Sara Gonçalves

Physicochemical and biological evaluation of poly(ethylene glycol) methacrylate grafted onto poly(dimethyl siloxane) surfaces for prosthetic devices

Poly(dimethyl siloxane) (PDMS) was surface-polymerized with poly(ethylene glycol)methacrylate (PEGMA) by surface-initiated atom transfer radical polymerization (SI-ATRP) in aqueous media at room temperature. Modification of the PDMS surface followed a three-step procedure: (i) PDMS surface hydroxylation by UV/ozone exposure, immediately followed by (ii) covalent attachment of the initiator, 1-trichlorosilyl-2-(chloromethylphenyl)ethane, onto the hydroxylated PDMS, via chemical vapor deposition; finally (iii) PDMS surface-polymerization of PEGMA by ATRP. Modified PDMS was characterized by water contact angle measurement, SEM, FTIR-ATR, and XPS. Results showed that modified surfaces had a hydrophilic character, given the water contact angles around 60°; FTIR-ATR and XPS analysis confirmed the presence of polymerized PEGMA on the surface of PDMS and the adhesion of Staphylococcus aureus GB 2/1 and Streptococcus salivarius GB 24/9 onto the modified surfaces was inhibited 94% and 81%, respectively. Finally, the modified PDMS showed no evidence of cytotoxic effects in in vitro assays using human skin fibroblasts.

Bacterial Cellulose As a Support for the Growth of Retinal Pigment Epithelium

The feasibility of bacterial cellulose (BC) as a novel substrate for retinal pigment epithelium (RPE) culture was evaluated. Thin (41.6 ± 2.2 μm of average thickness) and heat-dried BC substrates were surface-modified via acetylation and polysaccharide adsorption, using chitosan and carboxymethyl cellulose. All substrates were characterized according to their surface chemistry, wettability, energy, topography, and also regarding their permeability, dimensional stability, mechanical properties, and endotoxin content. Then, their ability to promote RPE cell adhesion and proliferation in vitro was assessed. All surface-modified BC substrates presented similar permeation coefficients with solutes of up to 300 kDa. Acetylation of BC decreased its swelling and the amount of endotoxins. Surface modification of BC greatly enhanced the adhesion and proliferation of RPE cells. All samples showed similar stress-strain behavior; BC and acetylated BC showed the highest elastic modulus, but the latter exhibited a slightly smaller tensile strength and elongation at break as compared to pristine BC. Although similar proliferation rates were observed among the modified substrates, the acetylated ones showed higher initial cell adhesion. This difference may be mainly due to the moderately hydrophilic surface obtained after acetylation.

Poly(dimethyl siloxane) surface modification with biosurfactants isolated from probiotic strains.

Depending on the final application envisaged for a given biomaterial, many surfaces must be modified before use. The material performance in a biological environment is mainly mediated by its surface properties that can be improved using suitable modification methods. The aim of this work was to coat poly(dimethyl siloxane) (PDMS) surfaces with biosurfactants (BSs) and to evaluate how these compounds affect the PDMS surface properties. BSs isolated from four probiotic strains (Lactococcus lactis, Lactobacillus paracasei, Streptococcus thermophilus A, and Streptococcus thermophilus B) were used. Bare PDMS and PDMS coated with BSs were characterized by contact angle measurements, infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The influence of the surface modifications on the materials blood compatibility was studied through thrombosis and hemolysis assays. The cytotoxicity of these materials was tested against rat peritoneal macrophages. AFM results demonstrated the successful coating of the surfaces. Also, by contact angle measurements, an increase of the coated surfaces hydrophilicity was seen. Furthermore, XPS analysis indicated a decrease of the silicon content at the surface, and ATR-FTIR results showed the presence of BS characteristic groups as a consequence of the modification. All the studied materials revealed no toxicity and were found to be nonhemolytic. The proposed approach for the modification of PDMS surfaces was found to be effective and opens new possibilities for the application of these surfaces in the biomedical field.

Acetylated bacterial cellulose coated with urinary bladder matrix as a substrate for retinal pigment epithelium.

This work evaluated the effect of acetylated bacterial cellulose (ABC) substrates coated with urinary bladder matrix (UBM) on the behavior of retinal pigment epithelium (RPE), as assessed by cell adhesion, proliferation and development of cell polarity exhibiting transepithelial resistance and polygonal shaped-cells with microvilli. Acetylation of bacterial cellulose (BC) generated a moderate hydrophobic surface (around 65°) while the adsorption of UBM onto these acetylated substrates did not affect significantly the surface hydrophobicity. The ABS substrates coated with UBM enabled the development of a cell phenotype closer to that of native RPE cells. These cells were able to express proteins essential for their cytoskeletal organization and metabolic function (ZO-1 and RPE65), while showing a polygonal shaped morphology with microvilli and a monolayer configuration. The coated ABC substrates were also characterized, exhibiting low swelling effect (between 1.5-2.0 swelling/mm(3)), high mechanical strength (2048MPa) and non-pyrogenicity (2.12EU/L). Therefore, the ABC substrates coated with UBM exhibit interesting features as potential cell carriers in RPE transplantation that ought to be further explored.

Overview on Cell-Biomaterial Interactions

Biomaterials, a name given to express materials used as medical implants, indwelling devices, extracorporeal ones and other categories in several medical fields, have increasingly played a significant role when aiming at improving the quality of life in humans. The behavior of a biomaterial with the surrounding physiologic environment is of major relevance for determining the in vivo performance and host acceptance of any device. Indeed, the biocompatibility and bio-functionality of implantable devices remains a serious challenge in establishing the device’s function and lifetime. Several research efforts have been conducted to further understand and control the interactions between biomaterials and cell-mediated processes, aiming at the definition of the main guidelines that regulate materials biocompatibility. Several criteria should be met when considering a biomaterial for a specific application. On the materials’ perspective, its composition, mechanical, physicochemical, thermal, electrical properties must be well understood. In parallel, knowledge on the cell-biomaterial interaction mechanisms (including specific adhesion proteins and cell receptors, signal transduction, cell differentiation, tissue development, host immune response mechanisms, to name a few processes) must be attained, to better characterize, follow up and control cell-biomaterial interactions. This review attempts to define the basic phenomenon that take place when a biomaterial comes into contact with host living tissues. Numerous strategies have been investigated to overcome body reactions induced by the implantation of devices. These strategies, their advantages and limitations, along with the fundamentals underlying biomaterials-tissue interactions and current research on biomaterial surface modification are discussed. Besides, the use of polymeric biomaterials for use in age-related macular degeneration will be presented as a case study.

Correction to Bacterial Cellulose As a Support for the Growth of Retinal Pigment Epithelium

Retinal Pigment Epithelium Sara Goncalves,† Jorge Padrao,† Ineŝ Patricio Rodrigues,‡,§ Joao Pedro Silva,† Vitor Sencadas, Senentxu Lanceros-Mendez, Henrique Girao,‡ Fernando Dourado,† and Ligia R. Rodrigues*,† †Centre of Biological Engineering and Center/Department of Physics, University of Minho, Campus de Gualtar, 4710-057, Braga, Portugal ‡Centre of Ophthalmology and Vision Sciences, IBILI-Faculty of Medicine, University of Coimbra, 3000-354, Coimbra, Portugal CNC Center for Neuroscience and Cell Biology, University of Coimbra, 3004-517, Coimbra, Portugal