The development of suitable three-dimensional matrices for the maintenance of cellular viability and differentiation is critical for applications in tissue engineering and cell biology. To this end, gel matrices of different proportions of alginate/elastin/polythylene glycol (Alg/Ela/PEG) were prepared and examined. The composite matrix membranes were evaluated for their porous scaffold using SEM, enzymatic degradation and water content. An equal blend of Alg/Ela with a ratio of Alg/Ela: PEG (7: 3) was selected for fabricating Alg/Ela/PEG scaffolds for this study. The Alg/Ela/PEG membranes fabricated at 20°C and -20°C had a mean surface pore size of 35-45 μm. However, their ultrastructures had shown bigger pore structures (60-75 μm) compared to their surface. It is interesting to note that the membranes of Alg/Ela/PEG prepared at 20°C had larger ultrastructural pores than that of membranes prepared at -20°C. Further, the SEM studies revealed that in the absence of PEG the composite membranes of Alg/Ela formed with less porous structures. The water content of membranes prepared at 20°C was higher with Alg/Ela/PEG (61.6 ± 4.8%), compared to Alg/Ela (49.9 ± 0.3%). The enzymatic degradation and water content studies also revealed that the membranes fabricated at -20°C had high water uptake and low enzymatic degradation, as that of the membranes prepared at 20°C. In other words the larger pore structured membranes had less water content and high degradation profile. This study proposes that this novel composite matrix produces a hierarchical structure that is useful for generating tissue scaffolds for repairing the failing cardiac muscles. However, more detailed investigations with cytocompatibility studies are needed to find applications.

The development of injectable microparticles for protein delivery is a major challenge. We demonstrated the possibility of entrapping human serum albumin (HSA) and thrombin (Thr) in poly(ethylene glycol) (PEG)-coated, monodisperse, biodegradable microspheres with a mean diameter of about 10 gm. In our earlier studies, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis was used to characterize the surface of PEG-coated, taxol-loaded poly(lactic acid) (PLA) microspheres. An analysis by DRIFTS revealed that PEG was incorporated well on the PLA microsphere surface. An emulsion of protein (in water) and PLA dissolved in an acetone-dichloromethane (or acetone- chloroform) mixture were poured into an aqueous solution of PEG [or poly(vinyl alcohol) (PVA)] with stirring with a high-speed homogenizer for the formation of microparticles. HSA recovery in microspheres ranged from 13 to 40%, depending on the solvent and emulsification systems used for the preparation. PLA dissolved in a dichloromethane /acetone system and albumin loaded via a PEG emulsification solution (PLA-PEG-HSA) showed maximum drug recovery (39.5%) and drug content (9.9%). Scanning electron microscopy revealed that PEG-coated microspheres had less surface micropores than PVA-based preparations. The drug-release behavior of microspheres suspended in phosphate-buffered saline exhibited a biphasic pattern. An initial burst release (30%) followed by a constant slow release for 20 days was observed for HSA and Thr from PLA-PEG microspheres. PEG-coated PLA microspheres show great potential for protein-based drug delivery. (C) 2002 Wiley Periodicals, Inc.

Heparin remains the gold-standard inhibitor of the process involved in the vascular response to injury. Continued anticoagulation is achieved by subcutaneous administration of low-molecular-weight heparin (LMW Hep) or with an orally active anticoagulant such as warfarin. An oral heparin would avoid the inconvenience of subcutaneous injections and adverse events associated with warfarin. A mild chitosan/PEG/calcium alginate microencapsulation process, as applied to encapsulation of biological macromolecules such as heparin and LMW Hep was investigated. Heparin and LMW Hep entrapped alginate beads were further surface/enteric coated with chitosan and cellulose acetate phthalate (CAP) via carbodiimide (EDC) functionalities. It was observed that approximately 70% of the content is being released into Tris-HCl buffer, pH 7.4 within the initial 6 hours and no significant release of LMW Hep was observed from enteric coated microspheres (12%) during treatment with 0.1 M HCl, pH 1.0 for 4 hours. But acid treated capsules had released almost all the entrapped LMW Hep into Tris-HCl, pH 7.4 media within 6 hours. From scanning electron microscopic and swelling studies, it appeared that the surface coatings (via chitosan and CAP) had modified the alginate microspheres and subsequently the drug release. The released heparin and LMW Hep had shown their anticoagulant functions. These results established the feasibility of modifying the formulation in order to obtain the desired controlled release of bioactive agent (LMW Hep), for a convenient pH dependent delivery system.

Smooth muscle cell proliferation plays a major role in the genesis of restenosis after angioplasty or vascular injury. Local delivery of agents capable of modulating vascular responses, have the potential to prevent restenosis. However, the development of injectable microspheres for sustained drug delivery to the arterial wall is a major challenge. We demonstrated the possibility of entrapping an antiproliferative agent, cisplatin, in a series of surface coated biodegradable microspheres composed of poly(lactic acid)poly(caprolactone) blends, with a mean diameter of 2-10 pm. The microspheres were surface coated with poly ethylene glycol (PEG), chitosan (Chit), or alginate (Alg). A solution of cisplatin and a 50:50 blend of polylactic acid (PLA)-polycaprolactone (PCL) dissolved in acetone-dichloromethane mixture was poured into an aqueous solution of PEG (or polyvinyl alcohol or Chit or Alg) with stirring using a high speed homogenizer, for the formation of microspheres. Cisplatin recovery in microspheres ranged from 25-45% depending on the emulsification system used for the preparations. Scanning electron microscopy revealed that the PLA-PCL microspheres were spherical in shape and had a smooth surface texture. The amount of drug release was much higher initially (20-30%), this was followed by a constant slow-release profile for a 30-day period of study. It has been found that drug release depends on the amount of entrapped drug, on the presence of extra cisplatin in the dispensing phase, and on the polymer coatings. This PEG or Alg-coated PLA/PCL microsphere formulation may have potential for the targeted delivery of antiproliferative agents to treat restenosis.

Smooth muscle cell proliferation plays a major role in the genesis of restenosis after angioplasty or vascular injury. Controlled release of appropriate drugs alone and in combinations is one approach for treating coronary obstructions, balloon angioplasty, restenosis associated with thrombosis, and calcification. We demonstrated the possibility of encapsulating taxol-loaded polylactic acid (PLA) microspheres within heparin-chitosan spheres to develop a prolonged release co-matrix form. The in vitro release profile of taxol and heparin from this co-matrix system was monitored in phosphate buffered saline pH 7.4, using an ultraviolet spectrophotometer. The amount of taxol/heparin release was initially much higher, followed by a constant slow release profile for a prolonged period. The initial burst release of taxol (15.8%) and heparin (32.7%) from the co-matrix was modified with polyethylene glycol coatings (13.5% and 25.4%, respectively, for 24 hr). From scanning electron microscopy studies, it appears that these drugs diffuse out slowly to the dissolution medium through the micropores of the co-matrix. However, the surface micropores were modified with polyethylene glycol (PEG) coatings for a constant slow release profile. This PEG-coated PLA/chitosan co-matrix may target drug combinations having synergestic effects for prolonged periods to treat restenosis.

The development of injectable microspheres for sustained drug delivery to the arterial wall is a major challenge. We demonstrated the possibility of entrapping an antiproliferative agent, taxol, in poly(ethylene glycol) (PEG)-coated biodegradable poly(lactic acid) (PLA) microspheres with a mean diameter of 2-6 microm. A solution of taxol and PLA dissolved in an acetone/dichloromethane mixture was poured into an aqueous solution of PEG [or poly(vinyl alcohol) (PVA] with stirring with a high-speed homogenizer for the formation of microspheres. Taxol recovery in PLA-PEG microspheres was higher (61.2 +/- 2.3%) than with PVA-based (41.6 +/- 1.8%) preparations. An analysis by diffuse reflectance infrared Fourier transform spectroscopy revealed that PEG was incorporated well on the PLA microsphere surface. Scanning electron microscopy revealed that the PEG-coated PLA microspheres were spherical in shape and had a smooth surface texture like those of PVA-based preparations. The amount of drug release was much higher initially (25-30%); this was followed by a constant slow-release profile for a 30-day period of study. This PEG-coated PLA microsphere formulation may have potential for the targeted delivery of antiproliferative agents to treat restenosis.

The search for a nonthrombogenic material having patency to be used for small diameter vascular graft applications continues to be a field of extensive investigation. The purpose of the present study was to examine whether surface modification of polytetra fluoroethylene (PTFE, Teflon) and polyethylene-terephthalate (Dacron) vascular grafts might extend graft biocompatibility without modifying the graft structure. A series of surface coatings were prepared by modifying the argon plasma-treated PTFE and Dacron grafts with collagen IV and laminin and subsequently immobilizing bioactive molecules like PGE1, heparin or phosphatidyl choline via the carbodiimide functionalities. Surface analysis by Fourier transform infrared spectroscopy-attenuated total reflectance revealed the presence of new functional groups on the modified graft surfaces. In vitro studies showed that fibrinogen adsorption and platelet adhesion on modified grafts were significantly reduced. This study proposes that surface grafting of matrix components (collagen-type IV and laminin) and subsequent immobilization of bioactive molecules (PGE1, heparin or phosphatidyl choline) changed the surface conditioning of vascular grafts and subsequently improved their biocompatibility. However, more detailed in vivo studies are needed to confirm these observations.

Smooth muscle cell proliferation plays a major role in the genesis of restenosis after angioplasty or vascular injury. Local delivery of agents capable of modulating vascular responses have the potential to prevent restenosis. However, the development of injectable microspheres for maintaining high tissue levels of drugs at the site of vascular injury is a major challenge. We demonstrated the possibility of entrapping an antiproliferative agent, colchicine, in polyethylene glycol (PEG)-coated biodegradable microspheres composed of poly(lactic acid)/poly(epsilon-caprolactone) blends, with a mean diameter of 3-6 microm. A solution of colchicine and blends of polylactic acid (PLA)/polycaprolactone (PCL) dissolved in acetone-dichloromethane mixture was poured into an aqueous solution of PEG (or polyvinyl alcohol) with stirring by a high-speed homogenizer to form microspheres. Colchicine recovery in microspheres ranged from 30-50% depending on the emulsification system and the ratio of polymer blends used for the preparations. Scanning electron microscopy revealed that the PLA/PCL microspheres were spherical in shape and had a smooth surface texture. Results of in vitro release studies showed that it is possible to control the colchicine release by choosing the appropriate particle size, loading, and PLA/PCL composition. Water permeability through the PLA membrane was greater, when compared with PCL blends. The amount of drug release also was much higher (58.3%) in PLA compared with PCL (39.3%) microspheres, for 30 days. Therefore, we concluded that the drug release from the microspheres followed a diffusion mechanism where bulk erosion and surface deposition were negligible. These PEG-coated PLA/PCL microspheres may have potential for targeting antiproliferative agents for prolonged periods to treat restenosis.

The development of injectable microspheres for anticancer drug delivery into the brain is a major challenge. The possibility of entrapping 5-fluorouracil (5-FU) in chitosan coated monodisperse biodegradable microspheres with a mean diameter of 10-25 um was demonstrated. An emulsion of 5-FU (in water) and polylactic acid (PLA) dissolved in acetone-dichloromethane mixture was poured into an aqueous solution of chitosan (or poly-vinyl alcohol) with stirring using a high-speed homogenizer, for the formation of microspheres. 5-FU recovery in microspheres ranged from 44-66% depending on the polymer and emulsification systems used for the preparation. Scanning electron microscopy revealed that the chitosan coated microspheres had less surface micropores compared to PVA based preparations. The drug release behaviour from microspheres suspended in phosphate buffered saline exhibited a biphasic pattern. The amount of drug release was much higher initially (approximately 25%), followed by a constant slow release profile for a 30 days period of study. This chitosan coated PLA/PLGA microsphere formulation may have potential for the targeted delivery of 5-FU to treat cerebral tumours.

The AngelWings device is a newer transcatheter device used for closure of secundum atrial septal defects (ASD) and patent foramen ovale (PFO), which consists of a self-centering, 2-disk system. Transesophageal echocardiography (TEE) plays a pivotal role in the deployment of the 2 disks of this device, on the appropriate sides of the atrial septum. The objective of this study is to describe the echocardiographic findings associated with successful deployment of the AngelWings device for closure of ASD and PFO. We evaluated the TEE studies of 70 patients enrolled in 4 United States centers, for closure of ASD and PFO with the AngelWings device. The TEE characteristics of successful and unsuccessful deployments were analyzed. Residual shunts across the atrial septum were assessed by TEE at the end of the procedure, 24 hours later by transthoracic echocardiography, and at 6 months by TEE. The deployment of the device was successful in 65 patients (93%). In the unsuccessful group, ASD size by TEE was larger (13.4 ± 3.1 vs 8.9 ± 4.7 mm, p <0.05). TEE was successful in identifying snagging of the device by intracardiac structures and prolapse of corners of the left or right atrial disk through the ASD, features that were difficult to identify by fluoroscopy. The echocardiographic characteristics outlined here are important guidelines for successful deployment of the AngelWings device.

The search for a noncalcifying tissue material to be used for valve replacement application continues to be a field of extensive investigation. A series of porcine pericardial membranes was prepared by modifying the glutaraldehyde--treated tissues with albumin and subsequently immobilizing bioactive molecules like PGE1, PGI2 or heparin via the carbodiimide functionalities. The in vitro calcification and collagenase degradation of these modified tissues were studied as a function of exposure time. Furthermore, the biocompatibility aspects of such novel interfaces were established by platelet adhesion and fibrinogen adsorption. The results reported in this article propose that the treatment with antiplatelet agents such as albumin, heparin and prostaglandins (PGE1 or PGI2) change the surface conditioning of pericardial tissues, suggesting a possible role of deposited serum components in affecting mineralization process on bioprosthesis. Therefore, it is worthy to hypothesize that besides inhibiting the accumulation of calcium in the devitalized cells, the early formation of a conditioning layer on the bioprosthesis surface may affect salt precipitations, determining the propensity of the implant to calcify. More detailed studies are needed to understand the involvement of plasma proteins and cellular components of the recipient blood in tissue-associated calcification.

The Angel Wings Das device, a recently developed transcatheter atrial septal defect occluder, represents a new approach to therapy of this congenital cardiac lesion. Overall, successful defect occlusion occurs in > 90% of patients following device implantation. We describe the major design and technical issues pertinent to this device and review both international and personal local FDA Phase I trial results and complications. Future trial plans and device modifications are discussed.

Coronary arteries of transplanted hearts frequently develop a vasculopathy characterized by severe lumenal narrowing in the distal coronary arteries. It has been thought, on the basis of angiographic studies, that the coronary circulation of transplanted hearts with vasculopathy fails to develop collateral vessels normally. To determine the extent of the collateral circulation in transplanted hearts with a significant coronary stenosis, we measured an index of the collateral circulation, the coronary artery occlusion pressure, during single-vessel coronary angioplasty in seven patients with allograft vasculopathy and 18 patients with atherosclerotic disease who did not undergo transplantation. Aortic and coronary artery pressure distal to the stenosis in the epicardial artery were measured during balloon occlusion (> or = 45 seconds). Measurement variability for determination of coronary occlusion pressure was assessed by measuring occlusion pressure on two separate balloon inflations (n = 17). The severity of the dilated stenotic lesion was assessed with quantitative angiography (Reiber-PIE Data method). The indexes of stenosis severity were similar in coronary arteries of transplanted and native hearts. Coronary occlusion pressure measurements were highly reproducible (mean absolute difference between measurements, 1 +/- 1 mm Hg, r = 0.98). Coronary occlusion pressure in transplanted hearts (32 +/- 4 mm Hg) was nearly identical to that measured in coronary arteries of native hearts (29 +/- 2 mm Hg). When vessels with total occlusion were excluded and corrections were made for minor differences in hemodynamics (heart rate and blood pressure) were made, the coronary occlusion pressure in transplanted hearts remained nearly identical to native hearts.(ABSTRACT TRUNCATED AT 250 WORDS)

Background. Despite two decades of research, a transcatheter atrial septal defect closure device is not available for clinical use. We have designed a new superelastic Nitinol-Dacron, double-disk, self-centering, atrial septal defect closure device and studied its efficacy in a canine model of atrial septal defects.Methods and Results. Atrial septal defects were created surgically in 20 adult dogs using either a 7.5-mm or 10-mm punch. Percutaneous transcatheter closures were attempted using a new device. The device sizes used were 20 mm in 6 dogs, 22 mm in 9, and 25 mm in 5 (22.1+/-1.9 mm, mean+/-SD). The stretched atrial septal defect diameter was 10.5+/-1.3 mm, and the device to stretched atrial septal defect diameter ratio was 2.1+/-0.3. Closures were successful in 19 studies and unsuccessful in 1. Angiography showed a left-to-right shunt in all 20 dogs before closure. Immediately after closure (n=19), there were no shunts in 17 and trivial shunts in 2. Six dogs were followed for a period of 4.7+/-3.0 months (range, 2 to 8 months). The trivial shunt present in 1 animal immediately after closure had closed by the time of the repeat study. Spontaneous embolization of the device was not seen during follow-up. A solitary wire fracture was found 8 months after closure in 1 device. Light microscopy at 8 weeks in 3 dogs showed the devices to be covered by smooth endocardium, enmeshed in mature collagen tissue, with a minimal mononuclear cell infiltration. Retrievability was assessed by deliberately embolizing 4 devices in 2 dogs into the right atrium (n=1) and pulmonary artery (n=3). All devices were successfully retrieved with a snare.Conclusions. This feasibility study demonstrates that this new self-centering atrial septal defect closure device has a number of design features that permit effective and safe closures in a canine model. These results support the investigation of this device in human clinical trials.