Engineering neural stem cell fates with hydrogel design for central nervous system regeneration

Injuries and disease to the central nervous system (CNS) are accompanied by severe consequences, as the adult CNS has very limited capacity to replace the lost neural cells. Different sources of neural stem cells for CNS tissue regeneration exist, including embryonic stem cells (ESCs), fetal stem cells, adult stem cells, and induced pluripotent stem cells (iPSCs), and so on. However, before stem cell therapy can be a viable option for treatments, many issues still need to be resolved, including low viability, lack of control of stem cell fate, and low cell engraftment after transplantation. Though controlling these parameters is extremely challenging, engineering structures that create permissive niches for the transplanted cells, such as the use of biocompatible hydrogels, is a promising approach. This review will focus on highlighting existing hydrogel systems currently being investigated for CNS tissue regeneration, as well as discuss design criteria for hydrogels and methods for manipulating stem cells within hydrogels systems. Finally, the use of these hydrogel systems as carriers for stem cell transplantation in CNS injury and disease models will be discussed.     

Equilibrium-Staged Separations: A Bibliography Update (1992–1993)

This article provides a bibliographic listing of journal papers published during 1992–1993 concerned with distillation and other equilibrium-staged separation processes. The references are taken from the 40 most important chemical engineering journals. This paper provides an update to the literature as provided in previous bibliographic papers (1, 2). Liquid-liquid extraction is the subject of a separate bibliography (for 1992-1993) due to the number of publications on this topic (3). A bibliography detailing supercritical extraction from 1980- 1993 has also been published separately due to the current interest in this relatively new technology (4). A complete bibliography of the chemical engineering journal literature from 1967–1991 has been published by the author (5–7). An earlier bibliography (8) provides access to the literature prior to 1967. The following topics are included in this paper:     

Protein deposition on contact lenses: The past, the present, and the future

Proteins are a key component in body fluids and adhere to most biomaterials within seconds of their exposure. The tear film consists of more than 400 different proteins, ranging in size from 10 to 2360 kDa, with a net charge of pH 1-11. Protein deposition rates on poly-2-hydroxyethyl methacrylate (pHEMA) and silicone hydrogel soft contact lenses have been determined using a number of ex vivo and in vitro experiments. Ionic, high water pHEMA-based lenses attract the highest amount of tear film protein (1300 μg/lens), due to an electrostatic attraction between the material and positively charged lysozyme. All other types of pHEMA-based lenses deposit typically less than 100 μg/lens. Silicone hydrogel lenses attract less protein than pHEMA-based materials, with <10 μg/lens for non-ionic and up to 34 μg/lens for ionic materials. Despite the low protein rates on silicone hydrogel lenses, the percentage of denatured protein is typically higher than that seen on pHEMA-based lenses. Newer approaches incorporating phosphorylcholine, polyethers or hyaluronic acid into potential contact lens materials result in reduced protein deposition rates compared to current lens materials.     

Synthesis and Characterization of Chitosan-Albumin Conjugates as pH-Sensitive Biodegradable Hydrogels

A new kind of biodegradable pH-sensitive drug delivery system was developed via chitosan-albumin conjugate hydrogel. Through changing the feeding modes of reactants, two types of hydrogels(comb-type and reticulax-type) were synthesized by amidation reactions between 6-O-succinoylated N-phthaloyl chitosan and albumin. The structures and morphologies of the hydrogels were characterized by SEM. And their water swelling capacity, drug loading and releasing properties at different pH values were also investigated. It was found that the comb-type of hydrogels with looser space construction had better water swelling ratio(more than 400% of its original mass) than the reticular-type of ones did(about 180% of its original mass). In vitro release experiments of Rifampicin show that the hydrogels provided the controlled release of the entrapped drug for more than 50 h. The drug release rates of both types of hydrogels under acidic condition were lower than those under neutral or basic condition. The introduction of albumin not only improved the hydrophilicity of chitosan, but also provided the possibility of the carrier system combining other biologically active materials more easily to fulfill the delivery and therapy functions.     

A facile method to functionalize engineering solid membrane supports for rapid and efficient oil–water separation

A facile and low-cost method is developed to functionalize engineering metal membrane supports, such as stainless steel (SS), with epoxy-containing polymer poly(glycidyl methacrylate) (PGMA) to produce a versatile and universal platform for subsequent surface modification. With a PGMA anchoring layer, we have demonstrated that hydrogel particles, such as polyacrylamide-co-poly(acrylic acid) (PAM-co-PAA), can be subsequently grafted to form functional polymer membranes for rapid and efficient oil–water separation. By contact angle and AFM measurement, we have confirmed that PAM-co-PAA hydrogel particle layer grafted on a PGMA-modified SS surface exhibits excellent selectivity as required for liquid–liquid separation, showing high affinity to water but not to oils as an ideal membrane for oil–water separation. To evaluate the separation efficiency, a simple flow-through device is employed to separate free-floating oil from water in the mixture of varied initial oil volume fraction and oil composition. Under substantially high pump flow rate up to 1.3 L/min, PAM-co-PAA hydrogel treated SS mesh can achieve excellent separation efficiency with less than 5% oil or water in the respective filtrate at the flux of as high as 540 m³/(m²·h) and retentate at the flux of 1.95 m³/(m²·h). This separation efficiency is better than, or comparable to, the maximal performance achieved using conventional gravity methods at much lower flow rate. Similar approach could be also adapted to graft superhydrophobic and superoleophilic polymer membranes with PGMA-treated engineering support to separate water from oil.     

丙烯基类单体-壳聚糖共聚物水凝胶的辐射制备及性能研究

以壳聚糖、丙烯酰胺（AM）和二甲基二烯丙基氯化铵（DMDACC）为原料,N,N-亚甲基双丙烯酰胺（MBA）为交联剂,经^60Co γ-射线辐照,制备了丙烯基类单体一壳聚糖共聚物水凝胶,并研究了MBA的用量对丙烯基类单体一壳聚糖共聚物水凝胶吸水性能和保水性能的影响。结果表明,在吸收剂量为2kGy的条件下,MBA用量较低时,随着MBA用量的提高,水凝胶的平衡吸水率反而下降;而MBA用量较高时,水凝胶的平衡吸水率受MBA用量的影响较小;凝胶吸水率随着溶胀时间的延长而增加;水凝胶在溶胀初期的溶胀动力学可用non-Fickian扩散定律来描述：随着交联剂MBA用量的逐渐增加,水凝胶的初始失水率逐渐增大,而最大失水率逐渐下降。     

羧酸型乳酸酯基水凝胶的吸附性能探析

自制的不饱和乳酸酯基大单体（LEM）在过硫酸钾（KPS）引发下,与丙烯酸（AA）进行自由基交联反应,制得乳酸酯基凝胶（LEMA）。分析了LEMA凝胶的酸敏吸水溶胀、吸附重金属离子以及稀土金属离子的性能,并探讨了AA用量对凝胶吸附性能的影响。结果表明：m（AA）：m（LEM）=40％时所得的凝胶,其对金属离子的吸附容量大于m（AA）：m（LEM）=20％所得的凝胶;此外,凝胶对铅离子的吸附容量明显高于对铜和铈离子的吸附。     

Diffusional System Based on Tolazoline Hydrochloride Included in a Reticulated Carboxymethylcellulose Hydrogel

This paper presents a diffusional system consisting of tolazoline hydrochloride included into a carboxymethylcellulose based hydrogel, showing a high swelling capacity in water. The process kinetics of the drug inclusion into hydrogel as well as of the drug releasing have been studied. The tolazoline hydrochloride release was performed by elution with a simulated biological fluid within the digestive tract, at the small intestine level (pH = 8.2) where the drug is mostly absorbed. The results make evident a zero-order kinetics over the 30–400 min range, which would place the system among those with ‘sustained’ release, with obvious advantages compared with the classical drug administration.     

Synthesis, swelling and drug release behavior of poly(N,N-diethylacrylamide-co-N-hydroxymethyl acrylamide) hydrogel

In this study, poly(N,N-diethylacrylamide-co-N-hydroxymethyl acrylamide) (poly(DEA-co-NHMAA)) hydrogels were synthesized by changing the initial DEA/NHMAA mole ratio, N,N'-methylenebisacrylamide and total monomer concentration. The thermosensitive and mechanical performances were optimized by altering the above parameters. The hydrogels were characterized by using Fourier transform infrared (FTIR) spectroscope and scanning electron microscope (SEM). In comparison with the PDEA hydrogel, the equilibrium swelling ratio (ESR) and lower critical solution temperature (LCST) of the hydrogels increased with the increase of NHMAA content in the feed. The swelling kinetics was also studied. The release behaviors of the model drug, aminophylline, are found dependent on hydrogel composition and environmental temperature, which suggests that these materials have potential application as intelligent drug carriers.     

Synthesis of SiO2-polyacrylic acid hybrid hydrogel with high mechanical properties and salt tolerance using sodium silicate precursor through sol-gel process

SiO₂-polyacrylic acid hybrid hydrogel was synthesized using sodium silicate (SS) as precursor through sol-gel technology. The result showed a core-shell structure was formed with SiO₂ inner core and acrylic acid (AA) outer shell. The characteristics of the hydrogel were determined by FTIR and TEM. When the mol ratio of SS/AA was 0.13, the compressive strength of the hydrogel reached 45.6 kPa at 99.1% water content while the swelling ratio was 1017.2 g/g in deionized water. Moreover, a high salt tolerance was also obtained.