BACKGROUND: Cell migration is a vital process for growth and repair. In vitro migration assays, utilized to study cell migration, often rely on physical scraping of a cell monolayer to induce cell migration. The physical act of scrape injury results in numerous factors stimulating cell migration - some injury-related, some solely due to gap creation and loss of contact inhibition. Eliminating the effects of cell injury would be useful to examine the relative contribution of injury versus other mechanisms to cell migration. Cell exclusion assays can tease out the effects of injury and have become a new avenue for migration studies. Here, we developed two simple non-injury techniques for cell exclusion: 1) a Pyrex® cylinder - for outward migration of cells and 2) a polydimethylsiloxane (PDMS) insert - for inward migration of cells. Utilizing these assays smooth muscle cells (SMCs) and human umbilical vein endothelial cells (HUVECs) migratory behavior was studied on both polystyrene and gelatin-coated surfaces. RESULTS: Differences in migratory behavior could be detected for both smooth muscle cells (SMCs) and endothelial cells (ECs) when utilizing injury versus non-injury assays. SMCs migrated faster than HUVECs when stimulated by injury in the scrape wound assay, with rates of 1.26 % per hour and 1.59 % per hour on polystyrene and gelatin surfaces, respectively. The fastest overall migration took place with HUVECs on a gelatin-coated surface, with the in-growth assay, at a rate of 2.05 % per hour. The slowest migration occurred with the same conditions but on a polystyrene surface at a rate of 0.33 % per hour. CONCLUSION: For SMCs, injury is a dominating factor in migration when compared to the two cell exclusion assays, regardless of the surface tested: polystyrene or gelatin. In contrast, the migrating surface, namely gelatin, was a dominating factor for HUVEC migration, providing an increase in cell migration over the polystyrene surface. Overall, the cell exclusion assays - the in-growth and out-growth assays, provide a means to determine pure migratory behavior of cells in comparison to migration confounded by cell wounding and injury.

Surface interactions and reactivity are of critical importance in current biomedical technologies, for example, satisfactory cell attachment and long term viability are essential for optimal in vitro tissue culture and for successful implantation and stability of cardiovascular medical implants such as stents and grafts. To achieve this, the control of fundamental forces and the resulting molecular interactions between the relevant surface and absorbing or adhering species in the physiological system is compulsory. This work utilised the surface modification technique of Ultra-Violet/ Ozone to improve the polystyrene biocompatibility by oxidising the surface with additional polar oxygen functional groups without damaging the surface bulk property. UV/Ozone treatment utilised throughout this study produced controllable oxygen functional groups and led to an increase in surface atomic oxygen level to 41% on unwashed and 35% on washed polystyrene surfaces, washing resulted in the removal of low molecular weight oxidised materials. Surface energy was increased by the addition of oxygen functional groups with the combination of alcohol (C-OR), carbonyl (C=O) and carboxyl (O-C=O); Saturation state was reached after 300s of UV/Ozone treatment where no more oxygen functionalities were incorporated to the surface. Moreover, UV/ozone treatment did not show an effect on the surface roughness studied by atomic force microscopy. The biological responses of human endothelial umbilical vein cells (HUVECs) were studied at the different level of UV/Ozone treated surfaces. HUVEC adhesion, proliferation and migration were significantly improved by the treatment compared to untreated and tissue cultures plastics (TCPs). Among the levels of UV/ozone treatment studied, 120s and 180s were found to be the most effective and HUVEC proliferation did not seem to be affected by the high level of oxygen. Similarly, the surface oxygen level did not affect the migration over UV/Ozone treated over 60s. Hypoxic condition significantly increased HUVECs migration on UV/Ozone treated, TCPs and untreated surfaces compared to normoxia, the oxygen rich surface did not favour to HUVECs that underwent regulatory process to enable the cells to increase migration. Under laminar flow conditions, HUVECs did not only grow, proliferate and migrate but also showed standard responses on UV/Ozone treated polystyrene surface. A decrease in cell size was observed at all shear stress intensities studied (1 dyn/cm2, 9 dyn/cm2 and 25 dyn/cm2) and the decrease was more obvious at higher shear stress. High shear stress intensity also induced high cell turnovers, which may be related to air bubbles induced at high flow rate. The overall findings of this study clearly illustrate that UV/Ozone surface treatment can be applied on polystyrene to improve human endothelial cells functionalities in term of adhesion, proliferation and migration in both static and laminar flow environment.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007. / Hybrid A-B type block copolymers of polydimethylsiloxane (PDMS) and polystyrene (PS) were synthesised. Three different synthetic routes, which allowed control over polymer structure, were chosen to synthesise these block copolymers. The first technique, coupling of functional prepolymers, involved using anionic polymerisation to produce PDMS and PS functional prepolymers of controlled structure. These prepolymers were functionalised with either silane or allyl functionality and then coupled using a hydrosilylation reaction with Karstetds platinum catalyst. This technique was the least efficient in block synthesis due to the incompatibility of the disparate prepolymers. The second technique under study, sequential anionic polymerisation, gave excellent block copolymer formation with good control over the chain architecture. The final technique employed atom transfer radical polymerisation (ATRP) of styrene using a bromoisobutyrate functionalised PDMS macroinitiator. Silane functional PDMS molecules underwent a hydrosilylation reaction with allyl-2-bromo-2-methyl-propionate to produce the bromoisobutyrate functionalised polymer in excellent yields. Subsequent ATRP with styrene allowed the successful synthesis of block copolymers of controlled structure. Chromatographic systems that allowed liquid chromatography at the critical conditions (LC-CC) of PS and gradient elution chromatography (GEC) of the products were developed. GEC was used successfully in the monitoring of the presence and removal of PDMS homopolymer present in the block copolymer products. LCCC at the critical point of PS allowed successful chromatographic separation of PS homopolymer from the block material, as well as, the molecular weight distribution of the block material according to the segmental length of the PDMS component. LC-CC coupled to FT-IR using a LC-transform device allowed successful characterisation of the block copolymer chemical composition. Corona treatment was used to modify the surface structure of the block copolymer films. Optical microscopy and slow positron beam studies highlighted the formation of a thin silica like layer on the surface of the films after corona. The positron studies enabled determination of the silica like layer’s thickness. Contact angle studies provided the first evidence of hydrophobic loss and recovery for these PDMS containing hybrid polymer materials after corona treatment. A novel offline coupling technique was developed between LC-CC separation and transmission electron microscopy (TEM) analysis. This allowed easy sample preparation without the difficult bulk extraction procedures needed to remove homo-PS contaminants from the block copolymer. This technique also provided morphological information as a function of PDMS segmental length.

Thesis (MBA)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: The polystyrene foam tray manufacturing industry started with a monopoly in 1954, and lasted for more than 29 years. During the last ten years the industry has grown extremely competitive, seeing many new players enter (and exit) and a reduction in industry profitability. This mini thesis attempts to analyze the polystyrene foam tray manufacturing industry in its current form and to quantify the external, new challenges it currently faces. It attempts to identify potential pitfalls for new entrants to the industry and to construct an ideal strategy suited best for the industry, based on an industry analysis. The polystyrene foam container industry background is discussed to determine its origins in South Africa. An industry and competitive analysis is done to assess the strategically relevant aspects of the industry's macro environment. A technique developed by Thompson and Strickland (1998: 68) is utilized. The scope of the macro environment in the mini-thesis was limited to the South African scenario. Ultimately, an ideal strategy, which would deal with all the relevant challenges of the industry, is proposed. The industry and competitive analysis revealed important dominant economic traits. Competition is concentrated in the country's economic hub, namely Gauteng, but regional manufacturing bases leads to extended market share in those areas. The product range spans over several hundred coloured, printed and laminated trays, but the fiercest competition across the board takes place in a few sizes white, commodity flat trays to the meat industry, which also forms the bulk of sales to the industry. The growth rate has been organic for the last few years, mainly due to the mature status of polystyrene foam tray products and the introduction of alternative (though more expensive) media. The external macro economic environment has also not been conducive to abnormally high growth (GDP in South Africa has drifted between 1% and 3% for the last few years). Five competitors exist, and two of these competitors have 80% of the market share, but are also the furthest away from the largest part of the market, namely Gauteng. Customers are divided into two groups, distributors and end users. Small competitors make extensive use of distributors (since they do not own their own distribution channels), while large competitors limit the use of distributors to limit the potential buying power of distributors. The barrier to entry for a new entrant wanting to acquire up to 5% of market share is around R 10m, which includes working capital. The industry profitability varies from losses to extreme profits in some years. This becomes a vicious circle, since the latter attracts new entrants, which in turn causes price wars. Rivalry amongst competitive sellers is excessive, specifically when new entrants appear on the scene. Price cutting, although a very blunt tool, is used almost exclusively to obtain a volume advantage. Substitute products do not really pose a threat in the South African economic situation where cost is all-important. No other packaging medium can compete with the wide range of applicability, low cost and strength of polystyrene foam. Where end-user markets are more affluent, substitute products may have a minor impact. The power of suppliers in the industry is limited, since there is a manufacturing over capacity in the country, and there are no switching costs when changing from one supplier to another. The power of buyers, specifically ones that buy in bulk (distributors and the like), is thus quite strong. The main drivers of change include excessive movement in market pricing, product innovation, technological changes, increasing globalisation of the industry and changing societal concerns. Movement in market pricing is by far the most important and has the greatest affect on industry profitability, since the complete product range is affected. The latter four drivers affect mostly branded and speciality product. Strategic group mapping, combined with an in-depth analysis of each competitor, revealed that the largest two players, Kohler Versapak and Atlantic Forming, are definitely in the strongest position from a financial point of view. Although drawbacks such a corporate red tape, shareholder pressure and geographic location exist for these competitors, sheer financial strength to survive price wars will give them an edge. With the current amount of competitors and over capacity in the market there is bound to be some consolidation in the manufacturing industry. It seems that one of the larger two players (Kohler Versapak or Atlantic Forming) may acquire one of the smaller manufacturers in a bid to stabilize market prices. The most important key success factor is the ability to produce polystyrene foam trays at the lowest possible cost. The absence of switching costs, price wars and a manufacturing over capacity are all causes of the preceding success factor. Other less important success factors are distribution related (being close to the market is an advantage) and technology related (being able to develop advanced branded and functional trays). In its current status, where there is a supply-demand imbalance, the industry does not seem attractive. Although negative external forces such as environmental pressure, are limited, growth potential is limited and competition is fierce. In summary none of the competitors have attempted to utilize other tools than pricecutting to protect market share. From a geographic location point of view, Airshield and Mainpack are positioned best, but do not possess the financial momentum to optimally utilise their location in terms of finished product distribution and raw material acquisition. Atlantic Forming and Kohler Versapak seem to have expanded their product ranges to low profit and unprofitable products, while the other competitors have stayed focused on a few high volume items. It seems that it may have been a better idea for the larger players to utilize existing resources on other profitable media rather than expanding its interests in polystyrene foam trays. / AFRIKAANSE OPSOMMING: Polistireen skuim houer vervaardiging het in 1954 met 'n monopolie begin wat vir 29 jaar staande gebly het. Gedurende die laaste tien jaar het die polistireen skuim industrie baie kompeterend geraak, met heelwat kompeterende maatskappye wat die mark betree het (en uitgetree het), en 'n gevolglike afname in industrie profyt gehad het. Hierdie minitesis poog om die polistireen skuim bakkie industrie te analiseer in sy huidige vorm en om die eksterne uitdagings wat tans bestaan, te identifiseer. Die tesis poog verder om potensiele probleme te identifiseer wat nuwe kompeterende maatskappye in die industrie mag teëkom, en dan om 'n ideale strategie saam te stel, gebasseer op 'n industrie analise. Die polistireen skuim houer industrie is bespreek, sodat die oorsprong van die industrie in Suid-Afrika bepaal kon word. 'n Industrie en kompeterende analise is gedoen om die strategies belangrike aspekte van die industrie se makro omgewing te bepaal. Vir die bogenoemde analise is 'n tegniek soos ontwikkel deur Thompson en Strickland (1998: 68) gebruik. Die omvang van die makro omgewing in hierdie minitesis is beperk tot die Suid- Afrikaanse omgewing. Die uiteindelike ideale strategie sal al die relevante uitdagings van die industrie aanspreek. Die industrie en kompeterende analise het belangrike dominante ekonomiese eienskappe blootgelê. Markgerigte kompetisie is gekonsentreerd in die land se ekonomiese enjin, naamlik Gauteng, maar streeks gebaseerde vervaardigings aanlegte lei gewoonlik tot 'n verbeterde mark aandeel in 'n spesifieke streek. Die produk reeks bestaan uit honderde gekleurde, gedrukte en gelamineerde houers, maar die grootste kompetisie vind plaas oor slegs 'n paar plat, wit vleis bakkies - wat ook die grootste volume verkope in die industrie beslaan. Die groei tempo was organies vir die laaste paar jaar, hoofsaaklik as gevolg van die volwasse stand van polistireen skuim produkte en die bekendstelling van alternatiewe produkte. Die eksterne makro ekonomiese omgewing het ook nie bygedra tot bogemiddelde groei nie (BBP in Suid-Afrika het tussen I% en 3% gewissel vir die laaste paar jaar). Vyf produseerders van polistireen skuim houers ding mee in die mark, en twee van hulle besit 80% van die totale mark aandeel, alhoewel hulle ook die verste vanaf grootste mark, naamlik Gauteng, is. Kliënte word in twee groepe verdeel, naamlik verspreiders en eind-gebruikers. Klein produseerders maak meestal gebruik van verspreiders omdat hulle nie oor hulle eie verspreidings kanale beskik nie. Groter produseerders beperk die gebruik van verspreiders om uiteindelik potensiële koopkrag van verspreiders te beperk. Vaste kapitaal, asook lopende kapitaal om ongeveer 5% van die mark te bekom, is ongeveer R10m. Die industrie profyt variëer tussen verliese tot oorgrote profyt in sommige jare. Hierdie variasie vorm 'n afbrekende sirkel, aangesien oorgrote profyt potensiële nuwe produseerders aantrek wat dan weer tot prys oorloë lei. Mededinging tussen kompeterende produseerders is oormatig sterk, spesifiek wanneer nuwe produseerders die mark betree. Alhoewel prys verlaging 'n redelike kru metode is om markaandeel te bekom, word dit amper uitsluitlik gebruik. Alternatiewe, duurder vervangings produkte is nie werklik 'n gevaar vir polistireen skuim produkte in Suid-Afrika nie, aangesien prys die belangrikste element is. Geen ander verpakkingsmedia kan meeding met die toepasbaarheid, lae koste en sterkte van polistireen skuim nie. Slegs in sekere wel-gestelde segmente van die mark kan alternatiewe produkte 'n minimale impak op die polistireen skuim mark toon. Die mag van verskaffers in die industrie is beperk, aangesien daar 'n geweldige oorkapasiteit in die land is en omdat daar geen oorskakelingskoste bestaan wanneer daar van een verskaffer tot 'n ander geskuif word nie. Die mag van kopers, en spesifiek die wat in grootmaat koop, is dus redelik sterk. Die hoofdrywers van verandering sluit in sterk beweging in mark pryse, produk innovasie, tegnologiese veranderinge, toenemende globalisering van die industrie en veranderende sosiale standaarde. Variëerende beweging van markpryse is by verre die belangrikste en het ook die grootste effek op industrie profyt, aangesien die hele produk reeks geraak word. Die laaste vier drywers affekteer meestal handelsmerk produkte en spesialiteits produkte. Strategiese groep kaarte, gekombineerd met 'n indiepte analise van elke produseerder, het aangedui dat die twee grootste kompeteerders, Kohler Versapak en Atlantic Forming, definitief in die sterkste posisie is vanaf 'n finansiële oogpunt gesien. Alhoewel negatiewe punte soos korporatiewe sloering, aandeelhouer druk en geografiese posisie teen die twee mededingers tel, sal blote finansiele mag om prys oorloë te deurstaan hulle die oorhand gee. Met die huidige hoeveelheid oorkapasiteit in die mark moet daar uiteraard konsolidasie in die vervaardigings industrie plaasvind. Dit is waarskynlik dat een van die groter spelers (Kohler Versapak of Atlantic Forming) van die kleiner mededingers mag bekom in 'n poging om die mark te stabiliseer. Die mees belangrike sleutel sukses faktor is die vermoë om polistireen skuim bakkies teen die laagste koste te vervaardig. Die afwesigheid van oorskakelingskoste, die aanwesigheid van prys oorloë en vervaardigings oorkapasiteit is almal oorsake van die genoemde sukses faktor. Ander minder belangrike sukses faktore is verspreidings verwante (om nabyaan die mark te wees is 'n voordeel) en tegnologie verwante (om handelmerk produkte en moderne funksionele produkte te kan ontwikkel) faktore. In die mark se huidige vorm is daar nie 'n vraag-aanbod balans nie, en lyk die industrie nie aantreklik nie. Alhoewel negatiewe eksterne kragte soos omgewings druk beperk is, is groei potensiaal ook beperk en kompetisie agressief. Opsommendergewys het geen van die mededingers ander metodes as prys verlaging probeer gebruik om mark aandeel te beskerm nie. Vanaf 'n geografiese oogpunt gesien, is Airshield en Mainpack die beste geposisioneer, maar hulle het nie die finansiële momentum om hulle posisie optimaal te benut in terme van klaar produk verspreiding en rou material aankope nie. Atlantic Forming en Kohler Versapak het hulle produk reeks uitgebrei na lae profit en verlies-lyende produkte, terwyl ander mededingers gefokus gebly het op 'n paar hoë volume items. Dit lyk asof dit beter sou gewees het vir die groter spelers om bestaande bronne te gebruik het op ander winsgewinde media as om verder uit te brei in polistireen skuim.

In this thesis we used atomic force microscopy (AFM) to investigate systematically the behaviour of both electrostatically stabilised silica and sterically stabilised polystyrene (PS) colloidal systems on freshly cleaved mica substrates. For the silica colloidal nanoparticles we explored the effect of colloidal suspension concentration, particle size, and different application techniques on both the adsorption behaviour and subsequent structuring of the particles. For the PS colloidal nanoparticles we explored concentration effects and experimented with both dip-coating and droplet application techniques. We showed that silica nanoparticles adsorbed onto mica via irreversible adsorption that possessed lateral mobility due to the weak attraction between the nanoparticles and the substrate, facilitating subsequent capillary structuring of the nanoparticles during drying. We associated the effects of volume fraction with Debye screening, and kinetics effects with particle size and volume fraction. We also successfully imaged a partially dried film and showed the role of convective/capillary forces in the structuring of the nanoparticles. Studies with variations in particle size generated a number of different topography structures; with dewetting phenomena observed for 10 nm nanoparticles and the formation of crystalline structures for 100 nm nanoparticles. Spin coating techniques were used to produce even larger crystalline structures of nanoparticles. Size dependent ordering occurred for low concentration samples due to the polydispersity of the colloidal suspension. We showed that acceleration can affect interparticle spacing. We also studied the role of rotational speed on the crystallinity of the particle configurations and showed how fine tuning of rotational speed can generate large scale monolayer crystalline formations of nanoparticles.

Molecular weights of 2,000, 6,000 and 10,000 of silane functionalized atactic polystyrene (aPS) and α,ω-divinyl functionalized polydimethylsiloxane (PDMS) were prepared via living anionic polymerization and bulk anionic ring opening polymerization respectively. Functionalization of the homopolymers was confirmed by FT-IR and 1H-NMR spectroscopy and their molecular weights were determined via 1H-NMR end group analysis. A hydrosilylation reaction between the functionalized homopolymers of different molecular weights produced nine polystyrene-block-polydimethylsiloxane-block-polystyrene (aPS-b-PDMS-b-aPS) triblock copolymers. Field emission scanning electron microscopy observations revealed the copolymers self-assemble into supramolecular structures. Dynamic Light Scattering measurements show only small increase in the order of nanometers of its hydrodynamic radius as the individual molecular weights of the homopolymers were increased. Nanocomposites of the copolymers were prepared by incorporating 1% of oxidized single walled carbon nanotubes (SWNTs) within the aPS-PDMS-aPS matrices via coagulation precipitation. Differential scanning calorimetry (DSC) thermal analysis shows the SWNT interacting with both aPS and PDMS constituting blocks. SWNTs interaction with aPS block either increases the polymer glass transition temperature (Tg) by restricting its segmental motion or decreases the Tg by a plasticization effect. Within the PDMS block the SWNTs act as nucleating sites accelerating the crystallization rate of the polymer. This is evident by the appearance of single and double melting endotherms in the DSC thermograms.

High surface area gold electrodes are very good substrates for biosensors, catalysis and drug delivery. Their performance is characterized by good sensitivity, low detection limit and high signal. As a result, extensive research is being carried out in this field using different approaches of fabrication to generate high surface area porous electrodes of different morphology, pore size and structure. The morphology of the electrodes can be changed based on whether the approach involves a template or not, types of metal deposition, method and time of dealloying etc. The deposition of metal can be carried out using various approaches such as electroless deposition, electrochemical deposition, combination of electroless and electrochemical deposition, pulsed laser deposition, laser deposition etc. These electrodes can then be used in electrochemical measurements and their performance compared with an unmodified flat gold electrode. We used a template based approach, combined with electrochemical deposition, to fabricate macroporous, macro-nanoporous and nanoporous gold electrodes. To generate nanopores, in case of macro-nanoporous and nanoporous gold electrodes, we used gold-silver alloy electrochemical deposition method, followed by chemical dealloying. The morphology of electrodes was later observed under HITACHI Scanning Electron Microscope (SEM) and their elemental composition studied using HITACHI Energy Dispersion Spectroscopy (EDS). The electrodes were used in electrochemical measurements and their voltammetric data was compared. These measurements involved the determination of surface area, faradaic current using redox molecules with fast and slow electron transfer and charging current in KCl. Surface adsorption of dopamine was studied and detection of dopamine in the presence of ascorbic acid was carried out.

A characteristic feature of chronic wounds is a prolonged inflammatory response as well as susceptibility to infection. Studies have shown that during the inflammatory response, there is a significant increase in the levels of neutrophil-derived enzymes. The purpose of this work was to determine whether the anionic macromolecule polystyrene sulfonate (PSS) and five of its salt forms, namely PSS-calcium, PSS-chlorhexidine, PSS-doxycycline, PSS-glutathione and PSS-silver are able to inhibit the activity of three of the enzymes whose levels are elevated in chronic wounds: elastase, cathepsin G and myeloperoxidase. In addition to the enzyme inhibition study, the various formulations’ antimicrobial properties were analyzed by evaluating their ability to inhibit the growth of three common clinical isolates: Staphylococcus aureus, Pseudomonas aeruginosa and Acinetobacter baumanii. It is worthy to note that the structure of PSS makes it a very flexible platform to which other molecules can be added in order to address a variety of “targets” as well as tailor quantitative strength. The results from this project showed that purified PSS and the various salt derivatives were able to inhibit elastase and cathepsin G activity. In addition, three of the therapeutic cations attached to PSS: silver, doxycycline and chlorhexidine retained their intrinsic antimicrobial properties without having an adverse effect on healthy tissue. In summary, this study demonstrated that PSS possessed an intrinsic ability to inhibit a number of proteases and that it could also be used as a delivery vehicle for other compounds with potential therapeutic value.

Le moussage du polypropylène (PP) et du polystyrène (PS) par le scCO2 est étudié de manière systématique avec l’accent sur la relation entre le procédé, la microstructure et les propriétés mécaniques. La première partie de cette thèse porte sur l’amélioration de la résistance au choc du PP par cristallisation induite par le scCO2. Dans un deuxième temps, le PP fortement orienté avec des structures shish-kebab et sphérolite est utilisé pour étudier l’influence de la structure cristalline sur la nucléation et la croissance des cellules pendant le procédé de moussage sous le scCO2. Ensuite, les influences des conditions de moussage ainsi que celles des paramètres structuraux de la mousse de PS ont été étudiées. Les mousses de PS à cellules isotropes ont été comparées avec celles de PS à cellules orientées. Enfin, un procédé de moussage discontinu en deux étapes est développé afin de produire des mousses de PS à cellules bi-modales en utilisant le scCO2 en tant qu’agent de moussage. Cette structure unique de petites et grandes cellules réparties de manière homogène au travers de l’ensemble du volume de la mousse confère à cette dernière des propriétés particulières. / In this work, scCO2 induced foaming of PP or PS is systematically studied with emphasis on the relationship between process, microstructure and mechanical properties. The first part of the thesis deals with the toughening of iPP by scCO2 induced crystallization for the fine separation of rigid crystalline domains and soft amorphous ones in the polymer matrix. The highly oriented iPP with “shish-kebab” and “spherulite” are then used for CO2 foaming to investigate the effect of crystalline structure on the formation of cell nucleation and growth. In addition, the effect of the foaming conditions and the cell structural parameters of PS foams on the mechanical properties are studied systematically. PS foams with isotropic cell morphology and oriented cell one are prepared. Finally, a two-step depressurization batch process is developed to produce bi-modal cell structure PS foams by using scCO2 as the blowing agent. This unique cell structure with both small and large cells homogenously distributed throughout the entire volume of the foam sample might have particular properties.

A formação de biofilme representa preocupação à indústria de alimentos pois é uma fonte crônica de contaminação. Encontrar estratégias eficientes para controlar o crescimento de microrganismos continua a ser um importante desafio. Uma delas é o uso dos ramnolipídeos (RLs), um biossurfatante produzido tipicamente por P. aeruginosa que apresenta potencial como agente antimicrobiano, anti-adesivo e dispersivo. Sua baixa toxicidade, biodegradabilidade, eficiência e especificidade em comparação aos surfatantes sintéticos podem torná-los promissores agentes de biocontrole. O presente estudo teve como objetivo estudar o potencial de uso de ramnolipídeos, em diferentes condições de concentração e temperatura, no controle e remoção de biofilmes de patógenos alimentares formados em meio de cultura e leite. Foram utilizadas Escherichia coli ATCC 43895, Listeria monocytogenes ATCC 19112, Staphylococcus aureus ATCC 8095, reconhecidos patógenos alimentares. Os biofilmes foram formados em placas de microtitulação de poliestireno nos meios de cultivo: caldo nutriente (CN), extrato de levedura com triptona de soja (TSYE) e matriz alimentar (leite) à 37 °C, por 24 h (E. coli) e 48 h (S. aureus e L. monocytogenes). Os biofilmes foram avaliados pela quantificação da biomassa, viabilidade celular, hidrofobicidade de superfície e análises qualitativa (microscopia eletrônica de varredura e de fluorescência) e quantitativa (caracterização da matriz polimérica). O ramnolipídeo foi submetido à análise físico-química de espalhamento dinâmico de luz (DLS), espalhamento de raios-X a baixo ângulo (SAXS). Os resultados obtidos para E. coli mostraram que a concentração de RL que mais removeu o biofilme foi 2 ‰, porém em temperaturas diferentes, para o CN à 25 °C e para o leite à 37 °C, com 33 ‰ e 80 ‰ de remoção, respectivamente. Para o biofilme de S. aureus em caldo nutriente os resultados mais eficientes foram à 25 °C, na concentração de 0,1 ‰ de RL e em leite 4 °C, na concentração de 0,05 ‰ de RL, com remoção de 35 ‰ e 89 ‰, respectivamente. O biofilme de L. monocytogenes em TSYE mostrou-se mais sensível à 37 °C, na concentração 0,5 ‰ de RL, o qual foi possível remover 35,3 ‰ da biomassa. Enquanto que em leite a 4 °C e 0,5 ‰ de RL, com remoção de 63,6 ‰ .Quanto à redução das células viáveis foi observado que para as bactérias Gram-positivas o tratamento mais efetivo foi à 4 °C com 0,05 ‰ de RL, nos meios CN e TSYEe 1 ‰ em leite. Para os biofilmes de E. coli a maior redução da viabilidade ocorreu em leite, após tratamento com RL 0,05 ‰ à 37 °C. As imagens de microscopia mostraram uma morfologia heterogênea na presença dos diferentes meios de cultivos, com destaque para os biofilmes de S. aureus (leite) e L. monocytogenes (TSYE), nos quais houve grande produção de matriz polimérica extracelular (MPE), e também apresentaram as maiores quantidades de carboidratos e proteínas. O tratamento com o ramnolipídeo reduziu a hidrofobicidade dos biofilmes. As análises de DLS e SAXS mostraram uma predominância em número de micelas com diâmetro entre 1-10 nm, independente das concentrações e temperaturas analisadas. De modo geral, a aplicação de ramnolipídeo promoveu remoção da biomassa celular como também redução de células viáveis presentes no biofilme. As evidências obtidas aqui, podem ser importantes subsídios para futuras investigações sobre as interações físico-químicas entre ramnolipídeos e a camada de biofilme visando aplicação como agentes sanitizantes em indústria de alimentos. / Biofilm formation is a concern to the food industry because it is a chronic source of contamination. Finding effective strategies to control the growth of microorganisms remains a major challenge. One strategy is the use of rhamnolipids (RLs), a biosurfactant typically produced by P. aeruginosa that has potential as antimicrobial, anti-adhesive and biofilm disrupting agent. RLs low toxicity, biodegradability, efficiency and specificity comparatively to synthetic surfactants, makes them promising biocontrol agents. This work aimed to study the potential use of rhamnolipid at different conditions of concentration and temperature, to control and removal of biofilms of food pathogens established in culture medium and milk. The bacterial strain utilized Escherichia coli ATCC 43895, Listeria monocytogenes ATCC 19112, Staphylococcus aureus ATCC 8095, are well-recognized food pathogens. The biofilms were formed in polystyrene microtiter plates in culture media: nutrient broth (NB), yeast extract and tryptone soya (TSYE) and in food matrix (milk) at 37 °C for 24 h (E. coli) and 48 h (S. aureus and L. monocytogenes). Biofilms were assessed by biomass quantification, cell viability, surface hydrophobicity, qualitative (scanning electron microscopy and fluorescence) and quantitative (characterization of polymer matrix) analysis. The rhamnolipid was subjected to physical and chemical analysis of dynamic light scattering (DLS) and X-ray small angle scattering (SAXS). E. coli biofilms were removed more efficiently using 2 ‰ RL, but at different temperatures for NB (25 °C) and milk (37 °C) showing 33 ‰ and 80 ‰ respectively. For the biofilm of S. aureus in NB the best results was obtained at 25 °C and 0.1 ‰ RL and in milk medium at 4 °C with 0.05 ‰ RL showing 35 ‰ and 89 ‰ of biofilm disruption, respectively. The biofilm of L. monocytogenes in TSYE was more sensitive to the treatment at 37 °C with 0.5 ‰ RL, removing 35.3 ‰ of the biofilm; while in milk at 4 °C and 0.5 ‰ RL, biofilm removal reached 63.6 ‰. Reduction on cell viability was more effective for Gram-positive bacteria at 4 °C with 0.05 ‰ RL, for NB and TSYE and at 1 ‰ in milk. For E. coli biofilms the largest reduction of viability occurred in milk after treatment with 0.05 ‰ RL at 37 °C. The microscopy images showed a heterogeneous morphology in the presence of different media, especially biofilms of S. aureus (milk) and L. monocytogenes (TSYE), in which there was a great production of extracellular polymeric matrix (EPM), and also the highest amounts of carbohydrates and protein. The treatment with RL reduced the hydrophobicity of biofilms. The DLS and SAXS analysis of RL showed a predominance of micelles with diameters between 1-10 nm, independent of the concentrations and temperatures utilized. In general, the application of rhamnolipid promoted a reduction in biofilm mass as well in cell viability. The evidences obtained can provide a basis for future research on the physical and chemical interactions between rhamnolipid and biofilm layer aiming their application as sanitizers in food industry.