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Surface patterning for biomedical applications via Template-assisted electrohydrodynamic atomisation

Munir, GM; (2013) Surface patterning for biomedical applications via Template-assisted electrohydrodynamic atomisation. Doctoral thesis , UCL (University College London).

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The osteoconductive and osseointegrative nature of hydroxyapatite (HA) has made it a popular coating material for orthopaedic implants. HA coated metallic prostheses, which combine the osteoconductivity of HA and high strength of metallic alloys, have been increasingly favoured by surgeons for the ageing population. Topography is known to provide a powerful set of signals for cells to improve initial bonding of implant to the body. This project focuses on controlling the chemistry and topography of the implant surface in order to improve the initial attachment of bone cells to the implant surface by the creation of ordered topographical surfaces. Silicon-substitute hydroxyapatite (SiHA) was chosen as the material of choice for patterning due to its enhanced biological responses. Template-assisted electrohydrodynamic atomisation (TAEA) is an electrically driven jet-based deposition technique capable of producing patterns of regular and uniform nature on a substrate, which has been developed using the principles of electrohydrodynamic atomisation. The deposition of nanoSiHA patterns on titanium surface has been optimised by the set up configuration of the electrode and processing parameters, namely, flow rate, applied voltage, distance from substrate. It was found that decreasing the flow rate was able to increase the coverage of the template and reached to 80% of template space. The optimum distance between the needle and substrate was 50 mm, which allowed solvent evaporation to occur and resulted in clear, well-defined structures. The thickness of patterns was increased with spraying time, and the deposition rate was higher on the track patterns in comparison with that of pillar patterns. The template surface finishing also affected the resultant pattern with ridged edging reducing the surface coverage. To further understand how cells interact with surface topography and quantify the response, in vitro studies were carried out on human osteoblasts (HOB), murine osteoblasts (MC3T3-E1) and dental pulp stem (DPS) cells. In vitro cellular studies found that both pillar and track nanoSiHA patterns were able to encourage the attachment and growth of osteoblast cells, providing anchor point for cell attachment. Actin and cell body preferentially aligned parallel to the track pattern, linking the actin orientation to the entire cell placement. HOB cells were found to respond to pattern topography by stretching nearly three times of their original size when the distance between the tracks increased. AlamarBlue™ tests showed the proliferation rates of HOB cells increased when cultured on patterned substrates than those on nanoSiHA coating. An increase of alkaline phosphatase production, an osteoblast differentiation marker, was found on the HOB cells cultured on patterned surfaces, as well as on the pillar and track patterns when the thickness increased from 1 to 5 µm. The expression of ALPL, a gene involved in mineralisation, was higher for the HOB cells cultured on pillar patterns. Runx-2 expression and collagen production of HOB cells was also increased on track patterns when compared to pillar patterned and nanoSiHA coated Ti. In order to understand the influence of pattern topography on the mechanics of the cell, shear force modulation force microscopy was used to determine the elasticity of osteoblasts (MC3T3-E1) cell and dental pulp stem cell (DPS). This study found that increasing the thickness of the pattern, in both track and pillar, lead to an increased modulus of the MC3T3-E1 cells. MC3T3-E1 cells were found to have significantly higher moduli than DPS cells, regardless of location on the substrate or thickness of the pattern. Therefore, the study has provided an insight for future design of implant surfaces to control and guide cellular responses, while TAEA patterning provides a controllable technique to provide topography to medical implants.

Type: Thesis (Doctoral)
Title: Surface patterning for biomedical applications via Template-assisted electrohydrodynamic atomisation
Language: English
Additional information: Permission for digitisation not received.
Keywords: surface patterning, template-assisted electrohydrodynamic atomisation
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Mechanical Engineering
URI: https://discovery.ucl.ac.uk/id/eprint/1404375
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