The development of novel, multifunctional wound dressings is essential in the goal of achieving new therapies able to increase the quality of the treatment of patients suffering from insufficient wound healing, especially in the case of chronic and infected wounds. Based on the high social, economic and personal impact of skin wounds, ideal wound dressings able to actively protect the wounded skin and promote the healing process are in demand. Among other properties, modern wound dressings should be easy to produce (cost-effective) and should combine antibacterial with angiogenic properties in addition of being mechanically robust and pliable for easy application. Wound dressings, which can be used to deliver topically drugs or molecules, are of great interest as they can face the challenges leading to an effective wound healing process.
Bioactive glasses (BGs) are a class of non-crystalline, inorganic materials able to release biologically active ions during implantation in the human body, which can induce specific cell responses such as accelerating haemostasis and angiogenesis. Research on BGs has mainly focused on their use in the field of bone replacing devices and bone tissue engineering. However, an increasing amount of studies is reporting promising results on the use of BGs in the regeneration of soft tissues and in wound healing. By designing new BG compositions with the capability to release ions that induce specific biological reactions, the applications of BGs are being further expanded in soft tissue repair. In this context, BGs have shown great potential for wound healing applications especially when BG compositions incorporating biologically active ions have been considered. Therefore, in the first part of this study, copper and/or zinc containing borosilicate and borate BGs were designed for wound healing applications. Copper was chosen to impart angiogenic properties and zinc to introduce antibacterial effects. The fabricated BGs were chemically and physically characterized and they showed excellent dissolution properties which were investigated by dissolution experiments carried out in simulated body fluid, lactic acid and TRIS solutions. Most importantly, especially the series of borate BGs containing copper and/or zinc showed promising results in an antibacterial study and were additionally tested in contact with immune cells. It was found that by using different compositions and concentrations of BGs, immune reactions can be actively (depending on the final application) dampened or induced,which can be achieved by the controlled release of therapeutic ions, in the present case, Zn and Cu.
In order to be useful for applications in wound dressings, BGs must be applied in desired shapes having flexible and pliable characteristics and suitable pore structure. Therefore, in the second part of this thesis, BGs in particulate form (particle size range of 5-20 μm) were combined with methylcellulose (MC) crosslinked with Manuka honey (MH) to achieve flexible and mechanically stable structures. Due to its great biocompatibility and thermosensitive behaviour, MC was chosen, while MH was selected as an innovative cross-linker. Besides providing crosslinking potential, which could be proven in this work by Fourier transform infrared spectroscopy (FTIR), MH was also chosen due to its favourable effects such as promoting epithelialization and antibacterial activity. By using three different fabrication methods, namely freeze drying, electrospinning and 3D printing, different types of wound dressings composed of MC and MH doped with BG particles were fabricated. Freeze dried MC-MH foams containing Cu-doped borate BG particles showed a high porosity (around 95%) and improved wettability. Moreover, the foams showed suitable mechanical properties (compressive strength: ~40 kPa) while acellular in vitro dissolution tests in simulated body fluid indicated the bioactivity of the composite foams. Most importantly, cell biology tests using fibroblasts, keratinocytes and endothelial cells indicated the material biocompatibility and the foams showed superior antibacterial effects against both E. coli and S. aureus bacteria. By additionally combining MC-MH and BG particles with the polymer poly(ɛ-caprolactone) (PCL), which is well-known as a biocompatible and biodegradable polyester, composite fibre mats were fabricated by electrospinning. PCL-MH blend fibre mats containing BG particles (particle size of 5-20 μm) were composed of nanofibers in the range of 100-300 nm and showed a contact angle of around 45°, which is favourable to promote cell attachment due to the hydrophilic character of the surface. Although the ultimate tensile strength of the fibres was slightly reduced by the addition of MH and BG (from around 5 to 3 MPa), the tensile strain was not affected (in the range of 50%). In accordance with the freeze-dried foams, cell biology tests using fibroblasts and keratinocytes indicated the biocompatibility of the electrospun fibre mats. However, tests using E. coli and S. aureus showed no antibacterial efficiency of the fibre mats, indicating the need of further optimization by e.g. increasing the amount of MH and BG. By using phosphate buffer saline as solvent, MC-MH inks containing BG particles (particle size range of 5-20 μm) were successfully produced and used for 3D printing. Mechanical characterization of the 3D printed MC-MH scaffolds showed that the mechanical properties can be tuned by adding different amounts of BG particles into the ink. Moreover, the degradation properties of the resulting printed BG containing MC-MH scaffolds wereimproved in comparison to the too fast dissolving MC-MH scaffolds without the addition of BG. Cell biology tests using fibroblasts further showed the biocompatibility of the MC-MH-BG scaffolds, which indicates that MC-MH-BG inks are innovative for 3D printing and they should be further investigated for their use in the field of biofabrication of personalized wound dressings.
In summary, the use of ion-doped borate and borosilicate BGs is a promising strategy in the development of novel wound dressings that offer several therapeutic effects such as being antibacterial and angiogenic. In this thesis, BG particles were for the first time combined with MH and MC in different types of devices by using different fabrication methods, demonstrating the versatile nature of these material combinations. The successful application of MH as natural crosslinker in combination with ion-doped BGs, enable the fabrication of different wound dressings offering various advantages. Whereas freeze dried wound dressings are especially interesting in the treatment of infected, deep wounds, electrospun fibre mats are important for superficial wounds. Inks based on MC-MH in combination with BGs demonstrated an attractive biomaterial platform for 3D printing as they open a new field for further research focusing on biofabrication. Overall, the results obtained in this thesis showed the great potential of ion-doped BGs in combination with MC and MH for the fabrication of antibiotic-free wound dressings capable of preventing infections and with extra functionality to promote wound regeneration
