A novel superporous agarose medium for high-speed protein chromatography

Affinity chromatography for virus-like particle manufacturing: Challenges, solutions, and perspectives

The increasing medical application of virus-like particles (VLPs), notably vaccines and viral vectors, has increased the demand for commercial VLP production. However, VLP manufacturing has not yet reached the efficiency level achieved for recombinant protein therapeutics, especially in downstream processing. This review provides a comprehensive analysis of the challenges associated with affinity chromatography for VLP purification with respect to the diversity and complexity of VLPs and the associated upstream and downstream processes. The use of engineered affinity ligands and matrices for affinity chromatography is first discussed. Although several representative affinity ligands are currently available for VLP purification, most of them have difficulty in balancing ligand universality, ligand selectivity and mild operation conditions. Then, phage display technology and computer-assisted design are discussed as efficient methods for the rapid discovery of high-affinity peptide ligands. Finally, the VLP purification by affinity chromatography is analyzed. The process is significantly influenced by virus size and variation, ligand type and chromatographic mode. To address the updated regulatory requirements and epidemic outbreaks, technical innovations in affinity chromatography and process intensification and standardization in VLP purification should be promoted to achieve rapid process development and highly efficient VLP manufacturing, and emphasis is given to the discovery of universal ligands, applications of gigaporous matrices and platform technology. It is expected that the information in this review can provide a better understanding of the affinity chromatography methods available for VLP purification and offer useful guidance for the development of affinity chromatography for VLP manufacturing in the decades to come.

Application of cellulose to chromatographic media: Cellulose dissolution, and media fabrication and derivatization

As the cornerstone of chromatographic technology, the development of high-performance chromatographic media is a crucial means to enhance the purification efficiency of biological macromolecules. Cellulose is a popular biological separation medium due to its abundant hydroxyl group on the surface, easy modification and, weak non-specific adsorption. In this paper, the development of cellulosic solvent systems, typical preparation methods of cellulosic chromatographic media, and the enhancement of chromatographic properties of cellulosic chromatographic media by polymeric ligand grafting strategies and their mechanism of action are reviewed. Ultimately, based on the current research status, a promising outlook for the preparation of high-performance cellulose-based chromatographic media was presented.

Multi-size optimization of macroporous cellulose beads as protein anion exchangers: Effects of macropore size, protein size, and ligand length

Multi-size optimization of ion exchangers based on protein characteristics and understanding of underlying mechanism is crucial to achieve maximum separation performance in terms of adsorption capacity and uptake kinetic. Herein, we characterize the effects of three different sizes, macropore size, protein size, and ligand length, on the protein adsorption capacity and uptake kinetic of macroporous cellulose beads, and provide insights into the underlying mechanism. In detail, (1) for smaller bovine serum albumin, macropore size has a negligible effect on the adsorption capacity, while for larger γ-globulin, larger macropores improve the adsorption capacity due to the high accessibility of binding sites; (2) there is a critical pore size (CPZ), at which the adsorption uptake kinetic is minimum. When pore sizes are higher than the CPZ, uptake kinetics are enhanced by pore diffusion. When pore sizes are lower than CPZ, uptake kinetics are enhanced by surface diffusion; (3) increasing ligand length improves the adsorption capacity by three-dimensionally extended polymer chains in pores and enhances uptake kinetic by improved surface diffusion. This study offers an integrated perspective to qualitatively assess the effects of multiple sizes, providing guidance for designing advanced ion exchangers for protein chromatography.

Fabrication of copolymer brushes grafted superporous agarose gels: Towards the ultimate ideal particles for efficient affinity chromatography

A composite immobilized-metal affinity agarose particle was designed for the selective separation and purification of histidine-tagged proteins from complicated biological samples. The composite particle was constructed using superporous agarose particles as supporting matrix, flexible copolymer brushes as scaffolds to render higher ligand densities, and Ni²⁺-chelated iminodiacetic acids as recognition elements. Superporous agarose composite particles endow high permeability and interfering substance tolerance. The copolymer brush was prepared by surface-initiated atom transfer radical polymerization of N-isopropylacrylamide and glycidyl methacrylate, followed by iminodiacetic acids and Ni²⁺ ions. The physical and chemical properities of the composite particle were thoroughly investigated. The composite particles were shown to be able to selectively separate histidine-tagged recombinant proteins in the presence of high quantities of interfering chemicals in a model protein-binding experiment. By altering the temperature, the protein binding of the composite particles can be modulated. The superporous agarose particles supported polymer brush enables fast and efficient separation and purification of target proteins with high permeability, low backpressure, and high interfering matrix tolerance, which pave the path for bioseparation through designing and fabrication of novel agarose particles-based functional materials.

Kinetic investigation of protein adsorption into polyelectrolyte brushes by quartz crystal microbalance with dissipation: The implication of the chromatographic mechanism

With the growing concerns of polymer-grafted ion-exchange chromatography, the importance of protein adsorption on charged polymer-grafted surfaces cannot be stressed enough. However, a full understanding in adsorption in polymer brushes is still a great challenge due to the lack of in situ characterization technique. In this work, we use quartz crystal microbalance with dissipation to in situ investigate adsorption kinetics of γ-globulin and recombinant human lactoferrin on poly(3-sulfopropyl methacrylate) (pSPM) sensors prepared via atom transfer radical polymerization. With an increase of chain length and grafting density, great increasing amounts of proteins on pSPM-grafted sensors revealed that protein underwent a transition from monolayer to multilayer adsorption. It was attributed to direct protein binding into charged brushes, in which more binding sites involved and more coupled water lost. However, such a strong binding and rigid structure of proteins limited the protein transport in pSPM brushes and "chain delivery" effect. With an increase in grafting density, moreover, denser brushes hindered adjustment in protein conformation in pSPM brushes and further exacerbated protein transport in pSPM brushes. Furthermore, the influence of buffer pH and salt concentration further validated the ion exchange characteristics of protein adsorption into pSPM brushes. The research provided a variety of in situ evidence of protein binding and conformation evolution in pSPM brushes and elucidated mechanism of protein adsorption in pSPM brushes.

Purification of Modified Therapeutic Proteins Available on the Market: An Analysis of Chromatography-Based Strategies

Proteins, which have inherent biorecognition properties, have long been used as therapeutic agents for the treatment of a wide variety of clinical indications. Protein modification through covalent attachment to different moieties improves the therapeutic's pharmacokinetic properties, affinity, stability, confers protection against proteolytic degradation, and increases circulation half-life. Nowadays, several modified therapeutic proteins, including PEGylated, Fc-fused, lipidated, albumin-fused, and glycosylated proteins have obtained regulatory approval for commercialization. During its manufacturing, the purification steps of the therapeutic agent are decisive to ensure the quality, effectiveness, potency, and safety of the final product. Due to the robustness, selectivity, and high resolution of chromatographic methods, these are recognized as the gold standard in the downstream processing of therapeutic proteins. Moreover, depending on the modification strategy, the protein will suffer different physicochemical changes, which must be considered to define a purification approach. This review aims to deeply analyze the purification methods employed for modified therapeutic proteins that are currently available on the market, to understand why the selected strategies were successful. Emphasis is placed on chromatographic methods since they govern the purification processes within the pharmaceutical industry. Furthermore, to discuss how the modification type strongly influences the purification strategy, the purification processes of three different modified versions of coagulation factor IX are contrasted.

Fabrication of rigid and macroporous agarose microspheres by pre-cross-linking and surfactant micelles swelling method

A novel combined method of pre-cross-linking and surfactant micelles swelling was proposed in this study to fabricate highly cross-linked and macroporous agarose (HMA) microspheres. Agarose was chemically modified by allylglycidyl ether (AGE) as heterobifunctional cross-linker via its active glycidyl moieties before gel formation and pre-cross-linking was achieved. By this means, the effective concentration of cross-linker presented in agarose gel increased significantly, and thus cross-linking with a high-efficiency was achieved. Further to enhance the intraparticle mass transfer of agarose microspheres, the surfactant micelles swelling method was utilized to create interconnected macropores. Under the optimal condition, HMA microspheres with homogeneous reticular structure and pore size of hundreds nanometers were successfully prepared. They exhibited a low backpressure with a flow velocity as high as 1987 cm/h, which was much higher than that of commercial Sepharose 4 F F. HMA microspheres were then derivatized with carboxymethyl (CM) groups and applied in ion-exchange chromatography. As expected, CM-HMA column separated model proteins effectively even at a flow velocity three times higher than that of commercial CM-4 F F. Visualization of dynamic protein adsorption by confocal laser scanning microscope (CLSM) revealed that the intraparticle mass transfer of CM-HMA microspheres was intensified due to its macroporous structure. All of the results indicated the newly developed agarose microspheres were a promising medium for high-speed chromatography.

Simultaneous and combined detection of multiple tumor markers for cancer screening in human serum by an upgraded photonic crystal-encoded suspension array

The silica–agarose photonic beads array brings a novel approach to the combined detection of tumor markers in early cancer screening because it has high accuracy, detection reproducibility, and acceptable agreement with a common clinical method.

Microcalorimetric study of adsorption and disassembling of virus-like particles on anion exchange chromatography media

Chromatographic purification of virus-like particles (VLPs) is important to the development of modern vaccines. However, disassembly of the VLPs on the solid-liquid interface during chromatography process could be a serious problem. In this study, isothermal titration calorimetric (ITC) measurements, together with chromatography experiments, were performed on the adsorption and disassembling of multi-subunits hepatitis B virus surface antigen virus-like particles (HB-VLPs). Two gigaporous ion-exchange chromatography (IEC) media, DEAE-AP-280 nm and DEAE-POROS, were used. The application of gigaporous media with high ligand density led to significantly increased irreversible disassembling of HB-VLPs and consequently low antigen activity recovery during IEC process. To elucidate the thermodynamic mechanism of the effect of ligand density on the adsorption and conformational change of VLPs, a thermodynamic model was proposed. With this model, one can obtain the intrinsic molar enthalpy changes related to the binding of VLPs and the accompanying conformational change on the liquid-solid interface during its adsorption. This model assumes that, when intact HB-VLPs interact with the IEC media, the total adsorbed proteins contain two states, the intact formation and the disassembled formation; accordingly, the apparent adsorption enthalpy, ΔappH, which can be directly measured from ITC experiments, presents the sum of three terms: (1) the intrinsic molar enthalpy change associated to the binding of intact HB-VLPs (ΔbindHintact), (2) the intrinsic molar enthalpy change associated to the binding of HB-VLPs disassembled formation (ΔbindHdis), and (3) the enthalpy change accompanying the disassembling of HB-VLPs (ΔconfHdis). The intrinsic binding of intact HB-VLPs and the disassembled HB-VLPs to both kinds of gigaporous media (each of which has three different ligand densities), were all observed to be entropically driven as indicated by positive values of ΔbindHintact and ΔbindHdis; while the nagative ΔconfHdis values suggested a spontenous enthalpy-driven process for the forming of HB-VLPs disassembled formation at all conditions studied. As ligand density increases, ΔconfHdis became more negative, which was in agreement with the findings from chromatography experiments, that higher ligand density leads to more serious disassembling of HB-VLPs. Results from thermodynamic studies provided us insight understanding on the mechanism of adsorption and conformational change of VLPs, as well as the effect of ligand densities on the structural stability of VLPs during IEC process.

Protein adsorption to poly(ethylenimine)-modified Sepharose FF. IV. Dynamic adsorption and elution behaviors

We have previously investigated bovine serum albumin (BSA) uptake to poly(ethylenimine) (PEI)-grafted Sepharose FF. It was found that there was a critical ionic capacity (cIC; 600mmol/L) for BSA, above which the protein adsorption capacity and uptake kinetics increased drastically. In this work, two poly(ethylenimine) (PEI)-grafted resins with IC values of 271mmol/L (FF-PEI-L270) and 683mmol/L (FF-PEI-L680), which were below and above the cIC, respectively, were chosen to investigate the breakthrough and linear gradient elution (LGE) behaviors of BSA. Commercially available anion exchanger, Q Sepharose FF, was used for comparison. The DBC values of FF-PEI-L680 were much higher in the entire residence time range (2-10min) than the other two resins due to its high static adsorption capacity and uptake kinetics. At a residence time of 5.0min, the DBC of FF-PEI-L680 (104mg/mL) was about seven times that of FF-PEI-L270 and three times that of Q Sepharose FF. A rise-fall trend of the DBCs with increasing ionic strength (IS) was found for all the three resins studied, indicating the presence of electrostatic exclusion for protein uptake at low IS. With increasing NaCl concentration from 20 to 200mmol/L, FF-PEI-L680 kept very high DBC values (64-114mg/mL). In addition, FF-PEI-L270 showed more favorable adsorption properties than Q Sepharose FF at 100-300mmol/L NaCl. These results proved that the three-dimensional grafting ion exchange layer on the PEI resins enhanced their tolerance to IS. In the study of LGE, the three resins showed similar elution behaviors and no distinct peak tailings were observed. The salt concentrations at the elution peaks (IR) were in the order of FF-PEI-L680>FF-PEI-L270>Q Sepharose FF, indicating that the elution for the PEI resins needed higher salt concentrations, which was also an appearance of the salt-tolerant feature of the PEI resins. When protein loading amount was increased to the value equivalent to the DBC at 10% breakthrough, the adsorbed BSA could be eluted at lower salt concentrations. The chromatographic study has provided new insights into the practical application of the PEI-based anion exchangers.

Microbubbles as biocompatible porogens for hydrogel scaffolds

In this study, we explored the application of lipid-shelled, gas-filled microbubbles as a method for creating on-demand microporous hydrogels for cartilage tissue engineering. The technique allowed for homogenous distribution of cells and micropores within the scaffold, increasing the absorption coefficient of large solutes (70kDa dextran) over controls in a concentration-dependent manner. The stability of the gas phase of the microbubbles depended on several factors, including the initial size distribution of the microbubble suspension, as well as the temperature and pressure during culture. Application of pressure cycles provided controlled release of the gas phase to generate fluid-filled micropores with remnant lipid. The resulting microporous agarose scaffolds were biocompatible, leading to a twofold increase in engineered cartilage properties (E(Y)=492±42kPa for the bubble group vs. 249±49kPa for the bubble-free control group) over a 42-day culture period. Our results suggest that microbubbles offer a simple and robust method of modulating mass transfer in cell-seeded hydrogels through mild pressurization, and the methodology may be expanded in the future to include focused ultrasound for improved spatio-temporal control.

Living bacterial sacrificial porogens to engineer decellularized porous scaffolds

Decellularization and cellularization of organs have emerged as disruptive methods in tissue engineering and regenerative medicine. Porous hydrogel scaffolds have widespread applications in tissue engineering, regenerative medicine and drug discovery as viable tissue mimics. However, the existing hydrogel fabrication techniques suffer from limited control over pore interconnectivity, density and size, which leads to inefficient nutrient and oxygen transport to cells embedded in the scaffolds. Here, we demonstrated an innovative approach to develop a new platform for tissue engineered constructs using live bacteria as sacrificial porogens. E.coli were patterned and cultured in an interconnected three-dimensional (3D) hydrogel network. The growing bacteria created interconnected micropores and microchannels. Then, the scafold was decellularized, and bacteria were eliminated from the scaffold through lysing and washing steps. This 3D porous network method combined with bioprinting has the potential to be broadly applicable and compatible with tissue specific applications allowing seeding of stem cells and other cell types.

Microporous cell-laden hydrogels for engineered tissue constructs

In this article, we describe an approach to generate microporous cell-laden hydrogels for fabricating biomimetic tissue engineered constructs. Micropores at different length scales were fabricated in cell-laden hydrogels by micromolding fluidic channels and leaching sucrose crystals. Microengineered channels were created within cell-laden hydrogel precursors containing agarose solution mixed with sucrose crystals. The rapid cooling of the agarose solution was used to gel the solution and form micropores in place of the sucrose crystals. The sucrose leaching process generated homogeneously distributed micropores within the gels, while enabling the direct immobilization of cells within the gels. We also characterized the physical, mechanical, and biological properties (i.e., microporosity, diffusivity, and cell viability) of cell-laden agarose gels as a function of engineered porosity. The microporosity was controlled from 0% to 40% and the diffusivity of molecules in the porous agarose gels increased as compared to controls. Furthermore, the viability of human hepatic carcinoma cells that were cultured in microporous agarose gels corresponded to the diffusion profile generated away from the microchannels. Based on their enhanced diffusive properties, microporous cell-laden hydrogels containing a microengineered fluidic channel can be a useful tool for generating tissue structures for regenerative medicine and drug discovery applications.

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 of high-permeability and high-capacity monolith for protein chromatography

A novel approach for the fabrication of macroporous poly(glycidyl methacrylate-ethylene glycol dimethacrylate) monolith is presented. The method involved the use of sodium sulfate granules and organic solvents as co-porogens. Compared with the conventional monoliths [ML-(1-3)] using organic solvents only as a porogen, the improved monoliths [MLS-(1-3)] showed not only higher column efficiency and dynamic binding capacity (DBC) for protein (bovine serum albumin, BSA), but also higher column permeability and lower back pressure. It is considered that the superpores introduced by the solid granules played an important role for the improvement of the monolith performance. Moreover, poly(glycidyl methacrylate-diethylamine) tentacles were grafted onto the pore surface of MLS-3 monolith. This has further increased the DBC of BSA to 74.7 mg/ml, about three times higher than that of the monoliths without the grafted tentacles. This grafting does not obviously decrease the column permeability, so a new monolith of high column permeability and binding capacity has been produced for high-performance preparative protein chromatography.