Early Stage Researcher (PhD Year 1) Post-Doctoral Researcher/Senior Researcher/PI

Entry for the Engineers Ireland Biomedical Research Medal

Corresponding author has completed PhD and would like to review BinI abstract submissions

Please place an X in any appropriate categories

INTRODUCTION

Magnesium (Mg) alloys offer significant benefits for the fabrication of resorbable orthopaedic implants [1]. In addition to exhibiting suitable mechanical properties, Mg alloys are bioresorbable meaning, once implanted, Mg alloy devices will not require a second surgery for their subsequent removal. The key to creating a resorbable bone fixation Mg implant is the control of the alloy’s corrosion rate [2]. The application of a barrier coating, such as hydroxyapatite (HA), which has the added benefit of bioactivity, can potentially tailor implant resorption. The coating acts as a barrier layer whilst its osteoinductive nature will expedite the bone’s natural recovery process. The work reported here investigates the coating of Mg alloys with HA via radio frequency (RF) magnetron sputtering. Once applied the physico-mechanical properties of the coatings were characterised. Thereafter the degradation properties of both coated and uncoated substrates were studied, in relevant simulated physiological media. U2OS osteosarcoma cells were used to determine biocompatibility of coating and substrate.

MATERIALS AND METHODS

Commercial Mg alloy AZ31 (Goodfellow) was abraded using silicon carbide (SiC) papers beginning at p240 grade increasing to p1200 grade. The HA coating was applied using RF magnetron sputtering (150W, 10hrs, 3.3W/cm2, 0.00003Pa). The target used was pressed using commercial HA, (Plasma Biotal, UK) via a well-established methodology [3]. Characterisation of the produced samples included the use of Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX), Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS), micro Computed Tomography (µCT) and gravimetric analysis. Cell studies were conducted using the U2OS osteosarcoma cell line via an indirect method, determining viability through the use of Pico Green, DAPI and SEM analysis. Degradation studies were conducted using uncoated and HA coated AZ31 samples exposed to simulated body fluid over a period of 14 days.

RESULTS & DISCUSSION

ToF-SIMS results show coatings of ~70 nanometer (nm) and ~210 (nm) were achieved on the surface of the mg substrate. SEM images highlight the dense, coherent and homogenous coating produced via the RF magnetron sputtering method. In vitro results indicate

the hydroxyapatite coating offered significant degradation improvement, decreasing corrosion rate significantly from ~1.75 millimetres per year (mmpy) for uncoated AZ31 to ~1.55mmpy and ~1.00mmpy for 70nm and 210nm coatings respectively. Double lap shear mechanical testing has shown an increase in load required for coating failure due to increasing coating thickness. There is a decrease in load required for coating failure with higher polished substrate surfaces, owing to a lower surface roughness. Initial indirect cell studies have shown that HA coated samples exhibit a cell number increase at early stages of proliferation compared with pure AZ31. This study demonstrates the potential for a HA thin film coating to be used in the development of bioresorbable Mg implants to tailor

corrosion and improve bioactivity.Figure 1 a) SEM images of U2OS cells fixed to borosilicate glass cover slips at days 2, 5, & 7, using indirect method, of both pure AZ31 substrate and HA coated substrate b) µCT images of pure AZ31 substrate, 70nm and 210nm HA coated AZ31 post 14 day degradation study c) Load required for coating failure at 70hr and 100hr coating thickness at varying substrate roughness (p240, p800, p1200).REFERENCES

1. Gu XN et al. Acta Biomater. 8, 2360-74, 20122. Liu X et al. Applied Surface Science, 434, 1101–

1111, 2018

Bioengineering in Ireland26, January 17-18, 2020

CONTROL OF MAGNESIUM ALLOY CORROSION VIA BIOCOMPATIBLE THIN FILMS FOR RESORBABLE IMPLANT APPLICATIONS

Mckillop, S.1, Acheson, J.G.1 , Lemoine, P.1, Boyd, A.R.1, Meenan, B.J.1

1 Engineering Research Institute, School of Engineering, Ulster University, Northern Ireland, United Kingdom

Mckillop-s@ulster.ac.uk

c)

a)

b)

Early Stage Researcher (PhD Year 1) Post-Doctoral Researcher/Senior Researcher/PI

Entry for the Engineers Ireland Biomedical Research Medal

Corresponding author has completed PhD and would like to review BinI abstract submissions

Please place an X in any appropriate categories3. Boyd A. et al. Surf & Coatings Technol. 233, 131-

139 2013

Bioengineering in Ireland26, January 17-18, 2020