Small-caliber Vascular Grafts Research Articles

Formidable Challenges in the Search for Biomarkers of Psychiatric Disorders

BACKGROUND: Tissue engineered blood vessels could address the large clinical need for small caliber vascular grafts. Self-assembly approaches that employ transient scaffolds to form tissues from only cells and secreted matrix could form completely autologous vascular grafts that rapidly remodel and integrate with host tissue in vivo. The objective of this study was to develop a simple and rapid method to self-assemble vascular cells into vascular grafts. HYPOTHESIS: We hypothesized that entrapment in rapidly degrading fibrin gels could facilitate self-assembly of vascular smooth muscle cells into a tubular tissue comprised mainly of SMCs and secreted matrix. METHODS: Baboon SMCs were entrapped in fibrin around a silicone tube and cultured for 14 days without fibrinolysis inhibitor. Spontaneous delamination from the inner tube allowed for simple isolation of constructs with forceps. RESULTS: Engineered tissues are tubular, handleable, and highly cellular, with substantial collagen deposition. Fibrin is largely degraded within 14 days. Tensile elastic modulus of ring segments is 36.2 kPa and 1.60 MPa for the toe and heel regions of the stress-strain relation, respectively. CONCLUSION: Fibrin entrapment without fibrinolysis inhibitor can facilitate rapid self-assembly of SMCs into tubular tissues. Future work will focus on mechanical conditioning and co-culture with vascular endothelial cells to improve mechanical strength and impart antithrombogenicity.

Morphological study of small-caliber hybrid vascular grafts upon replacement of canine common carotid arteries

Objective To investigate the in vivo morphological change of hybrid vascular graft made of porcine fibrin and microprocessed SPU film under the hemodynamic condition for predetermined period of time. Methods Autologous vascular endothelial cells derived from the saphenous veins of 6 adult mongrel dogs were cultured and proliferated in vitro in M199 culture medium, prelined on the luminal surface of lyophilized porcine fibrin tube wrapped with a SPU thin film with multiple micropores as a compliant scaffold. After canine common carotid arteries were bilaterally replaced with these vascular grafts for 4 weeks, light and electron microscopy, radiological imaging examination and immunohistochemistry were performed to evaluate the patency and remodeling in vivo. Results Eight of 10 engineered vascular grafts were patent ( patency rate 80% ). The patent grafts possessed thin, smooth and glistening luminal surfaces at the predetermined observation period up to 4 weeks. The intimal layer was covered with confluent, cobblestone-like monolayered cells that were positively stained with factor Ⅷ-related antigen. The thickness of the neoarterial walls was about 900 μm at 4th week after implantation. Vascular medial tissue rich in smooth muscle cells in the hierarchic structures of arterial wall was observed, and more interestingly, mass of elastic fiber was found in the medial tissue as early as 4 weeks postoperatively. Conclusion The endothelialized hybrid vascular grafts can be transformed to similar hierarchic structures of arterial walls under the hemodynamic condition for as early as 4 weeks. Key words: Tissue engineering; Blood vessel; Fibrin; Transplantation

Seeding HSVECs on small-caliber vascular grafts for the endothelialization

Objective To study the feasibility of seeding human saphenous vein endothelial cells (HSVECs) onto luminal surface of prosthetic grafts for the endotheliazation of expanded polytetrafluoroethylene (ePTFE) small diameter artificial blood vessel. Methods HSVECs were harvested and cultured in vitro for 13-15 days. The proliferated HSVECs were seeded onto the surface of ePTFE small diameter pros thetic grafts precoated with fibrin glue. After another 9-12 days of culture, morphological change was observed under scanning electron microscope. Results After seeding the cells, the adhesion, crawling and spreading of the HSVECs were observed onto the surface of ePTFE prosthetic graft under the scanning electron microscopy. On the 12th day, surface of ePTFE prosthetic graft was covered completely with endothelial monolayer. Conclusion Endothelial cells derived from human saphanous veins can be used as seed cells for the endothelialization of ePTFE prosthetic graft. Key words: Vascular endothelial cell; Proliferation; Vascular grafts

Fibrin-polylactide-based tissue-engineered vascular graft in the arterial circulation

There is a clear clinical requirement for the design and development of living, functional, small-calibre arterial grafts. Here, we investigate the potential use of a small diameter, tissue-engineered artery in a pre-clinical study in the carotid artery position of sheep. Small-calibre (∼5 mm) vascular composite grafts were molded using a fibrin scaffold supported by a poly(L/D)lactide 96/4 (P(L/D)LA 96/4) mesh, and seeded with autologous arterial-derived cells prior to 28 days of dynamic conditioning. Conditioned grafts were subsequently implanted for up to 6 months as interposed carotid artery grafts in the same animals from which the cells were harvested. Explanted grafts ( n = 6) were patent in each of the study groups (1 month, 3 months, 6 months), with a significant stenosis in one explant (3 months). There was a complete absence of thrombus formation on the luminal surface of grafts, with no evidence for aneurysm formation or calcification after 6 months in vivo. Histological analyses revealed remodeling of the fibrin scaffold with mature autologous proteins, and excellent cell distribution within the graft wall. Positive vWf and eNOS staining, in addition to scanning electron microscopy, revealed a confluent monolayer of endothelial cells lining the luminal surface of the grafts. The present study demonstrates the successful production and mid-term application of an autologous, fibrin-based small-calibre vascular graft in the arterial circulation, and highlights the potential for the creation of autologous implantable arterial grafts in a number of settings.

Autologous small‐caliber “Biotube” vascular grafts with argatroban loading: A histomorphological examination after implantation to rabbits

Functional autologous tubular tissues, termed "biotubes," have been developed as small-caliber vascular grafts. Biotubes can be easily and safely constructed in vivo by using a novel concept in regenerative medicine-in body tissue architecture technology, which requires neither clean specialized laboratories nor complex cell management. Biotubes with "anastomotic reinforcement cuffs" were prepared by embedding a silicone rod (diameter, 3 mm; length, 30 mm) as a mold in the dorsal subcutaneous pouches of rabbits. The rod was covered at both ends with 2 pieces of polyurethane sponge tubes (length, 3 mm), and it was removed when the grafts were harvested. These biotubes had homogeneous thin connective tissue walls (thickness: 76 +/- 37 microm) that were primarily composed of collagen and fibroblasts. The resulting cuff-impregnated biotubes were auto-implanted in the carotid arteries for predetermined periods of up to 12 weeks and then morphologically examined. On implantation of the biotubes after argatroban loading, the total patency was 9/11 without any instance of aneurysm formation or rupture. At 12 weeks after implantation, no significant neointimal thickening was observed (170 +/- 30 microm). In addition, minimal thrombus formation was observed on the luminal surfaces, which were completely covered with endothelial cells regularly oriented longitudinally. The regenerated vascular walls comprised multilayered smooth muscle cells and dense collagen fibers with regular circumferential orientation with few elastin fibers and were similar to native arteries. Biotubes with argatroban loading could thus be used as small-caliber vascular prostheses that greatly facilitate healing process and exhibit excellent biocompatibility.

Human Blood Vessel–Derived Endothelial Progenitors for Endothelialization of Small Diameter Vascular Prosthesis

BackgroundCoronary bypass graft failure as a result of acute thrombosis and intimal hyperplasia has been the major challenge in surgical procedures involving small-diameter vascular prosthesis. Coating synthetic grafts with patients' own endothelial cells has been suggested to improve the patency rate and overall success of bypass surgeries.Methodology/Principal FindingsWe isolated endothelial progenitor cells (EPCs) from leftover pieces of human saphenous vein/mammary artery. We demonstrate that EPCs can be expanded to generate millions of cells under low-density culture conditions. Exposure to high-density conditions induces differentiation to endothelial cell phenotype. EPC–derived endothelial cells show expression of CD144high, CD31, and vWF. We then assessed the ability of differentiated endothelial cells to adhere and grow on small diameter expanded polytetrafluoroethylene (ePTFE) tubings. Since ePTFE tubings are highly hydrophobic, we optimized protocols to introduce hydrophilic groups on luminal surface of ePTFE tubings. We demonstrate here a stepwise protocol that involves introduction of hydrophilic moieties and coating with defined ECM components that support adhesion of endothelial cells, but not of blood platelets.Conclusion/SignificanceOur data confirms that endothelial progenitors obtained from adult human blood vessels can be expanded in vitro under xenoprotein-free conditions, for potential use in endothelialization of small diameter ePTFE grafts. These endothelialized grafts may represent a promising treatment strategy for improving the clinical outcome of small-caliber vascular grafts in cardiac bypass surgeries.

3‐Tesla magnetic resonance angiographic assessment of a tissue‐engineered small‐caliber vascular graft implanted in a rat

In the development of small-caliber vascular grafts (diameter; less than 3 mm), animal implantation studies have been mostly performed by using rat abdominal aortas, and their certain patency must evaluate with sacrificing every observation periods, which is both labor-intensive and time-consuming when performing a large number of experiments. This study is the first to demonstrate the application of 3-Tesla contrast-free time-of-flight magnetic resonance angiography (TOF-MRA) in the continuous assessment of the status of a tissue-engineered vascular graft in rat. As a model graft, a single connective tubular tissue (diameter; 1.5 mm), prepared by embedding the silicone rod (diameter; 1.5 mm) into a subcutaneous pouch of a rat for 2 weeks an in vivo tissue-engineering, was used. The graft was implanted in the abdominal aorta (diameter; 1.3 mm) of the rat by end-to-end anastomosis. Repeated TOF-MRA imaging of the graft obtained over a 3-month follow-up period after implantation made it possible to evaluate the patency of the graft, both simply and noninvasively. It also permitted visualization of the connected abdominal aorta and renal and common iliac arteries having smaller caliber (diameter; less than 1 mm). In addition, the degree of the stenosis or aneurysm could also be detected. 3-Tesla MRA allowed the simplified and noninvasive assessment of the status on the vascular graft, including the formation of a stenosis or aneurysm, in the same rat at different times, which will be contributing to enhance the development of tissue-engineered vascular grafts even with small caliber.

Paclitaxel-Eluting Biodegradable Synthetic Vascular Prostheses

Clinical small-caliber vascular prostheses are unsatisfactory. Reasons for failure are early thrombosis and late intimal hyperplasia. We thus prepared biodegradable small-caliber vascular prostheses using electrospun polycaprolactone (PCL) with slow-releasing paclitaxel (PTX), an antiproliferative drug. PCL solutions containing PTX were used to prepare nonwoven nanofibre-based 2-mm ID prostheses. Mechanical morphological properties and drug loading, distribution, and release were studied in vitro. Infrarenal abdominal aortic replacement was carried out with nondrug-loaded and drug-loaded prostheses in 18 rats and followed for 6 months. Patency, stenosis, tissue reaction, and drug effect on endothelialization, vascular remodeling, and neointima formation were studied in vivo. In vitro prostheses showed controlled morphology mimicking extracellular matrix with mechanical properties similar to those of native vessels. PTX-loaded grafts with suitable mechanical properties and controlled drug-release were obtained by factorial design. In vivo, both groups showed 100% patency, no stenosis, and no aneurysmal dilatation. Endothelial coverage and cell ingrowth were significantly reduced at 3 weeks and delayed at 12 and 24 weeks in PTX grafts, but as envisioned, neointima formation was significantly reduced in these grafts at 12 weeks and delayed at 6 months. Biodegradable, electrospun, nanofibre, polycaprolactone prostheses are promising because in vitro they maintain their mechanical properties (regardless of PTX loading), and in vivo show good patency, reendothelialize, and remodel with autologous cells. PTX loading delays endothelialization and cellular ingrowth. Conversely, it reduces neointima formation until the end point of our study and thus may be an interesting option for small caliber vascular grafts.

The endothelialization of small-caliber hybrid vascular graft fabricated with porcine fibrin

Objective To investigate the possibility of vascular endothelial cells(ECs)seeding onto the surface of the hybrid vascular grafts fabricated with porcine fibrin.Methods ECs which were seeded onto the tubular scaffold were harvested from canine saphenous vein by collagenase digestion and subculture.After another 7-12 days culture that enabled the maturation of eytoskeleton of ECs,the morpho logical characteristics of vascular ECs on the inner surface of the hybrid vascular grafts were studied under the light and electron microscopy.Results Compared with fresh jugular vein,the hybrid vascular grafts had similar in vitro burst[(2040.83±239.17)vs(2248.33±300.89)mmHg,P ＞ 0.05]and sutureholding[(190.75±41.47)vs(169.15±41.84)g,P ＞ 0.05]strength.Confluent lining of vascular ECs on the inner surface of the hybrid vascular grafts was observed under the light and electron microscopy,and ECs coverage rate was(99.2±0.5)%(n = 4)after 7 days of the culture.Conclusion The hybrid vascular graft provides structural basis for vascular ECs seeding. Key words: Tissue engineering; Blood vessel; Porcine; Fibrin; Endothelialization

Tissue-Engineered Small-Caliber Vascular Graft Based on a Novel Biodegradable Composite Fibrin-Polylactide Scaffold

Small-caliber vascular grafts (< or =5 mm) constructed from synthetic materials for coronary bypass or peripheral vascular repair below the knee have poor patency rates, while autologous vessels may not be available for harvesting. The present study aimed to create a completely autologous small-caliber vascular graft by utilizing a bioabsorbable, macroporous poly(L/D)lactide 96/4 [P(L/D)LA 96/4] mesh as a support scaffold system combined with an autologous fibrin cell carrier material. A novel molding device was used to integrate a P(L/D)LA 96/4 mesh in the wall of a fibrin-based vascular graft, which was seeded with arterial smooth muscle cells (SMCs)/fibroblasts and subsequently lined with endothelial cells. The mold was connected to a bioreactor circuit for dynamic mechanical conditioning of the graft over a 21-day period. Graft cell phenotype, proliferation, extracellular matrix (ECM) content, and mechanical strength were analyzed. alpha-SMA-positive SMCs and fibroblasts deposited ECM proteins into the graft wall, with a significant increase in both cell number and collagen content over 21 days. A luminal endothelial cell lining was evidenced by vWf staining, while the grafts exhibited supraphysiological burst pressure (>460 mmHg) after dynamic cultivation. The results of our study demonstrated the successful production of an autologous, biodegradable small-caliber vascular graft in vitro, with remodeling capabilities and supraphysiological mechanical properties after 21 days in culture. The approach may be suitable for a variety of clinical applications, including coronary artery and peripheral artery bypass procedures.

Preliminary Results of Small Arterial Substitute Performed with a New Cylindrical Biomaterial Composed of Bacterial Cellulose

Tissue-engineered blood vessels (TEBVs) represent an innovative approach for overcoming reconstructive problems associated with extended vascular diseases by providing small-calibre vascular grafts. This study aimed to evaluate a novel biomaterial of bacterially synthesised cellulose (BC) as a potential scaffold for TEBV. Highly crystalline cellulose was produced by a bacterium (Acetobacter xylinum) using glucose as a source of carbon. Using a patented process, hollow-shaped segments of BC were created with a length of 10mm, an inner diameter of 3.0-3.7mm and a wall thickness of 0.6-1.0mm. These grafts were used to replace the carotid arteries of eight pigs, and after a follow-up period of 3 months, the grafts were removed and analysed, both macro- and microscopically. Seven grafts (87.5%) remained patent, whereas one graft was found to be occluded. Scanning electron microscopic examination revealed rapid re-cellularisation by recipient endothelial cells. Light microscopic examination showed a three-layered wall structure of the BC segments, with cellulose still being present in the media. These data indicate that the innovative BC-engineering technique results in the production of stable vascular conduits, which exhibit attractive properties for their use in future TEBV programmes for vascular surgery.

Artificial vascular implants from bacterial cellulose: preliminary results of small arterial substitutes

The biomaterial bacterial cellulose (BC) represents an innovative approach for overcoming reconstructive problems associated with extended vascular diseases by providing small caliber vascular grafts (diameter 1.0-3.7, length 5.0-10.0, and wall-thickness 0.7 mm). In a first microsurgical study, the BC implants were attached in an artificial defect of the carotid artery of rats for 1 year. These long term results show the incorporation of the BC under formation of neointima and ingrowth of active fibroblasts. In a second study, the grafts were used to replace the carotid arteries of pigs. After 3 months, these grafts were removed and analyzed both macro- and microscopically. Seven grafts (87.5%) were patent whereas one graft was found occluded. These data indicate that the innovative BC engineering technique results in the production of stable vascular conduits and confirm a highly attractive approach to in vivo tissue engineered blood vessels as part of programs in cardiovascular surgery.

Development of a Composite Degradable/Nondegradable Tissue‐engineered Vascular Graft

The present study aimed to determine the feasibility of constructing a reinforced autologous vascular graft by combining the advantages of fibrin gel as an autologous cell carrier material with the inherent mechanical strength of an integrated mesh structure. It was hypothesized that the mesh and dynamic culture conditions could be combined to generate mechanically stable and implantable vascular grafts within a shorter cultivation period than traditional methods. A two-step moulding technique was developed to integrate a polyvinylidene fluoride (PVDF) mesh (pore size: 1-2 mm) in the wall of a fibrin-based vascular graft (I.D. 5 mm) seeded with carotid myofibroblasts. The graft was cultured under increasing physiological flow conditions for 2 weeks. Histology, burst strength, and suture retention strength were evaluated. Cell growth and tissue development was excellent within the fibrin gel matrix surrounding the PVDF fibers, and tissue structure demonstrated remarkable similarity to native tissue. The grafts were successfully subjected to physiological flow rates and pressure gradients from the outset, and mechanical properties were enhanced by the mesh structure. Mean suture retention strength of the graft tissue was 6.3 N and the burst strength was 236 mm Hg. Using the vascular composite graft technique, the production of tissue engineered, small-caliber vascular grafts with good mechanical properties within a conditioning period of 14 days is feasible.

In situ tissue regeneration using a novel tissue-engineered, small-caliber vascular graft without cell seeding

Various types of natural and synthetic scaffolds with arterial tissue cells or differentiated stem cells have recently attracted interest as potential small-caliber vascular grafts. It was thought that the synthetic graft with the potential to promote autologous tissue regeneration without any seeding would be more practical than a seeded graft. In this study, we investigated in situ tissue regeneration in small-diameter arteries using a novel tissue-engineered biodegradable vascular graft that did not require ex vivo cell seeding. Small-caliber vascular grafts (4 mm in diameter) were fabricated by compounding a collagen microsponge with a biodegradable woven polymer tube that was constructed in a plain weave pattern with a double layer of polyglycolic acid (core) and poly-L-lactic acid (sheath) fibers. We implanted these tissue-engineered vascular grafts bilaterally into the carotid arteries of mongrel dogs (body weight, 20-25 kg). No anticoagulation regimen was used after implantation. We sacrificed the dogs 2, 4, 6, and 12 months (n = 4 in each group) after implantation and evaluated the explants histologically and biochemically. All of the tissue-engineered vascular grafts were patent with no signs of thrombosis or aneurysm at any time. Histologic and biochemical examinations showed excellent in situ tissue regeneration with an endothelial cell monolayer, smooth muscle cells, and a reconstructed vessel wall with elastin and collagen fibers. Our study indicated that this novel tissue-engineered vascular graft promoted in situ tissue regeneration and did not require ex vivo cell seeding, thereby conferring better patency on small-caliber vascular prostheses.

Decellularized ureter for tissue-engineered small-caliber vascular graft

Previous attempts to create small-caliber vascular prostheses have been limited. The aim of this study was to generate tissue-engineered small-diameter vascular grafts using decellularized ureters (DUs). Canine ureters were decellularized using one of four different chemical agents [Triton-X 100 (Tx), deoxycholate (DCA), trypsin, or sodium dodecyl sulfate (SDS)] and the histology, residual DNA contents, and immunogenicity of the resulting DUs were compared. The mechanical properties of the DUs were evaluated in terms of water permeability, burst strength, tensile strength, and compliance. Cultured canine endothelial cells (ECs) and myofibroblasts were seeded onto DUs and evaluated histologically. Canine carotid arteries were replaced with the EC-seeded DUs (n = 4). As controls, nonseeded DUs (n = 5) and PTFE prostheses (n = 4) were also used to replace carotid arteries. The degree of decellularization and the maintenance of the matrix were best in the Tx-treated DUs. Tx-treated and DCA-treated DUs had lower remnant DNA contents and immunogenicity than the others. The burst strength of the DUs was more than 500 mmHg and the maximum tensile strength of the DUs was not different to that of native ureters. DU compliance was similar to that of native carotid artery. The cell seeding test resulted in monolayered ECs and multilayered alpha-smooth muscle actin-positive cells on the DUs. The animal implantation model showed that the EC-seeded DUs were patent for at least 6 months after the operation, whereas the nonseeded DUs and PTFE grafts become occluded within a week. These results suggest that tissue-engineered DUs may be a potential alternative conduit for bypass surgery.

A novel bioengineered small-caliber vascular graft incorporating heparin and sirolimus: Excellent 6-month patency

A bioengineered microporous polycarbonate-siloxane polyurethane graft has been developed for coronary artery bypass grafting. Biological agents can be impregnated into its absorbable collagen and hyaluronan microstructure and stable macrostructure to promote patency. The objective of this study was to examine the in vivo biological performance and biomechanical characteristics of this graft. Three types of graft (3.6-mm internal diameter, 24-mm length) were manufactured: heparin alone (H) grafts, heparin and sirolimus (HS) grafts, and grafts without any drug impregnation (C). All H and HS grafts were impregnated with 54 U of heparin in the microstructure for early elution to prevent acute graft thrombosis and 56 U of heparin in the macrostructure to prevent late thrombosis. In addition to the heparin, the HS graft was impregnated with 2.1 mg of sirolimus in the macrostructure for prolonged elution to inhibit intimal hyperplasia. All grafts (3.6-mm internal diameter, 24-mm length) were implanted into the abdominal aortas of rabbits (n = 55). Expanded polytetrafluoroethylene grafts (4.0-mm internal diameter, 24-mm length; n = 7) were implanted as controls. At 1, 3, and 6 months after surgery, the grafts were removed for histologic, scanning electron microscopic, immunohistochemical, and biomechanical evaluations. The patency rate was 100% in the H, HS, and C grafts at each time point. Although the expanded polytetrafluoroethylene grafts were patent at 1 and 3 months after surgery, 1 of 2 grafts (50%) were occluded at 6 months. None of the H or HS grafts had any stenosis or thrombus. Scanning electron microscopic examination proved that endothelial cells propagated smoothly from the anastomotic sites after 6 months in the H and HS grafts in comparison with the expanded polytetrafluoroethylene grafts, which had rare endothelialization. Neointima formation was inhibited in the HS graft compared with the H or C graft at 6 months (123 +/- 126 microm vs 206 +/- 158 microm or 202 +/- 67 microm; P < .05). In addition, the H, HS, and C grafts had greater cellular infiltration inside the graft than the expanded polytetrafluoroethylene grafts. All grafts except the expanded polytetrafluoroethylene graft had marked neocapillary formation 6 months after surgery. The graft compliance between 80 and 120 mm Hg was 6.0% +/- 2.5% and 6.2% +/- 0.9% at 6 months in the H and HS grafts, respectively. The graft macrostructure was unchanged according to the biomechanical evaluation in the H and HS grafts. A unique drug-eluting graft had excellent patency throughout the 6 months after implantation. The heparin-sirolimus graft encouraged luminal endothelialization without excessive intimal hyperplasia. This graft performed significantly better than the expanded polytetrafluoroethylene graft. This graft has the potential to become an implantable graft for coronary artery bypass grafting.

Preclinical development of tissue engineered vascular substitutes by means of re-endothelialisation of human decellularised veins

Objective: The Creation of human vascular substitutes using a decellularised scaffold and autologous endothelial cells. This research is clinically relevant with regard to the development of small calibre vascular grafts for CABG and venous replacement.

Potential of baboon endothelial progenitor cells for tissue engineered vascular grafts

Thrombosis and intimal hyperplasia limit the usefulness of small caliber vascular grafts. While some improvements have been reported for grafts seeded with mature endothelial cells (EC), the harvesting of ECs from autologous sources, for example, veins or adipose tissue, remains problematic. More recently, endothelial progenitor cells (EPCs) have been considered a promising source of ECs because EPCs can be readily isolated from whole blood then rapidly expanded in vitro. Additionally, EPCs are increasingly recognized to play important roles in hemostasis, angiogenesis, and arterial injury repair. However, the characterization of EPCs in relevant animal models remains poorly defined. Accordingly, we have characterized the isolation, growth, and functional characteristics of Baboon EPCs (BaEPCs) to evaluate their potential for an autologous cell source for tissue engineered vascular grafts. BaEPCs were successfully cultured from the peripheral blood with an average population doubling time of 1.17 +/- 0.43 days. While the BaEPCs were positive for typical EC markers of vWF, CD31, VE-cadherin, VEGF-R2, Thrombomodulin, and E-selectin, there was reduced eNOS expression. The BaEPCs cell body and actin filaments align in the direction of flow typical of mature ECs. Thus while the lack of eNOS expression is worthy of investigation, EPCs are an attractive cell source for tissue engineered vascular grafts and the baboon model has great potential for continuing evaluations of these cells.

Peptides Derived from Fibronectin Type III Connecting Segments Promote Endothelial Cell Adhesion but Not Platelet Adhesion: Implications in Tissue-Engineered Vascular Grafts

The development of a completely tissue-engineered small-caliber prosthesis suitable for incorporation into an in vivo vascular network is fraught with many challenges, including overcoming resistance to endothelialization and susceptibility to thrombogenesis. In this work, recombinant human fibronectin-derived low-molecular-weight peptide fragments were studied for their ability to promote cell type-specific alpha(4) integrin-mediated adhesion. Two populations of primary human endothelial cells were examined and found to express alpha(4) integrin receptors on their surfaces; on the contrary, human platelets were not found to be expressers of alpha(4) integrins. A peptide fragment isolated from the variably spliced human fibronectin type III connecting segment-1 (CS-1) domain was determined to mediate statistically significant endothelial cell alpha(4) integrin-mediated adhesion. In contrast, the fibronectin type III CS-1 fragment did not support human platelet adhesion under physiological fluid shear conditions, although fully intact human fibronectin molecules supported shear-induced platelet adhesion. This suggests that platelets bind to fibronectin in regions not encompassing the CS-1 domain. In conclusion, this work has demonstrated that the low-molecular-weight peptide CS-1 could serve as a cell-selective adhesion mediator in the engineering of a more-compatible small-caliber vascular graft lumen interface.

Autologous fibrin-coated small-caliber vascular prostheses improve antithrombogenicity by reducing immunologic response

We have recently developed a thrombin-free fibrin-coated vascular prosthesis that has a high performance rate in producing graft antithrombogenicity. We hypothesized that autologous, compared with xenologous, fibrin coatings could improve the antithrombogenicity of grafts by reducing immunologic response. Autologous fibrin-coated vascular prostheses and/or xenologous fibrin-coated vascular prostheses (internal diameter, 2 mm; length, 2.5 cm) were implanted in the bilateral carotid arteries of 50 Japanese white rabbits. They were classified into 2 groups by the selection of grafts in the individual: group I (autologous fibrin-coated vascular prosthesis and xenologous fibrin-coated vascular prosthesis); and group II (group IIa: both autologous fibrin-coated vascular prostheses, or group IIx: both xenologous fibrin-coated vascular prostheses). During a maximum of 180 days after implantation, we evaluated the thrombotic, inflammatory, and immunologic responses associated with both types of graft. All grafts were patent at each end point. In group I, both platelet deposition and anti-graft antibodies in autologous fibrin-coated vascular prostheses were significantly less than those in xenologous fibrin-coated vascular prostheses until postoperative day 30. At postoperative day 10, there were significantly fewer CD45-positive infiltrating cells in autologous fibrin-coated vascular prostheses, and intercellular adhesion molecule-1, vascular cell adhesion molecule-1, and nuclear factor-kappa B expression in autologous fibrin-coated vascular prostheses were less than those in xenologous fibrin-coated vascular prostheses. The neointimal hyperplasia in autologous fibrin-coated vascular prostheses was significantly decreased at postoperative day 180. In group II, serial changes of serum levels of immunoglobulin M, immunoglobulin G, interleukin-1beta, and tissue-type plasminogen activator/plasminogen activator inhibitor-1 ratio in autologous fibrin-coated vascular prostheses were significantly less than those in xenologous fibrin-coated vascular prostheses. In both grafts, platelet deposition significantly correlated with serum immunoglobulin G level and tissue-type plasminogen activator/plasminogen activator inhibitor-1 ratio. These findings suggest that autologous fibrin coating in thrombin-free fibrin-coated vascular prostheses improve antithrombogenicity by reducing immunologic response and have a potential for clinical use in hybrid small-caliber vascular grafts.