Modification of polymer surfaces to aid the attachment of cells derived from bone.

Polymeric materials such as polystyrene (PS) and ultra high molecular weight polyethylene (PE) have bulk properties which are attractive for biomaterials applications such as orthopaedic implants. However, both PS and PE have low surface energy, and it is well established that high-energy surfaces are more effective in promoting rapid cellular adhesion and spreading, whereas low energy surfaces do not. The overall response of a biological system to an implanted biomaterial is predominantly governed by surface state i.e. chemistry, energy, micro- and nano-structure. Hence, controlling surface properties is an integral area of biomaterials research. This thesis examines the use of UV/ozone oxidation treatment to improve the biological response to PS and PE by the addition of polar oxygen groups, thereby increasing their surface energy without affecting the bulk properties. The UV/ozone treatment is shown to give a controllable increase of surface oxygen as a function of treatment time up to 31 atomic % for PS and 26 atomic % for PE, which leads to an overall increase in the polar surface energy. The oxygen functional groups incorporated by the surface treatment were identified by XPS to be a combination of ether/alcohol (C-OR), carbonyl (C=O) and carboxylic acid/ester (O-C=O). The effect of the UV/ozone treatment was found by AFM not to alter the surface topography, and the depth of the surface treatment was determined in a previous study to be less than 10nm. The level of UV/ozone treatment was optimised on polystyrene (PS) by examining cell attachment and proliferation of human osteosarcoma (HOS) cells as a function of surface treatment time to determine the effect of surface chemistry on the cells. This led to optimised UV/ozone treatment times of 45sec, 90sec and 180sec which correspond to surface oxygen levels of 12, 22 and 26 atomic % on PS. As a result of the manufacturing process, commercially pure PE already contained 10 atomic % oxygen, regular striations on a micron scale and granular formations on the sub-micron scale. For this material treatment times of 150sec and 600sec led to 19 and 26 atomic % oxygen. Human primary osteoblast-like cell (HOB) attachment, extracellular matrix protein expression and mineralisation were examined on PS and PE surfaces with these optimised treatment levels. When compared to tissue culture polystyrene (TCPS) the optimised PS and PE surfaces were found to have improved cell adhesion by approximately 50%. The extracellular matrix production of fibronectin, collagen type I and osteopontin were determined by Western Blotting. Most significantly osteopontin was found to be considerably higher on the 12% PS surface substrates and the 19 and 26 % PE substrates. Characteristic levels of alkaline phosphatase (ALP) activity were produced on the modified surfaces over the 21 day experiments. Consequently higher levels of mineralisation were confirmed on the 12% surface oxygen PS and 19% surface oxygen PE substrates by alizarin red S staining. The optimised levels of UV/ozone surface modification of both PS and PE surfaces led to significantly improved cell attachment, differentiation along the osteoblast lineage, mineralisation and initial stages of de novo bone formation compared to TCPS. The findings throughout this study show that the UV/ozone treatment can be applied to different thermoplastic polymers, as a means of enhancing cellular attachment and function without detrimental effect to the properties of the materials, and increased the attachment and functionality of human primary osteoblast-like cells.

Author dc:creator

• Poulsson, Alexandra Herborg Cornelius

Advisor dc:contributor.advisor

• B. Bradley, N. Emmison and A. Johnstone

• UV/ozone surface modification
• Biomaterials surface engineering
• Polystyrene and polyethylene
• Surface energy and chemistry
• Osteoblast cell response
• Polymer implants

Language dc:language

en

Identifier

oai:rgu-repository.worktribe.com:2807535
https://doi.org/10.48526/rgu-wt-2807535

OAI identifier oai:identifier

oai:rgu-repository.worktribe.com:2807535