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- Development of novel alginate based hydrogel films for wound healing applicationsPublication . Pereira, Rúben; Carvalho, Anabela; Vaz, Daniela C.; Gil, M. H.; Mendes, Ausenda; Bártolo, PauloAlginate and Aloe vera are natural materials widely investigated and used in the biomedical field. In this research work, thin hydrogel films composed by alginate and Aloe vera gel in different proportions (95:5, 85:15 and 75:25, v/v) were prepared and characterized. The films were evaluated regarding the light transmission behavior, contact angle measurements, and chemical, thermal and mechanical properties. These thin hydrogel films, prepared by crosslinking reaction using 5% calcium chloride solution, were also investigated relatively to their water solubility and swelling behavior. Results showed that Aloe vera improved the transparency of the films, as well their thermal stability. The developed films present adequate mechanical properties for skin applications, while the solubility studies demonstrated the insolubility of the films after 24 h of immersion in distilled water. The water absorption and swelling behavior of these films were greatly improved by the increase in Aloe vera proportion.
- 3D bioprinting of photocrosslinkable hydrogel constructsPublication . Brás Pereira, Rúben Filipe; Bartolo, PauloThree‐dimensional (3D) bioprinting comprises a group of biofabrication technologies for the additive manufacturing of 3D constructs by precisely printing biocompatible materials, cells and biochemicals in predesigned spatial positions. These technologies have been successfully applied to fabricate biodegradable 3D constructs with intricate architectures and heterogeneous composition, assuming a pivotal role in the field of tissue engineering. However, the full implementation of bioprinting strongly depends on the development of novel biomaterials exhibiting fast crosslinking schemes and appropriate printability, cell‐compatibility and biomechanical properties. Photocrosslinkable hydrogels are attractive materials for bioprinting as they provide fast polymerization under cell‐compatible conditions and exceptional spatiotemporal control over the gelation process. Photopolymerization can also be performed during the bioprinting to promote the instantaneous formation of hydrogel with high well‐defined architecture and structural stability. In this review paper, we summarize the most recent developments on bioprinting of photocrosslinkable biodegradable hydrogels for tissue engineering, focusing on the chemical modification strategies and the combination of photocrosslinking reactions with other gelation modalities.
- Fotopolimerização de hidrogéis de ácido hialurónicoPublication . Duarte, Stacy; Pereira, Rúben; Campos, Carlos; Vaz, Daniela C.; Paulo Flores et al.O ácido hialurónico (HA) é um polissacarídeo amplamente presente no organismo humano e constitui um material com potencial para ser incorporado em hidrogéis direcionados para aplicações biomédicas. No entanto, as fracas propriedades mecânicas, rápida degradação e libertação in vivo do HA não reticulado solúvel limita muitas aplicações clínicas diretas. Deste modo, com vista melhorar as suas caraterísticas materiais procedemos à modificação química do HA com anidrido metacrílico (MA), com formação de ácido hialurónico metacrilado (MeHA), com propriedades fotopolimerizáveis, combinado ainda na presença e ausência de agente gelificante extra, tal como o polissacarídeo natural iota-carragenina. O HA utilizado foi caracterizado através de espectroscopia de ressonância magnética nuclear (RMN) e de dicroísmo circular (CD). Os hidrogéis produzidos foram analisados via testes de absorção de água e de degradação em meio aquoso, bem como através de análise mecânica dinâmica (DMA) à compressão. O estudo conduzido permitiu verificar que, enquanto os biofilmes de HA se mostraram quebradiços e com fracas propriedades mecânicas, o MeHA não só foi capaz de formar hidrogéis, por fotopolimerização, como a adição do iota-carragenina à formulação, possibilitou a formação de IPNs (Interpenetrating Polymer Networks) e de semi-IPNs com melhores propriedades físicas e mecânicas.
- Monitoring the modifications of Aloe vera by high performance liquid chromatographyPublication . Tojeira, Ana; Pereira, Rúben; Bártolo, Paulo; Mendes, Ausenda; Vaz, Daniela; Oliveira, Nelson SimõesAloe vera is a widely known and studied plant due to its therapeutic properties. The therapeutic properties exhibited by the Aloe vera exudates have been associated to the presence of certain compounds, such as, chromones, anthrones and anthraquinones. In this study, we have identified, and monitored by reversed phase high performance liquid chromatography (HPLC), six major compounds present in the Aloe vera exudates. The chromatographic profiles were followed in the course of time and at different wavelengths. This monitoring allowed us to verify the constitution and modifications of the samples, in order to identify the main changes responsible for the chemical degradation and loss of proprieties exhibited by the exudates over time.
- Cell-instructive pectin hydrogels crosslinked via thiol-norbornene photo-click chemistry for skin tissue engineeringPublication . Pereira, Rúben; Barrias, Cristina C.; Bártolo, Paulo J.; Granja, Pedro L.Cell-instructive hydrogels are attractive for skin repair and regeneration, serving as interactive matrices to promote cell adhesion, cell-driven remodeling and de novo deposition of extracellular matrix compo nents. This paper describes the synthesis and photocrosslinking of cell-instructive pectin hydrogels using cell-degradable peptide crosslinkers and integrin-specific adhesive ligands. Protease-degradable hydro gels obtained by photoinitiated thiol-norbornene click chemistry are rapidly formed in the presence of dermal fibroblasts, exhibit tunable properties and are capable of modulating the behavior of embedded cells, including the cell spreading, hydrogel contraction and secretion of matrix metalloproteases. Keratinocytes seeded on top of fibroblast-loaded hydrogels are able to adhere and form a compact and dense layer of epidermis, mimicking the architecture of the native skin. Thiol-ene photocrosslinkable pec tin hydrogels support the in vitro formation of full-thickness skin and are thus a highly promising plat form for skin tissue engineering applications, including wound healing and in vitro testing mod
- A single-component hydrogel bioink for bioprinting of bioengineered 3D constructs for dermal tissue engineeringPublication . Pereira, Rúben; Sousa, Aureliana; Barrias, Cristina C.; Bártolo, Paulo J.; Granja, Pedro L.Bioprinting is attractive to create cellularized constructs for skin repair. However, the vast majority of bioinks present limitations in the printing of chemically defined 3D constructs with controllable biophysical and biochemical properties. To address this challenge, a single-component hydrogel bioink with a controlled density of cell-adhesive ligands, tuneable mechanical properties and adjustable rheological behaviour is developed for extrusion bioprinting and applied for the biofabrication of 3D dermal constructs. A methacrylate modified pectin bioink is designed to allow the tethering of integrin-binding motifs and the formation of hydrogels by UV photopolymerization and ionic gelation. The rheological behaviour of a low polymer concentration (1.5 wt%) solution is adjusted by ionic crosslinking, yielding a printable bioink that holds the predesigned shape upon deposition for postprinting photocrosslinking. Printed constructs provide a suitablemicroenvironment that supports the deposition of endogenous extracellular matrix, rich in collagen and fibronectin, by entrapped dermal fibroblasts. This approach enables the design of chemically defined and cell-responsive bioinks for tissue engineering applications and particularly for the generation of biomimetic skin constructs.
- 3D Photo-Fabrication for Tissue Engineering and Drug DeliveryPublication . Brás Pereira, Rúben Filipe; Bartolo, PauloThe most promising strategies in tissue engineering involve the integration of a triad of biomaterials, living cells, and biologically active molecules to engineer synthetic environments that closely mimic the healing milieu present in human tissues, and that stimulate tissue repair and regeneration. To be clinically effective, these environments must replicate, as closely as possible, the main characteristics of the native extracellular matrix (ECM) on a cellular and subcellular scale. Photo-fabrication techniques have already been used to generate 3D environments with precise architectures and heterogeneous composition, through a multi-layer procedure involving the selective photocrosslinking reaction of a light-sensitive prepolymer. Cells and therapeutic molecules can be included in the initial hydrogel precursor solution, and processed into 3D constructs. Recently, photo-fabrication has also been explored to dynamically modulate hydrogel features in real time, providing enhanced control of cell fate and delivery of bioactive compounds. This paper focuses on the use of 3D photo-fabrication techniques to produce advanced constructs for tissue regeneration and drug delivery applications. State-of-the-art photo-fabrication techniques are described, with emphasis on the operating principles and biofabrication strategies to create spatially controlled patterns of cells and bioactive factors. Considering its fast processing, spatiotemporal control, high resolution, and accuracy, photo-fabrication is assuming a critical role in the design of sophisticated 3D constructs. This technology is capable of providing appropriate environments for tissue regeneration, and regulating the spatiotemporal delivery of therapeutics.
- Traditional Therapies for Skin Wound HealingPublication . Pereira, Rúben F.; Bártolo, Paulo J.Significance: The regeneration of healthy and functional skin remains a huge challenge due to its multilayer structure and the presence of different cell types within the extracellular matrix in an organized way. Despite recent advances in wound care products, traditional therapies based on natural origin compounds, such as plant extracts, honey, and larvae, are interesting alternatives. These therapies offer new possibilities for the treatment of skin diseases, enhancing the access to the healthcare, and allowing overcoming some limitations associated to the modern products and therapies, such as the high costs, the long manufacturing times, and the increase in the bacterial resistance. This article gives a general overview about the recent advances in traditional therapies for skin wound healing, focusing on the therapeutic activity, action mechanisms, and clinical trials of the most commonly used natural compounds. New insights in the combination of traditional products with modern treatments and future challenges in the field are also highlighted. Recent Advances: Natural compounds have been used in skin wound care for many years due to their therapeutic activities, including anti-inflammatory, antimicrobial, and cell-stimulating properties. The clinical efficacy of these compounds has been investigated through in vitro and in vivo trials using both animal models and humans. Besides the important progress regarding the development of novel extraction methods, purification procedures, quality control assessment, and treatment protocols, the exact mechanisms of action, side effects, and safety of these compounds need further research. Critical Issues: The repair of skin lesions is one of the most complex biological processes in humans, occurring throughout an orchestrated cascade of overlapping biochemical and cellular events. To stimulate the regeneration process and prevent the wound to fail the healing, traditional therapies and natural products have been used with promising results. Although these products are in general less expensive than the modern treatments, they can be sensitive to the geographic location and season, and exhibit batch-to-batch variation, which can lead to unexpected allergic reactions, side effects, and contradictory clinical results. Future Directions: The scientific evidence for the use of traditional therapies in wound healing indicates beneficial effects in the treatment of different lesions. However, specific challenges remain unsolved. To extend the efficacy and the usage of natural substances inwound care,multidisciplinary efforts are necessary to prove the safety of these products, investigate their side effects, and develop standard controlled trials. The development of good manufacturing practices and regulatory legislation also assume a pivotal role in order to improve the use of traditional therapies by the clinicians and to promote their integration into the national health system. Current trends move to the development of innovative wound care treatments, combining the use of traditional healing agents and modern products/practices, such as nanofibers containing silver nanoparticles,Aloe veraloaded into alginate hydrogels, propolis into dressing films, and hydrogel sheets containing honey.
- Low-Cost Smart Surveillance System for Smart CitiesPublication . Brás Pereira, Rúben Filipe; Correia, Diogo; Mendes, Luís; Rabadão, Carlos; Barroso, João; Pereira, AntónioThe safety of people and spaces is of paramount importance for societies. With time, the implementation of safety measures is rapidly changing from a need to a priority. Video surveillance systems play a key role in the surveillance of crucial and critical areas as these systems help the authorities keep places safer. With the rapid growth of technology and the implementation of the smart city concept, it is becoming possible to develop and deploy wide area surveillance systems. The ease with which these systems can be installed in private and public spaces (e.g., homes, streets and parks) allow for the creation of ubiquitous monitored environments. Rapid intervention responses to any abnormal situation or the use of recorded video as evidence are some advantages of the use of this type of surveillance systems. Although ubiquitous video surveillance systems are relevant for present modern societies, their cost is still high. To solve or, at least to mitigate this problem, a low-cost smart surveillance system was developed, which is presented and described in this paper. The developed surveillance system, based on available low-cost technology, can help keep critical spaces under surveillance 24/7. The proposed solution was found to have a minimal cost, a low bandwidth, and to be scalable and adaptable to every client’s needs. Thus, the solution can be used by anybody (private and public) and applied in different contexts (e.g., residential, industrial). The system can provide still images, captured from surveillance video cameras, real time video and real time video processing, which can be used for motion detection. When this happens, the user is warned via an e-mail containing the identification of the respective surveillance camera. Only the relevant video events are sent, recorded and maintained in the cloud platform system, consequently reducing the amount of storage space required to maintain all the historical video events. The results of the tests carried out show that it is possible to stream a video from the surveillance cameras with an insignificant delay and that motion detection can be attained through real time video processing. The system presented potentiates a low-cost solution for a smart city in the surveillance field.
- Recent Advances in Additive BiomanufacturingPublication . Pereira, Rúben Filipe Brás; Bartolo, PauloThe principles of tissue engineering and regenerative medicine have been used for the development of innovative medical therapies for engineering tissues and organs. These therapies involve the use of biomaterials, cells, and biologically active molecules, according to two fundamental strategies: the top-down and bottom-up approaches. Top-down approaches, which are the most commonly used, involve the implantation of porous scaffolds, with or without living cells and bioactive agents, into the defect site in the patient. In these approaches, scaffolds act as temporary templates for the seeded cells, mimicking the properties of the native extracellular matrix and providing an adequate environment for the growth of the new tissue. Scaffolds can be produced by using either conventional or additive techniques, resulting in structures with different levels of porosity, pore size, interconnectivity, and spatial distribution. Additive biomanufacturing techniques allow significantly more control over the scaffold characteristics (e.g., architecture, porosity, permeability, etc.), enabling the automatic and reproducible fabrication of scaffolds in a wide range of polymeric, ceramic, and composite materials. Some of these techniques also allow the fabrication of constructs encapsulating living cells. This chapter describes the most recent advances in the top-down approach to fabricate scaffolds for tissue regeneration, presenting the most important additive biomanufacturing techniques and processable materials. Future perspectives in the field and challenges for future research are also discussed.