published_or_final_version / Medicine / Doctoral / Doctor of Philosophy

Background: Blood clot formation is one of the first events in bone regeneration and osseointegration. The blood clot adheres to dental implants with hydrophilic surfaces more favorably than to those with hydrophobic surfaces. This appears to result in better bone healing and bone fill of defects around dental implants. Objective: To assess the impact of blood clot stabilization at modSLA titanium implants on bone formation in chronic-type defects in a dog model. Material & methods: Ten modSLA implants were installed in 5 dogs after creation of saddle-type buccal-lingual bony defects. In 5 implants (test sites), the blood clot was removed by sterile saline irrigation, while the clot was left undisturbed on the other 5 implants (control sites). After 8 weeks of healing, the animals were sacrificed and sections were prepared for histomorphometric analysis. The following measurements were performed: The residual defect length (DL), the buccal and lingual most coronal level of bone in contact with the implant (CBI-b and CPI-l), the new bone height (NBH), the percentage of bone to implant contact (BIC), the area of new bone fill (BF), the difference in buccal and lingual dimensions of CBI (D-CBI), and percentage of linear bone fill (PLF). Results: the mean values of DL were similar in both groups (3.4 mm). All parameters assessed were consistently more favorable in control sites: CBI-b: 1.3 vs. 1.5, CBI-l: 1.3 vs. 0.8, D-CBI: -0.2 vs -0.5, NBH: 1.9 mm vs. 2.1 mm, PLF: 57.1% vs. 64.5% and BF: 4.4 mm? vs. 6.0 mm?. However, these differences were not statistically significant. Conclusion: In the light of consistently more favorable parameters assessed for the healing of saddle-shaped bony defects around implants, it is assumed that a stabilized blood clot contributed to early bone regeneration and osseointegration. Undisturbed blood clot formation may, indeed, be a prerequisite for optimal treatment outcomes. However, owing to the small sample size in the present study, these tendencies ought to be explored in further studies. / published_or_final_version / Dental Surgery / Master / Master of Dental Surgery

Current treatments to intervertebral disc degeneration alter spine biomechanics and have complications. Tissue engineering offers an approach to regenerate a biological disc that provides flexibility and stability to, and integrates with the spine. To date, a scaffold that mimics the extracellular matrix composition and mechanical strength of a native disc is lacked. In this project, a biphasic scaffold was fabricated using glycosaminoglycan (GAG) and collagen, the prevalent ma-trix components in a native disc. It also adapted the structure of the disc, with la-mellae of collagen surrounding a collagen-GAG (CG) core. The first part of this project studied chemical modification of CG and evaluated the physiochemical and biological properties of modified CGs. As only loosely bound by GAG under physiological environment, collagen was modified by deamination, methylation and amination, and yielded Deaminated, Methylated and Aminated CGs upon co-precipitation with GAG. While GAG was mostly lost within 1 day in Untreated and Deaminated CGs, 20% and 40% GAG was retained after 6 days in Methylated and Aminated CGs respectively. In cell-seeded Aminated CG, over 60% GAG was retained after 8 days. Aminated CG, having the highest GAG/HYP of 4.5, best simulated the GAG-rich nucleus pulposus tissue. In ultrastructural analysis, Aminated CG consisted of abundant granular sub-stances that resembled the nucleus pulposus. Despite the differential initial number adhered to the CG scaffolds, human mesenchymal stem cells (hMSCs) had over 90% viability at all time points. Cell morphology was distinct, being round in Untreated and Methylated CGs but elongated in Deaminated and Aminated ones. The adhesion of hMSCs via collagen receptor, integrin alpha2beta1, was observed in all CG scaffolds, while adhesion via general matrix receptor, integrin alphaV, was extensive in all but Aminated CG. Based on improved GAG incor-poration and retention, which approximate the matrix composition of nucleus pulposus, Aminated CG was chosen as the core of the biphasic scaffold. The second part of this project studied lamination in biphasic disc scaffold and evaluated its mechanical properties in creep, recovery and dynamic loadings. A process was optimized to encapsulate a CG under physiological condition whilst producing an intact collagen gel, which allowed the CG to retain more GAGs and to be confined by the annulus structurally as was in the disc. This encasing approach was repeated for multiple lamellae, one lamella per day. Scaffolds with more lamellae had increased viscous compliance in creep and recovery, which was explained by the less laminated scaffolds being overloaded. Another lamination approach replaced most encasing lamellae with coiling ones. Despite low sample size, it was shown that this combined approach produced scaffolds with lower elastic and viscous compliances and longer equilibrating time in both creep and recovery, and higher complex modulus under dynamic loading. Full recovery was not achieved by any scaffold. This study demonstrated that a biphasic disc scaffold, made of GAG and collagen, contained similar matrix components to native disc, was almost mechanically comparable to the disc, and was cyto-compatible. It paved way towards tissue engineering of intervertebral disc and the intervertebral disc motion segment. / published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

Introduction Peripheral nerve injury is common in clinical practice. The usual etiologies are penetrating injury, stretch, compression, crush and ischemia. Outcome of nerve injury depends on the etiology and also the management. Nerve defect is a challenging scenario. The current gold standard of managing a nerve defect is autologous nerve graft. However, due to the selection of nerve graft and donor site morbidity, artificial nerve conduits are gaining popularity. However, there are drawbacks of single hollow conduit such as lack of internal support to prevent conduit collapse and inability so as to recreate the proper native spatial arrangement of cells and extracellular matrix within the conduit. In this study, the biocompatibility and efficacy of five-channel and eight-channel Crosslinked Urethane-doped Polyester Elastomers (CUPEs) as nerve guidance conduit will be evaluated through a rat model with reconstruction of segmental peripheral nerve defect. Material and method Eighteen adult Sprague-Dawley rats were used. Tthey were randomly allocated to three groups: autograft group, five-channel conduit group and eight-channel conduit group with each consisted of six rats. A 10mm nerve defects were created at the right sciatic nerve. They were bridged with reverse autograft, 5-channel conduit and 8-channel conduit. After eight weeks the rats were euthanized and the reconstructed nerves were harvested for histomorphometric analysis. Results All conduits showed regenerated nerve tissue inside. There was no collapse of the conduits. There were no severe tissue reaction or scarring near the reconstructed nerve. No neuroma was formed. Histomorphometric analysis showed nerve regeneration was enhanced with increasing number of channels inside conduit. There was overall drop in fiber density between proximal and distal segment among all groups. Conclusions CUPE nerve guidance conduit is biocompatible and shows good nerve regeneration in reconstructing nerve defect. / published_or_final_version / Obstetrics and Gynaecology / Master / Master of Medical Sciences

abstract / Biochemistry / Doctoral / Doctor of Philosophy

Mesenchymal stem cell (MSC) transplantation has achieved only modest success in the treatment of ischemic heart disease due to poor cell viability in the diseased microenvironment. Genetic manipulation on the MSCs holds promising prospects in enhancing cell tolerance against adverse environmental conditions. Recent studies demonstrate that the activation of the NRG1 (neuregulin 1) - ERBB4 (v-erb-b2 avian erythroblastic leukemia viral oncogene homolog 4) pathway can enhance pro-survival signaling, stimulate mature cardiomyocyte cell cycle re-entry and cell division. In this study, I aimed to determine whether activating NRG1-ERBB4 in MSCs can enhance their cardioprotective effects following myocardial infarction. In chapter 3, I determined that MSC endogenously expresses NRG1, but not ERBB4. Considering the absence of ERBB4 in the MSCs might lead to mute response to its ligand NRG1, I exogenously manipulated ERBB4 into MSCs. In chapter 4, MSCs, with or without ERBB4 overexpression were transplanted into mice following myocardial infarction. The transplantation of MSCs with ERBB4 expression considerably improved left ventricular ejection fraction and reduced infarctsize, compared to unmodified MSCs and direct NRG1 injection. ERBB4 overexpression induced greater MSC survival following infarction. The transduction of ERBB4 in MSCs increased cell mobility and apoptotic resistance via a PI3K/Akt pathway under hypoxic conditions in the presence of NRG1. The transplantation of MSCs with ERBB4 expression induced cardiomyocyte division and protected them against apoptosis during early phase of infarction. In chapter 5, a novel autocrine loop regarding to NRG1-ERBB4-NRG1 signaling was identified. MSCs with ERBB4 overexpression in turn increased NRG1 synthesis and secretion. Conditioned medium of ERBB4-expressing MSCs containing elevated NRG1, promoted cardiomyocyte growth, division and anti-senescence, whereas neutralization of NRG1 blunted these effects. Injecting ERBB4-expressing MSCs restored NRG1 in the infarcted myocardium to a level comparable with that of the normal myocardium. These findings collectively suggest overexpressing ERBB4 in MSCs enhances the effectiveness of MSCtherapy following myocardial in farction through potentiating MSC survival and revitalizing endogenous repair and regeneration. The combination of ERBB4 and MSC is more efficient than naïve MSC or solely recombinant NRG1 injection, emerging as potential target for developing novel strategy in treating myocardial diseases. / published_or_final_version / Medicine / Doctoral / Doctor of Philosophy

Not available / text

Previous studies from our lab showed that terminal Schwann cells (TSCs) are actively involved in the restoration of functional synapses during reinnervation at mammalian neuromuscular junctions (NMJs). However, it is unclear what induces TSCs to extend processes that guide the nerve growth (Son and Thompson, 1995a,b). Is it the loss of the axon or instead, some signal arising from denervated muscle fibers? The main objective of my dissertation was to examine whether muscle fibers can be the source of signals affecting TSC growth. In Chapter 2, I report that both TSCs and nerve terminals are maintained at the former junction even after their underlying muscle fiber degenerates. Some of the original AChRs are surprisingly sustained at the synaptic sites for a long time with the preserved pretzel pattern. These results show that the postsynaptic target is not necessary for the maintenance of presynaptic structures. In Chapter 3, I report that following fiber regeneration, newly formed AChRs are clearly separated from the persisting receptors at most locations and they are apposed by the nerves. Moreover, as the fiber regenerates, TSCs begin to grow processes. Nerve sprouts then follow these processes to form new synaptic sites beyond the old receptor territory. My observations therefore show that signals for nerve growth arise from regenerating fibers and they appear to act by first affecting TSCs. Such signals seem diffusible because I saw that TSCs on surrounding fibers also began to grow during regeneration. In Chapter 4, I report that new junctions on the regenerated fibers are very dynamic. They undergo continual remodeling and eventually take on an 'en grappe' pattern. Since the synapses on undamaged fibers are normally very stable, these observations suggest that regeneration has set in place a process whereby the synapses are unable to stabilize. Interestingly, this appears to be the case in muscles that degenerate as a consequence of muscular dystrophy. My findings are important because they suggest an active role of the postsynaptic muscle fiber not in synapse maintenance but rather in generating signals that attract innervation after injury. / text

Background Explore the mystery of seasonal organizations and how they are able to (re)create themselves as “the same” after a period of dormancy. Aim To find out the organizational mechanisms that enables such (re)creation. Methodology This qualitative study was done at Astrid Lindgren’s World, a seasonal organization open from mid-May until the beginning of November. The study conducted ten interviews with both permanent and seasonal employees to find out how a year in the organization looked like to later be able to identify the seasonal mechanism. Findings This study has provided seven organizational mechanisms that are vital for Astrid Lindgren’s World to (re)create itself as “the same” from season to season. Concepts Regeneration: the process of reproducing a seasonal organization as “the same” from season to season.(Re)create: The creation of an organization that has previously been existent.“The same”: Due to individuals being subjective an organization cannot completely be (re)created as exactly the same, but rather very similar.

published_or_final_version / Anatomy / Master / Master of Philosophy