While the evolution of nanotechnology poses a vast potential in improving the quality of human life in areas such as electronics, energy, health care, and several of other fields, consumer and occupational exposure to these engineered nanomaterials significantly increases, which presents an enormous health concern. For instance, carbon nanotubes (CNTs) are projected to become trillion-dollar industry in the next decade. Animal exposure studies have shown that inhaled CNTs rapidly enter the interstitium to stimulate collagen production and induce progressive interstitial lung fibrosis, which is a fatal and incurable disease with no known effective treatment. To map the hazards of the nanomaterials, animal studies are conducted but they are expensive, time consuming and facility limited. Conventional in vitro models suffer drawbacks, most importantly, they lack characteristics of in vivo microenvironment, leading to losses of critical in vivo cell phenotypes and responsiveness. Efforts are being made to integrate physiological features into in vitro models. There is still a critical need to develop in vitro models to provide reliable, rapid and inexpensive methods for toxicological studies of the nanomaterials. Here, we developed a biomimetic alveolar interstitium microfluidic platform to study CNTs induced fibrosis.
The polydimethylsiloxane (PDMS)-based microfluidic platform comprised of three microchannels. The central channel was comparted by a microporous PDMS membrane, one side of which was fabricated with nanotopography defined by electron beam lithography. Normal human lung fibroblast and human alveolar epithelial cells were cultured on bottom (with nanotopography) and top (flat) of the membrane, respectively. The outer two microchannels were pumped with water to generate a cyclic loading of the chamber walls to stretch the porous membrane. Multi-walled CNTs (MWCNTs) were injected into the upper central channel. Cell adhesion and nuclear deformation of fibroblasts on PDMS nanotopography were analyzed. Collagen I production of fibroblasts on the nanotopography and in the microfluidic platform in response to MWCNTs was assayed.
The shape and dimensions, in particular the height of nanotopographies have profound effects on the phenotype and function of the fibroblasts. When the height of nanotopographies increased and the cells perceived less substrate surface accompanied with reduced spreading; the nuclear volume significantly decreased from larger to smaller than the flat control. The height-modulated nuclear deformation further affected proliferation of fibroblasts. The nanotopography-restrained cell spreading reduced Collagen I production and promoted the toxic sensitivity of fibroblasts to MWCNTs. The nanotopography and stiffness cues, together with the mechanical cues in the microfluidic platform further modulated the cell sensing MWCNTs.
The engineered microfluidic platform mimics the key physical (substrate nanotopography and stiffness), mechanical (fluidic forces and cyclic mechanical strain) and structural (co-culture of fibroblasts and epithelial cells) characteristics of a native alveolar interstitium. This biomimetic model will provide a useful tool to elucidate key pathways in cell responses to nanomaterials, and potentially promote sustainable development of nanotechnology.
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