Development of multifunctional biopolymeric materials for teatment of decubitus ulcers
Authors:   , Rocasalbas Lozano Guillermo 
Published: September 2023

Chronic wounds including pressure, venous, arterial and diabetic neuropathic ulcers, represent a significant burden to the healthcare system. These different chronic wound types do not share origin or cause, however they have common features as bacterial infection and continuing influx of polymorphonuclear neutrophils that release high concentrations of matrix metalloproteases (MMPs), myeloperoxidase (MPO) and reactive oxidative species causing excessive degradation of the extracellular matrix (ECM) and the growth factors. Because of the multifactorial nature of virtually all chronic wounds, the therapeutic wound healing approach should emphasize the necessity to investigate wound dressings that possess the ability to directly and indirectly modulate the biochemical environment based on the pathology of chronic to encourage the healing process.
The overall aim of the present work was to develop biopolymer wound dressings capable to improve the management of chronic wounds. The specific research objective was defined in three main targets: i) to balance the proteolytic activity of MMPs, ii) to balance the MPO activity and the oxidative environment, and iii) antimicrobial protection.
The first part of the thesis aimed to provide suitable materials to perform bioactive biopolymer-based wound dressings. The first step was to provide a versatile functionalization of chitosan platform to improve the sequestering ability over metal dependent enzymes (MMPs) in chronic wounds. In order to impart to chitosan the ability to inhibit MMP, chitosan was functionalized with deferent thiol moieties, which can chelate the zinc cation in the active site of the enzyme, modifying MMP activity. In addition the combination of -NH2 and -SH chemistry allowed grafting of other active agents on the chitosan platform.
The second step was the identification and evaluation of natural active agents as chronic wound healing promoters. Polyphenols from bark, twigs and leaf extracts from the medicinal plant Hamamelis virginiana (Witch hazel) were studied for this porpoise and it was found to have both a strong antioxidant activity and an inhibitory effect on MPO and collagenase.
The second part of the thesis was focused in the performance and evaluation of new materials for wound healing applications. To this aim, chitosan and/or thiolated chitosan were modified with H. virginiana extracts following different approaches.
The first approach was focused to develop a new method for covalent functionalization of thiolated chitosan with polyphenols from H. virginiana extracts. The novelty of this approach consists in the use of thiolysis - a common analytical method for proanthocyanidins characterization - to covalently functionalize natural macromolecules such as chitosan with bioactive phenolic moieties. The phenolics-functionalized chitosan showed improved therapeutic properties in vitro.
The second approach focused on the use of laccase-assisted cross-linking between phenolic moieties of H. virginiana with chitosan and gelatin as a functionalization method to obtain stable and bioactive hydrogel wound dressings. H. virginiana extract was oxidized by laccase in a one-step process under mild reaction conditions to covalently crosslink chitosan and gelatin. The physical and mechanical properties of these hydrogels were investigated using different analytical techniques and their potential for chronic wound treatment was evaluated in vitro in terms of antibacterial and inhibitory effect on MPO and collagenase. The results indicated that the polyphenols exerted a dual role in the hydrogel: i) "passive" being a structural element, and ii) "active" modifying the chronic wound environment by attenuating the deleterious MMPs, MPO and ROS activities, and reducing the bacterial load.