Lívia Santos

Bacterial adhesion to worn silicone hydrogel contact lenses

Purpose. The aim of this study was to, firstly, investigate whether silicone-hydrogel contact lenses (CL) are more or less susceptible to bacterial adhesion than conventional ones and, secondly, assess the influence of lens wear in the extent of bacterial adhesion. Four silicone-hydrogel CL (galyfilcon A, balafilcon A, lotrafilcon A, and lotrafilcon B) and one conventional hydrogel (etafilcon A) CL were tested. Methods. Bacterial adhesion experiments were performed on unworn and worn CL using the strain Staphylococcus epidermidis 9142. Worn lenses were obtained from a group of 31 subjects fitted with a silicone-hydrogel CL in one eye and a conventional hydrogel CL as contralateral pair. These lenses were used on a daily basis in combination with a multipurpose lens care solution. Adhesion assays were carried out in a parallel plate flow chamber, followed by image analysis. Hydrophobicity, roughness, and topography of the lenses surfaces were assessed through contact angle measurements and atomic force microscopy. Results. Unworn conventional and silicone-hydrogel CL were equally susceptible to bacterial adhesion of S. epidermidis. Conversely, worn conventional hydrogel (etafilcon A) were more prone to bacterial adhesion than worn silicone-hydrogel materials, which exhibited similar adhesion extents among them. The results also showed that the lens surface properties such as hydrophobicity, roughness, and surface topography changed during wear. The alteration of surface hydrophobicity of silicone and conventional hydrogel CL during wear had a great impact on lens bacterial adhesion susceptibility. Accordingly, balafilcon A becomes significantly less hydrophobic and less prone to bacterial adhesion after lens wear, whereas etafilcon A becomes more hydrophobic and also more susceptible to bacterial adhesion (p < 0.05). Conclusions. Worn silicone-hydrogel galyfilcon A, balafilcon A, lotrafilcon A, and lotrafilcon B are equally prone to microbial adhesion of S. epidermidis and generally less susceptible than the conventional hydrogel.

Harnessing magnetic-mechano actuation in regenerative medicine and tissue engineering

Mechanical stimulus is of upmost importance in tissues developmental and regeneration processes as well as in maintaining body homeostasis. Classical physiological reactions encompass an increase of blood vessel diameter upon exposure to high blood pressure, or the expansion of cortical bone after continuous high-impact exercise. At a cellular level, it is well established that extracellular stiffness, topography, and remote magnetic actuation are instructive mechanical signals for stem cell differentiation. Based on this, biomaterials and their properties can be designed to act as true stem cell regulators, eventually leading to important advances in conventional tissue engineering techniques. This review identifies the latest advances and tremendous potential of magnetic actuation within the scope of regenerative medicine and tissue engineering.

Extracellular Vesicles Derived from Preosteoblasts Influence Embryonic Stem Cell Differentiation

Embryonic stem cells (ESCs) can differentiate into all cell types of the body and, therefore, hold tremendous promise for cell-based regenerative medicine therapies. One significant challenge that should be addressed before using ESCs in the clinic is to improve methods of efficiently and effectively directing the differentiation of this heterogeneous cell population. The work presented here examines the potential of harnessing naturally derived extracellular vesicles to deliver genetic material from mature cells to undifferentiated ESCs for the purpose of manipulating stem cell fate. Vesicles were isolated from preosteoblast cells and were found to be ∼170 nm in diameter and to express the CD40 surface marker. Multiple interactions were visualized between vesicles and ESCs using confocal microscopy, and no significant difference in cell viability was noted. Incubation with vesicles caused significant changes in ESC gene expression, including persistence of pluripotent gene levels as well as increased neurectoderm differentiation. Genetic cargo of the vesicles as well as the cells from which they were derived were examined using a small microRNA (miRNA) gene array. Interestingly, ∼20% of the examined miRNAs were increased more than twofold in the vesicles compared with preosteoblast cells. Together, these results suggest that extracellular vesicles may be utilized as a novel method of directing stem cell differentiation. Future work examining methods for controlled delivery of vesicles may improve the clinical potential of these physiological liposomes for therapeutic applications.

Extracellular Stiffness Modulates the Expression of Functional Proteins and Growth Factors in Endothelial Cells

Angiogenesis, the formation of blood vessels from pre-existing ones, is of vital importance during the early stages of bone healing. Extracellular stiffness plays an important role in regulating endothelial cell behavior and angiogenesis, but how this mechanical cue affects proliferation kinetics, gene regulation, and the expression of proteins implicated in angiogenesis and bone regeneration remains unclear. Using collagen-coated polyacrylamide (PAAm) hydrogels, human umbilical vein endothelial cells (HUVECs) are exposed to an environment that mimics the elastic properties of collagenous bone, and cellular proliferation and gene and protein expressions are assessed. The proliferation and gene expression of HUVECs are not differentially affected by culture on 3 or 30 kPa PAAm hydrogels, henceforth referred to as low and high stiffness gels, respectively. Although the proliferation and gene transcript levels remain unchanged, significant differences are found in the expressions of functional proteins and growth factors implicated both in the angiogenic and osteogenic processes. The down-regulation of the vascular endothelial growth factor receptor-2 protein with concomitant over-expression of caveolin-1, wingless-type 2, bone morphogenic protein 2, and basic fibroblast growth factor on the high stiffness PAAm hydrogel suggests that rigidity has a pro-angiogenic effect with inherent benefits for bone regeneration.

Changes in UV-visible transmittance of silicone-hydrogel contact lenses induced by wear

Purpose: To evaluate the influence of wear of silicone-hydrogel contact lenses on lens ultraviolet and visible spectrum transmittance by studying several contact lenses before and after wear. Methods: To investigate the ability of contact lenses to maintain their transmittance characteristics, we measured 104 different contact lenses in the ultraviolet (UV) and visible range from 200 to 700 nm, with a Shimadzu UV3101-PC UV-vis-NIR spectrophotometer equipped with an integrating sphere. The lenses used in this study were Acuvue Advance (Johnson & Johnson Vision Care, Inc.), Air Optix Night & Day (CIBA Vision), Air Optix (CIBA Vision), and PureVision (Bausch & Lomb). A conventional hydrogel contact lens was also tested, Acuvue (Johnson & Johnson Vision Care Inc.). Results: Our study indicates that lenses that do not have UV absorbers incorporated into the polymer transmitted most of the UV radiation (UVR) before and after wear. The results of the statistical analysis show that for the UVC portion of the spectrum significant difference exists within the measurements obtained before and after wear for all the lenses, with the exception of PureVision. Acuvue Advance is the only material in which significant transmittance differences were observed in the visible spectral range. Conclusions: Transmittance is modified after contact lenses wear, probably due to the formation of biofilms on the contact lens surface, being more noticeable in the UVR region of the spectrum (200–400 nm). Silicone-hydrogel and conventional hydrogel contact lens materials that provide UVR protection (UV-blocker) maintain this property even after being worn. The changes observed in the visible spectrum seem not to have any implications in visual performance of silicone-hydrogel contact lenses.

In vitro and in vivo assessment of magnetically actuated biomaterials and prospects in tendon healing

AIM To expand our understanding on the effect of magnetically actuated biomaterials in stem cells, inflammation and fibrous tissue growth. MATERIALS & METHODS Magnetic biomaterials were obtained by doping iron oxide particles into starch poly-ϵ-caprolactone (SPCL) to create two formulations, magSPCL-1.8 and 3.6. Stem cell behavior was assessed in vitro and the inflammatory response, subcutaneously in Wistar rats. RESULTS Metabolic activity and proliferation increased significantly overtime in SPCL and magSPCL-1.8. Electromagnetic fields attenuated the presence of mast cells and macrophages in tissues surrounding SPCL and magSPCL-1.8, between weeks 1 and 9. Macrophage reduction was more pronounced for magSPCL-1.8, which could explain why this material prevented growth of fibrous tissue overtime. CONCLUSION Magnetically actuated biomaterials have potential to modulate inflammation and the growth of fibrous tissue.

The influence of lens material and lens wear on the removal and viability of Staphylococcus epidermidis

PURPOSE The aim of this study was to evaluate the influence of lens material and lens wear on the removal capability of Staphylococcus epidermidis. Assessment of viability of remaining adhered bacteria was another goal of this work. Four silicone hydrogel materials (galyfilcon A, balafilcon A, lotrafilcon A, lotrafilcon B) and one conventional hydrogel material (etafilcon A) were assayed. METHODS Detachment studies on S. epidermidis were carried out in a parallel plate flow chamber. Contact lenses (CLs) were fitted to the bottom of the flow chamber and a bacterial suspension was perfused into the system, promoting bacterial adhesion. Afterwards, detachment was stimulated using a multipurpose solution (MPS, ReNu Multiplus) and the percentage of removed bacteria estimated through microscopic observation and enumeration. Remaining adhered bacteria were stained with propidium iodide (PI) and enumerated in order to assess their viability. Additionally, the worn lenses were observed by confocal laser scanning microscopy (CLSM) to visualize bacterial distribution along the lens surfaces. RESULTS Bacterial removal was significant (p<0.05) for both unworn and worn galyfilcon A and etafilcon A. Galyfilcon A exhibited a detachment percentage of 59.1 and 63.5 while etafilcon A of 62.6 and 69.3, both for unworn and worn lenses, respectively. As far as bacterial viability is concerned, it was found that worn lenses exhibit a superior amount of non-viable bacteria than unworn CLs. Images obtained by CLSM revealed an irregular bacterial distribution for all lens materials. CONCLUSIONS It appears that surface and/or bulk structure of the lens material affects removal of S. epidermidis while CL wear influences their viability.

Degradation Studies and Biological Behavior on an Artificial Cornea Material

PURPOSE Patients with dry eye syndrome, Stevens-Johnson syndrome, or recurrent transplant rejections are unsuitable to receive a keratoprosthesis. The present work aims at developing a highly biocompatible keratoprosthesis that could be successfully implanted in such patients. METHODS Glass-reinforced hydroxyapatite (GRHA) was used to construct this new artificial cornea. To grant the device an adequate porosity, a porogen agent was added in the following percentages: 10, 30, and 50%. Samples were physicochemically analyzed in terms of density, porosity, roughness, degradation, and surface imaging. Biological relevance was assessed by cell culture, MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrasodium bromide) assays, and cell imaging. RESULTS Samples B (30% porogen) and C (50% porogen) were found to be the most porous and also had the roughest topography. Degradation studies showed that under simulated physiologic conditions, no mass loss was found. Conversely, under acidic conditions, a significant mass loss was found. The biological performance of these samples was satisfactory when cultured with human fibroblasts. The MTT assay revealed that samples B and C had greater propensity to cell invasion and proliferation than that of the other tested materials. Cell imaging demonstrated that fibroblasts organized around the pore edges before colonizing it. CONCLUSIONS A material with physicochemical and biological characteristics close to an ideal artificial cornea has been fabricated. The GRHA cornea containing 30% porogen is the most promising substitute material due to the biological performance, adequate porosity, and low degradation propensity.

Exercise and bone health across the lifespan

With ageing, bone tissue undergoes significant compositional, architectural and metabolic alterations potentially leading to osteoporosis. Osteoporosis is the most prevalent bone disorder, which is characterised by progressive bone weakening and an increased risk of fragility fractures. Although this metabolic disease is conventionally associated with ageing and menopause, the predisposing factors are thought to be established during childhood and adolescence. In light of this, exercise interventions implemented during maturation are likely to be highly beneficial as part of a long-term strategy to maximise peak bone mass and hence delay the onset of age- or menopause-related osteoporosis. This notion is supported by data on exercise interventions implemented during childhood and adolescence, which confirmed that weight-bearing activity, particularly if undertaken during peripubertal development, is capable of generating a significant osteogenic response leading to bone anabolism. Recent work on human ageing and epigenetics suggests that undertaking exercise after the fourth decade of life is still important, given the anti-ageing effect and health benefits provided, potentially occurring via a delay in telomere shortening and modification of DNA methylation patterns associated with ageing. Exercise is among the primary modifiable factors capable of influencing bone health by preserving bone mass and strength, preventing the death of bone cells and anti-ageing action provided.

CHAPTER 18. Magnetic-Responsive Materials for Tissue Engineering and Regenerative Medicine

Novel tissue engineering approaches are emerging to meet regenerative medicine demands and challenges towards successful therapies to completely restore the function in damaged or degenerated tissues. Among them, magnetic tissue engineering envisions the development of complex systems in which magnetic elements are exploited as remotely controlled multidimensional tools with potential for diagnostic and therapeutic actions. This chapter provides an overview of the latest developments in the design and assessment of magnetic tissue engineering strategies with particular emphasis on smart magnetic materials and their relevance for tissue regeneration. Special attention will be given to the fabrication of sophisticated systems from the nano to the macro scale, and to the role of magnetic smart materials for providing alternative approaches to address the demanding tissue requirements and meet successful alternative strategies for regenerative medicine. The cellular response to the presence of magnetic elements will also be considered in this chapter, including internalization and clearance mechanisms as well as the relevance of magnetic stimulation for cell proliferation and differentiation among other biological processes.