Engineering of bypass conduits to improve patency

Effect of hyaluronic acid incorporation method on the stability and biological properties of polyurethane-hyaluronic acid biomaterials

The high failure rate of small diameter vascular grafts continues to drive the development of new materials and modification strategies that address this clinical problem, with biomolecule incorporation typically achieved via surface-based modification of various biomaterials. In this work, we examined whether the method of biomolecule incorporation (i.e., bulk versus surface modification) into a polyurethane (PU) polymer impacted biomaterial performance in the context of vascular applications. Specifically, hyaluronic acid (HA) was incorporated into a poly(ether urethane) via bulk copolymerization or covalent surface tethering, and the resulting PU-HA materials characterized with respect to both physical and biological properties. Modification of PU with HA by either surface or bulk methods yielded materials that, when tested under static conditions, possessed no significant differences in their ability to resist protein adsorption, platelet adhesion, and bacterial adhesion, while supporting endothelial cell culture. However, only bulk-modified PU-HA materials were able to fully retain these characteristics following material exposure to flow, demonstrating a superior ability to retain the incorporated HA and minimize enzymatic degradation, protein adsorption, platelet adhesion, and bacterial adhesion. Thus, despite bulk methods rarely being implemented in the context of biomolecule attachment, these results demonstrate improved performance of PU-HA upon bulk, rather than surface, incorporation of HA. Although explored only in the context of PU-HA, the findings revealed by these experiments have broader implications for the design and evaluation of vascular graft modification strategies.

Elastic, double-layered poly (l-lactide-co-ϵ-caprolactone) scaffold for long-term vascular reconstruction

Synthetic vessel grafts have been used as vascular substitutes for cardiovascular bypass procedures. In this study, we developed a novel tubular double-layered poly(l-lactide-co-ϵ-caprolactone) scaffold that did not require pretreatment with cell seeding by promoting autologous tissue regeneration by inducing the proliferation and differentiation of endothelial and smooth muscle progenitor cells after implantation. The patency and mechanical properties were maintained for one year after implantation, although 95% of the poly(l-lactide-co-ϵ-caprolactone) scaffolds had degraded. After this period, there was a lining of endothelial cells, an accumulation of collagen and elastin, and the development of neovascularization inside the poly(l-lactide-co-ϵ-caprolactone).

Concise review: tissue-engineered vascular grafts for cardiac surgery: past, present, and future

In surgical repair for heart or vascular disease, it is often necessary to implant conduits or correct tissue defects. The most commonly used graft materials to date are (a) artificial grafts; (b) autologous tissues, such as pericardium and saphenous vein; (c) allografts; and (d) xenografts. However, none of these four options offer growth potential, and all are associated with varying levels of thrombogenicity and susceptibility to infection. The lack of growth potential of these four options is particularly important in pediatric cardiac surgery, where patients will often outgrow their vascular grafts and require additional operations. Thus, developing a material with sufficient durability and growth potential that will function as the child grows older will eliminate the need for reoperation and significantly reduce morbidity and mortality of some types of congenital heart defects. Vascular tissue engineering is a relatively new field that has undergone enormous growth over the last decade. The goal of vascular tissue engineering is to produce neovessels and neo-organ tissue from autologous cells using a biodegradable polymer as a scaffold. The most important advantage of tissue-engineered implants is that these tissues can grow, remodel, rebuild, and respond to injury. Once the seeded autologous cells have deposited an extracellular matrix and the original scaffold is biodegraded, the tissue resembles and behaves as native tissue. When tissue-engineered vascular grafts are eventually put to use in the clinical arena, the quality of life in patients after surgery will be drastically improved.

Exploring cell compatibility of a fibronectin-functionalized physically crosslinked poly(vinyl alcohol) hydrogel

Physically crosslinked poly(vinyl alcohol) (PVA) hydrogels prepared using a low-temperature thermally cycled process have tunable mechanical properties that fall within the range of soft tissues, including cardiovascular tissue. An approach to render it hemocompatible is by endothelization, but its hydrophilic nature is not conducive to cell adhesion and spreading. We investigated the functionalization reaction of this class of PVA hydrogel with fibronectin (FN) for adhesion and spreading of primary porcine radial artery cells and vascular endothelial cells. These are cells relevant to small-diameter vascular graft development. FN functionalization was achieved using a multistep reaction, but the activation step involving carbonyl diimidazole normally required for chemically crosslinked PVA was found to be unnecessary. The reaction resulted in an increase in the elastic modulus of the PVA hydrogel but is still well within the range of cardiovascular tissue. Confocal microscopy confirmed the adhesion and spreading of both cell types on the PVA-FN surfaces, whereas cells failed to adhere to the PVA control. This is a first step toward an alternative for the realization of a synthetic replacement small-diameter vascular graft.

Adipose-derived stem cells for clinical applications: a review

The use of stem cells derived from adipose tissue as an autologous and self-replenishing source for a variety of differentiated cell phenotypes, provides a great deal of promise for reconstructive surgery. In this article, we review available literature encompassing methods of extraction of pluripotent adipose stem cells (ASCs) from lipoaspirate locations, their storage, options for culture, growth and differentiation, cryopreservation and its effect on stem cell survival and proliferation, and new technologies involving biomaterials and scaffolds. We will conclude by assessing potential avenues for developing this incredibly promising field.

AAA stent-grafts: past problems and future prospects

Endovascular aneurysm repair (EVAR) has quickly gained popularity for infrarenal abdominal aortic aneurysm repair during the last two decades. The improvement of available EVAR devices is critical for the advancement of patient care in vascular surgery. Problems are still associated with the grafts, many of which can necessitate the conversion of the patient to open repair, or even result in rupture of the aneurysm. This review attempts to address these problems, by highlighting why they occur and what the failings of the currently available stent grafts are, respectively. In addition, the review gives critical appraisal as to the novel methods required for dealing with these problems and identifies the new generation of stent grafts that are being or need to be designed and constructed in order to overcome the issues that are associated with the existing first- and second-generation devices.

Development of decellularized human umbilical arteries as small-diameter vascular grafts

OBJECTIVE

Developing a tissue-engineered small-diameter (<6mm) vascular graft for reconstructive surgery has remained a challenge for the past several decades. This study was conducted to develop a decellularized umbilical artery and to evaluate its composition, endothelial cell compatibility, mechanical properties, and in vivo stability for potential use as a small-diameter vascular graft.

METHODS AND RESULTS

Human umbilical arteries were isolated and decellularized by incubation in CHAPS and sodium dodecyl sulfate buffers followed by incubation in endothelial growth media-2. Decellularized umbilical arteries were completely devoid of cellular and nuclear material while retaining the integrity of extracellular collagenous matrix. The mechanical strength of the decellularized umbilical artery as assessed by its burst pressure in vitro showed no significant change from its native form. Decellularized umbilical arteries supported endothelial adherence as indicated by the re-endotheliazation with a monolayer of human umbilical vein endothelial cells. Furthermore, decellularized vessels that were implanted into nude rats as abdominal aorta interposition grafts remained mechanically intact and patent for up to 8 weeks.

CONCLUSION

Decellularized human umbilical arteries preserved the extracellular matrix, supported endothelialization, and retained function in vivo for up to 8 weeks. These properties suggest the potential use of decellularized umbilical arteries as small-diameter vascular grafts.

Smooth muscle alpha-actin and calponin expression and extracellular matrix production of human coronary artery smooth muscle cells in 3D scaffolds

For a tissue-engineered coronary artery substitute to be a viable clinical option in the treatment of vascular diseases, it is necessary to use tissue-specific human cells. Coronary artery smooth muscle cells are the main resident cells in the tunica media of arteries. In this work, we examined the behavior and differentiation state of human coronary artery smooth muscle cells (HCASMCs) when cultured on 3D polyurethane scaffolds to fabricate hybrid vascular tissues. As the mechanical strength of the scaffold is an important element in engineered hybrid vascular substitutes, porous 3D polyurethane scaffolds fabricated using paraffin spheres and ammonium chloride particles were tested for their mechanical properties both in tension and in compression. The use of ammonium chloride particles as porogen generated scaffolds with superior mechanical properties, which are suitable for vascular tissue engineering. When seeded on uncoated, fibronectin-coated, and Matrigel-coated scaffolds, HCASMCs were well spread and started producing collagen as judged by histochemical analysis but appeared to lack elastin production. Fibronectin coating appeared to promote the infiltration of HCASMCs into the scaffold better than Matrigel coating but did not appear to affect the expression of collagen and elastin. Western blot analyses after successful cell recovery from the scaffolds indicated that HCASMCs, after culturing for 4 and 7 days, expressed similar amounts of smooth muscle alpha-actin and calponin regardless of extracellular matrix coating. Taken together, our data showed that the behavior and differentiation phenotype of HCASMCs can be analyzed after culture in 3D polyurethane scaffolds to establish appropriate conditions that will favor the fabrication of hybrid-engineered vascular substitutes.

Vascular Grafts and the Endothelium

This article discusses the importance of the endothelium for successful vascular grafts derived from both native arteries and synthetic materials. It also discusses the fundamental strategies to endothelialize synthetic grafts in animal experiments and in the clinic, as well as the use of endothelial progenitor cells (EPCs), bone marrow-derived cells, and mesothelium as endothelial substitutes.

Assessment of the potential of progenitor stem cells extracted from human peripheral blood for seeding a novel vascular graft material

OBJECTIVE

A novel nanocomposite has recently been developed based on polyhedral oligomeric silsesquioxane attached by direct reaction onto a urethane segment, as a potential vascular graft material; its trade name is UCL-Nano. The UCL-Nano has been demonstrated to have similar viscoelastic properties to the walls of a natural artery, to be resistant to degradation and to be able to sustain endothelial cell seeding. Human peripheral blood contains both circulating endothelial cells and endothelial progenitor cells, which may be suitable for conduit seeding. The aim of this study was to develop a system with the potential to deliver an endothelial cell-seeded bypass graft in a realistic time frame.

MATERIALS AND METHODS

Endothelial progenitor cells and circulating endothelial cells were isolated from human peripheral blood and were characterized by fluorescent-activated cell sorting, reverse transcriptase-polymerase chain reaction and immunohistochemistry. Isolated cells were seeded on nanocomposite and were maintained in culture for 35 days.

RESULTS

The UCL-Nano was successfully seeded with cells and a confluent cell layer was achieved after 14-day culture. Cells remained viable and confluent on the nanocomposite for 35 days.

CONCLUSION

In conclusion, these results suggest that this process has potential both for a realistic and achievable two-stage seeding process for vascular bypass grafts and for the potential development of a device, with the aim of achieving in situ seeding once implanted.

The development of tissue-engineered grafts for reconstructive cardiothoracic surgical applications

Surgical correction of congenital heart defects often requires the use of valves, patches, or conduits to establish anatomic continuity. Homografts, xenografts, or mechanical prosthetic devices are frequently implanted during these surgical procedures. These grafts however lack growth potential, are associated with increased risk of thrombosis and infection and have limited durability, thus increasing the morbidity and mortality of their application in pediatric cardiac surgery. These limitations are being addressed through the development of living, biologic tissue-engineered valves, patches, and conduits. Pilot studies and phase 1 clinical trials are currently underway to evaluate their feasibility, safety, and efficacy. The optimal scaffold, cell source, and conditioning parameters, however, still remain to be determined and are areas of active research.

Nitric oxide: what a vascular surgeon needs to know

Atherosclerosis in the form of peripheral arterial disease results in significant morbidity and mortality. Surgical treatment options for peripheral arterial disease include angioplasty with and without stenting, endarterectomy, and bypass grafting. Unfortunately, all of these procedures injure the vascular endothelium, which impairs its ability to produce nitric oxide (NO) and ultimately leads to neointimal hyperplasia and restenosis. To improve on current patency rates after vascular procedures, investigators are engaged in research to improve the bioavailability of NO at the site of vascular injury in an attempt to reduce the risk of thrombosis and restenosis after successful revascularization. This article reviews some of the previous research that has aimed to improve NO bioavailability after vascular procedures whether through systemic or local delivery, as well as to describe some of the NO-releasing products that are currently undergoing study for use in clinical practice.

Development of small-diameter vascular grafts

INTRODUCTION

Cardiovascular disease, including coronary artery and peripheral vascular pathologies, is the leading cause of mortality in the United States and Western countries. There is a pressing need to develop small-diameter vascular vessels for bypass surgery and other vascular reconstructive procedures. Tissue engineering offers the prospect of being able to meet the demand for replacement of diseased vessels. Significant advances have been made in recent studies and provide confidence that success is attainable. For instance, a completely cellular approach culturing cells into tissue sheets and wrapping these layers was able to form a layered cellular vascular graft with impressive strength.

METHODS/RESULTS

In our experiments, decellularization and heparin immobilization grafts from porcine tissues implanted in a canine model could be repopulated from the host cells, indicating the grafts' potential to develop into living tissues that can adapt and respond to changes in the body.

CONCLUSIONS

This review summarizes the current status of vascular grafts used clinically, updates the most recent developments on vascular tissue engineering, and discusses the challenges for the future.

Applying elastic fibre biology in vascular tissue engineering

For the treatment of vascular disease, the major cause of death in Western society, there is an urgent need for tissue-engineered, biocompatible, small calibre artery substitutes that restore biological function. Vascular tissue engineering of such grafts involves the development of compliant synthetic or biomaterial scaffolds that incorporate vascular cells and extracellular matrix. Elastic fibres are major structural elements of arterial walls that can enhance vascular graft design and patency. In blood vessels, they endow vessels with the critical property of elastic recoil. They also influence vascular cell behaviour through direct interactions and by regulating growth factor activation. This review addresses physiological elastic fibre assembly and contributions to vessel structure and function, and how elastic fibre biology is now being exploited in small diameter vascular graft design.

Cytomics - importance of multimodal analysis of cell function and proliferation in oncology

Cancer is a highly complex and heterogeneous disease involving a succession of genetic changes (frequently caused or accompanied by exogenous trauma), and resulting in a molecular phenotype that in turn results in a malignant specification. The development of malignancy has been described as a multistep process involving self-sufficiency in growth signals, insensitivity to antigrowth signals, evasion of apoptosis, limitless replicative potential, sustained angiogenesis, and finally tissue invasion and metastasis. The quantitative analysis of networking molecules within the cells might be applied to understand native-state tissue signalling biology, complex drug actions and dysfunctional signalling in transformed cells, that is, in cancer cells. High-content and high-throughput single-cell analysis can lead to systems biology and cytomics. The application of cytomics in cancer research and diagnostics is very broad, ranging from the better understanding of the tumour cell biology to the identification of residual tumour cells after treatment, to drug discovery. The ultimate goal is to pinpoint in detail these processes on the molecular, cellular and tissue level. A comprehensive knowledge of these will require tissue analysis, which is multiplex and functional; thus, vast amounts of data are being collected from current genomic and proteomic platforms for integration and interpretation as well as for new varieties of updated cytomics technology. This overview will briefly highlight the most important aspects of this continuously developing field.

Properties of the Human Umbilical Vein as a Living Scaffold for a Tissue-Engineered Vessel Graft

Umbilical cords are usually discarded after delivery, even though they contain a set of functional vessels. We investigated whether the human umbilical vein (HUV) is suitable as a storable scaffold for the tissue engineering of small-caliber vessel grafts. Isolated HUVs were cryopreserved by freezing or vitrification. The reaction of the vessels to vasoactive compounds and the mechanical properties were determined in an organ bath. Mitochondrial metabolism, release of antithrombotic compounds, and platelet adhesion were measured on the luminal vessel surface. Seeding with endothelial cells was tested on denuded HUVs. The vessels showed a weak response to norepinephrine but were readily contracted by serotonin and by the thromboxane A2 mimetic U46619. Endothelium-dependent vasorelaxation was weak, reaching significance only for histamine. However, the vessels relaxed to sodium nitroprusside, and to acetylcholine if sandwiched with human saphenous vein. Cryopreservation did not change the mechanical properties in the relevant tension range. Vasoconstriction to potassium chloride and serotonin were reduced after freezing (22.9+/-7.6%, 27.7+/-10.2%) and after vitrification (2.6+/-5.8%, 4.3+/-7.1%). The mitochondrial metabolism was also attenuated after freezing (57.9+/-25.9%) and after vitrification (21.7+/-6.7%). Prostacyclin release was elevated after both cryopreservation procedures (4.0-fold, 3.9-fold), whereas there was no significant change in the adhesion of platelets. Denuded HUVs could readily be seeded with isolated endothelial cells before and after freezing. We conclude that HUV is suitable as a storable living scaffold with antithrombogenic properties.

PEG-hirudin/iloprost Coating of Small Diameter ePTFE Grafts Effectively Prevents Pseudointima and Intimal Hyperplasia Development

OBJECTIVES

Small diameter PTFE grafts are prone to thrombosis and intimal hyperplasia development. Heparin graft coating has beneficial effects but also potential drawbacks. The purpose of this study was to evaluate the experimental efficacy of PEG-hirudin/iloprost coated small caliber PTFE grafts.

METHODS

Thirty-six femoro-popliteal ePTFE grafts (expanded polytetrafluoroethylene, diameter 4 mm) were inserted into 18 pigs. Grafts were randomised individually for each leg and grouped for 3 groups. Group I consisted of native ePTFE grafts, group II were grafts coated with a polylactide polymer (PLA) without drugs and group III grafts were coated with PLA containing a polyethylene glycol (PEG)-hirudin/iloprost combination. The follow-up period was 6 weeks. Patency rates were calculated and development of pseudointima inside the grafts was noted. Thickness of intimal hyperplasia at the distal anastomoses was measured using light microscopy.

RESULTS

Patency rates for group I were 6/9 (67%), for group II 9/10 (90%) and 12/12 (100%) for group III. In groups I and II there was a significant reduction of blood flow proximal to the graft at graft harvest, to 29+/-12 and 28+/-20 ml/min respectively (both p<0.01 versus preoperative value), whilst in group III blood flow, 99+/-21 ml/min, remained at the preoperative level. Subtotal stenosis due to development of pseudointima was noted in each of the native and PLA coated grafts but not in group III grafts. Intimal hyperplasia at the distal anastomosis was lowest in group III.

CONCLUSIONS

The PEG-hirudin/iloprost coating of ePTFE prostheses effectively reduced pseudointima and intimal hyperplasia development and led to superior graft patency.

Slide-based cytometry for cytomics--a minireview

In the postgenomic era, to gain the most detailed quantitative data from biological specimens has become increasingly important in the emerging new fields of high-content and high-throughput single-cell analysis for systems biology and cytomics. Areas of research and diagnosis with the demand to virtually measure "anything" in the cell include immunophenotyping, rare cell detection and characterization in the case of stem cells and residual tumor cells, tissue analysis, and drug discovery. Systemic analysis is also a prerequisite for predictive medicine by genomics, proteomics, and cytomics. This issue of Cytometry Part A is dedicated to innovative concepts of system wide single cells analysis and manipulation, new technologies, data analysis and display, and, finally, quality assessment. The manuscripts to these chapters are provided by cutting edge experts in the fields. This overview will briefly highlight the most important aspects of this continuously developing field.

Thrombogenicity and Related Biological Properties of Heparin Bonded Collagen Coated Polyester and Human Umbilical Vein Prosthetic Vascular Grafts

BACKGROUND

Multiple factors contribute to the process of prosthetic graft failure. Some of them are specifically related to the biological behavior of the used materials. To pursue the ideal substitute for the autologous vein graft, many materials have been taken into consideration. Of these, polyester (Dacron) and human umbilical vein (HUV, Dardik) bypass grafts have gained much attention in vascular surgical practice over the years. This study compares the results of both in vivo and in vitro investigations on graft thrombogenicity and neo-intimal formation in collagen-coated heparin bonded Dacron and in HUV bypass grafts. It is an adjunct to our clinical comparison of graft materials in infrainguinal arterial reconstruction.

METHODS

In 12 adult Beagle dogs, a patch was sewn onto the abdominal aorta (Dacron, n = 6; HUV, n = 6). At defined interval times, thrombocyte aggregation was measured with nuclear imaging of 99mTechnetium labeled platelets. Post-mortem histological analysis of the interface between the native vessel wall and the patch was performed in all animals.

RESULTS

At 4 h (2.67, SD = 0.77) and after 2 weeks (2.21, SD = 0.28) after implantation, significantly higher thrombogenicity was measured in the HUV grafts compared to Dacron grafts (1.98, SD = 0.10 and 1.98, SD = 0.11, P = 0.02 and 0.025, respectively). At 4 weeks, no significant difference could be found (HUV, 2.26; SD = 0.29; Dacron, 2.11; SD = 0.16; P = 0.23). Measurement of 'neo-intimal' thickness after explantation of the patch at 28 days after the initial procedure showed a significant difference: in HUV grafts the mean thickness of the inner lining was 0.76 mm (SD = 0.50), compared to 0.16 mm (SD = 0.10) in the Dacron grafts (P = 0.013).

CONCLUSION

HUV grafts showed a higher thrombogenicity at 4 h and 2 weeks after insertion of the graft compared to Dacron grafts. At 4 weeks this difference is not present. After 28 days the inner ('neo-intimal') lining is significantly more pronounced in HUV grafts than in Dacron grafts.

Surgical treatment of coronary multivessel disease

Coronary artery bypass grafting has had a significant impact on the treatment of angina, and has been the 'gold standard' since 1969. Its use and efficacy has been increased by revascularization in cardiac arrest and the use of the internal mammary artery. In parallel, catheter techniques have evolved by means of balloon dilatation and additional stenting. This has effected the referral to surgery despite the development of new arterialization techniques and minimally invasive surgery. As competing techniques, an acceptable equilibrium between surgery and stenting will be found within the next years.

Vitreous cryopreservation maintains the viscoelastic property of human vascular grafts

Assess the effects of cryopreservation (cryo) and vitrification (vitro) on the viscoelastic properties of blood vessels. Human external Iliac artery vessels were harvested from liver organ donors (n=8). In each case the vessel was segmented into 3 equal parts, which were randomly placed in one of 3 categories: Fresh (stored in 4 degrees C UW for 6 h), Cryo (Placed in 10% Dulbecco's modified Eagle medium (DMEM) and slowly frozen to -196 degrees C), or Vitro (Placed in 40% DMEM and rapidly cooled to -196 degrees C). A pulsatile flow circuit was used to perfuse arterial segments at physiological pulse pressure and flow. Intraluminal pressure was measured using a Millar Mikro-tip catheter transducer, and vessel wall motion was determined with duplex ultrasonography coupled with a novel echo-locked vessel wall tracking system. Diametrical compliance (DC), Petersons elastic modulus (Ep), and stiffness index (beta) were then calculated for each of the three groups over 3 mean pressure ranging from 40 to 80 mmHg. The change in the viscous component of arterial wall (lag phase angle, theta) was calculated from hysteresis plots. No significant changes were observed in the elastic properties of fresh and vitrified vessels (P>0.05 for each of DC, Ep, and beta). Similarly, variation in the wall viscosity between fresh and vitrified vessels appeared to be nonsignificant (theta=12.60+/-4.04 vs. 17.60+/-1.14, respectively). In contrast, statistical analysis of results obtained for cryopreserved vessels to the fresh vessels showed significant reduction in elastic parameter values. There was also a significant increase in the phase angle theta of the cryopreserved vessels (theta=24.30+/-6.32; P<0.001) compared with fresh vessel. Results suggest that vitrification maintains both elastic and viscous components of the mechanical properties of vascular grafts, which is positively correlated with their functional patency. In contrast, damage caused during cryopreservation significantly affects the overall tensile strength and elasticity of the vessel (i.e., Ep and beta), the dynamic properties (DC), and appears to significantly affect the viscous component of the vessel wall (theta), which is likely reduce the patency of the graft for transplantation purposes.

Systems biology and clinical cytomics: The 10th Leipziger Workshop and the 3rd International Workshop on Slide-Based Cytometry, Leipzig, Germany, April 2005

Despite very significant technical and software improvements in flow cytometry (FCM) since the 1980's, the demand for a cytometric technology combining both quantitative cell analysis and morphological documentation in Cytomics became evident. Improvements in microtechnology and computing permit nowadays similar quantitative and stoichiometric single cell-based high-throughput analyses by microscopic instruments, like Slide-Based Cytometry (SBC). SBC and related techniques offer unique tools to perform complex immunophenotyping, thereby enabling diagnostic procedures during early disease stages. Multicolor or polychromatic analysis of cells by SBC is of special importance not only as a cytomics technology platform but also because of low quantities of required reagents and biological material. The exact knowledge of the location of each cell on the slide permits repetitive restaining and reanalysis of specimens. Various separate measurements of the same specimen can be ultimately fused to one database increasing the information obtained per cell. Relocation and optical evaluation of cells as typical SBC feature, can be of integral importance for cytometric analysis, since artifacts can be excluded and morphology of measured cells can be documented. Progress in cell analytic: In the SBC, new horizons can be opened by the new techniques of structural and functional analysis with the high resolution from intracellular and membrane (confocal microscopy, nanoscopy, total internal fluorescence microscopy (TIRFM), and tissue level (tissomics), to organ and organism level (in vivo cytometry, optical whole body imaging). Predictive medicine aims at the detection of changes in patient's state prior to the manifestation of the disease or the complication. Such instances concern immune consequences of surgeries or noninfectious posttraumatic shock in intensive care patients or the pretherapeutic identification of high risk patients in cancer cytostatic therapy. Preventive anti-infectious or anti-shock therapy as well as curative chemotherapy in combination with stem cell transplantation may provide better survival chances for patient at concomitant cost containment. Predictive medicine-guided optimization of therapy could lead to individualized medicine that gives significant therapeutic effect and may lower or abrogate potential therapeutic side effects. The 10th Leipziger Workshop combined with the 3rd International Workshop on SBC aimed to offer new methods in Image- and Slide-Based Cytometry for solutions in clinical research. It moved towards practical applications in the clinics and the clinical laboratory. This development will be continued in 2006 at the upcoming Leipziger Workshop and the International Workshop on Slide-Based Cytometry.

Novel aspects of systems biology and clinical cytomics

The area of Cytomics and Systems Biology became of great impact during the last years. In some fields of the leading cytometric techniques it represents the cutting edge today. Many different applications/variations of multicolor staining were developed for flow- or slide-based cytometric analysis of suspensions and sections to whole animal analysis. Multispectral optical imaging can be used for studying immunological and tumorigenic processes. New methods resulted in the establishment of lipidomics as the systemic research of lipids and their behavior. All of these development push the systemic approach of the analysis of biological specimens to enhance the outcome in the clinic and in drug discovery programs.

In vivo regeneration of small‐diameter (2 mm) arteries using a polymer scaffold

The difficulty of obtaining significant long-term patency and good wall mechanical strength in vivo has been a significant obstacle in achieving small-diameter vascular prostheses. The aim of the present study was to develop a prosthetic graft that could perform as a small-diameter vascular conduit. Tubular structures of hyaluronan (HYAFF-11 tubules, 2 mm diameter, 1 cm length) were grafted in the abdominal aorta of 30 rats as temporary absorbable guides to promote regeneration of vascular structures. Performance was assessed by histology, immunohistochemistry, and ultra-structural analysis. These experiments resulted in three novel findings: 1) complete endothelialization of the tube's luminal surface occurred; 2) sequential regeneration of vascular components led to complete vascular wall regeneration 15 days after surgery; and 3) the biomaterial used created the ideal environment for the delicate regeneration process during the critical initial phases, yet its biodegradability allowed for complete degradation of the construct four months after implantation, at which time, a new artery remained to connect the artery stumps. This study assesses the feasibility to create a completely biodegradable vascular regeneration guide in vivo, able to sequentially orchestrate vascular regeneration events needed for very small artery reconstruction.

Advancing vascular tissue engineering: the role of stem cell technology

Atherosclerosis and heart disease are still the leading causes of morbidity and mortality worldwide. The lack of suitable autologous grafts has produced a need for artificial grafts but the patency of such grafts is limited compared to natural materials. Tissue engineering, whereby living tissue replacements can be constructed, has emerged as a solution to some of these difficulties. This, in turn, is limited by the availability of suitable cells from which to construct the vessels. The development of prosthesis using progenitor cells and switching these into endothelial cells is an important and exciting advance in the field of tissue engineering. Here, we describe recent developments in the use of stem cells for the development of replacement vessels. These paradigm shifts in vascular engineering now offer a new route for effective clinical therapy.

Tissue-engineered blood vessels: alternative to autologous grafts?

Although vascular bypass grafting remains the mainstay for revascularization for ischemic heart disease and peripheral vascular disease, many patients do not have healthy vessels suitable for harvest. Thus, prosthetic grafts made of synthetic polymers were developed, but their use is limited to high-flow/low-resistance conditions because of poor elasticity, low compliance, and thrombogenicity of their synthetic surfaces. To fill this need, several laboratories have produced in vivo or in vitro tissue-engineered blood vessels using molds or prosthetic or biodegradable scaffolds, but each artificial graft has significant problems. Recently, conduits have been grown in the peritoneal cavity of the same animals in which they will be grafted, ensuring no rejection, in the short time of 2 to 3 weeks. Remodeling occurs after grafting such that the tissue is almost indistinguishable from native vessels. This conduit is derived from cells of bone marrow origin, opening new possibilities in vascular modeling and remodeling.