Mulberry non-engineered silk gland protein vis-à-vis silk cocoon protein engineered by silkworms as biomaterial matrices

Silk fibroin from silk gland of Bombyx mori 5th instar larvae was utilized to fabricate films, which may find possible applications as two-dimensional matrices for tissue engineering. Bombyx mori cocoon fibroin is well characterized as potential biomaterial by virtue of its good mechanical strength, water stability, thermal properties, surface roughness and biocompatibility. The present study aims to characterize the biophysical, thermal, mechanical, rheological, swelling properties along with spectroscopic analysis, surface morphology and biocompatibility of the silk gland fibroin films compared with cocoon fibroin. Fibroin solutions showed increased turbidity and shear thinning at higher concentration. The films after methanol treatment swelled moderately and were less hydrophilic compared to the untreated. The spectroscopic analysis of the films illustrated the presence of various amide peaks and conformational transition from random coil to beta sheet on methanol treatment. X-ray diffraction studies also confirmed the secondary structure. Thermogravimetric analysis showed distinct weight loss of the films. The films were mechanically stronger and AFM studies showed surfaces were rougher on methanol treatment. The matrices were biocompatible and supported L929 mouse fibroblast cell growth and proliferation. The results substantiate the silk gland fibroin films as potential biomaterial matrices.     

Bovine pericardium coated with biopolymeric films as an alternative to prevent calcification: In vitro calcification and cytotoxicity results

Bovine pericardium, for cardiac valve fabrication, was coated with either chitosan or silk fibroin film. In vitro calcification tests of coated and non coated bovine pericardium were performed in simulated body fluid solution in order to investigate potential alternatives to minimize calcification on implanted heart valves. Complementary, morphology was assessed by scanning electron microscopy — SEM; X-ray diffraction (XRD) and infrared spectroscopy (FTIR-ATR) were performed for structural characterization of coatings and biocompatibility of chitosan. Silk fibroin films were assayed by in vitro cytotoxicity and endothelial cell growth tests. Bovine pericardium coated with silk fibroin or chitosan did not present calcification during in vitro calcification tests, indicating that these biopolymeric coatings do not induce bovine pericardium calcification. Chitosan and silk fibroin films were characterized as non cytotoxic and silk fibroin films presented high affinity to endothelial cells. The results indicate that bovine pericardium coated with silk fibroin is a potential candidate for cardiac valve fabrication, since the affinity of silk fibroin to endothelial cells can be explored to induce the tissue endothelization and therefore, increase valve durability by increasing their mechanical resistance and protecting them against calcification.     

Novel cyclodextrin-based film formulation intended for buccal delivery of atenolol

Background: Unknown influence of cyclodextrin on the properties of the film formulation aimed for buccal application. Aim: Development and characterization of a novel bioadhesive film formulation for buccal atenolol delivery containing drug/cyclodextrin inclusion. Method: Interaction between atenolol and randomly methylated β-cyclodextrin (RAMEB) in solution was studied by phase solubility studies. The complex in solid state was prepared by the freeze-drying method and characterized by differential scanning calorimetry and Fourier-transformed infrared spectroscopy (FTIR). The drug, free or in complex form, was incorporated into polymeric films prepared by the casting method using ethylcellulose (EC), polyvinyl alcohol (PVA), and hydroxypropyl methylcellulose (HPMC). The prepared film formulations were characterized in terms of swelling, bioadhesion, and in vitro drug release. Results: The formation of a stabile inclusion complex (K_s = 783.4?±?21.6 M^?1) in 1:1 molar stoichiometry was confirmed in solution and in solid state. The swelling properties of films were predominated by the type of polymer used in the formulation. In vitro bioadhesive properties of the films were well correlated with the swelling properties of the polymers used in the formulation. Although incorporation of the drug, free or in complex form, decreased the bioadhesion of the films, PVA- and HPMC-based formulations retained suitable bioadhesive properties. Higher atenolol solubility upon complexation with RAMEB increased the drug dissolution rate under conditions designed to be similar to those on the buccal mucosa, but it has decreased the drug release rate from the PVA and HPMC film formulation, leading to a sustained drug release pattern. In the case of EC-based films, RAMEB promoted drug release. Other parameters that influenced the drug release rate were associated with the structure of the polymer used in the formulation, swelling characteristics of the films, and the interaction between atenolol and hydrophilic polymers that was demonstrated by FTIR analysis. Conclusion: Incorporation of atenolol in the form of an inclusion complex into hydrophilic films may be an appropriate strategy to prepare a suitable formulation for buccal drug delivery.     

Physicochemical Characterization and Evaluation of Buccal Adhesive Tablets Containing Omeprazole

The objective of this study was to develop an effective omeprazole buccal adhesive tablet with excellent bioadhesive force and good drug stability in human saliva. The omeprazole buccal adhesive tablets were prepared with various bioadhesive polymers, alkali materials, and croscarmellose sodium. Their physicochemical properties, such as bioadhesive force and drug stability in human saliva, were investigated. The release and bioavailability of omeprazole delivered by the buccal adhesive tablets were studied. As bioadhesive additives for the omeprazole tablet, a mixture of sodium alginate and hydroxypropylmethylcellulose (HPMC) was selected. The omeprazole tablets prepared with bioadhesive polymers alone had bioadhesive forces suitable for a buccal adhesive tablet, but the stability of omeprazole in human saliva was not satisfactory. Among alkali materials, only magnesium oxide could be an alkali stabilizer for omeprazole buccal adhesive tablets due to its strong waterproofing effect. Croscarmellose sodium enhanced the release of omeprazole from the tablets; however, it decreased the bioadhesive forces and stability of omeprazole tablets in human saliva. The tablet composed of omeprazole/sodium alginate/HPMC/magnesium oxide/croscarmellose sodium (20/24/6/50/10 mg) could be attached on the human cheek without disintegration, and it enhanced the stability of omeprazole in human saliva for at least 4 h and gave fast release of omeprazole. The plasma concentration of omeprazole in hamsters increased to a maximum of 370 ng/ml at 45 min after buccal administration and continuously maintained a high level of 146–366 ng/ml until 6 h. The buccal bioavailability of omeprazole in hamsters was 13.7% ± 3.2%. These results demonstrate that the omeprazole buccal adhesive tablet would be useful for delivery of an omeprazole that degrades very rapidly in acidic aqueous medium and undergoes hepatic first-pass metabolism after oral administration.     

Physicochemical Characterization and Evaluation of Buccal Adhesive Tablets Containing Omeprazole

The objective of this study was to develop an effective omeprazole buccal adhesive tablet with excellent bioadhesive force and good drug stability in human saliva. The omeprazole buccal adhesive tablets were prepared with various bioadhesive polymers, alkali materials, and croscarmellose sodium. Their physicochemical properties, such as bioadhesive force and drug stability in human saliva, were investigated. The release and bioavailability of omeprazole delivered by the buccal adhesive tablets were studied. As bioadhesive additives for the omeprazole tablet, a mixture of sodium alginate and hydroxypropylmethylcellulose (HPMC) was selected. The omeprazole tablets prepared with bioadhesive polymers alone had bioadhesive forces suitable for a buccal adhesive tablet, but the stability of omeprazole in human saliva was not satisfactory. Among alkali materials, only magnesium oxide could be an alkali stabilizer for omeprazole buccal adhesive tablets due to its strong waterproofing effect. Croscarmellose sodium enhanced the release of omeprazole from the tablets; however, it decreased the bioadhesive forces and stability of omeprazole tablets in human saliva. The tablet composed of omeprazole/sodium alginate/HPMC/magnesium oxide/croscarmellose sodium (20/24/6/50/10 mg) could be attached on the human cheek without disintegration, and it enhanced the stability of omeprazole in human saliva for at least 4 h and gave fast release of omeprazole. The plasma concentration of omeprazole in hamsters increased to a maximum of 370 ng/ml at 45 min after buccal administration and continuously maintained a high level of 146-366 ng/ml until 6 h. The buccal bioavailability of omeprazole in hamsters was 13.7% ± 3.2%. These results demonstrate that the omeprazole buccal adhesive tablet would be useful for delivery of an omeprazole that degrades very rapidly in acidic aqueous medium and undergoes hepatic first-pass metabolism after oral administration.     

Fabrication of a composite vascular scaffold using electrospinning technology

Intermolecular forces and morphology demonstrated that there was an excellent compatibility between silk fibroin and gelatin. The silk fibroin/gelatin composite vascular scaffold (inner diameter 4.5 mm) was prepared successfully by electrospinning. The scaffold was treated with ethanol to enhance the water-resistant ability and biomechanical properties. After ethanol treatment, the scaffold could hardly dissolve in the water, and FTIR showed that the conformation of the treated silk fibroin/gelatin composite vascular scaffold was mainly β-sheets. The electrospun silk fibroin/gelatin vascular scaffold possessed outstanding biomechanical properties. In vitro cell culture and in vivo subcutaneous implantation demonstrated that the electrospun silk fibroin/gelatin vascular scaffold had an appropriate biocompatibility. The results indicated that the electrospun silk fibroin/gelatin composite vascular scaffold could be considered as an ideal candidate for tissue-engineered blood vessel.     

On the strength of β-sheet crystallites of Bombyx mori silk fibroin

Silk fibroin, a natural multi-domain protein, has attracted great attention due to its superior mechanical properties such as ultra-high strength and stretchability, biocompatibility, as well as its versatile biodegradability and processability. It is mainly composed of β-sheet crystallites and amorphous domains. Although its strength is well known to be controlled by the dissociation of protein chains from β-sheet crystallites, the way that water as the solvent affects its strength and the reason that its theoretically predicted strength is several times higher than experimental measurement remain unclear. We perform all-atom molecular dynamics simulations on a β-sheet crystallite of Bombyx mori silk. We find that water solvent reduces the number and strength of hydrogen bonds between β-chains, and thus greatly weakens the strength of silk fibroin. By dissociating protein chains at different locations from the crystallite, we also find that the pulling strength for the interior chains is several times higher than that for the surface/corner chains, with the former being consistent with the theoretically predicted value, while the latter on par with the experimental value. It is shown that the weakest rupture strength controls the failure strength of silk fibre. Hence, this work sheds light on the role of water in the strength of silk fibroin and also provides clues on the origin of the strength difference between theory and experiment.     

MWNTs/丝素/聚酰胺共混静电纺纳米纤维毡的结构和性能

静电纺再生丝素纤雏具有在水中易溶胀、结构稳定性和力学性能差等缺陷.在前期研究聚酰胺6/66对静电纺丝素纤维的结构和性能改进效果的基础上,以多壁碳纳米管(MWNTs)增强静电纺丝素/聚酰胺6/66复合纳米纤维.研究发现,随着MWNTs含量的增加复合纤维毡的颜色由白色变成黑色,纤维直径逐渐减小,并且都在90nm以下.MWNTs的加入,还有效地提高了纤维的结晶度、热稳定性以及纤维毡的拉伸力学性能.     

HPMC/KGM水溶性包装薄膜的制备及性能研究

目的以魔芋葡苷聚糖(KGM)为基体,加入羟丙基甲基纤维素(HPMC)改性制备水溶性包装薄膜,探索HPMC改性后其力学性能最佳时HPMC的质量分数。方法通过将HPMC,KGM依次加入去离子水中制备共混溶液,再采用流延法制备薄膜,调节HPMC质量分数,测试并分析对薄膜结构和性能的影响。结果随着HPMC质量分数的增加,薄膜的拉伸强度和断裂伸长率呈先增大后减小的趋势,存在最大值;其水溶性基本呈逐渐降低的趋势,水溶性降低的幅度不大,仍能满足水溶性包装的需求;透光度逐渐升高,雾度逐渐降低,有利于应用在包装中。结论 HPMC和KGM质量分数为1%的成膜液,在HPMC质量分数为总量的20%时,薄膜力学性能较好。     

纳米TiO_2改性丝素膜制备工艺优化及其性能研究

设计正交试验法并采用溶胶一凝胶法制备了性能良好纳米TiO2溶胶丝素复合膜,并利用SEM、FTIR及XRD等分析手段对丝素膜进行表征,结果表明:纳米TiO2均匀分散在丝素膜中,纳米TiO2与丝素分子相互作用,导致丝素分子的重排,并诱导丝素构象从Silk Ⅰ向SilkⅡ转变.     

丝素蛋白对胶原膜性能改善的研究

天然高分子由于其良好的生物相容性而受到广泛的关注。本研究用酶法自制了具有一定水溶性的猪皮胶原。尝试利用丝素和胶原蛋白各自的优点。用简单的溶液浇铸法制备了胶原-丝素共混膜。并通过FTIR、TGA、SEM等手段对其结构进行了表征。结果表明。由于共混膜中俩组份间存在的分子间作用力，加入小于50％的丝素的胶原膜经乙醇处理后与纯胶原膜相比。其力学性能及热稳定性有所的改善。通过改变丝素比例可以调整共混膜的吸水性。由于两组分良好的生物相容性，预料该共混膜可用作生物材料。     

The preparation of insoluble fibroin films induced by degummed fibroin or fibroin microspheres

Blending degummed fibroin (DF) or insoluble fibroin microspheres with concentrated fibroin solution, the insoluble films were obtained through drying the solution at 40–45 ^∘C. The conformation of silk fibroin films was analyzed by infrared spectrum and X-ray diffractometry. The results demonstrated that β-sheet conformation increased rapidly when the degummed silk or insoluble microspheres blended with fibroin, while the pure SF membrane was mainly composed of α/random coil conformation when the other conditions kept same. This suggested that fibroin microspheres and degummed fibroin could induce the formation of β-sheet crystal and the insoluble films, without methanol after-treatment, could be obtained at approximately room temperature. Although the fibroin films blending with DF had many protuberances, the films containing fibroin microspheres had the smooth surface and could be used effectively in biotechnological materials and biomedical application.     

Silk fibroin/chitosan scaffold: preparation,characterization, and culture with HepG2 cell

Tissue engineering requires the development of three-dimensional water-stable scaffolds. In this study, silk fibroin/chitosan (SFCS) scaffold was successfully prepared by freeze-drying method. The scaffold is water-stable, only swelling to a limited extent depending on its composition. Fourier Transform Infrared (FTIR) spectra and X-Ray diffraction curves confirmed the different structure of SFCS scaffolds from both chitosan and silk fibroin. The homogeneous porous structure, together with nano-scale compatibility of the two naturally derived polymers, gives rise to the controllable mechanical properties of SFCS scaffolds. By varying the composition, both the compressive modulus and compressive strength of SFCS scaffolds can be controlled. The porosity of SFCS scaffolds is above 95% when the total concentration of silk fibroin and chitosan is below 6 wt%. The pore sizes of the SFCS scaffolds range from 100 μm to 150 μm, which can be regulated by changing the total concentration. MTT assay showed that SFCS scaffolds can promote the proliferation of HepG2 cells (human hepatoma cell line) significantly. All these results make SFCS scaffold a suitable candidate for tissue engineering.     

Time-Dependent Mechanical Properties of Polymeric Coatings Used in Rupturable Pulsatile Release Dosage Forms

Abstract

The mechanical properties of polymer films used in pharmaceutical coatings of pulsatile drug delivery systems were evaluated in the dry and the wet state by a newly developed puncture test, which allowed the time-dependent measurement of the mechanical properties on the same film specimen. Force, puncture strength, energy at break, modulus, and strain were investigated as a function of water exposure time with respect to the type of polymer and the type and concentration of plasticizer and pore former (hydroxypropyl methylcellulose, HPMC). Eudragit® RS films were very flexible, had a high strain, and broke upon puncture with only small cracks. In contrast, ethylcellulose films were more brittle with a lower strain and showed complete film rupture. Increased amounts of the hydrophilic pore former, HPMC, resulted in a reduced puncture strength and in an increase in water uptake and weight loss of the films. The puncture strength decreased with increasing plasticizer concentration and was lower with the lipophilic dibutyl sebacate than with the hydrophilic triethyl citrate.     

Novel silk fibroin/hydroxyapatite composite films: Structure and properties

Novel composite films of Bombyx mori silk fibroin (SF) and hydroxyapatite (HA) composite films, with glycerin as an additive, were fabricated by means of co-precipitation, where the theoretical HA content was varied from 2 (w/w)% to 31 (w/w)%. The structure and properties of the composite films were investigated by SEM, XRD, AFM, TGA and tensile testing. The results showed that the composite films were smooth and transparent with the uniform distribution of HA into the composites when the final HA content was lower than 21 (w/w)%. XRD and TGA data showed that the silk fibroin in the composites was predominantly in a β-sheet crystalline structure, which was induced not only by the addition of glycerin, also by the HA crystal growth during the composite fabrication, leading to the thermal stable composite films. On the other hand, the HA crystals had the anisotropic growth with high extent of lattice imperfection and the preferential orientation along c-axis, probably promoted by the silk fibroin. The mechanical testing results showed that both break strain and stress were declined with the increase of HA content in the composites, presumably due to the original brittleness of HA compound.     

Time-dependent mechanical properties of polymeric coatings used in rupturable pulsatile release dosage forms

The mechanical properties of polymer films used in pharmaceutical coatings of pulsatile drug delivery systems were evaluated in the dry and the wet state by a newly developed puncture test, which allowed the time-dependent measurement of the mechanical properties on the same film specimen. Force, puncture strength, energy at break, modulus, and strain were investigated as a function of water exposure time with respect to the type of polymer and the type and concentration of plasticizer and pore former (hydroxypropyl methylcellulose, HPMC). Eudragit® RS films were very flexible, had a high strain, and broke upon puncture with only small cracks. In contrast, ethylcellulose films were more brittle with a lower strain and showed complete film rupture. Increased amounts of the hydrophilic pore former, HPMC, resulted in a reduced puncture strength and in an increase in water uptake and weight loss of the films. The puncture strength decreased with increasing plasticizer concentration and was lower with the lipophilic dibutyl sebacate than with the hydrophilic triethyl citrate.     

丝素共混膜的结构、性能及应用研究进展

丝素膜是一种性能优良、用途广泛的天然高分子生物材料、但纯丝素膜存在着在干燥情况下力学性能很差等缺点，这些缺点可以通过与其他高分子化合物共混得到改善，从而拓宽丝素膜的应用范围，综述了丝素与其它天然或合成高分子形成的共混膜的种类，结构、性能及应用发展状况。     

淀粉/PVA膜在血浆模拟液及唾液模拟液中的体外降解行为及相关体外生物相容性评价

通过熔融浇注法制备出一系列厚度在0.05 mm～0.10 mm的淀粉/聚乙烯醇（PVA）（SP）薄膜。研究了薄膜在血浆（SBF）及唾液模拟液（SSF）中的降解行为,分析了降解过程中力学性能、失重率、溶胀度、热性能以及表面形态的变化。研究结果表明,膜在30天的降解过程中能够维持良好的尺寸稳定性和一定的力学强度。通过细胞毒性、细胞贴壁及溶血试验表征了膜的体外生物相容性。结果表明,SP膜具有良好的细胞和血液相容性。所有测试结果证明,SP薄膜是一种应用于诱导组织再生薄膜的潜在材料。      

Bioadhesive Polymer Buccal Patches for Buprenorphine Controlled Delivery: Formulation, In-vitro Adhesion and Release Properties

A new bioadhesive polymer patch formulation for buprenorphine controlled delivery and consisting of polyisobutylene, polyisoprene, and Carbopol® 934P was prepared using a two-roll milling method. Carbopol® 934P was the bioadhesive of choice for the current formulation because it demonstrated a higher average peeling strength than hydroxypropyl methylcellulose, chitosan, or acacia as measured during in vitro testing. Other in vitro analyses showed that the milling process did not alter the viscosity or the thermodynamic and rheologic properties of polyisobutylene and polyisoprene. Nearly 75% of the buprenorphine was released from the patches following a 24 hour incubation in phosphate buffer (pH = 7). Data obtained from dissolution studies suggested that the major mechanism of buprenorphine release is patch swelling. It was also shown that patch adhesion increased with increasing thickness and up to three months of aging had little effect on adhesive properties. In addition, this formulation maintained the majority of its adhesive strength for at least 24 hours with a linear decline in average peeling load thereafter. In conclusion, buccal patches consisting of a homogeneous mixture of polyisobutylene, polyisoprene, and Carbopol® 934P formed by a two-roll milling process appear to possess physical properties that are well suited for the transmucosal controlled delivery of buprenorphine.     

纳米CaCO3/柞蚕丝素复合膜的制备及结构表征

制备了一种含有纳米CaCO3的新型柞蚕丝素蛋白膜,通过SEM、DSC、TG、XRD和IR研究了纳米CaCO3的加入对这种丝素蛋白膜性能的影响。SEM测试表明,纳米CaCO3粒子能均匀分散在丝素膜中不团聚;DSC测试表明,适量加入纳米CaCO3复合膜的Tm有所提高,但随着纳米CaCO3含量增加,Tm又有所降低;TG测试结果表明,随着纳米CaCO3加入量增加,复合膜的热稳定性得到提高;XRD测试结果表明,丝素结晶结构从silk I向silk II转化,结晶度得到提高。IR测试结果佐证了前面的推断。