Colorimetric method for the assay of heparin content in immobilized heparin preparations

Nerve growth factor loaded heparin/chitosan scaffolds for accelerating peripheral nerve regeneration

Artificial chitosan scaffolds have been widely investigated for peripheral nerve regeneration. However, the effect was not as good as that of autologous grafts and therefore could not meet the clinical requirement. In the present study, the nerve growth factor (NGF) loaded heparin/chitosan scaffolds were fabricated via electrostatic interaction for further improving nerve regeneration. The physicochemical properties including morphology, wettability and composition were measured. The heparin immobilization, NGF loading and release were quantitatively and qualitatively characterized, respectively. The effect of NGF loaded heparin/chitosan scaffolds on nerve regeneration was evaluated by Schwann cells culture for different periods. The results showed that the heparin immobilization and NGF loading did not cause the change of bulk properties of chitosan scaffolds except for morphology and wettability. The pre-immobilization of heparin in chitosan scaffolds could enhance the stability of subsequently loaded NGF. The NGF loaded heparin/chitosan scaffolds could obviously improve the attachment and proliferation of Schwann cells in vitro. More importantly, the NGF loaded heparin/chitosan scaffolds could effectively promote the morphology development of Schwann cells. The study may provide a useful experimental basis to design and develop artificial implants for peripheral nerve regeneration and other tissue regeneration.

Manufacture and property research of heparin grafted electrospinning PCU artificial vascular scaffolds

PCU (polycarbonate polyurethane) is supposed to be an ideal elastomer for manufacturing artificial vessel scaffold with perfect mechanical strength and biocompatibility. Surface grafting by heparin sodium can increase its anticoagulant hemorrhagic, achieving a better application in artificial vessels. Artificial vessels were preliminarily prepared by electrostatic spinning, treated by NH₃ plasma and cross-linked with the anticoagulant heparin sodium chemically. Performances of the PCU-Hep (heparin sodium grafted purethane artificial vessels) artificial vessel were calculated through the physical and chemical property tests, evaluation of blood and biocompatibility. Results manifested that heparin sodium was successfully grafted to the vascular surface, porosity, pore diameter and water permeability of the vascular prosthesis fitted the requirements of artificial vessels, the blood test results demonstrated that the vascular material had a low hemolysis, in vitro cytotoxicity experiment and animal experiments proved an excellent biocompatibility. Thus the heparin sodium grafted electrospinning vessels could reduce intravascular thrombus and had potential clinical application.

Platelet-derived growth factor-BB-immobilized asymmetrically porous membrane for enhanced rotator cuff tendon healing

Rotator cuff tear is a common musculoskeletal disease that often requires surgical repair. Despite of recent advances in surgical techniques, the re-tear rate of the rotator cuff tendon is very high. In this study, a platelet-derived growth factor-BB (PDGF-BB)-immobilized asymmetrically porous membrane was fabricated to investigate the feasibility for enhancing rotator cuff tendon regeneration through the membrane. PDGF-BB is recognized to promote tendon regeneration. The asymmetrically porous membrane was fabricated by polycaprolactone and Pluronic F127 using an immersion precipitation technique, which can allow selective permeability (preventing scar tissue invasion into defect region but allowing permeation of oxygen/nutrients) and incorporation of bioactive molecules (e.g., PDGF-BB) via heparin binding. The PDGF-BB immobilized on the membrane was released in a sustained manner over 42 days. In an animal study using Sprague-Dawley rats, the PDGF-BB-immobilized membrane group showed significantly greater regeneration of rotator cuff tendon in histological and biomechanical analyses compared with the groups of control (suturing) and membrane without PDGF-BB immobilization. The enhancing regeneration of rotator cuff tendon of the PDGF-BB-immobilized membrane may be caused from the synergistic effect of the asymmetrically porous membrane with unique properties (selective permeability and hydrophilicity) as a scaffold for guided tendon regeneration and PDGF-BB sustainedly released from the membrane.

LHD-Modified Mechanism-Based Liposome Coencapsulation of Mitoxantrone and Prednisolone Using Novel Lipid Bilayer Fusion for Tissue-Specific Colocalization and Synergistic Antitumor Effects

Coencapsulation liposomes are of interest to researchers because they maximize the synergistic effect of loaded drugs. A combination regimen of mitoxantrone (MTO) and prednisolone (PLP) has been ideal for tumor therapy. MTO and PLP offer synergistic antitumor effects confirmed by several experiments in this research. The deduced synergistic mechanism is regulation of Akt signaling pathway including the targets of p-Akt, p-GSK-3β, p-s6 ribosomal protein, and p-AMPK by MTO reactivating PLP-induced apoptosis. The liposome fusion method is adopted to create coencapsulation liposomes (PLP-MTO-YM). Low molecular weight heparin-sodium deoxycholate conjugate (LHD) then is used as a targeting ligand to prove target binding and inhibition of angiogenesis. LHD-modified liposomes (PLP-MTO-HM) have a high entrapment efficiency around 95% for both MTO and PLP. DSC results indicate that both drugs interacted with liposomes to prevent drug leak during liposome fusion. DiD-C6-HM dyes colocalize well to tumor tissue, and coadministration of DiD-HM and C6-CM did not achieve dye colocalization until 24 h after administration. In both CT26 and B16F10 mouse model, PLP-MTO-HM shows a significantly higher tumor inhibition rate relative to the coadministration of MTO-HM and PLP-CM (p < 0.05 or p < 0.01). Thus, the coencapsulation system (PLP-MTO-HM) offers ideal antitumor effects relative to coadministration therapy due to enhanced synergistic effect, and this suggests a promising future for the tumor targeting vectors.

Hemocompatibility of styrenic block copolymers for use in prosthetic heart valves

Certain styrenic thermoplastic block copolymer elastomers can be processed to exhibit anisotropic mechanical properties which may be desirable for imitating biological tissues. The ex-vivo hemocompatibility of four triblock (hard-soft-hard) copolymers with polystyrene hard blocks and polyethylene, polypropylene, polyisoprene, polybutadiene or polyisobutylene soft blocks are tested using the modified Chandler loop method using fresh human blood and direct contact cell proliferation of fibroblasts upon the materials. The hemocompatibility and durability performance of a heparin coating is also evaluated. Measures of platelet and coagulation cascade activation indicate that the test materials are superior to polyester but inferior to expanded polytetrafluoroethylene and bovine pericardium reference materials. Against inflammatory measures the test materials are superior to polyester and bovine pericardium. The addition of a heparin coating results in reduced protein adsorption and ex-vivo hemocompatibility performance superior to all reference materials, in all measures. The tested styrenic thermoplastic block copolymers demonstrate adequate performance for blood contacting applications.

Layer-by-layer self-assembled laminin/fucoidan films: towards better hemocompatibility and endothelialization

The laminin/fucoidan multilayer film is prepared on glass via layer-by-layer self-assembly technique and monitored the assembled process by QCM-D. This film can inhibit platelets adhesion and improve ECs and EPCs adhesion.

Human Urine-derived Stem Cells Seeded Surface Modified Composite Scaffold Grafts for Bladder Reconstruction in a Rat Model

We conducted this study to investigate the synergistic effect of human urine-derived stem cells (USCs) and surface modified composite scaffold for bladder reconstruction in a rat model. The composite scaffold (Polycaprolactone/Pluronic F127/3 wt% bladder submucosa matrix) was fabricated using an immersion precipitation method, and heparin was immobilized on the surface via covalent conjugation. Basic fibroblast growth factor (bFGF) was loaded onto the heparin-immobilized scaffold by a simple dipping method. In maximal bladder capacity and compliance analysis at 8 weeks post operation, the USCs-scaffold(heparin-bFGF) group showed significant functional improvement (2.34 ± 0.25 mL and 55.09 ± 11.81 µL/cm H2O) compared to the other groups (2.60 ± 0.23 mL and 56.14 ± 9.00 µL/cm H2O for the control group, 1.46 ± 0.18 mL and 34.27 ± 4.42 µL/cm H2O for the partial cystectomy group, 1.76 ± 0.22 mL and 35.62 ± 6.69 µL/cm H2O for the scaffold group, and 1.92 ± 0.29 mL and 40.74 ± 7.88 µL/cm H2O for the scaffold(heparin-bFGF) group, respectively). In histological and immunohistochemical analysis, the USC-scaffold(heparin-bFGF) group showed pronounced, well-differentiated, and organized smooth muscle bundle formation, a multi-layered and pan-cytokeratin-positive urothelium, and high condensation of submucosal area. The USCs seeded scaffold(heparin-bFGF) exhibits significantly increased bladder capacity, compliance, regeneration of smooth muscle tissue, multi-layered urothelium, and condensed submucosa layers at the in vivo study.

Successful endothelialization and remodeling of a cell-free small-diameter arterial graft in a large animal model

The large number of coronary artery bypass procedures necessitates development of off-the-shelf vascular grafts that do not require cell or tissue harvest from patients. However, immediate thrombus formation after implantation due to the absence of a healthy endothelium is very likely. Here we present the successful development of an acellular tissue engineered vessel (A-TEV) based on small intestinal submucosa that was functionalized sequentially with heparin and VEGF. A-TEVs were implanted into the carotid artery of an ovine model demonstrating high patency rates and significant host cell infiltration as early as one week post-implantation. At one month, a confluent and functional endothelium was present and the vascular wall showed significant infiltration of host smooth muscle cells exhibiting vascular contractility in response to vaso-agonists. After three months, the endothelium aligned in the direction of flow and the medial layer comprised of circumferentially aligned smooth muscle cells. A-TEVs demonstrated high elastin and collagen content as well as impressive mechanical properties and vascular contractility comparable to native arteries. This is the first demonstration of successful endothelialization, remodeling, and development of vascular function of a cell-free vascular graft that was implanted in the arterial circulation of a pre-clinical animal model.

Hemocompatibility improvement of perfusion-decellularized clinical-scale liver scaffold through heparin immobilization

Whole-liver perfusion-decellularization is an attractive scaffold–preparation technique for producing clinical transplantable liver tissue. However, the scaffold’s poor hemocompatibility poses a major obstacle. This study was intended to improve the hemocompatibility of perfusion-decellularized porcine liver scaffold via immobilization of heparin. Heparin was immobilized on decellularized liver scaffolds (DLSs) by electrostatic binding using a layer-by-layer self-assembly technique (/h-LBL scaffold), covalent binding via multi-point attachment (/h-MPA scaffold), or end-point attachment (/h-EPA scaffold). The effect of heparinization on anticoagulant ability and cytocompatibility were investigated. The result of heparin content and release tests revealed EPA technique performed higher efficiency of heparin immobilization than other two methods. Then, systematic in vitro investigation of prothrombin time (PT), thrombin time (TT), activated partial thromboplastin time (APTT), platelet adhesion and human platelet factor 4 (PF4, indicates platelet activation) confirmed the heparinized scaffolds, especially the /h-EPA counterparts, exhibited ultralow blood component activations and excellent hemocompatibility. Furthermore, heparin treatments prevented thrombosis successfully in DLSs with blood perfusion after implanted in vivo. Meanwhile, after heparin processes, both primary hepatocyte and endothelial cell viability were also well-maintained, which indicated that heparin treatments with improved biocompatibility might extend to various hemoperfusable whole-organ scaffolds’ preparation.

Improved poly(d,l-lactide-co-1,3-trimethylene carbonate)6 copolymer microparticle vehicles for sustained and controlled delivery of bioactive basic fibroblast growth factor

A novel, biocompatible and biodegradable six-arm branched copolymer poly(d,l-lactide)-co-(1,3-trimethylene carbonate)6 has been synthesized and fabricated as a porous microparticle with an oil-in-water single emulsion method. Poly(d,l-lactide-co-1,3-trimethylene carbonate)6 microparticles were further conjugated with heparin by 1-ethyl-3-3-dimethylamino-propylcarbodiimide/ N-hydroxysuccinimide chemistry and characterized using 1H-nuclear magnetic resonance and scanning electron microscopy. The heparin-loading capacity of poly(d,l-lactide-co-1,3-trimethylene carbonate)6 microparticles was identified as 213 ± 6 pmol/mg-particle determined with toluidine blue method. The resultant binding efficiency and release profile of basic fibroblast growth factor which is bound on heparin–poly(d,l-lactide-co-1,3-trimethylene carbonate)6 microparticles were quantitatively analyzed by enzyme-linked immunosorbent assay. Thus, the developed poly(d,l-lactide-co-1,3-trimethylene carbonate)6 porous microparticles presented superior capacity of growth factor cargo as 1965 ± 117 pg basic fibroblast growth factor per mg-microparticles and displayed a sustained release profile over 4 weeks with quite low initial burst. Additionally, the viability of dissociated basic fibroblast growth factor was confirmed with methylthiazolyltetrazolium quantitative assay along with in vitro culturing model of rodent neural stem cell. Collectively, our results demonstrate that heparin–poly(d,l-lactide-co-1,3-trimethylene carbonate)6 microparticles attained controllable and sustained delivery of bioactive basic fibroblast growth factor for 4 weeks with significantly reduced burst release. The present heparin–poly(d,l-lactide-co-1,3-trimethylene carbonate)6 porous microparticulate system could be potentially developed to foster a novel bioengineering platform for repair and regeneration of injured nervous system.

Capture of endothelial cells under flow using immobilized vascular endothelial growth factor

We demonstrate the ability of immobilized vascular endothelial growth factor (VEGF) to capture endothelial cells (EC) with high specificity under fluid flow. To this end, we engineered a surface consisting of heparin bound to poly-L-lysine to permit immobilization of VEGF through the C-terminal heparin-binding domain. The immobilized growth factor retained its biological activity as shown by proliferation of EC and prolonged activation of KDR signaling. Using a microfluidic device we assessed the ability to capture EC under a range of shear stresses from low (0.5 dyne/cm²) to physiological (15 dyne/cm²). Capture was significant for all shear stresses tested. Immobilized VEGF was highly selective for EC as evidenced by significant capture of human umbilical vein and ovine pulmonary artery EC but no capture of human dermal fibroblasts, human hair follicle derived mesenchymal stem cells, or mouse fibroblasts. Further, VEGF could capture EC from mixtures with non-EC under low and high shear conditions as well as from complex fluids like whole human blood under high shear. Our findings may have far reaching implications, as they suggest that VEGF could be used to promote endothelialization of vascular grafts or neovascularization of implanted tissues by rare but continuously circulating EC.

Dual growth factor-immobilized microspheres for tissue reinnervation: in vitro and preliminary in vivo studies

Growth factors (GFs) (basic fibroblast growth factor (bFGF) and/or nerve growth factor (NGF))-immobilized polycaprolactone (PCL)/Pluronic F127 microspheres were prepared using an isolated particulate-melting method and the sequential binding of heparin and GFs onto the microspheres. The GFs immobilized on the microspheres were released in a sustained manner over 28 days, regardless of GF type. From the in vitro culture of muscle-derived stem cells, it was observed that the NGF-immobilized microspheres induced more neurogenic differentiation than the bFGF-immobilized microspheres, as evidenced by a quantitative real-time polymerase chain reaction using specific neurogenic markers (Nestin, GFAP, β-tubulin, and MAP2) and Western blot (Nestin and β-tubulin) analyses. The dual bFGF/NGF-immobilized microspheres showed better neurogenic differentiation than the microspheres immobilized with single bFGF or NGF. From the preliminary animal study, the dual bFGF/NGF-immobilized microsphere group also showed effective nerve regeneration, as evaluated by immunocytochemistry using a marker - β-tubulin. The dual bFGF/NGF-immobilized PCL/Pluronic F127 microspheres may be a promising candidate for nerve regeneration in certain target tissues (i.e. muscles) leading to sufficient reinnervation.

A low-molecular-weight heparin-coated doxorubicin-liposome for the prevention of melanoma metastasis

Tumor metastasis is the biggest challenge in cancer therapy. During the metastasis process, metastatic cells could acquire stealth ability toward immune system through the formation of a protection cloak by hijacking platelets (PTs). Heparins, a heterogeneous mixture of glycosaminoglycans, can inhibit metastatic cascades by blocking P-selectin-mediated intercellular adhesion between tumor cells and PTs. In this study, low-molecular-weight heparin-coated doxorubicin-loaded liposome (LMWH-DOX-Lip) was developed for metastasis preventative therapy. The formation of LMWH-DOX-Lip was based on electrostatic interactions between the negatively charged heparins and cationic lipids. LMWH-DOX-Lip prepared at the optimum prescription possessed high entrapment efficiency, ideal particle size and zeta potential. Morphology of LMWH-DOX-Lip was characterized by atomic force microscopy and transmission electron microscopy. The results of confocal microscopic observations and flow cytometry analysis indicated that LMWH-DOX-Lip mediated an efficient cellular uptake in B16F10 melanoma cell line. Besides, LMWH-DOX-Lip displayed an increased cytotoxic over their unmodified counterparts. Furthermore, the inhibition effect of LMWH-DOX-Lip on adhesion between tumor cells and PTs/P-selectin was observed. In vivo study performed on a pulmonary melanoma mouse model revealed a substantially tumor metastasis prevention by LMWH-DOX-Lip. All these results suggested that LMWH-DOX-Lip could significantly inhibit metastasis through preventing the tumor cell-platelet interactions and in the meantime suppressed tumor growth.

Self-assembling lipid modified glycol-split heparin nanoparticles suppress lipopolysaccharide-induced inflammation through TLR4-NF-κB signaling

Self-assembling heparin nanoparticles have attracted much attention as promising drug carriers for various drugs, genes and imaging agents. In the present investigation, we found that heparin nanoparticles are selective Toll-like receptor 4 (TLR-4) antagonists and have a much greater anti-inflammatory effect than native heparin. More specifically, we developed self-assembling nanoparticles composed of glycol-split heparin/D-erythro-sphingosine conjugates (NAHNP), characterized their physicochemical properties and anti-inflammatory effect in vitro. Unlike native heparin, NAHNP significantly inhibited lipopolysaccharide-induced activation of MyD88-dependent NF-κB signaling pathway and production of pro-inflammatory cytokines such as TNF-alpha from mouse macrophages with IC50 = 0.019 mg/mL. Furthermore, we investigated the structure-activity relationship of the conjugates and identified the length of attached alkyl chains of d-erythro-sphingosine to be critical for anti-inflammatory effect. Decrease in alkyl chain length of NAHNP resulted in loss of inhibitory activity. In line with these findings, 6-O-sulfate groups of D-glucosamine residue were essential for effective inhibition, while removal of 2-O-sulfo and 3-O-sulfo groups as well as replacement of N-sulfo groups with N-acetyl did not alter anti-inflammatory activity. Therefore, NAHNP would be a promising candidate in acute and chronic inflammatory disorders, in addition to the nature of a drug carrier.

Heparin-chitosan nanoparticle functionalization of porous poly(ethylene glycol) hydrogels for localized lentivirus delivery of angiogenic factors

Hydrogels have been extensively used for regenerative medicine strategies given their tailorable mechanical and chemical properties. Gene delivery represents a promising strategy by which to enhance the bioactivity of the hydrogels, though the efficiency and localization of gene transfer have been challenging. Here, we functionalized porous poly(ethylene glycol) hydrogels with heparin-chitosan nanoparticles to retain the vectors locally and enhance lentivirus delivery while minimizing changes to hydrogel architecture and mechanical properties. The immobilization of nanoparticles, as compared to homogeneous heparin and/or chitosan, is essential to lentivirus immobilization and retention of activity. Using this gene-delivering platform, we over-expressed the angiogenic factors sonic hedgehog (Shh) and vascular endothelial growth factor (Vegf) to promote blood vessel recruitment to the implant site. Shh enhanced endothelial recruitment and blood vessel formation around the hydrogel compared to both Vegf-delivering and control hydrogels. The nanoparticle-modified porous hydrogels for delivering gene therapy vectors can provide a platform for numerous regenerative medicine applications.

Surface modification with dopamine and heparin/poly-L-lysine nanoparticles provides a favorable release behavior for the healing of vascular stent lesions

Surface biofunctional modification of coronary artery stents to prevent thrombosis and restenosis formation, as well as accelerate endothelialization, has become a new hot spot. However, bioactive coatings on implants are not yet sufficiently developed for long-term activity, as they quickly lose efficiency in vivo and finally fail. On the basis of a novel time-ordered concept of biofunctionality for vascular stents, heparin/poly l-lysine nanoparticle (NP) was developed and immobilized on a polydopamine-coated titanium surface, with the aim of regulating and maintaining the intravascular biological response within the normal range after biomaterial implantation. An in vitro dynamic release model was established to mimic the blood flow condition in vivo with three phases: (1) An early phase (1-7 days) with release of predominantly anticoagulant and anti-inflammatory substances and to a minor degree antiproliferative effects against smooth muscle cells (SMCs); (2) this is followed by a phase (7-14 days) of supported endothelial cell (ECs) proliferation and suppressed SMC proliferation with persisting high antithrombogenicity and anti-inflammatory properties of the surface. (3) Finally, a stable stage (14-28 days) with adequate biomolecules on the surface that maintain hemocompatibility and anti inflammation as well as inhibit SMCs proliferation and promote ECs growth. In vivo animal tests further confirmed that the NP-modified surface provides a favorable release behavior to apply a stage-adjusted remedy. We suggested that these observations provide important guidance and potential means for reasonable and suitable platform construction on a stent surface.

Electrodeposition of nanostructured bioactive hydroxyapatite-heparin composite coatings on titanium for dental implant applications

In this paper we describe the one-pot fabrication of hydroxyapatite (HA)-heparin composites by electrodeposition onto Ti substrates and their characterisation in terms of structure, morphology, heparin content and bioactivity. HA coatings are well known and widely applied osteointegration enhancers, but post-implant healing rate in dental applications is still suboptimal: e.g. coagulation control plays a key role and the incorporation of an anticoagulant is considered a highly desirable option. In this study, we have developed an improved, simple and robust growth procedure for single-phase, pure HA-heparin films of thickness 1/3 μm. HA-heparin, forming nanowires, has the ideal morphology for bone mineralisation. Staining assays revealed homogeneous incorporation of sizable amounts of heparin in the composite films. The bioactivities of the HA and HA-heparin coatings on Ti were compared by HeLa cell proliferation/viability tests and found to be enhanced by the presence of the anticoagulant.

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.

Porous membrane with reverse gradients of PDGF-BB and BMP-2 for tendon-to-bone repair: in vitro evaluation on adipose-derived stem cell differentiation

Polycaprolactone (PCL)/Pluronic F127 membrane with reverse gradients of dual platelet-derived growth factor-β (PDGF-BB) and bone morphogenetic protein 2 (BMP-2) concentrations was fabricated using a diffusion method to investigate the effect of reverse gradients of dual growth factor concentrations on adipose-derived stem cell (ASC) differentiations, such as tenogenesis and osteogenesis. The PDGF-BB and BMP-2 were continuously released from the membrane for up to 35 days, with reversely increasing/decreasing growth factors along the membrane length. Human ASCs were seeded on the membrane with reverse PDGF-BB and BMP-2 gradients. The cells were confluent after 1 week of culture, regardless of growth factor types or concentrations on the membrane. Gene expression (real-time polymerase chain reaction), Western blot and immunohistological analyses after 1 and 2 weeks of ASC culture showed that the membrane sections with higher PDGF-BB and lower BMP-2 concentrations provided a better environment for ASC tenogenesis, while the membrane sections with higher BMP-2 and lower PDGF-BB concentrations were better for promoting osteogenesis. The results suggest that the membrane with reverse gradients of PDGF-BB and BMP-2 may be promising for tendon-to-bone repair, as most essential biological processes are mediated by gradients of biological molecules in the body.

Dual drug-eluting stents coated with multilayers of hydrophobic heparin and sirolimus

Polymer coatings for stents are considered one of the key factors that lead to adverse cardiac events after coronary arterial stenting. This study presents a dual drug-eluting stent (DES) that is coated with multilayers of Duraflo heparin and sirolimus but containing no other organic polymers. The hydrophobic Duraflo heparin coating was used to improve the hemocompatibility of the stent and serve as a drug reservoir for the controlled release of sirolimus, thus avoiding inflammatory reactions induced by the conventional polymers. The Duraflo heparin and sirolimus were coated layer-by-layer onto the stent surface using a homemade spray-coating device. The drug loading amount can be easily controlled by adjusting the numbers of layers applied and the concentration of the drug solution, indicating the developed coating process is reproducible and well-controlled. After balloon expansion, the coating did not crack or peel off, which demonstrates that the sirolimus/Duraflo heparin coating layers tightly adhere to the stent surface. The activated partial thromboplastin time (APTT) assay showed that the Duraflo heparin coating significantly prolonged the APTT from 27.3 ± 0.3 s to 69.7 ± 6.2 s, demonstrating the anticoagulant ability of the coated stents. The dual DES exhibited a nearly linear sustained-release profile of Duraflo heparin and an initial burst release followed by a slow release of sirolimus. Less than 15% of heparin was released from the DES within 14 days, indicating the stent can maintain its antithrombotic surface for a long time. Because of the layer-by-layer structure, the most outer layer of Duraflo heparin coating may act as a diffusion barrier to retard sirolimus release from the stent. These results confirm that the dual DESs enable simultaneous delivery of antithrombotic and antiproliferative drugs and have potential for the treatment of coronary artery disease.

A novel fluorescent nanosensor for detection of heparin and heparinase based on CuInS2 quantum dots

In this work, a novel fluorescence "turn off-on" nanosensor for the determination of heparin and heparinase based on CuInS2 quantum dots (QDs) was established. CuInS2 QDs (modified by l-cysteine) featuring amino groups were directly prepared in aqueous solution via a hydrothermal synthesis method. The amino groups on the surface of CuInS2 QDs can interact with sulfate and carboxylate groups in heparin via electrostatic interactions and hydrogen bonding, which led the fluorescence of CuInS2 QDs to "turn-off". However, the heparin could be hydrolyzed into small fragments in the presence of heparinase, which resulted in the fluorescence of CuInS2 QDs being recovered. Therefore, the addition of heparinase to the heparin/CuInS2 QDs system activated the fluorescence of CuInS2 QDs to "turn-on" state. Thus, the determination of heparin and heparinase could be achieved by monitoring the fluorescence "turn off-on". Under the optimum conditions, there was a good linear relationship between I/I0 (I and I0 were the fluorescence intensity of CuInS2 QDs in the presence and absence of heparin, respectively) and heparin concentration in the range of 0.05-15 μmol L(-1) with the detection limit of 12.46 nmol L(-1). The linear detection for heparinase was in the range of 0.2-5 μg mL(-1) with the detection limit of 0.07 μg mL(-1). The proposed nanosensor was employed for the detection of heparin in fetal bovine serum samples with satisfactory results.

Non-covalent synthesis of metal oxide nanoparticle-heparin hybrid systems: a new approach to bioactive nanoparticles

Heparin has been conjugated to Fe3O4, Co3O4, and NiO nanoparticles (NPs) through electrostatic interactions, producing colloidal suspensions of hybrid metal oxide heparin NPs that are stable in water. Negative zeta potentials and retention of heparin's ability to capture toluidine blue indicate that heparin's negative charges are exposed on the surface of the coated NPs. IR results confirmed the formation of nanohybrids as did NMR experiments, which were also interpreted on the basis of toluidine blue tests. Transmission electron microscopy results revealed that the heparin coating does not modify the shape or dimension of the NPs. Dynamic light scattering and negative zeta potential measurements confirmed that heparin surface functionalisation is an effective strategy to prevent NP aggregation.

Polysaccharide-modified scaffolds for controlled lentivirus delivery in vitro and after spinal cord injury

Gene delivering biomaterials have increasingly been employed to modulate the cellular microenvironment to promote tissue regeneration, yet low transduction efficiency has been a persistent challenge for in vivo applications. In this report, we investigated the surface modification of poly(lactide-co-glycolide) (PLG) scaffolds with polysaccharides, which have been implicated in binding lentivirus but have not been used for delivery. Chitosan was directly conjugated onto PLG scaffolds, whereas heparin and hyaluronan were indirectly conjugated onto PLG scaffolds with multi-amine crosslinkers. The addition of chitosan and heparin onto PLG promoted the association of lentivirus to these scaffolds and enhanced their transduction efficiency in vitro relative to hyaluronan-conjugated and control scaffolds that had limited lentivirus association and transduction. Transduction efficiency in vitro was increased partly due to an enhanced retention of virus on the scaffold as well as an extended half-life of viral activity. Transduction efficiency was also evaluated in vivo using porous, multiple channel PLG bridges that delivered lentivirus to the injured mouse spinal cord. Transgene expression persisted for weeks after implantation, and was able to enhance axon growth and myelination. These studies support gene-delivering PLG scaffolds for in vivo regenerative medicine applications.

Bone morphogenetic proteins-immobilized polydioxanone porous particles as an artificial bone graft

Bone morphogenetic proteins (BMPs)-immobilized polydioxanone (PDO)/Pluronic F127 porous particles were prepared as a bone graft using a melt-molding particulate-leaching method, and the sequential binding of heparin and BMPs (BMP-2 and BMP-7, single or dual) onto the porous particles. The prepared PDO/Pluronic F127 porous particles gradually degraded with time, with ∼30% of the initial particle weight remaining after 16 weeks. The degradation rate of the PDO/Pluronic F127 porous particles may parallel the bone-healing rate. The BMPs were easily immobilized onto the pore surfaces of PDO/Pluronic F127 particles via heparin binding and were released in a sustained manner for up to 21 days, regardless of BMP type. The BMPs (single BMP-2 or dual BMP-2/BMP-7)-immobilized porous particles were effective for in vitro osteogenesis of bone marrow stem cells (BMSCs), as analyzed by alkaline phosphatase activity, calcium content, time polymerase chain reaction using specific markers for osteogenesis (Type I collagen, osteocalcin, osteopotin, and RunX2), and immunohistochemical staining. The BMPs (single BMP-2 or dual BMP-2/BMP-7)-immobilized porous particles were also effective in promoting new bone formation, as analyzed by the preliminary animal study using a full-thickness skull defect model of Sprague-Dawley rats (microcomputed tomography). The synergistic effect of dual BMPs on the osteogenesis of BMSCs and bone regeneration was not significant in our system. The BMP-2 or dual BMPs (BMP-2/BMP-7)-immobilized PDO/Pluronic F127 porous particles may be a promising candidate as a bone graft for the delayed and insufficient bone healing in clinical fields.

Effect of surface pore structure of nerve guide conduit on peripheral nerve regeneration

Polycaprolactone (PCL)/Pluronic F127 nerve guide conduits (NGCs) with different surface pore structures (nano-porous inner surface vs. micro-porous inner surface) but similar physical and chemical properties were fabricated by rolling the opposite side of asymmetrically porous PCL/F127 membranes. The effect of the pore structure on peripheral nerve regeneration through the NGCs was investigated using a sciatic nerve defect model of rats. The nerve fibers and tissues were shown to have regenerated along the longitudinal direction through the NGC with a nano-porous inner surface (Nanopore NGC), while they grew toward the porous wall of the NGC with a micro-porous inner surface (Micropore NGC) and, thus, their growth was restricted when compared with the Nanopore NGC, as investigated by immunohistochemical evaluations (by fluorescence microscopy with anti-neurofilament staining and Hoechst staining for growth pattern of nerve fibers), histological evaluations (by light microscopy with Meyer's modified trichrome staining and Toluidine blue staining and transmission electron microscopy for the regeneration of axon and myelin sheath), and FluoroGold retrograde tracing (for reconnection between proximal and distal stumps). The effect of nerve growth factor (NGF) immobilized on the pore surfaces of the NGCs on nerve regeneration was not so significant when compared with NGCs not containing immobilized NGF. The NGC system with different surface pore structures but the same chemical/physical properties seems to be a good tool that is used for elucidating the surface pore effect of NGCs on nerve regeneration.

Heparin-conjugated pluronic nanogels as multi-drug nanocarriers for combination chemotherapy

Combination chemotherapy using more than two therapeutic agents with different modes of action is a promising strategy that can be used to enhance the therapeutic efficacy of cancer treatment, even though it is a complicated treatment modality. The aim of this study was to investigate how a novel multidrug nanocarrier is effective for combination chemotherapy in vitro and, more specifically, whether combined agents with different modes of action and physicochemical properties show synergistic cytotoxicity with the use of this nanocarrier. A heparin-Pluronic (Hep-Pr) nanogel encapsulating both paclitaxel and DNase was shown to be efficient for intracellular delivery with respect to size, encapsulation efficiency, and intracellular uptake/fates. As a result of these properties, a Hep-Pr nanogel combined with paclitaxel and DNase exhibited a dose-dependent synergistic cytotoxicity compared to single drug and free-drug treatments, whose combination indices were 0.93 and 0.45 at higher concentrations (250 and 500 μg/mL). Therefore, Hep-Pr nanogels have the potential to deliver multitherapeutic agents with different characteristics and thereby enhance the therapeutic efficacy of combination cancer chemotherapy.

Heparin nanomodification improves biocompatibility and biomechanical stability of decellularized vascular scaffolds

Biocompatibility and biomechanical stability are two of the main obstacles limiting the effectiveness of vascular scaffolds. To improve the biomechanical stability and biocompatibility of these scaffolds, we created a heparin-nanomodified acellular bovine jugular vein scaffold by alternating linkage of heparin and dihydroxy-iron via self-assembly. Features of the scaffold were evaluated in vitro and in vivo. Heparin was firmly linked to and formed nanoscale coatings around the fibers of the scaffold, and the amount of heparin linked was about 808 ± 86 μg/cm² (101 ± 11 USP/cm²) per assembly cycle. The scaffolds showed significantly strengthened biomechanical stability with sustained release of heparin for several weeks in vitro. Importantly, the modified scaffolds showed significantly reduced platelet adhesion, stimulated proliferation of endothelial cells in vitro, and reduced calcification in a subcutaneous implantation rat model in vivo. Heparin nanomodification improves the biocompatibility and biomechanical stability of vascular scaffolds.

The blood and vascular cell compatibility of heparin-modified ePTFE vascular grafts

Prosthetic vascular grafts do not mimic the antithrombogenic properties of native blood vessels and therefore have higher rates of complications that involve thrombosis and restenosis. We developed an approach for grafting bioactive heparin, a potent anticoagulant glycosaminoglycan, to the lumen of ePTFE vascular grafts to improve their interactions with blood and vascular cells. Heparin was bound to aminated poly(1,8-octanediol-co-citrate) (POC) via its carboxyl functional groups onto POC-modified ePTFE grafts. The bioactivity and stability of the POC-immobilized heparin (POC-Heparin) were characterized via platelet adhesion and clotting assays. The effects of POC-Heparin on the adhesion, viability and phenotype of primary endothelial cells (EC), blood outgrowth endothelial cells (BOECs) obtained from endothelial progenitor cells (EPCs) isolated from human peripheral blood, and smooth muscle cells were also investigated. POC-Heparin grafts maintained bioactivity under physiologically relevant conditions in vitro for at least one month. Specifically, POC-Heparin-coated ePTFE grafts significantly reduced platelet adhesion and inhibited whole blood clotting kinetics. POC-Heparin supported EC and BOEC adhesion, viability, proliferation, NO production, and expression of endothelial cell-specific markers von Willebrand factor (vWF) and vascular endothelial-cadherin (VE-cadherin). Smooth muscle cells cultured on POC-Heparin showed increased expression of α-actin and decreased cell proliferation. This approach can be easily adapted to modify other blood contacting devices such as stents where antithrombogenicity and improved endothelialization are desirable properties.

BIOACTIVE ASSESSMENT AND BACTERIA TEST FOR THE VARIED DEGREES OF ULTRA-VIOLET RADIATION ONTO THE COLLAGEN-IMMOBILIZED POLYPROPYLENE NON-WOVEN FABRIC

Exposure to ultra-violet (UV)-C radiation is a frequently used method to prevent bacteria from invasion of blood-contact biomedical products. Potential damage induced by UV radiation to collagen is of concern due to the decay of bioactivity, considerably correlated with structural alterations. Current investigation indicates to the collagen-immobilized non-woven polypropylene (PP) fabrics with sample temperature ca. 4 °C; the samples are then exposed to UV-254 nm radiation for different time intervals. Using Fourier-Transformed Infrared with Attenuated Total Reflection (FTIR-ATR) and XPS (X-ray Photoelectron Spectroscopy), we examine the chemical structures of samples with different treatments. Blood-clotting effects on the modified samples are assessed by activated partial thromboplastin time, thrombin time, and fibrinogen concentration tests. By means of cell counter and Scanning Electron Microscopy we count red blood cells and platelets adhesion in the modified porous matrix. Applying standard plate count for bacteria tests, E. coli, Bacillus stearothermophilus, Staph. aureus, P. aeruginosa, and Candida albieans are applied. For human plasma incubated samples of various intervals of UV-254 nm radiation, fibrinogen concentration decreases in human plasma, while platelets and red blood cells adhesions increase before UV radiation. The required time for thrombination shows significant change for UV exposure of less than 20 hrs (α = 0.05). Surface analyses indicate that the decrease of R-COOH (derivated from grafted-pAAc or decarboxylation of collagen), amides degradation (broken–NH), and phenylalanine scission (terminated by −OH, tyrosine formation) may gradually damage collagen by increasing the intervals of UV radiation. The XPS measurements of C 1s core levels at 288.1 eV (O=C-NH) and at 289.3 eV (O=C-O) illustrate significant decreases of intensity after radiation time ca. 44 hrs. It is clear that UV-254 nm radiation exposure for ca. 20 hrs has the potential impact to moderate the bioactivities of collagen and therefore act as a vital factor to accelerate bio-degradation. Bacteria test also supports that around 20 hrs of UV radiation, no bacteria clone formation is found on the immobilized collagen. However, the relation between eventual bioactivity of immobilized collagen after UV radiation and the capability of bacteria proliferation should be measured.

Synthesis and characterization of novel polyurethane cationomers with dipeptide sequences and alkylammonium groups

A synthetic approach to polyurethane cationomers containing S-pyroglutamyl-S-glutamic acid dipeptide (S-PyGlu-S-Glu) and alkylammonium groups is presented. Two segmented polycations, based on polycaprolactone diol, isophorone diisocyanate and dipeptide together with N-methyldiethanolamine, subsequently quaternized with dodecylbromide, were synthesized and characterized by IR spectroscopy, GPC, DSC and reduced viscosity measurements. Such polycations exhibited excellent film forming properties and their soft elastomeric nature provides adequate physical properties. Optical rotation varying from +10 (monomer) to -15 (polycation) could be associated with a configuration pertubation through the asymmetric carbon atoms of glutamic residues. Susceptibility of the cationic surface to heparinization and then to blood-polymer interaction suggested an anticoagulant activity of the heparinized polymeric films.