Design approaches for 3D cell culture and 3D bioprinting platforms.

The natural habitat of most cells consists of complex and disordered 3D microenvironments with spatiotemporally dynamic material properties. However, prevalent methods of in vitro culture study cells under poorly biomimetic 2D confinement or homogeneous conditions that often neglect critical topographical cues and mechanical stimuli. It has also become increasingly apparent that cells in a 3D conformation exhibit dramatically altered morphological and phenotypical states. In response, efforts toward designing biomaterial platforms for 3D cell culture have taken centerstage over the past few decades. Herein, we present a broad overview of biomaterials for 3D cell culture and 3D bioprinting, spanning both monolithic and granular systems. We first critically evaluate conventional monolithic hydrogel networks, with an emphasis on specific experimental requirements. Building on this, we document the recent emergence of microgel-based 3D growth media as a promising biomaterial platform enabling interrogation of cells within porous and granular scaffolds. We also explore how jammed microgel systems have been leveraged to spatially design and manipulate cellular structures using 3D bioprinting. The advent of these techniques heralds an unprecedented ability to experimentally model complex physiological niches, with important implications for tissue bioengineering and biomedical applications.

Jammed microgel growth medium prepared by flash-solidification of agarose for 3D cell culture and 3D bioprinting.

Although cells cultured in three-dimensional (3D) platforms are proven to be beneficial for studying cellular behavior in settings similar to their physiological state, due to the ease, convenience, and accessibility, traditional 2D culturing approaches are widely adopted. Jammed microgels are a promising class of biomaterials extensively suited for 3D cell culture, tissue bioengineering, and 3D bioprinting. However, existing protocols for fabricating such microgels either involve complex synthesis steps, long preparation times, or polyelectrolyte hydrogel formulations that sequester ionic elements from the cell growth media. Hence, there is an unmet need for a broadly biocompatible, high-throughput, and easily accessible manufacturing process. We address these demands by introducing a rapid, high-throughput, and remarkably straightforward method to synthesize jammed microgels composed of flash-solidified agarose granules directly prepared in a culture medium of choice. Our jammed growth media are optically transparent, porous, yield stress materials with tunable stiffness and self-healing properties, which makes them ideal for 3D cell culture as well as 3D bioprinting. The charge-neutral and inert nature of agarose make them suitable for culturing various cell types and species, the specific growth media for which do not alter the chemistry of the manufacturing process. Unlike several existing 3D platforms, these microgels are readily compatible with standard techniques such as absorbance-based growth assays, antibiotic selection, RNA extraction, and live cell encapsulation. In effect, we present a versatile, highly accessible, inexpensive, and easily adoptable biomaterial for 3D cell culture and 3D bioprinting. We envision their widespread application not just in routine laboratory settings but also in designing multicellular tissue mimics and dynamic co-culture models of physiological niches.

Circular RNA as an Additional Player in the Conflicts Between the Host and the Virus.

Circular RNA (circRNA), a relatively new member of the non-coding RNA family, has spurred great interest among researchers following its discovery as a ubiquitous class within the RNA world. Rapid progress in circRNA biology has coincided with its identification in a plethora of diverse roles including regulation of gene expression and probable coding potential, as well as competing interactions with proteins and microRNAs in various pathological conditions. Emerging evidence suggests that circRNAs also function in viral infections. The deregulation of circRNAs during viral infection has prompted investigations into the possibilities of circRNA as a competing endogenous RNA (ceRNA) that modulates response to infection. Recently, viruses have been shown to encode circRNAs with proviral functions, providing a strong impetus for focused efforts to elucidate the networks coaxed by circRNAs during infection. This review elaborates on recent insights gained on the roles of circRNAs during virus infection and immunity.

SARS CoV-2 Nucleoprotein Enhances the Infectivity of Lentiviral Spike Particles.

The establishment of SARS CoV-2 spike-pseudotyped lentiviral (LV) systems has enabled the rapid identification of entry inhibitors and neutralizing agents, alongside allowing for the study of this emerging pathogen in BSL-2 level facilities. While such frameworks recapitulate the cellular entry process in ACE2+ cells, they are largely unable to factor in supplemental contributions by other SARS CoV-2 genes. To address this, we performed an unbiased ORF screen and identified the nucleoprotein (N) as a potent enhancer of spike-pseudotyped LV particle infectivity. We further demonstrate that the spike protein is better enriched in virions when the particles are produced in the presence of N protein. This enrichment of spike renders LV particles more infectious as well as less vulnerable to the neutralizing effects of a human IgG-Fc fused ACE2 microbody. Importantly, this improvement in infectivity is observed with both wild-type spike protein as well as the D614G mutant. Our results hold important implications for the design and interpretation of similar LV pseudotyping-based studies.

SARS-CoV-2: phylogenetic origins, pathogenesis, modes of transmission, and the potential role of nanotechnology.

The COVID-19 pandemic has elicited a rapid response from the scientific community with significant advances in understanding the causative pathogen (SARS-CoV-2). Mechanisms of viral transmission and pathogenesis, as well as structural and genomic details, have been reported, which are essential in guiding containment, treatment, and vaccine development efforts. Here, we present a concise review of the recent research in these domains and an exhaustive analysis of the genomic origins of SARS-CoV-2. Particular emphasis has been placed on the pathology and disease progression of COVID-19 as documented by recent clinical studies, in addition to the characteristic immune responses involved therein. Furthermore, we explore the potential of nanomaterials and nanotechnology to develop diagnostic tools, drug delivery systems, and personal protective equipment design within the ongoing pandemic context. We present this as a ready resource for researchers to gain succinct, up-to-date insights on SARS-CoV-2.

SARS CoV-2 nucleoprotein enhances the infectivity of lentiviral spike particles

The establishment of SARS CoV-2 spike-pseudotyped lentiviral (LV) systems has enabled the rapid identification of entry inhibitors and neutralizing agents, alongside allowing for the study of this emerging pathogen in BSL-2 level facilities. While such frameworks recapitulate the cellular entry process in ACE2+ cells, they are largely unable to factor in supplemental contributions by other SARS CoV-2 genes. To address this, we performed an unbiased ORF screen and identified the nucleoprotein (N) as a potent enhancer of spike-pseudotyped LV particle infectivity. We further demonstrate that this augmentation by N renders LV spike particles less vulnerable to the neutralizing effects of a human IgG-Fc fused ACE2 microbody. Biochemical analysis revealed that the spike protein is better enriched in virions when the particles are produced in the presence of SARS CoV-2 nucleoprotein. Importantly, this improvement in infectivity is achieved without a concomitant increase in sensitivity towards RBD binding-based neutralization. Our results hold important implications for the design and interpretation of similar LV pseudotyping-based studies.

COVID-19: Advances in diagnostic tools, treatment strategies, and vaccine development.

An unprecedented worldwide spread of the SARS-CoV-2 has imposed severe challenges on healthcare facilities and medical infrastructure. The global research community faces urgent calls for the development of rapid diagnostic tools, effective treatment protocols, and most importantly, vaccines against the pathogen. Pooling together expertise across broad domains to innovate effective solutions is the need of the hour. With these requirements in mind, in this review, we provide detailed critical accounts on the leading efforts at developing diagnostics tools, therapeutic agents, and vaccine candidates. Importantly, we furnish the reader with a multidisciplinary perspective on how conventional methods like serology and RT-PCR, as well as cutting-edge technologies like CRISPR/Cas and artificial intelligence/machine learning, are being employed to inform and guide such investigations. We expect this narrative to serve a broad audience of both active and aspiring researchers in the field of biomedical sciences and engineering and help inspire radical new approaches towards effective detection, treatment, and prevention of this global pandemic.

Investigations into the cancer stem cell niche using in-vitro 3-D tumor models and microfluidics.

The concept of Cancer Stem Cells (CSCs) and the CSC Niche/Tumor Microenvironment (TME) as the central driving force behind tumor progression and maintenance has garnered much attention in recent years. Concomitantly, the widespread adoption of 3D tissue models, organotypic co-cultures, and the revolutionary microfluidic technology has resulted in a plethora of ground-breaking fundamental discoveries and has enabled investigations which were previously unfeasible. A large number of existing review papers concern themselves with either a broad look at the TME and CSC Niche, or on the studies undertaken on a particular niche component alone. In this article, we attempt to bring out a harmonic, expansive look at the concept of CSCs, the TME, and the various advancements in answering key biological queries enabled by these emerging new technologies. Our primary goal is to present a fundamental understanding of CSCs, as well as the CSC niche, and elucidate note-worthy examples of investigations being carried out with regard to each of the major TME components, along with our insights into the potential for further research. We hope that this serves as an impetus to new, as well as existing researchers in this area, to gain fresh perspectives on the CSC niche, as well as provide them with a glimpse at the kind of progress being made using 3D tumor models and microfluidic devices.