Turdean-Ionescu, Claudia Adriana (2010) Multinuclear solid state NMR of novel bioactive glass and nanocomposite tissue scaffolds. PhD thesis, University of Warwick.

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Abstract

Sol-gel derived bioactive glasses are promising candidates for bone regeneration,
where bone is a natural nanocomposite of collagen (organic polymer) and hydroxyapatite
(inorganic mineral) with a complex hierarchical structure and excellent mechanical
properties. Solid-state NMR is a sensitive probe and offers atomic-level information on the
structure of sol-gel derived bioactive glasses. In this thesis, a multinuclear solid state NMR
approach, as part of an extensive study, has been applied to a key range of sol-gel derived
materials related to novel nanocomposites to act as tissue scaffolds.
The nanostructure evolution of sol-gel derived bioactive glasses 70S30C (70 mol%
SiO2 and 30 mol% CaO) was characterised by 29Si, 1H and 13C CP MAS NMR. Calcium was
found to be incorporated into the silica network during the stabilisation stage and to
increases its disorder. The inhomogeneity found within 70S30C bioactive glass monoliths
showed that the calcium concentration was higher in the outer region of the monolith caused
by the way calcium only enters into the structure after breakbown of the nitrate.
Trimethylsilylation reaction mechanisms used to tailor the nanoporosity of sol-gel derived
70S30C bioactive glass was also studied. The 29Si NMR results showed that the modification
processes affected the atomic scale structure of the glass, such as Qn structure and network
connectivity. 1H and 13C NMR was used to follow the loss of hydroxyls and organic
groups directly.
The study was extended to 58S (60 mol% SiO2, 36 mol% CaO, 4 mol% P2O5)
systems and compared for two synthesis routes: inorganic and alkoxide. Via the inorganic
route high temperatures were needed for calcium incorporation, while via alkoxide route
calcium was found to be incorporated at low temperatures. Reactive surface Ca ions were
involved in the formation of different types of carbonates for the two routes. The addition of
P2O5 to the silica-calcium oxide system results in a scavenging of calcium ions by phosphate
groups to give orthophosphate and pyrophosphate units.
Solid-state NMR of new organic-inorganic hybrid scaffolds, class II, in the silicagelatin
and silica-calcium oxide-poly(γ-glutamic acid) (γ-PGA) systems indicates that 3-
glycidoxypropyltrimethoxysilane (GPTMS) provides a covalent link between the organic
and inorganic networks and increased the inorganic condensation. 1H-1H intra- and
intermolecular proximities have been identified using 1H DQ (double-quantum) CRAMPS
(combined rotation and multiple pulse spectroscopy) techniques. 13C NMR results indicate
that an efficient promotion of epoxide ring opening of GPTMS was reached by either gelatin
or γ-PGA. 43Ca NMR identified different calcium environments in the hybrid systems.
The last part of this thesis is focused on the comparison studies in the mechanism of
apatite growth on both melt-derived (Bioglass®) and sol-gel derived (TheraGlass®) bioactive
glass surfaces. By using a combination of 1H, 13C, 31P, 29Si and 23Na, using one and two
dimensional NMR spectroscopy, the inhibitive effects of serum proteins in the mechanism of
the apatite growth was revealed. The solid-state NMR experimental data support the
hydroxycarbonate apatite formation mechanism proposed by Hench. Apatite formation takes
place from the largely amorphous phosphate ions initially deposited on the glass surface.
Serum proteins adsorbed on the glass surface have been found to significantly inhibit the
apatite formation. Multiple sodium sites have been identified in Bioglass® composition with
the formation of a more ordered local structure on increasing immersion time.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QC Physics R Medicine > R Medicine (General)
Library of Congress Subject Headings (LCSH):	Glass-ceramics, Biomedical materials, Tissue scaffolds, Nuclear magnetic resonance
Official Date:	October 2010
Dates:	Date Event October 2010 Submitted
Institution:	University of Warwick
Theses Department:	Department of Physics
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Smith, Mark E. ; Hanna, John V.
Sponsors:	University of Warwick ; Engineering and Physical Sciences Research Council (EPSRC)
Extent:	xv, 212 leaves : ill., charts
Language:	eng

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