Chitosan/gelatin porous bone scaffolds made by crosslinking treatment and freeze‐drying technology: Effects of crosslinking durations on the porous structure,compressive strength,and in vitro cytotoxicity

In this study, freezing was used to separate a solute (polymer) and solvent (deionized water). The polymer in the ice crystals was then crosslinked with solvents, and this diminished the linear pores to form a porous structure. Gelatin and chitosan were blended and frozen, after which crosslinking agents were added, and the whole was frozen again and then freeze‐dried to form chitosan/gelatin porous bone scaffolds. Stereomicroscopy, scanning electron microscopy, compressive strength testing, porosity testing, in vitro biocompatibility, and cytotoxicity were used to evaluate the properties of the bone scaffolds. The test results show that both crosslinking agents, glutaraldehyde (GA) and 1‐ethyl‐3‐(3‐dimethylaminopropyl) carbodiimide, were able to form a porous structure. In addition, the compressive strength increased as a result of the increased crosslinking time. However, the porosity and cell viability were not correlated with the crosslinking times. The optimal porous and interconnected pore structure occurred when the bone scaffolds were crosslinked with GA for 20 min. It was proven that crosslinking the frozen polymers successfully resulted in a division of the linear pores, and this resulted in interconnected multiple pores and a compressively strong structure. The 48‐h cytotoxicity did not affect the cell viability. This study successfully produced chitosan/gelatin porous materials for biomaterials application. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41851.     

Porous poly(2-hydroxyethyl acrylate) hydrogels prepared by radical polymerisation with methanol as diluent

Dynamic-mechanical and water sorption properties of porous and non-porous hydrogels have been studied as a function of their porosity and crosslinking density. Porous hydrogels with different crosslinking densities were prepared by co-polymerisation of 2-hydroxyethyl acrylate and ethyleneglycol dimethacrylate in solution in methanol. Pores were formed due to the segregation of the solvent from the polymer network during the polymerisation process. The porosity of the samples was observed by scanning electron microscopy. The pores collapse during the drying process after polymerisation but they reopen when the xerogel is immersed in liquid water. Bulk polymer networks with varying crosslinking densities were also synthesised and used as a reference in the analysis of the porous hydrogels. Water sorption from the gas phase and from the liquid phase was studied by means of equilibrium sorption isotherms and immersion experiments, respectively. Dynamic-mechanical spectroscopy conducted on the xerogels shows that the elastic modulus in the rubber-like state highly depends on the amount of solvent used in the polymerisation what is attributed to the presence of discontinuity surfaces in the xerogel although the pores are closed.     

Preparation of interconnected poly(ε-caprolactone) porous scaffolds by a combination of polymer and salt particulate leaching

This paper examines a new technique for the preparation of porous scaffolds by combining selective polymer leaching in a co-continuous blend and salt particulate leaching. In the first step of this technique, a co-continuous blend of two biodegradable polymers, poly(ε-caprolactone) (PCL) and polyethylene oxide (PEO), and a certain amount of sodium chloride salt particles are melt blended using a twin screw extruder. Subsequently, extraction of the continuous PEO and mineral salts using water as a selective solvent yields a highly porous PCL scaffold with fully interconnected pores. Since, the salt particles and the co-continuous polymer blend morphology lead to very different pore sizes, a particular feature of this technique is the creation of a bimodal pore size distribution. Scanning electron microscopy, mercury intrusion porosimetry and laser diffraction particle size analysis were carried out to characterize the pore morphology. The prepared scaffolds have relatively homogeneous pore structure throughout the matrix and the porosity can be controlled between 75% and about 88% by altering the initial volume fraction of salt particles and to a lesser extent by changing the PCL/PEO composition ratio. Compared to the conventional salt leaching technique and to its different variants, the proposed process allows a better interconnection between the large pores left by the salt leaching and a fully interconnected porous structure resulting from the selective polymer leaching. The average compressive modulus of the different porous scaffolds was found to decrease from 5.2 MPa to about 1 MPa with increasing porosity, according to a power-law relationship. Since, the blending and molding of the scaffold (prior to leaching) can be made using conventional polymer processing equipment, this process seems very promising for a large scale production of porous scaffold of many sizes and in an economic way.     

A simple and effective approach to produce tubular polysaccharide-based hydrogel scaffolds

The production of porous tubular scaffolds is of great interest in the field of tissue engineering, given the existence of several tubular structures in the human body. In this work, a methodology was developed for the fabrication of tubular-shaped scaffolds based on the casting of polymeric solutions by controlled crosslinking mediated by a semipermeable cast. The fabrication of hydrogel tubular scaffolds from chitosan–pectin polymeric mixtures (tCh-P, 3% w/v) was performed to attest the feasibility of the technique. Tubular structures with about 4.15 mm internal diameter and 1.55 mm wall thickness were produced. The structures are highly porous, presenting interconnected pores with average diameter of about 360 μm. Seeding of human smooth muscle cells on the material was successfully achieved by using collagen gel to facilitate cell migration and retention inside the structure of the scaffold. The methodology herein proposed was successfully validated for the production of tubular constructs, opening new perspectives for the fabrication of matrices based on polymers that are passive of crosslinking with small molecules. Besides being an interesting approach to produce tubular scaffolds, this methodology can be considered an useful platform to obtain materials for drug screening and diagnostic studies. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48510.     

Fabrication and characterization of three-dimensional macroscopic all-carbon scaffolds

We report a simple method to fabricate macroscopic, 3-D, free standing, all-carbon scaffolds (porous structures) using multiwalled carbon nanotubes (MWCNTs) as the initial materials. The scaffolds prepared by radical initiated thermal crosslinking, and annealing of MWCNTs possess macroscale interconnected pores, robust structural integrity, stability, and electrical conductivity. The porosity of the three-dimensional structure can be controlled by varying the amount of radical initiator, thereby allowing the design of porous scaffolds tailored towards specific potential applications. This method also allows the fabrication of 3-D scaffolds using other carbon nanomaterials such as single-walled carbon nanotubes, fullerenes, and graphene indicating that it could be used as a versatile method for 3-D assembly of carbon nanostructures with pi bond networks.     

Synthesis of molecularly imprinted microspheres for recognition of trans‐aconitic acid

In the presence of a template molecule, trans‐aconitic acid and, using acetonitrile as solvent and dispersing medium, monodispersed microspheres with a diameter of 600–700 nm bearing molecularly imprinted binding sites were prepared by precipitation polymerization. It was found that the concentrations of template, monomer, and crosslinking agent as well as the chemical structure of the template greatly affect the polymer configuration. Microspheres are produced only when the concentration of the template molecule and the functional monomer are finely tuned. Comparison with the performance of a conventional imprinted polymer monolith showed that the imprinted microsphere had obvious advantages in specific binding to template molecule. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 542–547, 2004     

Fabrication of porous (Ba,Sr)(Co,Fe)O3-δ (BSCF) ceramics using gelatinization and retrogradation phenomena of starch as pore-forming agent

Porous (Ba,Sr)(Co,Fe)O_3-δ (BSCF) ceramics with high open porosity and good electrical conductivity was fabricated using Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF), which shows a high mixed ionic-electronic conductivity. In general, during the fabrication of porous ceramics by the sacrificial template method using pore former particles, closed pores are easily formed unless sufficient pore former particles are added. In this study, we have devised a method using the gelatinization-retrogradation phenomena of starch for producing a porous body with an excellent percolated pore network structure. By dispersing BSCF and starch in an aqueous slurry (0–50% by weight) and heating, gelatinization of the starch occurred and the starch particles adhered to each other. Furthermore, in order to retain the percolated structure, the water solvent was removed by freeze-drying without heating to obtain a dried green body. The sintering behavior of the porous BSCF bodies prepared under various conditions was characterized by microstructural observations and relative density measurements. By optimizing the process conditions of the gelatinization and retrogradation, a porous body having an open porosity of 48.3%, and with 99% of the total pores open, was obtained. The matrix was also well connected and showed a sufficiently high conductivity which was similar to the porous bodies made by the traditional sacrificial template method.     

Preparation and cell compatibility evaluation of chitosan/collagen composite scaffolds using amino acids as crosslinking bridges

In this study, a novel freeze‐gelation method instead of the conventional freeze‐drying method was used to fabricate porous chitosan/collagen‐based composite scaffolds for skin‐related tissue engineering applications. To improve the performance of chitosan/collagen composite scaffolds, we added 1‐ethyl‐3‐(3‐dimethylaminopropyl)‐carbodiimide (EDC) and amino acids (including alanine, glycine, and glutamic acid) in the fabrication procedure of the composite scaffolds, in which amino acid molecules act as crosslinking bridges to enhance the EDC‐mediated crosslinking. This novel combination enhanced the tensile strength of the scaffolds from 0.70 N/g for uncrosslinked scaffolds to 2.2 N/g for crosslinked ones; the crosslinked scaffolds also exhibited slower degradation rates. The hydrophilicity of the scaffolds was also significantly enhanced by the addition of amino acids to the scaffolds. Cell compatibility was demonstrated by the in vitro culture of human skin fibroblasts on the scaffolds. The fibroblasts attached and proliferated well on the chitosan/collagen composite scaffolds, especially the one with glutamic acid molecules as crosslinking bridges, whereas cells did not grow on the chitosan scaffolds. Our results suggest that the collagen‐modified chitosan scaffolds with glutamic acid molecules as crosslinking bridges are very promising biomaterials for skin‐related tissue engineering applications because of their enhanced tensile strength and improved cell compatibility with skin fibroblasts. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Mechanism of solvent entrapment within the network scaffolding in organogels: thermodynamic and kinetic investigations

A detailed investigation on the thermodynamic behaviour of the physical and chemical organogels, using differential scanning calorimetry (DSC) and modulated thermogravimetric analysis (MTGA), is presented. Aluminium soap of fatty acid was used as the physical gelator and in situ crosslinking of siloxane copolymer was used for chemical gelation. The effects of the type and concentration of the gelators and the corresponding mesh‐size distribution of the gel network scaffolding on the trapped‐solvent crystallization, melting and evaporation mechanism, and kinetics are examined. It appears that the kinetics of crystallization of the trapped‐solvent are significantly affected by the quality of the gel network scaffolding and can be treated successfully by the Avrami equation of crystallization. From the melting behaviour of the entrapped‐solvent crystallites, quantitative information about the number of solvent molecules bound per molecule of the gelator has been extracted. The effect of gelation network structure on the kinetics of evaporation of the solvent from the gel network scaffolding has been evaluated. DSC appears to be the reliable technique to evaluate the population distribution of solvent molecules trapped in the gel network scaffolding. Copyright © 2003 Society of Chemical Industry     

Fabrication and characterizations of crosslinked porous polymer films with varying chemical compositions

In this paper, we demonstrated the successful fabrication of crosslinked porous films with varying monomer-crosslinker ratios, by photo-induced crosslinking during the breath figure formation. For all the samples fabricated, the pores at the peripheral regions appeared more uniform in size and showed higher degree of ordering, due to the interplay between the solvent evaporation and crosslinking reaction. The pore morphology remains similar despite varying film compositions, suggesting that the pore-fixing process is still dominated by the solvent evaporation similar to that of conventional breath figure process, and is less dependent on the crosslinking process. Detailed characterizations of the chemical and physical properties, including the glass transition temperature, thermal stability, and surface wettability of the porous films were carried out.     

生物可降解聚合物多孔支架的制备研究进展

组织工程的关键技术之一在于运用生物可降解聚合物制备出具有特定结构、内部连通性好并具有良好力学性能的三维多孔支架,本文对近几年来制备支架的方法以及研究热点做了综述,并对组织工程用生物可降解聚合物多孔支架的发展方向做了展望。     

Random stacking template of polymer spheres and water soluble particles to fabricate porous hydroxyapatite with interconnected pores

Particle stacking simulation is applied in the fabrication of porous hydroxyapatite (HA) ceramics to predict the relationship between the template preparation process and the porosity of porous ceramics. The stacking of multi-diameter spherical particles, such as polymer spheres and NaCl particles, in three-dimensional space is simulated by using continuous generation method. The porosity of porous HA is predicted by calculating the stacking density of large spheres (the ratio of large sphere volume and container volume). The model of three-dimensional random stacking spheres is implemented by using the C++ program. Porous HA ceramics with interconnected spherical pores were fabricated by slipcasting which the use of a polymer template. Templates were produced by randomly stacking polymer spheres and NaCl particles. The arithmetic average error between the porosity of porous HA ceramics and the stacking density of polymer spheres (large spheres) is 3.52%. Simulation results obtained by using the proposed method are consistent with the experimental results.     

The effect of fabrication methods on the mechanical and thermal properties of poly(lactide‐co‐glycolide) scaffolds

The purpose of this research was to evaluate the effects of the fabrication method, poly(ethylene glycol) (PEG) molecular weight, and PEG concentration on the mechanical and thermal properties of blended poly (lactide‐co‐glycolide) (PLGA)/PEG scaffolds. The manufacturing process was the dominant factor. The tested fabrication processes were compression, heat molding, and solvent casting/vacuum drying. The scaffolds produced by compression were strong and brittle with mechanical properties [compressive modulus (E) ～ 400 N/mm²] comparable to those of trabecular bone. The heat‐molded scaffolds were weaker and more ductile (E ～ 45 N/mm²) than the compressed scaffolds, so they were more applicable to non‐load‐bearing applications. The vacuum‐dried scaffolds completely lacked compressive strength (E ～ 5 N/mm²) and were considered unsuitable for scaffolding applications. The miscibilities of the blends were also affected by the processing method and were evaluated on the basis of the melting‐point depression of crystalline PEG. The miscibility of PLGA in PEG was greatest with vacuum drying (6–13%), followed by heat molding (0.4–1.5%) and then compression (0.2–0.8%). The application of heat and solvent to the blend successfully altered the miscibility of the two polymers. Overall, this study demonstrates the ability to fabricate scaffolds with distinct thermal and mechanical characteristics by the manipulation of the fabrication method. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 944–949, 2007     

Fabrication and characterization of electrospun fibrous nanocomposite scaffolds based on poly(lactide‐co‐glycolide)/poly(vinyl alcohol) blends

Tissue engineering involves the fabrication of three‐dimensional scaffolds to support cellular in‐growth and proliferation. Ideally, the scaffolds should be similar to the native extracellular matrix (ECM). Electrospun polymer nanofibrous scaffolds are appropriate candidates for ECM mimetic materials since they mimic the nanoscale properties of ECM. Electrospun polymer nanocomposites based on poly(lactide‐co‐glycolide) (PLGA)/poly(vinyl alcohol) (PVA) and organically modified montmorillonite (OMMT) were prepared by a solution intercalation technique followed by electrospinning. The morphology of fibrous scaffolds based on these nanocomposites was investigated using scanning electron microscopy. The scaffolds showed highly porous structure within the nanofibres of diameters ranging from 400 to 700 nm. X‐ray diffractometry gave evidence of good dispersion of the OMMT in the blends with exfoliated morphology. Measurements of the water uptake and water contact angle of the fibrous scaffolds indicated significant improvement in the hydrophilicity of the scaffolds. Evaluations of the mechanical properties and unrestricted somatic stem cell culture of the electrospun fibrous nanocomposite scaffolds revealed that the PLGA90/PVA10/1.5% OMMT and PLGA90/PVA10/3% OMMT samples are the most useful from the tissue engineering application viewpoint. Copyright © 2010 Society of Chemical Industry     

Chitosan scaffolds formation by a supercritical freeze extraction process

A crucial step of Tissue Engineering (TE) approach is the fabrication of 3-D biodegradable scaffolds. It has been achieved using various techniques, such as gas foaming, fiber bonding, solvent casting/particulate leaching, phase separation and 3D-printing. Each technique presents specific advantages and disadvantages; but, all of them share the difficulty to obtain simultaneously the macro, micro and nanostructure. In this work, a Supercritical Freeze Extraction Process (SFEP) is proposed for the formation of chitosan structures suitable for TE applications. We showed that it is possible to produce chitosan scaffolds characterized by a micrometric cellular structure, nanofibrous sub-structure and porous surfaces. The low process temperature allows to obtain 3-D solids, whose structure is preserved during supercritical drying. Preliminary results on cell cultivation confirmed that the generated chitosan scaffolds are characterized by a morphology that is potentially suitable for TE applications. A good cell adhesion was obtained and a large percentage of living cells was observed. This result can depend on the micrometric morphology of the scaffolds, that assures a good nutrient diffusion, and on the nanometric sub-structure that allows an adequate cells adhesion.     

Direct ink writing of wollastonite-diopside glass-ceramic scaffolds from a silicone resin and engineered fillers

Wollastonite-diopside scaffolds have been successfully developed by direct ink writing of an ink made of silicone polymer and inorganic fillers. The main reason for using a silicone in the ink formulation consisted in its double effect, in controlling the ink rheology and in developing of wollastonite and diopside crystalline phases upon heat treatment. The obtained 3D wollastonite-diopside scaffolds featured regular geometries, and a high compressive strength (3.9–4.9 MPa) when considering the large amount of porosity (68–76 vol.%). A glass with the same oxide composition as the silicone-based ink and crystallizing into wollastonite and diopside, was produced and used as additional filler. This addition enabled the fabrication of even stronger 3D printed scaffolds (∼8 MPa for a porosity of 67 vol%), owing to the enhanced viscous flow upon firing which reduced the micro-cracks in the scaffold struts generated by the preceramic polymer decomposition. The obtained highly porous wollastonite-diopside glass-ceramic scaffolds are suitable candidates for bone tissue engineering.     

Synthesis and characterization of dense and porous cellulose films

Whereas cellulose‐derived polymers are routinely used as membrane materials, the cellulose polymer itself is not directly used to synthesize dense/porous films for membrane applications. Recently, N‐methylmorpholine N‐oxide (NMMO) and dimethylacetamide (DMAc)/lithium chloride (LiCl) have been successfully employed for dissolving unmodified cellulose. This provides a strong rationale for reexamining the possibility of cellulose membrane fabrication using these solvents. By judiciously selecting solvents, casting conditions, and solvent exchange steps, we successfully synthesized dense/asymmetric‐porous cellulose films. The pore size and porosity of the porous films decreased systematically with increasing cellulose concentration. SEM analysis of the cross sections revealed an asymmetric skinned structure with monotonically increasing pore size away from the skin. The measured pore diameters were in the range 1.8–4.8 μm. Mechanical testing indicated that the dense films possessed tensile properties comparable to those of cellulose acetate (CA) films. Though nitrogen permeability values were comparable for cellulose and CA dense films, cellulose film permeability depended upon the type of drying protocol employed. Overall, these results demonstrate that processability need not be a constraint in the use of cellulose polymer for membrane fabrication. In selected applications, cellulose membranes could become a cost‐effective, environmentally friendly alternative to other more commonly employed membrane polymers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

京尼平交联明胶多孔支架的制备及降解

采用天然交联剂京尼平,结合相分离技术与冷冻干燥方法,制备不同交联度的明胶多孔支架。结果表明,支架的交联度随着京尼平浓度的增加而升高,最高可以达到65．3％;不同交联度的明胶支架微观呈相互连通的多孔结构,且孔径随交联度的升高而降低;通过调控明胶支架的交联度,可以调控支架的降解时间。     

Ultraporous 3D polymer meshes by low‐temperature electrospinning: Use of ice crystals as a removable void template

While electrospinning provides an excellent preparation method for the manufacturing of polymer fibers with defined diameter, controlling the overall porosity of the resulting fiber assemblies has remained elusive, particularly at higher porosities. In this study, the use of a low‐temperature fiber collection device in air with controlled humidity allowed the simultaneous deposition of polymer fibers and ice particles from condensing humidity. The ice particles were intimately embedded within the polymer fibers and served as a pore template thus defining the mesh porosity after drying of the collected fiber assemblies. The amount of water condensation therefore contributes to the control of the mean interfiber distance and the resulting porosity. This simple and well accessible use of ice crystals as void templates gives access to the preparation of biodegradable tissue engineering scaffolds with an up to four times higher porosity if compared to conventional fiber electrospinning. The successful application of low‐temperature electrospinning using polyesters or polyurethanes suggests a broad, material independent applicability of the process for the preparation of highly porous polymer structures. POLYM. ENG. SCI., 47:2020–2026, 2007. © 2007 Society of Plastics Engineers     

Facile fabrication of poly(methyl methacrylate) monolith via thermally induced phase separation by utilizing unique cosolvency

Poly(methyl methacrylate) (PMMA) monoliths with a three-dimensional continuous interconnected porous structure in a single piece were fabricated via thermally induced phase separation (TIPS) by utilizing unique cosolvency toward PMMA. We found that PMMA was soluble in a mixture of non-solvents (ethanol and water) at 60 °C. Cooling the solution resulted in formation of a monolith having interconnected pores. Cross-sectional analysis using scanning electron microscopy (SEM) showed a continuous porous network with submicron-sized skeleton. The pore size of the monolith was readily controlled by varying the fabrication parameters such as the polymer concentration and molecular weight, the cooling temperature and the solvent composition. The cross-section of the monolith showed high water repellency. The PMMA monolith was also obtained in a mixture of isopropanol and water with an appropriate solvent ratio.