Quantifying cell adhesion through impingement of a controlled microjet

Residual protein analysis by SDS-PAGE in clinically manufactured BM-MSC products

Residual substances that are considered hazardous to the recipient must be removed from final cellular therapeutic products manufactured for clinical purposes. In doing so, quality rules determined by competent authorities (CAs) for the clinical use of tissue- and cell-based products can be met. In our study, we carried out residual substance analyses, and purity determination studies of trypsin and trypsin inhibitor in clinically manufactured bone marrow-derived mesenchymal stromal/stem cell products, using the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) method. Despite being a semiquantitative method, SDS-PAGE has several benefits over other methods for protein analysis, such as simplicity, convenience of use, and affordability. Due to its convenience and adaptability, SDS-PAGE is still a commonly used method in many laboratories, despite its limits in dynamic range and quantitative precision. Our goal in this work was to show that SDS-PAGE may be used effectively for protein measurement, especially where practicality and affordability are the major factors. The results of our study suggest a validated method to guide tissue and cell manufacturing sites for making use of an agreeable, accessible, and cost-effective method for residual substance analyses in clinically manufactured cellular therapies.

Integrating Shear Flow and Trypsin Treatment to Assess Cell Adhesion Strength

Cell adhesion is of fundamental importance in cell and tissue organization, and for designing cell-laden constructs for tissue engineering. Prior methods to assess cell adhesion strength for strongly adherent cells using hydrodynamic shear flow either involved the use of specialized flow devices to generate high shear stress or used simpler implementations like larger height parallel plate chambers that enable multi-hour cell culture but generate low shear stress and are hence more applicable for weakly adherent cells. Here, we propose a shear flow assay for adhesion strength assessment of strongly adherent cells that employs off-the-shelf parallel plate chambers for shear flow as well as simultaneous trypsin treatment to tune down the adhesion strength of cells. We implement the assay with a strongly adherent cell type and show that shear stress in the 0.07 to 7 Pa range is sufficient to dislodge the cells with simultaneous trypsin treatment. Imaging of cells over a square centimeter area allows cell morphological analysis of hundreds of cells. We show that the cell area of cells that are dislodged, on average, does not monotonically increase with shear stress at the higher end of shear stresses used and suggest that this can be explained by the likely higher resistance of high circularity cells to trypsin digestion. The adhesion strength assay proposed can be easily adapted by labs to assess the adhesion strength of both weakly and strongly adherent cell types and has the potential to be adapted for substrate stiffness-dependent adhesion strength assessment in mechanobiology studies.

Replacement of Trypsin by Proteases for Medical Applications

Background

Cell culture has a crucial role in many applications in biotechnology. The production of vaccines, recombinant proteins, tissue engineering, and stem cell therapy all need cell culture. Most of these activities needed adherent cells to move, which should be trypsinized several times until received on a large scale. Although trypsin is manufactured from the bovine or porcine pancreas, the problem of contamination by unwanted animal proteins, unwanted immune reactions, or contamination to pathogen reagents is the main problem.

Objectives

This study investigated microbial proteases as a safe alternative for trypsin replacement in cell culture experiments for the detachment of adherent cells.

Methods

The bacteria were isolated from the leather industry effluent based on their protease enzymes. After sequencing their 16S ribosomal deoxyribonucleic acid, their protease enzymes were purified, and their enzyme activities were assayed. The alteration of enzymatic activities using different substrates and the effect of substrate concentrations on enzyme activities were determined. The purified proteases were evaluated for cell detachment in the L929 fibroblast cells compared to trypsin. The separated cells were cultured again, and cell proliferation was determined by the MTT assay.

Results

The results showed that the isolated bacteria were Bacillus pumilus, Stenotrophomonas sp., Klebsiella aerogenes, Stenotrophomonas maltophilia, and Bacillus licheniformis. Among the isolated bacteria, the highest and the lowest protease activity belonged to Stenotrophomonas sp. and K. aerogenes, with 60.34 and 11.09 U/mL protease activity, respectively. All the isolated microbial proteases successfully affected L929 fibroblast cells' surface proteins and detached the cells. A significant induction in cell proliferation was observed in the cells treated with K. aerogenes protease and B. pumilus protease, respectively (P < 0.05).

Conclusions

The obtained results suggested that microbial proteases can be used as safe and efficient alternatives to trypsin in cell culture in biopharmaceutical applications.

Integrating shear flow and trypsin treatment to assess cell adhesion strength

Cell adhesion is of fundamental importance in cell and tissue organization and for designing cell-laden constructs for tissue engineering. Prior methods to assess cell adhesion strength for strongly adherent cells using hydrodynamic shear flow either involved the use of specialized flow devices to generate high shear stress or used simpler implementations like larger height parallel plate chambers that enable multihour cell culture but generate low wall shear stress and are, hence, more applicable for weakly adherent cells. Here, we propose a shear flow assay for adhesion strength assessment of strongly adherent cells that employs off-the-shelf parallel plate chambers for shear flow as well as simultaneous trypsin treatment to tune down the adhesion strength of cells. We implement the assay with a strongly adherent cell type and show that wall shear stress in the 0.07-7 Pa range is sufficient to dislodge the cells with simultaneous trypsin treatment. Imaging of cells over a square centimeter area allows cell morphological analysis of hundreds of cells. We show that the cell area of cells that are dislodged, on average, does not monotonically increase with wall shear stress at the higher end of wall shear stresses used and suggest that this can be explained by the likely higher resistance of high circularity cells to trypsin digestion. The adhesion strength assay proposed can be used to assess the adhesion strength of both weakly and strongly adherent cell types and has the potential to be adapted for substrate stiffness-dependent adhesion strength assessment in mechanobiology studies.

Creating wounds in cell monolayers using micro-jets

Many wound-healing assays are used in cell biology and biomedicine; they are often labor intensive and/or require specialized and costly equipment. We describe a contactless method to create wounds with any imaginable 2D pattern in cell monolayers using the micro-jets of either media or an immiscible and biocompatible fluorocarbon (i.e., FC40). We also combine this with another method that allows automation and multiplexing using standard Petri dishes. A dish is filled with a thin film of media overlaid with FC40, and the two liquids are reshaped into an array of microchambers within minutes. Each chamber in such a grid is isolated from others by the fluid walls of FC40. Cells are now added, allowed to grow into a monolayer, and wounds are created using the microjets; then, healing is monitored by microscopy. As arrays of chambers can be made using media and Petri dishes familiar to biologists, and as dishes fit seamlessly into their incubators, microscopes, and workflows, we anticipate that this assay will find wide application in wound healing.

Towards smart self-clearing glaucoma drainage device

For patients who are unresponsive to pharmacological treatments of glaucoma, an implantable glaucoma drainage devices (GDD) are often used to manage the intraocular pressure. However, the microscale channel that removes excess aqueous humor from the anterior chamber often gets obstructed due to biofouling, which necessitates additional surgical intervention. Here we demonstrate the proof-of-concept for smart self-clearing GDD by integrating magnetic microactuators inside the drainage tube of GDD. The magnetic microactuators can be controlled using externally applied magnetic fields to mechanically clear biofouling-based obstruction, thereby eliminating the need for surgical intervention. In this work, our prototype magnetic microactuators were fabricated using low-cost maskless photolithography to expedite design iteration. The fabricated devices were evaluated for their static and dynamic mechanical responses. Using transient numerical analysis, the fluid-structure interaction of our microactuator inside a microtube was characterized to better understand the amount of shear force generated by the device motion. Finally, the anti-biofouling performance of our device was evaluated using fluorescein isothiocyanate labeled bovine serum albumin. The microactuators were effective in removing proteinaceous film deposited on device surface as well as on the inner surface of the microchannel, which supports our hypothesis that a smart self-clearing GDD may be possible by integrating microfabricated magnetic actuators in chronically implanted microtubes.

Topography of Cells Revealed by Variable-Angle Total Internal Reflection Fluorescence Microscopy

We propose an improved version of variable-angle total internal reflection fluorescence microscopy (vaTIRFM) adapted to modern TIRF setup. This technique involves the recording of a stack of TIRF images, by gradually increasing the incident angle of the light beam on the sample. A comprehensive theory was developed to extract the membrane/substrate separation distance from fluorescently labeled cell membranes. A straightforward image processing was then established to compute the topography of cells with a nanometric axial resolution, typically 10-20 nm. To highlight the new opportunities offered by vaTIRFM to quantify adhesion process of motile cells, adhesion of MDA-MB-231 cancer cells on glass substrate coated with fibronectin was examined.

Maximizing Fibroblast Adhesion on Protein-Coated Surfaces Using Microfluidic Cell Printing

translation of in vitro cell based assays to in vivo cellular response is imprecise at best. The advent of three-dimensional cell cultures in addition to bioreactor type microfluidics has improved the situation. However, these technical advances cannot be easily combined due to practical limitations. Development of a vertical microfluidic cell printer overcomes this obstacle, providing the ability to more closely recapitulate complex cellular environments and responses. As a proof of concept, we investigated the adhesion of fibroblasts under flow on protein-coated surfaces using a novel vertical microfluidic print head to isolate and manipulate both mechanical and biological factors as a model of fibroblast behavior during the foreign body response following implant insertion. A low flow rate with larger microfluidic channels onto a serum-coated surface has been determined to allow the highest density of viable fibroblasts to attach to the surface. While these insights into fibroblast surface attachment may lead to better material designs, the methods developed herein will certainly be useful as a biomaterials testing platform.