XRD studies of chitin-based polyurethane elastomers

Chitin-based polyurethane elastomers (PUEs) were synthesized by step growth polymerization techniques using poly(epsilon-caprolactone) (PCL) varying diisocyanate and chain extender structures. The viscosity average molecular weight (M(v)) of chitin was deduced from the intrinsic viscosity and found; M(v)=6.067 x 10(5). The conventional spectroscopic characterization of the samples with FTIR, (1)H NMR and (13)C NMR were in accordance with proposed PUEs structure. The crystalline behavior of the synthesized polymers were investigated by X-ray diffraction (XRD), differential scanning calorimetery (DSC) and loss tangent curves (tan delta peaks). The observed patterns of the crystalline peaks for the lower angle for chitin in the 2theta range were indexed as 9.39 degrees, 19.72 degrees, 20.73 degrees, 23.41 degrees and 26.39 degrees. Results showed that crystallinity of the synthesized PUEs samples was affected by varying the structure of the diisocyanate and chain extender. Crystallinity decreased from aliphatic to aromatic characters of the diisocyanates used in the final PU. The presence of chitin also favors the formation of more ordered structure, as higher peak intensities was obtained from the PU extended with chitin than 1,4-butane diol (BDO). The value of peak enthalpy (DeltaH) of chitin was found to be 47.13 J g(-1). The higher DeltaH value of 46.35 J g(-1) was found in the samples extended with chitin than BDO (39.73 J g(-1)).     

A Simple Method to Functionalize PCL Surface by Grafting Bioactive Polymers Using UV Irradiation

Background

Polycaprolactone (PCL) is a biodegradable polymer which is used in tissue engineering applications thanks to its many favorable characteristics. However, PCL surfaces are known as hydrophobic leading to a lack of favorable cell response. To overcome this problem, PCL surfaces will undergo a surface functionalization by grafting bioactive polymers bearing ionic groups.

Synthesis, characterization and thermal sensitivity of chitosan-based graft copolymers

Novel chitosan-based graft copolymers (CECTS-g-PDMA) were synthesized through homogeneous graft copolymerization of (N,N-dimethylamino)ethyl methacrylate (DMA) onto N-carboxyethylchitosan (CECTS) in aqueous solution by using ammonium persulfate (APS) as the initiator. The effect of polymerization variables, including initiator concentration, monomer concentration, reaction time and temperature, on grafting percentage was studied. XRD, FTIR, DSC and TGA were used to characterize the graft copolymers. Surface-tension measurements, turbidity measurements and temperature-variable (1)H NMR analysis were combined to investigate the thermal sensitivity of CECTS-g-PDMAs in aqueous solution.     

Synthesis of superabsorbent from carbohydrate waste

A mixture of acrylamide (AM) and acrylic acid (AA) monomers were grafted on germinated gelatinized wheat starch using potassium persulfate (KPS) as an initiator to yield superabsorbent. The effects of different parameters such as time, temperature, monomer feed (AM:AA), starch: monomers ratio and initiator concentration on graft add-on were studied, and the optimized values were found to be 2 h, 60 °C, 1:1 (w/w), 1:1(w/w) & 1% (with respect to starch powder), respectively. The product so formed was saponified with 0.1N NaOH, dried and finely powdered sample was characterized using FT-IR, TGA. Product showed maximum absorbency of 150 g/g.     

Cloning and characterization of a gene encoding wheat starch synthase I

 A cDNA clone, and a corresponding genomic DNA clone, containing full-length sequences encoding wheat starch synthase I, were isolated from a cDNA library of hexaploid wheat (Triticum aestivum) and a genomic DNA library of Triticum tauschii, respectively. The entire sequence of the starch synthase-I cDNA (wSSI-cDNA) is 2591 bp, and it encodes a polypeptide of 647 amino-acid residues that shows 81% and 61% identity to the amino-acid sequences of SSI-type starch synthases from rice and potato, respectively. In addition, the putative N-terminal amino-acid sequence of the encoded protein is identical to that determined for the N-terminal region of the 75-kDa starch synthase present in the starch granule of hexaploid wheat. Two prominent starch synthase activities were demonstrated to be present in the soluble fraction of wheat endosperm by activity staining of the non-denaturing PAGE gels. The most anodal band (wheat SSI) shows the highest staining intensity and results from the activity of a 75-kDa protein. The wheat SSI mRNA is expressed in the endosperm during the early to mid stages of wheat grain development but was not detected by Northern blotting in other tissues from the wheat plant. The gene encoding the wheat SSI (SsI-D1) consists of 15 exons and 14 introns, similar to the structure of the rice starch synthase-I gene. While the exons of wheat and rice are virtually identical in length, the wheat SsI-D1 gene has longer sequences in introns 1, 2, 4 and 10, and shorter sequences in introns 6, 11 and 14, than the corresponding rice gene. Received: 5 June 1998 / Accepted: 29 September 1998     

高取代度CMS合成新工艺研究

研究以玉米淀粉为原料,用溶煤法合成CMS(2%水溶液,DS≥0.90,η≥120.0mpa.s)的新工艺;讨论了影响其合成的几种因素,确定了最佳技术参数和工艺条件,经工业性试验,证明本法切实可行。     

Synthesis of chitosan–polycaprolactone blend for control delivery of ofloxacin drug

In the present research work chitosan has been blended with different amounts of polycaprolactone (PCL) (80:20, 75:25, 60:40 and 50:50) for using them for control delivery of ofloxacin. The blends were characterized by Fourier transmission infra red spectroscopy (FTIR), UV–visible spectroscopy (UV), scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis. From the FTIR spectra the various groups present in chitosan and PCL blend were monitored. The homogeneity, morphology and crystallinity of the blends were ascertained from SEM and XRD data, respectively. The swelling studies have been measured at different drug loading. The kinetics of the drug delivery system has been systematically studied. Drug release kinetics was analyzed by plotting the cumulative release data vs. time by fitting to an exponential equation which indicated the non-Fickian type of kinetics. The drug release was investigated at different pH medium and it was found that the drug release depends upon the pH medium as well as the nature of matrix.     

Synthesis of Keratin-based Nanofiber for Biomedical Engineering

Electrospinning, due to its versatility and potential for applications in various fields, is being frequently used to fabricate nanofibers. Production of these porous nanofibers is of great interest due to their unique physiochemical properties. Here we elaborate on the fabrication of keratin containing poly (ε-caprolactone) (PCL) nanofibers (i.e., PCL/keratin composite fiber). Water soluble keratin was first extracted from human hair and mixed with PCL in different ratios. The blended solution of PCL/keratin was transformed into nanofibrous membranes using a laboratory designed electrospinning set up. Fiber morphology and mechanical properties of the obtained nanofiber were observed and measured using scanning electron microscopy and tensile tester. Furthermore, degradability and chemical properties of the nanofiber were studied by FTIR. SEM images showed uniform surface morphology for PCL/keratin fibers of different compositions. These PCL/keratin fibers also showed excellent mechanical properties such as Young''s modulus and failure point. Fibroblast cells were able to attach and proliferate thus proving good cell viability. Based on the characteristics discussed above, we can strongly argue that the blended nanofibers of natural and synthetic polymers can represent an excellent development of composite materials that can be used for different biomedical applications.     

Synthesis and properties of carboxymethylchitosan hydrogels modified with poly(ester-urethane)

Preparation and properties of carboxymethylchitosan (CMC) modified with polyurethane (PU) containing poly(ethylene adipate) (PEA) as a soft segment is described. Urethane prepolymer was first synthesized by the reaction of PEA with an excess of 1,6-hexamethylene diisocyanate (HDI) to terminate its ends with isocyanate functional groups, followed by chain extension reaction using ethylene glycol as a chain extender. Its chemical structure was characterized by ¹H NMR and FTIR, molecular weight by GPC, and thermal behavior by DSC. To prepare PU-modified CMC (CMC-PU), 1–60 wt% of PU were introduced into the CMC solution of THF:H₂O mixture (50:50 v/v) in the presence of 10 wt% of hexamethylene-1,6-di-(aminocarboxysulfonate) (HDA) to increase network density. Formation of the network structure was confirmed by investigating percent crosslinking and water swelling properties of CMC-PU compared to CMC network without PU. When percent of PU increased from 1 to 60 wt%, percent crosslinking of CMC-PU gradually increased up to 82%, whereas equilibrium water content (EWC) dropped and retained at 1000%. SEM showed microphase separation of PU (10–50 μm) thoroughly dispersed in CMC surface and in the bulk. In addition, CMC-PU exhibited a slight enhancement in toughness properties. Cytotoxicity and biocompatibility tests indicated that CMC-PU was non-toxic.     

Structural characterization and properties of starch/konjac glucomannan blend films

In this work, a series of glycerol-plasticized pea starch/konjac glucomannan (ST/KGM) blend films was prepared by a casting and solvent evaporation method. The structure, thermal behavior, and mechanical properties of the films were investigated by means of Fourier Transform Infrared Spectroscopy, wide-angle X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, and tensile testing. The results indicated that strong hydrogen bonding formed between macromolecules of starch (ST) and konjac glucomannan (KGM), resulting in a good miscibility between ST and KGM in the blends. Compared with the neat ST, the tensile strength of the blend films were enhanced significantly from 7.4 to 68.1 MPa with an increase of KGM content from 0 to 70 wt%. The value of elongation at break of the blend films was higher than that of ST and reached a maximum value of 59.0% when the KGM content was 70 wt% and 20% of glycerol as plasticizer. The incorporation of KGM into the ST matrix also led to an increase of moisture uptake for the ST-based materials. The structure and properties of pea starch-based films were modified and improved by blending with KGM.     

Preparation and characterization of polyurethane foams using a palm oil-based polyol

Polyurethane (PU) foams were prepared using a palm oil-based polyol (PO-p). At the first stage, palm oil was converted to monoglycerides as a new type of polyol by glycerolysis. A yield of the product reached 70% at reaction temperature of 90 degrees C by using an alkali catalyst and a solvent. At the second stage, PU foams were prepared from mixtures of the polyol and polyethylene glycol (PEG) or diethylene glycol (DEG) and an isocyanate compound. Characterization of the foams was carried out by thermal and mechanical analyses. The analyses showed that the chain motion of polyurethane becomes more flexible at the higher PO-p content in the whole polymer, which indicates that the monoglyceride molecules work as soft segments. The study here may lead to a development of a new type of polyurethane foams using palm oil as a raw material.     

Preparation,characterization and laboratory-scale application of an immobilized glucoamylase

Glucoamylase (1,4-α-d-glucan glucohydrolase, EC 3.2.1.3) has been covalently immobilized on a polyacrylamide-type support containing carboxylic groups activated by water-soluble carbodiimide. The activity was 5.5– 6.0 units g^?1solid. The optimum pH for catalytic activity was pH 3.8. The apparent optimum temperature was found at 60°C. With soluble starch as substrate the K_m value was 14 mg ml^?1. The pH for maximum stability was pH 4.0–4.5. In the presence of 8 m urea the immobilized glucoamylase retained most of its catalytic activity but it was more susceptible to guanidinium hydrochloride than the soluble enzyme. The practical applicability of immobilized glucoamylase was tested in batch process and continuous operation.     

Thermal and structural properties of unusual starches from developmental corn lines

Starches from exotic corn lines were screened by using differential scanning calorimetry (DSC) to find thermal properties that were significantly different from those exhibited by starches from normal Corn Belt lines. Two independent gelatinization transitions, one corresponding to the melting of a peak at 66 °C and the other to a peak melting at 69 °C, were found in some starches. The melting characteristics were traced to two separate types of granules within the endosperm. Strong correlations were found between DSC properties and proportion of large granules with equivalent diameter ≥17 μm. Starches with a lower peak onset gelatinization temperature (T_oG), had a lower normalized concentration of chains with a degree of polymerization (dp) of 15–24 and/or a greater normalized concentration of chains with a dp of 6–12. These studies will aid in understanding structure–thermal property relationships of starches, and in identifying corn lines of interest for commercial breeding.     

Determination of the toluene diisocyanate binding sites on human serum albumin by tandem mass spectrometry

Diisocyanates are highly reactive chemical compounds widely used in the manufacture of polyurethanes. Although diisocyanates have been identified as causative agents of allergic respiratory diseases, the specific mechanism by which these diseases occur is largely unknown. To better understand the chemical species produced when diisocyanates react with protein, tandem mass spectrometry was employed to unambiguously identify the binding sites of the industrially important isomers, 2,4- and 2,6-toluene diisocyanate, on human serum albumin at varying diisocyanate/protein ratios. The 2,4-isomer results in approximately 2-fold higher conjugation product ion abundances than does the 2,6-isomer, suggesting that the 2,4-isomer has a higher reactivity toward albumin. Both isomers preferentially react with the N-terminal amine of the protein and the ε-NH₂ of lysine. At a low (1:2) diisocyanate/protein ratio, five binding sites are identified, whereas at a high (40:1) ratio, near-stoichiometric conjugation is observed with a maximum of 37 binding sites identified. Binding sites observed at the lowest conjugation ratios are conserved at higher binding ratios, suggesting a subset of 5–10 preferential binding sites on albumin. Diisocyanate–protein conjugation results in a variety of reaction products, including intra- and intermolecular crosslinking, diisocyanate self-polymerization, and diisocyanate hydrolysis.     

Synthesis of starch derivatives with labile cationic groups

A new route to starch derivatives bearing hydrolyzable cationic groups was developed. This was based on reacting starch compounds with betaine derivatives in the presence of diisopropylcarbodiimide and 4-dimethylaminopyridine as coupling reagents in an aprotic polar solvent. Water-soluble starches with a perfectly controlled degree of substitution were thus obtained which were fully characterized by infrared, ¹H and ¹³C spectroscopy and viscosity measurements. The cationic groups grafted on the polysaccharides are shown to hydrolyze slowly upon storage at room temperature.     

The basis of graft rejection in the earthworms Lumbricus terrestris and Eisenia foetida

Body wall grafts have been exchanged between Lumbricus terrestris and Eisenia foetida unicolor, and the survival times of second-set grafts and a limited number of third-set grafts have been compared with those of first-set grafts. Survival of grafts has also been studied following implantation. The results do not support the hypothesis that second-set rejection is accelerated due to an immune response as in higher vertebrates. Evidence is presented that Eisenia are individually different and that the differential graft survival may be due to tissue incompatibility, survival times depending on the degree of difference in the environment presented by the recipient.     

Synthesis and characterization of mannosylated oligoribonucleotides

Oligoribonucleotide (RNA)–carbohydrate conjugates bearing mono- and divalent mannosides were readily obtained using 3,4-diethoxy-3-cyclobutene-1,2-dione as the linking agent in the presence of trace amount of triethylamine. The glycoconjugates were purified by HPLC and characterized by electrospray mass spectroscopy.     

Synthesis of OH-group-containing, biodegradable polyurethane and protein fixation on its surface

A series of biodegradable polyurethanes containing free side hydroxyl groups (PUOH) were synthesized successfully in two steps: (1) PLA diol as soft segment, hexamethylene diisocyanate (HDI) as hard segment, and benzalpentaerythritol (BPO) as a chain extender were used to synthesize PUs with protected OH groups; (2) CF(3)COOH was used as a deprotection agent to remove the benzal groups on PU to prepare PUOH. The properties of PU and PUOH were characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), water contact angle measurement, and gel permeation chromatography (GPC). The benzal groups were removed completely in 15 min without detrimental effect on PU main chains to obtain PUOHs. 4-Azidobenzoic acid was conjugated to PUOH through its esterification with the free OH groups on PUOH. The results of immunofluorescence assay showed that the phenyl azide groups formed were capable of binding mouse IgG under UV (254 nm) irradiation in 3 min; the bound mouse IgG retained its own biological activity and could further bind the FITC-labeled anti(mouse IgG). Therefore, this material has a potential in immunofluorescence assay and related fields.