![]() Cellulose and PTFE filter membranes were among the first commercially available well-plate inserts for use in coculture investigations. Over time, several different types of filter membrane have been used in coculture applications. This smaller pore diameter prevents cell migration through the membrane and prevents contamination of the cells in culture on the well-plate surface below. In the most common setup, cells in a well-plate culture are exposed to factors expressed by a second colony of cells seeded onto a membrane with 0.4-µm diameter pores placed directly above the first culture, typically held within a Transwell® hanging insert. In filter coculture, separate colonies of cells can exchange factors without direct contact and mixing of the cell populations. 68 The high-throughput system enabled the cytotoxic effects of the drug on cancer cell number and cell morphology to be rapidly determined.Īs well as transport through membranes supporting the culture of thicker tissues and the investigation of drug delivery, diffusion through filter membranes has been widely used to facilitate the study of different types of coculture system. In one example, diffusion through an aluminum oxide porous membrane (55-nm pores) was used to investigate the cytotoxic effects of cisplatin on a patterned microarray of human esophageal squamous epithelial cancer cells entrapped in poly(ethylene glycol) hydrogel. Nanoporous anodized aluminum oxide membranes are also very suitable for use as culture supports in drug delivery studies. In one such example, the response of neutrophil cells to gradients of a chemotactic peptide was recorded using time lapse microscopy, 67 demonstrating that more than 70% of cells responded by migrating up the gradients. ![]() More recently, track-etched membranes have been combined with microfluidic systems to create chambers that can be used to measure the cellular response to gradients of drugs within cell cultures. 66 Confluent epithelial monolayers, shown to be impermeable to polyethylene glycol (MW 4000) after 10 days in culture, were used to investigate the rate of transport of beta-blocking agents. In an early report, the investigation of drug absorption through a monolayer of intestinal epithelium cultured on a PC track-etched filter membrane was described. 65ĭiffusion through porous membranes has also been used in the investigation of drug delivery to cells and transport of drugs through cell sheets. ![]() It is thought the membranes can better represent the stem cell niche in comparison to conventional dish-culture techniques, enabling cells to take up and secrete molecules from both basal and apical surfaces. 64 Diffusion through filters has even been reported to promote human embryonic stem cell growth and differentiation. 62 Filter membranes have also been used to culture other tissue types, such as rat adipose tissue slices to better localize adipose progenitor cells 63 and, more recently, filter cultures have enabled the investigation of the growth of mouse embryos in vitro permitting the study and manipulation of developmental events in a dish. ![]() 10 Organotypic filter membrane culture of animal brain slices has since become an established technique, used both in electrophysiological research and in developmental studies such as the investigation of neural precursor cell migration into slices. Cells within the cultured slices remained viable for up to a week on the filter membranes, facilitating long-term recordings of extra- and intracellular excitatory and inhibitory synaptic potentials. One of the first reported uses of this type of system replaced the use of roller drum cultures, and enabled long term culture of one to four cell layer thick neonatal mice and hippocampal slices. Cells cultured in this way can remain viable for many days or weeks of study. For some tissue types, long-term cell viability is further improved by placing the membrane at the air–liquid interface, which increases gaseous diffusion in and out of the cell layer or tissue slice. ![]() Unlike nonporous culture surfaces, culture medium can diffuse through porous filter membranes and cellular waste products can diffuse away from the cell mass into the membrane. Hua Ye, in Comprehensive Membrane Science and Engineering (Second Edition), 2017 4.13.4.2 Using Filter Membranes for Increased Diffusionįilter membranes are also used as culture substrates to support the long-term viability of tissue slices and layers of cultured cells. ![]()
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