Chronic wounds present a major unmet clinical problem. They arise from wounds that fail to progress through the normal phases of healing due to factors that compound healing such as vascular complications, or diabetes. Despite improvements in treatments for difficult wounds, the incidence of limb amputation remains high. Therefore there is a need for more active therapies.
Mesenchymal stem cells (MSCs) have the capacity to differentiate into multiple cell-types, however they have also been shown to release a plethora of growth factors and cytokines which are beneficial to wound healing, consequently MSCs have shown to improve wound healing outcomes in a predominantly paracrine fashion. MSCs, for example, can increase angiogenesis/ neovascularisation, modulate inflammatory responses, accelerate re-epithelialisation, and increase collagen deposition.
The first objective of the work was to develop a synthetic material based delivery method for MSCs that could be used in the clinic. Plasma polymerisation was used to surface-functionalise medical grade silicone with acrylic acid. The acid surface chemistry enhanced cell attachment to the silicone, and cells could effectively be transferred from the silicone to model wound beds comprised of decellularised dermis (DED). Once the cells were delivered they remained viable, and the acrylic acid surface chemistry was found not to affect the MSC phenotype or their functional capacity prior to cell delivery.
The second part of the project involved developing a 3-D wound model using tissue-engineered (TE) skin, in which to assess the benefit of MSCs, and applying non-invasive imaging to monitor wound healing using optical coherence tomography (OCT). TE skin is reconstructed from DED by the addition of laboratory expanded fibroblasts and keratinocytes, and it possesses a functional epithelium. Full-thickness incisional wounds were created in TE skin, and fibrin clots containing cells could be inserted into the wound cavity; wounds healed after 14 days. OCT could clearly identity structural features of skin (including the dermis, epidermis and fibrin clot) with good correspondence to histology. Appropriate sampling of the wounds by OCT was determined, and consistency in identifying corresponding wound regions within a sample over time was addressed, so that wound volumes could be calculated and compared.
Finally MSCs were introduced to the wound model. MSCs were found not to reduce the rate of wound closure in the dermal portion of the wound, however they did accelerate re-epithelialisation and this was detectable by OCT. Additionally, cytokine analysis was performed on the surrounding medium under wound conditions. In the presence of MSCs, wound medium contained more hepatocyte growth factor (HGF) and basic fibroblast growth factor (bFGF). Elevated levels of these beneficial factors to wound healing were associated with an early onset of epithelialisation
