Thermally Induced Phase Separation Method Research Articles

Fabrication and characterization of PDLLA/pyrite composite bone scaffold for osteoblast culture

A series of highly interconnected porous poly(D,L-lactide acid) (PDLLA)/pyrite (Zi-Ran-Tong, FeS2) scaffold containing 5–20% of pyrite was fabricated by particle leaching combined with the thermal-induced phase separation method. Pyrite (FeS2, named as Zi-Ran-Tong in Chinese medicine), as a traditional Chinese medicine, has been used in the Chinese population to treat bone diseases and to promote bone healing. The mechanical properties of the PDLLA scaffold were significantly enhanced after the addition of pyrite. The osteoblastic ROS17/2.8 cell line was used and seeded on the PDLLA/pyrite scaffold to study its potential to support the growth of osteoblastic cells and to estimate the optimal dose of pyrite for bone tissue engineering. The effects of pyrite on cell proliferation and differentiation were evaluated by 3-[4, 5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide and alkaline phosphatase activity assay. The cells on the porous composite scaffold formed a continuous layer on the outer and inner surface observed by scanning electron microscopy and fluorescence microscope. The results strongly suggested that the PDLLA/pyrite composite scaffold could stimulate the growth of ROS17/2.8 cells in vitro and it could be potentially used as a scaffold for bone tissue engineering.

Surface functional modification of self-assembled insulin nanospheres for improving intestinal absorption

In this work we fabricated therapeutic protein drugs such as insulin as free-carrier delivery system to improve their oral absorption efficiency. The formulation involved self-assembly of insulin into nanospheres (INS) by a novel thermal induced phase separation method. In consideration of harsh environment in gastrointestinal tract, surface functional modification of INS with ɛ-poly-l-lysine (EPL) was employed to form a core–shell structure (INS@EPL) and protect them from too fast dissociation before their arriving at target uptake sites. Both INS and INS@EPL were characterized as uniformly spherical particles with mean diameter size of 150–300nm. The process of transient thermal treatment did not change their biological potency retention significantly. In vitro dissolution studies showed that shell cross-linked of INS with EPL improved the release profiles of insulin from the self-assembled nanospheres at intestinal pH. Confocal microscopy visualization and transport experiments proved the enhanced paracellular permeability of INS@EPL in Caco-2 cells. Compared to that of INS, enteral administration of INS@EPL at 20IU/kg resulted in more significant hypoglycemic effects in diabetic rats up to 12h. Accordingly, the results indicated that surface functional modification of self-assembled insulin nanospheres with shell cross-linked polycationic peptide could be a promising candidate for oral therapeutic protein delivery.

Epsilon-poly-l-lysine guided improving pulmonary delivery of supramolecular self-assembled insulin nanospheres

This work presents new spherical nanoparticles that are fabricated from supramolecular self-assembly of therapeutic proteins for inhalation treatment. The formation involved self-assembly of insulin into nanospheres (INS) by a novel thermal induced phase separation method. Surface functional modification of INS with ɛ-poly-l-lysine (EPL), a homopolymerized cationic peptide, was followed to form a core–shell structure (INS@EPL). Both INS and INS@EPL were characterized as spherical particles with mean diameter size of 150–250nm. The process of transient thermal treatment did not change their biological potency retention significantly. FTIR and CD characterizations indicated that their secondary structures and biological potencies were not changed significantly after self-assembly. The in vivo investigation after pulmonary administration, including lung deposition, alveoli distribution, pharmacological effects and serum pharmacokinetics were investigated. Compared to that of INS, intratracheal administration of INS@EPL offered a pronounced and prolonged lung distribution, as well as pharmacological effects which were indicated by the 23.4% vs 11.7% of relative bioavailability. Accordingly, the work described here demonstrates the possibility of spherical supramolecular self-assembly of therapeutic proteins in nano-scale for pulmonary delivery application.

Preparation and characterizations of poly(vinylidene fluoride)/oxidized multi-wall carbon nanotube membranes with bi-continuous structure by thermally induced phase separation method

Poly(vinylidene fluoride)/oxidized multi-wall carbon nanotube (PVDF/O-MWCNT) flat membranes with bi-continuous structures were successfully prepared via the thermally induced phase separation (TIPS) method. The effects of O-MWCNT content, PVDF concentration and quenching temperature on the membrane properties were systematically discussed. The results indicate that the membrane structure changes to a denser one and the pure water fluxes (PWFs) of the resultant membranes decline with the increase of O-MWCNT content. With the addition of O-MWCNTs from 0.0 to 0.6wt%, the BSA rejections of the resultant PVDF/O-MWCNT membranes are improved dramatically. The highest BSA rejection attained is above 90.0%, implying that a novel PVDF/O-MWCNT ultrafiltration membrane is fabricated. The surface hydrophilicity and anti-fouling ability of the membranes are improved with the addition of O-MWCNTs. Furthermore, the mechanical properties of the resultant membranes are enhanced compared with the pristine PVDF membranes. This work demonstrates that O-MWCNTs play a critical role in determining the morphologies and performances of PVDF/O-MWCNT membranes prepared via the TIPS method.

Effects of cooling temperature and aging treatment on the morphology of nano‐ and micro‐porous poly(ethylene‐co‐vinyl alcohol) membranes by thermal induced phase separation method

ABSTRACTPoly(ethylene‐co‐vinyl alcohol) (EVOH 32) / 1,3‐propanediol mixtures are processed by thermally induced phase separation for the formation of porous membranes. The crystallization line was determined both by the cloud‐point and DSC methods. Two precursor solution compositions, four quench temperatures and various aging times were explored. It is found possible to generate both polymer‐crystallization controlled morphologies (for high quenches and/or sufficiently aged dopes), especially globular microporous ones, and novel nano‐scale porous morphologies dominated by intra‐binodal phase separation (for low quenches and limited or no precursor solution aging). Structural characterization of the membranes was accomplished via application of scanning electron microscopy and wide angle X‐ray diffraction. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40374.

Preparation and Characterization of Layer Structured Porous Chitosan Scaffold for Tissue Engineering

In this study, layer structured porous chitosan scaffold was successfully fabricated using thermal induced phase separation method. The scaffold had a layer structure with interconnective pores (50- 300 μm) and high porosity (>90%) using citric or acetic acid as the solvent. However, the results of compressive modulus of the scaffold showed that acetic acid was a better choice, and the compressive modulus of scaffold increased with chitosan concentration in acetic acid. The scaffold is very promising for tissue engineering.

Effect of PVDF concentration on the morphology and performance of hollow fiber membrane employed as gas–liquid membrane contactor for CO2 absorption

In this study, poly(vinylidene fluoride) (PVDF) hollow fiber membranes were fabricated and used in gas–liquid contacting process. Porous PVDF hollow fiber membranes were fabricated via thermal induced phase separation method. The polymer solution was formulated by varying polymer concentrations. The polymer concentration in dope solution varied from 25 to 34wt.% PVDF. Triacetin was used as solvent and internal coagulant while water as external coagulant. Measurement of membrane pore size, membrane porosity, liquid entry pressure of water (LEPw), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) were used for membrane characterization. The mean pore size, effective surface porosity and void fraction of membranes decreased as the polymer concentration increased, by contrast, LEPW and membrane density increased. Furthermore the performance of PVDF membrane in contactor applications in terms of CO2 absorption with 0.5M NaOH as absorbent liquid is compared with the absorption flux of commercial and in-house made hydrophobic membranes. Results showed that as polymer concentration in the dope solution increased, CO2 flux of membrane decreased. This means that outer skin layer of the membranes became apparently thicker and denser with increasing polymer concentration. Additionally, a mathematical model describing the non-wetted gas–liquid membrane contactors were solved using COMSOL software. Comparisons of model predictions with experimental data were in good agreement.

Fabrication of Nano-Fibrous Poly(L-Lactic Acid) Scaffold Enhanced by Silane Modified Chitosan Fibers

In this study, A PLLA/silane modified chitosan fiber composite scaffold was sucessfully prepared using thermal induced phase separation method. The PLLA was chemically coupled with chitosan fiber surface using γ-methacryloxypropyl-trimethoxysilane.The composite scaffold had a nano-fibrous PLLA matrix (fiber size 200-750 nm), an interconnective pores ((1-6 μm), high porosity (>90%). Introduced surface modified chitosan fibers into PLLA matrix, it significantly enhanced the nano-fibrous scaffold. The new nano composite scaffold is potentially a very promising scaffold for tissue engineering.

Effect of Non-Solvent Additive on Effectiveness of Polyvinylidene Fluoride Membrane Fabricated With Thermal Induced Phase Separation Method for Carbon Dioxide Absorption

In the present work porous poly (vinylidene fluoride) (PVDF) hollow fiber membranes were fabricated via thermally induced phase separation (TIPS) method for the application in gas-liquid membrane contactor. For this purpose long air gap distance was used (90 mm). Scanning electron microscopy (SEM) was used for membrane characterization. Gas permeation test was performed using carbon dioxide as test gas. It was observed that the effective surface porosity and membrane pore size increased with increased glycerol concentration. CO2 absorption using the fabricated hollow fiber membranes were measured in a gas-liquid hollow fiber membrane contactor. The results of the CO2 absorption rate of the tested fibers revealed that complete removal of CO2 was achieved using 7% glycerol added to the casted solution at normal operating conditions for equal gas to liquid volumetric flow rates using sodium hydroxide as absorbent liquid.

CHITOSAN IN APPLICATIONS OF BIOMEDICAL DEVICES

Chitosan is a natural polysaccharide with great potential for biomedical applications due to its biocompatibility, biodegradable capability, and nontoxicity. Various techniques used for preparing chitosan microspheres/membranes and evaluations of these fabrications have also been reviewed. The hydrophilicity of chitosan provides unique characteristics of hydrogel formation with the acidic media and may entrap the drug content inside of the matrix for controlled release. In order to improve upon the scope of preparation of chitosan microspheres, we had successfully employed and incorporated a high-voltage system into the direct pumping injection process. The wide range of drug release profiles could be attributed to the surface characteristics, porosities, and various structures of chitosan microspheres upon treatment with Na5P3O10/NaOH solutions of various volume ratios. We also demonstrated that with the addition of chitosan/β-TCP microspheres as a constituent into the PMMA cement significantly decreases the curing peak temperature and increases the setting time. The excellent gelforming property of chitosan offers another biomedical application in membrane separation fields. Chitosan membranes were prepared by a thermal induced phase separation method, following treatment with nontoxic NaOH gelating and Na5P3O10, Na2SO3 crosslinking agents. In order to further improve the mechanical strength and biocompatibility and to expand the potential of chitosan GTR membranes in periodontal applications, various chitosan membranes incorporating with negatively charged alginate, bioactive tricalcium phosphate, and platelet rich plasma, respectively, were also prepared and characterized. Moreover, we had also utilized chitosan, which with good blood-clotting, cheap, and easy preparation characteristics, as the raw material to prepare rapid clotting wound dressing and tooth plug.

Effect of diluents on the characteristics of cellulose diacetate membranes prepared via thermally induced phase separation method

Cellulose diacetate hollow fiber membranes were fabricated via thermally induced phase separation (TIPS) method to investigate the effect of diluent on membrane characteristics. Ethylene glycol (EG), diethylene glycol, triethylene glycol and tetraethylene glycol were used as diluent. Asymmetric membrane structures with dense layers on the outer surfaces and porous structures on the inner surfaces were obtained. When EG was used as diluent, the phase separation temperature of the cellulose diacetate solution was high, resulting in the large pore on the inner surface of the fabricated membrane. This is because solution with higher phase separation temperature has the longer coarsening time for the structure. The rejection experiment elucidated that the membrane fabricated from diluent of lower phase separation temperatures showed the higher rejection. The membranes with ultrafiltration property were successfully prepared by TIPS method.

Preparation of microporous particles of isotactic polypropylene via a thermally induced phaseseparation method

AbstractA new method for the preparation of microporous particles of isotactic polypropylene (IPP) using thermally induced phase separation (TIPS) was developed in this study, in which chloroform was used as a diluent and Span80 was used as a pore‐forming agent. The morphology and properties of the microporous IPP particles thus produced were characterized with scanning electron microscopy, mercury intrusion porosimetry, and differential scanning calorimetry, and they were compared with IPP particles produced by a cryogenic pulverization method. The results showed that IPP particles with a fully developed microporous structure, an average particle size between 50 and 120 μm, and a specific area of about 5.19 m2/g can be obtained via the TIPS method under definite conditions. The influence of some factors on the size and porosity of IPP particles is discussed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

FABRICATION AND EVALUATION OF CHITOSAN MEMBRANES FOR GUIDED TISSUE REGENERATION

Chitosan membranes were prepared by a thermal induced phase separation method, following treatment with nontoxic NaOH gelating and Na5P3O10, Na5SO3 crosslinking agents. Effects of these reaction agents on chitosan membranes were evaluated to survey the feasibility of using these membranes in guided tissue regeneration (GTR) application. The preliminary results showed chitosan membranes crosslinked with Na5P3O10 and Na2SO3 had gel content of 53.5% and 52.2%r, respectively. Contrarily, the chitosan matrix gelated with NaOH dissolved completely during gel content measurement. Chitosan membrane treated with Na5P3O10 had lowest elastic modulus of 12.9 Mpa as compared with other membranes treated with Na2SO3 (17.9Mpa) and NaOH(23.6Mpa). From SEM observations, NaOH gelated chitosan membrane had the smoothest surface morphology than others. However, Na5P3O10 crosslinked chitosan membrane had better cell adhesion and proliferation results in cell culture test. All three chitosan membranes degraded by about 23%∼28% of initial weight after a 90-day in vitro shaking test.

Controlled release of plasmid DNA from biodegradable scaffolds fabricated using a thermally-induced phase-separation method

Highly porous poly(D, L-lactic-co-glycolic acid) (PLGA) scaffolds were fabricated by a thermally-induced phase-separation (TIPS) method to deliver plasmid DNA in a controlled manner. A variety of TIPS parameters directly affecting pore structures and their interconnectivities of the scaffold, such as polymer concentration, solvent/non-solvent ratio, quenching methods and annealing time, were systematically examined to explore their effects on sustained release behaviors of plasmid DNA. Plasmid DNA was directly loaded into the inner pore region of the scaffold during the TIPS process. By optimizing the parameters, PLGA scaffolds releasing plasmid DNA over 21 days were successfully fabricated. DNA release profiles were mainly affected by the pore structures and their interconnectivities of the scaffolds. Plasmid DNA released from the scaffolds fully maintained its structural integrity and showed comparable transfection efficiency to native plasmid DNA. These biodegradable polymeric scaffolds capable of sustained DNA release can be potentially applied for various tissue engineering purposes requiring a combined gene delivery strategy.

Thermomechanical analysis of a polymer dispersed liquid crystal containing a thermoplastic elastomer

Bulk samples of polymer dispersed liquid crystals (PDLCs) containing polystyrene (PS) and a thermoelastic elastomer as polymer matrices, have been prepared by a thermally-induced phase separation method. Thermomechanical analysis measurements revealed that the PDLC containing the thermoplastic elastomer possessed rubber-like elasticity even in the mesomorphic temperature range of the LC while the PDLC based on PS showed plastic deformation during the measurement.

Comparison of Mobility Modes in Polymer Solutions Undergoing Thermal-Induced Phase Separation

ABSTRACTThe thermal-induced phase separation method is used to fabricate polymer membranes and polymer-dispersed liquid crystal films from polymer solutions. The resultant morphology consists of solvent droplets dispersed uniformly in a solid polymer matrix. Up till now, the modeling and computer simulation of the thermal-induced phase separation phenomenon in polymer solutions have considered the mobility to be a constant. The objective of this presentation is to compare the following three mobility modes: (1) mobility as a constant, (2) mobility following fast mode theory, and (3) mobility following slow mode theory. We present computer simulation results from models composed of the Cahn-Hilliard theory for phase separation, Flory-Huggins free energy density for polymer solutions, and the three aforementioned mobility modes. The numerical results indicate that there is no significant difference in the morphology formed; the only difference occurs in the phase separation time. Furthermore, the numerical results show that the only difference between the slow and fast mode theories is a factor of two; the mobility of the fast mode theory is twice that of the slow mode theory.

96/00058 An improved method for extracting sulfate from bituminous coals using formic acid

Poor mechanical performance of porous chitosan-hydroxyapatite systems is the main limitation in bone tissue engineering. If we merge good mechanical performance of poly(lactic acid) construct with osteoinductive and bioresorbable properties of chitosan-hydroxyapatite porous hydrogel, we can obtain a material that meets necessary requirement for bone tissue substituent. With this in mind, we propose the combination of 3D printing technique and the thermally-induced phase separation method for simultaneous modification of biological properties of poly(lactic acid) and load-bearing properties of chitosan-hydroxyapatite porous hydrogel. 3D printed poly(lactic acid), PLA, construct has been used as a mechanical support with very large pore diameter of 960 ± 50 μm allowing enough free space (∼60% of porosity) to form porous composite hydrogel by freeze gelation. In situ formation of hydroxyapatite within chitosan hydrogel has ensured higher human mesenchymal stem cell osteogenesis during 21 days of culture. Positive modification of poly(lactic acid) has been simultaneously utilized to improve the compressive strength of composite hydrogel which has been confirmed by Young’s modulus ranging from lower values reported for cancellous bone in dry state. Considering positive osteogenic signal accompanied with suitable mechanical properties, our scaffolds have shown good potential as bone tissue substituent.