Biodegradable magnesium ureteral implant materials are gaining increasing research interest duo to their constantly degrading surface, which are immune to biofilm formation. Here, we develop a new Mg-Sr-Ag alloy (JQ alloy), and intensively study its biocompatibility and the antibacterial effect in urinary system. Semi-solid rheo-solidification led to evident grain refinement strengthening effect. The JQ alloy obtained ca. 111% increase in ultimate tensile strength (223.7 MPa). The CCK 8 results showed no significant difference between the LO2 cell proliferation rate in JQ and Mg groups, demonstrating that JQ alloy has equivalent cellular compatibility with pure magnesium. Absence of necrotic tissue and similar cellular structures were observed in both magnesium and JQ groups. The bladder wall structure appeared normal after 12 weeks implantation, and there were no inflammatory infiltrates in the outer mucosa and the muscularis. Cystometric results revealed less negative influence on bladder functions of JQ groups than Mg groups. Higher bladder capacity and starting filling pressure (15.8 ± 6.2 cm H2O) were observed in Mg group after operation. The cells in JQ group showed more compact nucleus with uniformly distributed loose chromatin. Narrow bands of condensed chromatin were observed on the inner nuclear membrane. The smooth endoplasmic reticulum was better developed in JQ group, and a decreased lamina propria widening was also observed in JQ group. Our findings suggest that JQ stent shows satisfactory urinary compatibility and well improves the post-operative bladder functions. We also observed significantly less CFUs in urine, which further led to an absence of nucleus fragmentation and recovered lamina propria. These discoveries make antibacterial biodegradable metallic materials represented by JQ alloy particularly noteworthy candidates as ureteral implant materials.

Magnesium (Mg) alloys present a promising alternative to traditional non-degradable titanium implants due to their biodegradability, biocompatibility, and mechanical properties similar to cortical bone. This study explores the impact of Mg-based implants on bone mechanical properties and ossification processes, focusing on early-stage healing. Using a multiscale analysis approach, methods such as micro-computed tomography (μCT), in situ diffraction nanoindentation, histology, EDX analysis, and quantitative backscattered electron microscopy (qBEI) will be employed. Tibiae of rats implanted with Mg alloy WE43 and titanium alloys (control) were analyzed at various time points. Results indicated that Mg implants stimulated bone turnover, resulting in lower mineralization and calcium heterogeneity. Both 2D and 3D analyses showed decreased lacuna density and bone volume fraction (BV/TV) for Mg implants compared to titanium. The study highlights the significant influence of Mg implant degradation on bone formation and morphology, providing insights into the differences in bone formation between degradable and non-degradable implants.

INTRODUCTION: Magnesium (Mg)-based implants are gaining attention as innovative solutions for fracture fixation, owing to their biocompatibility, biodegradability, and favorable mechanical characteristics. Unlike traditional permanent implants, Mg-based implants naturally resorb, avoiding the need for surgical removal. Nevertheless, Mg’s accelerated degradation in vivo presents a significant challenge. Surface treatments such as autoclaving and Atomic Layer Deposition (ALD) have emerged as promising strategies to tailor degradation rates, and therefore, do not interfere with bone healing. Autoclaving generates a protective oxide layer, whereas ALD enables the application of uniform, ultrathin coatings. METHODS: Bioresorbable Mg-based ZX00 pins (<0.5 wt% Zn, <0.5 wt% Ca; diameter = 1.6 mm, length = 8 mm) were transcortically implanted into the femoral diaphysis of 6-week-old male Sprague Dawley rats (n=6 per group). Five experimental groups were studied: untreated controls, autoclaved once (1xa) or three times (3xa), and two ALD-coated groups (ALD1 and ALD2). Implant degradation was assessed using in vivo micro-computed tomography (µCT), with imaging conducted immediately after implantation and at 2, 6, 12, 18, and 26 weeks. Ex vivo µCT imaging was carried out at 26 weeks post-surgery. Additionally, histological analyses were conducted at the end of the study period. RESULTS: Initial implant volumes and surface areas were larger in the treated groups than in the controls. Throughout the 26-week period, degradation rates were higher in treated samples, particularly those autoclaved three times. ALD-coated implants (ALD1, ALD2) exhibited reduced degradation during the critical early healing phase (weeks 6–12), suggesting a protective influence. Surface area changes between groups were less prominent. Gas formation remained low across all groups, except at isolated time points, with no significant differences. Histological evaluations are ongoing to verify that there is no negative impact on new bone formation. DISCUSSION & CONCLUSIONS: The bioresorbable ZX00 implants, whether untreated or surface-modified, are not anticipated to impair bone regeneration. Our findings show the complexity of optimizing surface treatments to control Mg implant degradation. In this study, ALD coatings showed the greatest potential to moderate degradation during the essential early healing period, highlighting their promise for future clinical application.

Powder production plays a critical role in the outcomes of additive manufacturing (AM), as the properties of the powder directly impact the quality and precision of the manufactured parts. Ultrasonic atomization (UA) enables the production of powders with a narrow size distribution, spherical particles, and minimal impurities. However, given their limited commercial availability, thorough characterization of the powders produced by UA-based systems is essential to ensure they meet the requirements of AM applications. In this study, UA via induction melting of WE43MEO and ZX00MEO magnesium alloys was performed using two feedstock configurations: a crucible-based system and a rod feeder. ZX00MEO was processed via rod feeding, while WE43MEO rods were cut and melted in the crucible. Powders were sieved below 90 µm prior to analysis. Morphology and particle size distribution (PSD) were evaluated using 3D laser scanning microscopy and analyzed in ImageJ, with D10, D50, D90, span, and circularity reported. WE43MEO powder exhibited D10 = 26.2 µm, D50 = 72.5 µm, D90 = 91.4 µm, with a span of 0.90 and mean circularity of 0.94 ± 0.04. ZX00MEO showed D10 = 20.7 µm, D50 = 65.6 µm, D90 = 87.9 µm, with a span of 1.02 and mean circularity of 0.95 ± 0.06. These preliminary findings confirm that UA using induction melting can produce magnesium alloy powders with morphologies and size distributions suitable for AM. Further experiments will complete the setup matrix and include SEM and EDS analyses to investigate microstructure and compositional uniformity.

High concentrations of Mg ions from the degraded Mg implants have been shown to have a local influence on the structure and formation of the bone mineral, i.e hydroxyapatite (HAP), as revealed by small-angle X-ray scattering (SAXS) and X-ray diffraction (XRD). However, these techniques do not reveal the diffusion pathway and precise spatial distribution of the Mg enrichment within the complex interconnected network of bone at the desired length scale to understand the biomineralization mechanism. In addition, it is analytically difficult to quantify elements with low Z numbers using spectroscopic techniques, which hinders rationalizing the Mg distribution at the nanoscale. Bone is the largest reservoir of Mg in the organism and is one of the major cofactors for the enzymes involved in bone matrix synthesis. This raises the question of how Mg from implant degradation gets integrated in to the bone. It can be incorporated either directly into the HAP crystals, as Mg2+ cations can replace Ca2+ in HAP; or into the collagen matrix between the HAP crystals. To answer this question, it is necessary to simultaneously characterize the three-dimensional (3D) composition of bone at the nanometre scale, which can in principle be achieved using atom probe tomography (APT).

INTRODUCTION: Fractures are primarily treated with titanium and stainless-steel implants. However, their high Young’s modulus can cause stress shielding1. Often, they also require extraction surgeries. Biodegradable alternatives, such as magnesium (Mg) alloys, combine mechanical support with gradual resorption. WE43 (MgYREZr) and ZX00, are already in clinical use, valued for their biocompatibility and mechanical properties. The physiologically relevant elements in ZX002 further support biocompatibility and osteogenic potential. In this study, we investigate the fracture healing in an osteotomy model in adult sheep treated with either WE43 or ZX00 implants. By evaluating the fracture healing and osseointegration associated with both alloys, we aim to determine how both alloying systems perform and assess their potential as alternatives for fracture fixation. METHODS: Twenty-four adult sheep underwent proximal tibial osteotomies, stabilized using either WE43 (d: 3.2 mm, l: 40mm) or ZX00 (d: 3.5 mm, l: 40 mm) screws (n = 2 per animal). The sheep were sacrificed at either 6 or 12 weeks (n = 6 animals per material and time point). For all animals, ex vivo µCT of excised tibiae was performed. For the 12-week group, healing was monitored via X-ray and clinical CT (cCT) at 3, 6, and 12 weeks (n = 4 animals per material). Additionally, histology was performed on all animals in which slides were prepared in two cut types: cross-sectional for evaluating fracture healing, longitudinal for overview of screw integration. For each cut, three slides were prepared. RESULTS: In vivo cCT revealed comparable fracture healing progression in both groups (Figure 1). Ex vivo µCT images were qualitatively analyzed using a fracture healing score3 (Figure 2). The fracture gap started to fill with woven bone by week 6. At 12 weeks, all animals achieved a grade of 3, except one WE43 animal scoring 2. Histology demonstrated good implant integration for both alloys, with new bone in direct contact with implant surfaces or degradation layer. Fracture gaps were filled with woven bone, showing early bone remodeling processes toward lamellar bone. Fig 1. Representative image on fracture healing progression over the 12-week study period. Fig 2. Examples illustrating the fracture healing evaluation scale. Green arrowheads = fracture gaps, red arrowheads = fully consolidated bone. 1 = no consolidation, 2 = incipient consolidation, and 3 = consolidation in all 3 planes. DISCUSSION & CONCLUSIONS: Both WE43 and ZX00 supported effective fracture healing as seen in cCT, µCT, and histology. Fracture gaps were filling over time with woven bone, and lamellar remodeling was visible. The findings support the clinical viability of ZX00 and WE43 as biodegradable alternative. LIMITATIONS: Small sample sizes, different screw dimensions, qualitative analysis. REFERENCES: 1H. Weinans et al., J. Biomech. 33(7):809–817, 2000. 2B. Okutan et al., Biomaterials Adv. 146:213287, 2023. 3P. Holweg et al., Acta Biomater. 113:646–659, 2020. ACKNOWLEDGEMENTS: This study was supported by Bioretec Ltd.