Dissertations / Theses on the topic 'Poly(L-lactide-co-glycolide)'

Aquesta tesi aprofundeix en l'estudi de les nanopartícules de poli-(D, L-làctid-co-glicòlid) (PLGA) o poli-(D, L-làctid) (PLA) i les seves nanopartícules homòlogues recobertes amb polietilenglicol (PEG) com a sistemes de vehiculització per fotosensibilitzadors emprats en teràpia fotodinàmica. En primer lloc s'ha investigat la influència de la matriu polimèrica i del recobriment superficial amb PEG sobre les característiques fisicoquímiques, fotofísiques i fotobiològiques de suspensions amb un fotosensibilitzador atrapat físicament. El recobriment amb PEG confereix una major estabilitat a les nanopartícules en medi biològic. L'oxigen singlet generat en les nanopartícules de PLGA resta confinat en el seu interior, mentre que la presència de PEG facilita la difusió de l'oxigen singlet al medi extern, així com un alliberament més ràpid del fotosensibilitzador. En ambdós casos, el fotosensibilitzador es localitza als lisosomes a l'interior de les cèl·lules i indueix la mort cel·lular per apoptosi, la qual cosa indica que ambdós tipus de nanopartícules alliberen el fotosensibilitzador dins de la cèl·lula. L'efecte fototòxic és tanmateix major i més ràpid per a les nanopartícules PEGilades d'acord amb les observacions d'oxigen singlet. El paper de l'estructura química del fotosensibilitzador en les propietats fotofísiques i fotobiològiques de les nanopartícules també s'ha investigat. Els fotosensibilitzadors no metal·lats s'agreguen dins de les nanopartícules, mentre que els metal·lats romanen en forma monomèrica. Les seves propietats químiques també influeixen en la seva localització i, en conseqüència, en les propietats fotofísiques de les nanopartícules quan hi estan units covalentment, encara que hi siguin fotofísicament actius. Els fotosensibilitzadors encapsulats són capaços d'induir mortalitat cel·lular encara que estiguin agregats dins de les nanopartícules, mentre que els que estan units covalentment no ho són. Aquest fet permet concloure que l'alliberament del fotosensibilitzador dins de la cèl·lula és crucial per aconseguir una resposta fotodinàmica, i que les nanopartícules de PEG-PLGA no són internalitzades per les cèl·lules sinó que alliberen el fotosensibilitzador en la superfície cel·lular, cosa que no passa quan el fotosensibilitzador s'uneix covalentment a les nanopartícules. Finalment, s'ha examinat el potencial de la vehiculització activa mitjançant la conjugació del pèptid cRGDfK a la superfície de les nanopartícules. La presència de PEG és essencial per aconseguir un major augment en la concentració cel·lular de fotosensibilitzador. No obstant això, aquesta major concentració no produeix una major fototoxicitat en comparació amb les nanopartícules no marcades, el que suggereix que una major internalització no és l'únic factor important en el resultat final de la teràpia fotodinàmica.<br>Esta tesis profundiza en el estudio de nanopartículas de poli-(D,L-láctido-co-glicólido) (PLGA) o poli-(D,L-láctido) (PLA) y sus homólogas recubiertas con polietilenglicol (PEG) como sistemas de vehiculización para fotosensibilizadores empleados en terapia fotodinámica. En primer lugar se ha investigado la influencia de la matriz polimérica y del recubrimiento superficial con PEG sobre las características fisicoquímicas, fotofísicas y fotobiológicas de suspensiones con un fotosensibilizador atrapado físicamente. El recubrimiento con PEG confiere una mayor estabilidad a las nanopartículas en medio biológico. El oxígeno singlete generado en las nanopartículas de PLGA permanece confinado en su interior, mientras que la presencia de PEG facilita la difusión del oxígeno singlete al medio externo, así como una liberación más rápida del fotosensibilizador. En ambos casos, éste se localiza en los lisosomas en el interior de las células e induce muerte celular por apoptosis, lo que indica que ambos tipos de nanopartículas liberan el fotosensibilizador dentro de la célula. El efecto fototóxico es sin embargo superior y más rápido para las nanopartículas PEGiladas de acuerdo con las observaciones de oxígeno singlete. El papel de la estructura química del fotosensibilizador en las propiedades fotofísicas y fotobiológicas de las nanopartículas también se ha investigado. Los fotosensibilizadores no metalados se agregan dentro de las nanopartículas, mientras que los metalados restan en forma monomérica. Cuando éstos se unen covalentemente a las nanopartículas, sus propiedades químicas influyen en su localización en las mismas y, en consecuencia, en las propiedades fotofísicas de la suspensión, aunque preservan sus propiedades fotofísicas. Los fotosensibilizadores encapsulados son capaces de inducir mortalidad celular aunque estén agregados dentro de las nanopartículas, mientras que los que están unidos covalentemente no lo son. Este hecho permite concluir que la liberación del fotosensibilizador dentro de la célula es crucial para lograr una respuesta fotodinámica, y que las nanopartículas de PEG-PLGA no son internalizadas por las células, sino que liberan el fotosensibilizador en la superficie celular, lo que no ocurre cuando el fotosensibilizador se une covalentemente a las nanopartículas. Finalmente, se ha examinado el potencial de la vehiculización activa mediante la conjugación del péptido cRGDfK a la superficie de las nanopartículas. La presencia de PEG es esencial para lograr un mayor aumento en la concentración celular de fotosensibilizador. Sin embargo, dicha mayor concentración no produce una mayor fototoxicidad en comparación con las nanopartículas no marcadas, lo que sugiere que una mayor internalización no es el único factor importante en el resultado final de la terapia fotodinámica.<br>This thesis reports the study of poly-(D,L-lactide-co-glycolide) (PLGA) and poly-(D,L-lactide) (PLA) nanoparticles and their poly-(ethylene glycol) (PEG)-coated counterparts as delivery systems for photosensitizers in photodynamic therapy. First, the influence of the polymeric matrix and of the PEG surface coating on the physicochemical, photophysical and photobiological properties of nanoparticle suspensions containing a physically entrapped photosensitizer has been studied. PEG coating confers a higher stability to the nanoparticles in biological media containing serum proteins. Singlet oxygen produced in bare PLGA nanoparticles remains confined within them, while PEG surface coating facilitates singlet oxygen diffusion to the external medium as well as a faster drug release from the nanoparticles. In both cases, the photosensitizer localizes in lysosomes and induces cell death by apoptosis. The phototoxic effect is superior and faster for PEGylated NPs, in agreement with the singlet oxygen observations. The role of the chemical structure of the photosensitizer on the photophysical and photobiological properties of the colloidal suspensions has been subsequently investigated. Free base photosensitizers aggregate when entrapped in the nanoparticles, whereas metallated ones are incorporated in monomeric form. When the photosensitizers are covalently conjugated to the nanoparticles, their chemical properties influence their localization in the nanoparticles and consequently, the photophysical properties of the suspension, although they remain photophysically active. Physically entrapped photosensitizers are able to induce cell mortality in cells even if they are aggregated in the nanoparticles, while covalently conjugated photosensitizers are not. This drives us to the conclusions that the delivery of the photosensitizer into the cell is crucial to achieve a photodynamic response, and that PEG-PLGA nanoparticles are not internalized by cells but they rather deliver their cargo at the cell surface, which does not occur when the photosensitizer is covalently bound to the nanoparticles. Finally, we have explored the potential of the active targeting strategy by conjugating the cRGDfK peptide to the surface of the nanoparticles. The presence of a PEG side chain is essential to achieve an enhanced increase in the photosensitizer delivery into the cell, but unfortunately, it does not render a higher phototoxicity to the cells compared to the non-targeted nanoparticles, which suggests that a higher internalization is not the only important factor in the final outcome of photodynamic therapy.

Breast cancer is the most frequent type of cancer seen in woman. Chemotherapy is one of the most important treatments for breast cancer. However, systemic toxicity, drug resistance and unstable kinetics of the drug in the blood are serious problems of chemotherapy. The use of biodegradable polymers for controlled release of anticancer drugs has gained popularity in recent years. Controlled release of anticancer drugs from polymeric carriers has some advantages such as improvement in the efficiency of treatment, reduction in systemic toxicity and prevention of the drug resistance that is developed by the cancer cells. In this study, it was aimed to prepare such a controlled release system for anticancer drugs which are used in breast cancer treatment by using biodegradable copolymer poly(D,L-lactide-co-glycolide) and to characterize in terms of morphology, size, drug content and drug release rate. In the first part of this study<br>empty and drug loaded poly (D,L-lactide-co-glycolide) microspheres were prepared. Two sets of empty poly(D,L-lactide-co-glycolide) microspheres were prepared by solvent evaporation technique with single emulsion (oil/water) to determine the effect of stirring rate on size of microspheres. Increase in stirring rate caused decrease in size of microspheres. Drug loaded poly(D,L-lactide-co-glycolide) microspheres were prepared for controlled release of anticancer drugs which are used in breast cancer treatment namely<br>5-fluorouracil, methotrexate and tamoxifen by using solvent evaporation technique either with double emulsion (water/oil/water) or single emulsion (oil/water). In the second part of this study<br>empty and drug loaded microspheres were characterized. Inverted light microscopy and scanning electron microscopy were used to examine morphology and size of microspheres. Drug content of microspheres and amount of released drug were determined and drug release profile was obtained for each anticancer drug separetely.

Thesis (Ph. D.)--School of Pharmacy and Dept. of Chemistry. University of Missouri--Kansas City, 2005.<br>"A dissertation in pharmaceutical science and chemistry." Advisor: Ashim K. Mitra. Typescript. Vita. Description based on contents viewed Mar. 12, 2007; title from "catalog record" of the print edition. Includes bibliographical references (leaves 138-147). Online version of the print edition.

“Blood vessel mimics” (BVMs) are tissue-engineered constructs that serve as in vitro preclinical testing models for intravascular devices. The Cal Poly Tissue Engineering lab specifically uses BVMs to test the cellular response to stent implantation. PLGA scaffolds are electrospun in-house using the current “Standard Protocol” and used as the framework for these constructs. The performance of BVMs greatly depends on material and mechanical properties of the scaffolds. It is desirable to create BVMs with reproducible properties so that they can be consistent models that ultimately generate more reliable results for intravascular device testing. Reproducibility stems from the consistency of the scaffolds. Thus, scaffolds with consistent material and mechanical properties are necessary for creating reproducible BVMs. The aim of this thesis was to characterize the reproducibility of the electrospun PLGA scaffolds using fiber diameter measurements and compliance testing. Initial work in this investigation involved designing and testing several experimental electrospinning protocols to obtain smaller fiber diameters, which have been shown to elicit more ideal cellular responses. The most successful protocol in that regard was then analyzed for the reproducibility of fiber diameters and compared to the reproducibility of the Standard Protocol. After determining that the Standard Protocol produced scaffolds with more consistent fibers, a large-scale reproducibility study was performed using this protocol. In this expanded study, both fiber diameter and compliance were analyzed and used to characterize the scaffolds. It was established that the scaffolds demonstrated inconsistent mean fiber diameter and mean compliance. The current standard electrospinning protocol therefore does not create PLGA scaffolds with statistically reproducible properties. Future modifications should be made to the electrospinning parameters in order to reduce variability between the scaffolds and future studies should be performed to determine the acceptable range of properties.

PREPARATION AND CHARACTERIZATION OF ELECTROSPUN POLY(D,L-LACTIDE-CO-GLYCOLIDE) SCAFFFOLDS FOR VASCULAR TISSUE ENGINEERING AND THE ADVANCEMENT OF AN IN VITRO BLOOD VESSEL MIMIC Tiffany Richelle Peña Currently, an estimated 1 in every 3 adult Americans are affected by one or more cardiovascular complications. The most common complication is coronary artery disease, specifically atherosclerosis. Outcomes of balloon angioplasty treatments have been significantly improved with the addition of drug eluting stents to the process. Although both bare metal and drug eluting stents have greatly increased the effectiveness of angioplasty and decreased the occurrence of restenosis, several complications still exist. For this reason, the stent industry is continually advancing toward better stent and drug-eluting designs, deployment methods, and adjuvant drug therapies, necessitating fast, reliable pre-clinical test methods. Recently, advancements in tissue engineering have led to the development of an in vitro blood vessel mimic (BVM) and the feasibility of evaluating cellular response to intravascular device implantation has been demonstrated. There are several physiological and scalability limitations of the current BVM model that must be addressed before effective use of the model can be initiated. The limiting aspect addressed in this thesis is the use of expanded poly(tetrafluorethylene) [ePTFE] scaffolding for the development of the BVM. There are several disadvantages and limitations to ePTFE including high cost and non-native mechanical properties. The ability to produce and tailor scaffolds in-house would greatly impact the scalability, cost effectiveness, and control over scaffold properties for BVM optimization. Also, in-house fabrication will open up further avenues of research into optimum scaffold design for better cellular responses when cultured in vitro. Electrospinning is a relatively simple and economical method of creating tissue engineering constructs with micro-architecture similar to the native extracellular matrix. Based on the clinical problem and the potential for the BVM, the aim of this thesis is to employ electrospinning for the development of poly(D,L-lactide-co-glycolide) [PLGA] vascular scaffolds as a replacement to ePTFE for the BVM. After primary literature review, PLGA was determined an advantageous polymer for tissue engineering vascular scaffolds and electrospinning based on evidence of adequate endothelial cell attachment, mechanical properties similar to the native vessels, controlled degradation, and good biocompatibility. The first phase of this thesis was to develop an acceptable protocol for the fabrication of electrospun PLGA scaffolds by varying solution concentration, flow rate and applied voltage. Electrospun solutions of 15 wt% PLGA in CHCl3 resulted in continuous un-beaded fibers of 5-6 microns and tensile properties (3-5 MPa) similar to the native vessel. The optimum protocol for electrospinning 15 wt% PLGA incorporated a flow rate of 5.5 ml/hr and an applied voltage of 12,000 V. In the second phase of this thesis, final protocol PLGA scaffolds were cultured in vitro with human umbilical vein endothelial cells (HUVECs) up to 6 days. Fluorescent microscopy and SEM analysis suggest the porous nature of the scaffolds was conducive to sub-luminal cellular penetration. Although results were not optimal for developing an endothelium for the ideal BVM design, the potential of using electrospinning for in-house production of scaffolds for tissue engineering was established. Further optimization of the electrospinning protocol to develop nano-sized structural features could enhance the ability to form an intimal lining of endothelial cells for the next generation BVM design.

Developing an in vitro Blood Brain Barrier model that will replicate the physiological, anatomical, and functional characteristics of the native BBB has gained significant attention. Such a model would enable prediction of the penetration of CNS targeting drug candidates across the BBB, allow pre-screening and optimization strategies to be developed for new drugs and gene delivery formulations, and permit research groups to further understand how a dysfunctional BBB is involved in the pathogenesis of several neurological diseases. The Tissue Engineering laboratory at the California Polytechnic State University, San Luis Obispo is currently in the process of developing a dynamic in vitro blood brain barrier model that will implement an in-house fabricated electrospun PLGA scaffold pressure sodded with C6 glial cells and BAECs (Bovie Aortic Endothelial Cells). The aims of this thesis were to upgrade and refine the existing electrospinner system, develop a BBB scaffold electrospinning protocol, and characterize and evaluate the consistency of the scaffolds fabricated using the protocol. Ultimately, the electrospinner system was optimized in the following areas: the high voltage power supply, electrical layout and safety, as well as the syringe pump and stand. The modifications to the system will now permit new electrospinning strategies and ensure operator safety. The protocol developed for electrospinning scaffolds for the DIV-BBB system utilized 15 wt% PLGA in CHCl3 with a 4.5 ml/hr flow rate, an applied voltage of 18,000V with a negative polarity, and a gap distance of 25.4 cm. Characterization and consistency studies revealed that scaffolds electrospun were statistically inconsistent with one another with regards to fiber diameter (P < 0.0001), porosity (P < 0.0001), and wall thickness (P < 0.0001). However, the scaffolds were mechanically consistent (P-value of 0.6134) according to the calculated Young's modulii. The average fiber diameter for the electrospun scaffolds was 2.556 µm, and had an average porosity of 70.06 µm2. Additionally, the wall thickness between the electrospun scaffolds ranged between 0.31 and 0.54 mm. The average Young's modulus of the electrospun scaffolds was determined to be 86.141 MPa. While the results associated with fiber diameter, porosity, and wall thickness were statistically inconsistent, it will be important to evaluate whether the variation between each scaffold will translate to a difference when conducting cellular studies after the DIV-BBB system is complete.

Chemotherapy is one of the most important treatments for cancer. However, systemic toxicity, drug resistance and unstable kinetics of the drug in the blood are serious problems of chemotherapy. The use of biodegradable polymers for controlled release of anticancer drugs has gained popularity in recent years. Controlled release of drugs from polymeric carriers has some advantages such as improvement in the efficiency of treatment, reduction in systemic toxicity and prevention of the drug resistance that is developed by the cancer cells. In this study, poly(D,L-lactide-co-glycolide) microparticles were used as carriers for the controlled release of all-trans-Retinoic acid, tamoxifen, tamoxifen citrate and idarubicin. It was aimed to prepare a drug carrier system for controlled release of hydrophobic anticancer drugs. The empty and drug loaded poly (D,L-lactide-co-glycolide) microparticles were prepared by solvent extraction/evaporation technique with single emulsion (oil/water). Optimized microparticles were characterized by using inverted light microscopy and scanning electron microscopy to examine their morphology and sizes. Drug content of microparticles and the amount of released drug were determined spectrophotometrically. In vitro toxicity of the microparticles on MCF-7 human breast cancer cells was investigated. It was revealed that the microparticles were smooth and spherical in shape. Their sizes differed in the range of 2-20 &micro<br>m. atRA-loaded microparticles showed approximately 90% encapsulation efficiency and it was confirmed that changing in drug/polymer ratio affected the extend of drug content. Increase in drug content caused a slower release pattern. Moreover, although the empty microparticles caused some toxicity, atRA-loaded PLGA microparticles showed slight cell growth inhibition.

Cardiac disease causes approximately a third of the deaths in the United States. Furthermore, most of these deaths are due to a condition termed atherosclerosis, which is a buildup of plaque in the coronary arteries, leading to occlusion of normal blood flow to the cardiac muscle. Among the methods to treat the condition, stents are devices that are used to restore normal blood flow in the atherosclerotic arteries. Before advancement can be made to these devices and changes can be tested in live models, a reliable testing method that mimics the environment of the native blood vessel is needed. Dr. Kristen Cardinal developed a tissue engineered blood vessel mimic to test intravascular devices. Among the scaffolding material used, electrospun poly (lactide-co-glycolide) (PLGA) has been used as an economic option that can be made in house. PLGA is a biodegradable co-polymer, and when electrospun, creates a porous matrix with tailorable properties. Currently, the standard PLGA electrospinning protocol produces consistent fibrous scaffolds with a mean fiber diameter of 5-6 microns. Research indicates that cell adhesion is more successful in fibrous matrices with a mean fiber diameter at the nanometer level. However, because previous work in the Tissue Engineering Laboratory at Cal Poly sought to ensure a consistent fibrous, there was no model or equation to determine how to change the electrospinning parameter settings to create scaffolds with an optimal mean fiber diameter. To fill this need, biomedical engineering senior Steffi Wong created a design of experiment to systematically approach the electrospinning variables and determine how they interacted with each other, as well as their effect on fiber diameter. The aims of this thesis were to perform the said design of experiments and determine a model to predict the resulting mean fiber diameter of a scaffold based on the electrospinning parameters as well as to determine what combination of parameters would lead to a scaffold with an optimal mean fiber diameter between 100-200 nanometers. The variables tested were solution concentration, gap distance, flow rate, and applied voltage. Each scaffold was imaged and a mean fiber diameter was calculated and used as the predicted variable in a regression analysis, with the variables indicated above as the predictors. The goal of 100-200 nanometer mean fiber diameter was not reached. The smallest mean fiber diameter calculated was 2.74 microns—half of that of the standard protocol. The regression analysis did result in a model to describe how the voltage, gap distance, and flow rate affected the fiber diameter.

The use of various biodegradable polymers for the improvement of different controlled and long-lasting drug release systems is an active research area in recent years. The application of different metal prostheses, especially titanium based ones, to the human body is also very common. A most important disadvantage of these prostheses is the risk of infection at the application areas that necessitates the removing of the prosthesis with a second surgical operation and reapplication of it after recovery. One of the best ways to solve this problem is to render metal prostheses infection free with controlled and sustainable drug (antibiotic) release systems. The long term sustained release of relevant antibiotics from the various biodegradable polymer coated metal implants is studied in this thesis. Virtual fatigue analysis and drug loading capacities of titanium and stainless steel samples with different surface pattern and modifications were studied. Various biodegradable polymer and drug combinations were examined and used for coating of metal prosthesis. The aim is to design polymer-drug coated metal implants that are capable of releasing a feasible amount of drug up to a period of at least 1 month. Various coating techniques and surface modifications were also employed to improve the adhesional properties of the drug containing polymers. Their adhesion abilities on the metal substrates were tested by Lap-shear and T-peel tests. Polymer degradation kinetics was followed by viscosity studies. Calibration lines for different drugs were obtained and drug releases on different systems were followed by using UV spectroscopy and microbial antibiotic sensitivity tests. Among the techniques applied to prevent fast release of drugs initially, the coatings of Vancomycin absorbed &amp<br>#946<br>-TCP (&amp<br>#946<br>-tricalcium phosphate) homogeneously distributed in poly(D,L-lactide-co-glycolide) solution in chloroform followed by an inert coating with poly(L-lactide) system proved to be feasible. By this technique, initial burst release was minimized and drug release from implants lasted nearly 2 months. Multiple coatings on polymer plus drug coating layer also gave promising results. In vivo studies on dorsal muscles of native rabbits with antibiotic loaded implants gave no negative effect on the surrounding tissues with high compatibility free of infection.

<p>Degradable polymers have gained an increased attention in the field of biomedical applications over the past decades, for example in tissue engineering. One way of improving the biocompatibility of these polymers is by chemical surface modification, however the risk of degradation during the modification procedure is a limiting factor. In some biomedical applications, for example in nerve guides, a patterned surface is desired to improve the cell attachment and proliferation.</p><p>In this thesis a new non-destructive, single-step, and solvent free method for surface modification of degradable polymers is described. Poly(L-lactide) (PLLA) substrates have been functionalized with one of the following vinyl monomers; N-vinylpyrrolidone (VP), acrylamide (AAm), or maleic anhydride (MAH) grafts. The substrates were subjected to a vapor phase atmosphere constituted of a mixture of a vinyl monomer and a photoinitiator (benzophenone) in a closed chamber at very low pressure and under UV irradiation. Poly(ε-caprolactone) (PCL), poly(lactide-co-glycolide) (PLGA), and poly(trimethylene carbonate) (PTMC) have been surface modified with VP using the same procedure to show the versatility of the method. The wettability of all of the four substrates increased after grafting. The surface compositions were confirmed by ATR-FTIR and XPS. The VP grafted PLLA, PTMC and PLGA substrates have been shown to be good substrates for the normal human cells i.e. keratinocytes and fibroblasts, to adhere and proliferate on. The topography of substrates with well defined nano patterns was preserved during grafting, since the grafted layer is very thin. We have also shown that the method is useful for a simultaneous chemical and topographical modification of substrates by masked vapor phase grafting. The surface topography was determined with SEM and AFM.</p><br><p>Intresset för användningen av nedbrytbara polymerer till biomedicinska applikationer som till exempel vävnads rekonstruktion har ökat avsevärt de senaste decennierna. Ett sätt att öka biokompatibiliteten hos dessa polymerer är genom kemisk ytmodifiering, men risken för nedbrytning under själva modifieringen är en begränsande faktor. I vissa biomedicinska applikationer, till exempel nervguider, är det önskvärt att ha en väldefinierad ytstruktur för att öka vidhäftningen och tillväxten av celler.</p><p>I den här avhandlingen presenteras en ny ickeförstörande, lösningsmedelsfri enstegsprocess för ytmodifiering av nedbrytbara polymerer. Substrat av poly(L-laktid) (PLLA) har ytfunktionaliserats med var och en av följande vinylmonomerer, N-vinylpyrrolidon (VP), akrylamid (AAm) eller maleinsyraanhydrid (MAH). Substraten har exponerats för en gasfasatmosfär av en blandning av en vinylmonomer och en fotoinitiator (bensofenon) i en tillsluten reaktor vid mycket lågt tryck och under UV-strålning. Metodens mångsidighet har även påvisats genom att ytmodifiera substrat av poly(ε-kaprolakton) (PCL), poly(laktid-co-glykolid) (PLGA) och poly(trimetylen karbonat) (PTMC) med VP. Vätbarheten ökade för alla fyra materialen efter ympning med en vinylmonomer. Ytsammansättningen fastställdes med ATR-FTIR och XPS. De VP ympade filmerna av PLLA, PLGA och PTMC visade sig vara bra substrat för mänskliga celler, i detta fall keratinocyter och fibroblaster, att vidhäfta och växa på. Yttopografin hos filmer med väldefinierade nanomönstrade ytor kunde bevaras efter ympning, tack vare att det ympade lagret är så tunt. Gasfas metoden har också visat sig användbar för att simultant ytmodifiera både kemiskt och topografiskt genom maskad gasfasympning. Yttopografin bestämdes med SEM och AFM.</p>

Degradable polymers have gained an increased attention in the field of biomedical applications over the past decades, for example in tissue engineering. One way of improving the biocompatibility of these polymers is by chemical surface modification, however the risk of degradation during the modification procedure is a limiting factor. In some biomedical applications, for example in nerve guides, a patterned surface is desired to improve the cell attachment and proliferation. In this thesis a new non-destructive, single-step, and solvent free method for surface modification of degradable polymers is described. Poly(L-lactide) (PLLA) substrates have been functionalized with one of the following vinyl monomers; N-vinylpyrrolidone (VP), acrylamide (AAm), or maleic anhydride (MAH) grafts. The substrates were subjected to a vapor phase atmosphere constituted of a mixture of a vinyl monomer and a photoinitiator (benzophenone) in a closed chamber at very low pressure and under UV irradiation. Poly(ε-caprolactone) (PCL), poly(lactide-co-glycolide) (PLGA), and poly(trimethylene carbonate) (PTMC) have been surface modified with VP using the same procedure to show the versatility of the method. The wettability of all of the four substrates increased after grafting. The surface compositions were confirmed by ATR-FTIR and XPS. The VP grafted PLLA, PTMC and PLGA substrates have been shown to be good substrates for the normal human cells i.e. keratinocytes and fibroblasts, to adhere and proliferate on. The topography of substrates with well defined nano patterns was preserved during grafting, since the grafted layer is very thin. We have also shown that the method is useful for a simultaneous chemical and topographical modification of substrates by masked vapor phase grafting. The surface topography was determined with SEM and AFM.<br>Intresset för användningen av nedbrytbara polymerer till biomedicinska applikationer som till exempel vävnads rekonstruktion har ökat avsevärt de senaste decennierna. Ett sätt att öka biokompatibiliteten hos dessa polymerer är genom kemisk ytmodifiering, men risken för nedbrytning under själva modifieringen är en begränsande faktor. I vissa biomedicinska applikationer, till exempel nervguider, är det önskvärt att ha en väldefinierad ytstruktur för att öka vidhäftningen och tillväxten av celler. I den här avhandlingen presenteras en ny ickeförstörande, lösningsmedelsfri enstegsprocess för ytmodifiering av nedbrytbara polymerer. Substrat av poly(L-laktid) (PLLA) har ytfunktionaliserats med var och en av följande vinylmonomerer, N-vinylpyrrolidon (VP), akrylamid (AAm) eller maleinsyraanhydrid (MAH). Substraten har exponerats för en gasfasatmosfär av en blandning av en vinylmonomer och en fotoinitiator (bensofenon) i en tillsluten reaktor vid mycket lågt tryck och under UV-strålning. Metodens mångsidighet har även påvisats genom att ytmodifiera substrat av poly(ε-kaprolakton) (PCL), poly(laktid-co-glykolid) (PLGA) och poly(trimetylen karbonat) (PTMC) med VP. Vätbarheten ökade för alla fyra materialen efter ympning med en vinylmonomer. Ytsammansättningen fastställdes med ATR-FTIR och XPS. De VP ympade filmerna av PLLA, PLGA och PTMC visade sig vara bra substrat för mänskliga celler, i detta fall keratinocyter och fibroblaster, att vidhäfta och växa på. Yttopografin hos filmer med väldefinierade nanomönstrade ytor kunde bevaras efter ympning, tack vare att det ympade lagret är så tunt. Gasfas metoden har också visat sig användbar för att simultant ytmodifiera både kemiskt och topografiskt genom maskad gasfasympning. Yttopografin bestämdes med SEM och AFM.<br>QC 20101014

碩士<br>國立中興大學<br>材料科學與工程學系所<br>98<br>It is well known that the structure, biocompatibility and biodegradation of characteristic scaffold plays an important role to control the cell growth behavior. Therefore, in this study, the high porosity and surface area with interconnected pore network of biodegradable poly(L-lactide) (PLLA) and poly(lactide-co-glycolide) (PLGA) fiber scaffold were fabricated using electrospun technology. The structure of prepared PLLA and PLGA is similar to the dimension of extracellular matrix (ECM) scaffold. The micrographs of scanning electronic microscopy (SEM) illustrate that the fiber diameter was distributed between 1200 nm and 1500 nm for PLLA, 85/15 PLGA and 75/25 PLGA fiber scaffold. The structure and property of PLLA, 85/15 PLGA and 75/25 PLGA fiber scaffold were investigated by X-ray diffraction (XRD) and different scanning calorimeter (DSC). The XRD and DSC results indicated that the crystallinity of prepared fiber scaffold with a clear cold crystallization peak was relatively low. In addition, the fiber scaffold was annealed at 120 ℃ for 6 hr and then was measured by one-dimensional and two-dimensional XRD. Experimental result showed the crystallinities decreased by increasing content of PGA. At the same time, the orientation of polymer chain became apparent by adding the PGA. Thermal treatment of PLLA, 85/15 PLGA and 75/25 PLGA fiber scaffold revealed that the melting endotherm became weaker, broader and slightly shifted to low temperatures as content of PGA increased. The degradation of fiber scaffold was observed by SEM. Experimental result showed that the structural changes of PLLA fiber scaffold during the in vitro degradation, which the fiber scaffold started to break down. Compared to the date of different content of PGA fiber scaffold, the SEM micrographs illustrate that the degradation rate was decreased by increasing content of PGA. In vitro biocompatibility measurement of PLLA, 85/15 PLGA and 75/25 PLGA fiber scaffold was investigated by optical microscopy. Experimental result indicated that PLLA, 85/15 PLGA and 75/25 PLGA didn’t have toxic effect on MDCK cells, which can be used as the scaffold materials for MDCK cell growth.

Nanomedicine has viewed countless breakthroughs in drug implementation. Nanomaterials have been used to enable enhanced drug delivery to tumor cells with lower toxicity to healthy ones. Controlled Drug Delivery Systems (DDS) have several advantages compared to the traditional forms of drugs. Indeed, when a drug is transported efficiently to the place of action its influence on vital tissues and undesirable side effects can be significantly minimized. Its accumulation at the target site increases and, consequently, the required doses are lower. Different nanoparticles (NPs) have been developed using different polymers with or without surface modification to target tumor cells both passively and/or actively. With this work, it was intended to develop and test polymeric nanoparticles (PNPs), as DDS for anti-cancer therapy. This work focused on the development of Poly(L-lactide-co-caprolactone-co-glycolide) (PLCG) NPs, loaded with Doxorubicin, a drug widely used in cancer therapy. Different surfactants, such as Polyvinyl alcohol (PVA) and Dextran sulfate sodium, were used to have DDS with the optimized properties, in terms of size, superficial charge and colloidal stability, drug loading capacity and release over optimal time window. The structural features and the properties of prepared NPs were characterized with different techniques, including, dynamic light scattering (DLS), microscopy, fluorimetric analysis, thermogravimetric analysis. Moreover, the effects of the developed DDS were also tested on some selected tumorous cellular lines (MCF7) to assess their effectiveness in anti-cancer therapy.<br>A nanomedicina tem sido alvo de incontáveis avanços na implementação de fármacos. Cada vez mais são usados nanomateriais para permitir a libertação de fármacos, diminuindo os efeitos tóxicos nas células saudáveis, aumentando a liberação destes em células tumorais. Sistemas de liberação controlada de fármacos têm várias vantagens em comparação com as formas tradicionais de administração. Um fármaco é transportado para o local de ação, portanto, a sua influência sobre os tecidos vitais e os efeitos colaterais indesejáveis podem ser minimizados. A acumulação de compostos terapêuticos no local alvo aumenta e, consequentemente, as doses necessárias são menores. Diferentes nanopartículas poliméricas têm sido desenvolvidas, usando diferentes polímeros com ou sem modificação de superfície para atingir as células tumorais de forma passiva e/ou ativa. Com este trabalho, pretendeu-se desenvolver e testar nanopartículas poliméricas como sistema de libertação de fármacos para terapia anticancerígena. Este trabalho focou-se no desenvolvimento de nanoparticulas de Poly (L-lactide-co-caprolactona-co-glicolide) (PLCG), carregadas com Doxorrubicina. Foram testados diferentes surfactantes, tais como álcool polivinílico e sulfato de dextrano de sódio, de forma a obter sistemas com propriedades otimizadas, tais como tamanho, carga superficial e estabilidade coloidal, capacidade de carga de fármaco e a eficiência da libertação do fármaco. As características estruturais e as propriedades das nanoparticulas preparadas foram caracterizadas por diferentes técnicas, incluindo dispersão dinâmica de luz, microscopia, análise fluorimétrica, termogravimetria e espectrocopia de infravermelho. Além disso, os efeitos dos nanossistemas desenvolvidos também foram testados em algumas linhas celulares tumorais selecionadas (MCF7) para avaliar a sua eficácia no tratamento do cancro.

碩士<br>國立宜蘭大學<br>生物機電工程學系碩士班<br>99<br>In vitro release of hydrophilic colchicine from biodegradable poly(D,L-lactide-co-glycolide) (PLGA) copolymer films was studied by applying the high-performance liquid chromatography. The results showed that the release rates of hydrophilic colchicine from various PLGA films within 28 days exhibited a fast initial release and two-stage release involving zero-order kinetics and degradation release. Atomic force microscopy (AFM) is a high-resolution imaging tool that successfully visualizes the morphology of biological molecular assemblies at nanometer-scale under ambient or liquid conditions. This work utilizes an atomic force microscope to investigate the microstructures of casting PLGA films with or without colchicines. We investigated the microstructures of PLGA films before and after the drug release in order to realize the relation between degradable morphology and release rate. After soaking into PBS for 2 to 4hours, the PLGA film without colchicine starts to flake significantly, at the 4th day, degradation starts to take place. As the day goes by, the speed of this reaction accelerates. Meanwhile, the PLGA film contains colchicine shows no reaction to PBS within the first 4 hours. At the 6th day, the degradation starts to take place and maintains at this slow speed. However, at the 12th day, the effect of degradation on PLGA film starts to gain gradually and accelerates in speed. The result of this research confirms that the beginning stage of drug control release is not triggered by PLGA film degradation system; it also shows that PLGA film degradation changes the microstructure and has a direct and noticeable relationship with drug release.

Paclitaxel has been shown to cause significant regression of existing rheumatoid arthritis and to prevent the induction of collagen-induced arthritis (CIA) in animal models. Paclitaxel suppresses arthritis because rapidly proliferating inflammatory pannus cells in the joint are susceptible to the phase-specific cytotoxic effects of paclitaxel. Intra-articular therapy using anti-inflammatory steroids is used for patients in whom rheumatoid arthritis manifests itself in only a limited number of joints. The objective of the research was to prepare and characterize paclitaxel-loaded microspheres using lactide:glycolide (LA:GA) polymers, which might potentially be suitable for the intra-articular delivery of paclitaxel in arthritis. Paclitaxel-loaded poly(J,/-lactide-co-glycolide) (PLG) microspheres were prepared using the solvent evaporation method. PLG polymers having different compositions of lactide and glycolide as well as having different molecular weights with the same lactide and glycolide composition were chosen to study the influences of these factors on the paclitaxel release rate. The effects of paclitaxel loading in the polymer matrix and the sizes of the microspheres on the paclitaxel in vitro release behavior were also assessed. Paclitaxel was loaded into PLG microspheres with encapsulation efficiencies of over 90% due to the hydrophobicity of the drug. Differential scanning calorimetry (DSC) thermograms indicated that the glass transition temperatures increased with an increase in paclitaxel loading in the PLG matrices, which was believed to be due to an interaction involving the formation of hydrogen bonds between paclitaxel and PLG polymers. X-ray diffraction data showed only the presence of an amorphous matrix, with no evidence by either X-ray diffraction or DSC, of crystalline paclitaxel present in the microspheres matrix. Degradation studies of both control and paclitaxel-loaded microspheres in phosphate buffered saline (PBS) containing albumin at 37°C showed that the molecular weights of P L G microspheres with a 50:50 lactide:glycolide composition decreased rapidly with time. The molecular weights of PLG microspheres with higher lactide content (> 50 mole% of lactide) did not decrease significantly until after 3 weeks of incubation in PBS-albumin. The release profiles of paclitaxel from all PLG microsphere formulations showed a burst phase of release, followed by a phase of relatively steady release. The burst phase was caused by rapid release of paclitaxel from the superficial surface layers of the microspheres. The release rates of paclitaxel from PLG50:50 microspheres were influenced by paclitaxel loading and molecular weights of the PLG50:50 polymers. Increased loading and decreased molecular weight led to faster paclitaxel release rates. PLG microspheres prepared from polymers with LA : GA ratios of 85:15, 75:25 and 65:35 showed that the LA : GA compositions had minimal effect on paclitaxel release rates. The two size ranges of microspheres showed minimal effects on the rates of paclitaxel releases from the microspheres.

yes<br>Our overall aim is to develop a synthetic off-the-shelf alternative to human amniotic membrane which is currently used for delivering cultured limbal stem cells to the cornea in patients who suffer scarring of the cornea because of the loss of limbal stem cells. We have recently reported that both cultured cells and limbal explants grow well on electrospun Poly(D,L-lactide-co-glycolide) (PLGA) (44 kg/mol) with a 50:50 ratio of lactide and glycolide and sterilized with γ-irradiation. Prior to undertaking a clinical study our immediate aim now is to achieve long term storage of the membranes in convenient to use packaging. Membranes were electrospun from Poly(D,L-lactide-co-glycolide) (44 kg/mol) with a 50:50 ratio of lactide and glycolide and sterilized with γ-irradiation and then stored dry (with desiccant) for several months at -80°C and -20°C , Room temperature (UK and India), 37°C and 50°C. We explored the contribution of vacuum sealing and the use of a medical grade bag (PET/Foil/LDPE) to achieve a longer shelf life. Confirmation of membranes being suitable for clinical use was obtained by culturing tissue explants on membranes post storage. When scaffolds were stored dry the rate of breakdown was both temperature and time dependent. At -20°C and -80°C there was no change in fiber diameter over 18 months of storage, and membranes were stable for 12 months at 4°C while at 50°C (above the transition temperature for PLGA) scaffolds lost integrity after several weeks. The use of vacuum packaging and a medical grade bag both improved the storage shelf-life of the scaffolds. The impact of temperature on storage is summarized beneath. We report that this synthetic membrane can be used as an off-the-shelf or-out-of-the freezer alternative to the amniotic membrane for corneal regeneration.

碩士<br>國立成功大學<br>材料科學及工程學系碩博士班<br>93<br>Nerve bridging is suture a biomaterial-made conduit and to overpass the damaged nerve end to end with microsurgery. Peripheral nerve could be bridged between the proximal nerve and the distal stump to restore the function. Nerve conduits could eliminate tension at the healing site and induce the regeneration of axons. Nerve conduits also could permit neurobiological recovery to enhance neural regeneration and stop cells and their secretions from obstructing neural regeneration. In this study, we used poly L-latcide (PLLA), poly DL-latcide-co-glycolide 75:25 (PLGA7525) and poly DL-latcide-co-glycolide 50:50 (PLGA5050) during citric acid inducing ammonium bicarbonate gas forming process to form porous polymer film, and rolled the porous polymer film to make nerve conduits with pores and multi-layered. Electron Spectroscopy for Chemical Analyzer (ESCA) and Attenuated Total Reflectance – Fourier-Transform Infrared Spectrometer (ATR-FTIR) were employed for determining elements’ functionabilities and chemical compounds. Charge Coupled Device camera (CCD camera) and Scanning Electron Microscope (SEM) were employed for macroscopic and microscopic morphologies and structural observation. Differential Scanning Calorimetry (DSC) was employed for measuring glass-transition temperature (Tg). Nano-indentation system was employed for measuring elastic modulus and hardness. Biodegradation and water absorption ratios were measured to analyze their chemical properties and SEM was employed for microscopic morphology of the tested nerve conduit. Experiment results demonstrated that during citric acid inducing ammonium bicarbonate gas forming process, no salts (ammonium bicarbonate) remained, while Tg of PLGA5050 was lower than human body temperature. The porous structures of PLGA5050 conduit were dissolved into a condensed morphology after 28 testing days, while the material was completely degraded after 56 testing days. The degradation of PLGA7525 conduit was relatively slow, while the porous structures slightly changed their shapes after 56 testing days. Using citric acid inducing ammonium bicarbonate gas forming and unique rolling process, PLLA is relatively suitable to make multi-layered nerve conduits, which provide highly porous structures with many round openings. In addition, the porous structures with channeling characteristic can be preserved to 56 testing days.

博士<br>長庚大學<br>機械工程學系<br>102<br>The incidence of postoperative central nervous system infection (PCNSI) is higher than 5-7%. Successful treatment of a central nervous infection requires aspiration of the pus or excision of the abscess, followed by long-term (usually 4-8 weeks) parenteral antibiotic treatment. Local antibiotic delivery using biodegradable drug-impregnated carriers is effective in treating postoperative infections, thereby reducing the toxicity associated with parenteral antibiotic treatment and the expense involved with long-term hospitalization. Firstly, We developed vancomycin-loaded biodegradable poly[(d,l) - lactide - co - glycolide] (PLGA) nanofibrous membranes for the sustainable delivery of vancomycin to the brain tissue of rats by using the electrospinning technique. A high performance liquid chromatography assay was employed to characterize the in-vitro and in-vivo release behaviors of pharmaceuticals from the membranes. The experimental results suggested that the biodegradable PLGA/vancomycin nanofibers can release high concentrations of vancomycin for more than 8 weeks in the cerebral cavity of rats. Furthermore, the membranes can cover the wall of the cavity after the removal of abscess more completely and achieve better drug delivery without inducing adverse mass-effects in the brain. Histological examination also showed no inflammation reaction of the brain tissues. Secondary, duraform soaked in prepared bacterial solution was placed on the brain of rats to induce postoperative central nervous system infection (PCNSI). Virgin PLGA nanofibrous membranes (Group A) and vancomycin-eluting PLGA membranes (Group B) were implanted. In group A, the wounds and cerebral tissues necrosed with purulence and massively increased in PCNSI volume. Most rats died within 1 week and the survival rate was low (Odds ratio=0.0357, 95% confidence interval= from 0.0057 to 0.2254). In group B, the images of the serial MRIs revealed that the mean PCNSI volume is 283.25±118.50 x 10-3 ml initially, comparable to the volume in group A (273.18±118.64 x 10-3 ml). At the end of the study, the PCNSI volume (6.08±9.61 x 10-3 ml) in rats of group B significantly decreased (P<0.01) with excellent wound appearance. By adopting the biodegradable, nanofibrous vancomycin-eluting membranes, we will be able to achieve long-term deliveries of various antibiotics in the cerebral cavity to enhance the therapeutic efficacy of central nervous infection infections. The vancomycin-eluting PLGA nanofibers can be a good candidate for the treatment of PCNSI.