Fracture non-unions and bone defects represent a recalcitrant problem in the field of orthopaedic surgery. Although the current gold-standard treatment, autologous bone grafting, has a relatively high success rate, the technique is not without serious problems. The emerging field of regenerative medicine may have the potential to provide an alternative treatment. One promising strategy involves the delivery of both cells and multiple growth factors with different release profiles. A range of scaffolds was developed from Poly( -caprolactone) (PCL), Poly(lactideco- glycolide) (PLGA), and two blends of PCL (Mn 42,500) and PLGA. The scaffolds were manufactured utilising a novel modified fused deposition modelling system, using polymer/dichloromethane solutions. The scaffolds were found to have pore sizes suitable for bone regenerative medical applications (373±9.5 μm in the Ydirection and 460±13 μm in the X-direction). However, the scaffolds were found to be only 52±3 μm in height. This means that the two-layer scaffolds were relatively flat. This was undesirable, as direct control of the complete 3D geometry was the favoured strategy, though it may not be a necessary requirement. Five scaffold coatings were also developed from alginate, chitosan (crosslinked using sodium hydroxide or tripolyphosphate), Type-I collagen and Type-A gelatin. The scaffold coatings were screened in vitro for their cell-compatibility with human marrow stromal cells (hMSCs), human osteoblasts and MG63 cells. This was assessed using an assay for cell death, and assessing total cell counts. From these studies, Type-I collagen was found to be the optimum coating. For hMSCs, their death rates were found to be 19.1±6.3% for alginate, 5.3±3.6% and 2.9±1.4% for chitosan crosslinked with tripolyphosphate and sodium hydroxide respectively, compared to 0.11±0.07% for Type-I collagen, and 0.15±0.13% and 0.16±0.12% for 0.1% and 0.2% gelatin respectively. Type-I collagen was found to be the most cellcompatible coating, as it was consistently associated with higher cell counts than Type-A gelatin. Similarly, PCL scaffolds vacuum dried for 1 hr were found to be cell-compatible. No detectable clinically significant difference was found in either total cell counts, or the proportion of cell death in; hMSCs exposed to PCL scaffolds processed with dichloromethane, hMSCs either exposed to scaffolds known to be biocompatible, or hMSCs cultured in the absence of scaffolds. When cell morphology was compared, scaffolds vacuum dried for 1 hr or more were found to have a similar morphology to the cells cultured in the absence of scaffolds. It was therefore concluded that a vacuum drying time of 1 hr was sufficient for cell-compatibility. The scaffold materials were screened both for their encapsulation efficiencies and release characteristics using the model drug, methylene blue. The encapsulation efficiency was found to be both relatively high and consistent for both Mn 42,500 and 80,000 PCL as well as PCL:PLGA 66:33, at 71±6%, 71±5%, and 78±10% respectively, relative to the low efficiencies recorded for both PCL:PLGA 66:33 and PLGA: 57±5% and 38±10% respectively. The release rate of methylene blue from PCL (Mn 42,500), was found to be relatively slow, controlled, and consistent between batches (between 21±2% and 20±3% released in the first 24 hr). Despite the release rate being consistent for PCL (Mn 80,000), the release rate was thought to be too high, since between 29±3% and 39±5% of the test compound was released in the first 24 hr period. The release rate of methylene blue from the PCL/PLGA blends (between 17±2% – 30±7% and 18±4% – 31±6% in the first 24 hr) and PLGA (between 7.1±3.4% – 9.3±2.9% in the first 24 hr) were found to be inconsistent, and low in the case of PLGA, even taking the different loading efficiencies into account. Therefore, PCL (Mn 42,500) was selected as the favoured candidate scaffold material. The loading content and release profiles from methylene blue loaded collagen scaffold coatings were also evaluated. The drug loading capacity was found to be suitable for use as a drug delivery system (65±5 μg/g of methylene blue per unit scaffold mass). The release of methylene blue was observed to be rapid (between 54±10% – 70±17% in the first 24 hr), which was thought to be desirable for the coating delivery system. Recombinant human bone morphogenetic protein-7 (rhBMP-7) was used as a representative growth factor of interest for bone regenerative medical applications. It was loaded in collagen scaffold coatings (CoatBMP 1.25) and encapsulated within PCL (Mn 42,500) scaffolds (ScaffBMP 1.25). Control coatings and scaffolds were designated CoatPBS and ScaffPBS respectively. Both delivery systems were found to release detectable quantities of rhBMP-7 (releasing 2.8±0.2 μg/g and 87±7 ng/g respectively in the first 24 hr), even after 14 days. The release rate of the growth factor from the scaffold coating was higher than that from the encapsulating scaffolds. However, the cumulative release profiles were found to deviate from the desired ideal release profiles, and burst release was observed from both delivery systems. Although differences were observed for the two delivery systems, this difference may not be of clinical significance. Nevertheless, scaffolds with less than ideal delivery properties may still be of potential clinical use. The bioactivity of the rhBMP-7 released from the test scaffolds was therefore assessed by quantifying the area of normalised ALP staining of hMSCs. The release of rhBMP-7 from the collagen coating of the PCL (Mn 42,500) scaffolds (CoatBMP 1.25ScaffPBS) was capable of statistically significantly increasing hMSC normalised ALP expression, although the actual differences were often relatively small. Therefore, at least a proportion of the growth factor released is likely to have been bioactive. The release from scaffolds encapsulating rhBMP-7 (CoatPBSScaffBMP 1.25) did not have this effect on the hMSCs, indicating that either the concentration released was too low, or the growth factor released was no longer bioactive. However, when the cells were seeded directly onto the scaffolds, the activity of ALP, normalised by a DNA assay, was statistically significantly increased for the CoatPBSScaffBMP 1.25 scaffolds, in hMSCs from all three test patient donors (by 35±10% on the control). ALP activity was also significantly increased in hMSCs from two of the three patients seeded onto CoatBMP 1.25ScaffBMP 1.25 scaffolds (by 39±10% on the control). ALP activity was only statistically significantly increased for one of the hMSC patients when seeded onto CoatBMP 1.25ScaffPBS scaffolds (by 35±14% on the control). The functional osteoinductive capacity of Type-I collagen coated PCL (Mn 42,500) scaffolds loaded with rhBMP-7 was assessed using C2C12 cells seeded onto the scaffolds, and quantified using qRT-PCR. The genes of interest were; Type-I collagen (Col1), osteopontin (OP), ALP, osteocalcin (OC) and runt related transcription factor 2 (Runx2). The CoatBMP 1.25ScaffPBS scaffolds had an early osteoinductive effect on the C2C12 cells, as ALP, OC and Runx2 were elevated during the first 2 days only, compared to the control (e.g. by 44±12%, 128±42%, 60±25% and 46±25% respectively at the 24 hr mark). The CoatPBSScaffBMP 1.25 scaffolds also had an osteoinductive effect on the cells, which was more sustained than that observed for the CoatBMP 1.25ScaffPBS group. While OP, ALP and Runx2 were up-regulated in the first 24 hr compared to the control (by 38±10%, 208±82% and 72±31% respectively), statistically significant up-regulation of the late marker OC was delayed until the 48 hr mark (by 73±49%). The effect was found to be sustained until day 7, when OC and Runx2 were both statistically significantly up-regulated compared to the control (by 151±91% and 93±27% respectively). The CoatBMP 1.25ScaffBMP 1.25 scaffolds were found to combine the early effect of the CoatBMP 1.25ScaffPBS scaffolds, with the more sustained effect of the CoatPBSScaffBMP 1.25 scaffolds. ALP, OC and Runx2 were all up-regulated at the 24 hr mark (by 312±56%, 329±39% and 96±25% respectively). This osteoinductive effect was sustained until day 7 when Col1, ALP and Runx2 were still up-regulated compared to the control (by 174±78%, 72±24% and 178±78% respectively). These data suggest that the scaffolds containing rhBMP-7 have a weak osteoinductive effect on the cells seeded onto them. The different delivery systems were found to affect the cells differently. The clinical significance of this was not assessed in these studies. 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) was used as a model drug to assess the feasibility of releasing lipid-soluble active factors from the scaffolds. This was assessed by quantifying the area of normalised ALP staining of hMSCs. The release of 1,25(OH)2D3 from the loaded collagen scaffold coatings and the encapsulating scaffolds significantly increased ALP expression compared to the control scaffold groups (by 115±28% and 69±25% respectively). Furthermore, ALP expression was significantly increased when the two delivery systems were used together, when compared to either delivery system on its own. These data suggest that the delivery of lipid-soluble active factors is feasible from collagen coated PCL scaffolds, and that the coating and encapsulating delivery systems are mutually compatible.

No description available.

This thesis reports three projects on mussel-inspired biomimetic materials based on dopamine crosslinkers. First, polyethylene glycol diacrylate (PEGDA) hydrogels with excellent cell attachment and tunable stiffness was fabricated based on this novel crosslinker. In vitro tests proved that the designed hydrogels had excellent cell adhesion, suggesting the developed hydrogels are promising for applications in tissue engineering. Second, dopamine crosslinker-conjugated gelatin-polycparolactone (PCL) nanofibrous sheet was developed. The sheet was then employed successfully to treat stomach incision without suture during surgery, showing promising to deal with treatments of fragile tissues and to avoid suture caused stress concentration. Third, a facile strategy to wrap cell into a tissue-engineered scaffold was developed, which is a self-rolling and conductive dopamine-based film. The RTPCR test indicated that cells have higher level of differentiation with higher concentration of MWCNTs. This suggests that the self-rolling conductive WCNT-dopamine-PEG hydrogel is a promising scaffolding material for bone regeneration. / October 2015

Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references (p. 313-357). Also available online.

Zugl.: Giessen, Universiẗat, Diss., 2009.

Thesis(Ph.D.)--Case Western Reserve University, 2010 / Title from PDF (viewed on 2009-12-30) Department of Chemical Engineering Includes abstract Includes bibliographical references and appendices Available online via the OhioLINK ETD Center

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (Ph.D.)--Brown University, 2008. / Vita. Advisor : Edith Mathiowitz. Includes bibliographical references.

Bone grafting is an integral part of reconstructive surgery. In the United States alone over 250,000 bone grafts were harvested annually. While autogenic bone grafting has always been associated with donor site morbidity, bone graft substitutes have been suggested as a solution. In this project, a bone graft substitute using human dental pulp cells (HDPCs) and peptide nanofibre hydrogel was being developed. HDPCs were isolated from extracted teeth. After culture and expansion, unsorted HDPCs were encapsulated into peptide nanofibre hydrogel. These cell-gel constructs were cultured for two weeks in ordinary culture medium and then for 2-3 more weeks in osteogenic lineage induction medium. The post-induced cell-gel derived constructs were transplanted into skin pouches or calvarial bone defects of nude mice. When transplanted subcutaneously, the cell-gel derived constructs were harvested at four to twelve weeks postoperatively (n=5). Tissue samples were processed for contact radiograph, histological examination and antibody staining. These constructs developed into vascularised, mineralised tissue pieces. Though bone marker proteins (osteopontin, osteocalcin and osteonectin) were detected in these tissue pieces, the histological structure of their tissue matrix did not resemble bone matrix. Later, it was accidentally noted that portions of constructs touching the bone defect margin, would form bone through direct matrix transformation. This indicated that the current cell-gel model was potentially the first study model of tissue engineering bone by simulating intramembranous ossification. In the bone defect trial, obviously mineralized cell-gel derived constructs of matching shape and size were selected to patch the 3mm calvarial bone defects (n=5). Bone defect specimens were harvested at two weeks post-operation. The development of radio-opaque structures within the bone defects were evaluated in virtual 3-dimensional models constructed with data collected by microtomographic scanning. The bone nature of these radio-opaque structure were validated histologically (by staining with Hematoxylin and Eosin, Periodic acid-Schiff stain and Picrosirius red) and immunologically (with antibody against human collagen-I, osteonectin and parathyroid hormone receptor). The radio-opaque structures developed into the bone defect were evaluated positive for bone. And significantly more bone regeneration was observed in the test group (n=4) than in the control (n=2). The mean area percentages of regeneration were 46.3% and 0% respectively (p< 0.05). While the majority of studies in bone tissue engineering have worked with bone marrow stromal cells and scaffolds of synthetic polymer or calcium based materials, this is the first successful attempt of using HDPCs and peptide nanofibre hydrogel to engineer bone (in a nude mice mode). And the potential of these cell-gel derived constructs to promote bone regeneration was demonstrated. But this was the result from a single experiment of small sample size in one animal model only. It needs to be fortified by further experiments with larger population size and in other animal models. To increase clinical usefulness, the construct will need to be scaled up to centimetre size level. This will necessitate a change of its configuration from bead into meshwork. And, the data collected to date will shed light onto the redevelopment of all the relevant protocols. / published_or_final_version / Dentistry / Doctoral / Doctor of Philosophy

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy