published_or_final_version / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

Thesis (MScIng)--University of Stellenbosch, 2007. / Bibliography. Also available via the Internet.

Thesis (Ph. D.)--Drexel University, 2004. / Includes abstract and vita. Includes bibliographical references (leaves 168-182).

Introduction: Intervertebral disc (IVD) degeneration is suggested to begin from the nucleus pulposus (NP). Evidence from various studies highlights mesenchymal stem cells (MSC), in most cases using bone marrow derived MSC, as a potential stem cell source for NP regeneration. However MSC can be isolated from many sources with various characteristics. There are indications that fetal or close to fetal tissue sources contain MSC with relatively undifferentiated phenotype with respect to MSC from adult sources. Moreover, umbilical cord (C)-MSC may have better chondrogenic differentiation potential than bone marrow (B)-MSC. We hypothesize CMSC are different from BMSC, and more efficient than BMSC in stimulating NP regeneration. Methods: MSC were isolated from human bone marrow and umbilical cord with corresponding ethical approval. BMSC and CMSC were characterized for cell surface marker expression profile and differentiation potential.. RT-PCR of interest genes in NP cells isolated from scoliosis and degenerate discs was performed to search for NP degeneration indicators. Conditioned media (CM) was collected from confluent MSC monolayer, and used for stimulation of four batches of degenerated NP cells isolated from human degenerative intervertebral discs. Cell proliferation and cytotoxicity were assessed by MTT assay. Proteoglycan content were measured by DMMB assay. Gene expression of a series of degeneration related molecules including ACAN, SOX9, CDH2, CD55, KRT19, KRT18, FBLN1 and MGP, and fibrosis related molecules, including MMP12, HSP47, COL1A1, COL3A1 and FN1, of NP cells in MSC-CM were determined by real- time RT-PCR. All results were normalized to the control cells in basal medium. The expression of discogenic, chondrogenic and osteogenic markers on BMSC and CMSC were compared by RT-PCR. Results and Conclusion: CMSC were similar to BMSC and fulfilled the minimum criteria of MSC, however the expression of CD146, CD106 and Stro-1 was different, and BMSC had a spontaneous osteogenesis tendency while CMSC expressed chondrogenic marker even without TGF-beta stimulation. BMSC demonstrated a paracrine effect on modulating human degenerated NP cells towards a non-degenerative phenotype in stimulating cell proliferation, slightly enhancing proteoglycan production, upregulating KRT19 while downregulating MMP12. Compared with BMSC, a higher paracrine effect of CMSC was disclosed in modulating the phenotype of NP cells in all aspects tested, and an intrinsic higher expression on CMSC of ‘potential NP markers’, including KRT19, KRT18 and CD55, but lower expression of osteogenic markers, including RUNX2 and ALPL, was revealed, which indicate a higher potential of CMSC for future clinical application to treat IVD degeneration diseases. KRT19 and MMP12 were also confirmed to be the highest differentially expressed candidate genes between cultured scoliosis and degenerated human NP cells, indicating a high indicator potential of NP degeneration. Furthermore, a subpopulation was detected in the degenerated NP cells that possessed macrophage-like phenotype and activities, which may play a role in the pathogenesis of IVD degeneration. In conclusion, studies in this thesis highlighted CMSC as a superior source than BMSC for IVD repair. Further investigations into the active agents in the conditioned media and the signalling pathway may help to elucidate the mechanism of the effect. / published_or_final_version / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

Intervertebral disc tissue engineering is challenging because it involves the integration of multiple tissues with distinct structures and compositions such as lamellar annulus fibrosus, gel?like nucleus pulposus and cartilage endplate. Each of them has different compositions and different structures. It is hypothesized that integration of tissues can be enhanced with appropriate mechanical and biological stimuli. Meanwhile, effect of torsional stimulus on cell re?orientation in mesenchymal stem cell?collagen tubular constructs is investigated in this study. Furthermore, it is proposed that these findings can be used to fabricate a multicomponent unit for intervertebral disc tissue engineering. It has been demonstrated that mechanical and biological stimuli can stabilize the interface between osteogenic and chondrogenic differentiated constructs with enhanced ultimate tensile stress while the phenotype of osteogenic and chondrogenic differentiated constructs were maintained. Scanning electronic microscopic images have shown aligned collagen fibrils and presence of calcium at the interface, indicating the possibility of the formation of a calcified zone. In addition, it is proven that torsional stimulus triggered re?orientation of mesenchymal stem cells in collagen lamellae towards a preferred angle. Cell alignments were confirmed by using a MatLab?based program to analyze the actin filament and the cell alignment via Phalloidin and Hematoxylin staining, respectively. Cells and actin filaments were inclined around 30o from the vertical axis, while cells and filaments in the control group (static loading) aligned along the vertical axis. Furthermore, a double?layers bioengineered unit was fabricated, with intact osteogenic differentiated parts at both ends. Comparatively higher cell density was observed at the interface between layers, demonstrating the interactions between layers, while the phenotype of each part was maintained in 14 days culture. This study concludes that a multi?components bioengineered unit with preferred cell alignments can be fabricated. This provides new insights to future development of bioengineered spinal motion segment for treating late stage disc degeneration. / published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

No description available.

Thesis (Ph. D.)--Drexel University, 2006. / Includes abstract and vita. Includes bibliographical references (leaves 170-193).

Thesis (M.Eng.). / Written for the Dept. of Biomedical Engineering. Title from title page of PDF (viewed 2008/07/29). Includes bibliographical references.

Novel surgical strategies for spinal disc repair are currently being developed that require materials that (1) possess the appropriate mechanical properties to mimic the tissue the material is replacing or repairing and (2) maintain their mechanical function for long durations without negatively affecting the tissue response of adjacent tissue (i.e. bone). Polymers formed through photopolymerization have emerged as candidate biomaterials for many biomedical applications, but these materials possess limited toughness in vivo due to the presence of water inherent in most tissues. Therefore, the overall objective of this research was to develop photopolymerizable (meth)acrylate networks that are both mechanically and biologically compatible under physiological conditions to be implemented in spinal repair procedures. The fundamental approach was to determine structure-property relationships between toughness and network structure in the presence of phosphate buffered saline (PBS) using several model copolymer networks in order to facilitate the design of photopolymerizable networks that are tough in physiological solution. It was demonstrated that networks toughness could be optimized in PBS by tailoring the Tg of the copolymer network close to body temperature and incorporating the appropriate "tough" chemical structures. The ability to maintain toughness up to 9 months in PBS was dependent upon the viscoelastic state and overall hydrophobicity of the network. In tandem, the effect of network chemistry and stiffness on the response of MG63 pre-osteoblast cells was assessed in vitro. The ability of MG63 cells to differentiate on (meth)acrylate network surfaces was found to be primarily dependent on surface chemistry with PEG-based materials promoting a more mature osteoblast phenotype than 2HEMA surfaces. Amongst each copolymer group, copolymer stiffness was found to regulate osteoblast differentiation in a manner dependent upon the surface chemistry. In general, photopolymerizable (meth)acrylate networks that were deemed "tough" were able to promote osteoblast differentiation in a manner comparable if not exceeding that on tissue culture polystyrene (TCPS). This research will impact the field of biomaterials by elucidating the interrelationships between materials science, mechanics, and biology.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Neck pain is a common phenomenon that occurs in a large percentage of the population every day. While many occurrences are not deemed critical such as those from muscle strain which can be treated with rest and pain medication, others due to sports injuries, whiplash from car accidents, bad posture or degeneration of the intervertebral disc can be quite severe. In extreme cases failure of the vertebra(e) or the intervertebral disc requires surgery and possibly the use of cervical implants. Where intervertebral discs fail due to herniation or Degenerative Disc Disease (DDD), Anterior Cervical Discectomy and Fusion (ACDF) is a common surgical method used to remove the a ected disc and replace it with a cervical cage implant. These implants are designed to restore the height between the vertebrae, allowing bone from both vertebrae to grow through them and mineralise. Additive Manufacturing (AM) technologies can produce parts with complex geometries not possible using conventional manufacturing methods. This design freedom, coupled with CT scans of a patient, allow for tailoring an implant to the speci c anatomy of the a ected vertebrae using CAD software. Such an approach must be regulated and shown to be technically and commercially feasible before it can be implemented in industry. This study sought to develop a framework for manufacturing customized cervical cage implants using additive manufacturing. The e cacy of customization to reduce the risk of subsidence was investigated by means of non-destructive and destructive mechanical testing on six cadaver specimens, using readily available PEEK cage implants as a benchmark. The results showed that the customized implant was comparable to the PEEK, with no statistically signi cant di erence between the two. In extreme cases, where PEEK implants cannot be used, customized implants could be a suitable alternative to reduce the risk of subsidence. A manufacturing cost analysis was conducted to determine economic feasibility. The estimated cost and selling price of the customized implants under various utilization scenarios and mark-ups was compared to readily available PEEK implants. The estimated selling prices of the customized implants compared favourably to the PEEK verifying the economic viability of using AM. / AFRIKAANSE OPSOMMING: Nek pyn is 'n algemene verskynsel wat daagliks na tevore kom in die bevolking. Baie gevalle word nie as krities geklasi seer nie soos byvoorbeeld spier pyn wat behandel kan word deur genoegsame rus en pyn medikasie. Pyn wat deur sportbeserings, sweepslag beserings 'whiplash' tydens motor ongelukke, verkeerde postuur, of deur slytasie van 'n intervertebrale skyf veroorsaak is, word dikwels as ernstig geklasi seer. In ekstreme gevalle waar die werwel(s) of die inervertebrale skyf(we) faal, sal chirurgie en servikale inplantate moontlik nodig wees. Waneer intervertebrale skywe faal weens herniatie of Degeneratiewe Skyf Siekte (DDD) kan 'n algemene chirurgiese metode, Anterieure Servikale Discectomie en Fusie (ACDF), gebruik word om die gea ekteerde skyf te verwyder en dit te vervang met 'n servikale samesmelting implantaat. Hierdie implantate herstel die hoogte tussen rugwerwels en is ontwerp sodat die been deur dit kan groei en mineraliseer. Komplekse geometrieë kan vervaardig word deur toevoegingsvervaardiging (AM) tegnologieë. Die ontwerp vryheid, gepaard met CT-skanderings en CAD-sagteware stel mens in staat om die geometrie van die implantaat aan te pas tot die spese eke anatomie van die gea ekteerde vertebra. So 'n benadering moet gereguleer word en eers tegnies en kommersieel uitvoerbaar bewys word voordat dit in die bedryf geïmplementeer kan word. Hierdie studie poog verder om 'n raamwerk vir die vervaardiging van persoonlike servikale implantate deur middel van toevoegingsvervaardiging te ontwikkel. Die doeltre endheid van persoonlike implantate om te verhoed dat die chirurg die eind-plaat beskadig, en sodoende die risiko van insakking te verminder, is ondersoek deur middel van meganiese toetse op ses kadawer monsters. Hierdie toetse is gedoen met behulp van geredelik beskikbaar PEEK servikale implantate as 'n maatstaf. Die resultate het getoon dat die persoonlike- en PEEK implantate vergelykbaar is. In moontlike gevalle waar PEEK implantate nie geskik sou wees nie, kan persoonlike implantate 'n alternatiewe opsie wees om die risiko van insakking te verminder.