No abstract

Poly­(dimethylsiloxane) (PDMS) is a commonly used polymer in organ-on-a-chip devices and microphysiological systems. However, due to its hydrophobicity and permeability, it absorbs drug compounds, preventing accurate drug screening applications. Here, we developed an effective and facile method to prevent the absorption of drugs by utilizing a PDMS–PEG block copolymer additive and drug pretreatment. First, we incorporated a PDMS–PEG block copolymer into PDMS to address its inherent hydrophobicity. Next, we addressed the permeability of PDMS by eliminating the concentration gradient via pretreatment of the PDMS with the drug prior to experimentally testing drug absorption. The combined use of a PDMS–PEG block copolymer with drug pretreatment resulted in a mean reduction of drug absorption by 91.6% in the optimal condition. Finally, we demonstrated that the proposed method can be applied to prevent drug absorption in a PDMS-based cardiac microphysiological system, enabling more accurate drug studies.

Programmed −1 ribosomal frameshifts (−1 PRFs) are commonly used by viruses to regulate their enzymatic and structural protein levels. Human T-cell leukemia virus type 1 (HTLV-1) is a carcinogenic retrovirus that uses two independent −1 PRFs to express viral enzymes critical to establishing new HTLV-1 infections. How the cis-acting RNA elements in this viral transcript function to induce frameshifting is unknown. The objective of this work was to conclusively define the 3′ boundary of and the RNA elements within the HTLV-1 pro-pol frameshift site. We hypothesized that the frameshift site structure was a pseudoknot and that its 3′ boundary would be defined by the pseudoknot's 3′ end. To test these hypotheses, the in vitro frameshift efficiencies of three HTLV-1 pro-pol frameshift sites with different 3′ boundaries were quantified. The results indicated that nucleotides included in the longest construct were essential to highly efficient frameshift stimulation. Interestingly, only this construct could form the putative frameshift site pseudoknot. Next, the secondary structure of this frameshift site was determined. The dominant structure was an H-type pseudoknot which, together with the slippery sequence, stimulated frameshifting to 19.4(±0.3)%. The pseudoknot's critical role in frameshift stimulation was directly revealed by examining the impact of structural changes on HTLV-1 pro-pol −1 PRF. As predicted, mutations that occluded pseudoknot formation drastically reduced the frameshift efficiency. These results are significant because they demonstrate that a pseudoknot is important to HTLV-1 pro-pol −1 PRF and define the frameshift site's 3′ boundary.

In the scope of biomedical research, many advances have been made in the field of pulmonology with the use of multiple animal models and traditional cell culture experimentation. While these methods are useful when studying single cellular pathways or overarching biological processes, they often falter when studying the meticulous nature of human disease. In this work, we propose the development of a novel Lung‐on‐a‐Chip device that would more accurately mimic the physiological boundaries of human alveoli than animal models or traditional in vitro studies. Utilizing multiple microfabrication techniques, we are developing a microfluidic device with an ultra‐thin (25μm) biodegradable porous silicon membrane. Current data suggests that human pulmonary epithelial and endothelial cells are viable and prolific on the proposed microfabricated silicon membrane in extended studies (14 days). Due to the biodegradability of the fabricated novel silicon membranes, it has been observed in long term studies that cells can remodel and degrade the porous silicon membrane. This degradation allows for physiological cellular contact between membranes mimicking a true blood gas exchange interface as observed in vivo. To further validate this model’s ability to recapitulate human physiology, we have begun to co‐culture with immunological cell types and are monitoring for response to bacterial and tumor antigens. Preliminary data suggests that immunological cells are able to remodel the porous silicon membrane substrate and migrate across cellular boundaries in response to environmental cues as seen in vivo. Broadly, we believe that this model may be used to further characterize and study human pulmonary disease and drug toxicity. Support or Funding Information Maximizing Access to Research Careers Undergraduate Student Training in Academic Research Award# T34GM092711NSF PREM for Functional Nanomaterials, Award# 1827847STROBE NSF Science and Technology Center on Real‐Time Functional Imaging, Award# 1548924.