In vitro haemocompatibility and stability of two types of heparin-immobilized silicon surfaces

Formation of Zirconium(IV)-Heparin Complex Multilayers on Solid Surfaces for Long-Lasting Antiplatelet Application

A facile approach to enhancing the blood compatibility of solid surfaces based on Zr^IV -heparin complexation is reported. Solid surfaces are pretreated with tannic acid (TA)/Zr^IV complexes. Heparin is then deposited on the surface through a spin-coating process and fixed by a Zr^IV -mediated crosslinking reaction. Using this approach, TA/Zr^IV /heparin complex multilayers that are highly resistant to human platelet adhesion are formed on various substrates including metal, metal oxides, ceramics, and synthetic polymers. This approach presents a sustainable way for the immobilization of heparin onto surfaces because it does not require any derivatization of heparin molecule as well as time-consuming processes.

Accelerated skin wound healing by soy protein isolate-modified hydroxypropyl chitosan composite films

In this study, a series of hydroxypropyl chitosan (HPCS)/soy protein isolate (SPI) composite films (HCSFs) with different SPI contents were developed via crosslinking, solution casting, and evaporation process. Effects of the SPI content on the structure and physical properties of the HCSFs were characterized by Fourier transform infrared spectroscopy, X-ray diffraction patterns, scanning electron microscopy, swelling kinetics analysis, and mechanical testing. The HCSFs exhibited a lower swelling ratio with an increase in the SPI content. The tensile strength was in a tunable range from 7.88 ± 3.08 to 40.44 ± 2.31 MPa by adjusting the SPI content. Cytocompatibility and hemocompatibility of the HCSFs were evaluated by a series of in vitro assays, including MTT assay, live/dead assay, cell morphology observation, hemolysis ratio testing, and plasma recalcification time measurement. Results showed that the HCSFs support L929 cells attachment and proliferation without obvious hemolysis, indicating good cytocompatibility and hemocompatibility. The potential of resultant HCSFs as the wound dressings was investigated using a full-thickness skin wound model in rats. Results exhibited that the HCSFs with 50% SPI content had the fastest healing speed and the best skin regeneration efficiency and may be a potential candidate as the wound dressing.

Enzyme immobilization on silane-modified surface through short linkers: fate of interfacial phases and impact on catalytic activity

We investigated the mechanism of enzyme immobilization on silanized surfaces through coupling agents (cross-linkers) in order to understand the role of these molecules on interfacial processes and their effect on catalytic activity. To this end, we used a model multimeric enzyme (G6PDH) and several cross-linking molecules with different chemical properties, including the nature of the end-group (-NCO, -NCS, -CHO), the connecting chain (aliphatic vs aromatic), and geometrical constraints (meta vs para-disubstituted aromatics). There did not seem to be radical differences in the mechanism of enzyme adsorption according to the linker used as judged from QCM-D, except that in the case of DIC (1,4-phenylene diisocyanate) the adsorption occurred more rapidly. In contrast, the nature of the cross-linker exerted a strong influence on the amount of enzyme immobilized as estimated from XPS, and more unexpectedly on the stability of the underlying silane layer. DIC, PDC (1,4-phenylene diisothiocyanate), or GA (glutaraldehyde) allowed successful enzyme immobilization. When the geometry of the linker was changed from 1,4-phenylene diisothiocyanate to 1,3-phenylene diisothiocyanate (MDC), the silane layer was subjected to degradation, upon enzyme adsorption, and the amount of immobilized molecules was significantly lowered. TE (terephtalaldehyde) and direct enzyme deposition without cross-linker were similar to MDC. The organization of immobilized enzymes also depended on the immobilization procedure, as different degrees of aggregation were observed by AFM. A correlation between the size of the aggregates and the catalytic properties of the enzyme was established, suggesting that aggregation may enhance the thermostability of the multimeric enzyme, probably through a compaction of the 3D structure.

X-Ray Photoelectron Spectroscopy Investigation of the Nitrogen Species in Photoactive Perfluorophenylazide-Modified Surfaces

X-ray Photoelectron Spectroscopy (XPS) was used to characterize the nitrogen species in perfluorophenylazide (PFPA) self-assembled monolayers. PFPA chemistry is a novel immobilization method for tailoring the surface properties of materials. It is a simple route for the efficient immobilization of graphene, proteins, carbohydrates and synthetic polymers onto a variety of surfaces. Upon light irradiation, the azido group in PFPA is converted to a highly reactive singlet nitrene species that readily undergoes CH insertion and C=C addition reactions. Here, the challenge of characterizing the PFPA modified surfaces was addressed by detailed XPS experimental analyses. The three nitrogen peaks detected in the XPS N1s spectra were assigned to amine/amide (400.5 eV) and azide (402.1 and 405.6 eV) species. The observed 2:1 ratio of the areas from the 402.1 eV to 405.6 eV peaks suggests the assignment of the peak at 402.1 eV to the two outer nitrogen atoms in the azido group and assignment of the peak at 405.6 eV to the central nitrogen atom in the azido group. The azide decomposition as the function of x-ray exposure was also determined. Finally, XPS analyses were conducted on patterned graphene to investigate the covalent bond formation between the PFPA and graphene. This study provides strong evidence for the formation of covalent bonds during the PFPA photocoupling process.

Antibacterial and hemocompatibility switchable polypropylene nonwoven fabric membrane surface

In this article, a facile approach to fabricate a biofunctional polypropylene nonwoven fabric membrane (PP NWF) with a switchable surface from antibacterial property to hemocompatibility is presented. In the first step, a cationic carboxybetaine ester monomer, [(2-(methacryboxy) ethyl)]-N,N-dimethylamino-ethylammonium bromide, methyl ester (CABA-1-ester) was synthesized. Subsequently, this monomer was introduced on the PP NWF surface via plasma pretreatment and a UV-induced graft polymerization technique. Finally, a switchable surface from antibacterial property to hemocompatibility was easily realized by hydrolysis of poly(CABA-1-ester) moieties on the PP NWF surface under mild conditions. Surface hydrolysis behaviors under different pH conditions were investigated. These PP NWFs grafted with poly(CABA-1-ester) segments can cause significant suppression of S. aureus proliferation; after hydrolysis, these surfaces covered by poly[(2-(methacryloxy) ethyl)] carboxybetaine (poly(CABA)) chains exhibited obvious reduction in protein adsorption and platelet adhesion, and remarkably enhanced antithrombotic properties. This strategy demonstrated that a switchable PP NWF surface from antibacterial property to hemocompatibility was easily developed by plasma pretreatment and UV-induced surface graft polymerization and that this surface may become an attractive platform for a range of biomedical applications.

SURFACE CHARACTERIZATION AND HEMOCOMPATIBILITY OF HEPARINIZED 316L STAINLESS STEEL

Poor compatibility between blood and metallic coronary artery stents is one reason for arterial restenosis. Immobilization of heparin on stent's surface is feasible for improving compatibility. We examined possible surface-coupling agents for anticoagulant agent immobilization. Hexamethylene diisocyanate (HMDI) was examined as surface-coupling agent to activate 316L stainless steel (e.g. stent material). Afterwards, we grafted PEG on the HMDI activated surface to provide heparin with higher conformational freedom and a more hydrophilic environment. The effectiveness of HMDI activated and PEG grafted surface was confirmed by FTIR, XPS, and water contact angle test. Heparin was then immobilized onto the activated 316L stainless steel. The heparin surface density was 9.5 μg/cm2. Sessile drop water contact angles showed that the heparingrafted surface is even more hydrophilic than the PEG grafted one. The function of grafted heparin was evaluated by antithrombrin III (ATIII) adsorption testing and SEM. The surface with heparin grafting shows better ATIII binding ability and hemocompatibility than the native one.

In situ forming, metal-adhesive heparin hydrogel surfaces for blood-compatible coating

Durable and blood-compatible coating of metallic biomaterials remains a major issue in biomedical fields despite its long history of development. In this study, in situ forming, metal-adhesive heparin hydrogels were developed to coat metallic substrates to enhance blood compatibility. The hydrogels are composed of metal-adhesive and enzyme-reactive amphiphilic block copolymer (Tetronic-tyramine/dopamine; TTD) and enzyme-reactive heparin derivatives (heparin-tyramine or heparin-polyethylene glycol-tyramine), which are cross-linkable in situ via an enzyme reaction. The combinations of heparin and Tetronic formed hydrogels with relatively high mechanical strengths of 300-5000 Pa within several tens of seconds; this was also confirmed by observing a dried porous structure as coated on a metal surface. The introduction of dopamine to the hydrogel network enhanced the durability of the hydrogel layers coated on metal, such that more than 60% heparin remained for 7 days. Compared to bare metal surfaces, hydrogel-coated metal surfaces exhibited significantly enhanced blood compatibility. Reduced fibrinogen adsorption and platelet adhesion showed that blood compatibility was 3-5-fold-enhanced on coated hydrogel layers than on the bare metal surface. In conclusion, hydrogels containing heparin and dopamine prepared by enzyme reaction have the potential to be an alternative coating method for enhancing blood compatibility of metallic biomaterials.

Enhancement of blood compatibility of poly(urethane) substrates by mussel-inspired adhesive heparin coating

Heparin immobilization on surfaces has drawn a great deal of attention because of its potential application in enhancing blood compatibility of various biomedical devices such as catheters, grafts, and stents. Existing methods for the heparin immobilization are based on covalent linkage formation and electrostatic interaction between substrates and heparin molecules. However, complicated multistep procedures and uncontrolled desorption of heparin are limitations of these methods. In this work, we report a new heparin derivative that exhibits robust adhesion on surfaces. The derivative, called hepamine, was prepared via conjugation of dopamine, a mussel-inspired adhesive moiety, onto a heparin backbone. Immersion of poly(urethane) substrates into an aqueous solution of hepamine resulted in robust heparin coating of the poly(urethane), the most widely used polymeric material for blood-contacting medical devices. The hepamine-coated poly(urethane) substrate showed significant inhibition of blood coagulation and platelet adhesion. The use of hepamine for surface modification is advantageous for several reasons: for example, no chemical pretreatment of the substrates is necessary, and surface functionalization is a simple, one-step procedure. Thus, the heparin immobilization method described herein is an excellent alternative approach for the introduction of heparin molecules onto surfaces.

Improvement of blood compatibility on polysulfone-polyvinylpyrrolidone blend films as a model membrane of dialyzer by physical adsorption of recombinant soluble human thrombomodulin (ART-123)

ART-123 is a recombinant soluble human thrombomodulin (hTM) with potent anticoagulant activity, and is available for developing antithrombogenic surfaces by immobilization. We focused on improving blood compatibility on the dialyzer surface by the physical adsorption of ART-123 as a safe yet simple method without using chemical reagents. The physical adsorption mechanism and anticoagulant activities of adsorbed hTM on the surface of a polysulfone (PSF) membrane containing polyvinylpyrrolidone (PVP) as a model dialyzer were investigated in detail. The PVP content of the PSF-PVP films was saturated at 20 wt% after immersion in Tris-HCl buffer, even with the addition of over 20 wt% PVP. The surface morphology of the PSF-PVP films was strongly influenced by the PVP content, because PVP covered the outermost surface of the PSF-PVP films. The adsorption speed of hTM slowed dramatically with increasing PVP content up to 10 wt%, but the maximum adsorption amount of hTM onto the PSF-PVP film surface was almost the same, regardless of the PVP content. The PSF-PVP film with the physically adsorbed hTM showed higher protein C activity as compared to the PSF film, it showed excellent blood compatibility due to the protein C activity and the inhibition properties of platelet adhesion. The physical adsorption of hTM can be useful as a safe yet simple method to improve the blood compatibility of a dialyzer surface.

Nanoscale investigation on E. coli adhesion to modified silicone surfaces

Bacterial infection is a major challenge in biomaterials development. The adhesion of microorganisms to the material surface is the first step in infectious conditions and this quickly leads to the formation of biofilms on a material surface. A unique attribute of atomic force microscopy (AFM) is that it reveals not only the morphology of cells and the surface roughness of the substrate, but it can also quantify the adhesion force between bacteria and surfaces. We have shown that fluoroalkylsilane (FAS) and octadecyltrichlorosilane (OTS)-coated silicone samples exhibit greater potential for reducing E. coli JM 109 adhesion than heparin- and hyaluronan-modified samples. The force curves obtained from AFM can be used as a primary indicator in predicting bacterial adhesion.

Effects of immobilized glycosaminoglycans on the proliferation and differentiation of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are adult stem cells with potential for multilineage differentiation. They represent an attractive cell source alternative to embryonic stem cells for therapeutic applications. Optimal utilization of MSCs for tissue engineering requires improved biomaterials that can enhance their growth and direct differentiation. The biological activity of glycosaminoglycans (GAGs) has been previously exploited for use in tissue engineering applications. In this study, MSC proliferation and differentiation was studied on GAG-derivatized chitosan membranes. The GAGs included heparin, heparan sulfate, dermatan sulfate, chondroitin 4-sulfate, chondroitin 6-sulfate, and hyaluronic acid. The covalent GAG immobilization method and amount of immobilized GAG were varied. It was found that MSC growth increased as much as fivefold on GAG-immobilized surfaces compared to tissue culture plastic and chitosan-only controls. The MSC growth rates increased significantly with increasing GAG density on the culture surfaces. The MSC proliferation rates on heparin, heparan sulfate, dermatan sulfate, and chondroitin 6-sulfate exhibited nonlinear increases with the level of fibronectin binding on these surfaces. In contrast, MSC proliferation on hyaluronic acid and chondroitin 4-sulfate was found to be independent of fibronectin or vitronectin binding on the surfaces, suggesting that these GAGs influenced MSC proliferation through different mechanisms. In conclusion, the results indicate that GAG immobilization on chitosan scaffolds provides an effective means of manipulating MSC proliferation and has promising potential for directing MSC differentiation in tissue engineering applications employing chitosan.

Poly(N-isopropylacrylamide) grafted on plasma-activated poly(ethylene oxide): thermal response and interaction with proteins

Thermoresponsive polymer layers offer the possibility of preparing smart surfaces with properties that are switchable through a phase transition, usually close to the lower critical solution temperature of the polymer. In particular, poly( N-isopropylacrylamide) (pNIPAM) has gained a great deal of attention because it has such a phase transition in a physiologically interesting temperature range. We have prepared ultrathin thermoresponsive coatings by grafting pNIPAM on a plasma-CVD-deposited, poly(ethylene oxide)-like polymer substrate that was activated in an Ar plasma discharge to initiate the grafting. The presence and integrity of pNIPAM was verified by XPS and ToF-SIMS, and a dramatic change in the wettability during the phase transition was identified by temperature-dependent contact angle measurements. The transition from the hydrated to the collapsed conformation was analyzed by temperature-dependent QCM measurements and by AFM. An unusual, reversible behavior of the viscoelastic properties was seen directly at the phase transition from the swollen to the collapsed state. The phase transition leads to a switching from protein repulsion to a state that allows the adsorption of proteins.

Physical adsorption of human thrombomodulin (ART-123) onto polymeric biomaterials for developing an antithrombogenic blood-contacting material

Human thrombomodulin (hTM) is an endothelial cell-associated protein with potent natural anticoagulant activity by converting thrombin from a procoagulant protease to an anticoagulant. ART-123 is a recombinant soluble hTM (amino acid residues 1-498), and we focused on the physical adsorption of ART-123 onto a polymeric biomaterial surface to develop an antithrombogenic blood-contacting material with preventing the denaturation of hTM and the remaining chemical reagents. The adsorption of hTM onto polysulfone (PSF) films was analyzed quantitatively by quartz crystal microbalance analysis. The adsorption constant and the maximum adsorption amount, calculated by the assumption of a Langmuir-type adsorption, showed that hTM adsorbed with a relatively weak interaction onto the PSF film. The hydrophilic protein lysozyme also showed a Langmuir-type monolayer adsorption, although hydrophobic catalase and fibrinogen showed multilayer adsorption accompanying the denaturation. The physically adsorbed hTM showed high coenzymatic activity for the activation of protein C, as well as anticoagulant activity. Furthermore, the surface wettability of the PSF film was easily controllable by the physical adsorption of hydrophobic and hydrophilic bioactive proteins. The physical adsorption of hTM or bioactive proteins onto polymeric biomaterials will be instrumental for developing an antithrombogenic blood-contacting biomaterial, and for controlling the surface properties of biomaterials.

Effect of surface modification of siliconeon Staphylococcus epidermidis adhesion and colonization

Cerebrospinal fluid (CSF) shunts for the treatment of hydrocephalus are generally made of silicone rubber. The growth of bacterial colonies on the silicone surface leads to frequent CSF shunt complications. A systematic study of the effect of the surface modification of silicone on Staphylococcus epidermidis adhesion and colonization was performed for different incubation times by means of colony counting and scanning electron microscopy (SEM). Silicone was modified with different biopolymers and silanes, including heparin, hyaluronan, octadecyltrichlorosilane (OTS), and fluoroalkylsilane (FAS) to provide a stable and biocompatible surface with different surface functional groups and degrees of hydrophobicity. The modified silicone surfaces were studied by using contact angle measurements, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). After 4 and 8 h of incubation, the FAS- and OTS-coated silicone and the hyaluronan coated OTS/silicone surfaces showed significantly reduced bacterial adhesion and colonization compared to blank silicone by both quantification methods. However, the heparin coated OTS/silicone showed significantly increased bacterial adhesion. These results indicate that the nature of the surface functional group and surface roughness determine the extent of bacterial adhesion and colonization. However, the degree of hydrophobicity of the surface did not appear to play a determining role in bacterial adhesion and colonization.

Chronic performance of polyurethane catheters covalently coated with ATH complex: A rabbit jugular vein model

Covalent complexes of antithrombin (AT) and heparin (ATH) have superb anticoagulant activity towards thrombin and factor Xa. Stability of polyurethane central venous catheters covalently modified with radiolabeled ATH was studied using a roller pump with saline or protease P-5147. Saline wash removed loosely bound ATH molecules to decrease graft density from 26 to 12 pmol/cm2. However, only slightly more ATH was removed by strong protease (from 12 to 7 pmol/cm2). To evaluate ATH-coated, heparin-coated, and uncoated catheters, a chronic rabbit jugular vein model was developed with catheters maintained for up to 30-106 days. Lumen occlusion was tested by drawing blood twice daily. Although unmodified or heparin-coated catheters occluded within 5-7 days after insertion, all ATH catheters remained patent throughout the experiment. Scanning electron microscopy (SEM) analysis of heparin and uncoated catheters revealed extensive thrombosis (lumen+mural) while ATH catheters were unaffected. Visual observation showed significant deposition of protein and cells on control and heparin-modified catheters and, to a lesser degree, on ATH-coated surfaces. SEM showed no fibrin inside or outside of ATH catheters, which remained patent in extended studies out to 106 days. Although atomic force microscopy showed ATH coatings to be rough, 6-fold higher anti-factor Xa activity likely contributed to increased patency. Our data confirm that ATH-modified catheters are stable and have superior potency compared to heparin or control catheters.

Effect of surface proteins on Staphylococcus Epidermidis adhesion and colonization on silicone

Shunt infections are one of the most serious complications in shunt implant surgery. Previous studies have suggested that cerebrospinal fluid (CSF) proteins could affect bacterial adhesion and subsequent shunt infection. A systematic study using immobilized protein on the surface of silane-modified silicone was conducted to determine how these modifications influenced Staphylococcus epidermidis adhesion and colonization. A comparison was also made with silicone having physically adsorbed protein. A colony-counting adhesion assay and scanning electron microscopy (SEM) were used to provide quantitative analysis of bacterial adhesion and semi-quantitative analysis of bacterial colonization, respectively. In order to determine the appropriate silanization process for effective protein immobilization, the effect of bovine serum albumin (BSA) immobilized on n-3-(trimethoxysilyl)propyl-ethylenediamine (AEAPS)/silicone, aminopropyltriethoxysilane (APTMS)/silicone, 3-(glycidyloxypropyl)trimethoxysilane (GPTMS)/silicone, and octadecyltrichlorosilane (OTS)/silicone on bacterial adhesion was investigated. Upon identifying that OTS is the most effective silane, different types of proteins, including: BSA, human serum albumin (HSA), gamma-globulin, and fibrinogen were immobilized on OTS/silicone by a photo-immobilization method. Immobilized protein on modified silicone surfaces was found to be stable in saline for 30 days, while physically adsorbed protein showed instability within hours as determined by contact angle measurements and X-ray photoelectron spectroscopy (XPS). For HSA/OTS/silicone, BSA/OTS/silicone, gamma-globulin/OTS/silicone, fibrinogen/OTS/silicon, and physically absorbed BSA on silicone, the contact angles were 78.5 degrees, 80.7 degrees, 78.9 degrees, 81.3 degrees, and 96.5 degrees; and the amount of nitrogen content was found to be 4.6%, 5.0%, 5.6%, 7.2%, and 3.2%, respectively. All protein immobilized on OTS/silicone surfaces significantly reduced bacterial adhesion by around 75% compared to untreated silicone, while physically adsorbed BSA on silicone reduced by only 29.4%, as determined by colony-counting adhesion assay. However, there was no significant difference on bacterial adhesion among the different types of proteins immobilized on OTS/silicone. Minimizing bacterial adhesion and colonization can be attributed to the increased concentration of -NH2 group, and stability and more hydrophilic nature of the protein/OTS/silicone surfaces.