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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.
- 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.