Biomedical subjects

S Niu

Publications and source records attributed to S Niu.

60 records · Page 4Linked to original sources

PubMedDate not supplied

Endothelialization on various segmented polyurethanes: cellular behavior and its substrate dependency.

Endothelialization on artificial substrates is essential for providing vital function to artificial and hybrid vascular prostheses. The authors studied fundamental behaviors of endothelial cells (EC), including adhesion, spreading, migration, and growth, on various segmented polyurethanes (SPU) with a wide variety of wettability. Endothelialization has a synergistic action on these cellular behaviors that was quantitatively evaluated by phase contrast microscopy. Surface characteristics of SPU were analyzed by contact angle measurement and X-ray photoelectron spectroscopy. Adhesion, spreading, migration, growth, and endothelialization in vitro of bovine aortic EC on relatively hydrophobic SPU exceeded those on both a hydrophilic SPU, and a very hydrophobic siliconized one. Minimal interaction with EC was found for hydrophilic SPU. Adherent cells tended to be delaminated from siliconized SPU in a later culture period. The addition of a peptidyl antagonist of adhesive protein receptor inhibited adhesion of EC on SPU. These results suggest that surface characteristics, possibly regulating adsorption of adhesive proteins, are important factors in the development of vascular SPU prostheses.

Animals↗

PubMedDate not supplied

Development of an autologous connective tissue tube as a small caliber vascular substitute.

A small-caliber vascular graft with good healing properties was developed using an autologous connective tissue tube (ACTT) and in situ heparinization. ACTT is the best material for implantable grafts, but as a small-caliber vascular graft, both the high thrombogenicity and requirement for time to preparation in situ were serious problems. To overcome these difficulties, an ultrafine polyester fiber (UFPF) mesh was used for the framework of the graft. it has been shown that UFPF provides a good framework for fibroblast migration and proliferation both in vivo and in vitro. The granulomatous connective tissue tube could be constructed very rapidly and had numerous capillary blood vessels, which opened onto the luminal surface of the graft when it was implanted as a vascular substitute and provided colonies of endothelial cells. These colonies spread rapidly all over the luminal surface, and the graft developed permanent antithrombogenicity by endothelialization. The next problem was attainment of temporary antithrombogenicity of the graft before complete endothelialization. Since collagen fibrils are highly thrombogenic, the fact that ACTT collagen fibrils face the luminal surface requires greater antithrombogenicity. A new technique for binding heparin to collagen fibrils in situ was also developed. This was proved to be useful in maintaining the antithrombogenicity of the grafts (3 mm in inner diameter, 6 to 7 cm in length) in the animal studies. The graft showed rapid healing of the neonintima with endothelialization and long-term stability of the graft wall.

Angiography↗

PubMedDate not supplied

A functional neointima with regularly arranged smooth muscle cells in a fabric vascular prosthesis transplanted with autologous venous tissue fragments.

Regular arrangement of smooth muscle cells underneath an endothelial cell layer was observed in the neointima of a fabric vascular prosthesis treated with new technology to accelerate endothelialization, i.e., transplantation of autologous venous tissue fragments in the graft wall. This finding indicated that the neointima has a vital function as the intima of the blood vessel. A canine left jugular vein was minced and stirred into 20 ml of saline containing 1,000 IU heparin. It was injected with pressure into a fabric prosthesis (4 mm inner diameter [ID], 3.5 cm in length, Water porosity: 4,000 ml) to create the tissue fragmented, heparinized graft. The graft was implanted into the same animal from which the jugular vein was taken. Forty tissue fragmented heparinized (TFH) grafts were implanted in both carotid arteries of 20 dogs and explanted from 1 hr to 400 days after implantation. In this study, the neointimae of the grafts implanted for more than 1 month are analyzed, with a focus on the arrangement of smooth muscle cells in the neointima. A circumferential arrangement of smooth muscle cells with a thin layer of longitudinally arranged cells underneath was seen in the neointimae, which resemble the arrangement of smooth muscle cells in the natural arterial wall. Some areas had a thin smooth muscle cell layer in the longitudinal direction just under the endothelial cell layer. At anastomotic sites, they ran in parallel rows in the longitudinal direction. The authors previously clarified that the smooth muscle cells arrange in parallel rows in the direction of strain caused by tensile stress.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMedDate not supplied

Small diameter vascular prostheses with incorporated bioabsorbable matrices. A preliminary study.

The authors have designed small diameter vascular prostheses with incorporated matrices that can be absorbed into a growing anastomotic neointima. First, a gelatin-heparin complex was coated on the inner surface of tubular ultrafine polyester fabrics presealed with heat denatured albumin. Second, to control the bioabsorption rate, the prepared grafts were cross-linked with polyepoxy compounds for 3 days (Group I; n = 14) or 5 days (Group II; n = 4). These grafts, 3 mm in diameter and 4 cm long, replaced the carotid arteries of nine mongrel dogs weighing 9.5-14 kg. Six of eight (75%) grafts in Group I were patent when the animals were killed 4 weeks after surgery. Doppler sound examination revealed that the remaining six were patent for 16 weeks. In Group II, three of four (75%) grafts were patent when the animals were killed 8 weeks after surgery. In both groups, scanning electron microscopic study showed neither platelet aggregation nor fibrin formation on the midportion. However, these two groups significantly differed in histology. In Group I, thin anastomotic neointima advanced over the mostly absorbed gelatin-heparin complex layer. Connective tissue was well formed around the polyester scaffold. In contrast, thick neointima advanced over the gelatin-heparin complex layer that still remained on the luminal surface in Group II. These results suggest that the gelatin-heparin complex, when cross-linked adequately, could simultaneously function as a temporary antithrombogenic surface and as an excellent substructure of an anastomotic neointima.

Anastomosis, Surgical↗

PubMedDate not supplied

Progress in Cleveland Clinic-Nimbus total artificial heart development.

A totally implantable, Cleveland Clinic-Nimbus total artificial heart (TAH) uses electrohydraulic energy conversion and an automatic left master-alternate mode control scheme, with a filling sensitivity of 1.0 l/min/mmHg and a maximum output of 9.5 l/min. The TAHs were tested in 12 calves for 1-120 days with normal major organ and blood cell function. Post-operative suppression of platelet aggregation recovered by the second post-operative week. The gelatin-coated pump surface generally was clean without any anticoagulants and free from infection. Embolism, which occurred in two cases, was caused by complications attributable to fungal infection in a Dacron graft and by thrombus formed around a jugular vein catheter. A system with a hybridized microcircuit controller in the interventricular space has been tested successfully in the three most recent cases, with a peak device surface temperature elevation of 6.5 degrees C. Heat effects were confined to the tissues immediately adjacent to the hottest spots. The carbon fiber-reinforced epoxy housing and 60 ml butyl rubber compliance chamber showed good tissue compatibility with a thin, fibrous tissue capsule. The transcutaneous energy transmission system and the internal battery functioned well as designed in the most recent animal implant.

Animals↗

PubMedDate not supplied

A new double lumen balloon catheter for retrograde cerebral perfusion via jugular vein cannulation.

A new catheter for retrograde cerebral perfusion (RCP) was developed that can be used to deliver blood directly into the internal jugular vein (IJV) beyond the venous valves at the jugular-subclavian junction and prevent blood from draining into the lower half of the body. This catheter can be inserted into the IJV via a standard puncture technique by use of a 14 Fr sheath. The catheter shaft has two channels for balloon inflation and blood perfusion, respectively. A balloon for occlusion of drainage veins (superior vena cava and azygos vein) is installed at the catheter tip. Side holes, through which oxygenated cold blood is delivered into the IJV, are located 95 mm from the catheter tip. In a mock circulatory study, the pressure at the perfusion line (16-118 mmHg) increased with the increasing flow rate (0-400 ml/min). In clinical application, under circulatory arrest with profound hypothermia, inflation of the balloon effectively reduced blood drainage into the lower half of the body and, consequently, RCP was successfully performed (flow rate, 300-350 ml/min; pressure at the IJV, 15 mmHg). Because all of these procedures were controlled from outside the operative field, RCP by use of this catheter could be useful in distal arch replacement via left lateral thoracotomy.

Animals↗