Structural Control in Porous Cross-Linked Poly(methacrylate) Monoliths Using Supercritical Carbon Dioxide as a “Pressure-Adjustable” Porogenic Solvent (original) (raw)
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The polymerisation of functionalised methacrylate monomers in supercritical carbon dioxide
European Polymer Journal, 2003
This paper describes the homopolymerisations of isobornyl methacrylate (IBMA) and poly(ethylene glycol) methacrylate (PEGMA) in supercritical carbon dioxide (scCO 2 ) and copolymerisation with methyl methacrylate (MMA). We have used two different stabiliser systems poly(dimethyl siloxane) monomethylacrylate (PDMS-MMA) and Krytox 157FSL, both of which have been shown previously to be highly effective stabilisers for dispersion polymerisation in scCO 2 . The effect of initiator concentration and copolymer composition is studied. For the copolymerisation of IBMA and MMA, under optimised conditions it is possible to form discrete particles with diameters in the range 1.4-3.6 lm. The PDMS-MMA macromonomer was found to be less effective as a stabiliser, causing particle aggregation due to the low solubility of this stabiliser in the monomers. The copolymers of PEGMA and MMA are also studied. The materials have interesting solubility properties with a transition in solubility from aqueous to organic media on increasing the MMA content.
Journal of Materials Science, 2008
Supercritical carbon dioxide (SCCO 2) was used for the preparation of foamed sponges and intermingled fibers of biopolymers with potential applications in tissue engineering and drug delivery. The work was focused on the processing of both biodegradable polylactic acid (L-PLA) and non-biodegradable polymethylmethacrylate (PMMA) homopolymers. Monolithic porous sponges of amorphous PMMA were prepared using SCCO 2 as a porogen agent by simple swelling and foaming. Under similar experimental conditions, L-PLA was crystallized. The study also addresses the impregnation of biopolymers with an active agent dispersed in SCCO 2. The drug used for impregnation was triflusal, a platelet antiaggregant inhibitor for thrombogenic cardiovascular diseases. Foaming often leads to a closed pore structure after depressurization which is disadvantageous for 3D scaffolds as it does not fulfill the requirement of interconnectivity necessary for cell migration. To overcome these drawbacks, fibers forming macroporous structures were prepared using a semicontinuous antisolvent (SAS) technique.
Journal of Applied Polymer Science, 2003
Microspheres based on synthetic polymers such as poly(methyl methacrylate) (PMMA) and PMMA blends are known for their medical and optical applications. The development of methods for processing polymeric microspheres using a nontoxic solvent, like supercritical carbon dioxide (SCCO 2), is desirable. This work investigates the solubility and behavior of polymers (PMMA and PMMA/ polycaprolactone blend) and solutes (cholesterol and albumin) in SCCO 2 and SCCO 2 ϩ cosolvent (acetone, ethanol, and methylene chloride). The knowledge of solubility behavior of materials in SCCO 2 aids in the selection and/or design of the most appropriate technique for materials processing. Processing PMMA-based polymers with pure SCCO 2 leads to polymer swelling. The lack of polymer sol-ubility in pure CO 2 precludes their micronization by the RESS (rapid expansion of supercritical solutions) process, but on the other hand allows their impregnation. Polymer plasticization caused by CO 2 can be exploited in the PGSS (particles from gas-saturated solutions) process. Addition of a liquid cosolvent to CO 2 enhances the dissolution of solutes and polymers. Precipitation of the studied polymers by antisolvent techniques seems feasible only by use of CO 2 ϩ methylene chloride.
Advanced Drug Delivery Reviews, 2008
Supercritical CO 2 has the potential to be an excellent environment within which controlled release polymers and dry composites may be formed. The low temperature and dry conditions within the fluid offer obvious advantages in the processing of water, solvent or heat labile molecules. The low viscosity and high diffusivity of scCO 2 offer the possibility of novel processing routes for polymer drug composites, but there are still technical challenges to overcome. Moreover, the low solubility of most drug molecules in scCO 2 presents both challenges and advantages. This review explores the current methods that use high pressure and scCO 2 for the production of drug delivery systems and the more specialized application of the fluid in the formation of highly porous tissue engineering scaffolds.
Macromolecules, 1998
Particle growth rates were analyzed for the dispersion polymerization of methyl methacrylate (MMA) in supercritical carbon dioxide at 65°C stabilized with a poly(dimethyl siloxane)-methyl methacrylate (PDMS-mMA) macromonomer. Although pure CO 2 is a mediocre solvent for PDMS even at 4000 psia, the monomer behaves as a cosolvent to prevent flocculation. As pressure is decreased, the dispersion flocculates sooner, as expected due to the reduced solvent quality of CO2. Final particle size is only mildly dependent on pressure as a result of the solvation from the high monomer concentration during the particle formation stage, however particle coagulation increases with decreasing pressure. There exists both a minimum pressure (∼3000 psia) and stabilizer concentration (∼2 wt % stabilizer/ monomer) below which particles are highly coagulated due to insufficient steric stabilization. Here polymerization rates are reduced due to diffusional restrictions. This threshold pressure and stabilizer concentration are required to change the mechanism from precipitation polymerization to dispersion polymerization, as indicated by product morphology, molecular weight, and molecular weight polydispersity. Final particle size and number density determined from the model of Paine {Macromolecules 1990, 23, 3109} agree with the measured values.
Porous Biomaterials Obtained Using Supercritical CO 2 −Water Emulsions
Langmuir, 2007
Highly porous, hydrophilic porous matrices were fabricated by using a high internal phase supercritical-CO 2 (scCO 2 ) emulsion templating technique. The novel aspect of the work resides in the combination of a natural biopolymer (dextran) as the building component of the matrices and of an environmentally benign solvent (supercritical-CO 2 ) as the pore-generating phase. The synthetic route to the porous biomaterials involved the preliminary functionalization of the dextran chains with methacrylic moieties, formation of a scCO 2 -in-water concentrated emulsion, and curing of the external phase of the emulsion by radical polymerization. As the emulsion stabilizer a perfluoropolyether surfactant was chosen. The matrices obtained exhibit highly interconnected, trabecular morphologies. The porous biomaterial morphologies were qualitatively characterized by scanning electron microscopy (SEM) and the evaluation of void and interconnect sizes was carried out on the micrographs taken with the light microscope. To tailor the morphologies of the porous structures, the influence of the volume fraction of the internal phase and of the surfactant/ internal phase ratio was investigated. It was established that the variation of the volume fraction of the internal phase exerted only a limited influence on void and interconnect sizes. On the contrary the increase of surfactant concentration alters dramatically the distribution of void size, a large proportion of the void space enclosed within the matrix being attributable to voids with a diameter exceeding 100 µm. The free toxic solvent process of fabrication of the porous structures, the high water content, the expected biocompatibility, and the mechanical properties that resemble natural tissues make these porous hydrogels potentially useful for tissue engineering applications. Watson, M. S.; Whitaker, M. J.; Popov, V. K.; Davies, M. C.; Mandel, F. S.; Wang, J. D.; Shakesheff, K. M. Chem. Commun. (Cambridge) 2001, 109-110. (4) (a) Barbetta, A.; Dentini, M.; De Vecchis, M. S.; Filippini, P.; Formisano, G.; Caiazza, S. AdV. Funct. Mater. 2005, 15, 118-124. (b) Barbetta, A.; Dentini, M.; Zannoni, E. M.; De Stefano, M. E. Langmuir 2005, 15, 118-124. (c) Barbetta, A.; Dentini, M.; Massimi, M.; Conti Devirgiliis, L.