies strongly governed by localized shear strain. Importantly, cross-sectional analyses after load-holding demonstrate that, while surface cracks initially remain confined within the coating, cracks generated under higher mechanical loading can propagate through the entire coating thickness. These through-thickness cracks create direct pathways for corrosive fluids to access the underlying alloy, serving as initiation sites for stress corrosion cracking within the substrate. Furthermore, our results indicate that fluoride in the coating mitigates rapid corrosion. Overall, the study reveals that coating failure and the formation of through-thickness cracks play a critical role in facilitating localized corrosion and crack initiation within the alloy under combined mechanical and corrosive environments. Graphical Abstract

Resorbable Mg and Mg alloys have gained significant interest as promising biomedical materials. However, corrosion of these alloys can lead to premature reduction in their mechanical properties, and therefore their corrosion rate needs to be controlled. The aim of this study is to select an appropriate environment where the effects of coatings on the corrosion rate of the underlying Mg alloy can be discerned and measured in a relatively short time period. The corrosion resistance of uncoated AZ31 alloy in different solutions [Hank's Balanced Salt Solution, 1× phosphate buffered solution (PBS), 4× PBS, 0.9%, 3.5%, and 5 M sodium chloride (NaCl)] was determined by measuring the weight loss over a 2 week period. Upon exposure to physiological solutions, the uncoated AZ31 alloys exhibited a variable weight increase of 0.4 ± 0.4%. 3.5% and 5 M NaCl solutions led to 0.27 and 9.7 mm/year corrosion rates, respectively, where the compositions of corrosion products from AZ31 in all saline solutions were similar. However, the corrosion of the AZ31 alloy when coated by electrochemical oxidation with two phosphate coatings, one containing fluorine (PF) and another containing both fluorine and silica (PFS), showed 0.3 and 0.25 mm/year corrosion rates, respectively. This is more than 30 times lower than that of the uncoated alloy (7.8 mm/year), making them promising candidates for corrosion protection in severe corrosive environments. Cross-sections of the samples showed that the coatings protected the alloy from corrosion by preventing access of saline to the alloy surface, and this was further reinforced by corrosion products from both the alloy and the coatings forming an additional barrier. The information in this paper provides a methodology for evaluating the effects of coatings on the rate of corrosion of magnesium alloys.

Mesenchymal stem cells (MSCs) hold great promise for the treatment of cartilage related injuries. However, selectively promoting stem cell differentiation in vivo is still challenging. Chondrogenic differentiation of MSCs usually requires the use of growth factors that lead to the overexpression of hypertrophic markers. In this study, for the first time the effect of stiffness on MSC differentiation has been tested without the use of growth factors. Three-dimensional collagen and alginate scaffolds were developed and characterised. Stiffness significantly affected gene expression and ECM deposition. While, all hydrogels supported chondrogenic differentiation and allowed deposition of collagen type II and aggrecan, the 5.75 kPa hydrogel showed limited production of collagen type I compared to the other two formulations. These findings demonstrated for the first time that stiffness can guide MSCs differentiation without the use of growth factors within a tissue engineering scaffold suitable for the treatment of cartilage defects.

The successful application of magnesium (Mg) alloys as biodegradable bone substitutes for critical-sized defects may be comprised by their high degradation rate resulting in a loss of mechanical integrity. This study investigates the degradation pattern of an open-porous fluoride-coated Mg-based scaffold immersed in circulating Hanks' Balanced Salt Solution (HBSS) with and without in situ cyclic compression (30 N/1 Hz). The changes in morphological and mechanical properties have been studied by combining in situ high-resolution X-ray computed tomography mechanics and digital volume correlation. Although in situ cyclic compression induced acceleration of the corrosion rate, probably due to local disruption of the coating layer where fatigue microcracks were formed, no critical failures in the overall scaffold were observed, indicating that the mechanical integrity of the Mg scaffolds was preserved. Structural changes, due to the accumulation of corrosion debris between the scaffold fibres, resulted in a significant increase (p < 0.05) in the material volume fraction from 0.52 ± 0.07 to 0.47 ± 0.03 after 14 days of corrosion. However, despite an increase in fibre material loss, the accumulated corrosion products appear to have led to an increase in Young's modulus after 14 days as well as lower third principal strain (εp3) accumulation (−91000 ± 6361 με and −60093 ± 2414 με after 2 and 14 days, respectively). Therefore, this innovative Mg scaffold design and composition provide a bone replacement, capable of sustaining mechanical loads in situ during the postoperative phase allowing new bone formation to be initially supported as the scaffold resorbs.