ABSTRACT
Objective To fabricate an ultrasound/fluorescence bi-modal contrast agent by encapsulating fluorescent quantum dots into polymeric ultrasound contrast agent microbubbles.Methods Polylactic acid (PLA,500 mg),(1R)-(+)-camphor (50 mg) and CdSe/ZnS quantum dots (0.5 ml,2.3 μmol/L)were dissolved or dispersed in dichloromethane (10 ml) to form in an organic phase.Ammonium carbonate solution and poly (vinyl alcohol) solution were employed as the internal and external water phase,respectively.The fluorescent microbubbles were generated using double emulsion solvent evaporation and lyophilization methods.The morphology and illumination were characterized by scanning electron microscopy (SEM) and fluorescence spectrophotometry.Synchronized contrast-enhanced ultrasound and fluorescence imaging was acquired by injecting fluorescent microbubbles into the silicone tube coupled to a self-made ultrasound/fluorescence imaging device.Ultrasound/fluorescence bi-modal in vivo imaging was acquired on the kidney of New Zealand rabbits and suckling mice.Results The fluorescent microbubbles were hollow spheres with an averaged diameter of (1.62 ± 1.47) μm.More than 99％ of these microbubbles were less than 8 μm in diameter,which meeted the size criteria for ultrasound contrast agents.The fluorescence emission peak of the microbubbles appeared at 632 nm,indicating that good luminescence properties of quantum dots were maintained.In vitro ultrasound/fluorescence imaging showed no echoic signal when the silicone tube was filled with saline,but there was a strong echo when filled with fluorescent microbubbles.The liquid column with fluorescent microbubbles emitted red luminescence under ultraviolet irradiation.The kidney of the rabbit was remarkably enhanced after the administration of fluorescent microbubbles.Bright fluorescence could be observed at the injection site of the suckling mice via subcutaneous injection.Conclusions A bi-modal but single contrast agent based on polymeric microbubbles has been successfully fabricated for the use of ultrasound and fluorescence imaging.It retains the good characteristics of both echogenicity and fluorescence,which complement each other in case of limitations imposed by uni-modal,single agents.
ABSTRACT
Objective To manufacture magnetic microbubbles with dual-response to ultrasound and magnetic fields.Methods Microbubbles of ultrasound contrast agent (ST68) based on a surfactant were prepared by the acoustic cavitation method.Fe3O4 magnetic nanoparticles with negative charge were synthesized using the polyol procedure.Magnetic microbubbles were generated by depositing polyethylenimine and Fe3O4 magnetic nanoparticles alternately onto the microbubbles using the layer-by-layer self-assembly.In vitro ultrasonography was performed on a silicone tube with/without magnetic microbubbles (3 × 108/ml) by a self-made device to observe the movement of magnetic microbubbles under the effects of magnetic field.In vivo imaging was performed on the kidney of New Zealand rabbits before and after the injection of magnetic microbubbles.Results The Fe3O4 nanoparticles carried a stable negative charge of (-24.6 ± 6.7) mV and more than 98％ of the particles were less than 8 μm in diameter,meeting the size requirement of an ultrasound contrast agent for intravenous administration.There was no echoic signal in the silicone tube before injection of magnetic microbubbles,but there were strong echoic signals after injection.After applying a magnetic field,the magnetic microbubbles moved along the direction of the magnetic flux.In vivo ultrasound imaging could not visualize the kidney before injection of magnetic microbubbles,but could remarkably visualize the kidney after injection.Conclusions The magnetic microbubbles exhibit favorable magnetic targeting and ultrasound contrast enhancement characteristics.Such properties may serve as the foundation to study their potential for simultaneous diagnosis and treatment in the future.
ABSTRACT
BACKGROUND: For decades, liposome drug carrier has been used to enhance drug stability and efficacy, reduce drug toxicity and adverse effects. However, they fail to provide long-term delivery due to insufficient stability. Studies have demonstrated that silica is not toxic, with chemically inert and biological compatibility, and can be used as modified material. OBJECTIVE: To characterize the silica coated liposome and investigate the controlled release property. DESIGN, TIME AND SETTING: In vitro observation. The study was performed at the Nanomedicine and Biosensor Laboratory, Biomedical Engineering Center, Harbin Institute of Technology from May 2007 to June 2008. MATERIALS: Dipalmitoylphosphatidylcholine (DPPC) was purchased from Nanjing Kangsente Chemical Engineering Company; tetraethylorthosilicate (TEOS) was purchased from Aldrich, USA. Doxorubicin (DOX) was purchased from Beijing Huafeng United Technology Company; Sephadex G-50 was purchased from Amersham Biosciences, Sweden. All other chemical agents were of analytical purity. METHODS: Liposome was formed from DPPC following the precipitation of silica by sol-gel method. MAIN OUTCOME MEASURES: Zeta-potential and dynamic light scanning were used for zeta-potential measurement and particle size distribution; transmission electron microscopy was used to collect the image of particle morphology; Fourier transform infrared spectroscopy (FTIR) was used to display chemical characteristics of Si-O-Si structure; Spectrophotofluorimetry was used to determine DOX regression equation and was further used for calculation in drug encapsulation efficiency and in vitro release. RESULTS: ①Silica coated liposome was successfully prepared. ②FTIR proofed the presence of Si-O-Si at 1 166, 1 080, 859 and 526 cm-1. ③The DOX encapsulated silica coated liposome had encapsulation efficiency of 72.4%. ④Drug release profiles showed that sustained release of DOX was achieved after modification of silica on liposome. CONCLUSION: With Si-O-Si as protective layer, the liposome has increased stability and prolonged drug release.
ABSTRACT
BACKGROUND: The expanded polytetrafluoroethylene (ePTFE) vascular grafts hold promise for enhanced healing,extended suture retention, kink reduction and compression resistance. But thrombus formation still limits its use for revascularization of small-caliber vessels. It is the surface of ePTFE vascular graft that contacts with the blood. The current study focused on surface modification of ePTFE materials to improve its blood compatibility.OBJECTIVE: To characterize the heparin/alginate (H/A) gel modified ePTFE vascular graft and investigate the hemocompatibility and histocompatibility of the graft.DESIGN: Observation experiment.SETTING: Laboratory for Nanomedicine and Biosensor, Biomedicine Engineering Center, Harbin Institute of Technology.MATERIALS: The GORE-TEX ePTFE vascular grafts were 4 mm in internal diameter. Sodium alginate and 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC) were purchased from Sigma. Heparin sodium salt was obtained from Calbiochem. Nation and chitosan were purchased from Aldrich company. Human α-thrombin and AT Ⅲ were purchased from Haematologic Technologies, Inc. S-2238 was purchased from Chromogenix.METHODS: This study was performed at the Laboratory for Nanomedicine and Biosensor, Biomedicine Engineering Center, Harbin Institute of Technology between May 2006 and June 2007. The graft was first modified with Nation and then Chitosan/Nafion/Chitosan multilayer. Following the impregnation of heparin and alginate, covalent crosslinking was performed using ethylenediamine and EDC. Some characterization methods were employed: stastic water contact angle for the hydrophilicity; SEM for the surface morphology; ATR-FTIR for the surface chemical characteristics; APTT and PT,percent hemolysis and Chromogenic assay for the hemocompatibility of the ePTFE vascular graft after modification.MAIN OUTCOME MEASURES: ①Static water contact angles. ②Charactedzation of the surface morphology and platelet adhesion by SEM. ③ATR-FTIR ④APTT and PT. ⑤Percent hemolysis ⑥Chromogenic assay for heparin activity.RESULTS: ①ATR-FTIR revealed the presence of -CO-NH- at 1626 cm-1. ②The water contact angle was greatly decreased from (125±1)° to (84±2)° .③The prolonged APTT and PT, low percent hemolysis(0.065%) and low amount of platelet adhesion assay showed the H/A gel impregnated graft had good blood compatibility. ④Chromogenic assay showed the modified graft was less thrombogenic than the bare one, and the H/A coating had good stability in. PBS buffer.CONCLUSION: The H/A modified ePTFE vascular graft has great potential in applications utilizing small-diameter vascular grafts.
ABSTRACT
BACKGROUND: Thrombus formation and neointimal hyperplasia limit its use for revascularization of small-caliber vessels (<6mm diameter) in the coronary or peripheral circulation.OBJECTIVE: To improve hemocompatibility, the luminal surface of a small diameter expanded polytetrafluoroethylene (Eptfe) vascular prosthesis was modified with alginate and recombinant hirudin.DESIGN: Observational experiment.SETTING: This study was performed in Nanomedicine and Biosensor Laboratory, Bio-X Center, Harbin Institute of Technology from Marcy 2006 to June 2007.MATERIALS: The GORE-TEX Epife vascular grafts (W. L Gore & Associates, Inc., Flagstaff, AZ) used in this study were 4mm in internal diameter. rHir was obtained from Calbiochem, Germany. Sodium alginate (also called alginic acid sodium salt; medium viscosity) was purchased from Sigma.METHODS: A p-diazonium diphenyl amine polymer (PA) was used as an interlayer between alginate and recombinant hirudin (rHir). The diazonium moieties were capable of covalently coupling with electron-rich aromatic systems such as histidine and tyrosine residues of hirudin. No need for chemical pretreatment took all advantage by preserving the bulk properties with almost no effect on stability and elasticity of the Eptfe vascular graft. rHir amount on Epife surface Was determined by the Micro BCA (Bicinchoninic acid) Protein Assay kit.MAIN OUTCOME MEASURES: ① Determination rHir amount on Eptfe surface; ② Static water contact angles; ③ Attenuated total reflectance fourier transform infrared spectroscopy (ATR-FTIR) was employed to confirm the change taking place in the Eptfe graft surface modification process; ④ Characterization of the surface morphology and platelet adhesion by SEM; ⑤ APTT and PT; ⑥ Percent hemolysis.RESULTS: ① The amount of rHir adsorbed onto the Eptfe vascular was deduced to be 16.35 μg/cm2. ② Surface analysis ATR-FTTR revealed the presence of new functional groups on the modified graft surfaces. ③ The water contact angle of the modified graft surface decreased. ④ The longer APTT and PT value lower than 5% hemolysis level and dramatically decrease of platelet adhesion assay showed that rHir modified graft had great improved blood compatibility.CONCLUS10N: Cross-linked Alg/rHir onto Eptfe can improve luminal surface and hemocompatibility.
ABSTRACT
BACKGROUND:Thrombus formation and neointimal hyperplasia still limit the use of small-caliber expanded poly(tetrafluoroethylene) (ePTFE) vascular prosthesis with a diameter less than 6 mm for revascularization in the coronary or peripheral circulation. Bioactive surface heparin coating is one conceivable path for above-mentioned problems.OBJECTIVE: To elevate the anticoagulant property of ePTFE, this study promoted the patency of a novel small-caliber ePTFE vascular graft by modifying its luminal surface with covalently crosslinked poly(vinyl alcohol)/ p-diazonium diphenyl amine polymer/heparin gel (PVA/PA/Hep gel) and examined the hemocompatibility of the graft.DESIGN, TIME AND SETTING: Observational experiments were performed at the Nanomedicine and Biosensor Lab,Biomedical Engineering Center, Harbin Institute of Technology from May 2006 to June 2007.MATERIALS: The ePTFE vascular grafts (diameter of 4 mm), Nafion (Naf) and Poly(vinyl alcohol) (Aldrich, USA), heparin (Mw 12 000- 14 000) (Calbiochem, USA), p-diazonium diphenyl amine polymer (PA) (this lab, China) were used in this study.METHODS: ①The vascular graft surface was firstly modified with Nafion. ②Following the impregnation of the mixture of PVA/PA/Hep, covalent crosslinking between polyvinyl alcohol and heparin was performed using crosslinker PA under ultraviolet radiation.MAIN OUTCOME MEASURES: ①Contact angles, ②Attenuated total reflection-fourier transform infrared spectroscopy (ATR-FTIR), ③Activated partial thromboplastin time (APTT) and prothromhin time (PT), ④hemolysis test, ⑤platelet adhesion test and ⑥thrombosin inactivation test.RESULTS: ①The water contact angle of the vascular graft surface was greatly decreased after modifying. ATR-FTIR revealed the disappearance of diazonium groups at 2 172 cm-1 and 2 224 cm-1. Vascular prosthesis after modifying had prolonged APTT and PT, low percent hemolysis and low amount of platelet adhesion. Modified vascular prosthesis had inhibitory effect on thrombosin activity and good coating stability.CONCLUSION: Converage of PVA/PA/Hep has good antithrombotic function and low percent hemolysis, resulting in improving hemocompatibility of vascular prosthesis.