No abstract

One of greatest challenges to the successful treatment of cancer is drug resistance. An exciting approach is the eradication of cancer stem cells (CSCs). However, little is known about key signals regulating the formation and expansion of CSCs. Moreover, lack of a reliable predictive preclinical model has been a major obstacle to discover new cancer drugs and predict their clinical activity. Here, in ovarian cancer, a highly chemoresistant tumor that is rapidly fatal, we provide the first evidence demonstrating the causal involvement of mechanical stimulus in the CSC phenotype using a customizable microfluidic platform and three-dimensional spheroids, which most closely mimic tumor behavior. We found that ovarian cancer cells significantly acquired the expression of epithelial-to-mesenchymal transition and CSC markers and a remarkable chemoresistance to clinically relevant doses of frontline chemotherapeutic drugs cisplatin and paclitaxel when grown under fluid shear stress, which corroborates with the physiological attainable levels in the malignant ascites, but not under static condition. Furthermore, we uncovered a new link of microRNA-199a-3p, phosphatidylinositol 3-kinase/Akt, and multidrug transporter activation in shear stress-induced CSC enrichment. Our findings shed new light on the significance of hydrodynamics in cancer progression, emphasizing the need of a flow-informed framework in the development of therapeutics.

Inhibiting specific gene expression by short interfering RNA (siRNA) offers a new therapeutic strategy to tackle many diseases, including cancer, metabolic disorders, and viral infections, at the molecular level. The macromolecular and polar nature of siRNA hinders its cellular access to exert its effect. Nanoparticulate delivery systems can promote efficient intracellular delivery. Despite showing promise in many preclinical studies and potential in some clinical trials, siRNA has poor delivery efficiency, which continues to demand innovations, from carrier design to formulation, in order to overcome transport barriers. Previous findings for optimal plasmid DNA delivery cannot be generalized to siRNA delivery owing to significant discrepancy in size and subtle differences in chain flexibility between the two types of nucleic acids. In this review, we highlight the recent advances in improving the stability of siRNA nanoparticles, understanding their intracellular trafficking and release mechanisms, and applying judiciously the promising formulations to disease models.

Nanoparticle-mediated gene delivery is a promising alternative to viral methods; however, its use in vivo, particularly following systemic injection, has suffered from poor delivery efficiency. Although PEGylation of nanoparticles has been successfully demonstrated as a strategy to enhance colloidal stability, its success in improving delivery efficiency has been limited, largely due to reduced cell binding and uptake, leading to poor transfection efficiency. Here we identified an optimized PEGylation scheme for DNA micellar nanoparticles that delivers balanced colloidal stability and transfection activity. Using linear polyethylenimine (lPEI)-g-PEG as a carrier, we characterized the effect of graft length and density of polyethylene glycol (PEG) on nanoparticle assembly, micelle stability, and gene delivery efficiency. Through variation of PEG grafting degree, lPEI with short PEG grafts (molecular weight, MW 500–700 Da) generated micellar nanoparticles with various shapes including spherical, rodlike, and wormlike nanoparticles. DNA micellar nanoparticles prepared with short PEG grafts showed comparable colloidal stability in salt and serum-containing media to those prepared with longer PEG grafts (MW 2 kDa). Corresponding to this trend, nanoparticles prepared with short PEG grafts displayed significantly higher in vitro transfection efficiency compared to those with longer PEG grafts. More importantly, short PEG grafts permitted marked increase in transfection efficiency following ligand conjugation to the PEG terminal in metastatic prostate cancer-bearing mice. This study identifies that lPEI-g-PEG with short PEG grafts (MW 500–700 Da) is the most effective to ensure shape control and deliver high colloidal stability, transfection activity, and ligand effect for DNA nanoparticles in vitro and in vivo following intravenous administration.

Despite successful demonstration of linear polyethyleneimine (lPEI) as an effective carrier for a wide range of gene medicine, including DNA plasmids, small interfering RNAs, mRNAs, etc., and continuous improvement of the physical properties and biological performance of the polyelectrolyte complex nanoparticles prepared from lPEI and nucleic acids, there still exist major challenges to produce these nanocomplexes in a scalable manner, particularly for lPEI/DNA nanoparticles. This has significantly hindered the progress towards clinical translation of these nanoparticle-based gene medicine. Here we report a flash nanocomplexation (FNC) method that achieves continuous production of lPEI/plasmid DNA nanoparticles with narrow size distribution using a confined impinging jet device. The method involves the complex coacervation of negatively charged DNA plasmid and positive charged lPEI under rapid, highly dynamic, and homogeneous mixing conditions, producing polyelectrolyte complex nanoparticles with narrow distribution of particle size and shape. The average number of plasmid DNA packaged per nanoparticles and its distribution are similar between the FNC method and the small-scale batch mixing method. In addition, the nanoparticles prepared by these two methods exhibit similar cell transfection efficiency. These results confirm that FNC is an effective and scalable method that can produce well-controlled lPEI/plasmid DNA nanoparticles.

Microfluidic systems have advanced beyond natural and life science applications and lab‐on‐a‐chip uses. A growing trend of employing microfluidic technologies for environmental detection has emerged thanks to the precision, time‐effectiveness, and cost‐effectiveness of advanced microfluidic systems. This paper reviews state‐of‐the‐art microfluidic technologies for environmental applications, such as on‐site environmental monitoring and detection. Microdevices are extensively used in collecting environmental samples as a means to facilitate detection and quantification of targeted components with minimal quantities of samples. Likewise, microfluidic‐inspired approaches for separation and treatment of contaminated water and air, such as the removal of heavy metals and waterborne pathogens from wastewater and carbon capture are also investigated.

The breakup dynamics in non-Newtonian multiphase microsystems is associated with a variety of industrial applications such as food production and biomedical engineering. In this study, we numerically and experimentally characterize the dripping-to-jetting transition under various flow conditions in a Newtonian/shear-thinning multiphase microsystem. Our work can help to predict the formation of undesirable satellite droplets, which is one of the challenges in dispensing non-Newtonian fluids. We also demonstrate the variations in breakup dynamics between shear-thinning and Newtonian fluids under the same flow conditions. For shear-thinning fluids, the droplet size increases when the capillary number is smaller than a critical value, while it decreases when the capillary number is beyond the critical value. The variations highlight the importance of rheological effects in flows with a non-Newtonian fluid. The viscosity of shear-thinning fluids significantly affects the control over the droplet size, therefore necessitating the manipulation of the shear rate through adjusting the flow rate and the dimensions of the nozzle. Consequently, the droplet size can be tuned in a controlled manner. Our findings can guide the design of novel microdevices for generating droplets of shear-thinning fluids with a predetermined droplet size. This enhances the ability to fabricate functional particles using an emulsion-templated approach. Moreover, elastic effects are also investigated experimentally using a model shear-thinning fluid that also exhibits elastic behaviors: droplets are increasingly deformed with increasing elasticity of the continuous phase. The overall understanding in the model multiphase microsystem will facilitate the use of a droplet-based approach for non-Newtonian multiphase applications ranging from energy to biomedical sciences.

A series of polyphosphoramidates (PPA) with different molecular weights (MWs) and charge densities were synthesized and examined for their DNA compaction ability and transfection efficiency. A strong correlation was observed between the transfection efficiency of PPA/DNA nanoparticles and the MW and net positive charge density of the PPA gene carriers in three different cell lines (HeLa, HEK293 and HepG2 cells). An increase in MW and/or net positive charge density of PPA carrier yielded higher DNA compaction capacity, smaller nanoparticles with higher surface charges and higher complex stability against challenges by salt and polyanions. These favorable physicochemical properties of nanoparticles led to enhanced transfection efficiency. PPA/DNA nanoparticles with the highest complex stability showed comparable transfection efficiency as PEI/DNA nanoparticles likely by compensating the low buffering capacity with higher cellular uptake and affording higher level of protection to DNA in endolysosomal compartment. The differences in transfection efficiency were not attributed by any difference in cytotoxicity among the carriers, as all nanoparticles showed minimal level of cytotoxicity under the transfection conditions. Using PPA as a model system, we demonstrated the structural dependence of transfection efficiency of polymer gene carrier. These results offer more insights into nanoparticle engineering for non-viral gene delivery.