Enzymatic degradation of the hydrogels based on synthetic poly(α-amino acid)s

Biodegradable hydrogels are studied as potential scaffolds for soft tissue regeneration. In this work biodegradable hydrogels were prepared from synthetic poly(α-amino acid)s, poly(AA)s. The covalently crosslinked gels were formed by radical copolymerization of methacryloylated poly(AA)s, e.g. poly[N ⁵-(2-hydroxy-ethyl)-l-glutamine-ran-l-alanine-ran-N ⁶-methacryloyl-l-lysine], as a multifunctional macro-monomer with a low-molecular-weight methacrylic monofunctional monomer, e.g. 2-hydroxyethyl methacrylate (HEMA). Methacryloylated copolypeptides were synthesized by polymerization of N-carboxyanhydrides of respective amino acids and subsequent side-chain modification. Due to their polypeptide backbone, synthetic poly(AA)s are cleavable in biological environment by enzyme-catalyzed hydrolysis. The feasibility of enzymatic degradation of poly(AA)s alone and the hydrogels made from them was studied using elastase, a matrix proteinase involved in tissue healing processes, as a model enzyme. Specificity of elastase for cleavage of polypeptide chains behind the l-alanine residues was reflected in faster degradation of l-alanine-containing copolymers as well as of hydrogels composed of them.     

Development of macropores in calcium carbonate body using novel carbonation method of calcium hydroxide/sodium chloride composite

Calcium carbonate is one of the bioceramics and has been used clinically as a bone substitute in dental and orthopedic surgery. Introduction of macropores into the bioceramics is highly recommended because those pores enable tissue ingrowth and accelerated osteointegration. We tried to prepare calcium carbonate body with macropores through the new carbonation method of calcium hydroxide/sodium chloride composite. Sodium chloride acted as a water-soluble porogen in developing macropores in calcium carbonate body and was removed completely by washing with distilled water after carbonation. We investigated effects of sodium chloride content and molding pressure on the porosity and the mechanical strength of the calcium carbonate body. Through this study, it was found that the porosity of body increased with the sodium chloride content in composite and was hardly affected by molding pressure. On the other hand, the mechanical strength was increased with the molding pressure and reduced with the porosity. In addition, the increase in content of sodium chloride caused the enlargement of hole size as well as the enhancement of extent of interconnection among pores through hole. Especially, the calcium carbonate body with over 90% porosity could be prepared when 90 wt.% sodium chloride was used under 10 MPa molding pressure. Its average pore and hole size were 177 and 80 μm, respectively.     

Fabrication of three dimensional polymeric scaffolds with spherical pores

This paper reports polymeric scaffolds with spherical internal macropores and relatively large external dimension. Paraffin spheres with the diameter of several hundred microns were prepared by a suspension technique. Particulate leaching technique based on this kind of spherical porogens was combined with room-temperature compression molding technique to fabricate biodegradable poly(D,L-lactic-co-glycolic acid) (PLGA) porous scaffolds potentially for tissue engineering or in situ tissue induction. The scaffolds exhibited ordered macropores with good pore interconnectivity. The porosity ranged from 80 to 97% adjusted simply by varying porogen content. The foams with porosity around 90% have compressive modulus over 3 MPa and compressive strength over 0.2 MPa. As preliminary cell experiments with 3T3 fibroblasts cultured on the porous scaffolds indicate, the processing procedure of the scaffolds has not brought with problem in cytotoxicity.     

Aerogels and polymorphism of isotactic poly(4-methyl-pentene-1)

Monolithic and highly crystalline aerogels of isotactic poly(4-methyl-pentene-1) (i-P4MP1) have been prepared by sudden solvent extraction with supercritical carbon dioxide from thermoreversible gels. The cross-link junctions of i-P4MP1 gels, depending on the solvent, can be constituted by pure polymer crystalline phases (I or III or IV) or by polymer-solvent cocrystalline phases (for cyclohexane and carbon tetrachloride gels). Gels with cocrystalline phases lead to aerogels exhibiting the denser crystalline form II, whereas all the other considered gels lead to aerogels exhibiting the thermodynamically stable form I. Aerogels obtained from form I gels, which do not undergo a crystalline phase transition during the CO(2) extraction process present the high structural stability most suitable for the preparation of porous membranes. The effect of solvents on the aerogel pore structure and morphology has been also investigated by scanning electron microscopy and N(2) sorption measurements. In all cases, the aerogels present highly porous interconnected structures with macropores and mesopores presenting a large size distribution and a vanishing presence of micropores.     

气体发泡剂—NaHCO3和C6H8O7对可注射多孔硼酸盐玻璃基骨水泥性能的影响

硼酸盐玻璃具有优异的生物相容性、降解性和骨传导性, 在骨组织修复领域受到一定的关注。目前, 硼酸盐玻璃的主要应用形式是支架和微球, 而有关硼酸盐玻璃基骨水泥的制备及性能研究却较少涉及。基于孔隙在骨组织修复材料工程领域中的重要作用, 本研究以NaHCO₃和柠檬酸为气体发泡剂制备可注射的多孔硼酸盐玻璃基骨水泥, 通过SEM、XRD和FTIR等方法表征其对骨水泥性能的影响。结果表明: 发泡骨水泥具有良好的注射性, 其注射率高达80%。SEM形貌照片显示骨水泥中大孔已被成功引入, 且孔隙连通, 其孔径介于10 µm到800 µm之间。浸泡结果表明, 发泡骨水泥失重率明显提高。PBS溶液中浸泡30 d后, 发泡骨水泥的失重率高达70%, 而非发泡的骨水泥的失重率只有50%。此外, XRD和FTIR的结果表明, 浸泡产物为羟基磷灰石(HA)。ATR的结果进一步证明了BBG和PBS溶液的反应机理, 表明BBGC中孔隙的引入大大加快了其降解, 促进了矿化反应的进行。     

多孔性聚酰亚胺纳米粒子的制备

介绍了用"再沉淀法"并经亚胺化成功制成PI(BPDA-PDA)多孔性粒子,粒径为几百nm;在此同时,加入与PAA(PI的先驱体)有较好相容性聚丙烯酸PAS为多孔源(porogen),而在其粒子表面生成较深的、较高空穴率的空穴,在20～100nm之间.这种多孔性PI纳米粒子可作为下一代低k值PI膜材料候选者之一.     

含氟聚合物纳米多孔纳米纤维膜的制备

采用"电纺-相分离-沥滤"方法制备了聚(偏氟乙烯-co-六氟丙烯)(PVDF-HFP)以及聚偏氟乙烯(PVDF)纳米多孔纳米纤维膜.首先,将PVDF-HFP或PVDF和致孔剂聚乙烯吡咯烷酮(PVP)混合电纺,得到共混物纳米纤维膜.然后,将纳米纤维膜在水中沥洗出共混物中的PVP,获得纳米多孔纳米纤维膜.用场发射扫描电子显微镜(FESEM)观察水洗前后纤维表面精细结构.结果表明,纳米多孔纳米纤维表面呈多孔结构,孔径数10 nm.PVP的分子量对水洗后纤维表面结构有明显影响.致孔剂含量不同获得的PVDF-HFP纳米多孔纤维膜力学性能相近.     

Densification of porous 8 mol% yttria-stabilized zirconia component: modelling and experimental studies

In this paper, the densification of a ceramic powder matrix that contained large macropores of the size much larger than the average grain size of the matrix was studied. The grain-boundary diffusion controlled sintering models of ceramic matrix contained large macropores were first established. A sintering potential associated with the macropores was also verified and introduced into the models. The experimental data were collected for the sintering of porous 8 mol% yttria-stabilized zirconia system with 20 vol% large pores. The predictions of the model were found in good agreement with experimental data.     

Introducing porosity into polyimide nanoparticles

Novel porous polyimides (PIs) having diameters of several hundred nanometers have been fabricated successfully from precursor poly(amic acid) (PAA) derivatives with poly(acrylic acid) (PAS) as the porogen, using a reprecipitation method and subsequent imidization. The superficial high porosity with deep pores was introduced when using a more compatible combination of PAA and the porogen, i.e., PI (BPDA-PDA) and PAS rather than PI (10FEDA-4FMPD and PAS); the pore sizes ranged from 20 to 100 nm. The resulting porous PI nanoparticles had thermally stabilities (determined from their 5% weight loss temperatures at 400 degrees C) similar to those of corresponding PI nanoparticles lacking porous structures. Microphase separation within the PAA nanoparticles after reprecipitation induced the porous surface structure, the properties of which were influenced by the molecular weight of PAS and the chemical structure of PAA. These unique porous PI nanoparticles have great potential for application as low-k materials in next-generation technologies.     

Synthesis and characterization of bioresorbable in situ crosslinkable ultra low molecular weight poly(lactide) macromer

Reactive low molecular weight poly(l-latide) (PLA) is required to produce in situ hardened scaffolds with fast rate of crosslinking, high crosslink density, and adequate mechanical strength. The objective of this work was to synthesize unsaturated ultra low moelcular weight PLA (ULMW PLA) as an injectable in situ crosslinkable macromer for biomedical applications. Low molecular weight PLA was synthesized by ring-opening polymerization of l-lactide (LA) using diethylene glycol (DEG) as the initiator. The molar ratio of the LA to DEG ranged from 5 to 20. Non-solvents methanol, ether, and hexane were used for purification and fractionation. The PLA samples that were precipitated in methanol and ether had narrow distributions (PDI = 1.2) and resulted in a powder with M_n of 4.8 and a wax with M_n of 3.6 kDa, respectively. The PLA sample in which the supernatant from ether was re-precipitated in hexane produced a viscous ULMW PLA with M_n and PDI of 1.2 kDa and 1.2, respectively. The ULMW PLA was reacted with fumaryl chloride to produce unsaturated in situ crosslinkable poly(lactide fumarate) (PLAF) macromer. Porous scaffolds were produced after injection and in situ crosslinking of the PLAF macromer with NVP crosslinker in the presence of a porogen. New bone was formed in the scaffold when it was implanted in nude mice which demonstrated that the scaffold was osteoconductive. PLAF is potentially useful as a reactive macromer in fabrication of bioresorbable injectable in situ crosslinkable scaffolds for tissue regeneration.     

The double porogen approach as a new technique for the fabrication of interconnected poly(L-lactic acid) and starch based biodegradable scaffolds

One of the most widely used fabrication methods of three dimensional porous scaffolds involves compression moulding of a polymer salt mixture, followed by salt leaching. However, the scaffolds prepared by this technique have typically limited interconnectivity. In this study, besides salt particles, an additional polymeric porogen, poly(ethylene oxide), PEO, was added to poly(L-lactic acid), PLLA, to enhance the interconnectivity of the scaffolds. Compression moulded specimens were quenched and put into water, where PEO crystallized and phase separated. Following the leaching of PEO fraction, the permeability and interconnectivity among the macropores formed by salt leaching could be observed. The porosities obtained in the prepared scaffolds were between 76 to 86%. Moreover, the highest porosity of 86% was obtained with minimum fraction of total porogen. The water absorption of the porous scaffolds prepared with PEO could vary between 280 to 450% while water uptake of pure PLLA scaffolds was about 93%. The increase of interconnectivity induced by compounding PLLA with PEO could also be obtained in porous PLLA/starch blends and PLLA/hydroxyapatite composites demonstrating the versatility and wide applicability of this preparation protocol. The simplicity of this organic solvent free preparation procedure of three-dimensional porous scaffolds with high interconnectivity and high surface area to volume ratio holds a promise for several tissue engineering applications.     

Fabrication of silica monolithic columns with ordered meso/macropore structure

Recently, much effort has been focused on the materials with ordered meso/macropores, because of their potential applications in catalysis, separations, coatings, microelectronics and electro-optics. In this paper, silica monoliths with well-defined columnar shape more than 1 cm in length are successfully fabricated by using the micelles of triblock copolymer F127 and colloidal crystals composed of polystyrene (PS) latex microspheres as mesopore and macropore template, respectively. The column templated by PS microspheres 870 nm in diameter and 0.5 g F127 (MCL-0.5-870) shows uniform ordered macropores, contact pores connecting macropores together, and assembled and inter-particle pores increasing the BET specific surface area and adsorption capability of the monolithic column. The backpressure curve and hydraulic permeability experiment exhibit its good penetrability and mechanical stability. These excellent characteristics, together with high BET specific surface area (387.4 m² g⁻¹) and porosity (80%), may endow its potential application for chromatography separation. In addition, the size of macropores and mesopores can be easily regulated by changing the diameter of PS spheres and F127 weight, respectively. This indicates that this method is a facile and universal protocol to fabricate the applied monolithic column with ordered meso/macropores.     

Development and characterization of reinforced poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactide) scaffolds for bone tissue engineering

Novel reinforced poly(l-lactic acid) (PLLA) scaffolds such as solid shell, porous shell, one beam and two beam reinforced scaffolds were developed to improve the mechanical properties of a standard PLLA scaffold. Experimental results clearly indicated that the compressive mechanical properties such as the strength and the modulus are effectively improved by introducing the reinforcement structures. A linear elastic model consisting of three phases, that is, the reinforcement, the porous matrix and the boundary layer was also introduced in order to predict the compressive moduli of the reinforced scaffolds. The comparative study clearly showed that the simple theoretical model can reasonably predict the moduli of the scaffolds with three phase structures. The failure mechanism of the solid shell and the porous shell reinforced scaffolds under compression were found to be buckling of the solid shell and localized buckling of the struts constructing the pores in the porous shell, respectively. For the beam reinforced scaffolds, on the contrary, the primary failure mechanism was understood to be micro-cracking within the beams and the subsequent formation of the main-crack due to the coalescence of the micro-racks. The biological study was exhibited that osteoblast-like cells, MC3T3-E1, were well adhered and proliferated on the surfaces of the scaffolds after 12 days culturing.     

亲/疏水改性温敏凝胶最新研究进展

温度敏感性聚异丙基丙烯酰胺凝胶是一类具有广泛应用前景的软湿材料,但存在功能单一、响应速率慢、粒度分布宽和机械性能差等缺点,因而温敏凝胶的化学和物理改性成为凝胶研究的热点之一。综述了近5年温敏凝胶的亲疏水改性的最新研究进展。     

Porous biomedical composite microspheres developed for cell delivering scaffold in bone regeneration

Microspherical particles have attracted great interest as a delivery system of tissue cells in regenerative engineering. For hard tissue regeneration, here we exploited porous biomedical composite microspheres of hydroxyapatite-polycaprolactone (HA-PCL). The pore channels within the microsphere was facilitated by using camphene as the porogen, where the initial HA-PCL-camphene mixture in chloroform was solidified and the camphene was then sublimed to leave pore channels within the HA-PCL microspheres. The pore size increased with increasing camphene concentration, resulting in the generation of macropores (> 50 μm). Rat bone marrow mesenchymal stem cells were shown to proliferate actively on the porous microspheres penetrating deeply into the pore channels. Results suggest future applications of the porous composite microsphere as a cell delivery scaffold for bone tissue regeneration.     

One-pot synthesis of hierarchically macro/mesoporous Al2O3 monoliths from a facile sol–gel process

Based on the preparation of ordered mesoporous Al₂O₃ powder using P123/isopropoxide aluminum/HNO₃ reaction system, hierarchically macro/mesoporous alumina monoliths were successfully fabricated by introducing PEG8000 as the phase-segregation initiator to generate macropores. The effects of PEG8000 and P123 contents on the monolithic and hierarchical morphology were investigated systematically. With appropriate selection of the starting composition, monolithic skeletons with bimodal macropores interconnected by mesostructured walls can be synthesized in both the dried gels and calcined samples. The well-defined macropores are in close-celled structure dispersed in large-sized mesoporous matrix. The mesopore size can be regulated by adjusting the PEG8000 content while its shape is governed by P123 content. The well-developed alumina monolith, MMA-P20, exhibits high surface area of 287 m²/g and narrowly distributed mesopores with median size of 13 nm after calcinaton.     

Synthesis and characterization of nanoporous silica using dendrimer molecules

A water soluble porogen, e.g., poly(amido amine) dendrimer, has been used as a structure-directing agent to introduce porosity of nanometer scale in silica-based nanocomposite materials. Hydrothermal synthesis was carried out at different elevated temperatures (343-413 K) in a closed teflon-lined stainless steel autoclave under autogenerated pressure. The synthesis time varied from 2 to 6 days, depending upon pH, synthesis temperature, concentration of porogen, etc. X-ray diffraction, transmission and scanning electron microscopic analyses, as well as infrared absorption spectroscopic measurements, were carried out to characterize these materials. Mostly disordered mesostructures were observed. The porous silica particles with sphere-like morphology varied from 30 to 200 nm in size were prepared depending upon the conditions of preparation. The structure and nanoporosity were preserved after the removal of structure-directing porogen through calcination at 823 K. The pore size was in the range of the dendrimer molecule as a template, indicating the structure-directing role of the terminal amino groups in the dendrimer molecule for the synthesis of nanoporous silica, since the nanoporous silica could be prepared by the hydrogen bonding or electrostatic interaction of dendrimer amino groups and tetraethyl orthosilicate.     

Bending strength of silica gel with bimodal pores: II. Effect of variations in morphology and porosity

The bending strength of amorphous silica gels with bimodal pore structure was evaluated by changing macropore morphology and porosity, where the macropore morphology was controlled by inducing phase separation during gelation of silicate solution and the porosity was controlled by changing aging conditions and calcination temperature. At the same porosity, the bending strength was decreased for gels with larger macropores. In this preparation of bimodal porous silica gels, however, samples with large macropores also had many small particles in the macropores. Therefore, the decrease in bending strength with increasing macropore size was attributed to the presence of the particles that contributed to increasing bulk density but not bending strength. A power law applies to the bending strength and the bulk density of gels with the same macropore morphology, where the exponent depends on the morphology.     

Porogen residues detection in optical properties of low-k dielectrics cured by ultraviolet radiation

The optical properties of low dielectric constant (low-k) films have been determined by variable angle spectroscopic ellipsometry in the range from 2 eV to 9 eV to characterize the process of porogen removal during the UV-cure. The studied carbon doped oxide (SiCOH) porous dielectric films have been prepared by plasma enhanced chemical vapor deposition. The films have been deposited as a composition of a matrix precursor and an organic porogen. After deposition, the films have been cured by thermal annealing and UV irradiation (λ = 172 nm) to remove the porogen and create a porosity of 33%, reaching a dielectric constant of 2.3. The process of porogen decomposition and removal has been studied on series of low-k samples, UV-cured for various times. Additional samples have been prepared by the deposition and curing of the porogen film, without SiCOH matrix, and the matrix material itself, without porogen. The analysis of the optical response of the porous dielectric as a mixture of matrix material, porogen and voids, together with Fourier transform infrared analysis, allows the sensitive detection of the volume of the porogen and indicates the existence of decomposed porogen residues inside the pores, even for long curing time. The variation of the deposition and curing conditions can control the amount of the porogen residues and the final porosity.     

大孔钙铝石块体材料的制备及表征

以无机盐二水氯化钙(CaCl₂·2H₂O)和六水氯化铝(AlCl₃·6H₂O)为原料, 1,2-环氧丙烷(PO)为凝胶促进剂, 粘均分子量M_w= 100000的聚氧化乙烯(PEO)为相分离诱导剂, 乙二醇为络合剂, 甲酰胺为干燥控制化学添加剂(DCCA), 采用溶胶-凝胶伴随相分离制备了大孔钙铝石块体。利用扫描电镜(SEM)、压汞、X射线衍射(XRD)等测试技术对所得的块体进行了表征。结果表明: 加入PEO能诱导体系发生相分离; PEO用量和溶剂中醇水比会对多孔结构产生明显影响; 在合适凝胶温度下, 当加入适量PEO和溶剂时, 可以获得共连续大孔结构的钙铝石块体; 1000℃热处理后, 干凝胶由无定型转变为钙铝石晶型Ca₁₂Al₁₄O₃₂Cl₂, 块体的共连续大孔结构在热处理后被完整保留, 其大孔孔径分布在1~2 μm, 孔隙率为73.0%; 热处理前后的钙铝石块体均能保持光滑且致密的骨架。