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Multifunctional Biopolymer-Based Materials for Modulating the Activities of Chronic Wound Enzymes

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Multifunctional Biopolymer-Based Materials for Modulating the Activities of Chronic Wound Enzymes Multifunctional biopolymer-based materials for modulating the activities of chronic wound enzymes Antonio Francesko A thesis submitted in fulfilment of the requirements for the degree of European Doctor of Philosophy at the Universitat Politècnica de Catalunya This work was carried out under the supervision of Dr. Tzanko Tzanov Group of Molecular and Industrial Biotechnology (GBMI) Department of Chemical Engineering Universitat Politècnica de Catalunya Terrassa, 2012 The work carried out during the thesis as well as the financial support of the candidate was provided by: Becas FPI Ref beca: BES-2008-003744 GBMI Group of Molecular and Industrial Biotechnology FP6-026741 Mojoj porodici... i Abstract This thesis focuses on the development of active multifunctional dressing materials and nanoparticle formulations with suitable exploitation characteristics for chronic wounds treatment. Chronic wounds – a growing clinical challenge in the aging and/or reduced mobility population – include pressure, venous, arterial and diabetic neuropathic ulcers. Due to the non-healing character of these ulcers their management requires an intensive medical intervention at huge healthcare costs. The prolonged inflammation and elevated concentrations of oxidative and proteolytic enzymes in all chronic wounds, imposes the need for novel functional dressing materials to actively modulate the wound environment at molecular level and stimulate the healing process. Based on an extensive analysis of the current state-of-the-art in chronic wound healing, the proper dressings should combine both antimicrobial and enzyme inhibitory functions coupled to optimal hydrophilicity. Such integrated approach would allow for the suppression of the persistent inflammation and stimulation of the synthesis of the dermal tissue components. Biopolymers with intrinsic antimicrobial and wound repair properties appear as appropriate matrix materials to be further upgraded with bioactive molecules (therapeutics) that couple high reactivity with the ability to address specific targets in the biochemical environment of chronic wounds. Therapeutic devices can be designed in different forms depending on the particular clinical application, i.e. wound type and its characteristics. During the thesis realisation biopolymer-based platforms were generated in various designs and functionalised with active agents for controlled inhibition of major chronic wound enzymes. The capacity of all developed materials to inhibit proteolytic (e.g. collagenase) and oxidative (e.g. myeloperoxidase) enzymes involved in chronic inflammation was evaluated in vitro. In the first approach sponge-like biopolymer matrices were produced via freeze-drying technique and controlled chemical cross-linking. These matrices were further impregnated with natural polyphenolic compounds. Modulation of the deleterious wound enzyme activities was achieved upon release of active agent from the platform. The exploitation characteristics of the sponges, i.e. mechanical properties, biostability, biocompatibility, extent and duration of wound enzymes inhibition, were tuned by: the biopolymer composition, concentration of the cross-linking agent, and the proper selection of the bioactive phenolic compounds. The second approach aimed at the permanent functionalisation of the biopolymeric platforms with thiol-bearing compounds. In this case the active agent is expected to act from the platform, without being released into the wound. The obtained thiolated biopolymers were further processed into functional nanomaterials of different design: vii Nanoscale films/coatings were built using a layer-by-layer approach for alternate deposition of oppositely charged polyelectrolytes. Naturally occurring glycosaminoglycans were used as counterions to cationic thiolated conjugates. Nanoparticle formulations were obtained from thiolated conjugates in a one-step sonochemical process. In both cases the biopolymer thiolation degree was identified as a key factor for the successful fabrication of the multilayered coatings and nanoparticles, as well as to achieve control of the thickness/size of the functional nanomaterials. In addition, tuneable inhibition/adsorption of the deleterious enzymes coupled to fibroblast attachment/proliferation was observed by ruling the biopolymer modification degree. Keywords: Biopolymers • Polyphenols • Thiol compounds • Functionalisation • Cross-linking • Functional materials • Wound dressings • Myeloperoxidase • Collagenase • Chronic wounds • Enzyme inhibition • Wound healing viii Table of Contents Abstract ................................................................................................................................................. vii Table of Contents ................................................................................................................................... ix Abbreviation list................................................................................................................................... xiii List of Figures ....................................................................................................................................... xv List of tables ........................................................................................................................................ xvii List of Schemes .................................................................................................................................. xviii Section A: Background and objectives ................................................................................................... 1 Objective of the thesis ............................................................................................................................. 3 Chapter 1: General introduction .......................................................................................................... 5 1.1 Chronic wounds: formation and pathogenesis .................................................................... 7 1.1.1 Skin and its function ................................................................................................... 7 1.1.2 Acute wounds and healing process ............................................................................. 8 1.1.3 Chronic wounds and impaired healing ...................................................................... 10 1.1.4 Chronic wound pathogens ......................................................................................... 11 1.2 Chronic wound management ............................................................................................ 14 1.3 Biopolymers as dressing materials .................................................................................... 16 1.3.1 Chitosan .................................................................................................................... 16 1.3.2 Collagen .................................................................................................................... 18 1.3.3 Glycosaminoglycans ................................................................................................. 19 1.3.4 Problematic and advanced treatment solutions ......................................................... 20 1.4 Attenuating the enzymatic activities in chronic wounds ................................................... 21 1.4.1 Active agents to modulate the enzymes activities in chronic wounds – an integrated approach.. .................................................................................................................................. 22 1.5 Modification/functionalisation of biopolymers ................................................................. 23 1.5.1 Chemically modified chitosan .................................................................................. 24 1.5.2 Chemical cross-linking of biopolymers .................................................................... 26 1.5.3 Modification/blending of biopolymers using enzymatic tools .................................. 29 1.6 Dressing design ................................................................................................................. 31 1.7 Research objectives ........................................................................................................... 32 SECTION B: Dressing platforms loaded with plant polyphenols ........................................................ 35 Chapter 2: Cross-linked biopolymer sponges ................................................................................... 37 2.1 Introduction ....................................................................................................................... 39 2.2 Materials and methods ...................................................................................................... 40 2.2.1 Biopolymers .............................................................................................................. 40 2.2.2 Reagents .................................................................................................................... 40 2.2.3 Preparation of biopolymer sponges ........................................................................... 40 2.2.4 Determination of the degree of collagen cross-linking with genipin ........................ 41 2.2.5 Scanning electron microscopy (SEM) ...................................................................... 41 2.2.6 Fourier transform infrared spectroscopy (FTIR) ......................................................
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