Poly(l-lactic acid) (PLLA) Coatings with Controllable Hierarchical Porous Structures on Magnesium Substrate: An Evaluation of Corrosion Behavior and Cytocompatibility

Abstract

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.

Polymer coatings on magnesium‐based implants for orthopedic applications

“…Considering the tendency of coating crack and detachment caused by the collection of hydrogen gas (H 2 ) under the coating layer as well as the restrained release of Mg 2+ , dense coatings seem not to be an ideal choice for long‐term protection. Alternatively, porous coatings are capable of dredging the degradation products (H 2 , Mg 2+ ) through their inner interconnected channels, and rough surfaces are reported to be more favorable for cell adhesion in comparison with smooth ones, thus intensive studies have been shifted to construct functional porous PLA coatings on Mg and its alloys 48–52 . Phase separation techniques, 53–56 including thermally induced phase separation (TIPS) and nonsolvent induced phase separation (NIPS), are the predominant methods to prepare polymer membranes; by modulating the phase separation parameters, various porous structures can be generated.…”

“…The PLLA‐coating has then been successfully incorporated in a Mg‐titanium (Mg‐Ti) hybrid system by Tian et al 57 for rabbit long bone fracture fixation, demonstrating high healing efficacy, in which the PLLA coating effectively prevented the electrochemical corrosion from occurring at the contacting area of Mg and Ti. (Figure 6IF) Further, Zhu et al 49 applied a mixed nonsolvent system consisting of hexane (nonpolar) and ethanol (polar) to control the porosity of PLLA coatings on pure Mg rods, through which the corrosion behaviors of Mg could be easily regulated. The biological tests demonstrated the significantly promoted cytocompatibility with preosteoblasts after coated with PLLA.…”

“…( B ) Release curves of mg ions of uncoated mg and different PLLA‐coated Mg during immersion test in D. Hanks solution. (Reproduced from the study by Zhu et al 49 with the permission from American Chemical Society)…”

Study of Titanium–Silver Monolayer and Multilayer Films for Protective Applications in Biomedical Devices

“…In particular, titanium has been widely used in prostheses due to its harmlessness, low reactivity and good osseointegration (structural and functional connection between living bone and an implant surface) [ 2 , 3 ]. However, its high cost has led to the use of materials such as metallic alloys [ 4 ], ceramics [ 5 ], and polymers [ 6 ] that can be affected by the characteristics of the medium in which the implants are made by presenting microbial incompatibilities [ 7 ] and changes due to corrosion [ 8 ]. The search for coatings that extend an implant’s useful life has become necessary and indispensable, and it has set a trend in materials studies [ 9 ].…”

Facile Preparation of a Fluorine‐Free, Robust, Superhydrophobic Coating through Dip Coating Combined with Non‐Solvent Induced Phase Separation (Dip‐Coating‐NIPS) Method

“…We found that by changing the composition of the coagulation bath (non‐solvents) in NIPS, PLLA film structures, varying from dense to porous, could be easily regulated. [ 39,40 ] On the basis of these results, we first applied our previously developed dip‐coating‐NIPS method [ 39 ] to fabricate superhydrophobic coatings using bio‐based PLLA and hydrophobic SiO 2 nanoparticles in one step. During NIPS, SiO 2 nanoparticles could percolate inside the PLLA polymer matrix, generating hierarchical surface roughness, which induced superhydrophobicity.…”