Magnesium (Mg) and its alloys have been intensively explored as the next generation of metallic bone substitutes in past decades, but their rapid corrosion rate in physiological environments is still a great hindrance for further therapeutic applications. In the present study, we attempt to design biodegradable poly(L-lactic acid) (PLLA) coatings on pure Mg substrates (99.99 wt %) with tunable surface morphologies through dip-coating in combination with mixed nonsolvent induced phase separation (Dip-coating-mNIPS) method to regulate their corrosion behavior and biocompatibility. We applied the mixtures of ethanol and hexane as the coagulation baths, and changed the composition of mixed nonsolvent and the concentration of polymer solution to obtain PLLA coatings with different pore sizes and morphologies. Standard electrochemical measurements and immersion tests demonstrated that all PLLA coatings could effectively enhance the corrosion resistance of Mg substrates but that the corrosion behaviors varied among coatings with different surface and inner structures. A systematic investigation of cellular response through MTT assay, LIVE/DEAD staining, cell distribution, and cell attachment indicated that PLLA-coated Mg substrates could enhance cytocompatibility in comparison to pure Mg. In addition, the cellular behaviors were affected by the corrosion activity as well as the surface properties of different PLLA coatings. Our findings illustrated that through the Dip-coating-mNIPS method, the structure of the PLLA membrane on Mg substrates could easily be controlled to regulate the corrosion behaviors and further improve the biocompatibility. This presents great potential in designing functional polymer coatings on Mg-based orthopedic implants to meet specific clinical requirements.

Although numerous studies have been conducted to describe the gelation of multi-arm star polymers, reports on the relationship among rheological quantities, overlap concentration (c*), and microstructures have still remained insufficient. Here, we examine the sol–gel dynamics of hydrogels formed by 4-arm poly­(ethylene glycol) (PEG) near c* based on dynamic scaling theory. We investigated the evolution of viscoelastic modulus (storage modulus G′ and loss modulus G″) with reduced gelation time (τ) and the normalized extent of crosslinking (ϵ), and a divergent dependence was observed near c*. A general expression of the Hill equation was employed to evaluate the complex modulus spectra and critical relaxation exponent (Δ) at the gel point (i.e., G′ ∼ G″ ∼ ωΔ), providing a way to access such a critical exponent, regardless of how fast the gelation occurs. Besides, the dynamic scaling exponent with ϵ shows high sensitivity to the pre-gel clusters and post-gel networks. Moreover, two-dimensional time–frequency viscoelastic mapping indicates that the hydrogel formed at c* shows higher homogeneity than those away from c*, and inhomogeneity of the local cluster density would contribute to the large-scale fluctuation in rheological quantities during gelation.

Nowadays, the need for bio‐implants, which can gradually degrade after fulfilling the therapeutic tasks is continuously increasing. Under such situation, magnesium (Mg) and its alloys have been proposed and intensively studied as the new‐generation medical implants due to their favorable biodegradability and biocompatibility. However, their swift corrosion in physiological environments can always cause an early fracture and further the surgical failure, greatly hindering their broad applications. Therefore, great efforts have been made to alter the degradation behaviors of Mg‐based implants. Biodegradable polymeric surface coatings have been revealed to be a straightforward and effective strategy for retarding the fast degradation and improving the bioactivity of Mg and its alloys. This article reviews the recent progress of polymer‐based coatings on Mg substrates, regarding the coating strategies, coating properties, and their performance in corrosive protection and biocompatibility promotion via in vitro as well as some in vivo models. The specific pros and cons of different polymeric coatings are also discussed. Finally, we put forward some perspectives on the future direction of polymeric coatings on biomedical Mg‐based implants to better adapt to clinical trials.

Introduction Magnesium (Mg) has a prophylactic potential against the onset of hyperlipidemia. Similar to statin, Mg is recommended as lipid-lowering medication for hypercholesterolemia and concomitantly exhibits an association with increased bone mass. The combination of statin with Mg ions (Mg 2+ ) may be able to alleviate the high-fat diet (HFD)-induced bone loss and reduce the side-effects of statin. This study aimed to explore the feasibility of combined Mg 2+ with simvastatin (SIM) for treating HFD-induced bone loss in mice and the involving mechanisms. Materials and methods C57BL/6 male mice were fed with a HFD or a normal-fat diet (NFD). Mice were intraperitoneally injected SIM and/or orally received water with additional Mg 2+ until sacrificed. Enzyme-linked immunosorbent assay was performed to measure cytokines and cholesterol in serum and liver lysates. Bone mineral density (BMD) and microarchitecture were assessed by micro-computed tomography (μCT) in different groups. The adipogenesis in palmitate pre-treated HepG2 cells was performed under various treatments. Results μCT analysis showed that the trabecular bone mass was significantly lower in the HFD-fed group than that in NFD-fed group since week 8. The cortical thickness in HFD-fed group had a significant decrease at week 24, as compared with NFD-fed group. The combination of Mg 2+ and SIM significantly attenuated the trabecular bone loss in HFD-fed mice via arresting the osteoclast formation and bone resorption. Besides, such combination also reduced the hepatocytic synthesis of cholesterol and inhibited matrix metallopeptidase 13 ( Mmp13 ) mRNA expression in pre-osteoclasts. Conclusions The combination of Mg 2+ and SIM shows a synergistic effect on attenuating the HFD-induced bone loss. Our current formulation may be a cost-effective alternative treatment to be indicated for obesity-related bone loss.

No abstract