Retention dynamics of amphiphilic polymers PEG-lipids and PVA-Alkyl on the cell surface

Surface Engineering of Natural Killer Cells with CD44-targeting Ligands for Augmented Cancer Immunotherapy

Adoptive immunotherapy utilizing natural killer (NK) cells has demonstrated remarkable efficacy in treating hematologic malignancies. However, its clinical intervention for solid tumors is hindered by the limited expression of tumor-specific antigens. Herein, lipid-PEG conjugated hyaluronic acid (HA) materials (HA-PEG-Lipid) for the simple ex-vivo surface coating of NK cells is developed for 1) lipid-mediated cellular membrane anchoring via hydrophobic interaction and thereby 2) sufficient presentation of the CD44 ligand (i.e., HA) onto NK cells for cancer targeting, without the need for genetic manipulation. Membrane-engineered NK cells can selectively recognize CD44-overexpressing cancer cells through HA-CD44 affinity and subsequently induce in situ activation of NK cells for cancer elimination. Therefore, the surface-engineered NK cells using HA-PEG-Lipid (HANK cells) establish an immune synapse with CD44-overexpressing MIA PaCa-2 pancreatic cancer cells, triggering the "recognition-activation" mechanism, and ultimately eliminating cancer cells. Moreover, in mouse xenograft tumor models, administrated HANK cells demonstrate significant infiltration into solid tumors, resulting in tumor apoptosis/necrosis and effective suppression of tumor progression and metastasis, as compared to NK cells and gemcitabine. Taken together, the HA-PEG-Lipid biomaterials expedite the treatment of solid tumors by facilitating a sequential recognition-activation mechanism of surface-engineered HANK cells, suggesting a promising approach for NK cell-mediated immunotherapy.

Small Plasma Membrane-Targeted Fluorescent Dye for Long-Time Imaging and Protein Degradation Analyses

Plasma membrane (PM)-targeted fluorescent dyes have become an important tool to visualize morphological and dynamic changes in the cell membrane. However, most of these PM dyes are either too large and thus might potentially perturb the membrane and affect its functions or exhibit a short retention time on the cell membrane. The rapid internalization problem is particularly severe for PM dyes based on cationic and neutral hydrophobic fluorescent dyes, which can be easily transported into the cells by transmembrane potential and passive diffusion mechanisms. In this paper, we report a small but highly specific PM fluorescent dye, PM-1, which exhibits a very long retention time on the plasma membrane with a half-life of approximately 15 h. For biological applications, we demonstrated that PM-1 can be used in combination with protein labeling probes to study ectodomain shedding and endocytosis processes of cell surface proteins and successfully demonstrated that native transmembrane human carbonic anhydrase IX (hCAIX) is degraded via the ectodomain shedding mechanism. In contrast, hCAIX undergoes endocytic degradation in the presence of sheddase inhibitors. We believe that PM-1 can be a versatile tool to provide detailed insights into the dynamic processes of the cell surface proteins.

Precise assembly of inside-out cell membrane camouflaged nanoparticles via bioorthogonal reactions for improving drug leads capturing

Cell membrane camouflaged nanoparticles have been widely used in the field of drug leads discovery attribute to their unique biointerface targeting function. However, random orientation of cell membrane coating does not guarantee effective and appropriate binding of drugs to specific sites, especially when applied to intracellular regions of transmembrane proteins. Bioorthogonal reactions have been rapidly developed as a specific and reliable method for cell membrane functionalization without disturbing living biosystem. Herein, inside-out cell membrane camouflaged magnetic nanoparticles (IOCMMNPs) were accurately constructed via bioorthogonal reactions to screen small molecule inhibitors targeting intracellular tyrosine kinase domain of vascular endothelial growth factor recptor-2. Azide functionalized cell membrane acted as a platform for specific covalently coupling with alkynyl functionalized magnetic Fe₃O₄ nanoparticles to prepare IOCMMNPs. The inside-out orientation of cell membrane was successfully verified by immunogold staining and sialic acid quantification assay. Ultimately, two compounds, senkyunolide A and ligustilidel, were successfully captured, and their potential antiproliferative activities were further testified by pharmacological experiments. It is anticipated that the proposed inside-out cell membrane coating strategy endows tremendous versatility for engineering cell membrane camouflaged nanoparticles and promotes the development of drug leads discovery platforms.

Surface modulation of extracellular vesicles with cell-penetrating peptide-conjugated lipids for improvement of intracellular delivery to endothelial cells

Exosomes (diameter 30-200 nm) are a subtype of extracellular vesicles secreted by cells containing DNA, microRNA (miRNA), and proteins. Exosomes are expected to be valuable as a means of delivering drugs or functional miRNAs in treatment of diseases. However, the delivery of exosomes is not sufficiently effective, even though exosomes have intrinsic delivery functions. Cell-penetrating peptides (CPPs) are short peptide families that facilitate cellular intake of molecules and vesicles. We previously reported that the modification of cells, and liposomes with CPP-conjugated-lipids, CPPs conjugated with poly (ethylene glycol)-conjugated phospholipids (PEG-lipid), that induce adhesion by CPPs, can be useful for cell-based assays and harvesting liposomes. In this study, we aimed to modulate the exosome surface using Tat peptide (YGRKKRRQRRR)-PEG-lipids to improve intracellular delivery to endothelial cells. We isolated and characterized exosomes from the medium of HEK 293 T cell cultures. Tat conjugated PEG-lipids with different spacer molecular weights and lipid types were incorporated into exosomes using fluorescein isothiocyanate labeling to optimize the number of Tat-PEG-lipids immobilized on the exosome surface. The exosomes modified with Tat-PEG-lipids were incubated with human umbilical vein endothelial cells (HUVECs) to study the interaction. Tat conjugated with 5 kDa PEG and C16 lipids incorporated on the exosome surface were highly detected inside HUVECs by flow cytometry. Fluorescence was negligible in HUVECs for control groups. Thus, Tat-PEG-lipids can be modified on the exosome surface, improving the intracellular delivery of exosomes.

Lipid-mediated ex vivo cell surface engineering for augmented cellular functionalities

Once administrated, intercellular adhesion to recognize and/or arrest target cells is essential for specific treatments, especially for cancer or tumor. However, immune cells administrated into the tumor-microenvironment could lose their intrinsic functionalities such as target recognition ability, resulting in an ineffective cancer immunotherapy. Various manipulation techniques for decorating functional moieties onto cell surface and enhancing target recognition have been developed. A hydrophobic interaction-mediated ex-vivo cell surface engineering using lipid-based biomaterials could be a state-of-the-art engineering technique that could achieve high-efficiency cell surface modification by a single method without disturbance of intrinsic characteristics of cells. In this regard, this review provides design principles for the development of lipid-based biomaterials with a linear structure of lipid, polyethylene glycol, and functional group, strategies for the synthesis process, and their practical applications in biomedical engineering. Especially, we provide new insights into the development of a novel surface coating techniques for natural killer (NK) cells with engineering decoration of cancer targeting moieties on their cell surfaces. Among immune cells, NK cells are interesting cell population for substituting T cells because of their excellent safety and independent anticancer efficacy. Thus, optimal strategies to select cancer-type-specific targeting moieties and present them onto the surface of immune cells (especially, NK cells) using lipid-based biomaterials could provide additional tools to capture cancer cells for developing novel immune cell therapy products. Enhanced anticancer efficacies by surface-engineered NK cells have been demonstrated both in vitro and in vivo. Therefore, it could be speculated that recent progresses in cell surface modification technology via lipid-based biomaterials could strengthen immune surveillance and immune synapses for utilization in a next-generation cancer immunotherapy, beyond currently available genetic engineering tool such as chimeric antigen receptor-mediated immune cell modulation.

Sortase A: A chemoenzymatic approach for the labeling of cell surfaces

Sortase A, a transpeptidase enzyme is present in many Gram-positive bacteria and helps in the recruitment of the cell surface proteins. Over the last two decades, Sortase A has become an attractive tool for performing in vivo and in vitro ligations. Sortase A-mediated ligation has continuously been used for its specificity, robustness, and highly efficient nature. These properties make it a popular choice among protein engineers as well as researchers from different fields. In this review, we give an overview of Sortase A-mediated ligation of various molecules on the cell surfaces, which can have diverse applications in interdisciplinary fields.

A Decade of Advances in Single-Cell Nanocoating for Mammalian Cells

Strategic advances in the single-cell nanocoating of mammalian cells have noticeably been made during the last decade, and many potential applications have been demonstrated. Various cell-coating strategies have been proposed via adaptation of reported methods in the surface sciences and/or materials identification that ensure the sustainability of labile mammalian cells during chemical manipulation. Here an overview of the methodological development and potential applications to the healthcare sector in the nanocoating of mammalian cells made during the last decade is provided. The materials used for the nanocoating are categorized into polymers, hydrogels, polyphenolic compounds, nanoparticles, and minerals, and the corresponding strategies are described under the given set of materials. It also suggests, as a future direction, the creation of the cytospace system that is hierarchically composed of the physically separated but mutually interacting cellular hybrids.

Potential of Cell Surface Engineering with Biocompatible Polymers for Biomedical Applications

The regulation of the cellular surface with biomaterials can contribute to the progress of biomedical applications. In particular, the cell surface is exposed to immunological surveillance and reactions in transplantation therapy, and modulation of cell surface properties might improve transplantation outcomes. The transplantation of therapeutic cells, tissue, and organs is an effective and fundamental treatment and has contributed to saving lives and improving quality of life. Because of shortages, donor cells, tissues, and organs are carefully transplanted with the goal of retaining activity and viability. However, some issues remain to be resolved in terms of reducing side effects, improving graft survival, managing innate and adaptive immune responses, and improving transplant storage and procedures. Given that the transplantation process involves multiple steps and is technically complicated, an engineering approach together with medical approaches to resolving these issues could enhance success. In particular, cell surface engineering with biocompatible polymers looks promising for improving transplantation therapy and has potential for other biomedical applications. Here we review the significance of polymer-based surface modification of cells and organs for biomedical applications, focusing on the following three topics: Cell protection: cellular protection through local immune regulation using cell surface modification with biocompatible polymers. This protection could extend to preventing attack by the host immune system, freeing recipients from taking immunosuppressive drugs, and avoiding a second transplantation. Cell attachment: cell manipulation, which is an important technique for delivery of therapeutic cells and their alignment for recellularization of decellularized tissues and organs in regenerative therapy. Cell fusion: fusion of different cells, which can lead to the formation of new functional cells that could be useful for generating, e.g., immunologically competent or metabolically active cells.

100th Anniversary of Macromolecular Science Viewpoint: Re-Engineering Cellular Interfaces with Synthetic Macromolecules Using Metabolic Glycan Labeling

Cell-surface functionality is largely programmed by genetically encoded information through modulation of protein expression levels, including glycosylation enzymes. Genetic tools enable control over protein-based functionality, but are not easily adapted to recruit non-native functionality such as synthetic polymers and nanomaterials to tune biological responses and attach therapeutic or imaging payloads. Similar to how polymer-protein conjugation evolved from nonspecific PEGylation to site-selective bioconjugates, the same evolution is now occurring for polymer-cell conjugation. This Viewpoint discusses the potential of using metabolic glycan labeling to install bio-orthogonal reactive cell-surface anchors for the recruitment of synthetic polymers and nanomaterials to cell surfaces, exploring the expanding therapeutic and diagnostic potential. Comparisons to conventional approaches that target endogenous membrane components, such as hydrophobic, protein coupling and electrostatic conjugation, as well as enzymatic and genetic tools, have been made to highlight the huge potential of this approach in the emerging cellular engineering field.

Optimization and Stability of Cell-Polymer Hybrids Obtained by "Clicking" Synthetic Polymers to Metabolically Labeled Cell Surface Glycans

Re-engineering of mammalian cell surfaces with polymers enables the introduction of functionality including imaging agents, drug cargoes or antibodies for cell-based therapies, without resorting to genetic techniques. Glycan metabolic labeling has been reported as a tool for engineering cell surface glycans with synthetic polymers through the installation of biorthogonal handles, such as azides. Quantitative assessment of this approach and the robustness of the engineered coatings has yet to be explored. Here, we graft poly(hydroxyethyl acrylamide) onto azido-labeled cell surface glycans using strain-promoted azide-alkyne "click" cycloaddition and, using a combination of flow cytometry and confocal microscopy, evaluate the various parameters controlling the outcome of this "grafting to" process. In all cases, homogeneous cell coatings were formed with >95% of the treated cells being covalently modified, superior to nonspecific "grafting to" approaches. Controllable grafting densities could be achieved through modulation of polymer chain length and/or concentration, with longer polymers having lower densities. Cell surface bound polymers were retained for at least 72 h, persisting through several mitotic divisions during this period. Furthermore, we postulate that glycan/membrane recycling is slowed by the steric bulk of the polymers, demonstrating robustness and stability even during normal biological processes. This cytocompatible, versatile and simple approach shows potential for re-engineering of cell surfaces with new functionality for future use in cell tracking or cell-based therapies.

Simple and rapid extracellular vesicles quantification via membrane biotinylation strategy coupled with fluorescent nanospheres-based lateral flow assay

Extracellular vesicles (EVs) are cell-excreted membrane particles existing in a variety of biological fluids. As potential noninvasive biomarkers, EVs have received wide attention in recent years. However, usual EVs assays are complex, time-consuming and costly, thus limiting their clinical utility. Simple and rapid EVs quantification within biological fluids remains challenging. Here, we developed a simple, rapid strategy for EVs quantification, which combined with lateral flow assay and membrane biotinylation strategy. By utilizing biotin-functionalized phosphatidylethanolamine (DSPE-PEG-Biotin), the membrane of EVs could be successfully modified with biotin under strong hydrophobic interactions. Subsequently, based on the high affinity between streptavidin and biotin, quantification assay was achieved by lateral flow assay with fluorescent nanospheres (FNs) as a reporter. Biotinylation of biogenic EVs could be reached to 85%. This proposed method enables sensitive detection of 2.0 × 10³ particles/μL. The whole procedure time was within 1 h. Furthermore, this approach was used to detect EVs in biological samples, demonstrating potential clinical applications.

Synthetic Polyampholytes as Macromolecular Cryoprotective Agents

A series of polyampholytes based on different molar ratios on N, N-dimethylaminopropyl methacrylamide (DMAPMA), acrylic acid (AA), and optionally, N- tert-butylacrylamide ( t-BuAAm), were prepared by free radical copolymerization, and tested as DMSO-free cryoprotective agents for 3T3 fibroblast cells by using a standard freeze-rethaw protocol. Polybetaines prepared by reaction of DMAPMA homo and copolymers with 1,3-propane sultone were used as additional controls. Results showed strong effects of copolymer composition, molecular weight, polymer and NaCl concentrations, on post-thaw cell viability. Binary (DMAPMA/AA) copolymers showed best post-thaw cell viability of 70% at a 30/70 mol % ratio of DMAPMA/AA, which increased to 90% upon introduction of 9 mol % t-BuAAm while maintaining the 30/70 mol % cation/anion ratio. The use of acrylamide linkages in DMAPMA ensures absence of hydrolytic loss of cationic side chains. These polyampholytes were found to decrease ice crystal size and to form a polymer-rich, ice-free layer around cells, reducing damage from intercellular ice crystals during both freezing and thawing steps. These polyampholytes also dehydrate cells during freezing, which helps protect cells from intracellular ice damage. While cell viability immediately after thawing was high, subsequent culturing revealed poor attachment and long-term viability, which is attributed to residual cell damage from intracellular ice formation. Addition of 2 wt % DMSO or 1% BSA to the polymer-based freeze medium was found to mitigate this damage and result in post-thaw viabilities matching those achieved with 10 wt % DMSO.

Increasing Salt Rejection of Polybenzimidazole Nanofiltration Membranes via the Addition of Immobilized and Aligned Aquaporins

Aquaporins are water channel proteins in cell membrane, highly specific for water molecules while restricting the passage of contaminants and small molecules, such as urea and boric acid. Cysteine functional groups were installed on aquaporin Z for covalent attachment to the polymer membrane matrix so that the proteins could be immobilized to the membranes and aligned in the direction of the flow. Depth profiling using x-ray photoelectron spectrometer (XPS) analysis showed the presence of functional groups corresponding to aquaporin Z modified with cysteine (Aqp-SH). Aqp-SH modified membranes showed a higher salt rejection as compared to unmodified membranes. For 2 M NaCl and CaCl₂ solutions, the rejection obtained from Aqp-SH membranes was 49.3 ± 7.5% and 59.1 ± 5.1%. On the other hand, the rejections obtained for 2 M NaCl and CaCl₂ solutions from unmodified membranes were 0.8 ± 0.4% and 1.3 ± 0.2% respectively. Furthermore, Aqp-SH membranes did not show a significant decrease in salt rejection with increasing feed concentrations, as was observed with other membranes. Through simulation studies, it was determined that there was approximately 24% capping of membrane pores by dispersed aquaporins.

Long-Circulating Amphiphilic Doxorubicin for Tumor Mitochondria-Specific Targeting

The mitochondria have emerged as a novel target for cancer chemotherapy primarily due to their central roles in energy metabolism and apoptosis regulation. Here, we report a new molecular approach to achieve high levels of tumor- and mitochondria-selective deliveries of the anticancer drug doxorubicin. This is achieved by molecular engineering, which functionalizes doxorubicin with a hydrophobic lipid tail conjugated by a solubility-promoting poly(ethylene glycol) polymer (amphiphilic doxorubicin or amph-DOX). In vivo, the amphiphile conjugated to doxorubicin exhibits a dual function: (i) it binds avidly to serum albumin and hijacks albumin's circulating and transporting pathways, resulting in prolonged circulation in blood, increased accumulation in tumor, and reduced exposure to the heart; (ii) it also redirects doxorubicin to mitochondria by altering the drug molecule's intracellular sorting and transportation routes. Efficient mitochondrial targeting with amph-DOX causes a significant increase of reactive oxygen species levels in tumor cells, resulting in markedly improved antitumor efficacy than the unmodified doxorubicin. Amphiphilic modification provides a simple strategy to simultaneously increase the efficacy and safety of doxorubicin in cancer chemotherapy.

Cell surface engineering and application in cell delivery to heart diseases

Cell-based therapy has expanded its influence in cancer immunotherapy, regenerative medicine, and tissue engineering. Due to their secretory functions, differentiation capabilities, specific homing effects through chemotaxis, distinctive therapeutic potentials, and ex vivo expandability, cells have become an attractive reagent for advanced therapeutic strategies. Therefore, the ability to modify cells and manipulate their functions according to intended therapeutic designs has been the central scientific interest in the field of biomedical research. Many innovative methods have been developed with genetic modification of cells being the most advanced cell surface engineering technique. Although genetic modification is a powerful tool, it has a limited applicability due to the permanent modifications made on cells. Alternatively, many endeavors have been made to develop surface engineering techniques that can circumvent the limitations of genetic modification. In this review, current methods of non-genetic cell surface modification, including chemical conjugations, polymeric encapsulation, hydrophobic insertion, enzymatic and metabolic addition, will be introduced. Moreover, cell surface engineering plausible for cardiac remodeling and the future prospective will be discussed at the end.

Robust and Antibacterial Polymer/Mechanically Exfoliated Graphene Nanocomposite Fibers for Biomedical Applications

With the increasing demand for composites of multifunctional and integrated performance, graphene-based nanocomposites have been attracting increasing attention in biomedical applications because of their outstanding physicochemical properties and biocompatibility. High product yields and dispersion of graphene in the preparation process of graphene-based nanocomposites have long been a challenge. Further, the mechanical properties and biosafety of final nanocomposites are very important for real usage in biomedical applications. Here, we presented a novel high-throughput method of graphene on mechanical exfoliation in a natural honey medium, and a yield of ∼91% of graphene nanoflakes can be easily achieved with 97.76% of single-layer graphenes. The mechanically exfoliated graphene (MEG) can be well-dispersed in the poly(vinyl alcohol) (PVA) matrix. The PVA/MEG nanocomposite fibers are obtained by gel spinning and stretched 20 times. As a candidate for monofilament sutures, the PVA/MEG nanocomposite fibers with 0.3 wt % of MEG have an ultrahigh ultimate tensile strength of 2.1 GPa, which is far higher than that of the neat PVA fiber (0.75 GPa). In addition, the PVA/MEG nanocomposite fibers also have antibacterial property, low cytotoxicity, and other properties. On the basis of the above-mentioned properties, the effects of a common surgical suture and PVA/MEG nanocomposite fibers on wound healing are evaluated. As a result, the wounds treated with PVA/MEG nanocomposite fibers with 0.3 wt % of MEG show the best healing after 5 days of surgery. It is possible that this novel surgical suture will be available in the market relying on the gentle, inexpensive method of obtaining nonoxidized graphene and the simple process of obtaining nanocomposite fibers.

Ratiometric fluorescence imaging of cell surface pH by poly(ethylene glycol)-phospholipid conjugated with fluorescein isothiocyanate

Various physiological and pathological processes are accompanied with the alteration of pH at extracellular juxtamembrane region. Accordingly, the methods to analyze the cell surface pH have been demanded in biological and medical sciences. In this study, we have established a novel methodology for cell surface pH imaging using poly(ethylene glycol)-phospholipid (PEG-lipid) as a core structure of ratiometric fluorescent probes. PEG-lipid is a synthetic amphiphilic polymer originally developed for the cell surface modification in transplantation therapy. Via its hydrophobic alkyl chains of the phospholipid moiety, PEG-lipid is, when applied extracellularly, spontaneously inserted into the plasma membrane and retained at the surface of the cells. We have demonstrated that the PEG-lipid conjugated with fluorescein isothiocyanate (FITC-PEG-lipid) can be used as a sensitive and reversible cell-surface-anchored pH probe between weakly alkaline and acidic pH with an excellent spatiotemporal resolution. The remarkably simple procedure for cell-surface labeling with FITC-PEG-lipid would also be advantageous when considering its application to high-throughput in vitro assay. This study further indicates that various probes useful for the investigation of juxtamembrane environments could also be developed by using PEG-lipid as the core structure for bio-membrane anchoring.

Subcellular Fate of a Fluorescent Cholesterol-Poly(ethylene glycol) Conjugate: An Excellent Plasma Membrane Imaging Reagent

Cholesterol-containing molecules or nanoparticles play a significant role in achieving favorable plasma membrane imaging and efficient cellular uptake of drugs by the excellent membrane anchoring capability of the cholesterol moiety. By linking cholesterol to a water-soluble component (such as poly(ethylene glycol), PEG), the resulting cholesterol-PEG conjugate can form micelles in aqueous solution through self-assembly, and such a micellar structure represents an important drug delivery vehicle in which hydrophobic drugs can be encapsulated. However, the understanding of the subcellular fate and cytotoxicity of cholesterol-PEG conjugates themselves remains elusive. Herein, by using cholesterol-PEG2000-fluorescein isothiocyanate (Chol-PEG-FITC) as a model system, we found that the Chol-PEG-FITC molecules could attach to the plasma membranes of mammalian cells within 10 min and such a firm membrane attachment could last at least 1 h, displaying excellent plasma membrane staining performance that surpassed that of commonly used commercial membrane dyes such as DiD and CellMask. Besides, we systematically studied the endocytosis pathway and intracellular distribution of Chol-PEG-FITC and found that the cell surface adsorption and endocytosis processes of Chol-PEG-FITC molecules were lipid-raft-dependent. After internalization, the Chol-PEG-FITC molecules gradually reached many organelles with membrane structures. At 5 h, they were mainly distributed in lysosomes and the Golgi apparatus, with some in the endoplasmic reticulum (ER) and very few in the mitochondrion. At 12 h, the Chol-PEG-FITC molecules mostly aggregated in the Golgi apparatus and ER close to the nucleus. Finally, we demonstrated that Chol-PEG-FITC was toxic to mammalian cells only at concentrations above 50 μM. In summary, Chol-PEG-FITC can be a promising plasma membrane imaging reagent to avoid the fast cellular internalization and quick membrane detachment problems faced by commercial membrane dyes. We believe that the investigation of the dynamic subcellular fate of Chol-PEG-FITC can provide important knowledge to facilitate the use of cholesterol-PEG conjugates in fields such as cell surface engineering and drug delivery.

Long-Time Plasma Membrane Imaging Based on a Two-Step Synergistic Cell Surface Modification Strategy

Long-time stable plasma membrane imaging is difficult due to the fast cellular internalization of fluorescent dyes and the quick detachment of the dyes from the membrane. In this study, we developed a two-step synergistic cell surface modification and labeling strategy to realize long-time plasma membrane imaging. Initially, a multisite plasma membrane anchoring reagent, glycol chitosan-10% PEG2000 cholesterol-10% biotin (abbreviated as "GC-Chol-Biotin"), was incubated with cells to modify the plasma membranes with biotin groups with the assistance of the membrane anchoring ability of cholesterol moieties. Fluorescein isothiocyanate (FITC)-conjugated avidin was then introduced to achieve the fluorescence-labeled plasma membranes based on the supramolecular recognition between biotin and avidin. This strategy achieved stable plasma membrane imaging for up to 8 h without substantial internalization of the dyes, and avoided the quick fluorescence loss caused by the detachment of dyes from plasma membranes. We have also demonstrated that the imaging performance of our staining strategy far surpassed that of current commercial plasma membrane imaging reagents such as DiD and CellMask. Furthermore, the photodynamic damage of plasma membranes caused by a photosensitizer, Chlorin e6 (Ce6), was tracked in real time for 5 h during continuous laser irradiation. Plasma membrane behaviors including cell shrinkage, membrane blebbing, and plasma membrane vesiculation could be dynamically recorded. Therefore, the imaging strategy developed in this work may provide a novel platform to investigate plasma membrane behaviors over a relatively long time period.

Synthesis of lipo-glycopolymers for cell surface engineering

A novel synthetic lipo-glycopolymer was inserted into cell membranes for cell surface engineering.

Interaction of poly(ethylene glycol)-conjugated phospholipids with supported lipid membranes and their influence on protein adsorption

We studied real-time interaction between poly(ethylene glycol)-conjugated phospholipids (PEG-lipids) and a supported lipid membrane by surface plasmon resonance (SPR) spectroscopy to understand dynamic behaviors of PEG-lipids on living cell membranes. Supported lipid membranes formed on a hydrophobic surface were employed as a model of living cell membrane. We prepared three kinds of PEG-lipids that carried alkyl chains of different lengths for SPR measurements and also performed fluorescence recovery after photobleaching (FRAP) to study the influence of acyl chain length on dynamics on the supported membrane. PEG-lipids were uniformly anchored to lipid membranes with high fluidity without clustering. Incorporation and dissociation rates of PEG-lipids into supported membranes strongly depended on the length of acyl chains; longer acyl chains reduced the incorporation rate and the dissociation rate of PEG-lipid. Furthermore, protein adsorption experiment with bovine serum albumin indicated that PEG modification prevented the adsorption of bovine serum albumin on such supported membrane.

Influence of molecular weight of PEG chain on interaction between streptavidin and biotin-PEG-conjugated phospholipids studied with QCM-D

Poly(ethylene glycol)-conjugated phospholipid (PEG-lipid) derivatives spontaneously incorporate into lipid bilayer membranes, thus, they are useful for immobilizing bioactive substances onto cell surfaces. Here, we investigated how the density and molecular weight of PEG molecules influenced immobilization and cellular uptake of a bioactive substance. We analyzed how three biotin-PEG-lipids (1k, 5k, and 40k, with PEG molecular weights: 1kD, 5kD, and 40kD, respectively) interacted with streptavidin on a surface attached to a quartz crystal microbalance with dissipation (QCM-D). We found that the volume excluded by 1k PEG could not effectively prevent adsorption of bovine serum albumin (BSA). In contrast, 5k PEG chains could completely prevent protein adsorption. However, due to strong static repulsion, 40k PEG chains could not be packed at high density. Thus, BSA migrated between PEG chains, and adsorption was not effectively prevented. When streptavidin was added, it bound to multiple neighboring sites on 1k and 5k biotin-PEG-lipids, which reduced chain viscoelasticity. In contrast, streptavidins bound at a one-to-one stoichiometry with the 40k biotin-PEG-lipids, which increased chain viscoelasticity. However, differences in PEG viscoelasticity and PEG molecular weights did not influence cellular uptake of immobilized streptavidin. Therefore, these are not important factors in designing polymers that prevent cellular endocytosis.

STATEMENT OF SIGNIFICANCE

Poly(ethylene glycol)-conjugated phospholipid (PEG-lipid) derivatives have been widely used to modify not only liposome surface, but also the surfaces of cells and pancreatic islets for cell transplantation. Since the entire cell surface can be modified with PEG-lipid through hydrophobic interactions, it is a promising approach for improving graft survival in clinical settings. Although the surface modification is protective in the early stages of transplantation, it is important to understand the factors that influence on the cellular uptake. In this study, we examined the influence of the surface density and molecular weights of PEG-lipids on the cellular uptake by QCM-D and cellular experiments. It was found that the differences in viscoelasticity of PEG chain did not affect on the cellular uptake.

Impact of structural differences in hyperbranched polyglycerol–polyethylene glycol nanoparticles on dermal drug delivery and biocompatibility

Polyglycerol scaffolds and nanoparticles emerged as prominent material for various biomedical applications including topical drug delivery. The impact of slight structural modifications on the nanoparticles' properties, drug delivery potential, and biocompatibility, however, is still not fully understood.Hence, we explored the influence of structural modifications of five structurally related polyglycerol-based nanoparticles (PG-PEG, SK1-SK5) on dermal drug delivery efficiency and biocompatibility. The PG-PEG particles were synthesized via randomly and controlled alkylated chemo-enzymatic approaches resulting in significantly varying particle sizes and interactions with guest molecules. Furthermore, weobserved considerably improved dermal drug delivery with the smallest particles SK4 and SK5 (11 nm and 14 nm) which also correlated with well-defined surface properties achieved by the controlled alkylated synthesis approach. The consistently good biocompatibility for all PG-PEG particles was mainly attributed to the neutral surface charge. No irritation potential, major cytotoxicity or genotoxicity was observed. Nevertheless, slightly better biocompatibility was again seen for the particles characterized by alkyl chain substitution in the core and not on the particle surface.Despite the high structural similarity of the PG-PEG particles, the synthesis and the functionalization significantly influenced particle properties, biocompatibility, and most significantly the drug delivery efficiency.

Carbohydrate-derived amphiphilic macromolecules: a biophysical structural characterization and analysis of binding behaviors to model membranes

The design and synthesis of enhanced membrane-intercalating biomaterials for drug delivery or vascular membrane targeting is currently challenged by the lack of screening and prediction tools. The present work demonstrates the generation of a Quantitative Structural Activity Relationship model (QSAR) to make a priori predictions. Amphiphilic macromolecules (AMs) "stealth lipids" built on aldaric and uronic acids frameworks attached to poly(ethylene glycol) (PEG) polymer tails were developed to form self-assembling micelles. In the present study, a defined set of novel AM structures were investigated in terms of their binding to lipid membrane bilayers using Quartz Crystal Microbalance with Dissipation (QCM-D) experiments coupled with computational coarse-grained molecular dynamics (CG MD) and all-atom MD (AA MD) simulations. The CG MD simulations capture the insertion dynamics of the AM lipophilic backbones into the lipid bilayer with the PEGylated tail directed into bulk water. QCM-D measurements with Voigt viscoelastic model analysis enabled the quantitation of the mass gain and rate of interaction between the AM and the lipid bilayer surface. Thus, this study yielded insights about variations in the functional activity of AM materials with minute compositional or stereochemical differences based on membrane binding, which has translational potential for transplanting these materials in vivo. More broadly, it demonstrates an integrated computational-experimental approach, which can offer a promising strategy for the in silico design and screening of therapeutic candidate materials.

Imaging plasma membranes without cellular internalization: multisite membrane anchoring reagents based on glycol chitosan derivatives

Using a multisite membrane anchoring strategy, a new plasma membrane imaging reagent without cellular internalization was designed.

Cell Surface Engineering for Regulation of Immune Reactions in Cell Therapy

Transplantation of the pancreatic islets of Langerhans (islets) is a promising cell therapy for treating insulin-dependent type 1 diabetes mellitus. Islet transplantation is a minimally-invasive technique involving relatively simple surgery. However, after intraportal transplantation, the transplanted islets are attacked by the recipient's immune system, because they activate a number of systems, including coagulation, complement response, inflammation, immune rejection, and recurrence of autoimmune disease. We have developed a surface modification and microencapsulation technique that protects cells and islets with biomaterials and bioactive substances, which may be useful in clinical settings. This approach employs amphiphilic polymers, which can interact with lipid bilayer membranes, without increasing cell volume. Molecules attached to these polymers can protect transplanted cells and islets from attack by the host immune system. We expect that this surface modification technique will improve graft survival in clinical islet transplantation.

Short peptide motifs for long-lasting anchoring to the cell surface

A rational design strategy has been developed for the construction of stable peptide-based anchors for the efficient modification of cell surfaces. Six types of peptide composed of five residues with divalent hydrophobic groups have been designed using this new strategy. Among them, a peptide with a sequence of NBD-Lys-Lys(X)-Lys-Lys-Lys(X)-NH2 (NBD: fluorophore, Lys(X): N-ε-palmitoyl-l-lysine) was found to show the highest modification efficacy and longevity in culture medium. The good performance of this peptide was attributed to (1) its high aqueous solubility, which allowed it to partition from the medium to the cell surface, and (2) the high binding affinity of the saturated palmitoyl groups to the cell membrane. We found that the distribution of the peptide was affected by recycling endosome, which enabled the representation of the peptide following its endocytotic disappearance from the cell membrane. Biotin was also presented on the cell surface using this peptide-based anchor to examine its recognition by streptavidin. The efficacy of the recognition process increased as the length of the oligoethylene glycol spacer increased, indicating that it was necessary for the biotin tag to move away from the membrane glycoproteins on the cell surface to facilitate its efficient recognition by streptavidin.

Fluorescence-encoded gold nanoparticles: library design and modulation of cellular uptake into dendritic cells

In order to harness the unique properties of nanoparticles for novel clinical applications and to modulate their uptake into specific immune cells we designed a new library of homo- and hetero-functional fluorescence-encoded gold nanoparticles (Au-NPs) using different poly(vinyl alcohol) and poly(ethylene glycol)-based polymers for particle coating and stabilization. The encoded particles were fully characterized by UV-Vis and fluorescence spectroscopy, zeta potential and dynamic light scattering. The uptake by human monocyte derived dendritic cells in vitro was studied by confocal laser scanning microscopy and quantified by fluorescence-activated cell sorting and inductively coupled plasma atomic emission spectroscopy. We show how the chemical modification of particle surfaces, for instance by attaching fluorescent dyes, can conceal fundamental particle properties and modulate cellular uptake. In order to mask the influence of fluorescent dyes on cellular uptake while still exploiting its fluorescence for detection, we have created hetero-functionalized Au-NPs, which again show typical particle dependent cellular interactions. Our study clearly prove that the thorough characterization of nanoparticles at each modification step in the engineering process is absolutely essential and that it can be necessary to make substantial adjustments of the particles in order to obtain reliable cellular uptake data, which truly reflects particle properties.

Microencapsulation of cells, including islets, within stable ultra-thin membranes of maleimide-conjugated PEG-lipid with multifunctional crosslinkers

The encapsulation of islets of Langerhans (islets) and insulin-secreting cells within a semi-permeable membrane has been suggested as a safe and simple technique for islet transplantation to attenuate early graft loss and avoid immunosuppressive therapy. The total volume of these implants tends, however, to increase upon encapsulation of the islets and cells within the polymer membrane, limiting transport between encapsulated cells and the surrounding tissue. Ultra-thin membranes could potentially overcome these diffusion limitations to provide for clinically applicable implants. Here we propose a method to encapsulate islets and cells within a stable ultra-thin polymer membrane using poly(ethylene glycol)-conjugated phospholipid bearing a maleimide group (Mal-PEG-lipids) and multiple interactive polymers (e.g., 4-arm PEG-Mal and 8-arm PEG-SH). When Mal-PEG-lipids were added to islet and cell suspensions, spontaneous incorporation into a cell surface occurred from the micelles at an equilibrium state. The addition of 4-arm PEG-Mal and 8-arm PEG-SH to the mixture induced a substantial increase in the membrane thickness because a number of Mal-PEG-lipid micelles were involved in the membrane formation at the micrometer level. No appreciable increase in islet volume was observed after microencapsulation by this method. Microencapsulation of islets with the polymer membranes, which showed semi-permeability, did not impair insulin release in response to glucose stimulation, even after 7 days. The polymer membrane structure surrounding the islets and cells was well maintained for at least 30 days. In addition, the membrane formed showed much lower thrombogenicity and inhibited complement activation upon exposure to human whole blood and serum.

Interfacial Properties of Polyethylene Glycol/Vinyltriethoxysilane (PEG/VTES) Copolymers and their Application to Stain Resistance

In this study, polyethylene glycol (PEG) and vinyltriethoxysilane (VTES) were used in different proportions to produce a series of PEG–VTES copolymers. The copolymer molecular structures were confirmed by FTIR spectroscopy. In addition, their surface activities were evaluated by evaluating the surface tension, contact angle, and foaming properties. The results showed that these surfactants exhibited excellent surface activities and wetting power, as well as low foaming. Consequently, the application of a series of PEG/VTES copolymers can make cotton fabrics stain resistant.

The non-invasive cell surface modification of hepatocytes with PEG-lipid derivatives

Hepatocyte-based therapies are promising regenerative approaches for liver diseases. In this study, we sought to develop a versatile method to modify the surface of hepatocytes by immobilizing synthetic polymers around the cells. The surface of murine primary hepatocytes was modified using poly(ethylene glycol)-phospholipids conjugate bearing FITC (FITC-PEG-lipid) in suspension. Hepatocyte function was assessed in vitro by examining cell viability, plating efficiency, protein production, metabolizing activity, hepatocyte-specific gene expressions, and cytochrome P450 induction. The engraftment of the PEG-lipid modified cells was studied following transplantation to both the liver or alternate ectopic sites. Among the types of phospholipids analyzed in our study, 1,2-dimyristoil -sn-glycerol-3-phosphatidylethanolamine (DMPE) was found to be uniformly anchored to the hepatocyte cell membrane (>99% of hepatocytes). Cell surface modification using FITC-PEG-DMPE did not result in any loss of in vitro functional parameters nor affect the engraftment potential in vivo by the modified cells. This modification was also successfully performed on dispersed hepatocytes and engineered hepatocyte sheets. In all, the ability to modify the surface of isolated hepatocytes with functional proteins, instead of FITC as shown in our proof-of-concept study, has the potential to move hepatocyte-based cell therapy another step forward as a viable therapeutic application.

Islet surface modification with urokinase through DNA hybridization

Transplantation of islets of Langerhans (islets) has been proposed as a safe, effective approach to treating patients with insulin-dependent diabetes mellitus (type I diabetes). It has been reported, however, that many islets are lost in the early phase after intraportal transplantation by instant blood coagulation-mediated inflammatory reactions. In this study, DNA hybridization was applied to conjugate the fibrinolytic enzyme urokinase on the islet surface. We synthesized amphiphilic polymers, PEG-lipids carrying oligo(dT)(20) (oligo(dT)(20)-PEG-lipid; PEG MW = 5000) and urokinase (UK) carrying oligo(dA)(20). The oligo(dT)(20)-PEG-lipid was spontaneously incorporated into the cell membrane through interactions between the hydrophobic parts of the PEG-lipids and the lipid bilayer, and UK was conjugated on the cell surface through DNA hybridization between oligo(dT)(20) on the cell and complementary oligo(dA)(20) on the UK. The activity of UK was maintained on the islet surface. The surface modification with UK did not influence islet morphology or islet ability to secrete insulin in response to changes in glucose concentration. No practical volume increase was observed with our method, indicating that islet graft loss could be suppressed at the early stage of intraportal islet transplantation.