Development and fabrication of plant-based drug delivery polymeric systems for skin wound healing applications

Skin wound dressings are commonly used to stimulate and improve the repair of the injured tissue. In a healthy organism, the wound healing process is a highly articulate cascade of events that take place sequentially but with an overlap. Commercially available patches and sterile gauzes are commonly used to separate the wound from the external environment and avoid bacterial contaminations. Although constituting a physical barrier that protects the wound area, these systems do not possess some pivotal characteristics that can effectively guide the healing process. In the last decades, the interest in exploiting the properties of natural-based polymers (e.g. biocompatibility, non-toxicity, biodegradability) for wound dressing fabrication has been growing. Natural polymers are a promising class of materials able to improve the healing process and protect the wound against bacterial infections. In particular, plant-based biopolymers have been shown promising features that make them ideal for the fabrication of nano/micro-structured scaffolds for wound healing applications. More detailed considerations about it will be discussed in Chapter 1. This doctoral thesis aimed to develop and fabricate plant-based wound dressings, mainly composed of zein, an alcohol-soluble protein extracted from corn, and pectin, the most abundant polysaccharide placed in the plant cell wall. In the literature, there are some studies in which zein and pectin were mixed to produce micro/nanoparticles. Nonetheless, little is known about their blends used for the production of other types of micro and nanocomposites, such as films and nano/microfibers. In the first project, discussed in Chapter 2, zein and pectin were used to fabricate composite polymeric films. The samples were chemically and physically analyzed. The degradation rate of the samples was monitored over time after their immersion in various buffers with different pH values. The presence of the pectin inside the composite films led to a faster degradation rate, as also demonstrated by thermogravimetric analyses. This trend was also confirmed by monitoring the release of a hydrophilic model compound loaded inside the constructs, which resulted in a higher release for the samples containing pectin. Moreover, the films showed the ability to inhibit the growth of three skin pathogens (Staphylococcus aureus, Escherichia coli, and Candida albicans), demonstrating an excellent antimicrobial activity. Finally, in vitro biocompatibility was confirmed on a representative class of skin cells via MTS assay and through cell morphology inspection by confocal microscopy. In a second project, discussed in Chapter 3, plant-based microfibrous scaffolds were fabricated through vertical electrospinning, starting from various zein/pectin formulations. These systems were loaded with various concentrations of a bioactive molecule, Vitamin C (VitC), evaluating its release from the 3D scaffolds over time in parallel to its antioxidant properties and collagen synthesis stimulation activity. Pectin's ability to crosslink in the presence of Ca2+ was exploited by immersing the samples in a calcium chloride solution. In this way, non-crosslinked and crosslinked samples were obtained, characterized, and compared. The main comparisons were made in terms of degradation rate and water uptake ability. These analyses highlighted the ability of the crosslinked samples to behave as a hydrogel when immersed in an aqueous solution, resulting in a more susceptibility toward a tested protease. In vitro biocompatibility was confirmed on two representative skin cell populations through MTS assay, confocal microscopy investigation, and direct plating test. Subsequently, the ability of the VitC to stimulate the synthesis of collagen in fibroblasts was confirmed by RT-PCR. Finally, the samples that showed better biocompatibility and gene expression characteristics were selected for the in vivo test on a mouse model of skin burns. The investigation outcomes demonstrated the ability of our newly designed construct to significantly reduce the inflammatory cytokine in the wound area. Lastly, the general conclusions of this thesis study and some considerations for future steps are summarized in Chapter 4.