Blood-materials interactions: the minimum interfacial free energy and the optimum polar/apolar ratio hypotheses

Layered biocompatible pH-responsive antibacterial composite film based on HNT/PLGA/chitosan for controlled release of minocycline as burn wound dressing

In the present study, a promising pH-responsive wound dressing was prepared. Halloysite nanotube (HNT) composites were modified with different concentration of both poly (lactic-co-glycolic acid) (PLGA) and chitosan (CS) through the Layer-by-Layer (LbL) strategy for targeted and controlled drug delivery of minocycline (MC). The resulting composites were characterized by FT-IR, XRD, zeta-potential, TGA, FE-SEM and TEM studies. Studying the biodegradability, water uptake, photostability, and water vapor transmission of resulting composites revealed that the composite film absorbed wound secretions, did not degrade, and penetrated properly to wound during the treatment. The results of protein adsorption showed that the optimized composite (C₄₀P₆₀MNT) was blood-compatible. Studying the release profile of the drug showed pH-responsive behavior that was fitted with Korsmeyer-Peppas kinetic model. In-vitro antibacterial testing showed that the C₄₀P₆₀MNT sample had an acceptable effect on the inhibition of gram-positive and gram-negative bacteria. In wound healing test (in-vivo studies), this MC loaded composite film showed faster healing of the burn wound in rat compare to the control sample. Due to the characteristics of the optimized sample, it can be considered as a promising candidate for pH-responsive drug delivery in the treatment of chronic burn wounds.

High modulus hydrogels for ophthalmic and related biomedical applications

This paper presents three families of semi-interpenetrating polymer network (SIPN) hydrogels based on an ester-based polyurethane (EBPU) and hydrophilic monomers: N,N-dimethylacrylamide (NNDMA), N-vinyl pyrrolidone (NVP) and acryloylmorpholine (AMO) as potential materials for keratoprosthesis, orthokeratology and mini-scleral lens application. Hydrogels sheets were synthesized via free-radical polymerization with methods developed in-house. SIPN hydrogels were characterized for their equilibrium water content, mechanical and surface properties. Three families of optically clear SIPN-based hydrogels have been synthesized in the presence of water with >10% of composition attributable to EBPU. Water contents of SIPN materials ranged from 30% to 70%. SIPNs with ≤15% EBPU of total composition showed little influence to mechanical properties, whereas >15% EBPU contributed significantly to an increase in material stiffness. In the hydrated state, SIPNs with ≤15% EBPU of total composition show little difference in polar component (γ^p ) of surface free energy, whereas for >15% EBPU there is a decrease in γ^p . The EBPU SIPN hydrogels display complementary material properties for keratoprosthesis, orthokeratology, and mini-scleral applications. © 2018 The Authors. Journal of Biomedical Materials Research Part B: Applied Biomaterials published by Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1645-1653, 2019.

Synthesis of a novel biomedical poly(ester urethane) based on aliphatic uniform-size diisocyanate and the blood compatibility of PEG-grafted surfaces

The purpose of this study is to offer a novel kind of polyurethane with improved surface blood compatibility for long-term implant biomaterials. In this work, the aliphatic poly(ester-urethane) (PEU) with uniform-size hard segments was prepared and the PEU surface was grafted with hydrophilic poly(ethylene glycol) (PEG). The PEU was obtained by chain-extension of poly(ɛ-caprolactone) (PCL) with isocyanate-terminated urethane triblock. Free amino groups were introduced onto the surface of PEU film via aminolysis with hexamethylenediamine, and then the NH₂-grafted PEU surfaces (PEU-NH₂) were reacted with isocyanate-terminated monomethoxyl PEG (MPEG-NCO) to obtain the PEG-grafted PEU surfaces (PEU-PEG). Analysis by nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and gel permeation chromatography were performed to confirm the chemical structures of the chain extender, PCL, PEU, and PEU-PEG. Additionally, the influence of aminolysis on the physical-mechanical properties of PEU films was investigated. Two glass transition temperatures and a broad endothermic peak were observed in the differential scanning calorimetry curves of PEU, which demonstrated a microphase-separated and semicrystalline structure, respectively. The PEU-PEG film exhibited excellent mechanical properties with an ultimate stress of ∼39 MPa and an elongation at break of ∼1190%, which was slightly lower than that of PEU, indicating that the aminolysis has little influence on the tensile properties. Evaluation of the blood compatibility of the films by bovine serum albumin adsorption and the platelet adhesion test revealed that the PEG-grafted surface had improved resistance to protein adsorption and excellent resistance to platelet adhesion. In vitro degradation tests showed that the PEU-PEG film could maintain its mechanical properties for more than six months and only lost ∼25% weight after 18 months. Due to the excellent mechanical properties, good blood compatibility and slow degradability, this novel kind of polyurethane hold significant promise for long-term implant biomaterials, especially soft tissue augmentation and regeneration.

Study of locust bean gum reinforced cyst-chitosan and oxidized dextran based semi-IPN cryogel dressing for hemostatic application

Severe blood loss due to traumatic injuries remains one of the leading causes of death in emergency settings. Chitosan continues to be the candidate material for hemostatic applications due to its inherent hemostatic properties. However, available chitosan-based dressings have been reported to have an acidic odor at the wound site due to the incorporation of acid based solvents for their fabrication and deformation under compression owing to low mechanical strength limiting its usability. In the present study semi-IPN cryogel was fabricated via Schiff's base cross-linking between the polyaldehyde groups of oxidized dextran and thiolated chitosan in presence of locust bean gum (LBG) known for its hydrophilicity. Polymerization at -12 °C yielded macroporous semi-IPN cryogels with an average pore size of 124.57 ± 20.31 μm and 85.46% porosity. The hydrophobicity index of LBG reinforced semi-IPN cryogel was reduced 2.42 times whereas the swelling ratio was increased by 156.08% compare to control cryogel. The increased hydrophilicity and swelling ratio inflated the compressive modulus from 28.1 kPa to 33.85 for LBG reinforced semi-IPN cryogel. The structural stability and constant degradation medium pH were also recorded over a period of 12 weeks. The cryogels demonstrated lower adsorption affinity towards BSA. The cytotoxicity assays (direct, indirect) with 3T3-L1 fibroblast cells confirmed the cytocompatibility of the cryogels. The hemolysis assay showed <5% hemolysis confirming blood compatibility of the fabricated cryogel, while whole blood clotting and platelet adhesion assays confirmed the hemostatic potential of semi-IPN cryogel.

Responses of Vascular Endothelial Cells to Photoembossed Topographies on Poly(Methyl Methacrylate) Films

Failures of vascular grafts are normally caused by the lack of a durable and adherent endothelium covering the graft which leads to thrombus and neointima formation. A promising approach to overcome these issues is to create a functional, quiescent monolayer of endothelial cells on the surface of implants. The present study reports for the first time on the use of photoembossing as a technique to create polymer films with different topographical features for improved cell interaction in biomedical applications. For this, a photopolymer is created by mixing poly(methyl methacrylate) (PMMA) and trimethylolpropane ethoxylate triacrylate (TPETA) at a 1:1 ratio. This photopolymer demonstrated an improvement in biocompatibility over PMMA which is already known to be biocompatible and has been extensively used in the biomedical field. Additionally, photoembossed films showed significantly improved cell attachment and proliferation compared to their non-embossed counterparts. Surface texturing consisted of grooves of different pitches (6, 10, and 20 µm) and heights (1 µm and 2.5 µm). The 20 µm pitch photoembossed films significantly accelerated cell migration in a wound-healing assay, while films with a 6 µm pitch inhibited cells from detaching. Additionally, the relief structure obtained by photoembossing also changed the surface wettability of the substrates. Photoembossed PMMA-TPETA systems benefited from this change as it improved their water contact angle to around 70°, making it well suited for cell adhesion.

The Activity of Complement in the Presence of N-(2-hydroxypropyl)methacrylamide Copolymers

This study indicates that N-(2-hydroxypropyl)methacrylamide homopolymers and copolymers containing oligopeptide sequences terminated in carboxylic acid groups, amine groups, aromatic units, or puromycin have no prominent effect on the porcine complement system in vitro. Inhibition of both pathways of the complement system occurred at concentrations highly exceeding the dose suitable for therapeutic purposes.

Stealth nanotubes: strategies of shielding carbon nanotubes to evade opsonization and improve biodistribution

Carbon nanotubes (CNTs) have recently been in the limelight for their potential role in disease diagnostics and therapeutics, as well as in tissue engineering. Before these medical applications can be realized, there is a need to address issues like opsonization, phagocytosis by macrophages, and sequestration to the liver and spleen for eventual elimination from the body; along with equally important issues such as aqueous solubility, dispersion, biocompatibility, and biofunctionalization. CNTs have not been shown to be able to evade such biological obstacles, which include their nonspecific attachments to cells and other biological components in the bloodstream, before reaching target tissues and cells in vivo. This will eventually determine their longevity in circulation and clearance rate from the body. This review article discusses the current status, challenges, practical strategies, and implementations of coating CNTs with biocompatible and opsonin-resistant moieties, rendering CNTs transparent to opsonins and deceiving the innate immune response to make believe that the CNTs are not foreign. A holistic approach to the development of such "stealth" CNTs is presented, which encompasses not only several biophysicochemical factors that are not limited to surface treatment of CNTs, but also extraneous biological factors such as the protein corona formation that inevitably controls the in vivo fate of the particles. This review also discusses the present and potential applications, along with the future directions, of CNTs and their hybrid-based nanotheranostic agents for multiplex, multimodal molecular imaging and therapy, as well as in other applications, such as drug delivery and tissue engineering.

Haemocompatibility of titanium and its alloys

This review outlines the current understanding of the interactions of titanium and its alloys with blood components, and the ways in which surface modification techniques can be used to alter the surface physicochemical and topographical features that determine blood-material interactions. Surface modification of the spontaneously formed titanium oxide surface layer is a highly attractive means of improving haemocompatibility without forgoing the advantageous mechanical and physical properties of titanium and its alloys. A number of surface modification techniques and treatment processes are discussed in the context of enhancing the haemocompatibility of titanium and its alloys, with a view to optimising the clinical efficacy of blood-contacting devices and materials.

Gentamicin-loaded wound dressing with polyvinyl alcohol/dextran hydrogel: gel characterization and in vivo healing evaluation

To develop a gentamicin-loaded wound dressing, cross-linked hydrogel films were prepared with polyvinyl alcohol (PVA) and dextran using the freezing-thawing method. Their gel properties such as gel fraction, swelling, water vapor transmission test, morphology, tensile strength, and thermal property were investigated. In vitro protein adsorption test, in vivo wound healing test, and histopathology were performed. Dextran decreased the gel fraction, maximum strength, and thermal stability of hydrogels. However, it increased the swelling ability, water vapor transmission rate, elasticity, porosity, and protein adsorption. The drug gave a little positive effect on the gel properties of hydrogels. The gentamicin-loaded wound dressing composed of 2.5% PVA, 1.13% dextran, and 0.1% drug was more swellable, flexible, and elastic than that with only PVA because of its cross-linking interaction with PVA. In particular, it could provide an adequate level of moisture and build up the exudates on the wound area. From the in vivo wound healing and histological results, this gentamicin-loaded wound dressing enhanced the healing effect more compared to conventional product because of the potential healing effect of gentamicin. Thus, this gentamicin-loaded wound dressing would be used as a potential wound dressing with excellent forming and improved healing effect in wound care.

Surface Engineered Polymeric Biomaterials with Improved Biocontact Properties

We present many examples of surface engineered polymeric biomaterials with nanosize modified layers, controlled protein adsorption, and cellular interactions potentially applicable for tissue and/or blood contacting devices, scaffolds for cell culture and tissue engineering, biosensors, biological microchips as well as approaches to their preparation.

Smart hydrogels based on itaconic acid for biomedical application

pH and temperature sensitive hydrogels, based on 2-hydroxyethyl methacrylate (HEMA) and itaconic acid (IA) copolymers, were prepared by gamma irradiation and characterized in order to examine their potential use in biomedical applications. The influence of comonomer ratio in these smart copolymers on their morphology, mechanical properties, biocompatibility and microbe penetration capability was investigated. The mechanical properties of copolymers were investigated using the dynamic mechanical analysis (DMA), while their morphology was examined by scanning electron microscopy (SEM). The morphology and mechanical properties of these hydrogels were found to be suitable for most requirements of biomedical applications. The in vitro study of P(HEMA/IA) biocompatibility showed no evidence of cell toxicity nor any considerable hemolytic activity. Furthermore, the microbe penetration test showed that neither Staphylococcus aureus nor Escherichia coli passed through the hydogel dressing; thus the P(HEMA/IA) dressing could be considered a good barrier against microbes. All results indicate that stimuli-responsive P(HEMA/IA) hydrogels have great potential for biomedical applications, especially for skin treatment and wound dressings.

Molecularly engineered hydrogels for implant biocompatibility

The biocompatibility of biosmart polymer membranes synthesized from cross-linkable (2-hydroxyethyl methacrylate) (HEMA) and tetraethylene glycol diacrylate and containing different mole-percent polyethylene glycol methacrylate (PEGMA) and methacryloyloxyethyl phosphorylcholine (MPC), a phosphorylcholine-containing co-monomer, was investigated. The cytotoxicity (cell viability and proliferation) and the adhesion of extra cellular matrix proteins to these hydrogel surfaces were separately tested. Cell proliferation assays were conducted by cultivating human skeletal muscle fibroblasts onto the surfaces of these polymeric membranes prepared by in-situ polymerization in chemically derivatized 8-well cell-culture plates. The compositions containing MPC and PEGMA concentrations greater than 1.0 and 0.05 mole% respectively demonstrated good protein adhesion and cell viability (>90%) of human muscle fibroblast cells. Morphological deviances and partial colonization of the hydrogel surface has been noticed and suggests good compatibility of hydrogels for cellular viability but restricted proliferation. It is well known that the adsorption of proteins onto biomaterial surfaces modulates the cellular interaction with these surfaces. The extent of adsorption of fluorescein labeled proteins (laminin, collagen, and fibronectin) onto these polymer membrane surfaces was evaluated by measuring the resultant fluorescence intensity using a confocal fluorescence scanner.

Modulating bone cells response onto starch-based biomaterials by surface plasma treatment and protein adsorption

The effect of oxygen-based radio frequency glow discharge (rfGD) on the surface of different starch-based biomaterials (SBB) and the influence of proteins adsorption on modulating bone-cells behavior was studied. Bovine serum albumin, fibronectin and vitronectin were used in single and complex protein systems. RfGD-treated surfaces showed to increase in hydrophilicity and surface energy when compared to non-modified SBB. Biodegradable polymeric blends of cornstarch with cellulose acetate (SCA; 50/50wt%), ethylene vinyl alcohol (SEVA-C; 50/50wt%) and polycaprolactone (SPCL; 30/70wt%) were studied. SCA and SCA reinforced with 10% hydroxyapatite (HA) showed the highest degree of modification as result of the rfGD treatment. Protein and control solutions were used to incubate with the characterized SBB and, following this, MG63 osteoblast-like osteosarcoma cells were seeded over the surfaces. Cell adhesion and proliferation onto SCA was found to be enhanced for non-treated surfaces and on SCA+10%HA no alteration was brought up by the plasma modification. Onto SCA surfaces, BSA, FN and VN single solutions improved cell adhesion, and this same effect was found upscaled for ternary systems. In addition, plasma treated SEVA-C directed an increase in both adhesion and proliferation comparing to non-treated surfaces. Even though adhesion onto treated and untreated SPCL was quite similar, plasma modification clearly promoted MG63 cells proliferation. Regarding MG63 cells morphology it was shown that onto SEVA-C surfaces the variation of cell shape was primarily defined by the protein system, while onto SPCL it was mainly affected by the plasma treatment.

Parameters influencing the stealthiness of colloidal drug delivery systems

Over the last few decades, colloidal drug delivery systems (CDDS) such as nano-structures have been developed in order to improve the efficiency and the specificity of drug action. Their small size permits them to be injected intravenously in order to reach target tissues. However, it is known that they can be rapidly removed from blood circulation by the immune system. CDDS are removed via the complement system and via the cells of the mononuclear phagocyte system (MPS), after their recognition by opsonins and/or receptors present at the cell surface. This recognition is dependent on the physicochemical characteristics of the CDDS. In this study, we will focus on parameters influencing the interactions of opsonins and the macrophage plasma membrane with the surface of CDDS, whereby parameters of the polymer coating become necessary to provide good protection.

A new device for in vitro evaluation of thrombogenicity

A device to measure the time of coagulation of whole blood has been designed in order to facilitate testing of thrombogenicity of biomaterials. The principle of operation of the apparatus is to record the time taken for a sphere to fall through a sample of blood. The coagulation time is defined here as the time from collection of the blood sample to coagulation, coagulation having deemed to have occurred when the sphere is prevented from falling by the presence of the fibrin-cell network. The device was tested with homogeneous fluids of different viscosity, milk containing different amounts of rennin and calcium chloride and non anti-coagulated whole blood obtained from five volunteers. Repeat measurements made with each homogeneous fluid show that the variance in the transit time of the sphere is small and consistent with small dispersion. In contrast, the onset of coagulation in milk and blood samples was readily detected. The clotting of milk was highly dependant on the concentration of rennin and calcium chloride. The coagulation time of blood samples from five individuals ranged from 23 to 33 min but simultaneous measurements of samples from the same individual in two identical devices agreed to within +/-1 min in all cases. This device may be easily adapted for use in studies to determine the thromboresistance of biomaterials where the onset of coagulation of whole blood in contact with different materials may be readily compared.

Combination of electrografting and atom-transfer radical polymerization for making the stainless steel surface antibacterial and protein antiadhesive

A two-step "grafting from" method has been successfully carried out, which is based on the electrografting of polyacrylate chains containing an initiator for the atom transfer radical polymerization (ATRP) of 2-(tert-butylamino)ethyl methacrylate (TBAEMA) or copolymerization of TBAEMA with either monomethyl ether of poly(ethylene oxide) methacrylate (PEOMA) or acrylic acid (AA) or styrene. The chemisorption of this type of polymer brushes onto stainless steel surfaces has potential in orthopaedic surgery. These films have been characterized by ATR-FTIR, Raman spectroscopy, atomic force microscopy (AFM), and measurement of contact angles of water. The polymer formed in solution by ATRP and that one detached on purpose from the surface have been analyzed by size exclusion chromathography (SEC) and (1)H NMR spectroscopy. The strong adherence of the films onto stainless steel has been assessed by peeling tests. AFM analysis has shown that addition of hydrophilic comonomers to the grafted chains decreases the surface roughness. According to dynamic quartz crystal microbalance experiments, proteins (e.g., fibrinogen) are more effectively repelled whenever copolymer brushes contain neutral hydrophilic (PEOMA) co-units rather than negatively charged groups (PAA salt). Moreover, a 2- to 3-fold decrease in the fibrinogen adsorption is observed when TBAEMA is copolymerized with either PEOMA or AA rather than homopolymerized or copolymerized with styrene. Compared to the bare stainless steel surface, brushes of polyTBAEMA, poly(TBAEMA-co-PEOMA) and poly(TBAEMA-co-AA) decrease the bacteria adhesion by 3 to 4 orders of magnitude as revealed by Gram-positive bacteria S. aureus adhesion tests.

Just scratching the surface

BACKGROUND AND OBJECTIVE

Different types of polymer surfaces affect the activation of platelets and coagulation pathway containers depending on their surface qualities. Importantly, this could produce variability of coagulation results obtained with thrombelastographical analysis. We assessed the effects of blood storage on thrombelastograph, TEG, variables using polypropylene and polycarbonate containers.

METHODS

An in vitro experiment was performed, with eight volunteers in each limb. Fresh whole blood was stored in polypropylene or polycarbonate tubes prior to TEGanalysis, to assess the role of these plastics in the TEG results obtained.

RESULTS

The polycarbonate tubes displayed slower onset of coagulation and greater variability of data for all four basic TEG variables (r-time, k-time, alpha-angle and maximum amplitude, P < 0.05). Polycarbonate results fell outside manufacturer reference ranges.

CONCLUSIONS

It is likely that this is due to the altered surface properties and charge effects of the containers affecting proteins and platelets differently. Caution should be used in choosing which containers are used for storage of fresh blood prior to coagulation assessment, as variable results will follow where different types of plastic containers are employed.

Molecularly engineered p(HEMA)-based hydrogels for implant biochip biocompatibility

The strategy of phospholipid-based biomimicry has been used to molecularly engineer poly(2-hydroxyethyl methacrylate) [p(HEMA)]-based hydrogels for improved in vitro and potential in vivo biocompatibility. Two methacrylate-based monomers, poly(ethylene glycol) (200) monomethacrylate (PEGMA) and 2-methacryloyloxyethyl phosphorylcholine (MPC), were incorporated at varying mole fractions of 0.0-0.5 mol% PEGMA and 0-10 mol% MPC respectively, into 3 mol% tetraethyleneglycol diacrylate (TEGDA) cross-linked p(HEMA) networks. Upon hydration of these engineered hydrogels, a reduction in receding contact angle from 22+/-1.2 degrees for p(HEMA) to 8+/-2.7 degrees for p(HEMA) containing 0.5:10 mol% PEGMA:MPC was observed, reflecting the significant increase in surface hydrophilicity with increasing PEGMA and MPC content upon prolonged hydration. Hydrogels containing MPC showed a temporal increase in hydrophilicity following continuous immersion in DI water over 5 days. Hydrogels containing 0.5 mol% PEGMA and MPC in the range of 5-10 mol% displayed reduced protein adsorption when incubated with the common extracellular matrix proteins; fibronectin, collagen or laminin, producing up to 64% less protein adsorption compared to p(HEMA). Compositional optima for cell viability and proliferation established from two-factor Central Composite design analysis of human muscle fibroblasts cultured on these hydrogels suggest that those containing PEGMA between 0.3 and 0.5 mol% and MPC levels around 5-10 mol% exhibit desirable characteristics for implant material coatings-high viability (>80%) with low proliferation (<40%), confirming a lack of cytotoxicity.

In situ fabrication of self-transformable and hydrophilic poly(ethylene glycol) derivative-modified polysulfone membranes

A self-transformable sulfonated poly(ethylene glycol) acrylate diblock copolymer (PEG-SO3A/OA) entrapped into polysulfone membrane was studied. The asymmetric membrane structure was prepared by a phase inversion process. The induced hydrophilicity by reorientation of diblock copolymer at the interface was evaluated by contact angle measurement, platelet adhesion test, and electron spectroscopy for chemical analysis (ESCA) depth profiling with ion sputtering. Molecular dynamic (MD) simulations as a function of copolymer density were also performed to obtain optimum interfacial structure information. The dependency of water clustering behavior as a hydrophilicity parameter was described in terms of an atom-atom radial distribution function (RDF). The results showed that the sulfonated diblock copolymer enhanced the hydrophilicity and long-term stability more than the copolymer having no hydrophobic block. Also, according to the ESCA, oxygen composition significantly began to decrease along the membrane depth, indicating the reorientation of diblock chains. The copolymer-entrapped surfaces significantly induced the degree of water clustering, and the resulting equilibrium rearrangement of interfacial structure was distinctly dependent upon the density of the copolymer.

Self-curing controlled release systems for steroids. Application of prednisolone-based polymeric systems to ear diseases

An injectable delivery system for prednisolone has been prepared based on a self-curing formulation comprised of poly(methyl methacrylate) particles and hydroxyethyl methacrylate as monomer. The polymerisation reaction was initiated by the redox system 4,4'-bis (dimethylaminobenzydrol)/benzoyl peroxide (BZN/BPO) and followed at 25 degrees C by measuring the time-temperature profile. A maximum temperature of 53 degrees C and a setting time of 15 min were obtained, calculated according to standard specifications. The swelling of the cured system was studied in phosphate-buffered saline (PBS) at 37 degrees C giving a hydration degree at equilibrium of 20%. The swelling kinetics fitted a fickian behaviour at the initial stages of the experiments, with a diffusion coefficient of 0.72 x 10(-7) cm2/s. The release of the drug was sustained from the beginning without an initial drug burst. The study of the wettability showed a rather hydrophilic character of the surface of the loaded system, and the biocompatibility evaluated through MTT assay revealed the absence of cytotoxicity due to the release of toxic substances.

Surface modification and functionalization through the self-assembled monolayer and graft polymerization

The modification of a surface at the molecular level with precise control of the building blocks generates an integrated molecular system. This field has progressed rapidly in recent years through the use of self-assembled monolayer (SAM) interfaces. Recent developments on surface-initiated chemical reactions, functionalization, and graft polymerization on SAM interfaces are emphasized in the present review. A number of surface modifications by grafting are reviewed. The grafting of polyaniline on a glass surface, previously modified with a silane self-assembled monolayer (SAM), is examined in detail for both planar and 3-D systems, such as fibers, nanoparticles, and even polymer patterned surfaces. We also discuss the graft polymerization of water-soluble polymers on the surface of silicon nanoparticles, which generate stable aqueous colloidal solutions and have numerous applications. Finally, we compare and review some surface-modification techniques on the surfaces of polymers, such as two-solvent entrapment, polymer blending, and chemical grafting, which improve their biocompatibility.

Plasma deposition and surface characterization of oligoglyme, dioxane, and crown ether nonfouling films

Plasma-deposited PEG-like films are emerging as promising materials for preventing protein and bacterial attachment to surfaces. To date, there has not been a detailed surface analysis to examine the chemistry and molecular structure of these films as a function of both precursor size and structure. In this paper, we describe radio-frequency plasma deposition of a series of short-chain oligoglymes, dioxane, and crown ethers onto glass cover slips to create poly(ethylene glycol)-like coatings. The resultant films were characterized by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), dynamic contact angle goniometry, and radiolabeled fibrinogen adsorption. Detailed analysis of the high-mass (120-300 m/z) TOF-SIMS oligoglyme film spectra revealed six classes of significant fragments. Two new models are proposed to describe how these fragments could be formed by distinct film-building processes: incorporation of intact and fragmented precursor molecules. The models also provide for the incorporation of hydrocarbon--a species that is not present in the precursors but is evidenced in XPS C(1s) spectra of these films. Two additional models describe the effects of incorporating intact and fragmented cyclic precursors.

Electrokinetics of diffuse soft interfaces. 1. Limit of low Donnan potentials

The current theoretical approaches to electrokinetics of gels or polyelectrolyte layers are based on the assumption that the position of the very interface between the aqueous medium and the gel phase is well defined. Within this assumption, spatial profiles for the volume fraction of polymer segments (phi), the density of fixed charges in the porous layer (rho fix), and the coefficient modeling the friction to hydrodynamic flow (k) follow a step-function. In reality, the "fuzzy" nature of the charged soft layer is intrinsically incompatible with the concept of a sharp interface and therefore necessarily calls for more detailed spatial representations for phi, rho fix, and k. In this paper, the notion of diffuse interface is introduced. For the sake of illustration, linear spatial distributions for phi and rho fix are considered in the interfacial zone between the bulk of the porous charged layer and the bulk electrolyte solution. The corresponding distribution for k is inferred from the Brinkman equation, which for low phi reduces to Stokes' equation. Linear electrostatics, hydrodynamics, and electroosmosis issues are analytically solved within the context of streaming current and streaming potential of charged surface layers in a thin-layer cell. The hydrodynamic analysis clearly demonstrates the physical incorrectness of the concept of a discrete slip plane for diffuse interfaces. For moderate to low electrolyte concentrations and nanoscale spatial transition of phi from zero (bulk electrolyte) to phi o (bulk gel), the electrokinetic properties of the soft layer as predicted by the theory considerably deviate from those calculated on the basis of the discontinuous approximation by Ohshima.

Grafting of poly(ethylene oxide) to the surface of polyaniline films through a chlorosulfonation method and the biocompatibility of the modified films

Poly(ethylene oxide) (PEO) could be grafted on the surface of polyaniline (PANI) films by chlorosulfonating the films with chlorosulfonic acid followed by reacting the modified films with PEO in a pyridine solution. The modified PANI films were examined by X-ray photoelectron spectroscopy and water droplet contact angles. The surface of the PEO grafted to hydrophobic PANI films became hydrophilic and the amounts of bovine serum albumin and human blood plasma platelet adsorbed onto it were decreased by more than 80%. For comparison purposes, and because the water wetting angle can be used as a measure of biocompatibility, wetting angle experiments have been also carried out for Pluronic triblock copolymer grafted to PANI and PEO or Pluronic molecules entrapped on the surfaces of PANI films. PANI was selected as substrate because one can easily change its surface properties by PEO grafting and because being conductive can be used as a sensor.

Blood compatibility of titanium oxides with various crystal structure and element doping

BACKGROUND

Titanium oxides are known to be good hemocompatible, therefore they are suggested as coatings for blood contacting implants. But little is known about the influence of physical characteristics like crystal structure, roughness and electronic state on the activation of blood platelets and the blood clotting cascade.

METHODS

Titanium oxide films were produced by metal plasma deposition and implantation in the form of rutile, crystalline and nanocrystalline anatase + brookite and amorphous TiO2. The redox potential was reduced by implantation of chromium ions, the Fermi level of the semiconductive oxide was shifted by ion implantation of the electron donor phosphorous. Hemocompatibility was determined by measuring the adhesion of blood platelets, their P-selectine expression, and of the blood clotting time on these samples.

RESULTS

The crystalline titanium oxides had a slightly higher activation of the clotting cascade but lower platelet adhesion than nanocrystalline and amorphous titanium oxides. The surface roughness below 50 nm had no obvious effect. Both, implantation of phosphorous or chromium ions, strongly reduced the activation of the clotting cascade, but only the phosphorous implanted surface also showed a reduced platelet activation, whereas platelet adhesion and activation was strongly increased on the chromium implanted surfaces.

CONCLUSION

Phosphorous doping of rutile TiO2 can increase its hemocompatibility, both concerning blood platelets and blood clotting cascade, but the biochemical mechanism has to be worked out.

Modification of polymer surfaces: optimization of approaches

Modification of polymer surfaces to achieve a surface with enhanced compatibility is an important means of obtaining improved biomaterials. Techniques are available for altering the hydrophilicity or charge of a surface, attaching macromolecules or attempting to resemble cell membranes. Relevant to the clinical success of a modified surface is the modification procedure and a procedure based on incorporation as opposed to surface treatment has potential advantages. The modification of plasticized vinyl chloride (PVC) by the incorporation of cyclodextrins is described. In comparison to unmodified PVC controls, cyclodextrin incorporation reduced fibrinogen adsorption, with the extent of reduction dependent on the type and quantity of cyclodextrin incorporated.

The effect of surface wettability on induction and growth of neurites from the PC-12 cell on a polymer surface

Surface properties of polymeric devices that are used to regenerate nervous damage are a point to be considered for axon regeneration in nerve system. In our previous studies, we prepared a wettability gradient on polyethylene (PE) surfaces using a corona discharge treatment from a knife-type electrode whose power increases gradually along the sample length. The PE surfaces were oxidized gradually with increasing power. The effect of surface wettability on the different types of cells has an important role for cell adhesion and proliferation. The purpose of this study is to investigate neurite formation on polymer surfaces with different wettability. Induction and growth of neurites from the rat pheochromocytoma (PC-12) cells attached on the polymer surfaces with different hydrophilicity were investigated using the wettability gradient PE surfaces prepared by a corona discharge treatment. Neurites were investigated for number and length of neurites in terms of surface wettability. It was observed that neurite formation of PC-12 cells was increased more onto the positions with moderate hydrophilicity of the wettability gradient surface than onto the more hydrophobic or hydrophilic positions. From those results, it could be assumed that initial adhesion of PC-12 cells was caused by more calf serum (CS) protein than nerve growth factor (NGF), whereas the neurite formation of PC-12 cells was caused by more NGF than CS protein. It follows from what has been said thus far that PC-12 cells are a differentiated neuronal phenotype with a long neurite at around the position 2.5 cm (water contact angle of about 55 deg). In conclusion, surface wettability plays an important role for neurite formation on the polymer surfaces for axon regeneration.

Development of new hydroactive dressings based on chitosan membranes: characterization and in vivo behavior

Different poly(vinyl alcohol) (PVA)/chitosan lactate (ChL)-blended hydrogels containing nitrofurazone as a local anti-infective drug were prepared by the phase-inversion technique. The swelling degree, surface free energy, mechanical properties, and nitrofurazone release of these membranes were determined. Blood compatibility of these systems was evaluated by the open-static platelet adhesion test with whole human blood. The results showed that water absorption into the PVA/ChL membranes slowed down, governed by the rate at which the dressing interacted with the physiological fluid. Swelling degree values up to 200% were observed. The rate of release of nitrofurazone seemed to depend on the ChL percentage on the blend as well as the pH of the solution. The surface free energy values were in the range of 20-30 dynes/cm, which was appropriate for a favorable interaction with blood. From the Young's module curve, it could be seen that elastic hydrogels were obtained with increment of ChL in the PVA/ChL blends. Values of platelet adhesion and whole blood clotting times for the PVA/ChL blends as well as the increase of ChL, which appears to reduce the fibrinogen adsorption on the PVA/ChL membranes, demonstrated that the blood compatibility of PVP/ChL blends is superior to that separated polymers. The results of in vivo experiments in rats were in very good agreement with these observations, suggesting that PVA/ChL may serve as a new type of potential wound-dressing material.

In vitro biocompatibility of biodegradable dextran-based hydrogels tested with human fibroblasts

The cytotoxicity of dextran T40, methacrylated dextran (dex-MA) and hydroxyethyl-methacrylated dextran (dex-HEMA), dextran-based hydrogel discs and microspheres, and their degradation products, was studied by measuring the cell proliferation inhibition index (CPII) on human fibroblasts in vitro. In addition, during the 72 h incubation period light-microscopic observations were performed daily. After 24 h of incubation with dextran and dex-HEMA polymers, the cells showed elongated or spider-like forms, some lipid droplets and intracellular granula, indicative of pinocytosis and internalization of the polymers. During the next two days, the fibroblasts' appearance did not change. Methacrylic acid (MAA), formed by hydrolysis of dex-HEMA, did not influence the cell morphology. Dex-HEMA polymer solutions with a low and high degree of substitution (DS) at 100 mg/ml caused a CPII of 30-40% after 72 h. This is less than 10% growth inhibition per cell cycle and statistically not different from the CPII induced by 100 mg/ml dextran T40. Growth inhibition induced by MAA was also low. The various dex-MA hydrogel discs caused similar low growth inhibition. Interestingly, hydrogel microspheres of dex-MA and dex-(lactate-)HEMA caused a CPII of only 0-20% after 72 h. The results presented in this study demonstrate that methacrylate-derivatized dextran hydrogels show good biocompatibility in vitro making these degradable biomaterials promising systems for drug delivery purposes.

Plasma-deposited membranes for controlled release of antibiotic to prevent bacterial adhesion and biofilm formation

Bacterial infection on implanted medical devices is a significant clinical problem caused by the adhesion of bacteria to the biomaterial surface followed by biofilm formation and recruitment of other cells lines such as blood platelets, leading to potential thrombosis and thromboembolisms. To minimize biofilm formation and potential device-based infections, a polyurethane (Biospan) matrix was developed to release, in a controlled manner, an antibiotic (ciprofloxacin) locally at the implant interface. One material set consisted of the polyetherurethane (PEU) base matrix radiofrequency glow discharge plasma deposited with triethylene glycol dimethyl ether (triglyme); the other set had an additional coating of poly(butyl methyacrylate) (pBMA). Triglyme served as a nonfouling coating, whereas the pBMA served as a controlled porosity release membrane. The pBMA-coated PEU contained and released ciprofloxacin in a controlled manner. The efficacy of the modified PEU polymers against Pseudomonas aeruginosa suspensions was evaluated under flow conditions in a parallel plate flow cell. Bacterial adhesion and colonization, if any, to the test polymers were examined by direct microscopic image analysis and corroborated with destructive sampling, followed by direct cell counting. The rate of initial bacterial cell adhesion to triglyme-coated PEU was 0. 77%, and to the pBMA-coated PEU releasing ciprofloxacin was 6% of the observed adhesion rates for the control PEU. However, the rate of adherent cell accumulation due to cell growth and replication was approximately the same for the triglyme-coated PEU and the PEU controls, but was zero for the pBMA-coated PEU releasing ciprofloxacin.

Platelet adhesion onto segmented polyurethane film surfaces modified by addition and crosslinking of PEO-containing block copolymers

Polyethylene oxide (PEO) surfaces were prepared by the addition of PEO-containing amphiphilic block copolymers as surface modifying additives and of dicumyl peroxide (DCP) as a crosslinking agent in segmented polyurethane (PU). PEO-polypropylene oxide-PEO triblock copolymers (Pluronics) with different PEO chain length (from 0 to 98) were used as the surface modifying additives. The PEO additives in the PU film were then crosslinked to be stably entrapped in the PU matrix. The crosslinking was done by free radicals produced from the decomposition of DCP in the film through heating (120 degrees C) or ultraviolet irradiation (254 nm). The surface properties of the PEO additive-entrapped PU films were investigated by the measurement of water contact angles and electron spectroscopy for chemical analysis. The bulk properties such as water absorption, long-term film stability, and tensile strength and elongation at break, were also investigated. It was observed that addition of a small amount (5 wt% based on PU) of the PEO additives resulted in a considerable change of surface characteristics. The PEO additives were stably entrapped in the PU films by crosslinking of them, without significant changes of bulk properties of the films. From the platelet adhesion test on the prepared PEO additive-containing film surfaces, it was observed that the platelet adhesion on the surfaces decreases with increase in PEO chain length of PEO additives. The film surface containing additive with long PEO chains (chain length of 98) was particularly effective in preventing platelet adhesion. The crosslinking of the PEO additives in PU films did not affect the behavior of platelet adhesion on the surfaces; the films with crosslinked PEO additives showed similar platelet adhesion on the surfaces to the films with uncrosslinked ones.

Polyurethane surfaces modified by amphiphilic polymers: effects on protein adsorption

Surface modification of polyurethane (PUR) surfaces was carried out by using three different amphiphilic polymers. Two of the polymers were graft copolymers, having backbones consisting of poly(methyl methacrylate-co-ethylhexyl acrylate) and poly(styrene-co-acrylamide), respectively, and poly(ethylene oxide) PEO 2000 grafts. The third polymer was a commercially available poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) block copolymer, Pluronic 9400. The polymers were designated ACRY, STY2, and PE94, respectively. Surface modification was achieved by adsorption of the amphiphilic polymers at PUR surfaces from an aqueous solution, or by blending the amphiphiles into a PUR solution, followed by solution casting of films. The accumulation of the amphiphilic polymers at the PUR surfaces was observed by XPS and contact angle measurements. The ACRY and PE94 polymers were shown to adsorb poorly at the PUR surface, but gave strong surface effects when present in the PUR matrix. Protein adsorption was measured under static as well as under flow conditions. The modified surfaces had generally lower adsorption of blood proteins (HSA, Fg and IgG) than the unmodified PUR surfaces. ACRY blend modified surfaces had the lowest adsorption.