A modified motor-clutch model reveals that neuronal growth cones respond faster to soft substrates

Neuronal growth cones sense a variety of cues including chemical and mechanical ones to establish functional connections during nervous system development. Substrate-cytoskeletal coupling is an established model for adhesion-mediated growth cone advance; however, the detailed molecular and biophysical mechanisms underlying the mechanosensing and mechanotransduction process remain unclear. Here, we adapted a motor-clutch model to better understand the changes in clutch and cytoskeletal dynamics, traction forces, and substrate deformation when a growth cone interacts with adhesive substrates of different stiffnesses. Model parameters were optimized using experimental data from Aplysia growth cones probed with force-calibrated glass microneedles. We included a reinforcement mechanism at both motor and clutch level. Furthermore, we added a threshold for retrograde F-actin flow that indicates when the growth cone is strongly coupled to the substrate. Our modeling results are in strong agreement with experimental data with respect to the substrate deformation and the latency time after which substrate-cytoskeletal coupling is strong enough for the growth cone to advance. Our simulations show that it takes the shortest time to achieve strong coupling when substrate stiffness was low at 4 pN/nm. Taken together, these results suggest that Aplysia growth cones respond faster and more efficiently to soft than stiff substrates.

Oral Galvanism Side Effects: Comparing Alloy Ions and Galvanic Current Effects on the Mucosa-like Model

The interaction of different dental alloys with the oral environment may cause severe side effects (e.g., burning sensation, inflammatory reactions, carcinogenesis) as a result of oral galvanism. However, the pathogenesis of side effects associated with oral galvanism is still unclear, and the effects of direct current and alloy corrosion ions are considered potentially contributing factors. Therefore, the aim of this study was to systemically compare the damaging effects of (1) galvanism as a synergistic process (direct current + corrosion ions), (2) direct current separately, and (3) corrosion ions separately on an in vitro mucosa-like model based on a cell line of immortalized human keratinocytes (HaCaTs) to reveal the factors playing a pivotal role in dental alloys side effects. For this, we chose and compared the dental alloys with the highest risk of oral galvanism: Ti64-AgPd and NiCr-AgPd. We showed that galvanic current may be the leading damaging factor in the cytotoxic processes associated with galvanic coupling of metallic intraoral appliances in the oral cavity, especially in the short-term period (28 days). However, the contribution of corrosion ions (Ni2+) to the synergistic toxicity was also shown, and quite possibly, in the long term, it could be no less dangerous.

Phase transition and potential biomedical applications of thermoresponsive compositions based on polysaccharides, proteins and DNA: A review

Smart thermoresponsive polymers have long attracted attention as materials of a great potential for biomedical applications, mainly for drug delivery, tissue engineering and wound dressing, with a special interest to injectable hydrogels. Poly-N-isopropylacrylamide (PNIPAM) is the most important synthetic thermoresponsive polymer due to its physiologically relevant transition temperature. However, the use of unmodified PNIPAM encounters such problems as low biodegradability, low drug loading capacity, slow response to thermal stimuli, and insufficient mechanical robustness. The use of natural polysaccharides and proteins in combinations with PNIPAM, in the form of grafted copolymers, IPNs, microgels and physical mixtures, is aimed at overcoming these drawbacks and creating dual-functional materials with both synthetic and natural polymers' properties. When developing such compositions, special attention should be paid to preserving their key property, thermoresponsiveness. Addition of hydrophobic and hydrophilic fragments to PNIPAM is known to affect its transition temperature. This review covers various classes of natural polymers - polysaccharides, fibrous and non-fibrous proteins, DNA - used in combination with PNIPAM for the prospective biomedical purposes, with a focus on their phase transition temperatures and its relation to the natural polymer's structure.

Scanning ion-conductance microscopy technique for studying the topography and mechanical properties of Candida parapsilosis yeast microorganisms

Super-resolution microscopy is widely used in the development of novel antimicrobial testing in vitro. In the presented work, a scanning protocol was developed by the method of scanning ion-conducting microscopy (SICM), which makes it possible to study microorganisms without rigid fixation and in saline, obtaining an index map of nanosized structures. The effect of azole and echinocandins drugs on the morphology and mechanical properties of Candida parapsilosis yeast was studied. The findings are consistent with previously proposed drug mechanisms and reports that have examined antifungal agents using AFM, SEM, and TEM. We have shown that the SICM method is capable of scanning and detecting the nanomechanical properties of yeast non-invasively.

Tunable Self-Assembled Peptide Hydrogel Sensor for Pharma Cold Supply Chain

Defrost sensors are a crucial element for proper functioning of the pharmaceutical cold chain. In this paper, the self-assembled peptide-based hydrogels were used to construct a sensitive defrost sensor for the transportation and storage of medications and biomaterials. The turbidity of the peptide hydrogel was employed as a marker of the temperature regime. The gelation kinetics under different conditions was studied to detect various stages of hydrogel structural transitions aimed at tuning the system properties. The developed sensor can be stored at room temperature for a long period, irreversibly indicates whether the product has been thawed, and can be adjusted to a specific temperature range and detection time.

A defined road to tracheal reconstruction: laser structuring and cell support for rapid clinic translation

One of the severe complications occurring because of the patient's intubation is tracheal stenosis. Its incidence has significantly risen because of the COVID-19 pandemic and tends only to increase. Here, we propose an alternative to the donor trachea and synthetic prostheses-the tracheal equivalent. To form it, we applied the donor trachea samples, which were decellularized, cross-linked, and treated with laser to make wells on their surface, and inoculated them with human gingiva-derived mesenchymal stromal cells. The fabricated construct was assessed in vivo using nude (immunodeficient), immunosuppressed, and normal mice and rabbits. In comparison with the matrix ones, the tracheal equivalent samples demonstrated the thinning of the capsule, the significant vessel ingrowth into surrounding tissues, and the increase in the submucosa resorption. The developed construct was shown to be highly biocompatible and efficient in trachea restoration. These results can facilitate its clinical translation and be a base to design clinical trials.

A mathematical model of in vitro hepatocellular cholesterol and lipoprotein metabolism for hyperlipidemia therapy

Cardiovascular diseases associated with high cholesterol (hypercholesterolemia) and low-density lipoproteins (LDL) levels are significant contributors to total mortality in developing and developed countries. Mathematical modeling of LDL metabolism is an important step in the development of drugs for hypercholesterolemia. The aim of this work was to develop and to analyze an integrated mathematical model of cholesterol metabolism in liver cells and its interaction with two types of drugs, statins and PCSK9 inhibitors. The model consisted of 21 ordinary differential equations (ODE) describing cholesterol biosynthesis and lipoprotein endocytosis in liver cells in vitro. The model was tested for its ability to mimic known biochemical effects of familial hypercholesterolemia, statin therapy, and PCSK9 inhibitors. The model qualitatively reproduced the well-known biology of cholesterol regulation, which confirms its potential for minimizing cellular research in initial testing of new drugs for cardiology.

3D or not 3D: a guide to assess cell viability in 3D cell systems

Cell viability is the primary integrative parameter used for various purposes, particularly when fabricating tissue equivalents (e.g., using bioprinting or scaffolding techniques), optimizing conditions to cultivate cells, testing chemicals, drugs, and biomaterials, etc. Most of the conventional methods were originally designed for a monolayer (2D) culture; however, 2D approaches fail to adequately assess a tissue-engineered construct's viability and drug effects and recapitulate the host-pathogen interactions and infectivity. This study aims at revealing the influence of particular 3D cell systems' parameters such as the components' concentration, gel thickness, cell density, etc. on the cell viability and applicability of standard assays. Here, we present an approach to achieving adequate and reproducible results on the cell viability in 3D collagen- and fibrin-based systems using the Live/Dead, AlamarBlue, and PicoGreen assays. Our results have demonstrated that a routine precise analysis of 3D systems should be performed using a combination of at least three methods based on different cell properties, e.g. the metabolic activity, proliferative capacity, morphology, etc.

A Collagen Basketweave from the Giant Squid Mantle as a Robust Scaffold for Tissue Engineering

The growing applications of tissue engineering technologies warrant the search and development of biocompatible materials with an appropriate strength and elastic moduli. Here, we have extensively studied a collagenous membrane (GSCM) separated from the mantle of the Giant squid Dosidicus Gigas in order to test its potential applicability in regenerative medicine. To establish the composition and structure of the studied material, we analyzed the GSCM by a variety of techniques, including amino acid analysis, SDS-PAGE, and FTIR. It has been shown that collagen is a main component of the GSCM. The morphology study by different microscopic techniques from nano- to microscale revealed a peculiar packing of collagen fibers forming laminae oriented at 60-90 degrees in respect to each other, which, in turn, formed layers with the thickness of several microns (a basketweave motif). The macro- and micromechanical studies showed high values of the Young's modulus and tensile strength. No significant cytotoxicity of the studied material was found by the cytotoxicity assay. Thus, the GSCM consists of a reinforced collagen network, has high mechanical characteristics, and is non-toxic, which makes it a good candidate for the creation of a scaffold material for tissue engineering.

Thin Thermoresponsive Polymer Films for Cell Culture: Elucidating an Unexpected Thermal Phase Behavior by Atomic Force Microscopy

Application of poly-N-isopropylacrylamide (PNIPAM) and its more hydrophobic copolymers with N-tert-butylacrylamide (NtBA) as supports for cell sheets has been validated in numerous studies. The binary systems of these polymers with water are characterized by a lower critical solution temperature (LCST) in a physiologically favorable region. Upon lowering the temperature below the LCST, PNIPAM chains undergo a globule-to-coil transition, causing the film dissolution and cell sheet detachment. The character of the PNIPAM-water miscibility behavior is rather complex and not completely understood. Here, we applied atomic force microscopy to track the phase transition in thin films of linear thermoresponsive (co)polymers (PNIPAM and PNIPAM-co-NtBA) prepared by spin-coating. We studied the films' Young's modulus, roughness, and thickness in air and in distilled water in a full thermal cycle. In dry films, in the absence of water, all the measured parameters remained invariant. The swollen films in water above the LCST were softer by 2-3 orders of magnitude and about 10 times rougher than the corresponding dry films. Upon lowering the temperature to the LCST, the films passed through the phase transition observed as a drastic drop of Young's modulus (about an order of magnitude) and decrease in roughness in both polymers in a narrow temperature range. However, the films did not lose their integrity and demonstrated almost fully reversible changes in the mechanical properties and roughness. The thermal dependence of the films' thickness confirmed that they dissolved only partially and required an external force to induce the complete destruction. The reversible thermal behavior which is generally not expected from non-cross-linked polymers is a key finding, especially with respect to their practical application in cell culture. Both the thermodynamic and kinetic factors, as well as the confinement effect, may be responsible for this peculiar film robustness, which requires overcooling and the aid of an external force to destroy the film.

Fibrin-based Bioinks: New Tricks from an Old Dog

For the past 10 years, the main efforts of most bioprinting research teams have focused on creating new bioink formulations, rather than inventing new printing set-up concepts. New tissue-specific bioinks with good printability, shape fidelity, and biocompatibility are based on "old" (well-known) biomaterials, particularly fibrin. While the interest in fibrin-based bioinks is constantly growing, it is essential to provide a framework of material's properties and trends. This review aims to describe the fibrin properties and application in three-dimensional bioprinting and provide a view on further development of fibrin-based bioinks.

The Mechanical Properties, Secondary Structure, and Osteogenic Activity of Photopolymerized Fibroin

Previously, we have described the preparation of a novel fibroin methacrylamide (FbMA), a polymer network with improved functionality, capable of photocrosslinking into Fb hydrogels with elevated stiffness. However, it was unclear how this new functionality affects the structure of the material and its beta-sheet-associated crystallinity. Here, we show that the proposed method of Fb methacrylation does not disturb the protein's ability to self-aggregate into the stable beta-sheet-based crystalline domains. Fourier transform infrared spectroscopy (FTIR) shows that, although the precursor ethanol-untreated Fb films exhibited a slightly higher degree of beta-sheet content than the FbMA films (46.9% for Fb-F-aq and 41.5% for FbMA-F-aq), both materials could equally achieve the highest possible beta-sheet content after ethanol treatment (49.8% for Fb-F-et and 49.0% for FbMA-F-et). The elasticity modulus for the FbMA-F-et films was twofold higher than that of the Fb-F-et as measured by the uniaxial tension (130 ± 1 MPa vs. 64 ± 6 MPa), and 1.4 times higher (51 ± 11 MPa vs. 36 ± 4 MPa) as measured by atomic force microscopy. The culturing of human MG63 osteoblast-like cells on Fb-F-et, FbMA-F-et-w/oUV, and FbMA-F-et substrates revealed that the photocrosslinking-induced increment of stiffness increases the area covered by the cells, rearrangement of actin cytoskeleton, and vinculin distribution in focal contacts, altogether enhancing the osteoinductive activity of the substrate.

Cell Culture and Coculture for Oncological Research in Appropriate Microenvironments

With the increase in knowledge on the importance of the tumor microenvironment, cell culture models of cancers can be adapted to better recapitulate physiologically relevant situations. Three main microenvironmental factors influence tumor phenotype: the biochemical components that stimulate cells, the fibrous molecules that influence the stiffness of the extracellular matrix, and noncancerous cells like epithelial cells, fibroblasts, endothelial cells, and immune cells. Here we present methods for the culture of carcinomas in the presence of a matrix of specific stiffness, and for the coculture of tumors and fibroblasts as well as epithelial cells in the presence of matrix. Information is provided to help with choice and assessment of the matrix support and in working with serum-free medium. Using the example of a tissue chip recapitulating the environmental geometry of carcinomas, we also highlight the development of engineered platforms that provide exquisite control of cell culture parameters necessary in research and development. © 2019 by John Wiley & Sons, Inc.