Development of mechanobiomimetic strategies to drive stem cell behaviour for bone regeneration
Citation:
EICHHOLZ, KIAN, Development of mechanobiomimetic strategies to drive stem cell behaviour for bone regeneration, Trinity College Dublin.School of Engineering, 2019Download Item:
Thesis Kian Eichholz 29_04_2019.pdf (PhD Thesis, examined and approved) 10.19Mb
Abstract:
There are a host of cases where clinical intervention must be taken to treat diseased
or damaged bone, including severe fractures, defects, tumours requiring tissue removal, and
debilitating diseases such as osteoporosis. However, there are no current treatments which
adequately achieve this goal, with current autografting approaches having severe limitations
in terms of quantity of tissue available and additional surgical sites which damage healthy
tissue and increase infection risk. There is thus a need to develop new strategies for bone
regeneration. Understanding the mechanisms behind bone regeneration, and in particular,
the key role of the mesenchymal stem cell (MSC) in this process, would provide invaluable
information for the development of strategies to effectively regenerate bone in a
physiologically appropriate manner.
The overall aim of this thesis was to investigate the biophysical cues within the
stem cell niche in bone which drive the recruitment and osteogenesis of MSCs, with the
aim of developing strategies to recapitulate this behaviour and guide bone repair. The two
primary means by which MSC behaviour is mediated were investigated in this thesis:
indirect biophysical cues from osteocytes (stream 1 – chapter 3), and direct biophysical
cues from the underlying fibrous tissue (stream 2 – chapter 4-6), which were subsequently
combined to create a mechano-biomimetic scaffold for bone regeneration (chapter 7).
In this thesis, the indirect biophysical cues from osteocyte signalling to MSCs were
first investigated (chapter 3), where osteocytes were shown to release distinct mechanically
activated osteocyte-derived extracellular vesicles (MAEVs) which contained unique cargo
compared to extracellular vesicles (EVs) from statically cultured cells. These MAEVs
significantly enhanced MSC recruitment and osteogenesis, with trends being almost
identical to MSCs treated with conditioned medium from mechanically stimulated
osteocytes. This confirmed that EVs are a key component in osteocyte-MSC mechanosignaling, and reveals their potential alone for use as mechanotherapeutics to guide regeneration.
Next, the role of direct biophysical cues in mediating MSC behaviour was investigated. To facilitate this, a melt electrowriting (MEW) printer was designed and built (chapter 4) to facilitate the fabrication of defined fibrous microenvironments upon which to study MSC behaviour. Various architectures with 10 μm fibre diameter were fabricated, where it was demonstrated that a 90° architecture enhanced MSC spreading and Yesassociated protein (YAP) nuclear expression, a marker for osteogenesis (chapter 5). Long term culture of MSCs further revealed enhanced osteogenic differentiation in this scaffold architecture.
The role of mineral modifications in driving MSC osteogenesis was further investigated (chapter 6). A biomimetic nano-needle hydroxyapatite (nnHA) coating was developed, characterised and compared to other mineral modification methods, including a commonly used coating method which yields a micro-plate hydroxyapatite (pHA) morphology, and a composite polycaprolactone-hydroxyapatite material to fabricate fibres with incorporated mineral. The nnHA coating significantly enhanced MSC mineralisation compared to all other groups and was also shown to facilitate a more controlled release of BMP2, demonstrating its potential for use in applications requiring controlled drug release.
Finally, stream 1 and 2 were combined, with MAEVs being used for the functionalisation of nnHA scaffolds (chapter 7). The addition of MAEVS further significantly enhanced mineralisation almost 2-fold, in addition to a total 24-fold compared to the 90° scaffold developed in chapter 4 and a total of 52-fold compared to random fibrous scaffolds. This biomimetic scaffold which incorporates both direct and indirect biophysical cues inspired by the native stem cell niche in bone thus holds great potential as a more physiologically relevant and effective strategy to guide bone regeneration.
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European Research Council (ERC)
Irish Research Council (IRC)
Science Foundation Ireland (SFI)
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https://tcdlocalportal.tcd.ie/pls/EnterApex/f?p=800:71:0::::P71_USERNAME:EICHHOLKDescription:
APPROVED
Author: EICHHOLZ, KIAN
Advisor:
Hoey, DavidPublisher:
Trinity College Dublin. School of Engineering. Discipline of Mechanical & Manuf. EngType of material:
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