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

Optimized Design of Hyaluronic Acid-Lipid Conjugate Biomaterial for Augmenting CD44 Recognition of Surface-Engineered NK Cells

Triple-negative breast cancer (TNBC) presents treatment challenges due to a lack of detectable surface receptors. Natural killer (NK) cell-based adaptive immunotherapy is a promising treatment because of the characteristic anticancer effects of killing malignant cells directly by secreting cytokines and lytic granules. To maximize the cancer recognition ability of NK cells, biomaterial-mediated ex vivo cell surface engineering has been developed for sufficient cell membrane immobilization of tumor-targeting ligands via hydrophobic anchoring. In this study, we optimized amphiphilic balances of NK cell coating materials composed of CD44-targeting hyaluronic acid (HA)-poly(ethylene glycol) (PEG)-lipid to improve TNBC recognition and the anticancer effect. Changes in the modular design of our material by differentiating hydrophilic PEG length and incorporating lipid amount into HA backbones precisely regulated the amphiphilic nature of HA-PEG-lipid conjugates. The optimized biomaterial demonstrated improved anchoring into NK cell membranes and facilitating the surface presentation level of HA onto NK cell surfaces. This led to enhanced cancer targeting via increasing the formation of immune synapse, thereby augmenting the anticancer capability of NK cells specifically toward CD44-positive TNBC cells. Our approach addresses targeting ability of NK cell to solid tumors with a deficiency of surface tumor-specific antigens while offering a valuable material design strategy using amphiphilic balance in immune cell surface engineering techniques.

Glycosylation-on-a-Chip: A Flow-Based Microfluidic System for Cell-Free Glycoprotein Biosynthesis

In recent years, cell-free synthetic glycobiology technologies have emerged that enable production and remodeling of glycoproteins outside the confines of the cell. However, many of these systems combine multiple synthesis steps into one pot where there can be competing reactions and side products that ultimately lead to low yield of the desired product. In this work, we describe a microfluidic platform that integrates cell-free protein synthesis, glycosylation, and purification of a model glycoprotein in separate compartments where each step can be individually optimized. Microfluidics offer advantages such as reaction compartmentalization, tunable residence time, the ability to tether enzymes for reuse, and the potential for continuous manufacturing. Moreover, it affords an opportunity for spatiotemporal control of glycosylation reactions that is difficult to achieve with existing cell-based and cell-free glycosylation systems. In this work, we demonstrate a flow-based glycoprotein synthesis system that promotes enhanced cell-free protein synthesis, efficient protein glycosylation with an immobilized oligosaccharyltransferase, and enrichment of the protein product from cell-free lysate. Overall, this work represents a first-in-kind glycosylation-on-a-chip prototype that could find use as a laboratory tool for mechanistic dissection of the protein glycosylation process as well as a biomanufacturing platform for small batch, decentralized glycoprotein production.

Effect of liposome surface modification with water-soluble phospholipid polymer chain-conjugated lipids on interaction with human plasma proteins

Alternative liposome surface coatings for PEGylation to evade the immune system, particularly the complement system, have garnered significant interest. We previously reported poly(2-methacryloyloxyethyl phosphorylcholine) (MPC)-based lipids (PMPC-lipids) and investigated the surface modification of liposomes. In this study, we synthesize PMPC-lipids with polymerization degrees of 10 (MPC10-lipid), 20 (MPC20-lipid), 50 (MPC50-lipid), and 100 (MPC100-lipid), and coated liposomes with 1, 5, or 10 mol% PMPC-lipids (PMPC-liposomes). Non-modified and PEGylated liposomes are used as controls. We investigate the liposome size, surface charge, polydispersity index, and adsorption of plasma proteins to the liposomes post incubation in human plasma containing N,N,N',N'-ethylenediamine tetraacetic acid (EDTA) or lepirudin by some methods such as sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), western blotting, and automated capillary western blot, with emphasis on the binding of complement protein C3. It is shown that the coating of liposome PMPC-lipids can suppress protein adsorption more effectively with an increase in the molecular weight and molar ratio (1-10 mol%). Apolipoprotein A-I is detected on PMPC-liposomes with a higher molecular weight and higher molar ratio of PMPC-lipids, whereas α₂-macroglobulin is detected on non-modified, PEGylated, and PMPC-liposomes with a shorter polymer chain. In addition, a correlation is shown among the PMPC molecular weight, molar ratio, and C3 binding. The MPC10-lipid cannot inhibit C3 binding efficiently, whereas surface modifications with 10 mol% MPC20-lipid and 5 mol% and 10 mol% MPC50-lipid suppress both total protein and C3 binding. Hence, liposome modification with PMPC-lipids can be a possible strategy for avoiding complement activation.

Synthesis of poly(2-methacryloyloxyethyl phosphorylcholine)-conjugated lipids and their characterization and surface properties of modified liposomes for protein interactions

Poly(ethylene glycol) (PEG) is frequently used for liposomal surface modification. However, as PEGylated liposomes are cleared rapidly from circulation upon repeated injections, substitutes of PEG are being sought. We focused on a water-soluble polymer composed of 2-methacryloyloxyethyl phosphorylcholine (MPC) units, and synthesized poly(MPC) (PMPC)-conjugated lipid (PMPC-lipid) with degrees of MPC polymerization ranging from 10 to 100 (calculated molecular weight: 3 to 30 kDa). In addition, lipids with three different alkyl chains, myristoyl, palmitoyl, and stearoyl, were applied for liposomal surface coating. We studied the interactions of PMPC-lipids with plasma albumin, human complement protein C3 and fibrinogen using a quartz crystal microbalance with energy dissipation, and found that adsorption of albumin, C3 and fibrinogen could be suppressed by coating with PMPC-lipids. In particular, the effect was more pronounced for PMPC chains with higher molecular weight. We evaluated the size, polydispersity index, surface charge, and membrane fluidity of the PMPC-lipid-modified liposomes. We found that the effect of the coating on the dispersion stability was maintained over a long period (98 days). Furthermore, we also demonstrated that the anti-PEG antibody did not interact with PMPC-lipids. Thus, our findings suggest that PMPC-lipids can be used for liposomal coating.

Effects of polyethylene glycol on the surface of nanoparticles for targeted drug delivery

The rapid development of drug nanocarriers has benefited from the surface hydrophilic polymers of particles, which has improved the pharmacokinetics of the drugs. Polyethylene glycol (PEG) is a kind of polymeric material with unique hydrophilicity and electrical neutrality. PEG coating is a crucial factor to improve the biophysical and chemical properties of nanoparticles and is widely studied. Protein adherence and macrophage removal are effectively relieved due to the existence of PEG on the particles. This review discusses the PEGylation methods of nanoparticles and related techniques that have been used to detect the PEG coverage density and thickness on the surface of the nanoparticles in recent years. The molecular weight (MW) and coverage density of the PEG coating on the surface of nanoparticles are then described to explain the effects on the biophysical and chemical properties of nanoparticles.

Poly(Ethylene Glycol) Interacts with Hyaluronan in Aqueous Media

We report here the first evidence for the interaction of poly(ethylene glycol) (PEG) with hyaluronan (HA) in aqueous solutions. PEG-HA complexes (K_app = 45,000 ± 8000 M^-1) contained about 3.3 ± 0.1 of ethylene glycol units per disaccharide of HA. The carboxyl of the D-glucuronic acid and the amide of the N-acetyl-D-glucosamine did not participate in PEG binding. Similar experiments performed with dextran and monosaccharides showed that multiple free primary hydroxyls regularly distributed along the polysaccharide chain are necessary for PEG binding. Another novelty of our study is contraction of HA upon PEG binding. The effect was observed with HA in solution or adsorbed on positively charged liposomes. The thickness of the HA layer on the liposomes decreased 2-fold upon PEG addition. HA compaction induced by PEG may underlie the changes in the plasma membrane properties and resealing of mechanical injuries induced by Pluronics.

Enhancing Detection Sensitivity of ZnO-Based Infrared Plasmonic Sensors Using Capped Dielectric Ga2O3 Layers for Real-Time Monitoring of Biological Interactions

Surface plasmon resonances on Ga-doped ZnO (ZnO/Ga) layer surfaces (ZnO-SPRs) have attracted substantial attention as alternative plasmonic materials in the infrared range. We present further enhancement of the detection limits of ZnO-SPRs to monitor biological interactions by introducing thin dielectric layers into ZnO-SPRs, which remarkably modify the electric fields and the corresponding decay lengths on the sensing surfaces. The presence of a high-permittivity dielectric layer of Ga₂O₃ provides high wavelength sensitivities of the ZnO-SPRs due to the strongly confined electric fields. The superior sensing capabilities of the proposed samples were verified by real-time monitoring of the biological interactions between biotin and streptavidin molecules. Introduction of the high-permittivity dielectric layer into ZnO-SPRs effectively enhances the detection sensitivity and therefore allowed for the observation of biological interactions. This paper provides useful information for the development of optical detection techniques for use in biological fields based on ZnO from the viewpoints of plasmonic applications.

Influence of cell adhesive molecules attached onto PEG-lipid-modified fluid surfaces on cell adhesion

The involvement of intercellular interactions in various biological events indicates the importance of studying cell-cell interactions using fluid model surfaces. Here, we propose a fluid surface composed of a self-assembled monolayer (SAM) and poly(ethylene glycol)-conjugated phospholipid (PEG-lipid) derivatives, which can be an alternative to supported lipid membranes. The modification of SAM surfaces with PEG-lipids carrying functional peptides resulted in the formation of the fluid surfaces with different mobility, which was quantitatively determined by quartz crystal microbalance with dissipation (QCM-D) and fluorescence recovery after photobleaching (FRAP). Different types of fluid surfaces with calculated diffusion coefficients between 0.9 ± 0.25 and 0.16 ± 0.03 μm²/sec for PEG-lipids derivatives were fabricated, onto which arginylglycylaspartate (RGD) peptides were immobilized for cell adhesion, and compared to solid surfaces with the same surface density of RGD peptides. The fluid surfaces revealed that cell adhesions of epithelial cells (MCF-10 A) and human umbilical vein endothelial cells (HUVEC) could not be established on the surfaces with higher fluidity, while cells could adhere onto surfaces with lower fluidity, where the lateral diffusion of PEG-lipids was approximately 20 times lower, and solid surfaces. Interestingly, cells that adhered onto the surface with lower fluidity proliferated at a normal rate while maintaining their round morphology, which was a different shape from that observed on solid surfaces. Thus, the scaffold fluidity greatly influenced cell adhesion behaviors, demonstrating that it is an important parameter for designing novel biomimetic scaffolds for biomedical applications.

Morphology and Physical Properties of Hydrophilic-Polymer-Modified Lipids in Supported Lipid Bilayers

Lipid molecules such as glycolipids that are modified with hydrophilic biopolymers participate in the biochemical reactions occurring on cell membranes. Their functions and efficiency are determined by the formation of microdomains and their physical properties. We investigated the morphology and properties of domains induced by the hydrophilic-polymer-modified lipid applying a polyethylene glycol (PEG)-modified lipid as a model modified lipid. We formed supported lipid bilayers (SLBs) using a 0-10 mol % range of PEG-modified lipid concentration ( C_PEG). We studied their morphology and fluidity by fluorescence microscopy, the fluorescence recovery after photobleaching method, and atomic force microscopy (AFM). Fluorescence images showed that domains rich in the PEG-modified lipid appeared and SLB fluidity decreased when C_PEG ≥ 5%. AFM topographies showed that clusters of the PEG-modified lipid appeared prior to domain formation and the PEG-lipid-rich domains were observed as depressions. Frequency-modulation AFM revealed a force-dependent appearance of the PEG-lipid-rich domain.

Polymers and biopolymers at interfaces

This review updates recent progress in the understanding of the behaviour of polymers at surfaces and interfaces, highlighting examples in the areas of wetting, dewetting, crystallization, and 'smart' materials. Recent developments in analysis tools have yielded a large increase in the study of biological systems, and some of these will also be discussed, focussing on areas where surfaces are important. These areas include molecular binding events and protein adsorption as well as the mapping of the surfaces of cells. Important techniques commonly used for the analysis of surfaces and interfaces are discussed separately to aid the understanding of their application.

Electrochemical prostate specific antigen aptasensor based on hemin functionalized graphene-conjugated palladium nanocomposites

An electrochemical aptasensor is described for the detection of prostate specific antigen (PSA). The aptasensor is based on the use of hemin-functionalized graphene-conjugated palladium nanoparticles (H-Gr/PdNPs) deposited on a glassy carbon electrode. The nanocomposites integrate the high electrical conductivity of graphene with the easily functionalized surface chemistry of PdNPs and their excellent catalytic property. The hemin placed on graphene acts as both a protective agent and an in-situ redox probe. The PdNPs provide numerous binding sites for the immobilization of DNA-biotin via coordinative binding between Pd and amino groups. A sensitive and specific PSA assay was attained by immobilizing the PSA aptamer via biotin-streptavidin interaction. The resulting aptasensor has a linear response that covers the PSA concentration range from 0.025 to 205 ng·mL^-1, with a 8 pg·mL^-1 lower detection limit (at -0.362 V, scan rate: 0.1 mV·s^-1, S/N = 3). The method was applied to the quantitation of PSA in spiked serum samples, giving recoveries ranging from 95.0 to 100.3%. Graphical abstract A signal amplified and approving electrochemical aptasensor was constructed for the determination of prostate specific antigen (PSA) based on the use of hemin-functionalized graphene conjugated to palladium nanoparticles (H-Gr/PdNPs). The sensor has a wide linear range, a relatively low detection limit, satisfying stability and high specificity.

Surface modification of copolymerized films from three-armed biodegradable macromers - An analytical platform for modified tissue engineering scaffolds

The concept of macromers allows for a broad adjustment of biomaterial properties by macromer chemistry or copolymerization. Copolymerization strategies can also be used to introduce reactive sites for subsequent surface modification. Control over surface features enables adjustment of cellular reactions with regard to site and object of implantation. We designed macromer-derived polymer films which function as non-implantable analytical substrates for the investigation of surface properties of equally composed scaffolds for bone tissue engineering. To this end, a toolbox of nine different biodegradable, three-armed macromers was thermally cross-copolymerized with poly(ethylene glycol)-methacrylate (PEG-MA) to films. Subsequent activation of PEG-hydroxyl groups with succinic anhydride and N-hydroxysuccinimid allowed for covalent surface modification. We quantified the capacity to immobilize analytes of low (amino-functionalized fluorescent dye, Fcad, and RGD-peptides) and high (alkaline phosphatase, ALP) molecular weight. Fcad grafting level was controlled by macromer chemistry, content and molecular weight of PEG-MA, but also the solvent used for film synthesis. Fcad molar amount per surface area was twentyfive times higher on high-swelling compared to low-swelling films, but differences became smaller when large ALP (appr. 2:1) were employed. Similarly, small differences were observed on RGD peptide functionalized films that were investigated by cell adhesion studies. Presentation of PEG-derivatives on surfaces was visualized by atomic force microscopy (AFM) which unraveled composition-dependent domain formation influencing fluorescent dye immobilization. Surface wetting characteristics were investigated via static water contact angle. We conclude that macromer ethoxylation and lactic acid content determined film swelling, PEG domain formation and eventually efficiency of surface decoration.

STATEMENT OF SIGNIFICANCE

Surfaces of implantable biomaterials are the site of interaction with a host tissue. Accordingly, modifications in the composition of the surface will determine cellular response towards the material which is crucial for the success of innovations and control of tissue regeneration. We employed a macromer approach which is most flexible for the design of biomaterials with a broad spectrum of physicochemical characteristics. For ideal analytical accessibility of the material platform, we cross-copolymerized films on solid supports. Films allowed for the covalent immobilization of fluorescent labels, peptides and enzymes and thorough analytical characterization revealed that macromer hydrophilicity is the most relevant design parameter for surface analyte presentation in these materials. All analytical results were combined in a model describing PEG linker domain formation and ligand presentation.

Novel glycyrrhetinic acid conjugated pH-sensitive liposomes for the delivery of doxorubicin and its antitumor activities

A novel pH-sensitive conjugate glycyrrhetinic acid–polyethylene glycol–Schiff bond–cholesterol (GPSC) has been synthesized successfully and used to construct doxorubicin-loaded liposomes with both pH-sensitive features and active targeting ability.