Plants as a cost-effective source for customizable photosynthetic wound dressings: A proof of concept study.

Oxygen is essential for tissue regeneration, playing a crucial role in several processes, including cell metabolism and immune response. Therefore, the delivery of oxygen to wounds is an active field of research, and recent studies have highlighted the potential use of photosynthetic biomaterials as alternative oxygenation approach. However, while plants have traditionally been used to enhance tissue regeneration, their potential to produce and deliver local oxygen to wounds has not yet been explored. Hence, in this work we studied the oxygen-releasing capacity of Marchantia polymorpha explants, showing their capacity to release oxygen under different illumination settings and temperatures. Moreover, co-culture experiments revealed that the presence of these explants had no adverse effects on the viability and morphology of fibroblasts in vitro, nor on the viability of zebrafish larvae in vivo. Furthermore, oxygraphy assays demonstrate that these explants could fulfill the oxygen metabolic requirements of zebrafish larvae and freshly isolated skin biopsies ex vivo. Finally, the biocompatibility of explants was confirmed through a human skin irritation test conducted in healthy volunteers following the ISO-10993-10-2010. This proof-of-concept study provides valuable scientific insights, proposing the potential use of freshly isolated plants as biocompatible low-cost oxygen delivery systems for wound healing and tissue regeneration.

Microalgae share key features with human erythrocytes and can safely circulate through the vascular system in mice.

As animal cells cannot produce oxygen, erythrocytes are responsible for gas interchange, being able to capture and deliver oxygen upon tissue request. Interestingly, several other cells in nature produce oxygen by photosynthesis, raising the question of whether they could circulate within the vascular networks, acting as an alternative source for oxygen delivery. To address this long-term goal, here some physical and mechanical features of the photosynthetic microalga Chlamydomona reinhardtii were studied and compared with erythrocytes, revealing that both exhibit similar size and rheological properties. Moreover, key biocompatibility aspects of the microalgae were evaluated in vitro and in vivo, showing that C. reinhardtii can be co-cultured with endothelial cells, without affecting each other's morphology and viability. Moreover, short-term systemic perfusion of the microalgae showed a thoroughly intravascular distribution in mice. Finally, the systemic injection of high numbers of microalgae did not trigger deleterious responses in living mice. Altogether, this work provides key scientific insights to support the notion that photosynthetic oxygenation could be achieved by circulating microalgae, representing another important step towards human photosynthesis. KEY POINTS: • C. reinhardtii and endothelial cells are biocompatible in vitro. • C. reinhardtii distribute throughout the entire vasculature after mice perfusion. • C. reinhardtii do not trigger deleterious responses after injection in mice.

Development of an implantable three-dimensional model of a functional pathogenic multispecies biofilm to study infected wounds.

Chronic wounds cannot heal due to impairment of regeneration, mainly caused by the persistent infection of multispecies biofilms. Still, the effects of biofilm wound infection and its interaction with the host are not fully described. We aimed to study functional biofilms in physiological conditions in vitro, and their potential effects in health and regeneration in vivo. Therefore, Pseudomonas aeruginosa, Staphylococcus aureus and Enterococcus faecalis were seeded in collagen-based scaffolds for dermal regeneration. After 24 h, scaffolds had bacterial loads depending on the initial inoculum, containing viable biofilms with antibiotic tolerance. Afterwards, scaffolds were implanted onto full skin wounds in mice, together with daily supervision and antibiotic treatment. Although all mice survived their health was affected, displaying fever and weight loss. After ten days, histomorphology of scaffolds showed high heterogeneity in samples and within groups. Wounds were strongly, mildly, or not infected according to colony forming units, and P. aeruginosa had higher identification frequency. Biofilm infection induced leucocyte infiltration and elevated interferon-γ and interleukin-10 in scaffolds, increase of size and weight of spleen and high systemic pro-calcitonin concentrations. This functional and implantable 3D biofilm model allows to study host response during infection, providing a useful tool for infected wounds therapy development.

Development of a Novel Perfusable Solution for ex vivo Preservation: Towards Photosynthetic Oxygenation for Organ Transplantation.

Oxygen is the key molecule for aerobic metabolism, but no animal cells can produce it, creating an extreme dependency on external supply. In contrast, microalgae are photosynthetic microorganisms, therefore, they are able to produce oxygen as plant cells do. As hypoxia is one of the main issues in organ transplantation, especially during preservation, the main goal of this work was to develop the first generation of perfusable photosynthetic solutions, exploring its feasibility for ex vivo organ preservation. Here, the microalgae Chlamydomonas reinhardtii was incorporated in a standard preservation solution, and key aspects such as alterations in cell size, oxygen production and survival were studied. Osmolarity and rheological features of the photosynthetic solution were comparable to human blood. In terms of functionality, the photosynthetic solution proved to be not harmful and to provide sufficient oxygen to support the metabolic requirement of zebrafish larvae and rat kidney slices. Thereafter, isolated porcine kidneys were perfused, and microalgae reached all renal vasculature, without inducing damage. After perfusion and flushing, no signs of tissue damage were detected, and recovered microalgae survived the process. Altogether, this work proposes the use of photosynthetic microorganisms as vascular oxygen factories to generate and deliver oxygen in isolated organs, representing a novel and promising strategy for organ preservation.