Surface nano-structured materials to control bacterial contamination

The spread of bacteria and infections, initially associated with an increased number of hospital-acquired infections, has now extended into the community causing severe and difficult to treat diseases. Additionally, many of those diseases are evoked by bacteria that have become resistant to antibiotics. Overcoming the ability of bacteria to develop resistance will potentially reduce the burden of these infections on the healthcare systems worldwide and prevent thousands of deaths each year. The nano-scale particles are promising candidates to fight bacteria, since developing of resistance to their action is less likely to occur. Nanoparticles (NPs) can be incorporated into polymeric matrices to design a wide variety of nanocomposites. Such nano-structures consisting of inorganic and inorganic/organic NPs represent a novel class of materials with a broad range of applications. This thesis is about the development of antibacterial nano-structured materials aimed at preventing the spread of bacteria. To achieve this, two versatile physicochemical and biotechnological tools, namely sonochemistry and biocatalysis were innovatively combined. Ultrasound irradiation used for the generation of various nano-structures and its combination with biocatalysts (enzymes) opens new perspectives in materials processing, here illustrated by the production of NPs coated medical textiles, water treatment membranes and chronic wound dressings. The first part of the thesis aims at the development of antibacterial medical textiles to prevent the bacteria transmission and proliferation using two single step approaches for antibacterial NPs coating of textiles. In the first approach antibacterial zinc oxide NPs (ZnO NPs) and chitosan (CS) were deposited simultaneously on cotton fabric by ultrasound irradiation. The obtained hybrid NPs coatings demonstrated durable antibacterial properties after multiple washing cycles. Moreover, the presence of biopolymer in the NP hybrids improved the biocompatibility of the material in comparison with ZnO NPs coating alone. In the second approach, a simultaneous sonochemical/enzymatic process for durable antibacterial coating of cotton with ZnO NPs was carried out. The enzymatic treatment provides better adhesion of the ZnO NPs and, as a consequence, enhanced coating stability during exploitation. Likewise to the antibacterial coatings obtained in the first approach, the antibacterial efficiency of these textiles was maintained after multiple intensive laundry regimes used in hospitals. The NPs-coated cotton fabrics inhibited the growth of the most medically relevant bacteria species. In the second part of the thesis, hybrid antibacterial biopolymer/silver NPs and cork matrices, were enzymatically assembled into an antimicrobial material with potential for water remediation. Intrinsically antibacterial amino-functional biopolymers, namely CS and aminocellulose were used as doping agents to stabilize colloidal dispersions of silver NPs (AgNPs), additionally providing the particles with functionalities for covalent immobilization on cork to impart durable antibacterial effect. The biopolymers promoted the antibacterial efficacy of the obtained nanocomposites in conditions simulating a real situation in constructed wetlands. In the last, third part of the thesis, a bioactive nanocomposite hydrogel for wound treatment was developed. Sonochemically synthesized epigallocatechin gallate nanospheres (EGCG NSs) were incorporated and simultaneously crosslinked enzymatically into a thiolated chitosan hydrogel. The potential of the generated material for chronic wound treatment was evaluated by assessing its antibacterial properties and inhibitory effect on myeloperoxidase and collagenase biomarkers of chronic wound infection. Sustained release of the EGCG NSs from the biopolymer matrix was achieved. The latter, coupled with the good biocompatibility of the hydrogel, suggested its potential for chronic wound management.La propagación de bacterias e infecciones, inicialmente limitada a infecciones adquiridas en el hospital, se ha extendido al resto de la sociedad causando enfermedades muy graves y más difíciles de tratar. Además, muchas de estas enfermedades son provocadas por bacterias que se han hecho resistentes a los antibióticos convencionales. Por lo tanto, limitar la capacidad de estas bacterias para desarrollar resistencia puede potencialmente reducir la alta incidencia de estas infecciones y evitar miles de muertes cada año. Las partículas de escala nanométrica son unas candidatas prometedoras para combatir las bacterias, ya que su mecanismo de acción las hace disminuir las probabilidades en el desarrollo de resistencia. Las nanopartículas (NPs) se pueden incorporar en matrices poliméricas para diseñar una amplia variedad de materiales nanocompuestos. Estas nanoestructuras consisten en NPs orgánicas/inorgánicas e inorgánicas representando una nueva clase de materiales con una amplia gama de aplicaciones. Esta tesis trata sobre el desarrollo de materiales antibacterianos con estructura nanométrica dirigidos a prevenir la propagación de bacterias. Para lograr esto, dos herramientas fisicoquímicas y biotecnológicas versátiles tales como sonoquímica y biocatálisis, se combinaron de manera innovadora. La irradiación por ultrasonido se ha utilizado para la generación de nanoestructuras diversas y su combinación con biocatalizadores (enzimas) abre nuevas perspectivas en el tratamiento de materiales, aquí ilustrados por la producción de textiles médicos recubiertos con NPs, membranas de tratamiento de agua y apósitos para heridas crónicas. La primera parte de la tesis tiene como objetivo el desarrollo de textiles médicos antibacterianos para prevenir la transmisión y proliferación de bacterias utilizando dos estrategias "de un solo paso" para el recubrimiento antibacteriano de estos textiles con NPs. En el primer enfoque NPs antibacterianas de óxido de zinc (ZnO NPs) y quitosano (CS) fueron depositadas simultáneamente sobre tejido de algodón por irradiación de ultrasonido. Los recubrimientos híbridos de NPs obtenidos demostraron propiedades antibacterianas duraderas después de varios lavados exhaustivos. Por otra parte, la presencia de biopolímeros en las NPs híbridas mejoraba la biocompatibilidad del material en comparación con el recubrimiento de solamente de ZnO NPs. En la segunda parte de la tesis, híbridos antibacterianos hechos de biopolímeros y NPs de plata y matrices de corcho, fueron ensamblados enzimáticamente en un material antimicrobiano para su utilización en la remediación de aguas. Biopolímeros antibacterianos aminofuncionalizados (CS y aminocelulosa) se utilizaron como agentes dopantes para estabilizar las dispersiones coloidales de plata (Ag NPs). Además, estas partículas presentan todas las funciones necesarias para su inmovilización covalente en el corcho proporcionando un efecto antibacteriano duradero. Estos biopolímeros aumentaron la eficacia antibacteriana de estos nanocompuestos en condiciones que simulan una situación real en humedales construidos. En la tercera parte de la tesis, se desarrolló un hidrogel nanocompuesto bioactivo para el tratamiento de heridas crónicas. Nanoesferas de galato de epigalocatequina (EGCG NSs) fueron sintetizadas a través de sonoquimica y se incorporaron y simultáneamente reticularon enzimáticamente en un hidrogel de quitosano tiolado. El potencial del material generado para el tratamiento de heridas crónicas fue evaluado por sus propiedades antibacterianas y su efecto inhibidor sobre biomarcadores producidos en heridas crónicas infectadas (mieloperoxidasa y colagenasa). También se consiguió la liberación sostenida de EGCG NSs por parte de la matriz generada, que junto con su buena biocompatibilidad, demostraba su potencial para el tratamiento de heridas crónicas

Enzyme-assisted formation of hybrid biopolymer hydrogels incorporating active phenolic nanospheres

This work is about the synthesis of hybrid nanocomposite hydrogels comprising a thiolated chitosan platform that incorporates epigallocatechin gallate nanospheres as active polyphenolic agents for wound healing applications. The phenolic nanospheres were prepared using an industry-attractive, low-cost and fast sonochemical technology, whereas the gel formation was achieved via a green approach involving the enzymatic cross-linking with horseradish peroxidase, avoiding the use of harsh chemical cross-linkers. The superior functional properties of the phenolic nanospheres compared to their molecular counterparts are demonstrated by better attenuation of the chronicity factors found in non-healing wounds. Release of the intact and functional phenolic nanospheres coupled to good biocompatibility of the system during several days, reveals potential of this hybrid material as a dressing with prolonged activity for chronic wound management.Peer ReviewedPostprint (published version

Enzyme-assisted formation of hybrid biopolymer hydrogels incorporating active phenolic nanospheres

This work is about the synthesis of hybrid nanocomposite hydrogels comprising a thiolated chitosan platform that incorporates epigallocatechin gallate nanospheres as active polyphenolic agents for wound healing applications. The phenolic nanospheres were prepared using an industry-attractive, low-cost and fast sonochemical technology, whereas the gel formation was achieved via a green approach involving the enzymatic cross-linking with horseradish peroxidase, avoiding the use of harsh chemical cross-linkers. The superior functional properties of the phenolic nanospheres compared to their molecular counterparts are demonstrated by better attenuation of the chronicity factors found in non-healing wounds. Release of the intact and functional phenolic nanospheres coupled to good biocompatibility of the system during several days, reveals potential of this hybrid material as a dressing with prolonged activity for chronic wound management.Peer Reviewe

Variation in life history traits of cowpea weevil (Callosobruchus maculatus (F.) and Callosobruchus chinensis (L.)) With particular reference to oviposition behaviour

SIGLEAvailable from British Library Document Supply Centre- DSC:DX97499 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Simultaneous sonochemical-enzymatic coating of medical textiles with antibacterial ZnO nanoparticles

The antimicrobial finishing is a must for production of medical textiles, aiming at reducing the bioburden in clinical wards and consequently decreasing the risk of hospital-acquired infections. This work reports for the first time on a simultaneous sonochemical/enzymatic process for durable antibacterial coating of cotton with zinc oxide nanoparticles (ZnO NPs). The novel technology goes beyond th

Sonochemical coating of textiles with hybrid ZnO/chitosan antimicrobial nanoparticles

Textiles are good substrates for growth of microorg anisms especially under moisture and temperature conditions found in hospitals. Microbia l shedding from the body occurs continuously at contact of the patient with textile materials used in medical practice, contributing to the occurrence of hospital acquired infections. Thus, the use of efficient antimicrobial textiles is necessary to prevent the transfer of pathogens a nd the infection incidence. In this work, hybrid antimicrobial coatings were generated on cotton fab rics by means of a one-step simultaneous sonochemical deposition of ZnO nanoparticles (NPs) and chitosan. The process was further optimized in terms of reagents concentration and pr ocessing time in order to improve the antibacterial properties of the fabric and ensure t heir biocompatibility. The highest antibacterial activity of the fabrics against two medically relev ant bacterial species was achieved in a 30 min sonochemical coating process using 2 mM ZnO NPs sus pension. When chitosan was simultaneously deposited with the same amount of Zn O, the obtained hybrid NPs coating displayed higher by 48 and 17 % antibacterial activ ity against Staphylococcus aureus and Escherichia coli , respectively. The presence of biopolymer also imp roved the durability of the antimicrobial effect of the coatings by 21 % for Staphylococcus aureus and 40 % for Escherichia coli , evaluated after applying multiple washing cycles at hospital laundering regimes. Finally, 87 % biocompatibility improvement supported by fibrobl ast viability was observed for the hybrid ZnO/chitosan coating compared to the steady decreas e of cells viability over one week in contact with the fabrics coated with ZnO alone.Peer Reviewe

Sonochemical coating of textiles with hybrid ZnO/chitosan antimicrobial nanoparticles

Textiles are good substrates for growth of microorg anisms especially under moisture and temperature conditions found in hospitals. Microbia l shedding from the body occurs continuously at contact of the patient with textile materials used in medical practice, contributing to the occurrence of hospital acquired infections. Thus, the use of efficient antimicrobial textiles is necessary to prevent the transfer of pathogens a nd the infection incidence. In this work, hybrid antimicrobial coatings were generated on cotton fab rics by means of a one-step simultaneous sonochemical deposition of ZnO nanoparticles (NPs) and chitosan. The process was further optimized in terms of reagents concentration and pr ocessing time in order to improve the antibacterial properties of the fabric and ensure t heir biocompatibility. The highest antibacterial activity of the fabrics against two medically relev ant bacterial species was achieved in a 30 min sonochemical coating process using 2 mM ZnO NPs sus pension. When chitosan was simultaneously deposited with the same amount of Zn O, the obtained hybrid NPs coating displayed higher by 48 and 17 % antibacterial activ ity against Staphylococcus aureus and Escherichia coli , respectively. The presence of biopolymer also imp roved the durability of the antimicrobial effect of the coatings by 21 % for Staphylococcus aureus and 40 % for Escherichia coli , evaluated after applying multiple washing cycles at hospital laundering regimes. Finally, 87 % biocompatibility improvement supported by fibrobl ast viability was observed for the hybrid ZnO/chitosan coating compared to the steady decreas e of cells viability over one week in contact with the fabrics coated with ZnO alone.Peer Reviewe