Bone has the capacity to regenerate itself, however for challenging defects such as non-uniform factures, repair can be problematic. A similar challenge is presented in the repair of osteoporotic bone. Osteoporotic bone becomes increasingly porous and brittle and the risk of fracture is greatly increased. A drug mimic, poly(vinyl phosphonic acid – co – acrylic acid)(PVPA), has been incorporated into FDA approved poly(ε-caprolactone)(PCL), and aims to mimic the action of bisphosphonates to reduce the activity of osteoclasts. The PVPA polymer contains pendant phosphonic acid groups which are hypothesised to mimic the P-C-P backbone found in bisphosphonates. The PCL/PVPA scaffold has been found to have sufficient mechanical strength in order to be used as a bone void filler as well as providing a hydrophilic surface for superior cell attachment. The substrate has been found to significantly enhance the deposition of collagen, alkaline phosphatase activity and the expression of osteocalcin. Alizarin red staining revealed an increase in the rate of mineralisation in the presence of the drug mimic. The PCL/PVPA substrates have been suggested to induce osteoblast cells from a proliferative phase to a mineralisation stage. This is believed to be due to the presence of phosphorous within the scaffold which could lead to the critical concentration required for the initiation of mineralisation being reached more rapidly and effectively. The PVPA polymer has been found to mimic the action of bisphosphonates by inducing osteoclast apoptosis in vitro, and its actions of osteoclast apoptosis are comparable to that of Alendronate, a commonly administered bisphosphonate. A critical size defect model has demonstrated that the PVPA polymer has the ability to heal critical size defects; the healing potential was two fold greater than the control PCL substrate. Initial in vivo studies using a subcutaneous model demonstrated an improvement in mineralisation in the presence of PVPA. Untreated PCL/PVPA substrates displayed a high level of branched blood vessel formation, essential for healthy bone formation. However PVPA samples pre-treated with VEGF, hindered blood vessel formation and the infiltration of cells. This suggests that the PVPA alone is capable of inducing neovascularisation without the addition of VEGF. The findings suggest that the PCL/PVPA system could be used to treat challenging bone defects such as non-unions and osteoporotic fractures.

Biomaterials have been used for more than a century in the human body to improve body functions and replace damaged tissues. Currently approved and commonly used metallic biomaterials such as, stainless steel, titanium, cobalt chromium and other alloys have been found to have adverse effects leading in some cases, to mechanical failure and rejection of the implant. The physical or chemical nature of the degradation products of some implants initiates an adverse foreign body reaction in the tissue. Some metallic implants remain as permanent fixtures, whereas others such as plates, screws and pins used to secure serious fractures are removed by a second surgical procedure after the tissue has healed sufficiently. However, repeat surgical procedures increase the cost of health care and the possibility of patient morbidity. This study focuses on the development of magnesium based biodegradable alloys/metal matrix composites (MMCs) for orthopedic and cardiovascular applications. The Mg alloys/MMCs possessed good mechanical properties and biocompatible properties. Nine different compositions of Mg alloys/MMCs were manufactured and surface treated. Their degradation behavior, ion leaching, wettability, morphology, cytotoxicity and mechanical properties were determined. Alloying with Zn, Ca, HA and Gd and surface treatment resulted in improved mechanical properties, corrosion resistance, reduced cytotoxicity, lower pH and hydrogen evolution. Anodization resulted in the formation of a distinct oxide layer (thickness 5-10 μm) as compared with that produced on mechanically polished samples (~20-50 nm) under ambient conditions. It is envisaged that the findings of this research will introduce a new class of Mg based biodegradable alloys/MMCs and the emergence of innovative cardiovascular and orthopedic implant devices.

The awareness of environmental sustainability drives the composite industry to utilize natural fibres. Natural fibres are a readily available resource with a relatively low price. In this study natural fibre flax reinforced polylactic acid (PLA) biocomposites were made using a new technique incorporating an air-laying nonwoven process. Flax and PLA fibres were blended and converted to fibre webs in the air-laying process. Composite prepregs were then made from the fibre webs. The prepregs were finally converted to composites by compression moulding. The relationship between the main process variables and the properties of the biocomposite was investigated. It was found that with increasing flax content, the mechanical properties increased. As the moulding temperature and moulding time increased, the mechanical properties decreased. The physical, thermal and morphological properties of the biocomposites were also studied. The appropriate processing parameters for the biocomposites were established for different fibre contents. The biodegradability and water absorption properties of the composites were evaluated. The composites were incubated in compost under controlled conditions. The percentage weight loss and the reduction in mechanical properties of PLA and biocomposites were determined at different time intervals. It was found that with increasing flax content, the mechanical properties of the biocomposites decreased more rapidly during the burial trial. The increasing of flax content led to the acceleration of weight loss due to preferential degradation of flax. This was further confirmed by the surface morphology of the biodegraded composites from Scanning Electron Microscope (SEM) image analysis. This study also investigated the manufacturing of 3D PLA/Flax nonwoven prepregs by using a new system of 3D nonwoven web formation, and 3D biocomposite was made using these prepregs. A new mould unit for web and a new aluminium mould for biocomposite were developed. The physical properties of 3D biocomposites were investigated and it was found that there is no significant difference between 2D and 3D biocomposites in density and void content. The effects of fibre content and processing variables on the crushing behaviour, energy absorption and failure mode of 3D shell biocomposites were experimentally studied.

Supercritical CO2 foam processing of biopolymers represents a green processing route to environmentally friendly media and packaging foams. Mater-Bi, a multiconstituent biopolymer of polyester, starch and vegetable oils has shown much promise for biodegradation. The polymer, however, is not foamable with CO2 so blended with another polymer which is. Polycaprolactone is a biopolymer with potential of 4000% change in volume with CO2. Thus we investigate blends of Mater-Bi (MB) and polycaprolactone (PCL) foamed in supercritical CO2 using the batch process. Characterization of the foamed and unfoamed samples were done using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Micrographs of the samples from the SEM revealed that the cell size of the foams reduced and increased with increase in MB concentration and increase in the foaming temperature respectively. Mechanical tests; tensile, compression, shear and impact were performed on the foamed samples. It was noted that between the 20-25% wt. MB, there was an improvement in the mechanical properties. This suggests that at these compositions, there is a high interaction between PCL and MB at the molecular level compared to other compositions. The results indicate that green processing of polymer blends is viable.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第22339号 / 医博第4580号 / 新制||医||1042(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 木村 剛, 教授 髙橋 良輔, 教授 小池 薫 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

This thesis writes about biodegradable bone implants based on iron. The currently used metal-based implants have disadvantage in an often need of secondary surgery intervention to remove the implant. Therefore, there is a big research of biodegradable bone implants nowadays. In this work, iron-based materials with the addition of zinc and magnesium are being investigated. The produced samples have been immersed in a solution of NaCl and simulated body fluid, SBL. Subsequently there were regularly analysed changes of corrosion potential, pH, conductivity and also weight loss was watched.

Les stents sont aujourd’hui le traitement le plus courant des stades avancés de l’athérosclérose. Le concept de stents bioresorbables (BRS) est basé sur l’idée qu’un stent n’est nécessaire que jusqu’à la guérison de l’artère – suite à quoi il serait préférable que le stent disparaisse, afin de retrouver un état plus physiologique. Le déploiement d’un stent altère significativement les contraintes mécaniques exercées sur la paroi artérielle, or celles-ci jouent un rôle important dans l’incidence de complications telle que la resténose et l’hyperplasie néointimale. Dans le cas d’un BRS, les contraintes mécaniques dans le stent comme dans la paroi artérielle évoluent au fur et à mesure que le stent se dégrade. De plus, la dégradation du stent par hydrolyse peut être accélérée par ces contraintes : un couplage supplémentaire qui doit être pris en compte. Nous nous intéressons à la détermination de l’évolution des contraintes dans le stent et dans l’artère pendant le déploiement puis la dégradation du stent, ainsi qu’à l’influence de ces contraintes sur la dégradation du stent et sur le remodelage de la paroi, qui est également influencé par la dénudation de l’endothélium et par l’inflammation induite par l’implantation d’un BRS. Pour atteindre ces objectifs, nous avons développé un modèle 3D par éléments finis du déploiement et de la dégradation d’un BRS en acide polylactique tenant compte du couplage entre l’artère et le stent. Il permet notamment de prédire les zones de démantèlement dustent et l’évolution de l’épaisseur de la paroi artérielle en réponse à l’implantation d’un BRS. Etant donné que le modèle repose fortement sur des paramètres qui doivent être déterminés expérimentalement, nous nous sommes intéressés au développement d’une méthode expérimentale pour suivre la dégradation d’un BRS. Nous avons utilisé la tomographie par cohérence optique (OCT) pour suivre régulièrement la dégradation de stents déployés dans des tubes et immergés dans du sérum physiologique à 37°C pendant deux ans. Nous avons ensuite développé une méthode qui détecte automatiquement les struts des stents sur les images OCT et quantifie leur intensité de niveau de gris. Les résultats suggèrent que cette méthode automatisée d’analyse d’images OCT est un outil prometteur pour évaluer quantitativement l’état de dégradation d’un BRS. Enfin, nous nous sommes intéressés à la capacité d’une artère stentée à s’adapter à une modification du cisaillement ressenti. Nous avons étudié l’évolution de la lumière artérielle de porc stentés suivis in vivo par OCT ainsi que le cisaillement associé. Alors qu’un stent métallique bloque le remodelage artériel, nous avons observé qu’un BRS – probablement grâce au démantèlement du stade final de la dégradation – libère le vaisseau et permet ainsi l’adaptation de son diamètre de manière à diminuer le cisaillement et l’inadéquation avec l’artère non stentée. L’adaptation de la lumière artérielle permise par le démantèlement du stent pourrait être prise en compte dans de futurs modèles numériques. / Today, sent deployment is the most common treatment for symptomatic atherosclerosis. Bioresorbable stents (BRS) are based on the premise that a stent is needed only until arterial wound healing occurs after which it would be desirable for the stent to degrade so that the arterial wall recovers its natural compliance. Deployment of a stent profoundly alters the mechanical environment in the arterial wall, and these alterations play an important role in regulating the incidence of complications such as restenosis and neointimal hyperplasia. In the case of a BRS, the mechanical stresses in both the stent and the arterial wall evolve as the stent degrades. Furthermore, the hydrolysis-driven degradation of the stent can be accelerated by mechanical stresses in the stent, an additional coupling that needs to be taken into account. We are interested in determining the evolution of stresses in both the stent and the arterial wall during the stent deployment and degradation process and in elucidating the effect of these stresses on the stent degradation and on the remodeling process in the wall, which would also be influenced by the loss of endothelial cells and the amount of inflammation induced by the stent deployment and degradation. To this end, we have developed a 3D finite element model of the deployment and degradation of a polylactic acid (PLA) BRS that integrates the coupling between the stent and the artery.This allows one to predict the zones of dismantling of the stent and the evolution of the arterial thickness in response to a BRS stenting procedure. Since the model relies strongly on parameters that need to be determined experimentally, we became interested in developing methods to follow stent degradation. With this aim, we used optical coherence tomography (OCT) to image several BRS that were deployed into tubes and allowed to degrade in a saline solution at 37°C over a period of two years. We subsequently developed a versatile method for automatically detecting stent struts on the OCT images and quantifying the strut gray scale intensity. The results suggest that this automated method of OCT image analysis represents a promising tool to quantitatively assessing BRS degradation states. Lastly, we were interested in establishing the ability of a stented artery to adapt to a modification in its wall shear stress. Studying the in vivo evolution of the lumen of stented mini-swine arteries followed by OCT imaging allowed us to demonstrate that whereas a bare metal stent cages the artery, a BRS, presumably due to its degradation-induced dismantling, frees the vessel and enables it to adapt its lumen diameter in order to decrease its absolute level of shear stress and the compliance mismatch with the unstented portion of the artery. This lumen adaptation allowed by the stent dismantling could be taken into account in future computational models.

Consumers put higher demands on low environmental impact from the products they use, and the materials they consist of. As a result, more research is being made on finding environmentally friendly production techniques and materials. Hydrothermal carbonization (HTC) is a relatively environmentally friendly method that has been used in this study. Cellulose and pine, the latter, one sample with and one without bark, were carbonized at 220 °C and 240 °C for two hours. This generated solid carbon products that could be used in composites with the biopolymer Polylactide (PLA). The composites were thereafter extruded as filaments and used for 3D printing. X-ray powder diffraction (XRD), Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) showed that HTC of all precursors generated an amorphous carbon material, with carbon microspheres and increased aromaticity. Three different composites were produced from PLA and 0.1 wt% of the solid carbon products from all three precursors carbonized at 240 °C. Composites were also made from PLA and 1 wt% non-carbonized pine with bark, and 1 wt% of pine with bark carbonized at 240 °C. Filaments were extruded from neat PLA, as well as the composites of 0.1 wt% carbonized cellulose and 0.1 wt% carbonized pine with bark mentioned above. The filaments were used to 3D print six dog bones per filament according to the ISO standard ISO 527-2 1BA. There was one instance of clogging for each filament from the composite materials, but it was easily solved. No mechanical tests could be performed, although the 3D printed models’ physical properties were visually observed, and no deficiencies were found. Both extrusion and 3D printing were successful. / Konsumenter ställer högre krav på att material och produkter de använder har liten påverkan på miljön. Till följd av detta lägger forskningen mer resurser på att hitta miljövänliga tillverkningsmetoder och material. Hydrotermisk karbonisering (HTC) är en relativt miljövänlig process som har använts i denna studie. Tall (ett prov med och ett utan bark) samt cellulosa karboniserades vid 220 °C och 240 °C i två timmar, för att på detta vis producera en fast kolprodukt som kunde användas i en komposit med biopolymeren Polylaktid (PLA). Kompositen extruderades sedan till filament som användes vid 3D printing. Röntgenpulverdiffraktion (XRD), Svepelektronmikroskopi (SEM) och Fourier-transform infraröd spektroskopi (FTIR) visade på att HTC hade genererat amorfa kolmaterial, med mikrosfärer och ökad aromaticitet från både cellulosa och båda tallproverna. Samtliga produkter från karbonisering vid 240 °C användes för att göra tre olika kompositer med vardera 0,1 vikt% kolmaterial. Kompositer tillverkades även från PLA och 1 vikt% tall med bark, samt 1 vikt% tall med bark karboniserad vid 240 °C. Filament extruderades av ren PLA samt ovan nämnda kompositer med 0.1 vikt% karboniserad cellulosa och 0.1 vikt% karboniserad tall med bark. Dessa användes vid 3D printing för att skriva ut sex hundben per filament, enligt ISO standarden ISO 527-2 1BA. Vid ett tillfälle för vardera av de två kompositerna täpptes mynningen till 3D skrivaren igen av partiklar i filamenten. Detta löstes dock enkelt. Mekaniska tester kunde tyvärr inte utföras på hundbenen, men inga fysiska brister beskådades på dem. Både extrudering och 3D printing var lyckade.

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