Porous polyurethane coatings bonded onto surface-modified titanium substrates for the growth of an endothelial cell layer

Cardiovascular diseases refer to the class of diseases that involve the heart or blood vessels (arteries and veins). Examples of medical devices for treating the cardiovascular diseases include ventricular assist devices (VADs), artificial heart valves and stents. Metallic biomaterials such as titanium and its alloy are commonly used for ventricular assist devices. However, titanium and its alloy show unacceptable thrombosis, which represents a major obstacle to be overcome. Polyurethane (PU) polymer has better blood compatibility and has been used widely in cardiovascular devices. Thus one aim of the project was to coat a PU polymer onto a titanium substrate by increasing the surface roughness, and surface functionality. Since the endothelium of a blood vessel has the most ideal non-thrombogenic properties, it was the target of this research project to grow an endothelial cell layer as a biological coating based on the tissue engineering strategy. However, seeding endothelial cells on the smooth PU coating surfaces is problematic due to the quick loss of seeded cells which do not adhere to the PU surface. Thus it was another aim of the project to create a porous PU top layer on the dense PU pre-layer-coated titanium substrate. The method of preparing the porous PU layer was based on the solvent casting/particulate leaching (SCPL) modified with centrifugation. Without the step of centrifugation, the distribution of the salt particles was not uniform within the polymer solution, and the degree of interconnection between the salt particles was not well controlled. Using the centrifugal treatment, the pore distribution became uniform and the pore interconnectivity was improved even at a high polymer solution concentration (20%) as the maximal salt weight was added in the polymer solution. The titanium surfaces were modified by alkli and heat treatment, followed by functionlisation using hydrogen peroxide. A silane coupling agent was coated before the application of the dense PU pre-layer and the porous PU top layer. The ability of the porous top layer to grow and retain the endothelial cells was also assessed through cell culture techniques. The bonding strengths of the PU coatings to the modified titanium substrates were measured and related to the surface morphologies. The outcome of the project is that it has laid a foundation to achieve the strategy of endothelialisation for the blood compatibility of medical devices. This thesis is divided into seven chapters. Chapter 2 describes the current state of the art in the field of surface modification in cardiovascular devices such as ventricular assist devices (VADs). It also analyses the pros and cons of the existing coatings, particularly in the context of this research. The surface coatings for VADs have evolved from early organic/ inorganic (passive) coatings, to bioactive coatings (e.g. biomolecules), and to cell-based coatings. Based on the commercial applications and the potential of the coatings, the relevant review is focused on the following six types of coatings: (1) titanium nitride (TiN) coatings, (2) diamond-like carbon (DLC) coatings, (3) 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer coatings, (4) heparin coatings, (5) textured surfaces, and (6) endothelial cell lining. Chapter 3 reviews the polymer scaffolds and one relevant fabrication method. In tissue engineering, the function of a polymeric material is to provide a 3-dimensional architecture (scaffold) which is typically used to accommodate transplanted cells and to guide their growth and the regeneration of tissue. The success of these systems is dependent on the design of the tissue engineering scaffolds. Chapter 4 describes chemical surface treatments for titanium and titanium alloys to increase the bond strength to polymer by altering the substrate surface, for example, by increasing surface roughness or changing surface chemistry. The nature of the surface treatment prior to bonding is found to be a major factor controlling the bonding strength. By increasing surface roughness, an increase in surface area occurs, which allows the adhesive to flow in and around the irregularities on the surface to form a mechanical bond. Changing surface chemistry also results in the formation of a chemical bond. Chapter 5 shows that bond strengths between titanium and polyurethane could be significantly improved by surface treating the titanium prior to bonding. Alkaline heat treatment and H2O2 treatment were applied to change the surface roughness and the surface chemistry of titanium. Surface treatment increases the bond strength by altering the substrate surface in a number of ways, including increasing the surface roughness and changing the surface chemistry. Chapter 6 deals with the characterization of the polyurethane scaffolds, which were fabricated using an enhanced solvent casting/particulate (salt) leaching (SCPL) method developed for preparing three-dimensional porous scaffolds for cardiac tissue engineering. The enhanced method involves the combination of a conventional SCPL method and a step of centrifugation, with the centrifugation being employed to improve the pore uniformity and interconnectivity of the scaffolds. It is shown that the enhanced SCPL method and a collagen coating resulted in a spatially uniform distribution of cells throughout the collagen-coated PU scaffolds.In Chapter 7, the enhanced SCPL method is used to form porous features on the polyurethane-coated titanium substrate. The cavities anchored the endothelial cells to remain on the blood contacting surfaces. It is shown that the surface porosities created by the enhanced SCPL may be useful in forming a stable endothelial layer upon the blood contacting surface. Chapter 8 finally summarises the entire work performed on the fabrication and analysis of the polymer-Ti bonding, the enhanced SCPL method and the PU microporous surface on the metallic substrate. It then outlines the possibilities for future work and research in this area.

Aetiology of Hip dislocation

Written by the surgeons of the Exeter Hip Team and their colleagues from around the world, this book describes 40 years of innovation and development with cemented hip replacement. Topics covered include the basic science behind successful cemented hip replacement, modern surgical techniques and recent advances. There is also extensive coverage of the revision techniques developed at Exeter and elsewhere, focussing on femoral and acetabular impaction grafting. Each chapter is a self-contained article with an emphasis, where appropriate, on practical techniques and surgical tips, supported by line drawings and intra-operative photographs.

Clinical results in primary THR

Written by the surgeons of the Exeter Hip Team and their colleagues from around the world, this book describes 40 years of innovation and development with cemented hip replacement. Topics covered include the basic science behind successful cemented hip replacement, modern surgical techniques and recent advances. There is also extensive coverage of the revision techniques developed at Exeter and elsewhere, focussing on femoral and acetabular impaction grafting. Each chapter is a self-contained article with an emphasis, where appropriate, on practical techniques and surgical tips, supported by line drawings and intra-operative photographs.

The use of cement in hip arthroplasty

Written by the surgeons of the Exeter Hip Team and their colleagues from around the world, this book describes 40 years of innovation and development with cemented hip replacement. Topics covered include the basic science behind successful cemented hip replacement, modern surgical techniques and recent advances. There is also extensive coverage of the revision techniques developed at Exeter and elsewhere, focussing on femoral and acetabular impaction grafting. Each chapter is a self-contained article with an emphasis, where appropriate, on practical techniques and surgical tips, supported by line drawings and intra-operative photographs.

Operative technique : acetabulum

BOOK: Written by the surgeons of the Exeter Hip Team and their colleagues from around the world, this book describes 40 years of innovation and development with cemented hip replacement. Topics covered include the basic science behind successful cemented hip replacement, modern surgical techniques and recent advances. There is also extensive coverage of the revision techniques developed at Exeter and elsewhere, focussing on femoral and acetabular impaction grafting. Each chapter is a self-contained article with an emphasis, where appropriate, on practical techniques and surgical tips, supported by line drawings and intra-operative photographs.

The Exeter Hip. 40 Years of Innovation in Total Hip Arthroplasty

* Propoerties and use of acrylic cement * Design and biomechaniscs of a cemented hip replacement * The science of loosening, lysis and wear * Preparation of patients for surgery * Potential complications and their avoidance * Modern primary surgical techniques and new developments * Complex primary hip replacement and specialist techniques * Outcomes of cemented hip replacement * Principles of revision hip replacement * Basic science of bone grafting in revision surgery * Femoral acetabular impaction bone grafting techniques * Results of revision with bone graft and cement

Modulation of dermal microvascular endithelial cell responses to growth factors and haemostatic factors in the presence of vitronectin

In order to effect permanent closure in burns patients suffering from full thickness wounds, replacing their skin via split thickness autografting, is essential. Dermal substitutes in conjunction with widely meshed split thickness autografts (+/- cultured keratinocytes) reduce scarring at the donor and recipient sites of burns patients by reducing demand for autologous skin (both surface area and thickness), without compromising dermal delivery at the wound face. Tissue engineered products such as Integra consist of a dermal template which is rapidly remodelled to form a neodermis, at which time the temporary silicone outer layer is removed and replaced with autologous split thickness skin. Whilst provision of a thick tissue engineered dermis at full thickness burn sites reduces scarring, it is hampered by delays in vascularisation which results in clinical failure. The ultimate success of any skin graft product is dependent upon a number of basic factors including adherence, haemostasis and in the case of viable tissue grafts, success is ultimately dependent upon restoration of a normal blood supply, and hence this study. Ultimately, the goal of this research is to improve the therapeutic properties of tissue replacements, through impregnation with growth factors aimed at stimulating migration and proliferation of microvascular endothelial cells into the donor tissue post grafting. For the purpose of my masters, the aim was to evaluate the responsiveness of a dermal microvascular endothelial cell line to growth factors and haemostatic factors, in the presence of the glycoprotein vitronectin. Vitronectin formed the backbone for my hypothesis and research due to its association with both epithelial and, more specifically, endothelial migration and proliferation. Early work using a platform technology referred to as VitroGro (Tissue Therapies Ltd), which is comprised of vitronectin bound BP5/IGF-1, aided keratinocyte proliferation. I hypothesised that this result would translate to another epithelium - endothelium. VitroGro had no effect on endothelial proliferation or migration. Vitronectin increases the presence of Fibroblast Growth Factor (FGF) and Vascular Endothelial Growth Factor (VEGF) receptors, enhancing cell responsiveness to their respective ligands. So, although Human Microvascular Endothelial Cell line 1 (HMEC-1) VEGF receptor expression is generally low, it was hypothesised that exposure to vitronectin would up-regulate this receptor. HMEC-1 migration, but not proliferation, was enhanced by vitronectin bound VEGF, as well as vitronectin bound Epidermal Growth Factor (EGF), both of which could be used to stimulate microvascular endothelial cell migration for the purpose of transplantation. In addition to vitronectin's synergy with various growth factors, it has also been shown to play a role in haemostasis. Vitronectin binds thrombin-antithrombin III (TAT) to form a trimeric complex that takes on many of the attributes of vitronectin, such as heparin affinity, which results in its adherence to endothelium via heparan sulfate proteoglycans (HSP), followed by unaltered transcytosis through the endothelium, and ultimately its removal from the circulation. This has been documented as a mechanism designed to remove thrombin from the circulation. Equally, it could be argued that it is a mechanism for delivering vitronectin to the matrix. My results show that matrix-bound vitronectin dramatically alters the effect that conformationally altered antithrombin three (cATIII) has on proliferation of microvascular endothelial cells. cATIII stimulates HMEC-1 proliferation in the presence of matrix-bound vitronectin, as opposed to inhibiting proliferation in its absence. Binding vitronectin to tissues and organs prior to transplant, in the presence of cATIII, will have a profound effect on microvascular infiltration of the graft, by preventing occlusion of existing vessels whilst stimulating migration and proliferation of endothelium within the tissue.

Is it necessary to re-fuse a non-union of a hallux metatarsophalangeal joint arthrodesis?

BACKGROUND: The standard treatment for a non-union of the hallux metatarsophalangeal joint fusion has been to revise the fusion. Revision fusion is technically more demanding, often involving bone grafting, more substantial fixation and prolonged period of immobilization postoperatively. We present data to suggest that removal of hardware and debridement alone is an alternative treatment option. ---------- MATERIALS AND METHODS: A case note review identified patients with a symptomatic non-union after hallux metatarsophalangeal joint (MTPJ) fusion. It is our practice to offer these patients revision fusion or removal of hardware and debridement. For the seven patients that chose hardware removal and were left with a pseudarthrosis, a matched control group was selected from patients who had had successful fusions. Three outcome scores were used. Hallux valgus and dorsiflexion angles were recorded.---------- RESULTS: One hundred thirty-nine hallux MTPJ arthrodeses were carried out. Fourteen non-unions were identified. The rate of non-union in males and following previous hallux MTPJ surgery was 19% and 24%, respectively. In females undergoing a primary MTPJ fusion, the rate was 2.4%. Twelve non-union patients were reviewed at 27 months (mean). Eleven patients had elected to undergo removal of hardware and debridement. Four patients with pseudarthrosis were unhappy with the results and proceeded to either revision fusion or MTPJ replacement. Seven non-union patients, who had removal of hardware alone, had outcome scores marginally worse compared to those with successful fusions.---------- CONCLUSION: Removal of hardware alone is a reasonable option to offer as a relatively minor procedure following a failed arthrodesis of the first MTPJ. This must be accepted on the proviso that in this study four out of 11 (36%) patients proceeded to a revision first MTPJ fusion or first MTPJ replacement. We also found that the rate of non-union in primary first MTPJ fusion was significantly higher in males and those patients who had undergone previous surgery.

Resorbable composite scaffolds for craniofacial bone tissue engineering

Aim: Bone loss associated with trauma, osteo-degenerative diseases and tumors has tremendous socioeconomic impact related to personal and occupation disability and health care costs. In the present climate of increasing life expectancy with an ensuing increase in bone-related injuries, orthopaedic surgery is undergoing a paradigm shift from bone-grafting to bone engineering, where a scaffold is implanted to provide adequate load bearing and enhance tissue regeneration. We aim to develop composite scaffolds for bone tissue engineering applications to replace the current gold standard of autografting. ---------- Methods: Medical grade polycaprolactone-tricalcium phosphate (mPCL/TCP) scaffolds (80/20 wt%) were custom made using fused deposition modelling to produce 1x1.5x2 cm sized implants for critical-sized pig cranial implantations, empty defects were used as a control. Autologous bone marrow stromal cells (BMSCs) were extracted and precultured for 2 weeks, dispersed within fibrin glue and injected during scaffold implantation. After 2 years, microcomputed tomography and histology were used to assess bone regenerative capabilities of cell versus cell-free scaffolds. ---------- Results: Extensive bone regeneration was evident throughout the entire scaffold. Clear osteocytes embedded within mineralised matrix and active osteoblasts present around scaffold struts were observed. Cell groups performed better than cell-free scaffolds. ---------- Conclusions: Bone regeneration within defects which cannot heal unassisted can be achieved using mPCL/TCP scaffolds. This is improved by the inclusion of autogenous BMSCs. Further work will include the inclusion of growth factors including BMP-2, VEGF and PDGF to provide multifunctional scaffolds, where the three-dimensional (3D) template itself acts as a biomimetic, programmable and multi-drug delivery device.

Resorbable composite scaffolds for bone tissue engineering

Bone loss associated with trauma osteo-degenerative diseases and tumors has tremendous socioeconomic impact related to personal and occupation disability and health care costs. Bone grafting is often critical to surgical therapies. Autogenous bone is presently the preferred grafting material; however, this holds several disadvantages such as donor site morbidity. In the present climate of increasing life expectancy with an ensuing increase in bone-related injuries, orthopaedic surgery is undergoing a paradigm shift from bone-grafting to bone engineering, where a scaffold is implanted to provide adequate load bearing and enhance tissue regeneration. Our group at Queensland University of Technology (QUT) have developed, characterised and tested polycaprolactone/ tricalcium phosphate (PCL/TCP) composite scaffolds for low load-bearing bone defects. These scaffolds are being further developed for application in higher load bearing sites. Our approach emphasizes the importance of the biomaterials’ structural design, the scaffold architecture and structural and nutritional requirements for cell culture. These first-generation scaffolds made from medical grade PCL (mPCL) have been studied for more than 5 years within a clinical setting 1. This paper describes the application of second-generation scaffolds in small and large animal bone defect models and the ensuing bone regeneration as shown by histology and µCT.

Manipulating double-decker molecules at the liquid-solid interface

We have used a scanning tunneling microscope to manipulate heteroleptic phthalocyaninato, naphthalocyaninato, porphyrinato double-decker molecules at the liquid/solid interface between 1-phenyloctane solvent and graphite. We employed nano-grafting of phthalocyanines with eight octyl chains to place these molecules into a matrix of heteroleptic double-decker molecules; the overlayer structure is epitaxial on graphite. We have also used nano-grafting to place double-decker molecules in matrices of single-layer phthalocyanines with octyl chains. Rectangular scans with a scanning tunneling microscope at low bias voltage resulted in the removal of the adsorbed doubledecker molecular layer and substituted the double-decker molecules with bilayer-stacked phthalocyanines from phenyloctane solution. Single heteroleptic double-decker molecules with lutetium sandwiched between naphthalocyanine and octaethylporphyrin were decomposed with voltage pulses from the probe tip; the top octaethylporphyrin ligand was removed and the bottom naphthalocyanine ligand remained on the surface. A domain of decomposed molecules was formed within the double-decker molecular domain, and the boundary of the decomposed molecular domain self-cured to become rectangular. We demonstrated a molecular “sliding block puzzle” with cascades of double-decker molecules on the graphite surface.

Mechanical Behavior of Articular Cartilage After Osteochondral Autograft Transfer in an Ovine Model

BACKGROUND: Grafting of autologous hyaline cartilage and bone for articular cartilage repair is a well-accepted technique. Although encouraging midterm clinical results have been reported, no information on the mechanical competence of the transplanted joint surface is available. HYPOTHESIS: The mechanical competence of osteochondral autografts is maintained after transplantation. STUDY DESIGN: Controlled laboratory study. METHODS: Osteochondral defects were filled with autografts (7.45 mm in diameter) in one femoral condyle in 12 mature sheep. The ipsilateral femoral condyle served as the donor site, and the resulting defect (8.3 mm in diameter) was left empty. The repair response was examined after 3 and 6 months with mechanical and histologic assessment and histomorphometric techniques. RESULTS: Good surface congruity and plug placement was achieved. The Young modulus of the grafted cartilage significantly dropped to 57.5% of healthy tissue after 3 months (P < .05) but then recovered to 82.2% after 6 months. The aggregate and dynamic moduli behaved similarly. The graft edges showed fibrillation and, in some cases (4 of 6), hypercellularity and chondrocyte clustering. Subchondral bone sclerosis was observed in 8 of 12 cases, and the amount of mineralized bone in the graft area increased from 40% to 61%. CONCLUSIONS: The mechanical quality of transplanted cartilage varies considerably over a short period of time, potentially reflecting both degenerative and regenerative processes, while histologically signs of both cartilage and bone degeneration occur. CLINICAL RELEVANCE: Both the mechanically degenerative and restorative processes illustrate the complex progression of regeneration after osteochondral transplantation. The histologic evidence raises doubts as to the long-term durability of the osteochondral repair.

Surface modification of alumina nanofibres for the selective adsorption of alachlor and imazaquin herbicides

The effective removal of pollutants using a thermally and chemically stable substrate that has controllable absorption properties is a goal of water treatment. In this study, the surfaces of thin alumina (γ-Al2O3) nanofibres were modified by the grafting either of two organosilane agents, 3-chloro-propyl-triethoxysilane (CPTES) and octyl-triethoxysilane (OTES). These modified materials were then trialed as absorbents for the removal of two herbicides, alachlor and imazaquin from water. The formation of organic groups during the functionalisation process established super hydrophobic sites on the surfaces of the nanofibres. This super hydrophobic group is a kind of protruding adsorption site which facilitates the intimate contact with the pollutants. OTES grafted substrate were shown to be more selective for alachlor while imazaquin selectivity is shown by the CPTES grafted substrate. Kinetics studies revealed that imazaquin was rapidly adsorbed on CPTES-modified surfaces. However, the adsorption of alachlor by OTES grafted surface was achieved more slowly.