Evaluation of the in vitro degradation of macroporous hydrogels using gravimetry,confined compression testing,and microcomputed tomography

This study investigated the in vitro degradation characteristics of macroporous hydrogels based on poly(propylene fumarate-co-ethylene glycol) (P(PF-co-EG)). Four formulations were fabricated to test the effect of porosity and cross-linking density on the degradation of the resulting macroporous hydrogels. Macroporosity was introduced by the addition of sodium bicarbonate and ascorbic acid, the precursors of the carbon dioxide porogen, in the initiation system for the hydrogel cross-linking. Macroporous hydrogels with porosities of 0.80 +/- 0.03 and 0.89 +/- 0.03 were synthesized by the addition of sodium bicarbonate of concentrations 40 and 80 mg/mL and ascorbic acid of concentrations 0.05 and 0.1 mol/L, respectively. Poly(ethylene glycol) diacrylate (PEG-DA) was utilized as a cross-linker. The molecular weight between cross-links had a significant effect on weight loss after 12 weeks, where samples with M(C) of 1,880 +/- 320 synthesized with a P(PF-co-EG):PEG-DA ratio of 3:1 had a significantly greater mass loss due to degradation than those with M(C) of 1,000 +/- 100 synthesized with a P(PF-co-EG):PEG-DA ratio of 1:1. In contrast, porosity played a minimal role in determining the weight loss. Mechanical testing of the hydrogels under confined compression showed a decrease in compressive modulus over the degradation time for all formulations. In addition, an increase in hydrogel equilibrium water content and pore wall thickness was observed with degradation time, whereas the hydrogel porosity and surface area density remained invariant. The results from microcomputed tomography corroborated with the rest of the measurements and indicated a bulk degradation mechanism of the macroporous hydrogels.     

Application of Chitin Hydrogels for Seed Germination,Seedling Growth of Rapeseed

Chitin hydrogels were successfully prepared from chitin solution dissolved in NaOH/urea aqueous solution at low temperature by crosslinking with epichlorohydrin. The experimental results indicated that the chitin hydrogels were hydrophilic, had a microporous structure, and had a large surface area, leading to excellent water uptake ability and water-retention properties. Moreover, they exhibited good mechanical properties and a high equilibrium swelling ratio. The growth indexes of rapeseed, including the germination rate, root length, shoot length, fresh weight and dry weight, for chitin hydrogel (CG2) were not significantly different from those of soil and significantly higher than agar. Chitin hydrogel as a plant growth regulator could promote seed germination and growth when applied to Brassica napus rapeseed sowing. Moreover, chitin was safe and biodegradable so it would be suitable to use as soilless culture media for plant growth. This work provided a new pathway for the application of chitin hydrogels in the agriculture field.     

Enhancing protein capacity of rigid macroporous polymeric adsorbent.

A macroporous poly(glycidyl methacrylate-triallyl isocyanurate-divinylbenzene) resin was synthesized and modified with diethylamine to yield an anion-exchange resin suitable for protein adsorption. Efforts were made to enhance protein ion exchange capacity of the resin by investigating the copolymer composition. Different synthesis recipes were attempted, and the resultant resins were characterized by measuring the specific surface area and the adsorption ability using bovine serum albumin (BSA) as a model protein. The intraparticle pore size distribution measured by mercury porosimetry showed that the pores in the range of 40-120 nm took 75% of the total pore volume, indicating that the ion exchanger was favorable for protein adsorption. BSA capacity obtained with an appropriate recipe was as high as 78.6 mg/g wet resin or 50 mg/mL packed volume, which was higher than the capacities of some commercially available ion exchangers. Moreover, by using a pore diffusion model, the effective pore diffusivity of BSA was found to be 5.5 x 10(-12) m(2)/s, similar to those in the commercial ion exchangers.     

Characterization of pancreas-projecting rat dorsal motor nucleus of vagus neurons

The electrophysiological and morphological properties of rat dorsal motor nucleus of the vagus (DMV) neurons innervating the pancreas were examined by using whole cell patch clamp recordings from brain stem slices and postfixation morphological reconstructions of Neurobiotin-filled neurons. Recordings were made from 178 DMV neurons whose projections had been identified by previous apposition of the fluorescent neuronal tracer DiI to the body of the pancreas. DMV neurons projecting to the pancreas had an input resistance of 434 +/- 14 M omega, an action potential duration of 3 +/- 0.1 ms, and an afterhyperpolarization of 18 +/- 0.4 mV amplitude and 108 +/- 7 ms time constant of decay; these electrophysiological properties resembled those of gastric-projecting neurons but were significantly different from those of intestinal-projecting neurons. Interestingly, 14 of 178 pancreas-projecting neurons showed the presence of a slowly developing afterhyperpolarization whose presence was not reported in DMV neurons projecting to any other gastrointestinal area. The morphological characteristics of pancreas-projecting neurons (soma area 274 +/- 12 microm2; soma diameter of 25 +/- 0.7 microm; soma form factor 0.74 +/- 0.01; segments 9.7 +/- 0.41), however, were similar to those of intestinal- but differed from those of gastric-projecting neurons. In summary, these results suggest that pancreas-projecting rat DMV neurons are heterogeneous with respect to some electrophysiological and morphological properties. These differences might underlie functional differences in the vagal modulation of pancreatic functions.     

Biodegradable fumarate-based polyHIPEs as tissue engineering scaffolds

PolyHIPEs show great promise as tissue engineering scaffolds due to the tremendous control of pore size and interconnectivity afforded by this technique. Highly porous, fully biodegradable scaffolds were prepared by polymerization of the continuous phase of high internal phase emulsions (HIPEs) containing the macromer poly(propylene fumarate) (PPF) and the cross-linker propylene fumarate diacrylate (PFDA). Toluene was used as a diluent to reduce the viscosity of the organic phase to enable HIPE formation. A range of polyHIPE scaffolds of different pore sizes and morphologies were generated by varying the diluent concentration (40-60 wt %), cross-linker concentration (25-75 wt %), and macromer molecular weight ( M n = 800-1000 g/mol). Although some formulations resulted in macroporous monoliths (pore diameter >500 microm), the majority of the polyHIPEs studied were rigid, microporous monoliths with average pore diameters in the range 10-300 microm. Gravimetric analysis confirmed the porosity of the microporous monoliths as 80-89% with most scaffolds above 84%. These studies demonstrate that emulsion templating can be used to generate rigid, biodegradable scaffolds with highly interconnected pores suitable for tissue engineering scaffolds.     

Bone marrow stem cells and polymer hydrogels--two strategies for spinal cord injury repair

1. Emerging clinical studies of treating brain and spinal cord injury (SCI) led us to examine the effect of autologous adult stem cell transplantation as well as the use of polymer scaffolds in spinal cord regeneration. We compared an intravenous injection of mesenchymal stem cells (MSCs) or the injection of a freshly prepared mononuclear fraction of bone marrow cells (BMCs) on the treatment of an acute or chronic balloon-induced spinal cord compression lesion in rats. Based on our experimental studies, autologous BMC implantation has been used in a Phase I/II clinical trial in patients (n=20) with a transversal spinal cord lesion. 2. MSCs were isolated from rat bone marrow by their adherence to plastic, labeled with iron-oxide nanoparticles and expanded in vitro. Macroporous hydrogels based on derivatives of 2-hydroxyethyl methacrylate (HEMA) or 2-hydroxypropyl methacrylamide (HPMA) were prepared, then modified by their copolymerization with a hydrolytically degradable crosslinker, N,O-dimethacryloylhydroxylamine, or by different surface electric charges. Hydrogels or hydrogels seeded with MSCs were implanted into rats with hemisected spinal cords. 3. Lesioned animals grafted with MSCs or BMCs had smaller lesions 35 days postgrafting and higher scores in BBB testing than did control animals and also showed a faster recovery of sensitivity in their hind limbs using the plantar test. The functional improvement was more pronounced in MSC-treated rats. In MR images, the lesion populated by grafted cells appeared as a dark hypointense area and was considerably smaller than in control animals. Morphometric measurements showed an increase in the volume of spared white matter in cell-treated animals. In the clinical trial, we compared intraarterial (via a. vertebralis, n=6) versus intravenous administration of BMCs (n=14) in a group of subacute (10-33 days post-SCI, n=8) and chronic patients (2-18 months, n=12). For patient follow-up we used MEP, SEP, MRI, and the ASIA score. Our clinical study revealed that the implantation of BMCs into patients is safe, as there were no complications following cell administration. Partial improvement in the ASIA score and partial recovery of MEP or SEP have been observed in all subacute patients who received cells via a. vertebralis (n=4) and in one out of four subacute patients who received cells intravenously. Improvement was also found in one chronic patient who received cells via a. vertebralis. A much larger population of patients is needed before any conclusions can be drawn. The implantation of hydrogels into hemisected rat spinal cords showed that cellular ingrowth was most pronounced in copolymers of HEMA with a positive surface electric charge. Although most of the cells had the morphological properties of connective tissue elements, we found NF-160-positive axons invading all the implanted hydrogels from both the proximal and distal stumps. The biodegradable hydrogels degraded from the border that was in direct contact with the spinal cord tissue. They were resorbed by macrophages and replaced by newly formed tissue containing connective tissue elements, blood vessels, GFAP-positive astrocytic processes, and NF-160-positive neurofilaments. Additionally, we implanted hydrogels seeded with nanoparticle-labeled MSCs into hemisected rat spinal cords. Hydrogels seeded with MSCs were visible on MR images as hypointense areas, and subsequent Prussian blue histological staining confirmed positively stained cells within the hydrogels. 4. We conclude that treatment with different bone marrow cell populations had a positive effect on behavioral outcome and histopathological assessment after SCI in rats; this positive effect was most pronounced following MSC treatment. Our clinical study suggests a possible positive effect in patients with SCI. Bridging the lesion cavity can be an approach for further improving regeneration. Our preclinical studies showed that macroporous polymer hydrogels based on derivatives of HEMA or HPMA are suitable materials for bridging cavities after SCI; their chemical and physical properties can be modified to a specific use, and 3D implants seeded with different cell types may facilitate the ingrowth of axons.     

Biodegradablescaffolds based on chitosan: Preparation,properties, and use for the cultivation of animal cells

The influence of the conditions of the formation of chitosan hydrogels crosslinked with glutaraldehyde (GA) or genipin (the polysaccharide molecular weight, pH level, and concentration of the chitosan solution) on the gel time and the properties of biopolymer scaffolds for tissue engineering obtained by the freeze-drying of hydrogels was studied. The resulting scaffolds had different structures (morphology, degree of anisotropy, average pore size) and moisture-retaining capacities. The cytotoxicity of biodegradable scaffolds based on chitosan with a low content of genipin and GA was studied for the first time. Using the L929 mouse fibroblasts model line, we demonstrated that scaffolds based on chitosan with a molecular weight of 320 and 190 kDa crosslinked with genipin and GA (0.005 and 0.01 mol/mol of chitosan amino groups) are biocompatible. Using confocal laser microscopy, we demonstrated that the cells are uniformly distributed in all scaffold samples and they successfully grew and proliferated when cultured in vitro for 4 days.     

Viscoelastic characterization and modeling of gelation kinetics of injectable in situ cross-linkable poly(lactide-co-ethylene oxide-co-fumarate) hydrogels

Cell transplantation by injection of biodegradable hydrogels is a recently developed strategy for the treatment of degenerated tissues. A cell carrier should be cytocompatible, have suitable working time and rheological properties for injection, and harden in situ to attain dimensional stability and the desired mechanical strength. Hydrophilic macromer/cross-linker polymerizing systems, due to the relatively high molecular weight of the macromer and its inability to cross the cell membrane, are very attractive as injectable cell carriers. The objective of this research was to determine the effects of cross-linker, initiator, and accelerator concentrations on the gelation kinetics and ultimate modulus of a biodegradable, in situ cross-linkable poly(lactide-co-ethylene oxide-co-fumarate) (PLEOF) macromer. The in situ polymerizing mixture consisted of PLEOF macromer, methylene bisacrylamide cross-linker, and a neutral redox initiation system of ammonium persulfate initiator and tetramethylethylenediamine accelerator. Measurement of the time evolution of the viscoelastic properties of the network during the sol-gel transition showed the important influence of each component on the gel time and stiffness of the hydrogels. A kinetic model was developed to predict the modulus as a function of composition. Model predictions were consistent with most of the experimental findings. The values of the storage and loss moduli at the gel point were found to be approximately equal for samples with equal PLEOF concentrations, resulting in a simple method to predict the gelation time based on the Winter--Chambon criterion, with the use of the proposed kinetic model. The results of this study can be coupled with component cytocompatibility measurements to predict the effect of composition on the viability of the cells encapsulated in the hydrogel matrix.     

Capillary and fiber geometry in rat diaphragm perfusion fixed in situ at different sarcomere lengths.

To determine the potential range of diaphragm sarcomere lengths in situ and the effect of changes in sarcomere length on capillary and fiber geometry, rat diaphragms were perfusion fixed in situ with glutaraldehyde at different airway pressures and during electrical stimulation. The lengths of thick (1.517 +/- 0.007 microns) and thin (1.194 +/- 0.048 microns) filaments were not different from those established for rat limb muscle. Morphometric techniques were used to determine fiber cross-sectional area, sarcomere length, capillary orientation, and capillary length and surface area per fiber volume. All measurements were referenced to sarcomere length, which averaged 2.88 +/- 0.08 microns at -20 to -25 cmH2O airway pressure (residual volume) and 2.32 +/- 0.05 microns at +20 to +26 cmH2O airway pressure (total lung capacity). The contribution of capillary tortuosity and branching to total capillary length was dependent on sarcomere length and varied from 5 to 22%, consistent with that shown previously for mammalian limb muscles over this range of sarcomere lengths. Capillary length per fiber volume [Jv(c,f)] was significantly greater at residual volume (3,761 +/- 193 mm-2) than at total lung capacity (3,142 +/- 118 mm-2) and correlated with sarcomere length [l; r = 0.628, Jv(c,f) = 876l + 1,156, P less than 0.01; n = 18]. We conclude that the diaphragm is unusual in that the apparent in situ minimal sarcomere length is greater than 2.0 microns.(ABSTRACT TRUNCATED AT 250 WORDS)     

Synthesis and characterization of biodegradable cationic poly(propylene fumarate-co-ethylene glycol) copolymer hydrogels modified with agmatine for enhanced cell adhesion

We synthesized positively charged biodegradable hydrogels by cross-linking of agmatine-modified poly(ethylene glycol)-tethered fumarate (Agm-PEGF) and poly(propylene fumarate-co-ethylene glycol) (P(PF-co-EG)) to investigate the effect of the guanidino groups of the agmatine on hydrogel swelling behavior and smooth muscle cell adhesion to the hydrogels. The weight swelling ratio of these hydrogels at pH 7.0 increased from 279 +/- 4 to 306 +/- 7% as the initial Agm-PEGF content increased from 0 to 200 mg/g of P(PF-co-EG), respectively. The diffusional exponents, n, during the initial phase of water uptake were independent of the initial Agm-PEGF content and were determined to be 0.66 +/- 0.08, 0.71 +/- 0.07, and 0.60 +/- 0.05 for respective initial Agm-PEGF contents of 0, 100, and 200 mg/g. The heat of fusion of water present in the hydrogels increased from 214 +/- 11 to 254 +/- 4 J/g as the initial Agm-PEGF content increased from 0 to 200 mg/g. The number of adherent smooth muscle cells increased dose-dependently from 15 +/- 6 to 75 +/- 7% of the initial seeding density as the initial Agm-PEGF content increased from 0 to 200 mg/g. These results suggest that the incorporation of the guanidino groups of agmatine into P(PF-co-EG) hydrogels increases the hydrogel free water content and the total water content of the hydrogels and also enhances cell adhesion to the hydrogels.     

A new integrated concept for the improved preparation of sections of fresh or frozen tissue for light microscope histochemistry

In order to obtain thin sections of plant tissues which combined good morphological preservation and the preservation of the substances and enzyme activities in the tissues, a concept of section preparation by external stabilization was developed. The main components are as follows: appropriate supporting medium; surface coating before each sectioning process, the coating being either non-permanent, permanent, or semi-permanent; suitable techniques for affixing the coated sections to the slides using either pressure-sensitive adhesive or solvent-based adhesive; and mounting media with defined refractive indices (preferably UV-curable, water-soluble monomers). By this approach, sections exhibiting excellent morphological and physiological preservation were obtained using either a cryostat at -30 degrees C or a rotary microtome at room temperature.     

Imaging the distribution and secondary structure of immobilized enzymes using infrared microspectroscopy

Synchrotron infrared microspectroscopy (SIRMS) was used for the first time to image the distribution and secondary structure of an enzyme (lipase B from Candida antarctica, CALB) immobilized within a macroporous polymer matrix (poly(methyl methacrylate)) at 10 microm resolution. The beads of this catalyst (Novozyme435) were cut into thin sections (12 microm). SIRMS imaging of these thin sections revealed that the enzyme is localized in an external shell of the bead with a thickness of 80-100 microm. Also, the enzyme was unevenly distributed throughout this shell. Furthermore, by SIRMS-generated spectra, it was found that CALB secondary structure was not altered by immobilization. Unlike CALB, polystyrene molecules of similar molecular weight diffuse easily throughout Novozyme435 beads. Scanning electron micrograph (SEM) images of the Novozyme435 beads showed that the average pore size is 10 times larger than CALB or polystyrene molecules, implying that there is no physical barrier to enzyme or substrate diffusion throughout the bead. Thus, the difference between polystyrene and enzyme diffusivity suggests that protein-matrix and protein-protein interactions govern the distribution of the enzyme within the macroporous resin.     

Bone Marrow Stem Cells and Polymer Hydrogels—Two Strategies for Spinal Cord Injury Repair

Summary 1. Emerging clinical studies of treating brain and spinal cord injury (SCI) led us to examine the effect of autologous adult stem cell transplantation as well as the use of polymer scaffolds in spinal cord regeneration. We compared an intravenous injection of mesenchymal stem cells (MSCs) or the injection of a freshly prepared mononuclear fraction of bone marrow cells (BMCs) on the treatment of an acute or chronic balloon-induced spinal cord compression lesion in rats. Based on our experimental studies, autologous BMC implantation has been used in a Phase I/II clinical trial in patients (n=20) with a transversal spinal cord lesion.2. MSCs were isolated from rat bone marrow by their adherence to plastic, labeled with iron-oxide nanoparticles and expanded in vitro. Macroporous hydrogels based on derivatives of 2-hydroxyethyl methacrylate (HEMA) or 2-hydroxypropyl methacrylamide (HPMA) were prepared, then modified by their copolymerization with a hydrolytically degradable crosslinker, N,O-dimethacryloylhydroxylamine, or by different surface electric charges. Hydrogels or hydrogels seeded with MSCs were implanted into rats with hemisected spinal cords.3. Lesioned animals grafted with MSCs or BMCs had smaller lesions 35 days postgrafting and higher scores in BBB testing than did control animals and also showed a faster recovery of sensitivity in their hind limbs using the plantar test. The functional improvement was more pronounced in MSC-treated rats. In MR images, the lesion populated by grafted cells appeared as a dark hypointense area and was considerably smaller than in control animals. Morphometric measurements showed an increase in the volume of spared white matter in cell-treated animals. In the clinical trial, we compared intraarterial (via a. vertebralis, n=6) versus intravenous administration of BMCs (n=14) in a group of subacute (10–33 days post-SCI, n=8) and chronic patients (2–18 months, n=12). For patient follow-up we used MEP, SEP, MRI, and the ASIA score. Our clinical study revealed that the implantation of BMCs into patients is safe, as there were no complications following cell administration. Partial improvement in the ASIA score and partial recovery of MEP or SEP have been observed in all subacute patients who received cells via a. vertebralis (n=4) and in one out of four subacute patients who received cells intravenously. Improvement was also found in one chronic patient who received cells via a. vertebralis. A much larger population of patients is needed before any conclusions can be drawn. The implantation of hydrogels into hemisected rat spinal cords showed that cellular ingrowth was most pronounced in copolymers of HEMA with a positive surface electric charge. Although most of the cells had the morphological properties of connective tissue elements, we found NF-160-positive axons invading all the implanted hydrogels from both the proximal and distal stumps. The biodegradable hydrogels degraded from the border that was in direct contact with the spinal cord tissue. They were resorbed by macrophages and replaced by newly formed tissue containing connective tissue elements, blood vessels, GFAP-positive astrocytic processes, and NF-160-positive neurofilaments. Additionally, we implanted hydrogels seeded with nanoparticle-labeled MSCs into hemisected rat spinal cords. Hydrogels seeded with MSCs were visible on MR images as hypointense areas, and subsequent Prussian blue histological staining confirmed positively stained cells within the hydrogels.4. We conclude that treatment with different bone marrow cell populations had a positive effect on behavioral outcome and histopathological assessment after SCI in rats; this positive effect was most pronounced following MSC treatment. Our clinical study suggests a possible positive effect in patients with SCI. Bridging the lesion cavity can be an approach for further improving regeneration. Our preclinical studies showed that macroporous polymer hydrogels based on derivatives of HEMA or HPMA are suitable materials for bridging cavities after SCI; their chemical and physical properties can be modified to a specific use, and 3D implants seeded with different cell types may facilitate the ingrowth of axons.     

Evaluation of Physical and Mechanical Properties of Porous Poly (Ethylene Glycol)-co-(L-Lactic Acid) Hydrogels during Degradation

Porous hydrogels of poly(ethylene glycol) (PEG) have been shown to facilitate vascularized tissue formation. However, PEG hydrogels exhibit limited degradation under physiological conditions which hinders their ultimate applicability for tissue engineering therapies. Introduction of poly(_L-lactic acid) (PLLA) chains into the PEG backbone results in copolymers that exhibit degradation via hydrolysis that can be controlled, in part, by the copolymer conditions. In this study, porous, PEG-PLLA hydrogels were generated by solvent casting/particulate leaching and photopolymerization. The influence of polymer conditions on hydrogel architecture, degradation and mechanical properties was investigated. Autofluorescence exhibited by the hydrogels allowed for three-dimensional, non-destructive monitoring of hydrogel structure under fully swelled conditions. The initial pore size depended on particulate size but not polymer concentration, while degradation time was dependent on polymer concentration. Compressive modulus was a function of polymer concentration and decreased as the hydrogels degraded. Interestingly, pore size did not vary during degradation contrary to what has been observed in other polymer systems. These results provide a technique for generating porous, degradable PEG-PLLA hydrogels and insight into how the degradation, structure, and mechanical properties depend on synthesis conditions.     

Composite matrix membranes as synthetic receptor systems. 2. Structural-morphological characteristics

Structural and morphological characteristics of composite imprinted membranes for selective recognizing of adenosine 3',5'-cyclic monophosphate (cAMP) were studied. Composite polyvinylidene fluoride microfiltration membranes (Millipore) covered with a thin imprinted polymer layer were prepared using photoinitiated copolymerization of dimethylaminoethylmetacrylate with trimethylolpropanethrimethacrylate in the presence of cAMP as template. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to visualise surfaces and cross-sections of imprinted membranes and to determine their structural and morphological parameters such as pore size, thickness of selective imprinted layer, surface roughness as well as total surface contact area. The impact of structural characteristics on separation properties of the imprinted membranes was analyzed. It was found out that the thickness of the imprinted polymer layer with optimal recognizing properties is limited.     

Photocrosslinked hyaluronic acid hydrogels: natural,biodegradable tissue engineering scaffolds

Ideally, rationally designed tissue engineering scaffolds promote natural wound healing and regeneration. Therefore, we sought to synthesize a biomimetic hydrogel specifically designed to promote tissue repair and chose hyaluronic acid (HA; also called hyaluronan) as our initial material. Hyaluronic acid is a naturally occurring polymer associated with various cellular processes involved in wound healing, such as angiogenesis. Hyaluronic acid also presents unique advantages: it is easy to produce and modify, hydrophilic and nonadhesive, and naturally biodegradable. We prepared a range of glycidyl methacrylate-HA (GMHA) conjugates, which were subsequently photopolymerized to form crosslinked GMHA hydrogels. A range of hydrogel degradation rates was achieved as well as a corresponding, modest range of material properties (e.g., swelling, mesh size). Increased amounts of conjugated methacrylate groups corresponded with increased crosslink densities and decreased degradation rates and yet had an insignificant effect on human aortic endothelial cell cytocompatibility and proliferation. Rat subcutaneous implants of the GMHA hydrogels showed good biocompatibility, little inflammatory response, and similar levels of vascularization at the implant edge compared with those of fibrin positive controls. Therefore, these novel GMHA hydrogels are suitable for modification with adhesive peptide sequences (e.g., RGD) and use in a variety of wound-healing applications.     

Synthesis and characterization of thermosensitive graft copolymer of N-isopropylacrylamide with biodegradable carboxymethylchitosan

A novel thermosensitive and hydrogel was designed and synthesized by graft copolymerization of N-isopropylacrylamide (NIPAAm) with biodegradable carboxymethylchitosan (CMCS). The influence of the content of CMCS grafted on the properties of the resulted hydrogels was examined. The morphology of the hydrogels was observed by scanning electron microscopy (SEM), their thermal property was characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and deswelling/swelling kinetics upon external temperature changes. In comparison with the conventional PNIPAAm hydrogels, the resulted hydrogels have improved thermosensitive properties, including enlarged water content at room temperature and faster deswelling/swelling rate upon heating. The strategy described here presents a potential alternative to the traditional synthesis techniques for thermosensitive hydrogels.     

Microbial synthesis of poly(epsilon-lysine) and its various applications

This review article deals with the microbial synthesis, physiochemical properties, and potential applications of poly-epsilon-lysine (epsilon-PL), which is a naturally occurring biomaterial that is water soluble, biodegradable, edible and non-toxic toward humans and the environment. The potential applications of epsilon-PL as food preservatives, emulsifying agent, dietary agent, biodegradable fibers, highly water absorbable hydrogels, drug carriers, anticancer agent enhancer, biochip coatings in the fields of food, medicine, agriculture and electronics are also discussed in this review.     

Role of volume and prostaglandin synthesis in the suppression of renin by saline in the rat

To evaluate the contribution of plasma volume expansion per se on acute inhibition of renin release by sodium chloride infusion, renin responses to comparable plasma volume expansion with intravenous infusions of sodium chloride, sodium bicarbonate, or albumin were studied in separate groups of sodium chloride-depleted rats. In addition, urinary prostaglandin E2 (PGE2) excretion rate was compared in the saline- and sodium bicarbonate-infused animals to evaluate the relationship between acute changes in renin release and intrarenal PGE2 synthesis. All three groups were plasma volume-expanded by approximately 55%. Plasma renin activity (PRA) decreased in response to saline (12.3 +/- 1.0 to 6.7 +/- 0.7 ng AI/ml/hr; P less than 0.01) whereas PRA did not change with sodium bicarbonate (11.3 +/- 1.4 to 10.2 +/- 1.5) or albumin (9.9 +/- 0.7 to 8.2 +/- 1.0). The rate of PGE2 excretion was not changed by either saline (72.2 +/- 13.1 to 72.3 +/- 18.7 pg/min) or sodium bicarbonate infusion (70.7 +/- 8.8 to 64.9 +/- 7.0). These results support the hypothesis that acute suppression of PRA by infusion of saline is not dependent upon volume expansion per se. In confirmation of earlier observations, inhibition of renin release by sodium chloride was related to chloride. Finally, the results suggest that the renal tubular mechanism for inhibition of renin release by sodium chloride is not related to overall changes in renal PGE2 synthesis in the rat.     

Characterization of [(3)H]Quisqualate binding to recombinant rat metabotropic glutamate 1a and 5a receptors and to rat and human brain sections

We have investigated the binding properties of [(3)H]quisqualate to rat metabotropic glutamate (mGlu) 1a and 5a receptors and to rat and human brain sections. Saturation isotherms gave K:(D) values of 27 +/- 4 and 81 +/- 22 nM: for mGlu1a and mGlu5a receptors, respectively. Several compounds inhibited the binding to mGlu1a and mGlu5a receptors concentration-dependently. (S:)-4-Carboxyphenylglycine, (S:)-4-carboxy-3-hydroxyphenylglycine, and (R,S)-1-aminoindan-1,5-dicarboxylic acid, which completely inhibited [(3)H]quisqualate binding to the mGlu5a receptor, were inactive in a functional assay using this receptor. The distribution and abundance of binding sites in rat and human brain sections were studied by quantitative receptor radioautography and image analysis. Using 10 nM: [(3)H]quisqualate, a high density of binding was detected in various brain regions with the following rank order of increasing levels: medulla, thalamus, olfactory bulb, cerebral cortex, spinal cord dorsal horn, olfactory tubercle, dentate gyrus molecular layer, CA1-3 oriens layer of hippocampus, striatum, and cerebellar molecular layer. The ionotropic component of this binding could be inhibited by 30 microM: kainate, revealing the distribution of mGlu1+5 receptors. The latter were almost completely inhibited by the group I agonist (S:)-3,5-dihydroxyphenylglycine. The binding profile correlated well with the cellular sites of synthesis and regional expression of the respective group I receptor proteins revealed by in situ hybridization histochemistry and immunohistochemistry, respectively.