Multimodal ex vivo methods reveal that Gd-rich corrosion byproducts remain at the implant site of biodegradable Mg-Gd screws

Unraveling the synergistic effects of Ag, Li and Sr on Zn alloys in enhancing orthopedic repair potential

Recently, Li, which can greatly enhance the mechanical characteristics of zinc alloys, Ag, which has antibacterial properties, and Sr, which promotes bone formation, have been widely applied in biodegradable alloys. However, to our knowledge, there has been no research on the combined effects of Ag, Li, and Sr in zinc alloys. To address this, we have created a new quaternary alloy (Zn-3Ag-0.1Li-0.1Sr). The incorporation of Ag, Li, and Sr increased the yield strength (YS) of the at-cast (AC) zinc alloy to 188.83 ± 12.38 MPa. After extrusion and hot rolling, the strong plasticity of the alloy was further significantly enhanced, with ultimate tensile strength (UTS) exceeding 400 MPa, YS exceeding 350 MPa, and elongation (EL) greater than 50%. An in vitro cell study revealed that after three days of culture with a 50% extract, the proliferation rate of MC3T3-E1 cells was 101.527 ± 0.129%, and the cells maintained a healthy spindle-shaped appearance. The antibacterial experiments also demonstrated that the Zn-3Ag-0.1Li-0.1Sr quaternary alloy has strong antibacterial properties against both Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Therefore, the biodegradable Zn-3Ag-0.1Li-0.1Sr quaternary alloy, which exhibits high strength, good cytocompatibility, and satisfactory antibacterial performance, has greater potential for application in the field of orthopedic repair.

Multifaceted bone response to immunomodulatory magnesium implants: Osteopromotion at the interface and adipogenesis in the bone marrow

Orthopedic implants made of biodegradable magnesium (Mg) provide an alternative to nondegradable implants for fracture repair. Widely reported to be pro-osteogenic, Mg implants are also believed to be anti-inflammatory and anti-osteoclastic, but this is difficult to reconcile with the early clinical inflammation observed around these implants. Here, by surveying implant healing in a rat bone model, we determined the cellular responses and structural assembly of bone correlated with the surface changes of Mg implants inherent in degradation. We show that, compared to titanium, both high-purity (99.998 %) and clinical-grade, rare earth-alloyed (MgYREZr) Mg implants create an initial, transient proinflammatory environment that facilitates inducible nitric oxide synthase-mediated macrophage polarization, osteoclastogenesis, and neoangiogenesis programs. While this immunomodulation subsequently reinforces reparative osteogenesis at the surface of both Mg implants, the faster degradation of high-purity Mg implants, but not MgYREZr implants, elicits a compositional alteration in the interfacial bone and a previously unknown proadipogenic response with persistent low-grade inflammation in the surrounding bone marrow. Beyond the need for rigorous tailoring of Mg implants, these data highlight the need to closely monitor osseointegration not only at the immediate implant surface but also in the peri-implant bone and adjacent bone marrow.

Semi-quantitative elemental imaging of corrosion products from bioabsorbable Mg vascular implants in vivo

While metal materials historically have served as permanent implants and were designed to avoid degradation, next generation bioabsorbable metals for medical devices such as vascular stents are under development, which would elute metal ions and corrosion byproducts into tissues. The fate of these eluted products and their local distribution in vascular tissue largely under studied. In this study, we employ a high spatial resolution spectrometric imaging modality, laser ablation inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-TOF-MS) to map the metal distribution, (herein refered to as laser ablation mapping, or LAM) from Mg alloys within the mouse vascular system and approximate their local concentrations. We used a novel rare earth element bearing Mg alloy (WE22) wire implanted within the abdominal aorta of transgenic hypercholesterolemic mice (APOE-/-) to simulate a bioabsorbable vascular prosthesis for up to 30 days. We describe qualitatively and semi-quantitatively implant-derived corrosion product presence throughout the tissue cross sections, and their approximate concentrations within the various vessel structures. Additionally, we report the spatial changes of corrosion products, which we postulate are mediated by phagocytic inflammatory cells such as macrophages (MΦ's).

In situ phosphorus-modified Mg2Ge/Zn-Cu composite with improved mechanical, degradation, biotribological properties, and in vitro and in vivo osteogenesis and osteointegration performance for biodegradable bone-implant applications

Zinc (Zn)-based composites are promising biodegradable bone-implant materials because of their good biocompatibility, processability, and biodegradability. Nevertheless, the low interfacial bonding strength, coordinated deformation capacity, and mechanical strength of current Zn-based composites hinder their clinical application. In this study, we developed a biodegradable in situ 4Mg2Ge/Zn-0.3Cu-0.05P composite (denoted ZMGCP) via phosphorus (P) modification and hot-rolling for bone-implant applications. The mechanical properties, corrosion behavior, biotribological performance, in vitro cytocompatibility and osteogenic differentiation, and in vivo osteogenesis and osteointegration of the as-cast (AC) and hot-rolled (HR) ZMGCP samples were systematically evaluated and compared to those of 4Mg2Ge/Zn-0.3Cu (denoted ZMGC). The primary and eutectic reinforcement Mg2Ge phases formed during solidification were refined after P modification and hot-rolling. The HR ZMGCP exhibited the best tensile properties among all the samples with an ultimate tensile strength of 288.9 MPa, a yield strength of 194.5 MPa, and an elongation of 17.7 %. The HR ZMGCP showed the lowest corrosion rate of 336 μm/a, 186 μm/a, and 61.7 μm/a as measured by potentiodynamic polarization, electrochemical impedance spectroscopy, and immersion testing, respectively, among all the samples in Hanks' solution. The HR ZMGCP also showed higher biotribological resistance than its ZMGC counterpart. The HR ZMGCP exhibited the highest in vitro cytocompatibility, the best osteogenesis capability and angiogenesis property among the HR samples of pure Zn, ZMGC, and ZMGCP. Furthermore, the HR ZMGCP displayed complete in vivo biocompatibility, osteogenesis, osteointegration capability, and an appropriate degradation rate, showing significant potential for a biodegradable bone-implant material.

Study on the Synergistic Effects of Cu and Sr on Biodegradable Zn Alloys

Bone defect repair and postoperative infections are among the most challenging issues faced by orthopedic surgeons. Thus, the antibacterial agent Cu and the osteogenic promoter Sr have been widely incorporated into biodegradable alloys separately. However, to the best of our knowledge, the synergistic effects of Cu and Sr on zinc alloys have not been investigated. Therefore, we have developed a series of novel Zn-4Cu-xSr (x = 0.05, 0.1, and 0.3 wt %) alloys. Our results showed that the addition of Cu and Sr significantly increased the strength of pure zinc while maintaining a certain level of ductility. Plastic deformation further enhanced the strength and ductility of the alloys. The tensile strength of HR Zn-4Cu-xSr alloys remains between 233.34 ± 1.31 MPa and 235.81 ± 3.0 MPa, with elongation values ranging from 45.7 ± 1.56% to 49.6 ± 6.22%. The HE Zn-4Cu-0.05Sr alloy exhibits a high elongation of 95.05 ± 11.1%. Furthermore, the HE Zn-4Cu-0.1Sr alloy demonstrates the best overall mechanical performance with ultimate tensile strength (σuts), yield strength (σys), and elongation (ε) values of 252.73 ± 0.12 MPa, 181.0 ± 0.79 MPa, and 42.8 ± 1.13%, respectively. The corrosion rate of HE Zn-4Cu-xSr alloys increases with an increase in Sr content. All samples exhibit satisfactory cytocompatibility with the cells displaying a healthy spindle-like morphology. In vitro antibacterial tests show that the HE Zn-4Cu-xSr alloys exhibit significant antibacterial effects against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), with the antibacterial properties strengthening as the Sr content increases. Therefore, this study demonstrates the tremendous potential application of Zn-4Cu-xSr alloys in biodegradable zinc alloys for bone fracture fixation and repair.

Inflammatory response toward a Mg-based metallic biomaterial implanted in a rat femur fracture model

The immune system plays an important role in fracture healing, by modulating the pro-inflammatory and anti-inflammatory responses occurring instantly upon injury. An imbalance in these responses can lead to adverse outcomes, such as non-union of fractures. Implants are used to support and stabilize complex fractures. Biodegradable metallic implants offer the potential to avoid a second surgery for implant removal, unlike non-degradable implants. However, considering our dynamic immune system it is important to conduct in-depth studies on the immune response to these implants in living systems. In this study, we investigated the immune response to Mg and Mg-10Gd in vivo in a rat femur fracture model with external fixation. In vivo imaging using liposomal formulations was used to monitor the fluorescence-related inflammation over time. We combine ex vivo methods with our in vivo study to evaluate and understand the systemic and local effects of the implants on the immune response. We observed no significant local or systemic effects in the Mg-10Gd implanted group compared to the SHAM and Mg implanted groups over time. Our findings suggest that Mg-10Gd is a more compatible implant material than Mg, with no adverse effects observed in the early phase of fracture healing during our 4-week study. STATEMENT OF SIGNIFICANCE: Degradable metallic implants in form of Mg and Mg-10Gd intramedullary pins were assessed in a rat femur fracture model, alongside a non-implanted SHAM group with special respect to the potential to induce an inflammatory response. This pre-clinical study combines innovative non-invasive in vivo imaging techniques associated with multimodal, ex vivo cellular and molecular analytics. The study contributes to the development and evaluation of degradable biometals and their clinical application potential. The study results indicate that Mg-10Gd did not exhibit any significant harmful effects compared to the SHAM and Mg groups.

A biodegradable Zn-5Gd alloy with biomechanical compatibility, cytocompatibility, antibacterial ability, and in vitro and in vivo osteogenesis for orthopedic applications

Zinc (Zn) and some of its alloys are recognized as promising biodegradable implant materials due to their acceptable biocompatibility, facile processability, and moderate degradation rate. Nevertheless, the limited mechanical properties and stability of as-cast Zn alloys hinder their clinical application. In this work, hot-rolled (HR) and hot-extruded (HE) Zn-5 wt.% gadolinium (Zn-5Gd) samples were prepared by casting and respectively combining with hot rolling and hot extrusion for bone-implant applications. Their microstructure evolution, mechanical properties, corrosion behavior, cytotoxicity, antibacterial ability, and in vitro and in vivo osteogenesis were systematically evaluated. The HR and HE Zn-5Gd exhibited significantly improved mechanical properties compared with those of their pure Zn counterparts and the HR Zn-5Gd showed a unique combination of tensile properties with an ultimate tensile strength of ∼311.6 MPa, yield strength of ∼236.5 MPa, and elongation of ∼40.6%, all of which are greater than the mechanical properties required for bone-implant materials. The HR and HE Zn-5Gd showed higher corrosion resistance than their pure Zn counterpart in Hanks' solution and the HE Zn-5Gd had the lowest corrosion rate of 155 µm/y measured by electrochemical corrosion and degradation rate of 26.9 µm/y measured by immersion testing. The HR and HE Zn-5Gd showed high cytocompatibility toward MC3T3-E1 and MG-63 cells, high antibacterial effects against S. aureus, and better in vitro osteogenic activity than their pure Zn counterparts. Furthermore, the HE Zn-5Gd exhibited better in vivo biocompatibility, osteogenesis, and osteointegration ability than pure Zn and pure Ti. STATEMENT OF SIGNIFICANCE: This work reports the mechanical properties, corrosion behaviors, cytocompatibility, antibacterial ability, in vitro and in vivo osteogenesis of biodegradable Zn-Gd alloy for bone-implant applications. Our findings demonstrate that the hot-rolled (HR) Zn-5Gd showed a unique combination of tensile properties with an ultimate tensile strength of ∼311.6 MPa, yield strength of ∼236.5 MPa, and elongation of ∼40.6%. The HR and HE Zn-5Gd showed higher corrosion resistance than their pure Zn counterpart in Hanks' solution. The HR and HE Zn-5Gd showed high cytocompatibility toward MC3T3-E1 and MG-63 cells, good antibacterial effects against S. aureus, and better in vitro osteogenic activity. Furthermore, the HE Zn-5Gd exhibited better in vivo biocompatibility, osteogenesis, and osteointegration ability than pure Zn and pure Ti.

Multiscale morphological analysis of bone microarchitecture around Mg-10Gd implants

The utilization of biodegradable magnesium (Mg)-based implants for restoration of bone function following trauma represents a transformative approach in orthopaedic application. One such alloy, magnesium-10 weight percent gadolinium (Mg-10Gd), has been specifically developed to address the rapid degradation of Mg while enhancing its mechanical properties to promote bone healing. Previous studies have demonstrated that Mg-10Gd exhibits favorable osseointegration; however, it exhibits distinct ultrastructural adaptation in comparison to conventional implants like titanium (Ti). A crucial aspect that remains unexplored is the impact of Mg-10Gd degradation on the bone microarchitecture. To address this, we employed hierarchical three-dimensional imaging using synchrotron radiation in conjunction with image-based finite element modelling. By using the methods outlined, the vascular porosity, lacunar porosity and the lacunar-canaliculi network (LCN) morphology of bone around Mg-10Gd in comparison to Ti in a rat model from 4 weeks to 20 weeks post-implantation was investigated. Our investigation revealed that within our observation period, the degradation of Mg-10Gd implants was associated with significantly lower (p < 0.05) lacunar density in the surrounding bone, compared to Ti. Remarkably, the LCN morphology and the fluid flow analysis did not significantly differ for both implant types. In summary, a more pronounced lower lacunae distribution rather than their morphological changes was detected in the surrounding bone upon the degradation of Mg-10Gd implants. This implies potential disparities in bone remodelling rates when compared to Ti implants. Our findings shed light on the intricate relationship between Mg-10Gd degradation and bone microarchitecture, contributing to a deeper understanding of the implications for successful osseointegration.

Property Variation of Extruded Mg-Gd Alloys by Mn Addition and Processing

This paper presents how the mechanical properties, the microstructure and the degradation rate of extruded Mn-containing Mg-Gd alloys can be modified during extrusion. Gd as a rare earth element is particularly interesting due to the influence on the texture development in Mg, and is therefore studied as a base alloy system. The contents of Gd were investigated between 2 to 9 wt.%, with Mn additions of 0.5 and 1.0 wt.%. The grain sizes and the corresponding textures were modified by varying the extrusion parameters and the alloy content. It was shown that modification with Mn can lead to further grain refinement, an increase in the degree of recrystallization, as well as a decrease in the degradation rate in the biological medium compared with the binary Mg-Gd system from previous studies. The results suggest that the resulting properties are more robust compared with the binary alloy.