Achieving superior anticoagulation of endothelial membrane mimetic coating by heparin grafting at zwitterionic biocompatible interfaces

Thrombosis and bleeding are common complications of blood-contacting medical device therapies. In this work, an endothelium membrane mimetic coating (PMPCC/Hep) has been created to address these challenges. The coating is fabricated by multi-point anchoring of a phosphorylcholine copolymer (poly-MPC-co-MSA, PMPCC) with carboxylic side chains and end-group grafting of unfractionated heparin (Hep) onto polydopamine precoated blood-contacting material surfaces. The PMPCC coating forms an ultrathin cell outer membrane mimetic layer to resist protein adsorption and platelet adhesion. The tiny defects/pores of the PMPCC layer provide entrances for heparin end-group to be inserted and grafted onto the sub-layer amino groups. The combination of the PMPCC cell membrane mimetic anti-fouling nature with the grafted heparin bioactivity further enhances the anticoagulation performance of the formed endothelium membrane mimetic PMPCC/Hep coating. Compared to conventional Hep coating, the PMPCC/Hep coating further decreases protein adsorption and platelet adhesion by 50 % and 90 %, respectively. More significantly, the PMPCC/Hep coating shows a superior anticoagulation activity, even significantly higher than that of an end-point-attached heparin coating. Furthermore, the blood coagulation function is well preserved in the PMPCC/Hep coating anticoagulation strategy. All the results support that the PMPCC/Hep coating strategy has great potential in developing more efficient and safer blood-contacting medical devices.

Crosslinked biomimetic coating modified stainless-steel-mesh enables completely self-cleaning separation of crude oil/water mixtures

The development of high-flux, durable and completely self-cleaning membranes is highly desired for separation of massive oil/water mixtures. Herein, differently crosslinked poly(2-methacryloyloxylethyl phosphorylcholine) (PMPC) brush grafted stainless steel mesh (SSM) membranes (SSM/PMPCs) were fabricated by integrating of mussel inspired universal adhesion and crosslinking chemistry with surface-initiated activators regenerated by electron transfer atom transfer radical polymerization (SI-ARGET-ATRP). The durability and self-cleaning performance of the prepared SSM membranes were evaluated by separating sticky crude oil/water mixtures in a continuous recycling dead-end filtration device. The water filtration flux driven by gravity reached 60,000 L⋅m^-2⋅h^-1 with a separation efficiency of over 99.98%. Furthermore, zero-flux-decline was observed during a 5 h continuous filtration when assisted by mechanical stirring. More significantly, such a completely self-cleaning separation of the well crosslinked SSM/PMPC2 membrane under optimized flux and stirring conditions had been operated cumulatively for 190 h in 30 days without any additional cleaning. These significant advances are more promising for practical applications in crude oil-contaminated water treatments and massive oil/water mixture separation.

Smart MSN-Drug-Delivery System for Tumor Cell Targeting and Tumor Microenvironment Release

Tumor-targeted delivery and controlled release of antitumor drugs are promising strategies for increasing chemotherapeutic efficacy and reducing adverse effects. Although mesoporous silica nanoparticles (MSNs) have been known as a potential delivery system for doxorubicin (DOX), they have restricted applications due to their uncontrolled leakage and burst release from their large open pores. Herein, we engineered a smart drug-delivery system (smart MSN-drug) based on MSN-drug loading, cell membrane mimetic coating, on-demand pore blocking/opening, and tumor cell targeting strategies. The pore size of DOX-loaded MSNs was narrowed by polydopamine coating, and the pores/channels were blocked with tumor-targeting ligands anchored by tumor environment-rupturable -SS- chains. Furthermore, a cell membrane mimetic surface was constructed to enhance biocompatibility of the smart MSN-drug. Confocal microscopy results demonstrate highly selective uptake (12-fold in comparison with L929 cell) of the smart MSN-drug by HeLa cells and delivery into the HeLa cellular nuclei. Further in vitro IC₅₀ studies showed that the toxicity of the smart MSN-drug to HeLa cells was 4000-fold higher than to the normal fibroblast cells. These exciting results demonstrate the utility of the smart MSN-drug capable of selectively killing tumor cells and saving the normal cells.

Anchorable phosphorylcholine copolymer synthesis and cell membrane mimetic antifouling coating fabrication for blood compatible applications

Protein adsorption and platelet activation on biomedical devices contacting blood may lead to the formation of thrombus. The thrombogenicity of biomaterials could be minimized or prevented by anchoring a cell membrane mimetic antifouling coating (CMMAC). Here, we report the construction of a CMMAC by a newly designed 2-methacryloyloxyethyl phosphorylcholine (MPC) copolymer (PMPCC) containing 5-20 carboxylic long arm side chains. The long arm provides its end carboxylic group with more freedom and a larger reaction space for an easier and more efficient surface anchoring. With the assistance of mussel-inspired universal adhesive polydopamine (PDA), different material surfaces precoated with PDA can immobilize the PMPCC via multipoint anchoring of the randomly distributed carboxylic side chains. The multipoint anchoring results in a stabilized and condensed PDA-PMPCC coating. The phosphorylcholine zwitterions of the densely immobilized PMPCC polymers form a cell outer membrane mimetic interface in an aqueous environment, endowing excellent properties of resisting protein adsorption, platelet activation and blood cell adhesion. More importantly, the PDA-PMPCC-coated glass surface can suppress thrombus formation for more than 24 h, while the bare glass surface forms obvious thrombus in 6 h tested in the same blood. Furthermore, the fabrication of the PDA-PMPCC coating is simple and material-independent. Therefore, the simple synthesis, facile surface coating and excellent hemocompatibility of the PMPCC make it a promising material for biomimetic surface modification.

Universal Strategy for Efficient Fabrication of Blood Compatible Surfaces via Polydopamine-Assisted Surface-Initiated Activators Regenerated by Electron Transfer Atom-Transfer Radical Polymerization of Zwitterions

Implant and blood-contacting biomaterials are challenged by biofouling and thrombus formation at their interface. Zwitterionic polymer brush coating can achieve excellent hemocompatibility, but the preparation often involves tedious, expensive, and complicated procedures that are designed for specific substrates. Here, we report a facile and universal strategy of creating zwitterionic polymer brushes on variety of materials by polydopamine (PDA)-assisted and surface-initiated activators regenerated by electron transfer atom-transfer radical polymerization (PDA-SI-ARGET-ATRP). A PDA adhesive layer is first dipcoated on a substrate, followed by covalent immobilization of 3-trimethoxysilyl propyl 2-bromo-2-methylpropionate (SiBr, ATRP initiator) on the PDA via condensation. Meanwhile, the trimethoxysilyl group of SiBr also cross-links the PDA oligomers forming stabilized PDA/SiBr complex coating. Finally, SI-ARGET-ATRP is performed in a zwitterionic monomer solution catalyzed by the parts per million level of CuBr₂ without deoxygenization. The conveniently fabricated zwitterionic polymer brush coatings are demonstrated to have stable, ultralow fouling, and extremely blood compatible and functionalizable characteristics. This facile, versatile, and universal surface modification strategy is expected to be widely applicable in various advanced biomaterials and devices.

Folate Ligand Orientation Optimized during Cell Membrane Mimetic Micelle Formation for Enhanced Tumor Cell Targeting

Nanocarriers with strong tumor cell targeting ability have been expected to overcome limitations of cancer chemotherapy. Herein, cell membrane mimetic micelles were prepared from a random copolymer (PMNCF) containing cell membrane phosphorylcholine zwitterion, cholesterol, and tumor cell targeting folic acid (FA) at the side chain ends. Surface orientation of the FA ligand was optimized during PMNCF micelle preparation by controlling solvent solubility for FA. The out-oriented ligands on the micelles were immobilized by the strongly associated hydration layer around the closely packed phosphorylcholine zwitterions. The doxorubicin (DOX) loaded PMNCF micelles were demonstrated to reduce normal cell toxicity to less than 20%. More significantly, HeLa and MCF-7 tumor cell killing efficacy of the optimized formulation was enhanced to 160% compared with that of free DOX. The excellent performances of the drug loaded PMNCF micelles on both tumor cell killing and normal cell toxicity reducing efficacies reveal great potential for developing advanced drug delivery system.

A blood cell repelling and tumor cell capturing surface for high-purity enrichment of circulating tumor cells

A red blood cell membrane mimetic surface decorated with FA and RGD ligands can efficiently capture tumor cells with high selectivity.

Construction, mechanism, and antibacterial resistance insight into polypeptide-based nanoparticles

Demonstration of the bactericidal mechanism of self-assembled nanoparticles.

Quantitative fabrication, performance optimization and comparison of PEG and zwitterionic polymer antifouling coatings

A versatile fabrication and performance optimization strategy of PEG and zwitterionic polymer coatings is developed on the sensor chip of surface plasma resonance (SPR) instrument. A random copolymer bearing phosphorylcholine zwitterion and active ester side chains (PMEN) and carboxylic PEG coatings with comparable thicknesses were deposited on SPR sensor chips via amidation coupling on the precoated polydopamine (PDA) intermediate layer. The PMEN coating showed much stronger resistance to bovine serum albumin (BSA) adsorption than PEG coating at very thin thickness (∼1nm). However, the BSA resistant efficacy of PEG coating could exceed that of PMEN due to stronger steric repelling effect when the thickness increased to 1.5∼3.3nm. Interestingly, both the PEG and PMEN thick coatings (≈3.6nm) showed ultralow fouling by BSA and bovine plasma fibrinogen (Fg). Moreover, changes in the PEG end group from -OH to -COOH, protein adsorption amount could increase by 10-fold. Importantly, the optimized PMEN and PEG-OH coatings were easily duplicated on other substrates due to universal adhesion of the PDA layer, showed excellent resistance to platelet, bacteria and proteins, and no significant difference in the antifouling performances was observed. These detailed results can explain the reported discrepancy in performances between PEG and zwitterionic polymer coatings by thickness. This facile and substrate-independent coating strategy may benefit the design and manufacture of advanced antifouling biomedical devices and long circulating nanocarriers.

STATEMENT OF SIGNIFICANCE

Prevention of biofouling is one of the biggest challenges for all biomedical applications. However, it is very difficult to fabricate a highly hydrophilic antifouling coating on inert materials or large devices. In this study, PEG and zwitterion polymers, the most widely investigated polymers with best antifouling performance, are conveniently immobilized on different kinds of substrates from their aqueous solutions by precoating a polydopamine intermediate layer as the universal adhesive and readily re-modifiable surface. Importantly, the coating fabrication and antifouling performance can be monitored and optimized quantitatively by a surface plasma resonance (SPR) system. More significantly, the SPR on-line optimized coatings were successfully duplicated off-line on other substrates, and supported by their excellent antifouling properties.

Anti-phagocytosis and tumor cell targeting micelles prepared from multifunctional cell membrane mimetic polymers

“Stealthy bio-missile” kinds of micelles were fabricated for developing advanced anticancer formulations by cell membrane mimicking.

Long circulating micelles of an amphiphilic random copolymer bearing cell outer membrane phosphorylcholine zwitterions

Polymeric micelles with cell outer membrane mimetic structure were prepared in water from amphiphilic random copolymers bearing both the hydrophilic phosphorylcholine zwitterions and hydrophobic octadecyl side chains of cell outer membrane. The polymeric micelles showed sizes ranging from 80 nm to 120 nm in hydrodynamic diameter and zeta-potentials from -6.4 mV to -2.4 mV by dynamic light scattering measurements. The micelles loaded with 6-coumarin as a fluorescence probe were stable to investigate their blood circulation and biodistribution. The in vitro phagocytosis results using murine peritoneal macrophages showed 10-fold reduction compared with a reference micelle. The in vivo blood circulation half-life of the polymeric micelles following intravenous administration in New Zealand Rabbits was increased from 0.55 h to 90.5h. More interestingly, tissue distribution results showed that the concentration of the micelles in the kidney is 4-fold higher than that in the liver and other organs 48 h after administration. The results of this work show great promise for designing more effective stealth drug carriers that can minimize reticuloendothelial system clearance and circulate for long time to reach target by using simple cell membrane mimetic random copolymer micelles.

Biocompatible and antifouling coating of cell membrane phosphorylcholine and mussel catechol modified multi-arm PEGs

The design and easy fabrication of biocompatible and antifouling coatings on different materials are extremely important for biotechnological and biomedical devices. Here we report a substrate-independent biomimetic modification strategy for fabricating a biocompatible and antifouling ultra-thin coating. Cell membrane antifouling phosphorylcholine (PC) and/or mussel adhesive catechol (c) groups are grafted at the amino-ends of an 8-armed poly(ethylene glycol). The PC groups are introduced by grafting a random copolymer bearing both PC and active ester groups. The modified 8-arm PEGs (PEG-2c-23PC, PEG-6c-23PC and PEG-8c) anchor themselves onto various substrates from aqueous solution and form cell outer membrane mimetic surfaces. Static contact angle, atomic force microscope (AFM) and X-ray photoelectron spectra (XPS) measurements confirm the successful fabrication of coatings on polydopamine (PDA) precoated surfaces. Real-time interaction results between proteins/bacteria and the coatings measured by surface plasmon resonance (SPR) technique suggest excellent anti-protein adsorption and short-term anti-bacteria adhesion performance. The long-term bacteria adhesion, platelet and L929 cell attachment results strongly support the SPR conclusions. Furthermore, the cell membrane mimetic and mussel adhesive protein mimetic PEG-2c-23PC shows hardly any toxicity to L929 fibroblasts, and the coating surface demonstrates the best anti-biofouling performance. This PDA-assisted immobilization of PC and/or catechol modified multi-arm PEGs provides a convenient and universal way to produce a biocompatible and fouling-resistant surface with tailor-made functions, which hopefully can be expanded to a wider range of applications based on both structure and surface superiorities.

CCDC26 gene polymorphism and glioblastoma risk in the Han Chinese population

BACKGROUND

Glioblastoma (GBM) is an immunosuppressive tumor whose median survival time is only 12- 15 months, and patients with GBM have a uniformly poor prognosis. It is known that heredity contributes to formation of glioma, but there are few genetic studies concerning GBM.

MATERIALS AND METHODS

We genotyped six tagging SNPs (tSNP) in Han Chinese GBM and control patients. We used Microsoft Excel and SPSS 16.0 statistical package for statistical analysis and SNP Stats to test for associations between certain tSNPs and risk of GBM in five different models. ORs and 95%CIs were calculated for unconditional logistic-regression analysis with adjustment for age and gender. The SHEsis software platform was applied for analysis of linkage disequilibrium, haplotype construction, and genetic associations at polymorphism loci.

RESULTS

We found rs891835 in CCDC26 to be associated with GBM susceptibility at a level of p=0.009. The following genotypes of rs891835 were found to be associated with GBM risk in four different models of gene action: i) genotype GT (OR=2.26; 95%CI, 1.29-3.97; p=0.019) or GG (OR=1.33; 95%CI, 0.23-7.81; p=0.019) in the codominant model; ii) genotypes GT and GG (OR=2.18; 95%CI, 1.26-3.78; p=0.0061) in the dominant model; iii) GT (OR=2.24; 95%CI, 1.28-3.92; p=0.0053) in the overdominant model; iv) the allele G of rs891835 (OR=1.85; 95%CI, 1.14-3.00; p=0.015) in the additive model. In addition, "CG" and "CGGAG" were found by haplotype analysis to be associated with increased GBM risk. In contrast, genotype GG of CCDC26 rs6470745 was associated with decreased GBM risk (OR=0.34; 95%CI, 0.12-1.01; p=0.029) in the recessive model.

CONCLUSIONS

Our results, combined with those from previous studies, suggest a potential genetic contribution of CCDC26 to GBM progression among Han Chinese.

Substrate independent coating formation and anti-biofouling performance improvement of mussel inspired polydopamine

Anti-biofouling performance of mussel inspired polydopamine coating can be improved significantly by simple coordination, oxidation, heating or grafting treatment.

Mussel-inspired silver-releasing antibacterial hydrogels

A silver-releasing antibacterial hydrogel was developed that simultaneously allowed for silver nanoparticle formation and gel curing. Water-soluble polyethylene glycol (PEG) polymers were synthesized that contain reactive catechol moieties, inspired by mussel adhesive proteins, where the catechol containing amino acid 3,4-dihydroxyphenylalanine (DOPA) plays an important role in the ability of the mussel to adhere to almost any surface in an aqueous environment. We utilized silver nitrate to oxidize polymer catechols, leading to covalent cross-linking and hydrogel formation with simultaneous reduction of Ag(I). Silver release was sustained for periods of at least two weeks in PBS solution. Hydrogels were found to inhibit bacterial growth, consistent with the well-known antibacterial properties of silver, while not significantly affecting mammalian cell viability. In addition, thin hydrogel films were found to resist bacterial and mammalian cell attachment, consistent with the antifouling properties of PEG. We believe these materials have a strong potential for antibacterial biomaterial coatings and tissue adhesives, due to the material-independent adhesive properties of catechols.

Group reorientation and migration of amphiphilic polymer bearing phosphorylcholine functionalities on surface of cellular membrane mimicking coating

Amphiphilic polymers bearing phosphorylcholine (PC) groups can form films of interfacial structure similar to that of the outer membrane of living cells. The films, as prepared, present PC groups to the external aqueous environment and exhibit good biocompatibility. However, under certain conditions, the surface structure can change irreversibly due to the reorientation and deep migration of the surface groups. X-ray photoelectron spectroscopy (XPS), dynamic contact angle measurements, and cell culture experiments were used to investigate the reorientation and migration of the surface groups of an amphiphilic PC-polymer coating. When the polymer surface is immersed into or drawn out of water, significant reorientation and group migration occurs, as suggested by the large difference between the advancing and receding contact angles. Angle-resolved XPS measurements indicate that the hydrophobic groups move to the air/film interface while the hydrophilic groups migrate towards the bulk of the polymer coating. Long periods of aging may result in irreversible changes of the surface structure and decrease the biocompatibility of the materials.

Encapsulation of Recombinant Cells with a Novel Magnetized Alginate for Magnetic Resonance Imaging

Implanting recombinant cells encapsulated in alginate microcapsules to express therapeutic proteins has been proven effective in treating several mouse models of human diseases (neurological disorders, dwarfism, hemophilia, lysosomal storage disease, and cancer). In anticipation of clinical application, we have reported the synthesis and characterization of a magnetized ferrofluid alginate that potentially allows tracking of these microcapsules in vivo by magnetic resonance imaging (MRI). We now report the properties of these ferrofluid microcapsules important for applications in gene therapy. When a mouse myoblast cell line was encapsulated in these microcapsules, it showed similar viability as in regular unmodified alginate capsules, both in vitro and in vivo, in mice. The permeability of these magnetized microcapsules, a critical parameter for immunoisolation devices, was comparable to that of classic alginate in the transit of various recombinant molecules of various molecular masses (human factor IX, 65 kDa; murine IgG, 150 kDa; and beta-glucuronidase, 300 kDa). When followed by MRI in vitro and in vivo, the ferrofluid microcapsules remained intact and visible for extended periods, allowing quantitative monitoring of microcapsules. At autopsy, the ferrofluid microcapsules were mostly free within the intraperitoneal cavities, with no overt inflammatory response. Serological analyses demonstrated a high level of biocompatibility comparable to that of unmodified alginate. In conclusion, ferrofluid-enhanced alginate microcapsules are comparable to classic alginate microcapsules in permeability and biocompatibility. Their visibility and stability to MRI monitoring permitted qualitative and quantitative tracking of the implanted microcapsules without invasive surgery. These properties are important advantages for the application of immunoisolation devices in human gene therapy.

Promotion of U937 cell adhesion on polypropylene surfaces bearing phosphorylcholine functionalities

Phosphorylcholine (PC) groups were grafted onto ammonia plasma-treated biaxially-oriented polypropylene (BOPP) surfaces, via (a) reductive amination of phosphorylcholine glyceraldehyde and (b) a two-step procedure involving the chemical amplification of surface amine groups with tris(2-aminoethyl amine) and subsequent reductive amination of phosphorylcholine glyceraldehyde. The occurrence of grafting was ascertained by X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance Fourier-transform infrared (ATR-FT-IR) spectroscopy. The wettability of PC-modified surfaces was assessed by dynamic contact-angle measurements using the Wilhelmy plate method. Human U937 macrophages adhered and proliferated to a significantly larger extent on PC-modified surfaces, compared to unmodified or ammonia plasma-modified BOPP.

Adhesion of human U937 macrophages to phosphorylcholine-coated surfaces

A new type of amphiphilic phosphorylcholine (PC) polymer was used in this work to develop a cell culture surface that allows the attachment of U937 macrophages. The PC polymer was a random copolymer of N-isopropylacrylamide (45%), N-(phosphorylcholine)-N'-(ethylenedioxy-bis(ethyl)) acrylamide (41%), and the hydrophobic monomer N-(n-octadecyl) acrylamide (14%). Polypropylene (PP) films (1 cm2) were coated with the polymer solution by immersion. U937 macrophage suspensions were applied on PC polymer-coated surfaces and incubated for up to 72 h at 37 degrees C. While U937 cells did not adhere to PP, ammonia, nitrogen, or oxygen plasma-treated surfaces, they attached rapidly on PC-coated surfaces (< 1 h), proliferated, and stayed attached to the modified surface for at least 72 h, suggesting that unique features of the PC polymer, and the U937 macrophages, are responsible for the attachment of these cells. We compared the effect of Co2+ and Cr3+ ions on the expression of bone-resorbing cytokines (TNF-alpha, IL-6, IL-1beta) in U937 macrophages cultured on PC-coated surfaces to the response of U937 macrophages in suspension. Cytokine gene expression was analyzed by reverse transcription polymerase chain reaction (RT-PCR). Addition of Co2+ and Cr3+ ions led to a significant increased expression of TNF-alpha in both cultured and suspension cells. On the other hand, Co2+ and Cr3+ ions had a weak stimulatory effect or no effect on IL-1beta and IL-6, respectively, in both cultured and suspension cells. In conclusion, the use of PC polymer-modified surfaces might offer promising new opportunities for the culture of human U937 cells and may also point to the mechanism by which macrophages interact with lipid bilayers of biological membranes.

Resonance energy transfer from dibucaine to acriflavine in polystyrene latex dispersions

Resonance energy transfer from dibucaine (DC) to acriflavine (AF) has been investigated both in homogeneous aqueous solutions and in polystyrene latex dispersions. The energy transfer reaction is observed by monitoring fluorescence quenching of DC as well as sensitized emission of AF. It is found that the energy transfer from DC to AF is remarkably enhanced on going from the aqueous homogeneous solution to the latex dispersion. This is mainly attributed to the fact that both the donor and acceptor are effectively adsorbed onto the latex particles, as evidenced by the measurement of adsorption isotherms. From the adsorption experiments, it is also elucidated that electrostatic interaction is significant at low DC concentration, while hydrophobic interaction dominates at the higher concentration especially at higher pH.

Penetration of pyrene and its derivatives into polystyrene latex particles as studied by fluorescence spectroscopy

Small hydrophobic pores (channels) in polystyrene latex particles were found by investigating the penetration of pyrene using fluorescence techniques.