[Experimental study on prevention of postsurgical adhesions by using O-carboxymethylchitosan solution after an abdominal operation].

O-Carboxymethylchitosan (O-CMC) in 1000 g batch was prepared from chitin as starting material and its chemical structure was confirmed by analysis of IR and NMR. O-CMC solution, sodium hyaluronate (HA) solution and physiological saline were used in Sprague-Dawley rat model for prevention of postsurgical adhesions; after 7 days of an abdominal operation, the 3 groups were evaluated according to Belluco standard, the mean scores of O-CMC group, HA group and physiological saline group were 2.5 +/- 3.1, 3.3 +/- 3.6 and 10.3 +/- 1.0, respectively. Histological inspection showed that in O-CMC group, mesothelial cells on peritonaeum or cecum surfaces were almost restored; in HA group the injured surface of peritonaeum was mostly repaired, but in physiological saline group the injured surface of cecum was just a little repaired; there were extensive adhesions between peritonaeum and cecum, and inflammatory response was quite serious. Experimental results indicated that O-CMC and HA had excellent efficiency and O-CMC was slightly better than HA for the prevention of postsurgical adhesions.

[Compliance of small diameter polyurethane artificial vascular graft ].

The radical compliance of small diameter artificial vascular grafts was measured by a device made of laser micrometer, pressure transducer, A/D card, micro computer and pulsed circulation loop, the volumetric compliance was measured by a device made of micro-syringe and pressure transducer; the longitudinal compliance was calculated from volumetric compliance and radical compliance. The research results showed that the radical compliance, volumetric compliance and longitudinal compliance would rise not only with the increase in polyurethane (PU) elasticity and salt/polymer ratio (or porosity), but also with the decrease in dipping layers (or wall thickness). Circumferential moduli E zeta and longitudinal moduli E theta could be calculated from volumetric compliance and longitudinal compliance respectively; E theta and E zeta would decrease with the increase in PU elasticity and salt/polymer ratio, but was independent on number of dipping layers. Small diameter PU artificial vascular grafts with compliance close to natural vein or artery can be prepared by choosing of more elastic PU materials (Chro or PCU1500), optimization of salt/polymer ratio (6:1), and the number of dipping layers (4-6 layers).

[Test of carotid artery replacement by polyurethane artificial vascular graft with recombinant fibrinolytic enzyme factor II-modified lumina in dogs].

OBJECTIVE: To evaluate the implantation effect of artificial vascular grafts with recombinant fibrinolytic enzyme factor II (rF II)-immobilized lumina in animal test. METHODS: Four mm internal diameter (ID) polyurethane (PU) artificial vascular grafts were prepared by dipping and leaching method. The micro-pore size and morphology of the graft walls were observed by SEM. The graft lumina were immobilized with rF II. Twenty hybrid male dogs [weighing (20 +/- 1) kg] were used for animal model of carotid artery defect and were randomly divided into 3 groups: rF II -immobilized PU group, no rF II -immobilized PU group and expanded polytetrafluoroethylene (ePTFE) group. The vascular grafts were implanted for repairing injured segments of carotid artery in dogs. The general health state of animals was recorded. At 30 days and 60 days, the patency rate of every group was calculated. At 60 days IDs were measured, cell proliferation in neointima was inspected by light microscope, morphology on neointima was observed by SEM. RESULTS: The ID of the PU vascular grafts was (3.74 +/- 0.06) mm, wall thickness was 0.4-0.6 mm, the wall density was 0.25 g/cm3, the porosity was 79.8%, racial compliance was 8.57%/100 mmHg. In the wall, micropores were well distributed and opened-pores structure was observed. Pore size was (140 +/- 41) microm in the outside layer, pore size was (100 +/- 3) microm in the inside layer, thickness ratio of outside / inside layers was 2 : 1, the pore size was (40 +/- 16) microm on the lumina surface. After operation the wounds on neck healed, all the animals survived and had no complication. At 30 days and 60 days after implantation, the patency rate for rF II -immobilized PU group were 100% and 66.7%, for no rF II -immobilized PU group were 66.7% and 33.3%, and for ePTFE group were 67.7% and 0 respectively, but at 60 days there were thrombosis at anastomotic sites of some grafts occluded. Before operation the IDs for rF II-immobilized PU group, no rF II -immobilized PU group and ePTFE group were (3.74 +/- 0.06), (3.74 +/- 0.06) and (4.00 +/- 0.03) mm, at 60 days after operation the IDs were (4.51 +/- 0.05), (4.31 +/- 0.24) and (4.43 +/- 0.12) mm respectively, showing no statistically significant differences between 3 groups (P > 0.05). Histological inspection indicated that at 15 days a layer of plasma protein deposited on the lumina, at 30 days some cells adhered to the lumina, at 60 days neointima could be observed on the lumina. Thickness of the neointima became larger with implantation time. At 60 days neointima thickness at proximal end, middle site and distal end of graft were (560 +/- 22), (78 +/- 5) and (323 +/- 31) microm respectively for rF II -immobilized PU group. The results of SEM showed that neointima surface consisted of flat and long cells which long axes ranged with blood flow direction and was similar to lumina morphology of carotid artery of dog. CONCLUSION: Immobilization of rF II to lumina of grafts could enhance fibrinolytic activity and inhibited formation of thrombo-embolic which led to an increase in patency rate after implantation.

[Effect of preparation conditions for small-diameter artificial polyurethane vascular graft on microstructure and mechanical properties].

OBJECTIVE: To study the effect of preparation conditions for small-diameter polyurethane(PU) vascular graft on microstructure and mechanical properties. METHODS: The small-diameter microporous PU artificial vascular grafts were prepared by dipping and leaching method. The dimension and microstructure were controlled by changing mold diameter, PU materials, salt sizes, salt to polymer ratio, times of dipping layers etc. The mechanical properties of PU grafts including radical compliance, water permeability, longitudinal strength, burst strength, and suture tearing strength were measured and the effect of the graft dimension and microstructure on their properties were studied. RESULTS: The internal diameter of grafts prepared was 2-4 mm depending on mold diameter. The wall thickness was 0.6-1.2 mm after dipping 4-8 layers. The density was 0.23-0.49 g/cm3. The pore was 42-95 microm in diameter. The porosity was 56%-80%. The radical compliance was 1.2%-7.4% x 13.3 kPa(-1) and higher compliances could be obtained by using more elastic polyurethane, higher salt to polymer ratio, longer diameter and less wall thickness. The water permeability, mainly depending on salt to polymer ratio, diameter, and wall thickness, was 0.29-12.44 g/(cm2 x min). The longitudinal strength was 1.55-4.36 MPa correlating with tensile strength of polyurethane and salt to polymer ratio. The burst strength was 60-300 kPa also depending on tensile strength of polyurethane and salt to polymer ratio. The suture tearing strength was 19.5-96.2 N/cm2 depending on tensile strength of polyurethane but not on the angle of tearing and graft axial directions. The compliance and water permeability of Chronoflex grafts were higher than those of PCU-1500 grafts, but longitudinal strength, burst strength, and suture tearing strength of PCU-1500 grafts were better than those of Chronoflex grafts. Conclusion Small-diameter grafts with proper pore sizes, porosity, matching compliance can be obtained by selecting PU materials and optimizing the preparation conditions.