Introdução: A aplicação clínica de biomateriais está se expandindo para diversas especialidades médicas. Dentre os diversos tipos de biomateriais, os classificados como temporários merecem atenção especial, pois são assimilados pelo organismo após exercerem sua função, evitando, assim, procedimento cirúrgico para sua retirada. O copolímero de poli (ácido láctico-co-glicólico) (PLGA) é um tipo de biomaterial temporário, rotineiramente utilizado na medicina na forma de fios de sutura e implantes ortopédicos. A mistura do PLGA com o poli (isopreno) resulta em uma blenda (PLGA / PI), de alta resistência e tenacidade, que foi desenvolvida pelo Laboratório de Biomateriais do Instituto de Engenharia da UFRGS. Entretanto, não existem estudos “in vivo” testando a reação óssea desta blenda. Objetivo: Testar a histotoxicidade da blenda de PLGA / PI em relação ao biopolímero já consagrado PLGA. Método: Foram utilizados 46 ratos machos wistar (Rattusnorvegicus - linhagem albina), divididos em 2 grupos conforme o material implantado (PLGA ou PLGA / PI) na calota craniana, e subdivididos em tempos de morte (15, 30, 60 e 90 dias). Os procedimentos foram realizados na Unidade de Experimentação Animal (UEA) do Hospital de Clínicas de Porto Alegre (HCPA). Após a morte, a calota craniana foi retirada, submetida ao exame histopatológico e aplicado o escore de Dadas e cols (14) modificado. Resultados: A diferença da histotoxicidade dos dois materiais não foi significativa nos períodos 15, 30 e 90 dias, porém foi significativa no período 60 dias. Conclusão: A histotoxicidade do PLGA / PI, ao final do estudo (90 dias), foi semelhante ao PLGA, demonstrando equivalência em longo prazo. O período de 60 dias pós-cirúrgico (grupo da blenda) foi o único em que a histotoxicidade mostrou-se significativamente maior. Mais estudos devem ser feitos para melhorar o entendimento desta variação. / Introduction: Clinical application of biomaterials is expanding to various medical specialties. Among the different types of biomaterials, those classified as temporary deserve special attention because they are assimilated by the body after exercising their function, thereby avoiding surgical procedure for their removal. Co-polymer poly (lactic-co-glycolic acid) (PLGA) is a type of temporary biomaterial, routinely used in medicine as suture threads and orthopedic implants. The mixture of PLGA with poly (isoprene) results in a high-strength and thoughness blend (PLGA / PI), developed by the Biomaterials Laboratory of the Engineering Institute/ UFRGS. However, there are no studies “in vivo” testing the bone reaction of that blend. Objective: To Test histotoxicity of PLGA / PI blend over the already established biopolymer, PLGA. Method: Forty six male Wistar rats (Rattus norvegicus – albino strain), divided into 2 groups according to the material (PLGA or PLGA / PI) implanted in the skull and sub divided into periods of death (15, 30, 60 and 90 days). The procedures were developed in the Animal Experiment Unit (AEU) of Hospital de Clínicas de Porto Alegre (HCPA). After death, the skull was removed, submitted to histopathologic examination and the modified Dadas’ et all score was used (14). Results: The histotoxicity difference of the two materials was not significant in the periods of 15, 30 and 90 days, but it was significant in the period of 60 days. Conclusion: At the end of the study (90 days), the PLGA / PI histotoxicity was similar to PLGA, showing longterm equivalence. The 60-day post-surgical period was the only one in which histotoxicity was significantly higher (blend group). More studies shall be done in in order to better understand that variation.

Introdução: A aplicação clínica de biomateriais está se expandindo para diversas especialidades médicas. Dentre os diversos tipos de biomateriais, os classificados como temporários merecem atenção especial, pois são assimilados pelo organismo após exercerem sua função, evitando, assim, procedimento cirúrgico para sua retirada. O copolímero de poli (ácido láctico-co-glicólico) (PLGA) é um tipo de biomaterial temporário, rotineiramente utilizado na medicina na forma de fios de sutura e implantes ortopédicos. A mistura do PLGA com o poli (isopreno) resulta em uma blenda (PLGA / PI), de alta resistência e tenacidade, que foi desenvolvida pelo Laboratório de Biomateriais do Instituto de Engenharia da UFRGS. Entretanto, não existem estudos “in vivo” testando a reação óssea desta blenda. Objetivo: Testar a histotoxicidade da blenda de PLGA / PI em relação ao biopolímero já consagrado PLGA. Método: Foram utilizados 46 ratos machos wistar (Rattusnorvegicus - linhagem albina), divididos em 2 grupos conforme o material implantado (PLGA ou PLGA / PI) na calota craniana, e subdivididos em tempos de morte (15, 30, 60 e 90 dias). Os procedimentos foram realizados na Unidade de Experimentação Animal (UEA) do Hospital de Clínicas de Porto Alegre (HCPA). Após a morte, a calota craniana foi retirada, submetida ao exame histopatológico e aplicado o escore de Dadas e cols (14) modificado. Resultados: A diferença da histotoxicidade dos dois materiais não foi significativa nos períodos 15, 30 e 90 dias, porém foi significativa no período 60 dias. Conclusão: A histotoxicidade do PLGA / PI, ao final do estudo (90 dias), foi semelhante ao PLGA, demonstrando equivalência em longo prazo. O período de 60 dias pós-cirúrgico (grupo da blenda) foi o único em que a histotoxicidade mostrou-se significativamente maior. Mais estudos devem ser feitos para melhorar o entendimento desta variação. / Introduction: Clinical application of biomaterials is expanding to various medical specialties. Among the different types of biomaterials, those classified as temporary deserve special attention because they are assimilated by the body after exercising their function, thereby avoiding surgical procedure for their removal. Co-polymer poly (lactic-co-glycolic acid) (PLGA) is a type of temporary biomaterial, routinely used in medicine as suture threads and orthopedic implants. The mixture of PLGA with poly (isoprene) results in a high-strength and thoughness blend (PLGA / PI), developed by the Biomaterials Laboratory of the Engineering Institute/ UFRGS. However, there are no studies “in vivo” testing the bone reaction of that blend. Objective: To Test histotoxicity of PLGA / PI blend over the already established biopolymer, PLGA. Method: Forty six male Wistar rats (Rattus norvegicus – albino strain), divided into 2 groups according to the material (PLGA or PLGA / PI) implanted in the skull and sub divided into periods of death (15, 30, 60 and 90 days). The procedures were developed in the Animal Experiment Unit (AEU) of Hospital de Clínicas de Porto Alegre (HCPA). After death, the skull was removed, submitted to histopathologic examination and the modified Dadas’ et all score was used (14). Results: The histotoxicity difference of the two materials was not significant in the periods of 15, 30 and 90 days, but it was significant in the period of 60 days. Conclusion: At the end of the study (90 days), the PLGA / PI histotoxicity was similar to PLGA, showing longterm equivalence. The 60-day post-surgical period was the only one in which histotoxicity was significantly higher (blend group). More studies shall be done in in order to better understand that variation.

Introdução: A aplicação clínica de biomateriais está se expandindo para diversas especialidades médicas. Dentre os diversos tipos de biomateriais, os classificados como temporários merecem atenção especial, pois são assimilados pelo organismo após exercerem sua função, evitando, assim, procedimento cirúrgico para sua retirada. O copolímero de poli (ácido láctico-co-glicólico) (PLGA) é um tipo de biomaterial temporário, rotineiramente utilizado na medicina na forma de fios de sutura e implantes ortopédicos. A mistura do PLGA com o poli (isopreno) resulta em uma blenda (PLGA / PI), de alta resistência e tenacidade, que foi desenvolvida pelo Laboratório de Biomateriais do Instituto de Engenharia da UFRGS. Entretanto, não existem estudos “in vivo” testando a reação óssea desta blenda. Objetivo: Testar a histotoxicidade da blenda de PLGA / PI em relação ao biopolímero já consagrado PLGA. Método: Foram utilizados 46 ratos machos wistar (Rattusnorvegicus - linhagem albina), divididos em 2 grupos conforme o material implantado (PLGA ou PLGA / PI) na calota craniana, e subdivididos em tempos de morte (15, 30, 60 e 90 dias). Os procedimentos foram realizados na Unidade de Experimentação Animal (UEA) do Hospital de Clínicas de Porto Alegre (HCPA). Após a morte, a calota craniana foi retirada, submetida ao exame histopatológico e aplicado o escore de Dadas e cols (14) modificado. Resultados: A diferença da histotoxicidade dos dois materiais não foi significativa nos períodos 15, 30 e 90 dias, porém foi significativa no período 60 dias. Conclusão: A histotoxicidade do PLGA / PI, ao final do estudo (90 dias), foi semelhante ao PLGA, demonstrando equivalência em longo prazo. O período de 60 dias pós-cirúrgico (grupo da blenda) foi o único em que a histotoxicidade mostrou-se significativamente maior. Mais estudos devem ser feitos para melhorar o entendimento desta variação. / Introduction: Clinical application of biomaterials is expanding to various medical specialties. Among the different types of biomaterials, those classified as temporary deserve special attention because they are assimilated by the body after exercising their function, thereby avoiding surgical procedure for their removal. Co-polymer poly (lactic-co-glycolic acid) (PLGA) is a type of temporary biomaterial, routinely used in medicine as suture threads and orthopedic implants. The mixture of PLGA with poly (isoprene) results in a high-strength and thoughness blend (PLGA / PI), developed by the Biomaterials Laboratory of the Engineering Institute/ UFRGS. However, there are no studies “in vivo” testing the bone reaction of that blend. Objective: To Test histotoxicity of PLGA / PI blend over the already established biopolymer, PLGA. Method: Forty six male Wistar rats (Rattus norvegicus – albino strain), divided into 2 groups according to the material (PLGA or PLGA / PI) implanted in the skull and sub divided into periods of death (15, 30, 60 and 90 days). The procedures were developed in the Animal Experiment Unit (AEU) of Hospital de Clínicas de Porto Alegre (HCPA). After death, the skull was removed, submitted to histopathologic examination and the modified Dadas’ et all score was used (14). Results: The histotoxicity difference of the two materials was not significant in the periods of 15, 30 and 90 days, but it was significant in the period of 60 days. Conclusion: At the end of the study (90 days), the PLGA / PI histotoxicity was similar to PLGA, showing longterm equivalence. The 60-day post-surgical period was the only one in which histotoxicity was significantly higher (blend group). More studies shall be done in in order to better understand that variation.

Implantable sensors have been extensively investigated to facilitate diagnosis or to provide a means to generated closed loop control of therapy by yielding in vivo measurements of physical and chemical signals. Biodegradable sensors which degrade gradually after they are no longer functionally needed exhibit great potential in acute or shorter-term medical diagnostic and sensing applications due to the advantages of (a) exclusion of the need to a secondary surgery for sensor removal, and (b) reduction of the risk of long-term infection. The objective of this research is to design and characterize microfabricated RF wireless pressure sensors that are made of completely biodegradable materials and degrade at time-controlled manner (in the order of years and months). This was achieved by means of investigation of appropriate biodegradable materials and development of appropriate fabrication processes for these non-standard (Microelectromechanical systems) MEMS materials. Four subareas of research are performed: (1) Design of sensors that operate wirelessly and are made of biodegradable materials. The structure of the wireless sensor consists a very compact and relatively simple design of passive LC resonant circuits embedded in a polymer dielectric package. To design the sensor with a particular resonant frequency range, an electromagnetic model of the sensor and a mechanical model for circular plate are developed. The geometry of the sensor is established based on the analytical and finite element simulations results. (2) Investigation of the biodegradable materials in the application of implantable biodegradable wireless sensors to achieve controllable degradation lifetimes. Commercially available and FDA approved biodegradable polymers poly(L-lactic acid) (PLLA) and a "shell-core" structure of poly(lactic-co-glycolic acid) (PLGA) and polyvinyl alcohol (PVA) are utilized as the dielectric package for slow and rapid degradation sensors, respectively. Biodegradable metallic zinc and zinc/iron couples are chosen as conductor materials. The degradation behavior of Zn and Zn/Fe-couple are investigated in vitro. (3) Development of novel fabrication processes. The process exploit the advantages of MEMS technology in fabricating miniaturized devices, while protecting vulnerable biodegradable materials from the strong and/or hazardous chemicals that are commonly used in conventional MEMS fabrication process. These new processes enable the fabrication of biocompatible and biodegradable 3-D devices with embedded, near-hermetic cavities. (4) Testing the pressure response functionality and studying the degradation behavior of the wireless biodegradable pressure sensors. Both PLLA-based and PLGA/PVA-based sensors are characterized in vitro by being immersed in 0.9% saline for prolonged time. All the sensors exhibit three stages of behavior in vitro: equilibration, functional lifetime, and performance degradation. During the functional lifetime, most sensors exhibit fully stable functionality. The PLLA-based sensors show no significant weight loss within 8 month and are expected to fully degrade after 2 years, while the PLGA/PVA-based sensors can degrade completely within 26 days.

L’Ingénierie tissulaire (IT) est un domaine interdisciplinaire qui applique les principes de l'ingénierie et des sciences de la vie au développement de substituts biologiques afin de restaurer, maintenir ou améliorer la fonction tissulaire. Sa première application consiste à remplacer les tissus endommagés par des produits cellulaires artificiels. Une autre application de l’IT est basée sur la production des modèles en 2 et 3 dimensions (2D et 3D) pour des études biologiques et pharmacologiques in vitro. Ces modèles ou remplacements de tissus peuvent être fabriqués en utilisant des différentes méthodes de médecine, biologie, chimie, physique, informatique et mécanique, fournissant un micro-environnement spécifique avec différents types de cellules, facteurs de croissance et matrice. L'un des principaux défis de l'IT la pénétration cellulaire limitée dans les parties internes des biomatériaux poreux. Une faible viabilité cellulaire au centre du produit d'IT est la conséquence de la diffusion limitée d'oxygène et de nutriments du fait d’un réseau vasculaire insuffisant dans l'ensemble de la construction 3D. Le BioAssembage couche-par-couche est une nouvelle approche basée sur l'assemblage de petites constructions cellularisées permettant une distribution cellulaire homogène et une vascularisation plus efficace dans des produits d’IT.Notre hypothèse est que l'approche couche-par-couche est plus adaptée à la régénération osseuse que l'approche conventionnelle de l'IT. L'objectif principal de cette thèse était d'évaluer les avantages de l'approche couche-par-couche en utilisant des membranes de polymères imprimées en 3D et ensemencées avec des cellules primaires humaines. Nous avons évalué l'efficacité de la formation du réseau vasculaire in vivo dans toute la construction 3D en utilisant cette approche et en la comparant à l'approche conventionnelle basée sur l'ensemencement des cellules sur la surface des scaffolds massives. Il n'y avait pas de différence significative dans le nombre de vaisseaux sanguins formés en 3D au niveau des parties externes des constructions implantées en site souscutanée chez des souris. Mais dans les parties internes des implants qui n'étaient pas en contact direct avec un tissu hôte, nous avons pu observer une formation des vaisseaux sanguins statistiquement plus efficace lorsque l'approche du bio-assemblage couche-par-couche a été utilisée. Cette formation de réseau vasculaire était plus importante dans le cas de co-cultures que de mono-cultures.Il y avait plusieurs objectifs secondaires dans ce travail. Le premier était de fabriquer des constructions 3D cellularisées pour l'IT en utilisant des membranes d'acide polylactique (PLA) et des cellules primaires humaines : des cellules de stroma de moelle osseuse humaine (HBMSCs) isolées de la moelle osseuse et des cellules progénitrices endothéliales (EPCs) isolées du sang du cordon ombilical. Ensuite, nous avons comparé différentes technologies de fabrication des scaffolds: impression 3D directe à partir de poudre de PLA et impression par fil fondu en utilisant une imprimante commerciale et une autre fabriquée sur mesure. L'imprimante sur mesure a permis le plus haut niveau de résolution d'impression spécialement adaptée à la forme et la taille des pores. Par ailleurs, nous avons évalué différents systèmes de stabilisation pour l'assemblage couche par couche : l’utilisation de clips en PLA imprimés en 3D a fourni une stabilisation plus efficace pour empiler les membranes PLA couche par couche. Un autre avantage de ce système de stabilisation est qu'il peut être implanté avec des implants. Ensuite, nous avons observé une prolifération et une différenciation cellulaire plus efficaces lorsque le système de co-culture était utilisé, en comparaison avec des mono-cultures.L'approche du bioassemblage couche-par-couche semble être une solution appropriée pour une vascularisation efficace dans des structures 3D entières d'ingénierie tissulaire. / Tissue Engineering (TE) is “an interdisciplinary field that applies principles of engineering and the life sciences toward development of biological substitutes that restore, maintain, or improve tissue function”. The First application of TE is to replace damaged tissues by artificial cell-materials products of tissue engineering (TE). Another TE application is to produce 2 or 3 dimensional (2D and 3D) models for biological and pharmacological in vitro studies. These models or tissue replacements can be fabricated using a combination of different interdisciplinary methods of medicine, biology, chemistry, physics, informatics and mechanics, providing specific micro-environment with different cell types, growth factors and matrix.One of the major challenges of tissue engineering is related to limited cell penetration in the inner parts of porous biomaterials. Poor cell viability in the center of engineered tissue is a consequence of limited oxygen and nutrients diffusion due to insufficient vascular network within the entire construct. Layer-by-layer (LBL) BioAssembly is a new approach based on assembly of small cellularized constructs that may lead to homogenous cell distribution and more efficient three dimensional vascularization of large tissue engineering constructs.Our hypothesis is that LBL Bioassembly approach is more suitable for bone regeneration than conventional tissue engineering approach. The primary objective of this thesis was to evaluate the advantages of LBL Bioassembly approach using 3D-printed polymer membranes seeded with human primary cells. We have evaluated the efficiency of vascular network formation in vivo within entire 3D tissue engineering construct using LBL bioassembly approach and comparing it to the conventional approach based on seeding of cells on the surface of massive 3D scaffolds. There was no significant difference in number of formed blood vessels in 3D at the outer parts of constructs implanted subcutaneously in mice 8 weeks post-implantation. But in the inner parts of implants which were not in direct contact with a host tissue, we could observe statistically more blood vessel formation when LBL bioassembly approach was used. This vascular network formation was more important in the case of co-cultures than mono-vultures of HBMSCs.There were several secondary objectives in this work. The first was to fabricate cellularized 3D constructs for bone tissue engineering using poly(lactic) acid (PLA) membranes and human primary cells: human bone marrow stroma cells (HBMSCs) isolated from the bone marrow, and endothelial progenitor cells (EPCs) isolated from the umbilical cord blood. Then, we have compared different Additive manufacturing technologies to fabricate scaffolds: direct 3D printing (3DP) starting from PLA powder dissolved in chloroform and fused deposition modelling (FDM) using a commercial or a custom-made printer with different resolutions.The custom-made printer equipped with 100 μm nozzle allowed the highest level of printing resolution concerning pores shape and size. In the meantime we evaluated different stabilization systems for layer-by-layer assembling of PLA membranes with human primary cells: the use of 3D printed PLA clips provided the most efficient stabilization to stack PLA membranes in 3D. Another advantage of this stabilization system is that it could be implanted together with LBL constructs. Then we investigated the most suitable cell culture system for such constructs and we observed more efficient cell proliferation and differentiation when co-culture system is used, comparing to mono-cultures.LBL bioassembly approach seems to be suitable solution for efficient vascularization within entire large 3D tissue engineering constructs especially when co-cultures of mesenchymal and endothelial cells are used.

Abstract Bone tissue engineering has become a rapidly expanding research area because it offers a promising new approach for bone repair and regeneration. Compared to traditional autograft and allograft procedures, bone tissue engineering techniques based on the use of scaffolding materials in combination with autogenous stem cells can eliminate problems of donor site morbidity associated with the harvest of bone tissue, and its short supply. Clearly, the choices of material as well as a scaffold design that enhance bone regeneration are major challenges in the tissue engineering approach. Fibers in the micro-range in combination with textile-based technologies are consider as potential routes for the production of complex scaffolds since they can be used to generate a wide range of morphological structures and geometrically varied structures with high precision. Therefore in this thesis the specific objects were to: (i) develop a biocompatible composite fiber from poly(lactic acid) (PLA) and hydroxyapatite (HA) by melt spinning, (ii) design a 3D textile scaffold utilizing weaving and (iii) evaluate the scaffolds’ performance as a bone substitute material in vitro. In the present study PLA/HA composite fibers were successfully produced, and found to possess sufficient mechanical strength even at high loading concentrations (i.e. 20wt %), to be useful in a textile process. In addition, the material was shown to be biocompatible and the presence of HA in the PLA composite significantly enhanced the initial cell attachment. In a 3D woven scaffold, bone marrow derived human mesenchymal stem cells (hMSCs) differentiated into osteoblasts and mineralized bone formation in vitro was observed through-the-thickness of the scaffold. Taken together, these results indicate the potential feasibility of PLA/HA composite fiber in a 3D woven scaffold for use as a bone substitute material in tissue engineering applications. / Tiivistelmä Luupuutosten korvaaminen kudosteknologisesti on kehittynyt nopeasti ja tutkimustulokset tarjoavat lupaavia mahdollisuuksia tuottaa uutta luuta luupuutosalueelle. Perinteisiin potilaan omasta luusta tehtyihin luusiirteisiin ja pankkiluusiirteisiin verrattuna potilaan omat kantasolut voivat vähentää ongelmia, joita ovat siirremateriaalin rajallinen saatavuus ja vieraan kudoksen aiheuttamat reaktiot. On tärkeä etsiä hyviä materiaaleja, joista voidaan valmistaa sellaisia kolmiulotteisia (3D) rakenteita, joilla tehostetaan luun paranemista ja uuden luun muodostumista. Kutomalla tuotetut tukirakenteet mahdollistavat kantasolusiirteille kolmiulotteisuuden, jota voidaan säädellä monipuolisesti ja tarkasti. Tämän väitöstutkimuksen tarkoituksena oli: (i) kehittää bioyhteensopiva kuitu maitohappopolymeeristä poly lactic acid (PLA) ja hydroksiapatiitista (HA) kuituekstruusiolla, (ii) suunnitella ja kutoa tästä kuidusta 3D tekstiilirakenne, ja (iii) tutkia sen toimivuus ja ominaisuudet luunmuodostusta tukevana materiaalina soluviljelyolosuhteissa. Tämä tutkimus osoittaa, että PLA kuitua voidaan seostaa hydroksiapatiitilla, ja PLA/HA kuidut ovat mekaanisesti kestäviä sisältäessään jopa 20 painoprosenttia hydroksiapatiittia. Siten kuidut ovat tekstiilin valmistuksessa käyttökelpoisia. Lisäksi materiaali osoittautui bioyhteensopivaksi, ja hydroksiapatiitti paransi solujen tarttumista PLA kuituun viljelyn alkuvaiheessa. Ihmisen luuytimestä peräisin olevat sidekudoksen kantasolut (hMSCs) erilaistuivat soluviljelmässä luuta muodostaviksi soluiksi eli osteoblasteiksi, ja tuottivat mineralisoitunutta luun väliainetta kautta koko kudotun tukirakenteen. Johtopäätöksenä on, että PLA/HA yhdistelmäkuitua voidaan kutoa kolmiulotteiseksi tukirakenteeksi, ja sitä on mahdollista käyttää apuna korvattaessa luupuutoksia kudosteknologian keinoin.

No description available.

Doctor of Philosophy / Department of Grain Science and Industry / X. Susan Sun / Biobased polymers derived from renewable resources are increasingly important due to acute concerns about the environmental issues and limited petroleum resources. Poly(lactic acid) (PLA) is such a polymer that has shown great potential to produce biodegradable plastics. However, low glass transition temperature (Tg), low thermal stability, slow biodegradation rate, and high cost limit its broad applications. This dissertation seeks to overcome these limitations by reinforcing PLA with inorganic nanoparticles and low-cost agricultural residues. We first synthesized PLA nanocomposites by in situ melt polycondensation of L-lactic acid and surface-hydroxylized nanoparticles (MgO nanocrystals and TiO2 nanowires) and investigated the structure-property relationships. PLA grafted nanoparticles (PLA-g-MgO, PLA-g-TiO2) were isolated from the bulk nanocomposites via repeated dispersion/centrifugation processes. The covalent grafting of PLA chains onto nanoparticle surface was confirmed by Fourier transform infrared spectroscopy and thermalgravimetric analysis (TGA). Transmission electron microscopy and differential scanning calorimetry (DSC) results also sustained the presence of the third phase. Morphological images showed uniform dispersion of nanoparticles in the PLA matrix and demonstrated a strong interfacial interaction between them. Calculation based on TGA revealed that more than 42.5% PLA was successfully grafted into PLA-g-MgO and more than 30% was grafted into PLA-g-TiO2. Those grafted PLA chains exhibited significantly increased thermal stability. The Tg of PLA-g-TiO2 was improved by 7 °C compared with that of pure PLA. We also reinforced PLA with low-value agricultural residues, including wood flour (WF), soy flour (SF), and distillers dried grains with solubles (DDGS) by thermal blending. Tensile measurements and morphological images indicated that methylene diphenyl diisocyanate (MDI) was an effective coupling agent for PLA/WF and PLA/DDGS systems. MDI compatibilized PLA/WF and PLA/DDGS composites showed comparable tensile strength and elongation at break as pure PLA, with obviously increased Young’s modulus. Increased crystallinity was observed for PLA composites with SF and DDGS. Such PLA composites have similar or superior properties compared with pure PLA, especially at a lower cost and higher biodegradation rate than pure PLA. The results from this study are promising. These novel PLA thermoplastic composites with enhanced properties have potential for many applications, such as packaging materials, textiles, appliance components, autoparts, and medical implants.

This project investigates the moisture barrier properties of bio-based polymers and ways of improving them. The first section addresses the effect of crystallinity on the water permeability of poly(lactic acid) (PLA). The second section investigates PLA/talc composites and PLA/ montmorillonite nanocomposites. The third section is focused on a new polymer, polybutylene succinate (PBS), and its nanocomposites with montmorillonite. In the first section, the water vapour transmission rates (WVTR) through samples of polylactic acid of different crystallinities have been measured. Three different grades of commercial PLA were used with different ratios of L-lactide and D-lactide to give a range of crystallinities from 0 to 50%. Sheets of PLA were prepared by melt compounding followed by compression moulding and annealing at different temperatures and for different times to give the range of crystallinities required. Crystallinity was measured by differential scanning calorimetry (DSC) and the morphology of the samples was observed under crossed polars in a transmitted light microscope. Water vapour transmission rates through the films were measured at 38°C and at a relative humidity of 90%. It was found that the measured values of WVTR decreased linearly with increasing crystallinity of the PLA from 0 to 50%. The results are discussed in terms of the effect of crystallinity on solubility and shown to fit the tortuous path model. The model was also successfully used to explain published data on water permeability of polyethylene terephthalate. In the second section, a series of PLA/talc composites and PLA/ montmorillonite nanocomposites were prepared by melt compounding followed by compression moulding. The morphologies of the composites were investigated using transmission electron microscopy (TEM) and wide-angle X-ray diffraction (WAXD) and it was found that the fillers were well dispersed in the polymer matrix. The average aspect ratio of the compounded talc was found to be 8, and that of the nanoclay was found to be 50. Water vapour transmission rates (WVTR) through the films were measured at 38°C and at a relative humidity of 90%. It was found that the measured values of WVTR decreased with increasing filler content and the results gave good agreement with predictions from the Nielsen tortuous path model. In the third section, PBS/ montmorillonite nanocomposites were prepared by melt compounding followed by compression moulding. The melting and crystallisation behaviour of the pure PBS samples were investigated using differential scanning calorimetry (DSC) and cross polarised optical microscopy. A slight decrease of the degree of crystallinity was found in PBS containing 5% nanoclay. The morphology of the composites was investigated using transmission electron microscopy (TEM) and wide-angle X-ray diffraction (WAXD) and it was confirmed that that composite structures were intercalated. Water vapour transmission rates (WVTR) through the PBS sheets were measured using a MOCON Permatran-W®398. The measured values of WVTR decreased with increasing nanoclay content. However, the experimental values were all higher than the values predicted by the Nielsen tortuosity model. This result shows that in the case of PBS, which is a highly crystalline polymer, the nanoclay is not as well dispersed and is not as effective in reducing water vapour permeability as in the case of PLA.

Nearly 60 m tonnes of waste is produced annually in Europe from “plastic packaging” engendering significant challenges for legislative controls and minimisation of environmental impact. There is an increasing demand for biodegradable packaging, which can be disposed of with minimum environmental impact, but the growing market is still in its infancy predominantly due to a lack of materials having environmental, practical and economic suitability. This research project dealt with some processing challenges of environmentally friendly packaging materials from renewable resources, as a long term solution to mitigate some issues associated with oil based plastic packaging. In this work, novel Polylactic acid (PLA) and starch based composites were developed with the requisite technical properties to fill the gap in the food packaging and cosmetic packaging industry. It was found that starch can be incorporated in a PLA matrix at the 10% level without difficulty in processing in the presence of 2% methyldiphenyl diisocyante. The blend shows properties similar to pure PLA. It was also found that the elongation at break and impact properties of PLA can be increased remarkably by the addition of a biostrength impact modifier. Furthermore, mixing of PLA and starch in the blend is efficient when the PLA particle size is reduced. It was also found that flexible and tougher PLA/starch blend pellets, that can be injection moulded, can be produced by an extrusion process with a range of additives. Each additive has a maximum level that exhibits optimum properties. The blends also established that 15% starch can be incorporated into the PLA matrix to reduce the cost without any processing difficulties. Encouragingly, the presence of an impact modifier in the PLA/starch blends has shown more desirable properties. Furthermore, the mechanical properties of the pellets exposed to increased residence time in the injection moulding barrel and of the test specimens stored for 9 months at 21ºC were also satisfactory for the new blend. The overall results exhibited some attractive properties in the tri blend system, which can be easily adopted by the plastics industry for development of an injection moulded product within the scope of applications such as dry food packaging or cosmetic packaging. A further finding of this project is that biodegradation under a home composting environment can be improved by incorporating starch and certain other modifiers into PLA.