β‐Cyclodextrin hydrogels containing naphthaleneacetic acid for pH‐sensitive release

β‐Cyclodextrin (β‐CD) hydrogel was prepared in a strong alkali condition using epichlorohydrin (EPI) as a cross‐linker, where the molar ratios of EPI to β‐CD were 8:1, 10:1, and 15:1. In order to endow a pH sensitivity to the hydrogel, naphthaleneacetic acid (NAA) was loaded in the hydrogel by taking advantage of its hydrophobic interaction with the cavities of β‐CD. The releases of blue dextran (a water‐soluble dye) from the hydrogels were promoted, as the pHs of the media increased. When the molar ratio of EPI to β‐CD was lower, the degrees of release were higher, and the pH dependency of the release became more prominent. In fact, the swelling ratio of the hydrogels having a lower molar ratio of EPI to β‐CD was higher. The higher swelling ratio would account for the higher degree of release and the marked pH sensitivity. Biotechnol. Bioeng. 2010;106: 295–302. © 2010 Wiley Periodicals, Inc.     

Influence of different magnetites on properties of magnetic Pseudomonas aeruginosa immobilizates used for biosurfactant production

During the last decades, whole‐cell immobilization has been used successfully in many bioprocesses. In particular, it is aimed at implementing continuous production processes, reaching higher production rates, and reusing the biocatalyst. In some cases, effective retention of immobilizates in the bioprocess is not feasible by membranes or sieves due to pore plugging or undesired losses of immobilizates. In the present publication, it is reported about the investigation of magnetic immobilizates of Pseudomonas aeruginosa for application in continuous biosurfactant production of rhamnolipids by foam fractionation and retention of entrained immobilizates by high‐gradient magnetic separation from foam. Different materials and methods were tested with respect to important parameters, such as stability, diffusion properties or magnetic separation. Good magnetic separation of immobilizates was achieved at 5% (w/w) magnetite loading. Best results in terms of homogeneous embedding, good diffusion properties, and stability enhancement vis‐à‐vis pure alginate beads was achieved with alginate beads with embedded Bayoxide® magnetite or MagPrep® silica particles. Although polyurethane immobilizates showed higher stabilities compared with alginate beads, rhamnolipid diffusion in immobilizates was superior in magnetic alginate beads. Regarding bead production, smaller immobilizates were achieved with suspension polymerization compared to droplet extrusion by the JetCutting® technology. In total, magnetic immobilizates are a promising tool for an easier handling of biocatalysts in a continuous biological production process, but they have to be adapted to the current production task.© 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

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.     

Enhanced tissue adhesiveness of injectable gelatin hydrogels through dual catalytic activity of horseradish peroxidase

Development of bioadhesives with tunable mechanical strength, high adhesiveness, biocompatibility, and injectability is greatly desirable in all surgeries to replace or complement the sutures and staples. Herein, the dual catalytic activity of horseradish peroxidase is exploited to in situ form the hydroxyphenyl propionic acid‐gelatin/thiolated gelatin (GH/GS) adhesive hydrogels including two alternative crosslinks (phenol‐phenol and disulfide bonds) with fast gelation (few seconds – several minutes) and improved physicochemical properties. Their elastic moduli increase from 6.7 to 10.3 kPa by adding GS polymer that leads to the better stability of GH/GS hydrogels than GH ones. GH/GS adhesive strength is respectively 6.5‐fold and 15.8‐fold higher than GH‐only and fibrin glue that is due to additional disulfide linkages between hydrogels and tissues. Moreover, in vitro cell study with human dermal fibroblast showed the cell‐compatibility of GH/GS hydrogels. Taken together, GH/GS hydrogels can be considered as promising potential adhesive materials for various biomedical applications.     

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.     

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).