It is still an open challenge to find a biodegradable metallic material exhibiting sufficient mechanical properties and degradation behavior to serve as an arterial stent. In this study, Zn-Mg alloys of 0.002 (Zn-002Mg), 0.005 (Zn-005Mg) and 0.08wt% Mg (Zn-08Mg) content were cast, extruded and drawn to 0.25mm diameter, and evaluated as potential biodegradable stent materials. Structural analysis confirmed formation of MgZn intermetallic in all three alloys with the average grain size decreasing with increasing Mg content. Tensile testing, fractography analysis and micro hardness measurements showed the best integration of strength, ductility and hardness for the Zn-08Mg alloy. Yield strength, tensile strength, and elongation to failure values of >200-300MPa, >300-400MPa, and >30% respectively, were recorded for Zn-08Mg. This metal appears to be the first formulated biodegradable material that satisfies benchmark values desirable for endovascular stenting. Unfortunately, the alloy reveals signs of age hardening and strain rate sensitivity, which need to be addressed before using this metal for stenting. The explants of Zn-08Mg alloy residing in the abdominal aorta of adult male Sprague-Dawley rats for 1.5, 3, 4.5, 6 and 11months demonstrated similar, yet slightly elevated inflammation and neointimal activation for the alloy relative to what was recently reported for pure zinc.

Purpose Medical imaging has the potential to noninvasively diagnose early disease onset and monitor the success of repair therapies. Unfortunately, few reliable imaging biomarkers exist to detect cartilage diseases prior to advanced degeneration in the tissue. Method In this study, we quantified the ability to detect osteoarthritis (OA) severity in human cartilage explants using a multicontrast magnetic resonance imaging (MRI) approach, inclusive of novel displacements under applied loading by MRI (dualMRI), relaxivity measures, and standard MRI. Results dualMRI measures, which characterized the spatial micromechanical environment by 2D finite and Von Mises strains, were strong predictors of histologically-assessed OA severity, both prior to and after controlling for factors e.g. patient, joint region, and morphology. Relaxivity measures, sensitive to local macromolecular weight and composition, including T1ρ, but not T1 or T2, were strong predictors of OA severity. A combined multicontrast approach that exploited spatial variations in tissue biomechanics and extracellular matrix structure yielded the strongest relationships to OA severity. Conclusion Our results indicate that combining multiple MRI-based biomarkers has high potential for the noninvasive measurement of OA severity and the evaluation of potential therapeutic agents used in the treatment of early OA in animal and human trials.

SUMMARY Objective: To noninvasively assay the mechanical and structural characteristics of articular cartilage from patients with osteoarthritis (OA) by magnetic resonance imaging (MRI), and to further relate spatial patterns of MRI-based mechanical strain to joint (depth-wise, regional) locations and disease severity. Methods: Cylindrical osteochondral explants harvested from human tissue obtained during total knee replacement surgery were loaded in unconfined compression and 2D deformation data was acquired at 14.1 T using a displacements under applied loading by MRI (dualMRI) approach. After imaging, samples were histologically assessed for OA severity. Strains were determined by depth, and statistically analyzed for dependence on region in the joint and OA severity. Results: Von Mises, axial, and transverse strains were highly depth-dependent. After accounting for other factors, Von Mises, axial, and shear strains varied significantly by region, with largest strain magnitudes observed in explants harvested from the tibial plateau and anterior condyle near exposed bone. Additionally, in all cases, strains in late-stage OA were significantly greater than either early- or mid-stage OA. Transverse strain in mid-stage OA explants, measured near the articular surface, was significantly higher than early-stage OA explants. Conclusion: dualMRI was demonstrated in human OA tissue to quantify the effects of depth, joint region, and OA severity, on strains resulting from mechanical compression. These data suggest dualMRI may possess a wide range of utility, such as validating computational models of soft tissue deformation, assaying changes in cartilage function over time, and perhaps, once implemented for cartilage imaging in vivo, as a new paradigm for diagnosis of early- to mid-stage OA.

Absorbable implants made of magnesium alloys may revolutionize surgical intervention, and fine magnesium wire will be critical to many applications. Functionally, the wires must have sufficient mechanical properties to withstand implantation and in-service loading, have excellent tissue tolerance, and exhibit an appropriate degradation rate for the application. Alloy chemistry and thermomechanical processing conditions will significantly impact the material's functional performance, but the exact translation of these parameters to implant performance is unclear. With this in mind, fine (127 µm) WE43B magnesium alloy wires in five thermomechanical process (TMP) conditions (90% cold work [CW], and 250, 375, 400, and 450°C heat treatments) were investigated for their effect on mechanical and corrosion behavior. The TMP conditions gave clear metallurgical differences: transverse grain dimensions ranged from 200 nm (CW) to 3 µm (450°C), UTS varied from 324 MPa (450°C) to 608 MPa (250°C), and surgical knotting showed some were suitable (CW, 400°C, 450°C) while others were not (250°C, 350°C). In vitro and in vivo corrosion testing yielded interesting and in some cases conflicting results. After 1 month immersion in cell culture medium, wire corrosion was extensive, and TMP conditions altered the macrocorrosion morphology but not the rate or total release of magnesium ions. After 1 month subdermal implantation in mice, all wires were well tolerated and showed very little corrosion (per µCT and histology), but differences in localized corrosion were detected between conditions. This study indicates that WE43B wires treated at 450°C may be most suitable for surgical knotting procedures. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1987-1997, 2018.

Metallic wires are critical components for various clinical applications, including orthopedic fixation, surgical staples, K-wires, and guide wires. They can also be knitted or woven to fabricate cardiovascular stents and bone scaffolds. [1][2][3] Conventionally, such devices are made by metals such as stainless steel (SS), titanium (Ti) alloys, and cobalt-chromium (CoCr) alloys because of their excellent corrosion resistance and superior mechanical properties compared to local biological tissues. [4] However, the nondegradability of these alloys can require a secondary surgery, and their high stiffness may enable stress shielding. [5,6] In contrast, polylactic acid (PLA), poly(lactide-co-glycolide) (PLGA), and polycaprolactone (PCL) possess biodegradability, which can avoid the need for a second surgery. However, the acidic nature of their corrosion byproducts can lower the local pH of the tissue microenvironment, resulting in elevated inflammatory responses. [7,8] Furthermore, they possess weak mechanical properties, which limit their use in load-bearing applications. [9,10] Magnesium (Mg) and its alloys offer a third type of material that possesses multiple promising properties. First, Mg is an essential element for human metabolism, and it has shown sufficient biocompatibility. [11,12] Second, Mg alloys have elastic moduli (40-45 GPa) and yield strengths (100-600 MPa) closer to those of natural bone (5-23 GPa, 35-283 MPa) than common, inert metallic implants, [13,14] effectively reducing stress concentrations around host tissue as well as stress shielding. [15] More importantly, Mg can degrade in the human body in a safe and controlled manner, thereby reducing the need for second surgeries to remove implants. [14,16,17] Currently, successful clinical trials of Mg-based alloys have been reported for orthopedic applications in Germany, [18] China, [19] and South Korea. [20] Conventional, cold-worked (CW) techniques are considered the most promising methods to fabricate fine Mg wires (diameter <1 mm), given their low cost and efficiency. [21] However, these processes are challenging for magnesium-based materials due to their hexagonal close-packed (HCP) crystal structure that has limited slip systems at room temperature. [22][23][24][25][26][27] In some cases, alloying can increase room-temperature ductility. Fine wires made from an Mg-aluminum (Al) alloy have been widely reported, [28][29][30][31][32][33][34] but accumulations of Al in the body are a concern as they can cause neurological disorders such as Alzheimer's disease and dementia. [35] Other elements, such as zinc (Zn), [36,37] silver (Ag), [38] and calcium (Ca), [39,40] have also been included in Mg alloys. For example, M. Zheng et al. [41] first reported