Open Cellular Morphology Research Articles

Preparation of PolyHIPE Scaffolds for 3D Cell Culture and the Application in Cytotoxicity Evaluation of Cigarette Smoke.

Polystyrene-based polyHIPE (polymerized high internal phase emulsion) materials were prepared by the copolymerization of styrene and divinylbenzene in the continuous phase of a HIPE. The resultant polyHIPE materials were found to have an open-cellular morphology and high porosity, and the polyHIPE structure could be well adjusted by varying the water/oil (W/O) ratio and the amount of emulsifier in the HIPE. Cell culture results showed that the resultant polyHIPE materials, which exhibited larger voids and connected windows as well as high porosity, could promote cell proliferation on the 3D scaffold. A 3D cell cytotoxicity evaluation system was constructed with the polystyrene-based polyHIPE materials as scaffolds and the cigarette smoke cytotoxicity was evaluated. Results showed that the smoke cytotoxicity against A549 cells is much lower in the 3D cell platform compared to the traditional 2D system, showing the great potential of the polyHIPE scaffolds for 3D cell culture and the cytotoxic evaluation of cigarette smoke.

Microcellular Foam Injection Molding of Thermoplastics Using Green Physical Blowing Agent

The microcellular injection molding technology, commercially offered by Trexel Inc. and other manufacturers, is primarily a close cell foaming technique. This process is capable of offering light weight non-porous thermoplastics moldings. The foaming of thermoplastics with open cellular morphology has got various high end applications among others like tissue engineering and membrane separation. Some of the researchers were successful in synthesis of open cellular thermoplastics at laboratory scale via solid state batch process. The growing demand for microporous thermoplastics, especially the biodegradable plastics (e.g. Polylactic acid), motivated the researchers develop a specialized microcellular injection molding process for processing of open cell thermoplastics using physical blowing agents such as supercritical nitrogen or carbon dioxide gas. A brief of theoretical and conceptual treatment of microcellular injection molding is presented.

Tailoring morphological features of cross-linked emulsion-templated poly(glycidyl methacrylate)

Porous poly(glycidyl methacrylate-co-ethyleneglycol dimethacrylate) samples with total porosity up to 91% were prepared by the polymerisation of high internal phase emulsions (HIPEs). Morphological features like cavity and interconnecting pore diameter were investigated and successfully controlled by changing the initiator system, surfactant ratio, pore volume ratio, stirring rate and reaction mixture temperature. All resulting porous polyHIPE monoliths had open cellular morphology with cavity diameters between sub-μm and 30 μm.

PolyHIPEs from Methyl methacrylate: Hierarchically structured microcellular polymers with exceptional mechanical properties

Highly porous monoliths with excellent mechanical properties and porosity of up to 90% were prepared by the polymerisation of high internal phase emulsions (HIPE) containing methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDMA). Materials with open cellular morphology and cavity diameters between 0.6 and 4.5 μm are obtained using a homogenizer and between 0.8 and 25 μm using a standard overhead stirrer. Samples with 80% pore volume have E-moduli up to 180 MPa, while 75% porous samples exhibit E-moduli up to 211 MPa. A dependence of mechanical properties on cavity size distribution is identified, where a more hierarchically developed porous structure results in significantly better mechanical properties.

Macroporous poly(dicyclopentadiene) γFe2O3/Fe3O4 nanocomposite foams by high internal phase emulsion templating

The high internal phase emulsion (HIPE) templating approach to macroporous poly(dicyclopentadiene) γFe2O3/Fe3O4 nanocomposite foams via ring opening metathesis polymerisation was elaborated and the influence of the formulation of the HIPE on structural and mechanical properties of the magnetic composite foams of 80% nominal porosity was studied. HIPEs solely stabilized with the nanoparticles resulted in considerably shrunken monolithic specimens characterized by an open cellular morphology with cavities bigger than 265 μm. Nanoparticles were situated in the bulk and on the surface of the polymeric foam skeleton. Precise control over the feature sizes could not be obtained in this case. In contrast, HIPE formulations co-stabilized with a surfactant yielded samples of good casting quality characterized by a fully open cellular morphology in all cases. The cavity and the window size could be controlled by the amount of surfactant in the emulsion. A low surfactant loading of 1.5 v% with respect to the monomer yielded diameters of the cavities of the order of 20 μm interconnected with windows with diameters in the order of 4 μm, while 10 v% surfactant resulted in smaller cavities (10 μm) and windows (2 μm). All these feature sizes are hardly affected by the nanoparticle loading which was varied from 1 to 30 wt%. Surfactant stabilized and cured HIPEs featured the nanoparticles predominantly on the surface of the cavities. Mechanical properties of the composite foams were assessed by stress–strain tests and revealed a strengthening of the foams prepared with 10 v% surfactant upon addition of the nanoparticles. Indicative of the strengthening is an increase of the Young's modulus from 13 ± 2 MPa in the case of a sample without nanoparticles to 104 ± 4 MPa in the case of the composite foam with 15 wt% nanoparticles. This trend was accompanied by a decrease of the elongation at break from 21 ± 4 to less than 1%. Specimens prepared with 1.5 v% surfactant are ductile and gave the same high Young's modulus (104 ± 9 MPa) irrespective of the nanoparticle loading and became stronger upon raising the nanoparticle amount reaching an ultimate strength of 3.4 ± 0.4 MPa at an elongation at break of 13 ± 4%.

Methacrylic acid microcellular highly porous monoliths: Preparation and functionalisation

By polymerisation of high internal phase emulsions (HIPEs), containing styrene (STY), divinylbenzene (DVB) and methacrylic acid (MAA) in the continuous phase, highly porous polymers including carboxylic functional groups were prepared. The ratio of methacrylic acid to divinylbenzene was varied in order to obtain polyHIPEs with a different degree of crosslinking which influenced a surface area of the polymers, being substantially higher (185m2/g) with a higher degree of crosslinking (51% DVB) than with a lower degree of crosslinking (24% DVB, 46m2/g). Up to 90% porous samples were prepared and the optimum hidrophilicity-lipophilicity balance (HLB) of the surfactant was found to be around 4.8–4.9. Both thermal and photo initiation were used to induce polymerisation. The resulting polymers had an open cellular morphology with cavity diameters between 21.8μm and 44.2μm and with interconnecting pores between 2.2μm and 5.0μm. Monolithic supports were used for further functionalisation with thionyl chloride and multifunctional amines, namely 1,4-diaminobutane and 1,12-diaminododecane. The functionalisation degree with thionyl chloride was 76%.

Ti-13Nb-13Zr Foams for Surgical Implants

The use of titanium and its alloy as biomaterial is increasing due to their low modulus, superior biocompatibility and enhanced corrosion resistance when compared to more conventional stainless steel and cobalt-based alloys. Ti-13Nb-13Zr is a titanium alloy specifically developed for surgical implants. In this work, highly porous titanium foams, with porosities above from 50%, are reached using an efficient powder metallurgical process, which includes the introduction of a selected spacer into the starting powders. Samples were produced by mixing of initial metallic powders followed by uniaxial and cold isostatic pressing with subsequent densification by sintering. The samples presented a Widmanstättenlike microstructure in an open cellular morphology with pore size between 200-500 μm.

Covalent Enzyme Immobilization onto Photopolymerized Highly Porous Monoliths

In recent years enzymes have found widespread use in areas as diverse as chemical synthesis, decontamination of waste streams, and biosensors. For ease of application and for stabilization purposes, enzymes are often immobilized on solid supports. These supports can include inorganic substrates such as silicon or glass, as well as organic materials such as polymers or hydrogels. In current industrial processes, enzymes are often simply adsorbed onto the material. Although this is a cost-effective method for supporting enzymes, these biocatalytic materials often suffer from decreased activity after prolonged usage because of the leakage of adsorbed enzymes during catalysis and recycling. Furthermore, since there is a lack of control over the enzyme positioning, only a fraction of the enzyme is in contact with the environment and therefore used effectively. In more sophisticated applications, such as sensors and analytical devices, covalent immobilization is achieved using carefully designed anchors and surface modification. These multistep procedures lead to welldefined systems, but costs are raised considerably and these methods are difficult to extend to large-scale applications. In this article we describe a simple and effective strategy for immobilizing enzymes covalently onto a solid porous support, and ascertain that a large fraction of the enzyme is available for catalysis. To achieve this, a support with a high surface to volume ratio is employed, namely a polymerized high internal phase emulsion (polyHIPE). N-Hydroxysuccinimide esters are introduced into this highly porous monolithic support for covalent coupling with the lysine residues present in proteins. When the activity of the well-known lipase Candida antarctica Lipase B (CAL-B) immobilized on polyHIPE was compared with the commercially available standard, Novozyme 435, a remarkable increase in both activity and stability was observed. PolyHIPEs are highly porous polymers obtained by polymerizing the continuous phase of a HIPE. The emulsion must have a droplet volume fraction of at least 0.74, and can exceed 0.99. The stability of this emulsion is mainly dependent on the nature of the surfactant, which should be soluble only in the continuous phase. PolyHIPEs have a well-defined open cellular morphology, with interconnecting holes (windows) between voids resulting from the continuous phase shrinkage during polymerization (see Fig. 1). Their unique morphology differentiates them from other porous polymers (e.g. gasblown foams), and yields excellent flow-through properties. Since the development of polyHIPEs in the 1980s, numerous applications have been developed, such as solid-phase peptide synthesis supports, catalyst supports, superabsorbents, ion-exchange resins, monolithic supports for cells, and membrane filters. However, the use of polyHIPEs as covalently immobilized enzyme supports for biocatalysis has not yet been reported. C O M M U N IC A TI O N S

Ultra-thin asymmetric gas separation membranes of modified PEEK prepared by the dry–wet phase inversion technique

Asymmetric membranes with a thin dense top layer of PEEKWC, a modified poly(ether ether ketone), were prepared by the dry-wet phase inversion technique. PEEKWC has good gas separation properties, with O 2/N 2 selectivity of about 6 and CO 2/CH 4 selectivity of 32. The influence of several experimental variables, e.g. the composition of the casting solution, the casting temperature and the evaporation time before immersion, on the thickness of the skin layer and sublayer were discussed. The preparation conditions were optimized in order to reduce the membrane top layer thickness. The membrane performance was tested in terms of gas permeance and permselectivity for N 2, O 2, CH 4, He and CO 2. In the case of pinhole defects, membranes were coated with dilute silicone solution. Under optimized conditions, membranes with an open cellular morphology and an ultra-thin dense skin of about 50 nm were obtained, presenting very high gas fluxes. Membranes were furthermore screened for possible use in pervaporation of ethanol/water mixtures.

Biomimetic apatite coating on biomorphous alumina scaffolds

Highly porous Al 2O 3 scaffolds were prepared from natural cellulosic sponges via pyrolysis and Al-vapour phase infiltration. Subsequent oxidation and sintering in air resulted in porous Al 2O 3 ceramics with an open cellular morphology and a total porosity of 95%. The Al 2O 3-sponges were immersed in highly supersaturated simulated body fluid (5 × SBF) solutions with different Mg 2+ and HCO 3− concentrations. After soaking of the porous Al 2O 3 sponges for 4 days a homogeneous calcium phosphate layer with a thickness of approximately 2 μm and a Ca : P ratio of 1.62 (apatite) was found.

Synthesis and Characterization of Poly(aryl ether sulfone) PolyHIPE Materials

The preparation and characterization of poly(aryl ether sulfone) (PES) PolyHIPE (polymerized high internal phase emulsion) materials is described. A maleimide-terminated aryl ether sulfone macromonomer was copolymerized with styrene, divinylbenzene (DVB), or a bis(vinyl ether) species, in the continuous phase of a HIPE. Furthermore, a novel, nonaqueous HIPE methodology was employed, since only dipolar aprotic solvents were able to cosolubilize the polymeric precursor and surfactant. HIPEs of petroleum ether, dispersed in a dipolar aprotic solution of maleimide-terminated PES, PEO−PPO−PEO block copolymer surfactants, comonomer, and AIBN, were successfully prepared and polymerized. The cellular structures and porosities of the resulting materials were characterized by SEM, solvent imbibition, mercury porosimetry, and a Brunauer-Emmett-Teller (BET) treatment of nitrogen adsorption results. All were shown to possess an open-cellular morphology and a secondary pore structure within the polymer walls. Thermogra...

Study of the formation of the open-cellular morphology of poly(styrene/divinylbenzene) polyHIPE materials by cryo-SEM

The formation of the interconnected morphology of open-cell styrene/divinylbenzene (DVB) PolyHIPE copolymers has been studied by scanning electron microscopy on frozen HIPE samples at different stages of polymerisation, a technique known as cryo-SEM. The transition from discrete emulsion droplets to interconnected cells was observed to occur around the gelpoint of the polymerising system. This would suggest that the formation of holes between adjacent cells is due to the contraction of the thin monomeric films on conversion of monomer to polymer, as a result of the higher density of the latter.