Development of rigid bidisperse porous microspheres for high-speed protein chromatography

Precise Control of the Surface and Internal Morphologies of Porous Particles Prepared Using a Spontaneous Emulsification Method

Porous particles with controllable surface and internal morphologies were successfully prepared by a "one-step mechanical emulsification" technique via the control of spontaneous emulsification where self-emulsification is followed by mechanical emulsification. The morphological changes in the porous particles were determined not by the preparation conditions of the water-in-oil-in-water (w/o/w) emulsion but by the proportion of solvents that favors the stabilization of the spontaneously prepared water-in-oil (w/o) emulsion droplets acting as porogens. The proposed method for controlling the morphology of the porous particles could be applied to all particle-preparation systems based on emulsion-solvent evaporation using organic solvents. The methodology for the morphological control of porous particles independent of the concentration or composition of the polymer is considered valuable for future investigations into the aerodynamic performance and drug-release behavior of biomedical porous particles with complex shapes.

Diffusion-limited dissolution of calcium carbonate in a hydrogel

In the process of fabricating porous polymers, we use dispersed calcite as a sacrificial solid that generates porosity after dissolution. To do this, we trap calcite particles in a hydrogel, dissolve the particles and dry the hydrogel; here, we describe in detail the dissolution kinetics. We prepare PEGDA [poly(ethylene glycol)-diacrylate] water solutions loaded with micron-sized calcite particles (containing mostly calcium carbonate) up to about 30% volume fraction; these dispersions are photo-polymerized into hydrogels as flat and shallow monoliths with a typical thickness of ≈100 μm and a lateral extent on the order of 1 cm. These soft hydrogels are then soaked into an acidic solution (HCl) which induces the dissolution of the carbonates. The dissolution fronts remain sharp throughout the dissolution and progress inward in a diffusive manner. Such a kinetics is well described numerically using a mean-field diffusion-reaction model where the diffusion of the acid strongly limits the process.

Construction of polyporous polymer microspheres with a tailored mesoporous wall

Polymer microspheres with a novel hierarchically porous structure (inner macropores and a mesoporous wall) were fabricated by taking advantage of γ-ray-radiation-initiated dispersion polymerization.

Porous microsphere and its applications

Porous microspheres have drawn great attention in the last two decades for their potential applications in many fields, such as carriers for drugs, absorption and desorption of substances, pulmonary drug delivery, and tissue regeneration. The application of porous microspheres has become a feasible way to address existing problems. In this essay, we give a brief introduction of the porous microsphere, its characteristics, preparation methods, applications, and a brief summary of existing problems and research tendencies.

Approaches to high-performance preparative chromatography of proteins

Preparative liquid chromatography is widely used for the purification of chemical and biological substances. Different from high-performance liquid chromatography for the analysis of many different components at minimized sample loading, high-performance preparative chromatography is of much larger scale and should be of high resolution and high capacity at high operation speed and low to moderate pressure drop. There are various approaches to this end. For biochemical engineers, the traditional way is to model and optimize a purification process to make it exert its maximum capability. For high-performance separations, however, we need to improve chromatographic technology itself. We herein discuss four approaches in this review, mainly based on the recent studies in our group. The first is the development of high-performance matrices, because packing material is the central component of chromatography. Progress in the fabrication of superporous materials in both beaded and monolithic forms are reviewed. The second topic is the discovery and design of affinity ligands for proteins. In most chromatographic methods, proteins are separated based on their interactions with the ligands attached to the surface of porous media. A target-specific ligand can offer selective purification of desired proteins. Third, electrochromatography is discussed. An electric field applied to a chromatographic column can induce additional separation mechanisms besides chromatography, and result in electrokinetic transport of protein molecules and/or the fluid inside pores, thus leading to high-performance separations. Finally, expanded-bed adsorption is described for process integration to reduce separation steps and process time.

Fabrication and characterization of superporous cellulose bead for high-speed protein chromatography

Novel superporous cellulose (SC) matrix has been fabricated by water-in-oil emulsification-thermal regeneration using granules of calcium carbonate as porogenic agents. As a control, microporous cellulose (MC) bead was fabricated in the absence of calcium carbonate. Simultaneously, double cross-linking was applied to enhance the mechanical strength of the particles. The photographs by scanning electron microscopy of the SC bead illustrated that there were more "craters" of several microns scattering on the surface of the beads. It led to a higher water content and effective porosity of the SC medium. The two beads were then modified with diethylaminoethyl (DEAE) group to prepare anion exchangers. The dynamic uptake results of bovine serum albumin (BSA) exhibited that the pore diffusivity of BSA in the DEAE-SC bead was two to three times larger than that in the DEAE-MC bead. In addition, the column packed with the DEAE-SC showed lower backpressure, higher column efficiency and dynamic binding capacity than the column packed with the DEAE-MC at a flow rate range of 150-900cm/h. Moreover, the column efficiency of the DEAE-SC column was independent of flow velocity up to a flow rate of 1200cm/h. All the results exhibited the superior characteristics of the SC bead as a potential medium for high-speed protein chromatography.

Monodisperse porous polymer particles with polyionic ligands for ion exchange separation of proteins

A new "grafting to" strategy was proposed for the preparation of polymer based ion exchange supports carrying polymeric ligands in the form of weak or strong ion exchangers. Monodisperse porous poly(glycidyl methacrylate-co-ethylene dimethacrylate), poly(GMA-co-EDM) particles 5.9 microm in size were synthesized by "modified seeded polymerization". Poly(2,3-dihydroxypropyl methacrylate-co-ethylene dimethacrylate), poly(DHPM-co-EDM) particles were then obtained by the acidic hydrolysis of poly(GMA-co-EDM) particles. The hydroxyl functionalized beads were treated with 3-(trimethoxysilyl)propyl methacrylate to have covalently linked methacrylate groups on the particle surface. The selected monomers carrying weak or strong ionizable groups (2-acrylamido-2-methyl-1-propane sulfonic acid, AMPS; 2-dimethylaminoethylmethacrylate, DMAEM and N-[3-(dimethylamino)propyl] methacrylamide, DMAPM) were subsequently grafted onto the particles via immobilized methacrylate groups. The final polymer based materials with polyionic ligands were tried as chromatographic packing in the separation of proteins by ion exchange chromatography. The proteins were successfully separated both in the anion and cation exchange mode with higher column yields with respect to the previously proposed materials. The plate heights obtained for poly(AMPS) and poly(DMAEM) grafted poly(DHPM-co-EDM) particles by using proteins as the analytes were 80 and 200 microm, respectively. Additionally, the plate height exhibited no significant increase with the increasing linear flow rate in the range of 1-20 cm/min. The most important property of the proposed strategy is to be applicable for the synthesis of any type of ion exchanger both in the strong and weak form.

Methacrylate-based chromatographic media

This review summarizes the preparation and application of chromatographic separation media based on methacrylate monomers with a major focus on highly crosslinked macroporous beads prepared from 2-hydroxyethyl methacrylate and glycidyl methacrylate, respectively. The effects of process variables such as composition of the polymerization mixture that includes monomers, porogenic solvents, and free radical initiator, suspension stabilizer, reaction temperature, and stirring are detailed for both classical and templated suspension polymerization. In addition, specific features of the preparation of monodisperse beads are also discussed. The performance of methacrylate-based separation media is demonstrated on numerous separations in a variety of chromatographic modes.

A novel superporous agarose medium for high-speed protein chromatography

A novel superporous agarose (SA) bead characterized by the presence of wide pores has been fabricated by water-in-oil emulsification using solid granules of calcium carbonate as porogenic agent. After cross-linking, the solid granules were removed by dissolving them in hydrochloric acid. Then, the gel was modified with diethylaminoethyl groups to create an anion exchanger, SA-DEAE, for protein adsorption. A homogeneous agarose (HA) bead was also produced and modified with DEAE for comparison. It was found that the porosity of SA-DEAE was about 6% larger than that of HA-DEAE. Moreover, both optical micrographs and confocal laser scanning microscopy (CLSM) of the ion exchangers with adsorbed fluorescein isothiocyanate (FITC) labeled IgG revealed the superporous structure of the SA medium. In addition, the SA-DEAE column had lower backpressure than the HA-DEAE column, confirming the convective flow of mobile phase through the wide pores. Due to the presence of the wide pores, more channels were available for protein transport and, furthermore, more diffusive pores in the agarose network were accessible for the protein approach from different directions. This led to 40% higher protein capacity and two times higher effective pore diffusivity in the SA-DEAE than in HA-DEAE. Moreover, an increase of the efficiency of the SA-DEAE column until a flow rate of 5 cm/min and the independency of the column efficiency at flow rates from 5 to 17.8 cm/min was found, indicating that intraparticle mass transfer was intensified by convective flow at elevated flow rates. Therefore, the chromatographic resolution of IgG and BSA was little affected up to a flow rate of 17.8 cm/min. The results indicate that the SA medium is favorable for high-speed protein chromatography.

Novel biporous polymeric stationary phase for high-speed protein chromatography

A novel rigid biporous bead (BiPB) had been fabricated by double emulsification to prepare a (w/o)/w emulsion and a subsequent polymerization. The polymerization of monomers, glycidyl methacrylate and ethylene glycol dimethacrylate, was initiated with benzoin ethyl ether by ultraviolet irradiation. The BiPB with an average diameter of 42.8 microm was characterized to possess two types of pores, i.e., micropores (20-100nm) and superpores (300-4000nm). Its specific surface area was determined to be 41.9m2/g, about 20% smaller than that of a microporous bead (MiPB) (52.1 m2/g). Flow hydrodynamic experiments showed that the BiPB column had smaller backpressure and plate height than those of the MiPB column at a given flow rate. Derivatized with diethylamine (DEA), the static adsorption capacity of the DEA-BiPB was about 7% smaller than that of the DEA-MiPB for BSA (bovine serum albumin). However, frontal analysis demonstrated that the dynamic binding capacity of the DEA-BiPB column was 1.6-2.4 times higher than that of the DEA-MiPB at high flow rate range of 1200-2400cm/h. Moreover, separation of a model protein mixture (myoglobin and BSA) was conducted at mobile phase velocities up to 3000cm/h to compare the performance of the two stationary phases. All the results indicate that the BiPB contains interconnected flowthrough pores and the BiPB column is promising for high-speed protein chromatography.

Functionalisation of allergen-loaded microspheres with wheat germ agglutinin for targeting enterocytes

In this study, we constructed particles applicable for oral immunotherapy of type I allergy by protecting allergens from digestion and supporting intestinal antigen uptake. Therefore, birch-pollen allergens were entrapped in poly(d,l-lactic-co-glycolic acid) microspheres by spray-drying rendering microspheres with a main population of 1-3microm. Microspheres were further coated with wheat germ agglutinin (WGA) to target enterocytes. Coating with WGA did not alter the surface characteristics of the microspheres as demonstrated in scanning electron microscopy. Binding of WGA was specific and could be inhibited by chitotriose to 14.7+/-6.9%. Comparable amounts of allergen were released from both particle-types with 46.3+/-1.7% and 44.5+/-2.6% during 21 days. Simulating gastric digestion in vitro, antigenicity of allergens entrapped in WGA-microspheres was preserved to 59.8+/-1.5% even after 2h. Feedings of BALB/c mice with WGA-microspheres induced higher levels of allergen-specific IgG-levels than gavages of uncoated microparticles or naked protein. Thus, we conclude that WGA-microspheres are suitable vehicles for oral delivery and mucosal targeting due to lectin-mediated bioadhesion.

Characterization of a continuous supermacroporous monolithic matrix for chromatographic separation of large bioparticles

A continuous supermacroporous monolithic chromatographic matrix has been characterized using a capillary model, experimental breakthrough curves, and pressure drop experiments. The model describes the convective flow and its dispersive mixing effects, mass transfer resistance, pore size distribution, and the adsorption behavior of the monolithic matrix. It is possible to determine an effective pore size distribution by fitting the capillary model to experimental breakthrough curves and pressure drop experiments. The model is able to describe the flow rate dependence of the experimental breakthrough curves. Mass transport resistance was due to: (i) dispersive mixing effects in the convective flow in the pores; and (ii) slow diffusion in the stagnant film covering the surface within each pore, under adsorption conditions. The monolithic matrix can be described by a very narrow pore size distribution, illustrating one of the advantages of the gel. A broader pore size distribution results in increased band broadening. This can be studied easily using the model developed in this investigation.