Additive manufacturing and surface functionalisation of Ti6Al4V components using self-assembled monolayers for biomedical applications

Vaithilingam, Jayasheelan (2015) Additive manufacturing and surface functionalisation of Ti6Al4V components using self-assembled monolayers for biomedical applications. PhD thesis, University of Nottingham.

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The ability to provide mass customised and biocompatible implants is increasingly important to improve the quality of life. Additive manufacturing (AM) techniques have obtained increasing popularity and selective laser melting (SLM), a metal-based AM technique with an ability to build complex and well defined porous structures, has been identified as a route to fabricate customised biomedical implants. Surface modification of an implant with a biomolecule is used to improve its biocompatibility and to reduce post-implant complications. In this thesis, the potential of a novel approach to use self-assembled monolayers to modify SLM fabricated surfaces with therapeutic drugs has been evaluated.

Although there are numerous studies on the material development, process optimisation and mechanical testing of SLM fabricated parts, the surface chemistry of these parts is poorly understood. Initially, the surface chemistry of SLM as-fabricated (SLM-AF), SLM fabricated and mechanically polished (SLM-MP) and forged and mechanically polished (FGD-MP) parts made of Ti6Al4V was determined using an X-ray photoelectron spectrophotometer (XPS). Later the impact of laser power on the surface chemistry of the parts was also studied. A non-homogeneous surface chemistry was observed due to a change in the distribution of the alloying elements titanium, aluminium and vanadium on the surface oxide layer. Surface modification of the SLM fabricated component would be beneficial to obtain a homogenous surface chemistry, especially for biomedical application.

Coating of self-assembled monolayers (SAMs) onto SLM fabricated Ti6Al4V structures was performed to modify their surface chemistry. 16-phosphanohexadecanoic acid monolayers (16-PhDA) were used to modify SLM-AF and SLM-MP surfaces. XPS and static water contact angle measurements confirmed the chemisorption of monolayers on these surfaces. The obtained results confirmed that SAMs were stable on the Ti6Al4V surface for over 28 days before its desorption. It was also witnessed that the stability of monolayers on the rough SLM-AF and smooth SLM-MP surfaces were not significantly different. Later, the 16-PhDA SAM coated Ti6Al4V SLM-MP surface was functionalised with a model drug, Paracetamol. An esterification reaction was performed to functionalise the phosphonic acid monolayers with Paracetamol. Surface characterisation revealed the sucessful attachment of Paracetamol to the SAMs.

Bacterial infections from biomedical implants and surgical devices are reported to be a major problem in orthopaedic, dental and vascular surgery. Hence, to further explore the potential of the proposed method, Ciprofloxacin® a broad spectrum antibiotic was immobilised to the SAMs, previously adsorbed on the SLM-MP Ti6Al4V surfaces. Using the proposed approach, approximately 1.12 µg/cm2 of the drug was coated to the surface. Results showed that Ciprofloxacin® is highly stable under the oxidative conditions used in this study. Under in vitro condition, the drug was observed to release in a sustained manner. Antibacterial susceptibility tests revealed that the immobilised Ciprofloxacin® was therapeutically active upon its release. Thus, a novel methodology to fabricate customised and functionalised implants has been demonstrated for an improved biocompatibility and reduced post-implant complications.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Goodridge, Ruth D.
Hague, Richard J.
Keywords: Additive manufacturing, 3D printing, Self-assembled monolayers, Biomedical implants
Subjects: R Medicine > R Medicine (General) > R855 Medical technology. Biomedical engineering. Electronics
Faculties/Schools: UK Campuses > Faculty of Engineering
Item ID: 28474
Depositing User: Vaithilingam, Jayasheelan
Date Deposited: 03 May 2016 12:19
Last Modified: 15 Dec 2017 14:19

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