Preparation and characterization of novel multi-core chitosan microspheres for stomach-specific delivery of hydrophilic antibiotics

Insufficient gastric mucosa drug concentration and short contact time were the main reason for the lack of eradication efficacy of Helicobacter pylori for peptic ulcer patients. Novel multi-core chitosan microspheres were prepared for stomach-specific delivery of hydrophilic antibiotics for the treatment of peptic ulcer. Chitosan microspheres with multiple Eudragit L100 cores were easily prepared by a new emulsification/coagulation encapsulating method. Swelling behaviors, surface amino groups and mucin absorption ability were investigated and the formulation that showed best mucoadhesive potential was adopted. The multi-core chitosan microspheres exhibited good mucoadhesiveness as well as controlled release manner for incorporated antibiotics in acidic environment. The release rate could be easily modulated with accumulative release ranging from 47.3 to 79.3% in 6 h. Accordingly, the multi-core chitosan microspheres could serve as a satisfactory vehicle for stomach-specific delivery of hydrophilic antibiotics.     

Preparation and characterization of nano-hydroxyapatite/polymer composite scaffolds

Polycaprolactone/chitosan (PCL/CS) porous composite scaffolds were prepared by solution phase separation method, and the scaffolds were further enhanced by filling with nano-hydroxyapatite/polyvinyl alcohol (n-HA/PVA) composite slurry to prepare n-HA-PVA/PCL-CS composite porous scaffolds through slurry centrifugal filling technique. The morphology, microstructure, component, porosity and mechanical property of the scaffolds were characterized using scanning electron microscope, X-ray diffraction, Fourier transform infrared spectroscope, elemental analyzer and material test machine. The results show that PCL/CS scaffolds have mutual transfixion porous structure just like honeycombs. The porosity of the scaffolds can achieve 60-80%. As the content of CS increases, the porosity increases while the compressive strength decreases. After filled with HA/PVA composite slurry, the porosity of n-HA/PCL-CS composite scaffolds decreases, but still greater than 60%, while the compression modulus can increase to 25.7 MPa.     

In situ synthesis and characterization of porous polymer-ceramic composites as scaffolds for gene delivery

The use of three-dimensional scaffolds in gene delivery has emerged as a popular and necessary delivery vehicle for obtaining controlled gene delivery. In this report, techniques to synthesize composite scaffolds by combining natural polymers such as agarose and alginate with calcium phosphate (CaP) are described. The incorporation of CaP into the agarose or alginate hydrogels was performed in situ and the presence of CaP was confirmed by X-ray diffraction (XRD). The crystallite size of the CaP particles was determined to be 7.20 nm. Lyophilized, porous composites were examined under scanning electron microscopy (SEM) to estimate the size of the pores, an essential requirement for an ideal scaffold. The swelling properties of the composite samples were also investigated to study the effect of CaP incorporation on the behavior of the hydrogels. By incorporating CaP into the hydrogel, the aim is to synthesize a scaffold that is mechanically strong and chemically suitable for use as a gene delivery vehicle in tissue engineering.     

Preparation and characterization of genipin-crosslinked rat acellular spinal cord scaffolds

The feasibility of rat acellular spinal cord scaffolds for tissue engineering applications was investigated. Fresh rat spinal cords were decellularized and crosslinked with genipin (GP) to improve their structural stability and mechanical properties. The GP-crosslinked spinal cord scaffolds possessed a porous structure with an average pore diameter of 31.1 μm and a porosity of 81.5%. The resultant scaffolds exhibited a water uptake ratio of 229%, and moderate in vitro degradation rates of less than 5% in phosphate-buffered saline (PBS) and slightly more than 20% in trypsin-containing buffer, within 14 days. The ultimate tensile strength and elastic modulus of GP-crosslinked spinal cord scaffolds were determined to be 0.193 ± 0.064 MPa and 1.541 ± 0.082 MPa, respectively. Compared with glutaraldehyde (GA)-crosslinked acellular spinal cord scaffolds, GP-crosslinked scaffolds demonstrated similar microstructure and mechanical properties but superior biocompatibility as indicated by cytotoxicity evaluation and rat mesenchymal stem cell (MSC) adhesion behavior. Cells were able to penetrate throughout the crosslinked scaffold due to the presence of an interconnected porous structure. The low cytotoxicity of GP facilitated cell proliferation and extracellular matrix (ECM) secretion in vitro on the crosslinked scaffolds over 7 days. Thus, these GP-crosslinked spinal cord scaffolds show great promise for tissue engineering applications.     

Preparation and characterization of bioactive collagen/wollastonite composite scaffolds

A novel biodegradable collagen/wollastonite composite was prepared as three-dimensional scaffolds by freeze-drying method. Scanning electron microscope (SEM) micrographs of scaffolds showed a continuous structure of interconnected pores, and pore size was about 100 m. The tensile strength of the scaffolds was improved by incorporation of wollastonite and the in vitro bioactivity of the scaffolds was evaluated by examining the hydroxyapatite (HA) deposition on their surface in simulated body fluid (SBF). After soaking in SBF for 7 days, collagen reconstituted to fibers and HA nodules formed on collagen fibers. The result suggests that the incorporation of wollastonite could improve the mechanical strength and the in vitro bioactivity of the composite. The scaffolds could be a potential biomaterial for bone tissue engineering.     

Preparation and characterization of thermosensitive submicron particles for gene delivery

In this study, a new thermosensitive material was proposed as a carrier for gene delivery. The thermosensitive submicron particles were synthesized by the dispersion copolymerization of N-isopropylacylamide (NIPA) with a relatively new, cationic comonomer, N-3-dimethylaminopropylmethacrylamide (DMAPM) with higher ionization ability with respect to the commonly used cationic comonomers. To achieve particle sizes smaller than 1 microm, suitable for gene delivery, the total monomer concentration in the dispersion copolymerization was kept at a sufficiently low level. The size of poly(NIPA-co-DMAPM) particles was determined as 454 nm, by AFM in dry state. The poly(NIPA-co-DMAPM) particles showed both temperature and pH sensitivity in the aqueous media.The plasmid DNA adsorption onto the thermosensitive cationic particles was investigated at different temperatures and pHs. The adsorbed amount of plasmid DNA onto the particles was significantly increased by the introduction of cationic comonomer. The equilibrium plasmid DNA adsorptions up to 13 mg/g dry particles were achieved at physiological pH. Approximately 36% w/w of adsorbed plasmid could be desorbed from the cationic nanolatex. The results of biocompatibility studies performed with mouse fibroblast cells showed the suitability of thermosensitive cationic particles for intended application.     

Preparation and characterization of macroporous chitosan/wollastonite composite scaffolds for tissue engineering

Chitosan/wollastonite composite scaffolds were prepared by a thermally induced phase separation method. The microstructure, mechanical performance and in vitro bioactivity of the composite scaffolds were investigated. The composite scaffolds were macroporous and wollastonite particles were dispersed uniformly on the surface of the pore walls. Scanning electron microscope images of the composite scaffolds demonstrated that the scaffolds had interconnected pores with diameters from 60 to 200 microm. Both the pore size and structure were affected by freezing temperature. The mechanical performance of the composite scaffolds was improved compared to that of pure chitosan scaffolds. The in vitro bioactivity of the scaffolds was evaluated by soaking samples in simulated body fluid and the apatite layer was observed on the surface of the pore walls of the composite scaffolds. Our results suggest that the incorporation of wollastonite into chitosan could enhance both the mechanical strength and the in vitro bioactivity of the resultant composite. The macroporous chitosan/wollastonite scaffolds may be a potential candidate for application in tissue engineering.     

羟基磷灰石基多孔复合支架的制备及其表征

研究利用造孔剂法制备高度贯通的多孔羟基磷灰石(HA)支架,孔隙率约为78%,并利用聚己内酯(PCL)分别复合纳米HA(nHA)或微纳米生物玻璃(nBG)粉末对其进行涂覆改性,粉末的添加量均为10%~40%(质量分数)。4种类型支架分别记为HA、PCL/HA、nHA-PCL/HA和nBG-PCL/HA。实验结果发现,nHA-PCL/HA和nBG-PCL/HA复合支架最大抗压强度分别为1.41~1.98 MPa和1.35~1.78MPa。4类支架矿化实验显示,浸泡21d后nBG-PCL/HA表面促进生成较多的磷灰石矿化物;细胞实验结果显示细胞在4类支架上均生长良好,说明支架具有良好的生物相容性。支架在实验犬背部肌肉组织内植入2个月的组织学检测显示,4种支架内均有新骨形成,尤其是nHA-PCL/HA和nBG-PCL/HA孔内有更多的新生骨组织,说明这两种支架表面复合涂层中的生物活性纳米颗粒对诱导新骨生成具有积极的促进作用。     

N-组氨酸壳聚糖/左旋聚乳酸支架的制备及表征

在冷冻诱导相分离制备N-组氨酸壳聚糖支架(NHCS)的基础上进行二次相分离,利用不同取代度的NHCS和不同N-组氨酸壳聚糖/聚乳酸质量比制备一系列N-组氨酸壳聚糖/聚乳酸(NHCS/PLLA)支架。通过红外光谱、广角X射线衍射、热分析和扫描电镜等来表征NHCS/PLLA支架。结果表明,同一种N-组氨酸壳聚糖支架(50kD-NHCS-3),N-组氨酸壳聚糖/聚乳酸质量比减小,支架孔隙率减小,密度增大。支架材料的孔尺寸约在12~25μm,孔隙率均大于92%,抗压强度和弹性模量分别在0.33~0.78 MPa和1.75~5.28 MPa之间,有望适用于软骨组织工程支架。     

静电纺丝制备壳聚糖/聚己内酯血管支架及表征

结合壳聚糖(CS)和聚己内酯(PCL)二者的优点, 以静电纺丝的方法制备了CS/PCL血管支架。采用SEM和电子万能试验机检测了该支架的结构和力学性能, 将内皮祖细胞(EPCs)与该支架膜复合培养, 评估了该血管支架维持细胞黏附、 繁殖和分化的能力。SEM结果显示: 通过静电纺丝可以得到多孔、 类似于天然细胞外基质的直径约400nm的纤维微结构; 当CS与PCL质量比为0.5时, 静电纺丝所制备的CS/PCL血管支架弹性最大形变达到31.64%, 应力-应变曲线显示其弹性变形能力较强; EPCs在CS/PCL血管支架黏附率可达95.1%, 荧光显微镜观察结果也显示了CS/PCL血管支架利于细胞黏附、 生长。      

Preparation and characterization of 2,3-dialdehyde bacterial cellulose for potential biodegradable tissue engineering scaffolds

Bacterial cellulose (BC) is suitable for applications as scaffolds in tissue engineering due to its unique properties. However, BC is not enzymatically degradable in vivo and this has become an essential limiting factor in its potential applications. In this work, BC was modified by periodate oxidation to give rise to a biodegradable 2,3-dialdehyde bacterial cellulose (DABC). After characterization by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), attenuated total reflectance–Fourier transform infrared (ATR–FTIR) spectroscopy, thin-film X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS), we demonstrated that the modified DABC nano-network was able to degrade into porous scaffold with micro-sized pores in water, phosphate buffered saline (PBS) and the simulated body fluid (SBF). The degradation process began from the oxidized amorphous part of the network and concurrently hydroxyapatite formed on the scaffold surface during the process in SBF. Our data also demonstrated that the tensile mechanical properties of the DABC nano-network were suitable for its use in tissue engineering scaffolds.     

Preparation and characterization of chitosan/galactosylated hyaluronic acid scaffolds for primary hepatocytes culture

Hepatocyte-specific three-dimensional tissue-engineeringed scaffold plays an important role for developing bioartificial liver devices. In the present study, galactose moieties were covalently coupled with hyaluronic acid through ethylenediamine. Highly porous sponge composed of chitosan (CS) and galactosylated hyaluronic acid (GHA) was prepared by freezing-drying technique. The morphology of the scaffolds was observed via scanning electron microscopy. Porosity and pore size of the sponge were greatly dependent on the content of GHA and freezing temperature. The addition of GHA not only improved the wettability and changed their mechanical properties, but also significantly influenced the cell attachment ratio. Moreover, liver functions of the hepatocytes such as albumin secretion, urea synthesis and ammonia elimination in the CS/GHA scaffolds were improved in comparison with those in the chitosan scaffolds.     

Surface and adsorption characteristics of three elastin-like polypeptide coatings with varying sequence lengths

The surface properties of a family of elastin-like polypeptides (ELPs), differing in molecular weight and sequence length, were investigated to understand how the nature of the polypeptide film might contribute to their thrombogenic profile. Physical adsorption of the ELPs onto Mylar increased surface wettability as the sequence length decreased while X-ray spectroscopy analysis showed an increasing amide content with sequence length. Chemical force microscopy analysis revealed that the ELP-coated surfaces displayed purely hydrophilic adhesion forces that increased as the ELP sequence length decreased. Adsorption isotherms performed using the quartz crystal microbalance with dissipation, showed that the surface coverage increased with ELP sequence length. The longer polypeptides (ELP2 and ELP4) also displayed higher specific dissipation values indicating that they established films with greater structural flexibility and associated water content than the shorter polypeptide, ELP1. Additionally, the stability of the ELP coating was lower with the shorter polypeptides. This study highlights the different surface properties of the ELP coatings as well as the dynamic nature of the ELP adsorbed layer wherein the conformational state may be an important factor contributing to their blood response.     

可注射海藻酸钙水凝胶的制备研究

海藻酸钙水凝胶因其良好的生物相容性广泛应用于组织工程支架材料的研究。以海藻酸钠(SA),碳酸钙,葡萄糖酸内酯(GDL)为原料,通过原位相转变制备可注射凝胶,用于软骨组织微创修复材料的研究。测定了单一变量条件下不同海藻酸钠浓度、f值(钙离子与羧基的摩尔比)及n值(葡萄糖酸内酯与钙离子的摩尔比)对海藻酸凝胶力学强度、溶胀率、浸提液pH值等的影响,从而获得各组分最适的配比;另外,通过原位接种软骨细胞,研究了软骨细胞在凝胶中的生长行为。综合海藻酸钙凝胶性能,最终确定海藻酸钠浓度为2.5%、f=0.5及n=0.6为最佳配比;细胞培养结果表明软骨细胞在凝胶中具有较高的活性且维持了其软骨细胞形态,证实了研究制得的海藻酸钙水凝胶是一种优良的可注射软骨组织工程支架材料。     

Preparation,characterization and cytocompatibility of bioactive coatings on porous calcium-silicate-hydrate scaffolds

The major goal of this research was to investigate and characterize the deposition of a biomimetic apatite-like coating onto the surface of 3D porous calcium-silicate-hydrate scaffolds with suitable bioactivity for potential application in bone tissue engineering. Basically, Portland cement, water, sand and lime were mixed for preparing the slurry which was poured into molds, and fine aluminum powder was added as foaming agent resulting on the formation of porous 3D structures. After aging for 28 days, these porous inorganic scaffolds were immersed in calcium chloride supersaturated solution in PBS for 7 days at 37 °C for the biomimetic layer deposition. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier Transformed Infrared Spectroscopy (FTIR) techniques were used in order to characterize the porous scaffolds and the apatite-like biomimetic coating. The results have showed that 3D constructs were successfully produced with interconnected porosity, compressive strength and cytocompatibility appropriate for potential use as an alternative in trabecular bone repair.     

Preparation and characterization of a novel COL/BC composite for potential tissue engineering scaffolds

This paper describes the biosynthesis of a novel collagen-bacterial cellulose (COL/BC) composite by adding collagen to the culture medium of Acetobacter xylinum. The morphology of COL/BC composite was observed by SEM and TEM and compared with pristine BC. The composite was further characterized by FTIR and XRD. It is found that the structure of BC network changes when collagen is present in the nutrient medium. Further work is underway to gain insights into the mechanisms governing the experimental phenomena.     

Preparation and characterization of polycaprolactone/forsterite nanocomposite porous scaffolds designed for bone tissue regeneration

Biocomposite scaffolds made from polymers and bioceramics can provide the mechanical structure necessary for osteoinductivity in the growth of new bone. The aim of this research was to investigate the properties of a novel nanocomposite scaffold made from a combination of polycaprolactone (PCL) and forsterite nanopowder which could find use in bone tissue engineering applications. The scaffold itself was fabricated by a method of solvent casting and particle leaching. The effect of forsterite content on the mechanical properties, bioactivity, biodegradability, and cytotoxicity of the scaffolds was investigated. Significant improvement in the mechanical properties was observed in the nanocomposite scaffolds as compared to that seen in the pure PCL scaffolds. Bioactivity was also observed in the nanocomposite scaffolds, a trait which was not present in the pure PCL scaffolds. Biodegradation assay indicated that the addition of forsterite nanopowder could modulate the degradation rate of PCL. In vitro tests of cytotoxicity and osteoblast proliferation showed that the nanocomposite scaffolds were non-cytotoxic, thereby allowing cells to adhere, grow, and proliferate on the surface of these scaffolds. The results obtained in this experiment suggest that the combination of PCL with forsterite nanopowder can be used to form scaffolds suitable for use in bone tissue engineering. The exact material behavior required can be adjusted through variation of the ratio between PCL and forsterite nanopowder used to form the scaffold.     

Preparation and in vitro characterization of pluronic-attached polyamidoamine dendrimers for drug delivery

Context: Polyamidoamine (PAMAM) dendrimers have attracted lots of interest as drug carriers. And little study about whether pluronic-attached PAMAM dendrimers could be potential drug delivery systems has been carried on.

Objective: Pluronic F127 (PF127) attached PAMAM dendrimers were designed as novel drug carriers.

Methods: Two conjugation ratios of PF127-attached PAMAM dendrimers were synthesized. ¹H nuclear magnetic resonance (¹H-NMR), Fourier transform infrared spectrum (FTIR), element analysis and ninhydrin assay were used to characterize the conjugates. Size, zeta potential and critical micelle concentrations (CMC) were also detected. And DOX was incorporated into the hydrophobic interior of the conjugates. Studies on their drug loading and drug release were carried on. Furthermore, hemolysis and cytotoxicity assay were used to evaluate the toxicity of the conjugates.

Results and discussion: PF127 was successfully conjugated to the fifth generation PAMAM dendrimer at two molar ratios of 19% and 57% (PF127 to surface amine per PAMAM dendrimer molecular). The conjugates showed an increased size and a reduced zeta potential. And higher CMC values were obtained than pure PF127. Compared with unconjugated PAMAM dendrimer, PF127 conjugation significantly reduced the hemolytic toxicity and cytotoxicity of PAMAM dendrimer in vitro. The encapsulation results showed that the ability to encapsulate DOX by the conjugate of 19% conjugation ratio was better than that of 57% conjugation ratio. And the maximum is ～12.87 DOX molecules per conjugate molecule. Moreover, the complexes showed a sustained release behavior compared to pure DOX.

Conclusion: Findings from the in vitro study show that the PF127-attached PAMAM dendrimers may be potential carriers for drug delivery.     

Preparation and characterization of amidated pectin based hydrogels for drug delivery system

In the current studies attempts were made to prepare hydrogels by chemical modification of pectin with ethanolamine (EA) in different proportions. Chemically modified pectin products were crosslinked with glutaraldehyde reagent for preparing hydrogels. The hydrogels were characterized by Fourier transform infrared spectroscopy (FTIR), organic elemental analysis, X-ray diffraction studies (XRD), swelling studies, biocompatibility and hemocompatibility studies. Mechanical properties of the prepared hydrogels were evaluated by tensile test. The hydrogels were loaded with salicylic acid (used as a model drug) and drug release studies were done in a modified Franz’s diffusion cell. FTIR spectroscopy indicated the presence of primary and secondary amide absorption bands. XRD studies indicated increase in crystallinity in the hydrogels as compared to unmodified pectin. The degree of amidation (D _A) and molar and mass reaction yields (Y _M and Y _N) was calculated based on the results of organic elemental analysis. The hydrogels showed good water holding properties and were found to be compatible with B-16 melanoma cells & human blood.     

Preparation and characterization of PEG-modified polyurethane pressure-sensitive adhesives for transdermal drug delivery

Background: The purpose of this work was to develop novel pressure-sensitive adhesives (PSAs) for transdermal drug-delivery systems (TDDS) with proper adhesive properties, hydrophilicity, biocompatibility and high drug loading. Method: Polyethyleneglycol-modified polyurethane PSAs (PEG-PU-PSAs) were synthesized by prepolymerization method with PEG-modified co-polyether and hexamethylene diisocyanate. The effects of reaction temperature, catalyst, ratios of NCO/OH, co-polyether composition, and chain extender were investigated. Drug loading was studied by using thiamazole (hydrophilic drug), diclofenac sodium (slightly hydrophilic drug), and ibuprofen (lipophilic drug) as model drugs. In vitro drug-release kinetics obtained with Franz diffusion cell and dialysis membrane. Results: The results showed that when reaction temperature at 80°C, weight percentage of stannous octoate as catalyst at 0.05%, ratio of NCO/OH at 2.0–2.2, ratio of PEG/polypropylene glycol (PPG)/polytetramethylene ether glycol (PTMG) at 30/25–30/50–55, and weight percentage of glycol as chain extender at 4.5%, PEGPU-PSAs synthesized performed well on adhesive properties. Actually, PEG on the main chain of the PU could improve the hydrophilicity of PSAs, whereas PPG and PTMG could offer proper adhesive properties. Skin compatibility test on volunteers indicated that PEG-PU-PSAs would not cause any skin irritations. All the model drugs had excellent stabilizations in PEG-PU-PSAs. In vitro drug-release kinetics demonstrated that the drug release depended on drug-loading level and solubility of the drug. Conclusion: These experimental results indicated that PEG-PU-PSAs have good potential for applications in TDDS.