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Spinal cages can be used to treat degenerated discs, by restoring height and stability in the segment and facilitating fusion between vertebrae. Bone grafts, often placed in the cage to enhance bioactivity, may be replaced with synthetic calcium phosphates (CPs). However, their inherent brittleness presents a challenge. This study aimed to design a cervical cage using topology optimization to accommodate bioactive but weak materials, while minimizing the amount of non-resorbable material, herein Ti6Al4V. A design space of a typical cage was subjected to 1Nm in flexion-extension, axial rotation, and lateral bending with 100 N preload in compression and compression-shear, resulting in an optimized design retaining only 21 % of the volume. The design was verified and experimentally validated using additively manufactured Ti6Al4V cages, applying ASTM-F2077 quasi-static testing with and without the inclusion of CP. The results showed no migration or cracking of the CP, and a mechanical performance in the upper range of approved cages. A significant increase in torsional strength and stiffness for the CP-containing cages of 11 % and 17 % was found, respectively. Overall, the study demonstrated the potential of topology optimization in creating spinal cages with reduced permanent material content and adequate mechanical properties for incorporating brittle materials like CPs.

Biodegradable magnesium (Mg) alloys have emerged as promising implant materials; however, their clinical application remains constrained by high corrosion rates. This study addresses this limitation through surface modification of 3D-printed WE43 Mg alloy using a composite coating comprising calcium phosphate (CaP) and phosphoserine (PS) fabricated via a wet chemistry approach at varying molar ratios. Structural and chemical analyses were conducted using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) to examine the effect of PS incorporation on dicalcium phosphate dihydrate (DCPD) and octacalcium phosphate (OCP) phases. PS addition to DCPD reduced crystallinity, increased surface roughness, and decreased the contact angle, thereby enhancing wettability. The incorporation of PS into OCP slightly alters the XRD peak intensities, suggesting a modification in crystallinity. XPS analysis confirmed chemical bonding between the coating and substrate, resulting in enhanced interfacial adhesion. The DCPD-PS-WE43 (1:1) and OCP-PS-WE43 (1:2) compositions exhibited the highest adhesion strengths as measured by shear test (5.00 +/- 0.41 N and 10.33 +/- 0.60 N, respectively). Electrochemical analyses demonstrated that coatings with higher adhesion strength exhibited lower corrosion current densities and reduced corrosion rates. In vitro testing using MC3T3-E1 pre-osteoblasts showed improved cell morphology and proliferation on OCP-PS-WE43 (1:2) compared with uncoated alloy. These findings indicate that the OCP-PS-WE43 (1:2) composite coating enhances both corrosion resistance and biocompatibility, supporting its potential as a surface modification for next-generation biodegradable orthopaedic implants.

Spinal implants have been successfully used to treat various spine conditions. However, concerns remain regarding the release of ions and particles that can cause adverse host responses. Moreover, the biological response from cells of the central nervous system to implant wear particles is not well documented. This research studied the interaction of silicon nitride, cobalt oxide, or chromium oxide particles with relevant glial cells, astrocytes and microglia, to assess their effects on viability and activation using a range of relevant concentrations. Astrocyte viability was not impaired by the particles, and expression levels of the astrocyte reactivity markers GFAP and vimentin were unaffected following 24 h of exposure. Moreover, the particles did not alter microglial phagocytic activity, or stimulate the release of the inflammatory cytokines TNF-α and IL-6. Together, these results suggest that the release of such particles from a spinal implant would not induce an inflammatory response in surrounding glial cells. Interestingly, high concentrations of SiN particles reduced microglial cell viability, potentially due to their tendency to form large agglomerates and/or their high dissolution rate. The present work highlights the importance of studying the potential effects of SiN particles on glial cells and encourages further investigations to fully understand the safety aspects of the use of SiN in spinal implants.

Powder bed fusion laser beam (PBF-LB) of Mg alloys shows strong potential for biodegradable, patient-specific implants. A key challenge is achieving adequate corrosion resistance and mechanical strength while maintaining biocompatibility. This study investigates whether varying hatch distance can balance these properties in PBF-LB processed WE43 (Mg-4Y-3RE-Zr; RE: rare earth elements). Optimal laser parameters were developed for hatch distances of 40, 50, and 60 μm (h40, h50, and h60), and samples were analyzed for microstructure, corrosion resistance, and mechanical properties. Results showed that h60 had a weaker texture and narrower grain size distribution, with fewer grains under 200 μm². It also had the lowest degradation rate while maintaining comparable ultimate tensile strength to h50, which had the highest degradation rate. The improved corrosion resistance in h60 was attributed to a more homogeneous distribution of Mg-RE precipitates due to fewer and more homogenously distributed grain boundaries. Extracts from h60 and control materials were used to culture osteoblasts, showing no cytotoxicity after 3 days. Notably, osteoblasts exposed to 3D-printed WE43 extracts produced more lactate dehydrogenase (LDH) than those exposed to extruded WE43, suggesting faster cell proliferation. This study demonstrates the importance of hatch distance in the PBF-LB processing of WE43, as well as its potential in balancing corrosion and tensile properties while maintaining a good in vitro cellular response of bone resident cells.

Bone defects in the skull often require cranioplasty, which has high complication rates. Implants combining a titanium (Ti) mesh and calcium phosphate (CP) tiles have reduced complications, but titanium is non-resorbable, interferes with imaging, and may require revision. In this study, it was hypothesized that fully degradable, printable polymers could replace titanium. Therefore, poly L-lactic acid (PLLA) was evaluated as support material in CP-based composite cranial implants.

Specimens consisting of a centered 3D-printed support beam (PLLA or Ti) embedded in molded brushitic CP were used to assess the hypothesis, with CP-only and PLLA-only controls. An accelerated degradation study was conducted at 37°C in NaOH (pH 13) for 24 h, 72 h, and 7 days, followed by mechanical, morphological, chemical, and thermal analyses.

Four-point bending showed that the thicker PLLA substantially reinforced the structure, similarly to titanium (failure load at t0: 250 N for PLLA-CP, 344 N for Ti-CP, vs 116 N for CP-only). First cracking occurred at lower loads after 72 h and 7 days, but DSC showed no detrimental polymer changes. Results indicated bulk CP degradation and surface polymer degradation, with no evidence of mutual interference. Overall, PLLA appears promising as a degradable substitute for titanium.

Hyaluronic acid (HA) derivatives are widely used to design biomaterials, but quantifying their degree of chemical modification (DoM) remains challenging with traditional analytical techniques. We present a counterion-based approach that determines DoM by measuring the loss of sodium counterions when carboxylate groups of HA are chemically modified. By focusing on the unmodified carboxylate fraction and its associated Na⁺, this method provides a universal, label-free readout of modifications. We implement the concept with two complementary techniques: thermogravimetric analysis (TGA) to quantify inorganic residue (sodium carbonate) after decomposition, and inductively coupled plasma optical emission spectroscopy (ICP-OES) to measure sodium content in solution. These methods applied to a series of HA derivatives (aldehyde, furan, thiol, and hydrazide-functionalized HA), yielded DoM consistent with nuclear magnetic resonance and ultraviolet-visible (UV-Vis) spectroscopy reference assays. Each method offers distinct advantages: TGA could analyze insoluble or cross-linked samples hands-free with lower user-induced uncertainty, while ICP-OES provides high sensitivity for soluble samples and multielement detection. Using both in parallel allowed cross-validation of results and highlighted the importance of controlling analysis conditions for certain functional groups. Overall, the counterion-counting strategy is simple, modification-agnostic, and broadly applicable, enabling accurate DoM measurements that support the development and quality control of biomaterials.

Ureteral stents are fundamental devices in urology but currently used stents are associated with adverse events such as encrustation and infections. Biodegradable magnesium yttrium (Mg-Y) has shown potential as base material for a next-generation biodegradable ureteral stent due to reported lower corrosion rates than pure Mg, homogeneous corrosion and associated antibacterial activity. In the present work, meshed tubes were produced via additive manufacturing (AM) and extruded, and coiled, wire tubes were fabricated. The corrosion behavior in dynamic conditions was studied, as well as the cytotoxicity and antibacterial activity. AM samples showed faster corrosion (associated with higher surface area and impurity level), while the extruded ones showed some localized corrosion points. Additionally, AM samples demonstrated lower toxicity compared with the extruded-coiled ones to urinary tract derived cell lines, at a low metal exposed surface area/volume ratio of 27.5 mm2/ml. AM samples also showed antibacterial activity against E. coli. This study highlights the potential of Mg-Y for the development of a biodegradable ureteral stent, an innovative concept with expected improved patient outcomes.

Urinary stents are widely used medical devices, however, the necessity of a second surgery for the stent removal is a significant drawback. Hence, using biodegradable materials for stent development has been considered a promising approach. Biodegradable Mg alloys have been gaining popularity for biodegradable medical devices due to the recognized biocompatibility and mechanical characteristics. This work explored the suitability of a WE43 alloy for urinary stent applications using additive manufacturing (AM). This manufacturing technique allows the creation of intricate geometries with high resolution, thus presenting a significant potential for stent design development. The corrosion behaviour of WE43-printed tubes and wires, potential precursors for ureteral stents, were investigated under simulated dynamic urinary tract conditions.

While the corrosion pattern was found to be greatly influenced by the different designs and process parameters, where the corrosion rates varied considerably among the samples over time, the resulting corrosion layer exhibited similarities, all presenting a non-homogeneous coverage and the same chemical elements. This work highlighted the challenge of obtaining homogeneous corrosion but suggested that this type of design exploration could be a useful approach to optimize and tune the stents' corrosion pattern, given the considerable influence of the design on the corrosion pattern. AM is hence a promising research strategy for the exploration of ureteral stent designs given the possibility to easily print a high number of samples with different printing parameters.

In this study, we developed and characterized a fully biodegradable composite bone cement reinforced with short, randomly oriented amorphous magnesium fibers. Fibers of composition Mg₆₀Zn₃₅Ca₅ (in at.%) with 50 μm diameter and 2 mm length were produced by wire spinning and then mixed with a magnesium calcium phosphate cement using fiber volume fractions between 10 and 20 %. The interface strength between the fibers and cement was improved by treating the fibers with diammonium hydrogen phosphate. Compared to the reference cement without fibers, flexural strength was increased by 18 % for the composites with 13 and 18 vol% fibers, and the work of fracture was increased by over 1000× in all cases (p < 0.05, n = 6). Immersion in simulated body fluid for two and four weeks showed that the cement's struvite phase degrades first, and overall, the composite degrades slower. The degradation rate can be tailored to the application by changing the fiber percentage or the cement/fiber composition. Murine pre-osteoblastic cells (MC3T3) cultured in extracts of reference and composite cements had significantly higher cell viability, and composites with 13 vol% fibers also had a significantly higher number of cells compared to the control, indicating that the fibers can enhance and promote pre-osteoblastic cell growth. The results demonstrate that amorphous magnesium fibers enhance both the mechanical and biological properties of ceramic bone cement, expanding their prospects for clinical application.