Dissolution control of Mg by cellulose acetate-polyelectrolyte membranes

Polymeric Coatings for Magnesium Alloys for Biodegradable Implant Application: A Review

Magnesium (Mg) alloys are a very attractive material of construction for biodegradable temporary implants. However, Mg alloys suffer unacceptably rapid corrosion rates in aqueous environments, including physiological fluid, that may cause premature mechanical failure of the implant. This necessitates a biodegradable surface barrier coating that should delay the corrosion of the implant until the fractured/damaged bone has healed. This review takes a brief account of the merits and demerits of various existing coating methodologies for the mitigation of Mg alloy corrosion. Since among the different coating approaches investigated, no single coating recipe seems to address the degradation control and functionality entirely, this review argues the need for polymer-based and biodegradable composite coatings.

Effect of Filler Types on Cellulose-Acetate-Based Composite Used as Coatings for Biodegradable Magnesium Implants for Trauma

Magnesium alloys are considered one of the most promising materials for biodegradable trauma implants because they promote bone healing and exhibit adequate mechanical strength during their biodegradation in relation to the bone healing process. Surface modification of biodegradable magnesium alloys is an important research field that is analyzed in many publications as the biodegradation due to the corrosion process and the interface with human tissue is improved. The aim of the current preliminary study is to develop a polymeric-based composite coating on biodegradable magnesium alloys by the solvent evaporation method to reduce the biodegradation rate much more than in the case of simple polymeric coatings by involving some bioactive filler in the form of particles consisting of hydroxyapatite and magnesium. Various techniques such as SEM coupled with EDS, FTIR, and RAMAN spectroscopy, and contact angle were used for the structural and morphological characterization of the coatings. In addition, thermogravimetric analysis (TGA) was used to study the effect of filler particles on polymer thermostability. In vitro cytotoxicity assays were performed on MG-63 cells (human osteosarcomas). The experimental analysis highlights the positive effect of magnesium and hydroxyapatite particles as filler for cellulose acetate when they are used alone from biocompatibility and surface analysis points of view, and it is not recommended to use both types of particles (hydroxyapatite and magnesium) as hybrid filling. In future studies focused on implantation testing, we will use only CA-based composite coatings with one filler on magnesium alloys because these composite coatings have shown better results from the in vitro testing point of view for future potential orthopedic biodegradable implants for trauma.

Vapor deposition of polyionic nanocoatings for reduction of microglia adhesion

Polyionics have great potential in improving the performance of neural probes by regulating microglial response. With the shrinkage of microelectrode size and increase in device complexity, challenges arise during liquid-based synthesis of polyionic compounds on neural probes. Nanocoatings of polyionics, with highly crosslinked bulk structure and abundant ionic functional groups on the surface, were synthesized using a process combining chemical vapor deposition and free radical polymerization. Both conformal surface engineering of neural microelectrodes and facile tailoring of surface ionic composition was achieved using this single-step vapor-based method. Adhesion of microglia was reduced on all the polyionic modified surfaces after a seven-day in vitro test, and polyionics with mixed charges presented much lower microglial adhesion than surfaces with single charges. Laminin adsorption on polyionics with mixed charges was significantly reduced due to the surface electrical neutrality and the enhanced wettability. These findings provide valuable information towards the development of neural probes with enhanced biocompatibility and signal stability.

Controlled "golf ball shape" structuring of Mg surface under acoustic cavitation

This manuscript describes the original structuring of Mg materials under ultrasound irradiation in mild conditions. Golf ball like extended structures can be prepared in dilute oxalic solutions at 20°C under high frequency ultrasound (200kHz). An original approach carried out through iterative 3D reconstruction of sonicated surfaces is used to describe surface evolutions and characterize the formed microstructures. A combination of SEM, ICP-AES, contact-angle measurements, and 3D image analyses allows to characterize the roughness and mass loss evolutions, and investigate the mechanism of formation for such architectures. A screening of the sonication experiments clearly points out an ultrasound frequency dependency for the effects generated at the surface. 200kHz sonication in 0.01M oxalic acid provides an unprecedented manufacturing of Mg samples which result from a controlled and localized dissolution of the material and characterized by a strong wetting surface with a roughness of 170nm. The additional formation of newly formed secondary phases appearing with surface dissolution progress is also deciphered. More generally, the ultrasonic procedure used to prepare these engineered surfaces opens new alternatives for the nano- and micro-structuring of metallic materials which may exhibit advanced physical and chemical properties of potential interest for a large community.

Characterization and In Vitro and In Vivo Assessment of a Novel Cellulose Acetate-Coated Mg-Based Alloy for Orthopedic Applications

Despite their good biocompatibility and adequate mechanical behavior, the main limitation of Mg alloys might be their high degradation rates in a physiological environment. In this study, a novel Mg-based alloy exhibiting an elastic modulus E = 42 GPa, Mg-1Ca-0.2Mn-0.6Zr, was synthesized and thermo-mechanically processed. In order to improve its performance as a temporary bone implant, a coating based on cellulose acetate (CA) was realized by using the dipping method. The formation of the polymer coating was demonstrated by FT-IR, XPS, SEM and corrosion behavior comparative analyses of both uncoated and CA-coated alloys. The potentiodynamic polarization test revealed that the CA coating significantly improved the corrosion resistance of the Mg alloy. Using a series of in vitro and in vivo experiments, the biocompatibility of both groups of biomaterials was assessed. In vitro experiments demonstrated that the media containing their extracts showed good cytocompatibility on MC3T3-E1 pre-osteoblasts in terms of cell adhesion and spreading, viability, proliferation and osteogenic differentiation. In vivo studies conducted in rats revealed that the intramedullary coated implant for fixation of femur fracture was more efficient in inducing bone regeneration than the uncoated one. In this manner, the present study suggests that the CA-coated Mg-based alloy holds promise for orthopedic aplications.

Tackling Mg alloy corrosion by natural polymer coatings-A review

The field of protective coatings for magnesium and its alloys (e.g., AZ31) using natural polymers is reviewed. Polymers utilized are broadly divided into polysaccharides and proteins. For both polymer classes examples are given focusing on coating processing and characterization. Several analysing methods reported in literature are summarized highlighting the different characterization approaches applied in different studies, which makes difficult a direct comparison of the outcomes. In most cases, the protective behavior of coatings was determined using electrochemical impedance spectroscopy or by assessing hydrogen evolution in different fluids. Mechanical tests and in vitro cell culture studies have been also carried out on selected coating systems. Overall, the results show the possibility of applying protective coatings based on natural polymers on magnesium and its alloys, however, in vivo investigations are scarce so that long-term results in relevant conditions are not yet available. A comparison with the use of synthetic polymers is presented and current challenges and areas for future research are discussed, highlighting the need for further investigations in the field, which should enable broadening the applications of Mg and Mg alloys in medicine. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2628-2641, 2016.