Label-Free Separation of Induced Pluripotent Stem Cells with Anti-SSEA-1 Antibody Immobilized Microfluidic Channel

Temperature-modulated separation of vascular cells using thermoresponsive-anionic block copolymer-modified glass

Introduction

Vascular tissue engineering is a key technology in the field of regenerative medicine. In tissue engineering, the separation of vascular cells without cell modification is required, as cell modifications affect the intrinsic properties of the cells. In this study, we have developed an effective method for separating vascular cells without cell modification, using a thermoresponsive anionic block copolymer.

Methods

A thermoresponsive anionic block copolymer, poly(acrylic acid)-b-poly(N-isopropylacryl-amide) (PAAc-b-PNIPAAm), with various PNIPAAm segment lengths, was prepared in two steps: atom transfer radical polymerization and subsequent deprotection. Normal human umbilical vein endothelial cells (HUVECs), normal human dermal fibroblasts, and human aortic smooth muscle cells (SMCs) were seeded onto the prepared thermoresponsive anionic block copolymer brush-modified glass. The adhesion behavior of cells on the copolymer brush was observed at 37 °C and 20 °C.

Results

A thermoresponsive anionic block copolymer, poly(acrylic acid)-b-poly(N-isopropylacrylamide) (PAAc-b-PNIPAAm), with various PNIPAAm segment lengths was prepared. The prepared copolymer-modified glass exhibited anionic properties attributed to the bottom PAAc segment of the copolymer brush. On the PAAc-b-PNIPAAm, which had a moderate PNIPAAm length, a high adhesion ratio of HUVECs and low adhesion ratio of SMCs were observed at 37 °C. By reducing temperature from 37 °C to 20 °C, the adhered HUVECs were detached, whereas the SMCs maintained adhesion, leading to the recovery of purified HUVECs by changing the temperature.

Conclusions

The prepared thermoresponsive anionic copolymer-modified glass could be used to separate HUVECs and SMCs by changing the temperature without modifying the cell surface. Therefore, the developed cell separation method will be useful for vascular tissue engineering.

High-Density Microporous Drainage-Integrating Sheath Flow Generator for Streamlining Microfluidic Cell Sorting Systems

Tremendous efforts have been made to develop practical and efficient microfluidic cell and particle sorting systems; however, there are technological limitations in terms of system complexity and low operability. Here, we propose a sheath flow generator that can dramatically simplify operational procedures and enhance the usability of microfluidic cell sorters. The device utilizes an embedded polydimethylsiloxane (PDMS) sponge with interconnected micropores, which is in direct contact with microchannels and seamlessly integrated into the microfluidic platform. The high-density micropores on the sponge surface facilitated fluid drainage, and the drained fluid was used as the sheath flow for downstream cell sorting processes. To fabricate the integrated device, a new process for sponge-embedded substrates was developed through the accumulation, incorporation, and dissolution of PMMA microparticles as sacrificial porogens. The effects of the microchannel geometry and flow velocity on the sheath flow generation were investigated. Furthermore, an asymmetric lattice-shaped microchannel network for cell/particle sorting was connected to the sheath flow generator in series, and the sorting performances of model particles, blood cells, and spiked tumor cells were investigated. The sheath flow generation technique developed in this study is expected to streamline conventional microfluidic cell-sorting systems as it dramatically improves versatility and operability.

Thermoresponsive mixed polymer brush to effectively control the adhesion and separation of stem cells by altering temperature

During the last few decades, thermoresponsive materials for modulating cell adhesion have been investigated for the application of tissue engineering. In this study, we developed thermoresponsive mixed polymer brushes consisting of poly(N-isopropylacrylamide) (PNIPAAm) and poly(N,N-dimethylaminopropylacrylamide) (PDMAPAAm). The mixed polymer brushes were prepared on a glass substrate via the reversible addition-fragmentation chain transfer polymerization of DMAPAAm and subsequent atom transfer radical polymerization of NIPAAm. The mixed polymer brushes grafted to glass exhibited increased cationic properties by increasing the grafted PDMAPAAm length. The shrinking and extension of PNIPAAm exposed and concealed PDMAPAAm, respectively, indicating that the surface cationic properties can be controlled by changing the temperature. At 37 ​°C, the prepared mixed polymer brushes enhanced cell adhesion through their electrostatic interactions with cells. They also exhibited various thermoresponsive adhesion and detachment properties using various types of cells, such as mesenchymal stem cells. Temperature-controlled cell adhesion and detachment behavior differed between cell types. Using the prepared mixed polymer brush, we separated MSCs from adipocytes and HeLa cells by simply changing the temperature. Thus, the thermoresponsive mixed polymer brushes may be used to separate mesenchymal stem cells from their differentiated or contaminant cells by altering the temperature.

Thermoresponsive block copolymer brush for temperature-modulated hepatocyte separation

Hepatic tissue engineering may be an effective approach for the treatment of liver disease; however, its practical application requires hepatic cell separation technologies that do not involve cell surface modification and maintain cell activity. In this study, we developed hepatocyte cell separation materials using a thermoresponsive polymer and a polymer with high affinity to hepatocytes. A block copolymer of poly(N-p-vinylbenzyl-O-β-D-galactopyranosyl-(1→4)-D-gluconamide) (PVLA) and poly(N-isopropylacrylamide) (PNIPAAm) [PVLA-b-PNIPAAm] was prepared through two steps of atom transfer radical polymerization. On the prepared PVLA-b-PNIPAAm brush, HepG2 cells (model hepatocytes) adhered at 37 °C and detached at 20 °C, attributed to the temperature-modulated affinity between PVLA and HepG2. Cells from the immortalized human hepatic stellate cell line (TWNT-1) did not adhere to the copolymer brush, and RAW264.7 cells (mouse macrophage; model Kupffer cells) adhered to the copolymer brush, regardless of temperature. Using the difference in cell adhesion properties on the copolymer brush, temperature-modulated cell separation was successfully demonstrated. A mixture of HepG2, RAW264.7, and TWNT-1 cells was seeded on the copolymer brush at 37 °C for adherence. By reducing the temperature to 20 °C, adhered HepG2 cells were selectively recovered with a purity of approximately 85% and normal activity. In addition, induced pluripotent stem (iPS) cell-derived hepatocytes adhered on the PVLA-b-PNIPAAm brush at 37 °C and detached from the copolymer brush at 20 °C, whereas the undifferentiated iPS cells did not adhere, indicating that the prepared PVLA-b-PNIPAAm brush could be utilized to separate hepatocyte differentiated and undifferentiated cells. These results indicated that the newly developed PVLA-b-PNIPAAm brush can separate hepatic cells from contaminant cells by temperature modulation, without affecting cell activity or modifying the cell surface. Thus, the copolymer brush is expected to be a useful separation tool for cell therapy and tissue engineering using hepatocytes.

Downstream bioprocessing of human pluripotent stem cell-derived therapeutics

With the advancement in lineage-specific differentiation from human pluripotent stem cells (hPSCs), downstream cell separation has now become a critical step to produce hPSC-derived products. Since differentiation procedures usually result in a heterogeneous cell population, cell separation needs to be performed either to enrich the desired cell population or remove the undesired cell population. This article summarizes recent advances in separation processes for hPSC-derived cells, including the standard separation technologies, such as magnetic-activated cell sorting, as well as the novel separation strategies, such as those based on adhesion strength and metabolic flux. Specifically, the downstream bioprocessing flow and the identification of surface markers for various cell lineages are discussed. While challenges remain for large-scale downstream bioprocessing of hPSC-derived cells, the rational quality-by-design approach should be implemented to enhance the understanding of the relationship between process and the product and to ensure the safety of the produced cells.

Recent progress and perspectives in applications of 2-methacryloyloxyethyl phosphorylcholine polymers in biodevices at small scales

Bioinspired materials have attracted attention in a wide range of fields. Among these materials, a polymer family containing 2-methacryloyloxyethyl phosphorylcholine (MPC), which has a zwitterionic phosphorylcholine headgroup inspired by the...

Thermally-modulated cell separation columns using a thermoresponsive block copolymer brush as a packing material for the purification of mesenchymal stem cells

Cell therapy using mesenchymal stem cells (MSCs) is used as effective regenerative treatment. Cell therapy requires effective cell separation without cell modification and cellular activity reduction. In this study, we developed a temperature-modulated mesenchymal stem cell separation column. A temperature-responsive cationic block copolymer, poly(N,N-dimethylaminopropylacrylamide)-b-poly(N-isopropylacrylamide)(PDMAPAAm-b-PNIPAAm) brush with various cationic copolymer compositions, was grafted onto silica beads via two-step atom transfer radical polymerization. Using the packed beads, the elution behavior of the MSCs was observed. At 37 °C, the MSCs were adsorbed onto the column via both hydrophobic and electrostatic interactions with the PNIPAAm and PDMAPAAm segments of the copolymer brush, respectively. By reducing the temperature to 4 °C, the adsorbed MSCs were eluted from the column by reducing the hydrophobic and electrostatic interactions attributed to the hydration and extension of the PNIPAAm segment of the block copolymer brush. From the temperature-modulated adsorption and elution behavior of MSCs, a suitable DMAPAAm composition of the block copolymer brush was determined. Using the column, a mixture of MSC and BM-CD34⁺ cells was separated by simply changing the column temperature. The column was used to purify the MSCs, with purities of 78.2%, via a temperature change from 37 °C to 4 °C. Additionally, the cellular activity of the MSCs was retained throughout the column separation step. Overall, the obtained results show that the developed column is useful for MSC separation without cell modification and cellular activity reduction.

Impact of REDV peptide density and its linker structure on the capture, movement, and adhesion of flowing endothelial progenitor cells in microfluidic devices

Ligand-immobilization to stents and vascular grafts is expected to promote endothelialization by capturing flowing endothelial progenitor cells (EPCs). However, the optimized ligand density and linker structure have not been fully elucidated. Here, we report that flowing EPCs were selectively captured by the REDV peptide conjugated with a short linker. The microchannel surface was modified with the REDV peptide via Gly-Gly-Gly (G3), (Gly-Gly-Gly)₃ (G9), and diethylene glycol (diEG) linkers, and the moving velocity and captured ratio were evaluated. On the unmodified microchannels, the moving velocity of the cells exhibited a unimodal distribution similar to the liquid flow. The velocity of the endothelial cells and EPCs on the peptide-immobilized surface indicated a bimodal distribution, and approximately 20 to 30% of cells moved slower than the liquid flow, suggesting that the cells were captured and rolled on the surface. When the immobilized ligand density was lower than 1 molecule/nm², selective cell capture was observed only in REDV with G3 and diEG linkers, but not in G9 linkers. An in silico study revealed that the G9 linker tends to form a bent structure, and the REDV peptide is oriented to the substrate side. These results indicated that REDV captured the flowing EPC in a sequence-specific manner, and that the short linker was more adequate.

Thermoresponsive interfaces obtained using poly(N-isopropylacrylamide)-based copolymer for bioseparation and tissue engineering applications

Poly(N-isopropylacrylamide) (PNIPAAm) is the most well-known and widely used stimuli-responsive polymer in the biomedical field owing to its ability to undergo temperature-dependent hydration and dehydration with temperature variations, causing hydrophilic and hydrophobic alterations. This temperature-dependent property of PNIPAAm provides functionality to interfaces containing PNIPAAm. Notably, the hydrophilic and hydrophobic alterations caused by the change in the temperature-responsive property of PNIPAAm-modified interfaces induce temperature-modulated interactions with biomolecules, proteins, and cells. This intrinsic property of PNIPAAm can be effectively used in various biomedical applications, particularly in bioseparation and tissue engineering applications, owing to the functionality of PNIPAAm-modified interfaces based on the temperature modulation of the interaction between PNIPAAm-modified interfaces and biomolecules and cells. This review focuses on PNIPAAm-modified interfaces in terms of preparation method, properties, and their applications. Advances in PNIPAAm-modified interfaces for existing and developing applications are also summarized.

Selective capture and non-invasive release of cells using a thermoresponsive polymer brush with affinity peptides

Thermoresponsive block copolymer brush with cell affinity peptides was prepared via two steps of ATRP and subsequent click reaction. The prepared polymer brush can purify cells with high selectivity by simply changing temperature.

Bone-targeting phospholipid polymers to solubilize the lipophilic anticancer drug

Current chemotherapy methods have limited effectiveness in eliminating bone metastasis, which leads to a poor prognosis associated with severe bone disorders. To provide regional chemotherapy for this metastatic tumor, a bone-targeting drug carrier was produced by introducing the osteotropic bisphosphonate alendronate (ALN) units into an amphiphilic phospholipid polymer, poly(2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate). The polymer can form nanoparticles with a diameter of less than 30 nm; ALN units were exposed to the outer layer of the particle. A simple mixing procedure was used to encapsulate a hydrophobic anticancer drug, known as docetaxel (DTX), in the polymer nanoparticle, providing a uniform solution of a polymer-DTX complex in the aqueous phase. The complex showed anticancer activities against several breast cancer cell lines, and the complex formation did not hamper the pharmacological effect of DTX. The fluorescence observations evaluated by an in vivo imaging system and fluorescence microscopy showed that the addition of ALN to the polymer-DTX complex enhanced bone accumulation. Bone-targeting phospholipid polymers are potential solubilizing excipients used to formulate DTX and deliver the hydrophobic drug to bone tissues by blood administration.

Enhanced mechanical properties and cell separation with thermal control of PIPAAm-brushed polymer-blend microfibers

Thermoresponsive microfibers with enhanced mechanical properties for temperature-modulated cell separation were developed by electrospinning of blending PVBC and PBMA, and by subsequently modifying the microfibers with PIPAAm via ATRP.

Temperature-modulated cell-separation column using temperature-responsive cationic copolymer hydrogel-modified silica beads

There is strong demand for cell separation methods that do not decrease cell activity or modify cell surfaces. Here, new temperature-modulated cell-separation columns not requiring cell-surface premodification are described. The columns were packed with temperature-responsive cationic polymer hydrogel-modified silica beads. Poly(N-isopropylacrylamide-co-n-butyl methacrylate-co-N,N-dimethylaminopropyl acrylamide) hydrogels with various cationic moieties were attached to silica-bead surfaces by radical polymerization using N,N'-methylenebisacrylamide as a crosslinking agent. The beads were packed into solid-phase extraction columns, and temperature-dependent cell elution from the columns was found using HL-60 and Jurkat cells. The retention HL-60 and Jurkat cells in columns containing cationic beads at 37 °C was 95.3% to 99.6% and 95.0% to 98.8%, respectively. By contrast, beads without cationic properties exhibited low cell retention (20.6% for HL-60 and 32.5% for Jurkat cells). The cells were mainly retained through both electrostatic and hydrophobic interactions. The retained HL-60 (4.9%) and Jurkat cells (40%) were eluted at 4 °C from the column with a low composition of cationic monomer (DMAPAAm, 1 mol% in copolymer), because the temperature-responsive hydrogels on the beads became hydrophilic, decreasing the hydrophobic interactions between the cells and the beads. A higher number of Jurkat cells than HL-60 cells were eluted because of differences in their electrostatic properties (Jurkat cells: -2.53 mV; HL-60 cells: -20.7 mV). The results indicated that cell retention by the hydrogel-coated beads packed in a solid phase extraction column could be modulated simply by changing the temperature.

A surface graft polymerization process on chemically stable medical ePTFE for suppressing platelet adhesion and activation

An effective surface grafting method for chemically inert and elaborately porous medical expanded-polytetrafluoroethylene (ePTFE) was developed. Although surface graft polymerization onto basic polymeric biomaterials has been widely studied, successful modification of the ePTFE surface has been lacking due to its high chemical resistance. Herein, we succeeded in surface graft polymerization onto ePTFE through glycidyl methacrylate (GMA) as a bridge linkage following argon (Ar) plasma treatment. The epoxy group of GMA was expected to react with the peroxide groups produced on ePTFE by Ar plasma exposure, and its methacrylic groups can copolymerize with various monomers. In the present study, we selected 2-methacryloyloxyethyl phosphorylcholine (MPC) as a model monomer and the blood compatibility of modified ePTFE was evaluated. Two sequences of surface grafting were compared. In a two-step graft polymerization, GMA was first immobilized onto Ar plasma treated ePTFE, and then MPC was polymerized. In a one-step graft copolymerization, MPC and GMA were mixed and copolymerized simultaneously onto Ar plasma treated ePTFE, resulting in a poly(MPC-co-GMA) (PMG) graft surface. The roughness of the node-and-fibril structure of ePTFE was reduced by the uniform polymer layer, and the modified ePTFE had a good hydrophilic nature even after being stored in an aqueous environment for 30 days. The indispensable GMA in graft polymerization improved the surface grafting on ePTFE. The one-step and two-step graft polymerization methods could decrease the number of adhered platelets, and almost inhibit platelet activation. We concluded that graft polymerization with the GMA linker provides a novel strategy to modify the chemically inert ePTFE surfaces for functionalizing as new medical devices.