Surface Heparinization Research Articles

Fabrication of small-diameter in situ tissue engineered vascular grafts with core/shell fibrous structure and a one-year evaluation via rat abdominal vessel replacement model

A high vascular patency was realized in the bulk or surface heparinized small-diameter in situ tissue-engineered vascular grafts (TEVGs) via a rabbit carotid artery replacement model in our previous studies. Those surface heparinized TEVGs could reduce the occurrence of aneurysms, but with a low level of the remodeled elastin, whereas those bulk heparinized TEVGs displayed a faster degradation and an increasing occurrence of aneurysms, but with a high level of the regenerated elastin. To combine the advantages of the bulk and surface graft heparinization to boost the remodeling of elastin and defer the occurrence of aneurysms, a coaxial electro-spinning technique was used to fabricate a kind of small-diameter core/shell fibrous structural in situ TEVGs with a faster degradable poly(lactic-co-glycolic acid) (PLGA) as a core layer and a relatively lower degradable poly(ε-caprolactone) (PCL) as a shell layer followed by the surface heparinization. The in vitro mechanical performance and enzymatic degradation tests revealed the resulting PLGA@PCL-Hep in situ TEVGs possessing not only a faster degradation rate, but also the mechanical properties comparable to those of human saphenous veins. After implanted in the rat abdominal aorta for 12 months, the good endothelialization, low inflammation, and no calcification were evidenced. Furthermore, the neointima layer of regenerated new blood vessels was basically constructed with a well-organized arrangement of elastin and collagen proteins. The results showed the great potential of these in situ TEVGs to be used as a novel type of long-term small-diameter vascular grafts.

Surface Heparinization of a Magnesium-Based Alloy: A Comparison Study of Aminopropyltriethoxysilane (APTES) and Polyamidoamine (PAMAM) Dendrimers.

Magnesium (Mg)-based alloys are biodegradable metallic biomaterials that show promise in minimizing the risks of permanent metallic implants. However, their clinical applications are restricted due to their rapid in vivo degradation and low surface hemocompatibilities. Surface modifications are critically important for controlling the corrosion rates of Mg-based alloys and improving their hemocompatibilities. In the present study, two heparinization methods were developed to simultaneously increase the corrosion resistance and hemocompatibility of the AZ31 Mg alloy. In the first method, the surface of the AZ31 alloy was modified by alkali-heat treatment and then aminolyzed by 3-amino propyltriethoxy silane (APTES), a self-assembly molecule, and heparin was grafted onto the aminolyzed surface. In the second method, before heparinization, polyamidoamine dendrimers (PAMAM4-4) were grafted onto the aminolyzed surface with APTES to increase the number of surface functional groups, and heparinization was subsequently performed. The presence of a peak with a wavelength of about 1560 cm-1 in the FTIR spectrum for the sample modified with APTES and dendrimers indicated aminolysis of the surface. The results indicated that the corrosion resistance of the Mg alloy was significantly improved as a result of the formation of a passive layer following the alkali-heat treatment. The results obtained from a potentiodynamic polarization (PDP) test showed that the corrosion current in the uncoated sample decreased from 25 µA to 3.7 µA in the alkali-heat-treated sample. The corrosion current density was reduced by 14 and 50 times in samples treated with the self-assembly molecules, APTES and dendrimers, respectively. After heparinization, the clotting time for pristine Mg was greatly improved. Clotting time increased from 480 s for the pristine Mg sample to 630 s for the APTES- and heparin-modified samples and to 715 s for the PAMAM- and heparin-modified samples. Cell culture data showed a slight improvement in the cell-supporting behavior of the modified samples.

The polydopamine‐assisted heparin anchor enhances the hydrophilicity, hemocompatibility, and biocompatibility of polyurethane

AbstractSurface heparinization is an effective solution to resolve low endothelialization, poor anticoagulation, and hemocompatibility of polyurethane (PU) used as materials of small‐diameter vascular grafts. Here, the effects of polydopamine (PDA) and poly (acrylic acid) (PAA) as crosslinking agents on the surface heparinization were explored. The PU membranes grafted with heparin (Hep) via dopamine (PU/PDA‐Hep) showed better hydrophilicity and stability, compared to heparinized PU membranes via acrylic acid (PU/PAA‐Hep). The results of X‐ray photoelectron spectroscopy demonstrated that heparin was successfully grafted onto the PU surface and the grafting efficiency was high when PDA as a cross‐linking agent. The grafted heparin aggregated and formed nanoparticles, and increased the surface roughness of PU membranes. The heparinized membranes demonstrated good anti‐adhesion of bovine serum albumin and fibrin protein. In addition, no activated platelets or educts on heparinized PU were found by platelet adhesion tests, implying that heparin‐immobilized surfaces had good hemocompatibility. Moreover, the in vitro cytocompatibility assessment showed that the PU/PDA‐Hep significantly improved the proliferation of L929 cells and was superior to PU/AA‐Hep. These results demonstrated that PDA‐assisted surface heparinization was an effective method to improve the anticoagulant and biocompatibility of PU small‐diameter vascular materials and could be extended to other implantable materials.

Fabrication of heparinized small diameter TPU/PCL bi-layered artificial blood vessels and in vivo assessment in a rabbit carotid artery replacement model

Increasingly growing problems in vascular access for long-term hemodialysis lead to a considerable demand for synthetic small diameter vascular prostheses, which usually suffer from some drawbacks and are associated to high failure rates. Incorporating the concept of in situ tissue engineering (TE) into synthetic small diameter blood vessels, for example, thermoplastic poly(ether urethane) (TPU) ones, could provide an alternative approach for vascular access that profits from the advantages of excellent mechanical properties of synthetic polymer materials (early cannulation) and unique biointegration regeneration of autologous neovascular tissues (long-term fistulae). In this study, a kind of heparinized small diameter (d = 2.5 mm) TPU/poly(ε-caprolactone) (TPU/PCL-Hep) bi-layered blood vessels was electrospun with an inner layer of PCL and an outer layer of TPU. Afterward, the inner surface heparinization was conducted by coupling H2N-PEG-NH2 to the corroded PCL layer and then heparin to the attached H2N-PEG-NH2 via the EDCI/NHS chemistry. Herein a heparinized PCL inner layer could not only inhibit thrombosis, but also provide sufficient space for the neotissue regeneration via biodegradation with time. Meanwhile, a TPU outer layer could confer the vascular access the good mechanical properties, such as flexibility, viability and fitness of elasticity between the grafts and host blood vessels as evidenced by the adequate mechanical properties, such as compliance (4.43 ± 0.07%/ 100 mmHg), burst pressure (1447 ± 127 mmHg) and suture retention strength (1.26 ± 0.07 N) without blood seepage after implantation. Furthermore, a rabbit carotid aortic replacement model for 5 months was demonstrated 100% animal survival and 86% graft patency. Puncture assay also revealed the puncture resistance and self-sealing (hemostatic time < 2 min). Histological analysis highlighted neotissue regeneration, host cell infiltration and graft remodeling in terms of extracellular matrix turnover. Altogether, these results showed promising aspects of small diameter TPU/PCL-Hep bi-layered grafts for hemodialytic vascular access applications.

Remodeling of structurally reinforced (TPU+PCL/PCL)-Hep electrospun small-diameter bilayer vascular grafts interposed in rat abdominal aortas.

As thermoplastic polyurethane (TPU) elastomers possess good biocompatibility and mechanical properties similar to those of native vascular tissues, they were intended to be co-electrospun with poly(ε-caprolactone) (PCL) onto the outer surface of PCL electrospun small-diameter single-layer vascular grafts (SLVGs) in this study, combining with surface heparinization. In this work, a kind of structurally reinforced TPU+PCL/PCL small-diameter bilayer vascular graft (BLVG) was fabricated via layer-by-layer electrospinning followed by the heparinization of PCL via EDC/NHS chemistry. The resulting (TPU+PCL/PCL)-Hep BLVGs presented excellent mechanical strength and higher compliance, and sustainably released heparin exhibited enhanced anti-coagulation activity. During 6-month implantation in 18 rat abdominal aortas, these vascular prostheses induced the remodeling and regeneration of neovascular tissues, and promoted ECM deposition. Compared to heparinized PCL (PCL-Hep) SLVGs, the formation of aneurysm was completely inhibited and the onset of calcification was significantly delayed in (TPU+PCL/PCL)-Hep BLVGs. Not only vascular cell makers co-expressed by CD206+ cells were identified, but also a high content of elastin was evidenced due to the improvement of mechanical strength and compliance. These results indicated the feasibility and efficacy of inhibiting the aneurysm formation and boosting the vascular remodeling by incorporating TPU into PCL-Hep small-diameter artificial vascular grafts.

Endothelium-Mimicking Multifunctional Coating Modified Cardiovascular Stents via a Stepwise Metal-Catechol-(Amine) Surface Engineering Strategy.

Stenting is currently the major therapeutic treatment for cardiovascular diseases. However, the nonbiogenic metal stents are inclined to trigger a cascade of cellular and molecular events including inflammatory response, thrombogenic reactions, smooth muscle cell hyperproliferation accompanied by the delayed arterial healing, and poor reendothelialization, thus leading to restenosis along with late stent thrombosis. To address prevalence critical problems, we present an endothelium-mimicking coating capable of rapid regeneration of a competently functioning new endothelial layer on stents through a stepwise metal (copper)-catechol-(amine) (MCA) surface chemistry strategy, leading to combinatorial endothelium-like functions with glutathione peroxidase-like catalytic activity and surface heparinization. Apart from the stable nitric oxide (NO) generating rate at the physiological level (2.2 × 10−10 mol/cm2/min lasting for 60 days), this proposed strategy could also generate abundant amine groups for allowing a high heparin conjugation efficacy up to ∼1 μg/cm2, which is considerably higher than most of the conventional heparinized surfaces. The resultant coating could create an ideal microenvironment for bringing in enhanced anti-thrombogenicity, anti-inflammation, anti-proliferation of smooth muscle cells, re-endothelialization by regulating relevant gene expressions, hence preventing restenosis in vivo. We envision that the stepwise MCA coating strategy would facilitate the surface endothelium-mimicking engineering of vascular stents and be therefore helpful in the clinic to reduce complications associated with stenosis.

Anti-Adhesive And Antiproliferative Synergistic Surface Modification Of Intraocular Lens For Reduced Posterior Capsular Opacification.

BackgroundPosterior capsular opacification (PCO) is the main complication after intraocular lens (IOL) implantation in cataract surgery, which is the result of lens epithelial cell (LEC) adhesion, proliferation and migration on the IOL and at the lens capsule interface. Hydrophilic surface modification, such as surface heparinization, decreases the cell adhesion, which has been commercialized and used clinically. However, clinical long-term observation results show no significant difference between the pristine and heparinized IOLs.MethodsTo prevent PCO over the long time span, we modified the IOLs with an antiproliferative drug-loaded hydrophilic coating. The antiproliferative drug doxorubicin (DOX)-incorporated chitosan (CHI) nanoparticle was fabricated by sodium tripolyphosphate (TPP) gelation. Such antiproliferative drug-loaded CHI-TPP-DOX nanoparticles (CTDNP) were used as one of the building blocks to prepare polyelectrolyte multilayer with heparin (HEP) via layer-by-layer assembly, obtaining (HEP/CTDNP)n multilayers. The assembly process was characterized by quartz crystal microbalance with dissipation (QCM-D). The drug release behavior of the coating was investigated by ultra-HPLC (UPLC). In vitro cell experiments were carried out to monitor the effects of multifunctional coatings on cellular adhesion, proliferation and migration. And the intraocular implantation was performed on rabbits to evaluate the in vivo PCO inhibitory effect of such surface-functionalized IOLs.ResultsThe positively charged CTDNP was successfully prepared by ionic gelation. The QCM-D results indicate the successful preparation of the (HEP/CTDNP)n multilayer film. Drug release profiles showed that surface-multifunctionalized IOL had drug-sustained release properties. In vitro cell culture results showed significant inhibition of adhesion, proliferation and migration of LECs after surface modification. The in vivo results showed that the IOLs with multifunctionalized surface can effectively reduce the posterior hyperplasia and Soemmering’s ring (SR) formation.ConclusionThese findings suggested that such multifunctionalized drug-eluting IOLs can effectively reduce the posterior hyperplasia and SR formation when intraocular implantation has a major impact on reducing PCO incidence. Thus they have a great potential in improving patient vision recovery and maintenance.

Preparation and in vivo evaluation of surface heparinized small diameter tissue engineered vascular scaffolds of poly(ε-caprolactone) embedded with collagen suture.

Herein biodegradable poly(ε-caprolactone) was electrospun into tubular microfibrous scaffolds and modified by the surface heparinization and wrapping of Type I collagen suture for enhancing anticoagulation activity and mechanical properties. The resulting scaffolds were featured by a double distribution of microfiber diameters ranged in 2.74 ± 0.44 and 5.15 ± 0.63 µm on the outer surface with tensile strength of 1.36 ± 0.37 MPa and Young’s modulus of 8.31 ± 1.87 MPa. The burst pressure after embedded with collagen suture was increased to 2419 ± 121 mmHg, remarkably higher than that of the poly(ε-caprolactone)-only scaffolds (1500 ± 136 mmHg) and native vessels. The scaffolds were evaluated in six rabbits for 20 weeks via a carotid artery interpositional model demonstrating a good patency. The effective cell infiltration, and rapid endothelialization and smooth muscle cell maturation were observed. There was no calcification in 20 weeks, and only one developed the aneurysm dilation after 16 weeks. It suggested that the surface heparinization is beneficial to improve the hydrophilicity and anticoagulation property of scaffolds, and embedment of collagen suture is useful to reinforce the mechanical properties and burst pressure.

Layered double hydroxide/poly-dopamine composite coating with surface heparinization on Mg alloys: improved anticorrosion, endothelialization and hemocompatibility.

Magnesium (Mg) and its alloys are promising cardiovascular stent materials due to their favourable physical properties and complete degradation in vivo. However, rapid degradation and poor cytocompatibility hinder their clinical applications. To enhance the corrosion resistance and endothelialization of the AZ31 alloy, a layered double hydroxide (LDH)/poly-dopamine (PDA) composite coating (LDH/PDA) was successfully fabricated. Polarization curves and the electrochemical impedance spectroscopy Nyquist spectrum test proved that the corrosion resistance of the LDH/PDA sample was significantly improved in vitro. The LDH/PDA sample greatly improved the adherence process and the proliferation rate of human umbilical vein endothelial cells (HUVECs). After culturing for 10 days, the number of living HUVECs on the LDH/PDA sample was comparable to that on the Ti sample whereas the cells barely survived on the AZ31 or LDH coating. Furthermore, heparin was immobilized on LDH/PDA via a covalent bond (LDH/PDA/HEP). The corrosion resistance and long-term proliferation of HUVECs after the introduction of heparin were mildly decreased compared with the L/P sample, but were still greatly improved compared with AZ31, the LDH coating and the PDA coating. Furthermore, the LDH/PDA/HEP sample greatly improved the HUVEC migration rate compared with the LDH/PDA sample, and inhibited platelet adhesion which was intense on the LDH/PDA sample. Both LDH/PDA and LDH/PDA/HEP samples had a low hemolysis rate (2.52% and 0.65%, respectively) in vitro and eliminated the adverse biocompatible effects of the direct PDA coating on the AZ31 substrate in vivo. Our results suggest that the LDH/PDA composite coating with further heparinization is a promising method to modify the surface of Mg alloys by significantly improving corrosion resistance, endothelialization and hemocompatibility.

The Optimization of the Hepatocyte Surface Modification Procedures in Terms of Heparin and Apyrase for Improving Hepatocyte Engraftment

Background The rapid destruction of hepatocyte grafts immediately after transplantation has hampered the application of this procedure as a clinical treatment. The instant blood-mediated inflammatory reaction (IBMIR), which is characterized by the activation of both coagulation and complement cascades, is a plausible underlying cause for this poor engraftment. In pancreatic islet transplantation, which shares many aspects with hepatocyte transplantation, it has been reported that islet surface heparinization efficiently inhibits the IBMIR without increasing the bleeding risk. In the present study, we tried to optimize the hepatocyte surface modification procedures in terms of heparin and apyrase for improving hepatocyte engraftment. Methods Rat hepatocytes were isolated using a modified two-step collagenase perfusion technique and then purified by Percoll density gradient centrifugation. Hepatocytes (2.0 × 106) were mixed with heparin-binding peptide (CNSAHRTRGRQRS)-poly (ethylene glycol)-conjugated phospholipid (HBP-PEG-lipid) solution or Maleimide-PEG-lipid solution, and then a solution of heparin conjugate (Corline AB, Uppsala, Sweden) or apyrase-SH was added for 10 minutes. All of these procedures were performed at either room temperature (RT) or 4 °C using either phosphate-buffered saline (PBS) or optimized culture medium for hepatocytes with or without fetal bovine serum (FBS). The hepatocyte viability was evaluated by a trypan blue exclusion assay. The efficiency of the hepatocyte surface modification procedures was evaluated by detecting AlexaFluor 488 under fluorescence microscopy. Results Regarding both heparin and apyrase, the surfaces of hepatocytes were sufficiently coated in all groups. The hepatocyte viability prior to the surface modification procedures was 94.09±2.18%. When PBS was used for the procedures, the viability of heparin-coated hepatocytes was 26.78±5.27% at RT and 63.53±5.95% at 4 °C. Likewise, the viability of apyrase-coated hepatocytes was 33.04±11.37% at RT and 60.43±6.63% at 4 °C. Of particular note, the viability of non-coated hepatocytes was 57.03±17.25% at RT and 66.65±1.28% at 4 °C, suggesting that the hepatocyte viability was substantially damaged during the preservation period rather than due to the coating chemicals per se. When using optimized culture medium for hepatocytes at 4 °C, the viability of heparin-coated and apyrase-coated hepatocytes markedly increased to 85.76±0.74% and 85.96±3.51%, respectively, under the supplementation of FBS, whereas the viability of heparin-coated hepatocytes remained at 73.79±7.42% without FBS. Conclusions The present study revealed that hepatocyte surface modification in terms of heparin and apyrase could be efficiently performed with minimal damage to the hepatocytes by introducing an optimized culture medium for hepatocytes including FBS, instead of carrying out the standard procedure (PBS), at 4 °C.

Biomimetic modification of polyurethane-based nanofibrous vascular grafts: A promising approach towards stable endothelial lining

The emerging demand for small caliber vascular grafts to replace damaged vessels has attracted research attention. However, there is no perfect replacement in clinical use yet, mainly due to low patency rate of synthetic small caliber grafts. The main pathology behind low patency rate include thrombosis and graft/vessel hemodynamic mismatch, leading to intimal hyperplasia. Rapid in-situ endothelialization of vascular grafts is considered as one of the best strategies to overcome these complications. In the present study, Heparin and VEGF were immobilized via self-polymerization and deposition of polydopamine (PDA) on polyurethane (PU) nanofibrous scaffolds to improve endothelialization. Polyurethane nanofibrous scaffold (PUNF) that mimics vascular extracellular matrix (ECM) was chosen owing to its biocompatibility, biodegradability. Scanning electron microscopy (SEM), water contact angle (CA) measurement and Raman spectroscopy were used to characterize the surface, and tensile test was used to analyze mechanical properties before and after surface modification of the scaffolds. It was found that tensile strength and young's modulus were significantly increased after PDA coating on PUNF membranes. The hemocompatibility tests revealed that surface heparinization significantly inhibited the adhesion of platelet on the scaffolds. Immobilization of VEGF on the scaffolds significantly enhanced the proliferation of human umbilical vein endothelial cells (HUVECs) through enhanced cells adhesion and improved cell-scaffold interactions. The results suggest that dual-factor immobilization resulted in not only confluent monolayer of endothelial cells but also conferred excellent antithrombotic properties to the surface. This method of surface modification (immobilization of Heparin, VEGF by PDA layer) is suggested as a promising modification technique to increase hemocompatibility of small-diameter vascular grafts.

APTES assisted surface heparinization of polylactide porous membranes for improved hemocompatibility

The Hep-APTES/PLA was synthesized through the amidation reaction and results showed that surface heparinization significantly improved the hemocompatibility of PLA porous membrane.

Effects of biocompatible extracorporeal bypass circuit coating Bioline in cardiac surgery patients

Biocompatibility of heparin-based coating for extracorporeal circuits, the Bioline, was evaluated in cardiac surgery setting. Thirty six CABG pts, aged from 30 to 69 yrs, were randomly perfused with a circuit containing Bioline-coated Quadrox oxygenator (Bioline, n=18) or with a similar non-coated circuit (control, n=18). Leukocyte and platelet counts, levels of tumor necrosis factor, interleukin-6 and fibrinogen were assessed in arterial blood before, during and after cardiopulmonary bypass (CPB). Oxygenation and ventilation indices before and after surgery, post-operative chest tube drainage and transfusion volume as well as the duration of assisted ventilation were also measured. A platelet count and fibrinogen dropped less in the Bioline group significantly compared with that in control at the end of CPB (p&lt;0,05) and after protamine administration (p&lt;0,05). A leukocyte count and an interleukin-6 level increased more in controls after CPB (p&lt;0,05) as well as oxygenation and ventilation indices, bleeding volume and intubation time (all p&lt;0,05). Our results suggest surface heparinization with Bioline coating limited to the oxygenator ameliorates the inflammatory response, preserves fibrinogen and platelets, reduces blood loss postoperatively and improves lung function during CPB.

Progress in heparin and heparin-like/mimicking polymer-functionalized biomedical membranes.

Research into the design of heparin and heparin-like/mimicking polymer-functionalized biomedical membranes is of tremendous interest to the biomedical sector in particular and is driven by potential diverse biomedical applications such as blood purification, artificial organs and other clinical medical devices. In this review, we highlight the progress of the recent research and propose potential biomedical applications in the fields of surface heparinization and the heparin-inspired modification of polymeric membranes. We summarize various surface heparinization strategies such as blending, surface coating, grafting, layer-by-layer assembly and mussel-inspired coating. Then, we classify the heparin-like/mimicking polymers and their applications in the design of heparin-mimicking biomedical membranes and draw some conclusions. The general concept of heparin-like/mimicking polymers is usually defined as heparan sulfates or synthetic sulfated/carboxylated polymers with comparable biologically mimicking functionalities as heparin, especially anticoagulant activity. Moreover, the potential biomedical applications and benefits of heparin and heparin-like/mimicking polymer-functionalized membranes in blood purification, artificial organs and tissue engineering are also discussed in each section. The heparin and heparin-like/mimicking polymer-functionalized membranes presented are exceptional candidates for the treatment of organ failure and many other blood-contacting fields. Finally, we conclude with the challenges and future perspectives for the strategies toward the heparinization and heparin-like/mimicking modification of membrane surfaces. It is believed that this review will evoke more attention towards the design of heparinized and heparin-like/mimicking membranes and encourage future advancements of this emerging research field.

Mussel-inspired one-step adherent coating rich in amine groups for covalent immobilization of heparin: hemocompatibility, growth behaviors of vascular cells, and tissue response.

Heparin, an important polysaccharide, has been widely used for coatings of cardiovascular devices because of its multiple biological functions including anticoagulation and inhibition of intimal hyperplasia. In this study, surface heparinization of a commonly used 316L stainless steel (SS) was explored for preparation of a multifunctional vascular stent. Dip-coating of the stents in an aqueous solution of dopamine and hexamethylendiamine (HD) (PDAM/HD) was presented as a facile method to form an adhesive coating rich in primary amine groups, which was used for covalent heparin immobilization via active ester chemistry. A heparin grafting density of about 900 ng/cm(2) was achieved with this method. The retained bioactivity of the immobilized heparin was confirmed by a remarkable prolongation of the activated partial thromboplastin time (APTT) for about 15 s, suppression of platelet adhesion, and prevention of the denaturation of adsorbed fibrinogen. The Hep-PDAM/HD also presented a favorable microenvironment for selectively enhancing endothelial cell (EC) adhesion, proliferation, migration and release of nitric oxide (NO), and at the same time inhibiting smooth muscle cell (SMC) adhesion and proliferation. Upon subcutaneous implantation, the Hep-PDAM/HD exhibited mitigated tissue response, with thinner fibrous capsule and less granulation formation compared to the control 316L SS. This number of unique functions qualifies the heparinized coating as an attractive alternative for the design of a new generation of stents.

Hemocompatibility and selective cell fate of polydopamine-assisted heparinized PEO/PLLA composite coating on biodegradable AZ31 alloy

Biodegradable magnesium and its alloys have attracted much attention, as they have been used as cardiovascular stents recently because of their biodegradation after implantation. However, their corrosion resistance, hemocompatibility and surface biocompatibility are needed for practical applications. In this work, heparinization of the plasma electrolytic oxidation/poly(l-lactic acid) (PEO/PLLA) composite coating on biodegradable AZ31 alloy was achieved by the strong adhesion of mussel-inspired polydopamine (PDAM). The corrosion resistance of the coated substrates was evaluated in simulated body fluid. In particular, the hemolysis ratio and platelet adhesion tests were conducted to evaluate the hemocompatibility of the composite coatings. The in vitro cytotoxicity of the composite coatings was evaluated with human umbilical vein endothelial cells (HUVECs). The adhesion and proliferation of HUVECs and human umbilical artery smooth muscle cells (HUASMCs) directly incubated on the composite coatings were also investigated. The results showed that although PDAM modification and further heparinization reduced the corrosion resistance of the PEO/PLLA composite coating, the protection of the coating for the substrate was mainly maintained. Moreover, PDAM modification and further heparinization significantly suppressed the adhesion of platelets and had little influence on sustaining a low hemolysis ratio thus resulting in good surface hemocompatibility of the composite coating. The in vitro cell test demonstrated that none of the composite coatings presented obvious cytotoxicity. Significantly, after surface heparinization, the composite coating became more suitable for HUVEC growth and simultaneously inhibited HUASMC growth. The results show that further modification of the PEO/PLLA composite coating on biodegradable magnesium alloy is a promising method to obtain good surface hemocompatibility for anticoagulation and to regulate the cell fate for fast re-endothelialization while sustaining the corrosion resistance of biodegradable magnesium-based cardiovascular stents.

Route to hemocompatible polyethersulfone membranes via surface aminolysis and heparinization

Polyethersulfone (PES) membranes with improved hemocompatibility were prepared via solid–liquid interface aminolysis and heparinization. Reactive amino groups were generated by immersing solid PES membranes in proper diamine solution. Heparin was covalent immobilized on the surface via amide bond. The feasibility of surface aminolysis for the introduction of amino groups and the effectiveness for further heparin immobilization were confirmed by surface group analysis. The effect of aminolysis time on surface amino group concentration and bulk mechanical properties was investigated. The surface amino group concentration determined the amount and bioactivity of immobilized heparin chains. SEM images suggested that both the aminolysis and heparinization reaction had little effect on the surface morphology of PES membranes. Contact angle measurement, surface charge analysis, protein and platelet adsorption/adhesion experiment were applied to study the surface properties. The results showed that the heparinized PES membranes displayed enhanced hydrophilicity and hemocompatibility, indicating potential application in blood purification and other blood contacting fields.

Immobilization of heparin/poly-l-lysine nanoparticles on dopamine-coated surface to create a heparin density gradient for selective direction of platelet and vascular cells behavior

Restenosis, thrombosis formation and delayed endothelium regeneration continue to be problematic for coronary artery stent therapy. To improve the hemocompatibility of the cardiovascular implants and selectively direct vascular cell behavior, a novel kind of heparin/poly-l-lysine (Hep/PLL) nanoparticle was developed and immobilized on a dopamine-coated surface. The stability and structural characteristics of the nanoparticles changed with the Hep:PLL concentration ratio. A Hep density gradient was created on a surface by immobilizing nanoparticles with various Hep:PLL ratios on a dopamine-coated surface. Antithrombin III binding quantity was significantly enhanced, and in plasma the APTT and TT times as coagulation tests were prolonged, depending on the Hep density. A low Hep density is sufficient to prevent platelet adhesion and activation. The sensitivity of vascular cells to the Hep density is very different: high Hep density inhibits the growth of all vascular cells, while low Hep density could selectively inhibit smooth muscle cell hyperplasia but promote endothelial progenitor cells and endothelial cell proliferation. These observations provide important guidance for modification of surface heparinization. We suggest that this method will provide a potential means to construct a suitable platform on a stent surface for selective direction of vascular cell behavior with low side effects.

Preparation and evaluation of heparin-immobilized poly (lactic acid) (PLA) membrane for hemodialysis

Bio-based poly (lactic acid) membrane with asymmetric porous structure was developed for hemodialysis via phase inversion for the first time. Heparin was immobilized to PLA membrane surface through the strong adhesion ability of dopamine, as confirmed by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) respectively. The morphologies variations of PLA membranes induced by dopamine coating and heparin immobilization were analyzed by scanning electron microscope (SEM) and atomic force microscopy (AFM). Hydrophilicity and permeability of PLA membranes before and after modification were characterized. Particularly, platelet adsorption, plasma recalcification time and hemolysis ratio were executed to evaluate the blood compatibility of PLA membranes decorated by heparin. The in vitro results demonstrated that surface heparinization improved the hemocompatibility of PLA membrane, suppressed the adhesion of platelet, extended plasma recalcilication time, and also decreased hemolysis ratio. The dialysis simulation experiments including urea and lysozyme clearance as well as bovine serum albumin (BSA) rejection were implemented to determine the dialysis performances. The results showed that 79% of urea and 18% of lysozyme were cleaned and over 90% of BSA was retained. This study disclosed a window of opportunity to produce novel hemodialysis membranes using bio-based materials.

Haemocompatibility of Ti–3Zr–2Sn–3Mo–25Nb biomedical alloy with surface heparinization using electrostatic self assembly technology

The haemocompatibility of Ti–3Zr–2Sn–3Mo–25Nb biomedical alloy was studied after surface heparinization. A layer of sol–gel TiO2 films was applied on the alloy samples followed by active treatment in the bio-functionalized solution for introducing the OH− and NH−2 groups, and then the heparin was immobilized on the active TiO2 films through the electrostatic self assembly technology. It is shown that the heparinized films are mainly composed of anatase and rutile with smooth and dense surface. In vitro blood compatibility was evaluated by haemolysis test, clotting time and platelet adhesion behavior tests. The results show that the haemocompatibility of the alloy could be significantly improved by surface heparinization.