Magnesium (Mg) and its alloys have attracted increasing attention in recent years as medical implants for repairing musculoskeletal injuries because of their promising mechanical and biological properties. However, rapid degradation of Mg and its alloys in physiological fluids limited their clinical translation because the accumulation of hydrogen (H₂) gas and fast release of OH^- ions could adversely affect the healing process. Moreover, infection is a major concern for internally implanted devices because it could lead to biofilm formation, prevent host cell attachment on the implants, and interfere osseointegration, resulting in implant failure or other complications. Fabricating nanostructured magnesium oxide (MgO) on magnesium (Mg) substrates is promising in addressing both problems because it could slow down the degradation process and improve the antimicrobial activity. In this study, nanostructured MgO layers were created on Mg substrates using two different surface treatment techniques, i.e., anodization and electrophoretic deposition (EPD), and cultured with Staphylococcus aureus in vitro to determine their antimicrobial properties. At the end of the 24-h bacterial culture, the nanostructured MgO layers on Mg prepared by anodization or EPD both showed significant bactericidal effect against S. aureus. Thus, nanostructured MgO layers on Mg are promising for reducing implant-related infections and complications and should be further explored for clinical translation toward antimicrobial biodegradable implants.

Magnesium-zinc-calcium (Mg-Zn-Ca) alloys have attracted increasing attention for biomedical implant applications, especially for bone repair, because of their biocompatibility, biodegradability, and similar mechanical properties to human bone. The objectives of this study were to characterize Mg-2 wt % Zn-0.5 wt % Ca (named ZC21) alloy pins microstructurally and mechanically, and determine their degradation and interactions with host cells and pathogenic bacteria in vitro and in vivo in comparison with the previously studied Mg-4 wt % Zn-1 wt % strontium (named ZSr41) alloy and Mg control. Specifically, the in vitro degradation and cytocompatibility of ZC21 pins with bone marrow derived mesenchymal stem cells (BMSCs) were investigated using both direct culture and direct exposure culture methods. The adhesion density of BMSCs on ZC21 pins (i.e., direct contact) was significantly higher than on pure Mg pins in both in vitro culture methods; the cell adhesion density around ZC21 pins (i.e., indirect contact) was similar to the cell-only positive control in both in vitro culture methods. Interestingly, ZC21 showed a higher daily degradation rate, crack width and crack area ratio in the direct exposure culture than in the direct culture, suggesting different culture methods did affect its in vitro degradation behaviors. When cultured with Gram-positive bacteria methicillin-resistant Staphylococcus aureus (MRSA), ZC21 reduced bacterial adhesion on the surface more significantly than that of ZSr41 and Mg. The in vivo degradation and biocompatibility of the ZC21 pins for bone regeneration were studied in a mouse femoral defect model. The in vivo degradation rate of ZC21 pins was much slower than that of ZSr41 alloy and Mg control pins. After 12 weeks of implantation in vivo, the ZC21 group showed the shortest gap at the femoral defect, indicating that ZC21 pins promoted osteogenesis and bone healing more than ZSr41 and Mg control pins. Overall, the ZC21 alloy is promising for bone repair, while providing antibacterial activities, and should be further studied toward clinical translation.

Introduction

Congenital diaphragmatic hernia (CDH) repair is an area of active research. Large defects requiring patches have a hernia recurrence rate of up to 50%. We designed a biodegradable polyurethane (PU)-based elastic patch that matches the mechanical properties of native diaphragm muscle. We compared the PU patch to a non-biodegradable Gore-Tex™ (polytetrafluoroethylene) patch.

Methods

The biodegradable polyurethane was synthesized from polycaprolactone, hexadiisocyanate and putrescine, and then processed into fibrous PU patches by electrospinning. Rats underwent 4 mm diaphragmatic hernia (DH) creation via laparotomy followed by immediate repair with Gore-Tex™ (n = 6) or PU (n = 6) patches. Six rats underwent sham laparotomy without DH creation/repair. Diaphragm function was evaluated by fluoroscopy at 1 and 4 weeks. At 4 weeks, animals underwent gross inspection for recurrence and histologic evaluation for inflammatory reaction to the patch materials.

Results

There were no hernia recurrences in either cohort. Gore-Tex™ had limited diaphragm rise compared to sham at 4 weeks (1.3 mm vs 2.9 mm, p = 0.003), but no difference was found between PU and sham (1.7 mm vs 2.9 mm, p = 0.09). There were no differences between PU and Gore-Tex™ at any time point. Both patches formed an inflammatory capsule, with similar thicknesses between cohorts on the abdominal (Gore-Tex™ 0.07 mm vs. PU 0.13 mm, p = 0.39) and thoracic (Gore-Tex™ 0.3 mm vs. PU 0.6 mm, p = 0.09) sides.

Conclusion

The biodegradable PU patch allowed for similar diaphragmatic excursion compared to control animals. There were similar inflammatory responses to both patches. Further work is needed to evaluate long-term functional outcomes and further optimize the properties of the novel PU patch in vitro and in vivo.

Level of evidence

Level II, Prospective Comparative Study.