(484k) Chemically & Electrochemically Interactive Characterization of Biomaterials in vitro

The ever growing demand for advanced and high performance implantable biomedical materials entails development of better interactive in vitro characterization tools to obtain a more representative prediction of their performance in vivo. Herein cases of implantable biomaterials, for temporary bone scaffolding support and coronary stents applications have been discussed.

Temporary implants pose a great challenge where the implant is expected to degrade and dissolve after a period of time at which point it is either absorbed by the body or excreted in the urine. The two specific medical applications are the temporary scaffolding for bone fixation and the coronary stents application. This is to prevent the long term complications associated with presence of a foreign material in the body, for example inflammatory reactions, thrombosis and restenosis in stent applications associated with the permanent stainless steel stents. Research in this area has revolved around magnesium in the past decade as it is safely metabolized by human body upon degradation and yet possesses adequate mechanical and load-bearing properties to support a healing bone as a scaffold or an artery from elastic recoil after balloon angioplasty. The main shortcoming however is the rapid degradation of magnesium in physiological environment that causes premature failure of the implant. In a series of studies [1–7] magnesium alloys were designed and fabricated, the underlying degradation mechanism in simulated biological environment was unraveled and surface treatments were applied to fine-tune degradation rate and biocompatibility. Scanning electrochemical microscopy was extensively used as a uniquely interactive characterization technique to examine degradation of magnesium at high spatial resolution in-situ. A new bio-sensing method was introduced for detection of H2 which enabled detection of localized degradation. Localized degradation is one of the main reasons for the premature failure of load-bearing structures. The new insight into the degradation mechanism allowed for an informed exploration of surface treatments to fine-tune degradation rate of magnesium in a physiological environment. In particular, ionic liquid surface treatment, conversion coatings based on rare earth metal and a biodegradable conducting polymer coating were investigated in order to suppress the initial rapid degradation, alkalization and H2 evolution while in the longer term creating a self-healing surface film capable of maintaining uniform degradation pattern. Results of these works introduced candidates with optimized bio-degradation rate that would minimize the risk of early stage alkalization and inflammatory reaction for the surrounding tissue as well as minimizing risk of premature failure to ensure adequate mechanical support is provided during the healing (of the bone) or remodeling (of the artery).

In the field of biomaterials sciences, although there are standards developed to examine the performance of materials in certain in vitro environments, there is still major need for a testing procedure with holistic approach to take into account most environmental parameters, e.g. load and cycles, ions/electrolyte, proteins, cell adhesion, mobility, temperature etc. Currently the in vitro test can be considered only as a preliminary screening test with limited ability to give the realistic picture, and a holistic simulation procedure has to be developed to measure performance in the biological condition. For example a hip and knee simulators with the tribological test properties of the materials together with full consideration of the corrosivity in the cell culture environment and other interacting elements. It is only with a holistic approach and using a multi-array of sensors that the full impact of an implant material on the host can be determined. Surface modifications are often performed on the biomedical implants to improve corrosion resistance, wear resistance, surface texture and biocompatibility. The interactions that take place at the atomic level between the surface of the implant, the host and the biological environment including all types of micromotions of the implants similar to what is expected in the human system should be studied thoroughly in order to advance implant materials with predictable function in the body.

References

[1] S.S. Jamali, S.E. Moulton, D.E. Tallman, M. Forsyth, J. Weber, G.G. Wallace, Applications of scanning electrochemical microscopy (SECM) for local characterization of AZ31 surface during corrosion in a buffered media, Corros. Sci. 86 (2014) 93–100.
[2] S.S. Jamali, S.E. Moulton, D.E. Tallman, M. Forsyth, J. Weber, G.G. Wallace, Evaluating the corrosion behaviour of Magnesium alloy in simulated biological fluid by using SECM to detect hydrogen evolution, Electrochim. Acta. 152 (2015) 294–301.
[3] S.S. Jamali, S.E. Moulton, D.E. Tallman, M. Forsyth, J. Weber, A.S. Mirabedini, et al., Corrosion protection afforded by praseodymium conversion film on Mg alloy AZNd in simulated biological fluid studied by scanning electrochemical microscopy, J. Electroanal. Chem. 739 (2015) 211–217.
[4] Y. Zhang, X. Liu, S.S. Jamali, B.R.W. Hinton, S.E. Moulton, G.G. Wallace, et al., The effect of treatment time on the ionic liquid surface film formation: Promising surface coating for Mg alloy AZ31, Surf. Coatings Technol. 296 (2016) 192–202.
[5] S.S. Jamali, S.E. Moulton, D.E. Tallman, Y. Zhao, J. Weber, G.G. Wallace, Self-healing characteristic of praseodymium conversion coating on AZNd Mg alloy studied by scanning electrochemical microscopy, Electrochem. Commun. 76 (2017) 6–9.
[6] D. Liu, G. Xu, S.S. Jamali, Y. Zhao, M. Chen, Fabrication of biodegradable HA/Mg-Zn-Ca composites and the impact of heterogeneous microstructure on mechanical properties, in vitro degradation and cytocompatibility, Bioelectrochemistry. 129 (2019) 106–115.
[7] S.S. Jamali, S.E. Moulton, Y. Zhao, S. Gambhir, M. Forsyth, G. Gordon, A biodegradable conducting polymer coating to mitigate early stage degradation of magnesium in simulated biological fluid : an electrochemical mechanistic study, ChemElectroChem. 6 (2019) 4893–4901.