Poly(l-lactic acid) (PLLA)/MgSO₄·7H₂O Composite Coating on Magnesium Substrates for Corrosion Protection and Cytocompatibility Promotion

Abstract

Magnesium (Mg) and its alloys show excellent potential as orthopedic implantable materials, with their in vivo degraded Mg ions (Mg 2+ ) known to promote the growth of new bone. However, the swift corrosion process during implantation has greatly hindered its clinical applications. A method to counter the high rate of corrosion is to coat Mg substrates on surfaces with a thin layer of biodegradable polymer. Although such a coating reduces the long-term corrosion rate, it also prevents the shortterm release of bone-simulating Mg 2+ after orthopedic operations. To balance these contradicting short-and long-term characteristics, we present a polymer−inorganic composite coating on pure Mg substrates that enables Mg-based implants to achieve controllable release of Mg 2+ and high corrosion resistance simultaneously. The coatings were fabricated by adding an appropriate amount of inorganic magnesium sulfate heptahydrate (MgSO 4 •7H 2 O) salt particles into a biodegradable poly(L-lactic acid) (PLLA) polymer matrix, such that they can percolate inside to form an interconnected morphology during the phase separation between Mg salt and PLLA polymers as solvent evaporates during the drying process, resulting in the formation of an organic−inorganic composite coating. The in vitro corrosion tests indicated that the composite coatings with lower Mg salt loading had the best degradation behavior, resulting in controllable release of Mg 2+ and alkaline shift. Cytocompatibility of bare and coated Mg were investigated via MC3T3-E1 preosteoblasts through MTT assay and LIVE/DEAD imaging, along with the observation of cell distribution and adhesion behaviors. The results further demonstrated that the incorporation of a suitable amount of Mg salt particles could further improve the cytocompatibility as compared to the pristine PLLA coating. We believe such fabricated organic−inorganic composite coatings could have great potential for application on Mg substrates to obtain Mg-based biomaterials with higher practical value in clinical treatments. KEYWORDS: PLLA/MgSO 4 •7H 2 O composite coating, biodegradable pure magnesium, controllable Mg 2+ release, high corrosion resistance, orthopedic implants

Anticancer Activity of Samarium-Coated Magnesium Implants for Immunocompromised Patients

“…To restore the bone functions, the various biodegradable implant materials such as bioglass, hydroxyapatite, and so forth are utilized as prosthesis. Among them, magnesium was suggested as one of the suitable materials for bone augmentation and distraction osteotomy as it possesses better mechanical properties than polymers and superior biocompatibility than titanium. , Magnesium is vital for bones and dental health. The absence of Mg in the enamel on the teeth leads to dissolution in the acidic condition .…”

Polymer coatings on magnesium‐based implants for orthopedic applications

“…The hybrid coating with suitable amount of GO‐AgNPs simultaneously showed favorable biocompatibility, indicating its practical value in orthopedic implantation. Considering the great suppression of the initial release of Mg 2+ , which plays a vital role in the new bone formation, after the implementation of a anticorrosive barrier layer on Mg substrates will retard the bone fracture healing process, some researchers tried to add some Mg‐based compounds into the surface coating to increase the concentration level of Mg 2+ within the surrounding environment by the diffusion and dissolution of such loaded reagents 96,97 . We have proposed a PLLA/MgSO 4 ⋅7H 2 O composite coating system to solve the referred problem 96 .…”

“…Considering the great suppression of the initial release of Mg 2+ , which plays a vital role in the new bone formation, after the implementation of a anticorrosive barrier layer on Mg substrates will retard the bone fracture healing process, some researchers tried to add some Mg‐based compounds into the surface coating to increase the concentration level of Mg 2+ within the surrounding environment by the diffusion and dissolution of such loaded reagents 96,97 . We have proposed a PLLA/MgSO 4 ⋅7H 2 O composite coating system to solve the referred problem 96 . The embedded water‐soluble MgSO 4 ⋅7H 2 O particles can easily diffuse out and dissociate to generate Mg 2+ when contact with aqueous solution, so the quick release of Mg 2+ at early stage was achieved without deteriorating the corrosion resistance.…”

“…The cell culture plate was the blank control. (Reproduced from the study by Zhu et al 96 with the permission from American Chemical Society)…”

A Comprehensive Review on Surface Modifications of Biodegradable Magnesium-Based Implant Alloy: Polymer Coatings Opportunities and Challenges

“…Alaei et al [95] also revealed that CS-BG nanocomposite coatings had great adhesion to the Mg substrate and the ability to form apatite after 7 days in SBF. Zhu et al [113] showed that PLLA/magnesium sulfate heptahydrate (MgSO 4 •7H 2 O) composite-coated samples could enhance cell adhesion and proliferation and act as a productive barrier on the surface of pure Mg substrate. Jin et al [111] prepared a composite coating consisting of FHA and PLA that was fabricated on MAO-Mg alloy.…”