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- New drug-eluting lenses to be applied as bandages after keratoprosthesis implantationPublication . Carreira, Ana; Ferreira, Paula; Ribeiro, MP.; Correia, Tiago R.; Coutinho, Paula Isabel Teixeira Gonçalves; Correia, Ilídio Joaquim Sobreira; Gil, MariaCorneal tissue is the most commonly transplanted tissue worldwide. This work aimed to develop a new drug-eluting contact lens that may be used as a bandage after keratoprosthesis. During this work, films were produced using poly(vinyl alcohol) (PVA) and chitosan (CS) crosslinked with glyoxal (GL). Vancomycin chlorhydrate (VA) was impregnated in these systems by soaking. Attenuated total reflectance – Fourier transform infrared spectroscopy was used to confirm crosslinking. The cytotoxic and drug release profile, hydrophilicity, thermal and biodegradation as well as swelling capacity of the samples were assessed through in vitro studies. PVA and PVA/CS films were obtained by crosslinking with GL. The films were transparent, flexible with smooth surfaces, hydrophilic and able to load and release vancomycin for more than 8 h. Biodegradation in artificial lachrymal fluid (ALF) with lysozyme at 37 °C showed that mass loss was higher for the samples containing CS. Also, the samples prepared with CS showed the formation of pores which were visualized by SEM. All samples revealed a biocompatible character after 24 h in contact with cornea endothelial cells. As a general conclusion it was possible to determine that the 70PVA/30CS film showed to combine the necessary features to prepare vancomycin-eluting contact lenses to prevent inflammation after corneal substitution.
- Production and characterization of chitosan/gelatin/β-TCP scaffolds for improved bone tissue regenerationPublication . Serra, Inês Raquel Tavares; Fradique, Ricardo Gil; Vallejo, Mariana C. da S.; Correia, Tiago R.; Miguel, Sónia P.; Correia, Ilídio Joaquim SobreiraRecently, bone tissue engineering emerged as a viable therapeutic alternative, comprising bone implants and new personalized scaffolds to be used in bone replacement and regeneration. In this study, biocompatible scaffolds were produced by freeze-drying, using different formulations (chitosan, chitosan/gelatin, chitosan/β-TCP and chitosan/gelatin/β-TCP) to be used as temporary templates during bone tissue regeneration. Sample characterization was performed through attenuated total reflectance-Fourier transform infrared spectroscopy, X-ray diffraction and energy dispersive spectroscopy analysis. Mechanical characterization and porosity analysis were performed through uniaxial compression test and liquid displacement method, respectively. In vitro studies were also done to evaluate the biomineralization activity and the cytotoxic profile of the scaffolds. Scanning electron and confocal microscopy analysis were used to study cell adhesion and proliferation at the scaffold surface and within their structure. Moreover, the antibacterial activity of the scaffolds was also evaluated through the agar diffusion method. Overall, the results obtained revealed that the produced scaffolds are bioactive and biocompatible, allow cell internalization and show antimicrobial activity against Staphylococcus aureus. Such, make these 3D structures as potential candidates for being used on the bone tissue regeneration, since they promote cell adhesion and proliferation and also prevent biofilm development at their surfaces, which is usually the main cause of implant failure.
- Surface modification of an intraocular lens material by plasma-assisted grafting with 2-hydroxyethyl methacrylate (HEMA), for controlled release of moxifloxacinPublication . Vieira, Ana Paula; Pimenta, Andreia; Silva, Diana; Gil, Maria; Alves, Patrícia; Coimbra, Patrícia; Mata, Jose; Bozukova, Dimitriya; Correia, Tiago R.; Correia, Ilídio Joaquim Sobreira; Serro, Ana Paula; Guiomar, AntónioEndophthalmitis, an inflammation of the eye due to perioperative infection, may occur after cataract surgery. Intraocular lenses (IOLs) loaded with an antibiotic have been proposed as an alternative to the conventional postoperative endophthalmitis prophylaxis, since the antibiotic is delivered directly to the target site. In this work, an IOL-based antibiotic releasing system was prepared from a copolymer used in the production of IOLs and a fluoroquinolone used in endophthalmitis prophylaxis (moxifloxacin, MFX). Argon plasma-assisted grafting with 2-hydroxyethyl methacrylate (HEMA) in the presence of MFX was the approach selected for surface modification, with MFX loaded both by entrapment in the grafted polyHEMA coating and by soaking. Surface and bulk properties were evaluated before and after surface modification and the MFX release profiles were obtained both in batch mode (sink conditions) and under hydrodynamic conditions, employing a purpose-built microfluidic cell, which simulated the hydrodynamic conditions around the eye lens. The effect of storage on the release profile of the best system was also assessed. The best system released MFX for ca. 15 days above the minimum inhibitory concentration for Staphylococcus aureus and Staphylococcus epidermidis. The released MFX showed antimicrobial activity against these bacteria and was non-cytotoxic against corneal endothelial cells.
- Functionalization and photocuring of an L-lactic acid macromer for biomedical applicationsPublication . Marques, Dina; Santos, João; Ferreira, Paula; Correia, Tiago R.; Correia, Ilídio Joaquim Sobreira; Gil, Maria; Baptista, Cristina Maria dos Santos GaudêncioL-lactic acid was the starting material for obtaining bioahesives. Reaction with 1,4-butanediol provided a telechelic lactic acid prepolymer with hydroxyl end groups further functionalized with 2-isocyanatoethyl methacrylate. Films were produced upon UV irradiation, 2 min, after addition of Irgacure 2959. This was a solvent and catalyst free process. Thermal characterization of films confirmed stability at physiological temperature, enabling photocuring. Adhesion properties were assessed with good results. In vitro degradation tests showed moderate hydrolytic instability dependent on thickness. SEM images revealed a uniform and compact structure. Thrombosis tests confirmed the materials’ thrombogenicity while biocompatibility experiments showed fibroblast viability and antimicrobial behavior.
- Functionalization of polydimethylsiloxane membranes to be used in the production of voice prosthesesPublication . Ferreira, Paula; Carvalho, Álvaro; Correia, Tiago R.; Antunes, Bernardo Paiva; Correia, Ilídio Joaquim Sobreira; Alves, PatríciaThe voice is produced by the vibration of vocal cords which are located in the larynx. Therefore, one of the major consequences for patients subjected to laryngectomy is losing their voice. In these cases, a synthetic one-way valve set (voice prosthesis) can be implanted in order to allow restoration of speech. Most voice prostheses are produced with silicone-based materials such as polydimethylsiloxane (PDMS). This material has excellent properties, such as optical transparency, chemical and biological inertness, non-toxicity, permeability to gases and excellent mechanical resistance that are fundamental for its application in the biomedical field. However, PDMS is very hydrophobic and this property causes protein adsorption which is followed by microbial adhesion and biofilm formation. To overcome these problems, surface modification of materials has been proposed in this study. A commercial silicone elastomer, SylgardTM 184 was used to prepare membranes whose surface was modified by grafting 2-hydroxyethylmethacrylate and methacrylic acid by low-pressure plasma treatment. The hydrophilicity, hydrophobic recovery and surface energy of the produced materials were determined. Furthermore, the cytotoxicity and antibacterial activity of the materials were also assessed. The results obtained revealed that the PDMS surface modification performed did not affect the material's biocompatibility, but decreased their hydrophobic character and bacterial adhesion and growth on its surface.
- Production of new 3D scaffolds for bone tissue regeneration by rapid prototypingPublication . Fradique, Ricardo Gil; Correia, Tiago R.; Miguel, Sónia P.; Sá, Kevin; Figueira, Daniela Sofia Rodrigues; Mendonça, António; Correia, Ilídio Joaquim SobreiraThe incidence of bone disorders, whether due to trauma or pathology, has been trending upward with the aging of the worldwide population. The currently available treatments for bone injuries are rather limited, involving mainly bone grafts and implants. A particularly promising approach for bone regeneration uses rapid prototyping (RP) technologies to produce 3D scaffolds with highly controlled structure and orientation, based on computer-aided design models or medical data. Herein, tricalcium phosphate (TCP)/alginate scaffolds were produced using RP and subsequently their physicochemical, mechanical and biological properties were characterized. The results showed that 60/40 of TCP and alginate formulation was able to match the compression and present a similar Young modulus to that of trabecular bone while presenting an adequate biocompatibility. Moreover, the biomineralization ability, roughness and macro and microporosity of scaffolds allowed cell anchoring and proliferation at their surface, as well as cell migration to its interior, processes that are fundamental for osteointegration and bone regeneration.
- Photocurable bioadhesive based on lactic acidPublication . Marques, Dina; Santos, João; Ferreira, Paula; Correia, Tiago R.; Correia, Ilídio Joaquim Sobreira; Gil, Maria; Baptista, Cristina Maria dos Santos GaudêncioNovel photocurable and low molecular weight oligomers based on l-lactic acid with proven interest to be used as bioadhesive were successfully manufactured. Preparation of lactic acid oligomers with methacrylic end functionalizations was carried out in the absence of catalyst or solvents by self-esterification in two reaction steps: telechelic lactic acid oligomerization with OH end groups and further functionalization with methacrylic anhydride. The final adhesive composition was achieved by the addition of a reported biocompatible photoinitiator (Irgacure® 2959). Preliminary in vitro biodegradability was investigated by hydrolytic degradation in PBS (pH = 7.4) at 37 °C. The adhesion performance was evaluated using glued aminated substrates (gelatine pieces) subjected to pull-to-break test. Surface energy measured by contact angles is lower than the reported values of the skin and blood. The absence of cytoxicity was evaluated using human fibroblasts. A notable antimicrobial behaviour was observed using two bacterial models (Staphylococcus aureus and Escherichia coli). The cured material exhibited a strong thrombogenic character when placed in contact with blood, which can be predicted as a haemostatic effect for bleeding control. This novel material was subjected to an extensive characterization showing great potential for bioadhesive or other biomedical applications where biodegradable and biocompatible photocurable materials are required.
- Natural melanin: A potential pH-responsive drug release devicePublication . Araújo, Marco; Viveiros, Raquel; Correia, Tiago R.; Correia, Ilídio Joaquim Sobreira; Bonifácio, Vasco; Casimiro, Teresa; Ricardo, Ana AguiarThis work proposes melanin as a new nanocarrier for pH-responsive drug release. Melanin is an abundant natural polymer that can be easily extracted from cuttlefish as nanoparticles with a suitable size range for drug delivery. However, despite its high potentiality, the application of this biopolymer in the pharmaceutical and biomedical fields is yet to be explored. Herein, melanin nanoparticles were impregnated with metronidazole, chosen as model antibiotic drug, using supercritical carbon dioxide. The drug release profile was investigated at acidic and physiologic pH, and the dominant mechanism was found to follow a non-Fickian transport. Drug release from melanin shows a strong pH dependency, which allied to its biocompatibility and lack of cytotoxicity envisages its potential application as nanocarrier in formulations for colon and intestine targeted drug delivery.
- Polymeric Nanofibers for Biomedical and Biotechnologic ApplicationsPublication . Correia, Tiago R.; Correia, Ilídio Joaquim SobreiraBone tissue is a complex structure with the capacity to self-regenerate and responsible for different functions in our body. However, when bone integrity is disturbed, its self-regenerative capacity is lost. The available treatments are based on bone grafts and other bone substitutes which possess several limitations. Herein, a new approach to mimic the extracellular matrix of bone and cellular microenvironment was developed in this work. Therefore, an electrospinning apparatus was used to produce poly(ε-caprolactone), polyethylene oxide-sodium alginate and poly(vinyl)pirrolidone nanofibers. Subsequently, the same procedure was used for coating the alginate scaffold. In addition, poly(ε-caprolactone) electrospun nanofiber membranes were also produced and evaluated for phase separation applications. Membranes specific properties, such as pore size, fibers diameter and surface interactions were studied. The biological properties of the coated scaffolds were evaluated through in vitro cytotoxicity assays. The results showed that all the coated scaffolds had their biological performance improved. The membranes showed to be good candidates for phase separation area.
- Development of UV cross-linked gelatin coated electrospun poly(caprolactone) fibrous scaffolds for tissue engineeringPublication . Correia, Tiago R.; Ferreira, Paula; Vaz, Rita; Alves, Patrícia; Figueiredo, Margarida; Correia, Ilídio Joaquim Sobreira; Coimbra, PatríciaCardiovascular disease is the leading cause of morbidity and mortality among industrialized countries. Vascular grafts are often required for the surgical treatments. Considering the limitations associated with the use of autografts and with the currently available synthetic materials, a growing demand in tissue engineered vascular grafts has been registered. During the work here described, electrospinning technique was used to prepared fibrous matrices to be applied as vascular implants. For that purpose, electrospun polycaprolactone (PCL) fibrous mats were produced and afterwards coated with different hydrogel formulations based in photocrosslinkable gelatin (GelMA) and the macromers poly(ethylene glycol) acrylate (PEGA) and poly(ethylene glycol) diacrylate (PEGDA). These were further photocrosslinked under UV irradiation using Irgacure® 2959 (by BASF) as the photoinitiator. The suitability of the coated scaffolds for the intended application, was evaluated by assessing their chemical/physical properties as well as their interaction with blood and endothelial cells.