Part I: A novel in-vitro system for simultaneous mechanical stimulation and time-lapse microscopy in 3D

To investigate the migration response of cells to changes in their biophysical environment, a novel uniaxial cell stimulation device (UCSD) has been designed and tested. The device is capable of applying very precise user-defined static or dynamic mechanical stimuli in a physiologically relevant strain window (up to 50%) and frequency bandwidth (up to 2 Hz) to cells residing in a three-dimensional (3D) environment while single-cell migration is simultaneously measured by time-lapse microscopy. The system is an advancement over uniaxial loading devices reported to date in that it allows temporal and spatial quantification of migration as a function of the micromechanical environment. We make use of the favorable physical and biological properties of poly(ethylene glycol) hydrogels as model matrix and present a method for fabricating cell-containing hydrogel constructs. The 3D strain field within these constructs is modeled by finite element analysis. Fibroblasts reversibly altered their morphology and orientation in response to the strain field. In the succeeding companion paper we then exploit the system to analyze fibroblast motility induced by different stimulation regimes (refer to part II).     

Symmetric and Asymmetric Zeolitic Imidazolate Frameworks (ZIFs)/Polybenzimidazole (PBI) Nanocomposite Membranes for Hydrogen Purification at High Temperatures

High‐performance zeolitic imidazolate frameworks (ZIFs)/polybenzimidazole (PBI) nanocomposites are molecularly designed for hydrogen separation at high temperatures, and demonstrate it in a useful configuration as dual‐layer hollow fibers for the first time. By incorporating as‐synthesized nanoporous ZIF‐8 nanoparticles into the high thermal stability but extremely low permeability polybenzimidazole (PBI), the resultant mixed matrix membranes show an impressive enhancement in H₂ permeability as high as a hundred times without any significant deduction in H₂/CO₂ selectivity. The 30/70 ZIF‐8/PBI dense membrane has a H₂ permeability of 105.4 Barrer and a H₂/CO₂ selectivity of 12.3. This performance is far superior to ZIF‐7/PBI membranes and is the best ever reported data for H₂‐selective polymeric materials in the literature. Meanwhile, defect‐free ZIF‐8‐PBI/Matrimid dual‐layer hollow fibers are successfully fabricated, without post‐annealing and coating, by optimizing ZIF‐8 nanoparticle loadings, spinning conditions, and solvent‐exchange procedures. Two types of hollow fibers targeted at either high H₂/CO₂ selectivity or high H₂ permeance are developed: i) PZM10‐I B fibers with a medium H₂ permeance of 64.5 GPU (2.16 ×10^?8 mol m^?2 s^?1 Pa^?1) at 180°C and a high H₂/CO₂ selectivity of 12.3, and, ii) PZM33‐I B fibers with a high H₂ permeance of 202 GPU (6.77 ×10^?8 mol m^?2 s^?1 Pa^?1) at 180°C and a medium H₂/CO₂ selectivity of 7.7. This work not only molecularly designs novel nanocomposite materials for harsh industrial applications, such as syngas and hydrogen production, but also, for the first time, synergistically combines the strengths of both ZIF‐8 and PBI for energy‐related applications.     

Osmotic Pumping and Salt Rejection by Polyelectrolyte Hydrogel for Continuous Solar Desalination

Efficient mass transport and selective salt rejection are highly desirable for solar or thermally driven seawater desalination, but its realization is challenging. Here a new liquid supply mechanism is proposed, i.e., ionic pumping effect, using a polyelectrolyte hydrogel foam (PHF), demonstrated with poly(sodium acrylate) [P(SA)] embedded in a microporous carbon foam (CF). The PHF simultaneously possesses high osmotic pressure for liquid transport and a strong salt‐rejection effect. The PHF is able to sustain high flux of ≈24 L per m² per hour (LMH), comparable to the evaporative flux under 15 suns, and a salt rejection ratio over 80%. Compared to the porous carbon foam without the polyelectrolyte hydrogel, i.e., with only the capillary pumping effect, the PHF yields a 42.4% higher evaporative flux, at ≈1.6 LMH with DI water and ≈1.3 LMH with simulated seawater under one‐sun condition due to the more efficient ionic liquid pumping. More importantly, thanks to the strong salt‐rejection effect, the PHF shows a continuous and stable solar‐driven desalination flux of ≈1.3 LMH under one‐sun over 72 h, which has not been achieved before. The successful demonstration of both efficient ionic pumping and strong salt rejection effects makes the PHF an attractive platform for sustainable solar‐driven desalination.     

Fabrication techniques of biomimetic scaffolds in three‐dimensional cell culture: A review

In the last four decades, several researchers worldwide have routinely and meticulously exercised cell culture experiments in two‐dimensional (2D) platforms. Using traditionally existing 2D models, the therapeutic efficacy of drugs has been inappropriately validated due to the failure in generating the precise therapeutic response. Fortunately, a 3D model addresses the foregoing limitations by recapitulating the in vivo environment. In this context, one has to contemplate the design of an appropriate scaffold for favoring the organization of cell microenvironment. Instituting pertinent model on the platter will pave way for a precise mimicking of in vivo conditions. It is because animal cells in scaffolds oblige spontaneous formation of 3D colonies that molecularly, phenotypically, and histologically resemble the native environment. The 3D culture provides insight into the biochemical aspects of cell–cell communication, plasticity, cell division, cytoskeletal reorganization, signaling mechanisms, differentiation, and cell death. Focusing on these criteria, this paper discusses in detail, the diversification of polymeric scaffolds based on their available resources. The paper also reviews the well‐founded and latest techniques of scaffold fabrication, and their applications pertaining to tissue engineering, drug screening, and tumor model development.     

A Three‐Dimensionally Interconnected Carbon Nanotube–Conducting Polymer Hydrogel Network for High‐Performance Flexible Battery Electrodes

High‐performance flexible energy‐storage devices have great potential as power sources for wearable electronics. One major limitation to the realization of these applications is the lack of flexible electrodes with excellent mechanical and electrochemical properties. Currently employed batteries and supercapacitors are mainly based on electrodes that are not flexible enough for these purposes. Here, a three‐dimensionally interconnected hybrid hydrogel system based on carbon nanotube (CNT)‐conductive polymer network architecture is reported for high‐performance flexible lithium ion battery electrodes. Unlike previously reported conducting polymers (e.g., polyaniline, polypyrrole, polythiophene), which are mechanically fragile and incompatible with aqueous solution processing, this interpenetrating network of the CNT‐conducting polymer hydrogel exibits good mechanical properties, high conductivity, and facile ion transport, leading to facile electrode kinetics and high strain tolerance during electrode volume change. A high‐rate capability for TiO₂ and high cycling stability for SiNP electrodes are reported. Typically, the flexible TiO₂ electrodes achieved a capacity of 76 mAh g^–1 in 40 s of charge/discharge and a high areal capacity of 2.2 mAh cm^–2 can be obtained for flexible SiNP‐based electrodes at 0.1C rate. This simple yet efficient solution process is promising for the fabrication of a variety of high performance flexible electrodes.     

Synthesis of poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate)/chitosan/silver nanocomposite material with enhanced antimicrobial activity

This work aims to shed light in the fabrication of poly(3‐hydroxybutyrate‐co‐44%‐4‐hydroxybutyrate)[P(3HB‐co‐44%4HB)]/chitosan‐based silver nanocomposite material using different contents of silver nanoparticle (SNP); 1–9 wt%. Two approaches were applied in the fabrication; namely solvent casting and chemical crosslinking via glutaraldehyde (GA). A detailed characterization was conducted in order to yield information regarding the nanocomposite material. X‐ray diffraction analysis exhibited the nature of the three components that exist in the nanocomposite films: P(3HB‐co‐4HB), chitosan, and SNP. In term of mechanical properties, tensile strength, and elongation at break were significantly improved up to 125% and 22%, respectively with the impregnation of the SNP. The melting temperature of the nanocomposite materials was increased whereas their thermal stability was slightly changed. Scanning electron microscopy images revealed that incorporation of 9 wt% of SNP caused agglomeration but the surface roughness of the material was significantly improved with the loading. Staphylococcus aureus and Escherichia coli were completely inhibited by the nanocomposite films with 7 and 9 wt% of SNP, respectively. On the other hand, degradation of the nanocomposite materials outweighed the degradation of the pure copolymer. These bioactive and biodegradable materials stand a good chance to serve the vast need of biomedical applications namely management and care of wound as wound dressing. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 30:1469–1479, 2014     

A nanocomposite/crude extract enzyme-based xanthine biosensor

A novel amperometric biosensor for xanthine was developed based on covalent immobilization of crude xanthine oxidase (XOD) extracted from bovine milk onto a hybrid nanocomposite film via glutaraldehyde. Toward the preparation of the film, a stable colloids solution of core–shell Fe₃O₄/polyaniline nanoparticles (PANI/Fe₃O₄ NPs) was dispersed in solution containing chitosan (CHT) and H₂PtCl₆ and electrodeposited over the surface of a carbon paste electrode (CPE) in one step. Scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectrophotometry, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) were used for characterization of the electrode surface. The developed biosensor (XOD/CHT/Pt NPs/PANI/Fe₃O₄/CPE) was employed for determination of xanthine based on amperometric detection of hydrogen peroxide (H₂O₂) reduction at –0.35 V (vs. Ag/AgCl). The biosensor exhibited a fast response time to xanthine within 8 s and a linear working concentration range from 0.2 to 36.0 μM (R² = 0.997) with a detection limit of 0.1 μM (signal/noise [S/N] = 3). The sensitivity of the biosensor was 13.58 μA μM⁻¹ cm⁻². The apparent Michaelis–Menten (K_m) value for xanthine was found to be 4.7 μM. The fabricated biosensor was successfully applied for measurement of fish and chicken meat freshness, which was in agreement with the standard method at the 95% confidence level.     

Dynamic compressive loading influences degradation behavior of PEG-PLA hydrogels

Biodegradable hydrogels are attractive 3D environments for cell and tissue growth. In cartilage tissue engineering, mechanical stimulation has been shown to be an important regulator in promoting cartilage development. However, the impact of mechanical loading on the gel degradation kinetics has not been studied. In this study, we examined hydrolytically labile gels synthesized from poly(lactic acid)-b-poly(ethylene glycol)-b-poly-(lactic acid) dimethacrylate macromers, which have been used for cartilage tissue engineering. The gels were subject to physiological loading conditions in order to examine the effects of loading on hydrogel degradation. Initially, hydrogels were formed with two different cross-linking densities and subject to a dynamic compressive strain of 15% at 0.3, 1, or 3 Hz. Degradation behavior was assessed by mass loss, equilibrium swelling and compressive modulus as a function of degradation time. From equilibrium swelling, the pseudo-first-order reaction rate constants were determined as an indication of degradation kinetics. The application of dynamic loading significantly enhanced the degradation time for the low cross-linked gels (P < 0.01) while frequency showed no statistical differences in degradation rates or bulk erosion profiles. In the higher cross-linked gels, a 3 Hz dynamic strain significantly increased the degradation kinetics resulting in an overall faster degradation time by 6 days compared to gels subject to the 0.3 and 1 Hz loads (P < 0.0001). The bioreactor set-up also influenced overall degradation behavior where the use of impermeable versus permeable platens resulted in significantly lower degradation rate constants for both cross-linked gels (P < 0.001). The compressive modulus exponentially decreased with degradation time under dynamic loading. Together, our findings indicate that both loading regime and the bioreactor setup influence degradation and should be considered when designing and tuning a biodegradable hydrogel where mechanical stimulation is employed.     

Biocompatible epoxy modified bio-based polyurethane nanocomposites: Mechanical property, cytotoxicity and biodegradation

Epoxy modified Mesua ferrea L. seed oil (MFLSO) based polyurethane nanocomposites with different weight % of clay loadings (1%, 2.5% and 5%) have been evaluated as biocompatible materials. The nanocomposites were prepared by ex situ solution technique under high mechanical shearing and ultrasonication at room temperature. The partially exfoliated nanocomposites were characterized by Fourier transform infra-red (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The mechanical properties such as tensile strength and scratch hardness were improved 2 and 5 times, respectively by nanocomposites formation. Even the impact resistance improved a little. The thermostability of the nanocomposites was enhanced by about 40 °C. Biodegradation study confirmed 5–10 fold increase in biodegradation rate for the nanocomposites compared to the pristine polymers. All the nanocomposites showed non-cytotoxicity as evident from RBC hemolysis inhibition observed in anti-hemolytic assay carried over the sterilized films. The study reveals that the epoxy modified MFLSO based polyurethane nanocomposites deserve the potential to be applicable as biomaterials.