Fabrication and characterization of chitosan/gelatin porous scaffolds with predefined internal microstructures

The fabrication process for a novel three-dimensional (3D) chitosan/gelatin scaffold with predefined multilevel internal architectures and highly porous structures is presented combining solid freeform fabrication (SFF), microreplication and lyophilization techniques. The computer model of the scaffold is designed with biological data such as branching angle in liver vascular cast incorporated. Stereolithography (SL), known as a SFF technique, is utilized to build the resin mould, based on which poly-dimethylsilicone (PDMS) mould is produced by microreplication. The chitosan/gelatin hybrid solution is then cast onto the PDMS mould for pre-freeze and the monolayer porous structures with organized internal morphology are produced upon lyophilization. The 3D scaffold can be constructed via stacking these monolayer structures. The properties of porous structure, such as porosity, pore size and micromorphology as well as wall thickness, were investigated. Scanning electron microscopy (SEM) demonstrated that the scaffold possesses multilevel organized internal morphologies including vascular systems (portal vein, artery and hepatic vein) and parenchymal component (hepatocyte chamber). These organized structures enable orderly arrangement of hepatocyte and hepatic nonparenchymal cells and co-culture in the same 3D scaffold to guide liver regeneration in a controlled manner. Cell culture experiment in vitro showed that hepatocytes perform better in the well-defined chitosan/gelatin scaffold than in porous scaffold. This approach makes it flexible to investigate the relationship between internal scaffold microstructure and hepatocyte behavior in vitro. It also provides a new way to fabricate complex 3D scaffold using various natural biomaterials for vital organ engineering.     

Phase separation in poly(vinyl alcohol)/gelatin blend systems

Blends of a commercial poly(vinyl alcohol) (a-PVA) derived from vinyl acetate and gelatin obtained from collagen were prepared by mixing aqueous solutions of both samples under various conditions. For the blend hydrogels, the depression of melting temperatures was observed at high PVA content. Similarly to the a-PVA/silk fibroin (SF) system, when the degrees of polymerization of PVA increased, the microphase separation region in a phase diagram of the blend films increased for the a-PVA/gelatin system. In the IR spectra of the blend films, no absorption bands corresponding to a conformational change of gelatin appeared. Comparison of the mechanical properties of the a-PVA/gelatin and a-PVA/SF systems, showed the interaction between PVA and gelatin molecules to be smaller than that between PVA and SF molecules. © 1999 Society of Chemical Industry     

Phase behavior of gelatin in the presence of pectin in water-acid medium

Summary Phase separation of alkaline gelatin in water-acid solutions in the presence of low etherified pectin (ED 38%) were investigated. The effects of the pectin weight fraction in pectin/gelatin mixture (q_o) as well as two conditions of complex formation, namely, mixing of the binary biopolymer-solvent systems at pH 3.5 (‘mixing conditions’), or preparation of the ternary gelatin-pectin-water systems at pH 7.5 and their subsequent acidification up to pH 3.5 (‘titration conditions’), on phase equilibrium and macrostructure of the concentrated complex phase were established using phase analysis, and optical microscopy. At q_o<0.5 the aggregative phase separation was observed in both conditions of complex formation leading to the almost complete concentration of both biopolymers in the bottom phase at q_o=0.3 (‘mixing conditions’) and at q_o=0.5 (‘titration conditions’). At q_o>0.5 unusual three phase separation took place in the ‘mixing conditions’, leading to formation of supernatant (phase 1), complex coacervate (phase 2) and concentrated pectin solution (phase 3). Possible mechanism of such phenomenon was discussed in term of segregative and aggregative phase separations.     

Characteristics and gel properties of gelatin from goat skin as affected by spray drying

Gelatin powder from goat skin prepared by spray drying at various inlet temperatures (160–200°C) was characterized. Predominant particle sizes were in the range of 4.65–5.14?µm. Gelatin powder was mostly concave in shape with varying sizes, depending on inlet temperatures used. All gelatin powders were creamy whitish. Powder generally became more yellowish as the inlet temperature of spray drying increased (p?p?p?p?>?0.05). Goat skin gelatin spray dried with inlet temperatures of 160 or 180°C had higher gel strength than commercial bovine gelatin (p?相似文献   

Properties of polyelectrolyte complex films of chitosan and gelatin

A series of chitosan–gelatin complexes was prepared by varying the ratio of constituents. Differential scanning calorimetry was used to determine the amount of the different states of water. The interaction between chitosan and gelatin was checked by IR and X-ray analysis and was related to mechanical strength. The results indicate that the water take-up of a chitosan–gelatin complex is depressed by strong interactions within networks. Chitosan can improve the tensile strength of complex films, and even with high water content these can keep appropriate tensile strength and higher elongation. © 1999 Society of Chemical Industry     

Preparation and characterization of gelatin gel with a gradient structure

Gelatin gel with a gradient structure was produced by a vapour crosslinking procedure. The crosslinking degree at various depths (distance from plate surface) and its gradient are dependent on the crosslinking time and vapour temperature. The experimental data indicate that the gelatin gel with a gradient structure does not follow a second‐order swelling kinetics. The dissolution rate can also be regulated by crosslinking time and vapour temperature. © 2000 Society of Chemical Industry     

Use of chitosan derivatives as solid phase extractors for metal ions

This paper shows a comparative study between the two radiation grafted chitosan derivatives viz. cross-linked chitosan (CRC) and cross-linked chitosan after hydrolysis (CRCH). These chitosan derivatives were used as solid phase extractors for several radionuclides. The uptake of ¹³⁷Cs, ^85,89Sr, ¹⁵²Eu, ²⁴¹Am, ²³⁴Th and ²³³U by CRCH and CRC was studied using batch and column methods. The K_d, exchange capacity, breakthrough capacity for different metal ions with the functionalized polymers were determined. The uptake followed the following trend: UO₂²⁺>Th⁴⁺>Cs⁺>Eu³⁺>Am³⁺>Sr²⁺ for both sorbents. It was seen that CRCH has a greater uptake of metal ions compated to CRC but CRC was more selective of the two.     

Thermal and NMR investigation of the change in the states of water caused by volume phase transition of gelatin gel

The occurrence of volume phase transition (VPT) of a polymer gel is often accompanied by the loss of water. In view of the fact that few studies have been made on the change in different states of water during VPT, in this paper, DSC and NMR are used to check the variation in states of water during VPT of glutaraldehyde crosslinked gelatin gel caused by the variation in composition of water–acetone mixture. The results indicate that the volume of gel collapses at 50 % acetone concentration. The contents of free, intermediate and bound water absorbed by gelatin gel decrease with an increase in the amount of acetone. At 50 % and 60 % acetone content, free water disappears; because acetone accounts for 70 % and 85 %, there remains only bound water. Near VPT the relative content of bound water to total water increases sharply. The spin–lattice relaxation times (T₁) determined by NMR show that the T₁ values of intermediate and bound water, respectively, decrease by approximately four and ten times compared with that of free water. Before VPT, most of the water is freezable and highly mobile. After VPT, bound water gradually plays a dominant role in the mobility of water in the gel. The findings are helpful in understanding the dehydration process of protein induced by poor solvent. © 2000 Society of Chemical Industry     

Synthesis and characterization of biodegradable TPP/genipin co-crosslinked chitosan gel beads

Novel chitosan gel beads were synthesized by a coupled ionic and chemical co-crosslinking mechanism. Tripolyphosphate (TPP) and a naturally occurring crosslinking reagent, genipin, which has been used in herbal medicine, were employed, respectively, as an ionic and a chemical crosslinkers to prepare the chitosan-based networks of gel beads. The competitive crosslinking of chitosan with ionic crosslinker (TPP) and chemical crosslinker (genipin) was characterized by FTIR, UV and EDAX spectroscopy (X-ray energy dispersion) spectroscopy. The variation of characteristic peak of genipin observed from UV spectroscopy and the characteristic peak of tripolyphosphate in crosslinked chitosan-based networks observed from FTIR spectroscopy suggests that the co-crosslinking mechanism is dependent on the pH of TPP/genipin co-crosslinker. The energy profiles of carbon and phosphorus estimated from confirms that chemical crosslinking dominates the co-crosslinking reaction at higher pH condition (pH 7.0 and 9.0) and ionic crosslinking dominates the co-crosslinking reaction at lower pH condition (pH 1.0, 3.0 and 5.0). The pH-dependent ionic/chemical co-crosslinking mechanism shows an obvious effect on the swelling property and enzymatic degradation behavior of prepared chitosan networks. These results reveal that the ionic/chemical co-crosslinked chitosan networks may be suitable for biomedical applications.     

Weighted‐average isostrain and isostress model to describe the kinetic evolution of the mechanical properties of a composite gel: Application to the system gelatin:Maltodextrin

Application of a weighted‐average model (WAM) to the kinetic evolution of the elasticity during 16 h was successfully performed for a composite gel in which a maltodextrin phase is dispersed within a continuous gelatin phase. The results obtained using the model for different starting compositions along an initial higher‐temperature binodal are in good agreement with the phase diagram measured at high temperature and help to confirm the position of the binodal. A novel application of confocal Raman microscopy was used to measure the local concentration of the included phase of the composite gel and confirms the results given by the WAM. This model allows calculation of tie lines appropriate to the gel state and could be used for other biopolymer blends if the assumption is made that the gelation process involves a complete phase separation of both polymers before any gelation occurs. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1465–1477, 2000     

In situ atomic force microscopy measurement of the dynamic variation in the elastic modulus of swollen chitosan/gelatin hybrid polymer network gels in media of different pH

The surface morphology and elastic modulus of chitosan/gelatin hybrid polymer network (CS/GLN HPN) gels was investigated by in situ atomic force microscopy (AFM). The surface domains of hydrogel varied from irregular clumps to sponge-like patterns with increasing swelling time. The vertical height and width of the surface domains observed in alkali medium are smaller than in acidic medium. The indentation of the gels caused by the AFM tip increased with time and the elastic modulus of the gels estimated by the Hertz model decreased sharply compared with that of xerogel. In alkali medium, due to the reassociation of hydrogen bondings between networks, the elastic modulus increased slightly. © 1999 Society of Chemical Industry     

MTGase反胶束纯化及其催化合成壳聚糖胶原改性物的展望

综述了微生物转谷氨酰胺酶（MTGase）的性质、用途及反胶束萃取纯化效果,展望了用MTGase催化合成等日化用新功能性原料的可行性及其前景。     

Complexation of poly(vinylpyrrolidone) and gelatin with some transition metal chlorides in aqueous solution

Complexation of poly(vinylpyrrolidone) and gelatin with certain metal chlorides (HgCl₂, CdCl₂, CoCl₂, and ZnCl₂) have been investigated by viscosimetric and spectrophotometric techniques in aqueous solutions. While the change in intrinsic viscosity, [η], of poly(vinylpyrrolidone) has shown a discontinuity with a concentration of metal chlorides, gelatin showed a steady decrease with increasing metal chloride concentration. The decreasing order of effectiveness of cations in complex formation is Hg²⁺ > Cd²⁺ > Co²⁺ > Zn²⁺ for poly(vinylpyrrolidone) and Zn²⁺ > Co²⁺ > Cd²⁺ > Hg²⁺ for gelatin solutions. It has been suggested that the poly(vinylpyrrolidone)/metal cation interaction is a charge-controlled reaction, and gelatin/metal cation is a covalent coordination in character. A similar metal cation effect has been observed for poly(vinylpyrrolidone) by UV-VIS spectrophotometry. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 891–895, 1998     

Controlling absorbency in gelatin networks: Preparation and characterization of alkylated,crosslinked gelatin

Gelatin is a highly abundant and relatively inexpensive protein which is used in a variety of gel applications including photography, drug delivery, microencapsulation, and food preparation. Control of network formation in gelatin may therefore provide methods of preparing protein gels tailored for specific applications. In this study, circular dichroism (CD), Raman, and nuclear magnetic resonance (NMR) spectroscopies were used to characterize ordering processes which occur in gelatin and their relationship to absorbency. Ordering of the unmodified protein, studied as a function of concentration, temperature, and time after initial preparation, correlates inversely with absorbency. Chemical modification was used to control the absorbency and solubility of the protein gels. Alkylation of gelatin using glycidyltrimethylammonium chloride causes substantial increases in water absorbency with degrees of substitution as low as 0.5%. Increases in saline swelling were observed only after additional modification of the alkylated gelatin with a nonionic polyoxyalkyleneamine crosslinking agent (Jeffamine®). Limiting the initial degree of substitution prior to crosslinking (to just below 1%) plays a key role in optimizing the absorbency and minimizing the dissolution of the gel in saline. The methods and principles used to manipulate the absorbency of gelatin may also find use for other natural protein systems. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:281–292, 1998     

分散相的组成对水性多彩涂料凝胶彩粒的影响

运用控制变量法,分析了分散相中HEC、保护胶溶液、增稠剂等不同掺量对水性多彩涂料凝胶彩粒成粒效果的影响,重点研究了对凝胶彩粒稳定的影响。当选用弹性乳液,纤维素掺量1%,保护胶溶液掺量3%配制分散相时,制备所得的水性多彩涂料的凝胶彩粒有良好的稳定性,不易渗色。     

壳聚糖／水溶性高分子共混膜相容性的预测与表征

高分子（聚乙烯醇和聚乙二醇）间的相容性,壳聚糖与极性水溶性高分子在溶液状态时,分子间相互吸引,相容性好,向本体转化而成膜时,CS／PVA体系比CS／PEG体系有更好的本体相容性。原因可归结为PEG不能像PVA一样提供足够多的极性基团与壳聚糖分子形成强烈相互作用,CS与PEG间的氢键强度要弱于CS与PVA间的氢键;另一个方面,PEG结晶能力很强,在由溶液转化为本体而成膜过程中,PEG分子自身之间易于形成较规整的结晶而逐渐使体系发生分相。     

Dynamic removal of n-hexane from water using nanocomposite membranes: Serial coating of para-aminobenzoate alumoxane,boehmite-epoxide and chitosan on Kevlar fabrics

Nanocomposite membranes were fabricated by dip-coating technique. Para-aminobenzoate alumoxane, boehmite–epoxide and chitosan were consecutively coated on the Kevlar fabric surface. The membranes were utilized for removing n-hexane from water using a gravity-driven dead-end filtration setup. UV–vis, FTIR and SEM analyses were performed for characterization. Water affinity analyses revealed highly hydrophilic nature of the modified membranes. Effect of pH was examined with the pH 2 providing the best condition for oil–water separation. Maximum flux and rejection were obtained as 1128 L m⁻² h⁻¹) and 94%, respectively. Deposited oil layer was effectively removed from the membrane surface using hot citric acid solution.     

PEBA/EPH热可逆凝胶膜的制备及其气体分离性能

通过热致相分离法制备了具有高气体渗透性能的聚醚共聚酰胺/乙二醇苯醚凝胶膜(PEBA/EPH),并探讨了EPH含量对其物理化学结构及CO2/N2渗透性能的影响。结果表明,PEBA/EPH凝胶膜具有良好的力学性能及优异的气体渗透性能,EPH的添加使得膜结晶度及熔融温度下降,从而CO2、N2在凝胶膜内的渗透系数显著增加。同时,由于EPH对于CO2具有优先吸附性,凝胶膜的CO2/N2选择性也相应增加。当EPH含量从0%增加到60%时,凝胶膜的CO2渗透系数由234 barrer增加到1 040 barrer,CO2/N2的气体选择系数从22.5增加到40.5。     

Amphiphilic chitosan nanospheres: Factors to control nanosphere formation and its consequent pH responsive performance

Chitosan grafted with hydrophobic and hydrophilic groups initiates the formation of amphiphilic chitosan nanospheres. The molecular weight of mPEG plays an important role to control the particle size. As compared to mPEG 2000, which gives a bimodal nanosphere (∼200, and ∼300 nm), mPEG 5000 initiates a monodispersed nanosphere with the smaller size (150 nm). In aqueous solution, the nanosphere surface is negatively charged resulting in a well dispersion in neutral to high pH but a significant precipitation in low pH. A model drug incorporation using lidocaine is successful when amphiphilic chitosan nanospheres were dissolved in good solvent followed by allowing mixing with drug solution before dialysis. The particle size of the drug incorporated chitosan is significantly increased, that is, from 100-150 nm to approximately 400-500 nm when the amount of incorporated lidocaine was about 0.68 mg per mg of lidocaine-loaded nanosphere.     

Contribution to the study of the complexation of copper by chitosan and oligomers

The complexation of copper ions by chitosan and its oligomers is investigated using potentiometric and spectrophotometric methods to study the nature of the complexes involved and the role of the degree of polymerisation. Two complexes are demonstrated. Their structure is proposed, the pH range in which they are respectively stable is determined and their stability constants calculated. Finally a degree of polymerisation of 6 appeared as the threshold value for an efficient complexation of copper ions by chitosan oligomers.