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Synthesis and 3D printing of hydroxyapatite scaffolds for applications in bone tissue engineering
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Cox, Sophie C. (2013) Synthesis and 3D printing of hydroxyapatite scaffolds for applications in bone tissue engineering. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b2721434~S1
Abstract
It is known that chemical and physical features of bone contribute to its functionality,
reactivity and mechanical performance. This knowledge is the fundamental rationale
for this project. The aim of this thesis is to study the influence of synthesis conditions
on material composition and ultimately the biological performance of hydroxyapatite
(HA) as well as to fabricate scaffold structures that physically emulate bone tissue.
Concurrent characterisation of physiochemical properties and evaluations of in-vitro
cytocompatibility, and the degree of osteoblast proliferation on CDHA substrates
precipitated under different reaction conditions provides a novel contribution.
Non-viability of cells seeded on substrates prepared in a solution adjusted to pH 10
(AP07) was confirmed after 1 day of culture. Dead cells were also observed after 3
days on CDHA prepared at 70°C under a controlled pH level of 11 (AP12). XRD
found no discernible difference between these samples and CDHA substrates shown to
be cytocompatible. The source of cytotoxicity was concluded to be the presence acidic
DCPD in AP07, and positive surface charges for AP07 and AP12 that were revealed
by FTIR, DTA-TGA and ZP measurements. Control of pH, increased solute
concentration, the use of Toluene, and substitutions of 10mol% Mg or 2mol% Zn were
shown to enhance the proliferative rate of cells seeded on CDHA synthesised at RT.
CDHA prepared in a 60 Toluene: 40 DI water (% v/v) solvent system with a lower
dielectric constant (AP14) exhibited marked XRD peak broadening and 20% larger
surface area compared with CDHA prepared in DI water (AP09). These features are
suggested to explain the enhanced proliferation of cells on AP14, which was shown to
be more than double the fluorescence exhibited for AP09 after 7 days. XRF was used
to confirm the presence of Sr, Mg, and Zn that were selected due to their key
biological roles in bone apatite. Evidence of lattice incorporation of these divalent
cations was supported by XRD analysis that demonstrated shifts of characteristic HA
peaks. Mg ions inhibited the crystallisation process, which caused a 45% reduction in
the crystallite size, 60% increase in particle surface area and thermal conversion to
whitlockite at 600°C. The relatively low crystallinity and larger surface area of Mg
and Zn doped substrates is proposed to explain the respective 80 and 40% increase in
cell proliferation compared to a pure sample prepared under the same conditions.
Flowability of HA:PVOH precursor materials correlated well with the mechanical
stability, microstructure and porosity of 3D printed scaffolds. Anisotropic behaviour of
constructs and part failure at the boundaries of interlayer bonds was highlighted by
compressive strength testing. A trade-off between the ability to facilitate removal of
PVOH thermal degradation products during sintering and the compressive strength of
green parts was revealed. The maximum green scaffold strength of 0.85MPa was
exhibited by parts that were air or vacuum dried for 6hrs. Critically, the pores of 3D
printed constructs could be user designed ensuring interconnectivity and the imperfect
packing efficiency of precursor powders created an inherent surface roughness and
microporosity within scaffold struts. These features are known to be favourable for
osteogenesis, osteoconduction and osteointegration in-vivo.
This work establishes that changes to precipitation conditions cannot be deemed trivial
since they may alter material composition, which ultimately determines
cytocompatibility as well as the proliferative rate of cells. Due to the highly complex
structure of bone there are understandably a number of on-going medical challenges
and while the application of 3D printed HA bone tissue scaffolds is promising, the
name apatite derived from the Greek ‘απαταο’, meaning to deceive is concluded to be
very fitting.
Item Type: | Thesis (PhD) | ||||
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Subjects: | R Medicine > RC Internal medicine T Technology > TS Manufactures |
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Library of Congress Subject Headings (LCSH): | Bone regeneration, Tissue engineering, Bone-grafting, Three-dimensional printing, Bone -- Mechanical properties | ||||
Official Date: | September 2013 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Warwick Manufacturing Group | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Mallick, Kajal | ||||
Extent: | xxiv, 281 leaves : illustrations, charts. | ||||
Language: | eng |
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