A membrane film sensor with encapsulated fluorescent dyes towards express freshness monitoring of packaged food.

A new Membrane Film Sensor (MFS) has been developed to measure pH of fluids. MFS comprises a polyelectrolyte multilayer film with uniformly distributed compartments (microchambers) where a fluorescent sensing dye is encapsulated. Fabricated film is sealed onto a polyethylene film for a future use. MFS was applied to report changes in golden pomfret fillet upon its storage at 5 °C. MFS pH readings were correlated to bacteriological analysis of fish samples. A hike in pH of fish juices happens after 10 days of storage signaling bacterial spoilage of fish. The design of developed MFS allows easy integration with transparent packaging materials for future development of "SMART" packaging sensing food freshness.

Evaluation of the topographical influence on the cellular behavior of human umbilical vein endothelial cells.

Adhesion and proliferation of vascular endothelial cells are important parameters in the endothelialization of biomedical devices for vascular applications. Endothelialization is a complex process affected by endothelial cells and their interaction with the extracellular microenvironment. Although numerous approaches are taken to study the influence of the external environment, a systematic investigation of the impact of an engineered microenvironment on endothelial cell processes is needed. This study aims to investigate the influence of topography, initial cell seeding density, and collagen coating on human umbilical vein endothelial cells (HUVECs). Utilizing the MultiARChitecture (MARC) chamber, the effects of various topographies on HUVECs are identified, and those with more prominent effects were further evaluated individually using the MARC plate. Endothelial cell marker expression and monocyte adhesion assay are examined on the HUVEC monolayer. HUVECs on 1.8 µm convex and concave microlens topographies demonstrate the lowest cell adhesion and proliferation, regardless of initial cell seeding density and collagen I coating, and the HUVEC monolayer on the microlens shows the lowest monocyte adhesion. This property of lens topographies would potentially be a useful parameter in designing vascular biomedical devices. The MARC chamber and MARC plate show a great potential for faster and easy pattern identification for various cellular processes.

Planar and tubular patterning of micro and nano-topographies on poly(vinyl alcohol) hydrogel for improved endothelial cell responses.

Poly(vinyl alcohol) hydrogel (PVA) is a widely used material for biomedical devices, yet there is a need to enhance its biological functionality for in vitro and in vivo vascular application. Significance of surface topography in modulating cellular behaviour is increasingly evident. However, hydrogel patterning remains challenging. Using a casting method, planar PVA were patterned with micro-sized features. To achieve higher patterning resolution, nanoimprint lithography with high pressure and temperature was used. In vitro experiment showed enhanced human endothelial cell (EC) density and adhesion on patterned PVA. Additional chemical modification via nitrogen gas plasma on patterned PVA further improved EC density and adhesion. Only EC monolayer grown on plasma modified PVA with 2 µm gratings and 1.8 µm concave lens exhibited expression of vascular endothelial cadherin, indicating EC functionality. Patterning of the luminal surface of tubular hydrogels is not widely explored. The study presents the first method for simultaneous tubular molding and luminal surface patterning of hydrogel. PVA graft with 2 µm gratings showed patency and endothelialization, while unpatterned grafts were occluded after 20 days in rat aorta. The reproducible, high yield and high-fidelity methods enable planar and tubular patterning of PVA and other hydrogels to be used for biomedical applications.

Enhanced differentiation of neural progenitor cells into neurons of the mesencephalic dopaminergic subtype on topographical patterns.

Parkinson's disease (PD) is a neurodegenerative disease attributed to the loss of midbrain dopaminergic (DA) neurons. The current lack of predictive models for this disease has been hampered by the acquirement of robust cells, posing a major barrier to drug development. Differentiation of stem cells into subtype specific cells may be guided by appropriate topographical cues but the role of topography has hitherto not been well understood. We used a Multi-Architecture (MARC) chip with various topographical structures and identified three topographies, which generate DA neurons from murine hippocampal neural progenitor cells with the highest percentage of neuronal (ß-III-tubulin positive) and dopaminergic (tyrosine hydroxylase positive) populations. Analysis on single pattern structures showed that 2 µm gratings with 2 µm spacing and 2 µm height (2 µm gratings) and 2 µm gratings with hierarchical structure produced cells with the highest gene expression of TH and PITX3, with the longest neurite and highest percentage of alignment. Quantitative image analysis showed the 2 µm gratings produced cells with the highest expression of pituitary homeobox 3 (PITX3), LIM homeobox transcription factor 1 alpha (LMX1a), aldehyde dehydrogenase 1 family member A1 (ALDH1a1) and microtubule associated protein 2 (MAP2), as compared to nano-gratings and unpatterned controls. These patterns also enhance DA neuron differentiation on different substrate rigidities, as seen on both poly-dimethylsiloxane (PDMS) and tissue culture polystyrene (TCPS) substrates. These results show the use of topographical influence for neuronal subtype specification, which could be translated into a wide range of clinical applications for PD.

The effect of micro and nanotopography on endocytosis in drug and gene delivery systems.

Endocytosis is a fundamental biological process and is also the key mechanism for drug and non-viral gene delivery. The importance of topographical cues in modulating cell behaviors has become increasingly evident, but the influence of topography on endocytosis has however only been sparsely studied. We hypothesize that topography can enhance cellular endocytosis, and in turn the non-viral transfection efficiency. Nano- to microtopographical patterns were fabricated using nano-imprinting lithography (NIL). We first investigated if the substrate topographies could modulate endocytosis and in turn the cellular transfectability. Our results showed increased internalization of fluorescently labeled dextran by human mesenchymal stem cells (hMSCs) and monkey kidney fibroblasts (COS7) when they were cultured on micro- and nanopillars. When the hMSCs were introduced to green-fluorescent protein (GFP) encoding plasmid with Lipofectamine, highest transfection efficiency was observed in cells on nanopillars. Tunable detachable substrate topographies were also fabricated using NIL to promote endocytosis in different cell types, and our results show hMSCs phagocytosis of these polymeric structures. Besides being important in understanding the fundamental process of endocytosis, the current research results may also lead to applications utilizing nanotopography to enhance drug and gene delivery.