An encapsulated fibrin-based bioartificial tissue construct with integrated macrovessels, microchannels, and capillary tubes.

Facilitating sufficient nutrient and oxygen supply in large-scale bioartificial constructs is a critical step in organ bioengineering. Immediate perfusion not only depends on a dense capillary network, but also requires integrated large-diameter vessels that allow vascular anastomoses during implantation. These requirements set high demands for matrix generation as well as for in vitro cultivation techniques and remain mostly unsolved challenges up until today. Additionally, bioartificial constructs must have sufficient biomechanical stability to withstand mechanical stresses during and after implantation. We developed a bioartificial tissue construct with a fibrin matrix containing human umbilical vein endothelial cells and adipose tissue-derived stem cells facilitating capillary-like network formation. This core matrix was surrounded by a dense acellular fibrin capsule providing biomechanical stability. Two fibrin-based macrovessels were integrated on each side of the construct and interconnected via four 1.2 mm thick microchannels penetrating the cellularized core matrix. After 4 days of perfusion in a custom-built bioreactor, homogeneous capillary-like network formation throughout the core matrix was observed. The fibrin capsule stabilized the core matrix and facilitated the generation of a self-supporting construct. Thus, the encapsulated fibrin tissue construct could provide a universal prevascularized matrix for seeding with different cell types in various tissue engineering approaches.

Conventional culture diagnostics vs. multiplex PCR for the detection of causative agents of vascular graft infections - results of a single centre observational pilot study.

Background: Timely diagnosis of vascular graft infections is of major importance in vascular surgery. The detection of causative microorganisms is needed for specific medical treatment, but conventional culture is often slow, insensitive and inconclusive due to antibiotic pre-treatment. Detection of bacterial DNA by polymerase chain reaction (PCR) might bypass these problems. We hypothesised that multiplex PCR (mPCR) is feasible, fast and sensitive to detect causative microorganisms in vascular graft infections. Patients and methods: We performed a pilot observational prospective study comparing conventional culture and a commercial mPCR. Inclusion criteria were: confirmed graft infection, suspicious imaging, clinical suspicion, anastomotic aneurysm and repeated graft occlusion. Diagnostic methods were performed using identical samples. Time to result, microorganisms and antibiotic resistance in both groups were compared using Student's t-test or nonparametric tests. Results: 22 samples from 13 patients were assessed and 11 samples were negative for bacteria. Some showed multiple germs. In total, we found 15 different organisms. 13 samples matched, 9 had non-concordant results. Out of the mismatches 3 microorganisms identified in PCR were not detected by culture. Time to result with PCR was shorter (median 5 h vs. 72 h, p < 0.001) than with culture. No resistance genes were detected by mPCR, but conventional culture allowed susceptibility testing and revealed resistance in 5 samples. Conclusions: mPCR seems to be a feasible and quick tool to detect causes of vascular graft infections within 24 h and might be helpful in antibiotic pre-treated patients. The detection of antibiotic resistance with mPCR needs improvement for clinical practice.

Targeting Chemokine Receptor CXCR4 and Translocator Protein for Characterization of High-Risk Plaque in Carotid Stenosis Ex Vivo.

Background and Purpose- This pilot study aims to demonstrate the feasibility of targeting molecular characteristics of high-risk atherosclerotic plaque in symptomatic and asymptomatic carotid stenosis (CS), that is, upregulation of the translocator protein (TSPO) and the chemokine receptor type 4 (CXCR4), by means of molecular imaging. Methods- In a translational setting, specimens of carotid plaques of patients with symptomatic and asymptomatic CS obtained by carotid endarterectomy were analyzed for the presence of TSPO and CXCR4 by autoradiography, using the positron emission tomography tracers 18F-GE180 and 68Ga-Pentixafor and evaluated by histopathology. In addition, 68Ga-Pentixafor positron emission tomography/computed tomography was performed in a patient with high-grade CS. Results- Distinct patterns of upregulation of TSPO (18F-GE180 uptake) and CXCR4 (68Ga-Pentixafor uptake) were identified in carotid plaque by autoradiography. The spatial distribution was associated with specific histological hallmarks that are established features of high-risk plaque: TSPO upregulation correlated with activated macrophages infiltration, whereas CXCR4 upregulation also corresponded to areas of intraplaque hemorrhage. 68Ga-Pentixafor uptake was significantly higher in plaques of symptomatic compared with asymptomatic CS. Clinical positron emission tomography revealed marked 68Ga-Pentixafor uptake in carotid plaque of a patient with high-grade CS. Conclusions- Clinical imaging of molecular signatures of high-risk atherosclerotic plaque is feasible and may become a promising diagnostic tool for comprehensive characterization of carotid disease. This methodology provides a platform for future studies targeting carotid plaque.

Safety of Simultaneous Coronary Artery Bypass Grafting and Carotid Endarterectomy Versus Isolated Coronary Artery Bypass Grafting: A Randomized Clinical Trial.

BACKGROUND AND PURPOSE: The optimal operative strategy in patients with severe carotid artery disease undergoing coronary artery bypass grafting (CABG) is unknown. We sought to investigate the safety and efficacy of synchronous combined carotid endarterectomy and CABG as compared with isolated CABG. METHODS: Patients with asymptomatic high-grade carotid artery stenosis ≥80% according to ECST (European Carotid Surgery Trial) ultrasound criteria (corresponding to ≥70% NASCET [North American Symptomatic Carotid Endarterectomy Trial]) who required CABG surgery were randomly assigned to synchronous carotid endarterectomy+CABG or isolated CABG. To avoid unbalanced prognostic factor distributions, randomization was stratified by center, age, sex, and modified Rankin Scale. The primary composite end point was the rate of stroke or death at 30 days. RESULTS: From 2010 to 2014, a total of 129 patients were enrolled at 17 centers in Germany and the Czech Republic. Because of withdrawal of funding after insufficient recruitment, enrolment was terminated early. At 30 days, the rate of any stroke or death in the intention-to-treat population was 12/65 (18.5%) in patients receiving synchronous carotid endarterectomy+CABG as compared with 6/62 (9.7%) in patients receiving isolated CABG (absolute risk reduction, 8.8%; 95% confidence interval, -3.2% to 20.8%; PWALD=0.12). Also for all secondary end points at 30 days and 1 year, there was no evidence for a significant treatment-group effect although patients undergoing isolated CABG tended to have better outcomes. CONCLUSIONS: Although our results cannot rule out a treatment-group effect because of lack of power, a superiority of the synchronous combined carotid endarterectomy+CABG approach seems unlikely. Five-year follow-up of patients is still ongoing. CLINICAL TRIAL REGISTRATION: URL: https://www.controlled-trials.com. Unique identifier: ISRCTN13486906.

Antibody formation towards porcine tissue in patients implanted with crosslinked heart valves is directed to antigenic tissue proteins and αGal epitopes and is reduced in healthy vegetarian subjects.

BACKGROUND: Glutaraldehyde-fixed porcine heart valves (ga-pV) are one of the most frequently used substitutes for insufficient aortic and pulmonary heart valves which, however, degenerate after 10-15 years. Yet, xeno-immunogenicity of ga-pV in humans including identification of immunogens still needs to be investigated. We here determined the immunogenicity of ga-pV in patients with respect to antibody formation, identity of immunogens and potential options to reduce antibody levels. METHODS: Levels of tissue-specific and anti-αGal antibodies were determined retrospectively in patients who received ga-pV for 51 months (n=4), 25 months (n=6) or 5 months (n=4) and compared to age-matched untreated subjects (n=10) or younger subjects with or without vegetarian diet (n=12/15). Immunogenic proteins were investigated by Western blot approaches. RESULTS: Tissue-specific antibodies in patients were elevated after 5 (1.73-fold) and 25 (1.46-fold, both P<.0001) months but not after 51 months, whereas anti-Gal antibodies were induced 4.75-fold and 3.66-fold after 5 and 25 months (both P<.0001) and still were significantly elevated after 51 months (2.85-fold, P<.05). Western blots of porcine valve extracts with and without enzymatic deglycosylation revealed strong specific staining at ≈65 and ≈140 kDa by patient sera in either group which were identified by 2D Western blots and mass spectrometry as serum albumin and collagen 6A1. Vegetarian diet reduced significantly (0.63-fold, P<.01) the level of pre-formed αGal but not of tissue-specific antibodies. CONCLUSION: Immune response in patients towards ga-pV is induced by the porcine proteins albumin and collagen 6A1 as well as αGal epitopes, which seemed to be more sustained. In contrast, in healthy young subjects pre-formed anti-Gal antibodies were reduced by a meat-free nutrition.

The role of pericyte detachment in vascular rarefaction.

BACKGROUND: Pericytes surround endothelial cells at the perivascular interface. Signaling between endothelial cells and pericytes is crucial for capillary homeostasis, as pericytes stabilize vessels and regulate many microvascular functions. Recently it has been shown that pericytes are able to detach from the vascular wall and contribute to fibrosis by becoming scar-forming myofibroblasts in many organs including the kidney. At the same time, the loss of pericytes within the perivascular compartment results in vulnerable capillaries which are prone to instability, pathological angiogenesis, and, ultimately, rarefaction. AIMS: This review will give an overview of pericyte-endothelial cell interactions, summarize the signaling pathways that have been identified to be involved in pericyte detachment from the vascular wall, and present pathological endothelial responses in the context of disease of the kidney.

Fabrication and biomechanical characterization of a spider silk reinforced fibrin-based vascular prosthesis.

With fibrin-based vascular prostheses, vascular tissue engineering offers a promising approach for the fabrication of biologically active regenerative vascular grafts. As a potentially autologous biomaterial, fibrin exhibits excellent hemo- and biocompatibility. However, the major problem in the use of fibrin constructs in vascular tissue engineering, which has so far prevented their widespread clinical application, is the insufficient biomechanical stability of unprocessed fibrin matrices. In this proof-of-concept study, we investigated to what extent the addition of a spider silk network into the wall structure of fibrin-based vascular prostheses leads to an increase in biomechanical stability and an improvement in the biomimetic elastic behavior of the grafts. For the fabrication of hybrid prostheses composed of fibrin and spider silk, a statically cast tubular fibrin matrix was surrounded with an envelope layer of Trichonephila edulis silk using a custom built coiling machine. The fibrin matrix was then compacted and pressed into the spider silk network by transluminal balloon compression. This manufacturing process resulted in a hybrid prosthesis with a luminal diameter of 4 mm. Biomechanical characterization revealed a significant increase in biomechanical stability of spider silk reinforced grafts compared to exclusively compacted fibrin segments with a mean burst pressure of 362 ± 74 mmHg vs. 213 ± 14 mmHg (p < 0.05). Dynamic elastic behavior of the spider silk reinforced grafts was similar to native arteries. In addition, the coiling with spider silk allowed a significant increase in suture retention strength and resistance to external compression without compromising the endothelialization capacity of the grafts. Thus, spider silk reinforcement using the abluminal coiling technique represents an efficient and reproducible technique to optimize the biomechanical behavior of small-diameter fibrin-based vascular grafts.

Development, comparative structural analysis, and first in vivo evaluation of acellular implanted highly compacted fibrin tubes for arterial bypass grafting.

The generation of small-caliber vascular grafts remains a significant challenge within the field of tissue engineering. In pursuit of this objective, fibrin has emerged as a promising scaffold material. However, its lack of biomechanical strength has limited its utility in the construction of tissue engineered vascular grafts. We have previously reported about the implementation of centrifugal casting molding to generate compacted fibrin tubes with a highly increased biomechanical strength. In this study, we conducted a structural analysis of compacted fibrin tubes using the open-source software Fiji/BoneJ. The primary aim was to validate the hypothesis that the compaction of fibrin leads to a more complex structure characterized by increased crosslinking of fibrin fibers. Structural analysis revealed a strong correlation between fibrin's structure and its biomechanical strength. Moreover, we enhanced fibrin compaction in a subsequent dehydration process, leading to a significant increase of biomechanical strength. Thus, the presented method in combination with an adequate imaging, e.g., micro-CT, has substantial potential as a powerful tool for quality assurance in the development of fibrin-based vascular grafts. To validate this concept, acellular highly compacted fibrin tubes were implanted as substitutes of a segment of the carotid artery in a sheep model (n = 4). After 6 months explanted segments exhibited distinct remodeling, transitioning into newly formed arteries.

Open surgical replacement of the descending aorta: single-center experience.

Background: This study presents a single center's experience and analyzes clinical outcomes following elective open surgical descending aortic replacement. Methods: Between January 2000 and August 2019, 96 patients with mean age 64 years (range, 49.5-71 years) (62.5% (n=60) male) underwent elective descending aortic replacement due to aneurysm (n=60) or chronic dissection (n=36). Marfan syndrome was present in 12 patients (12.5%). Results: In-hospital mortality rate was 3.1% (n= 3. 2 in the aneurysm group, 1 in the dissection group). New-onset renal insufficiency postoperatively with (creatinine ≥ 2.5 mg/dl) manifested in 10 patients (10.8%). One patient (1%) suffered from stroke, and paraplegia developed in 1 pts (1%). The median follow-up time was 7 years (IQR: 2.5-13 years). The 5- and 10-year survival rates were 70.8% and 50.7% respectively. We did not observe any early or late prosthetic graft infection. The Cox proportional hazards regression analysis identified age (HR: 1.044, 95% CI: 1.009-1.080, p-value: 0.014), diabetes (HR: 2.544, 95% CI: 1.009-6.413, p-value: 0.048), and chronic obstructive pulmonary disease (COPD) (HR: 2.259, 95% CI: 1.044-4.890, p-value: 0.039) as risk factors for late mortality. Conclusions: This study showed that the elective open surgical replacement of the descending aorta can be achieved with excellent outcomes in terms of perioperative mortality and morbidity. Prosthetic graft is not a problem with open surgical descending aortic replacement, even in the long term. Supplementary Information: The online version contains supplementary material available at 10.1007/s12055-022-01443-x.

The potential impact of coagulation factor XIII in trauma-induced coagulopathy - a retrospective case series analysis.

BACKGROUND: The role of factor XIII (FXIII) in trauma-induced coagulopathy (TIC) is not fully understood. METHODS: We evaluated FXIII supplementation in severely injured patients with persistent bleeding. This was a retrospective case series analysis. RESULTS: Twenty-four patients received FXIII concentrate within 24 h of admission for bleeding that continued after transfusion of > 6 U red blood cells (RBCs); control patients (n = 27) did not receive FXIII concentrate. Both study groups were similar regarding injury severity score and global coagulation tests, but FXIII activity levels were significantly higher and lactate levels significantly lower in the control group, respectively. The differences in FXIII activity between the groups could be attributed to a more severe trauma-induced coagulopathy in FXIII-deficient patients, as demonstrated by lower fibrinogen and higher lactate levels. The median dose of FXIII concentrate within 24 h of admission was 2500 IU (IQR: 1250-4375). Median 24-h transfusion of RBCs (primary study endpoint) was significantly higher in the FXIII group versus controls (10.0 U, IQR 5-14 U vs. 2, IQR 0-6 U; p < 0.01). Subsequently, while patients were in the intensive care unit, there was no statistically significant difference regarding RBC transfusion anymore and the overall clinical outcomes were similar in both patient groups. CONCLUSIONS: The substitution of FXIII in patients who were more seriously compromised due to higher lactate levels and who presented with initially more severe bleedings than patients in the control group, resulted in a comparable transfusion necessity after 24 h. Thus, we guess that the substitution of FXIII in severely injured patients with ongoing bleeding might have an impact on their clinical outcome.

Establishment of a Modular Hemodynamic Simulator for Accurate In Vitro Simulation of Physiological and Pathological Pressure Waveforms in Native and Bioartificial Blood Vessels.

PURPOSE: In vitro stimulation of native and bioartificial vessels in perfusable systems simulating natural mechanical environments of the human vasculature represents an emerging approach in cardiovascular research. Promising results have been achieved for applications in both regenerative medicine and etiopathogenetic investigations. However, accurate and reliable simulation of the wide variety of physiological and pathological pressure environments observed in different vessels still remains an unmet challenge. METHODS: We established a modular hemodynamic simulator (MHS) with interchangeable and modifiable components suitable for the perfusion of native porcine-(i.e. the aorta, brachial and radial arteries and the inferior vena cava) and bioartificial fibrin-based vessels with anatomical site specific pressure curves. Additionally, different pathological pressure waveforms associated with cardiovascular diseases including hyper- and hypotension, tachy- and bradycardia, aortic valve stenosis and insufficiency, heart failure, obstructive cardiomyopathy and arterial stiffening were simulated. Pressure curves, cyclic distension and shear stress were measured for each vessel and compared to ideal clinical pressure waveforms. RESULTS: The pressure waveforms obtained in the MHS showed high similarity to the ideal anatomical site specific pressure curves of different vessel types. Moreover, the system facilitated accurate emulation of physiological and different pathological pressure conditions in small diameter fibrin-based vessels. CONCLUSION: The MHS serves as a variable in vitro platform for accurate emulation of physiological and pathological pressure environments in biological probes. Potential applications of the system include bioartificial vessel maturation in cardiovascular tissue engineering approaches as well as etiopathogenetic investigations of various cardiovascular pathologies.

Mechanical Stimulation Induces Vasa Vasorum Capillary Alignment in a Fibrin-Based Tunica Adventitia.

Generation of bioartificial blood vessels with a physiological three-layered wall architecture is a long pursued goal in vascular tissue engineering. While considerable advances have been made to resemble the physiological tunica intima and media morphology and function in bioartificial vessels, only very few studies have targeted the generation of a tunica adventitia, including its characteristic vascular network known as the vasa vasorum, which are essential for graft nutrition and integration. In healthy native blood vessels, capillary vasa vasorum are aligned longitudinally to the vessel axis. Thus, inducing longitudinal alignment of capillary tubes to generate a physiological tunica adventitia morphology and function may be advantageous in bioengineered vessels as well. In this study, we investigated the effect of two biomechanical stimulation parameters, longitudinal tension and physiological cyclic stretch, on tube alignment in capillary networks formed by self-assembly of human umbilical vein endothelial cells in tunica adventitia-equivalents of fibrin-based bioartificial blood vessels. Moreover, the effect of changes of the biomechanical environment on network remodeling after initial tube formation was analyzed. Both, longitudinal tension and cyclic stretch by pulsatile perfusion induced physiological capillary tube alignment parallel to the longitudinal vessel axis. This effect was even more pronounced when both biomechanical factors were applied simultaneously, which resulted in an alignment of 57.2 ± 5.2% within 5° of the main vessel axis. Opposed to that, a random tube orientation was observed in vessels incubated statically. Scanning electron microscopy showed that longitudinal tension also resulted in longitudinal alignment of fibrin fibrils, which may function as a guidance structure for directed capillary tube formation. Moreover, existing microvascular networks showed distinct remodeling in response to addition or withdrawal of mechanical stimulation with corresponding increase or decrease of the degree of alignment. With longitudinal tension and cyclic stretch, we identified two mechanical stimuli that facilitate the generation of a prevascularized tunica adventitia-equivalent with physiological tube alignment in bioartificial vascular grafts. Impact statement Fibrin-based bioartificial vessels represent a promising regenerative approach to generate vascular grafts with superior biocompatibility and hemocompatibility compared to currently available synthetic graft materials. Precapillarization of bioartificial vascular grafts may improve nutrition of the vessel wall and integration of the graft into the target organism's microvasculature. In native vessels, physiological vasa vasorum alignment is pivotal for proper function of the tunica adventitia. Thus, it is necessary to induce longitudinal capillary alignment in the tunica adventitia of bioengineered vessels as well to secure long-term graft patency and function. This alignment can be reliably achieved by controlled biomechanical stimulation in vitro.

Preliminary application of native Nephila edulis spider silk and fibrin implant causes granulomatous foreign body reaction in vivo in rat's spinal cord.

After spinal cord injury, gliomesenchymal scaring inhibits axonal regeneration as a physical barrier. In peripheral nerve injuries, native spider silk was shown to be an effective scaffold to facilitate axonal re-growth and nerve regeneration. This study tested a two-composite scaffold made of longitudinally oriented native spider silk containing a Haemocomplettan fibrin sheath to bridge lesions in the spinal cord and enhance axonal sprouting. In vitro cultivation of neuronal cells on spider silk and fibrin revealed no cytotoxicity of the scaffold components. When spinal cord tissue was cultured on spider silk that was reeled around a metal frame, migration of different cell types, including neurons and neural stem cells, was observed. The scaffold was implanted into spinal cord lesions of four Wistar rats to evaluate the physical stress caused on the animals and examine the bridging potential for axonal sprouting and spinal cord regeneration. However, the implantation in-vivo resulted in a granulomatous foreign body reaction. Spider silk might be responsible for the strong immune response. Thus, the immune response to native spider silk seems to be stronger in the central nervous system than it is known to be in the peripheral body complicating the application of native spider silk in spinal cord injury treatment.

Pressure-compacted and spider silk-reinforced fibrin demonstrates sufficient biomechanical stability as cardiac patch in vitro.

OBJECTIVE: The generation of bio-/hemocompatible cardiovascular patches with sufficient stability and regenerative potential remains an unmet goal. Thus, the aim of this study was the generation and in vitro biomechanical evaluation of a novel cardiovascular patch composed of pressure-compacted fibrin with embedded spider silk cocoons. METHODS: Fibrin-based patches were cast in a customized circular mold. One cocoon of Nephila odulis spider silk was embedded per patch during the casting process. After polymerization, the fibrin clot was compacted by 2 kg weight for 30 min resulting in thickness reduction from up to 2 cm to <1 mm. Tensile strength and burst pressure was determined after 0 weeks and 14 weeks of storage. A sewing strength test and a long-term load test were performed using a customized device to exert physiological pulsatile stretching of a silicon surface on which the patch had been sutured. RESULTS: Fibrin patches resisted supraphysiological pressures of well over 2000 mmHg. Embedding of spider silk increased tensile force 1.8-fold and tensile strength 1.45-fold (p < .001), resulting in a final strength of 1.07 MPa and increased sewing strength. Storage for 14 weeks decreased tensile strength, but not significantly and suturing properties of the spider silk patches were satisfactory. The long-term load test indicated that the patches were stable for 4 weeks although slight reduction in patch material was observed. CONCLUSION: The combination of compacted fibrin matrices and spider silk cocoons may represent a feasible concept to generate stable and biocompatible cardiovascular patches with regenerative potential.

Cryopreserved arterial homografts vs silver-coated Dacron grafts for abdominal aortic infections with intraoperative evidence of microorganisms.

OBJECTIVE: The gold standard for the treatment of abdominal aortic infections remains controversial. Cryopreserved arterial homografts and silver-coated Dacron grafts have both been advocated as reasonable grafts. Direct clinical or experimental comparisons between these two treatment options have not been published before. This study compared cryopreserved arterial homografts and silver-coated Dacron grafts for the treatment of abdominal aortic infections in a contaminated intraoperative field. METHODS: From January 2004 to December 2009, 56 patients underwent in situ arterial reconstruction for an abdominal aortic infection. Patients with negative intraoperative microbiologic specimens were excluded. We compared 22 of 36 patients (61%) receiving cryopreserved arterial homografts (group A) vs 11 of 20 (55%) receiving a silver-coated Dacron graft (group B). Primary outcomes were survival and limb salvage; secondary outcomes were graft patency and reinfection. Direct costs of therapy were also calculated. RESULTS: Thirty-day mortality was 14% in group A and 18% in group B (P >.99), and 2-year survival rates were 82% and 73%, respectively (P = .79). After 2 years, limb salvage was 96% and 100%, respectively (P = .50), whereas graft patency was 100% for both groups. Major complications were an aneurysmal degeneration in group A and graft reinfection in group B (n = 2). Median direct costs of therapy (in US $) were $41,697 (range, $28,347-$53,362) in group A and $15,531 (range, $11,310-$22,209) in group B (P = .02). CONCLUSIONS: Our results show comparable effectiveness between cryopreserved arterial homograft and silver-coated Dacron graft in the contaminated operative field with respect to early mortality and midterm survival. Graft-inherent complications, aneurysmal degeneration for homografts, and reinfection for silver graft, were also observed. The in situ arterial reconstruction with homografts is nearly three times more expensive than with silver graft.

Transluminal compression increases mechanical stability, stiffness and endothelialization capacity of fibrin-based bioartificial blood vessels.

Fibrin is used successfully as a biological matrix in various bioengineering approaches. Its unique combination of autologous availability, hemocompatibility and biological activity makes it an almost ideal matrix material for vascular tissue engineering. However, clinical application of fibrin-based bioartificial blood vessels is still limited due to insufficient mechanical stability and stiffness of fibrin matrices. Biomechanical properties of fibrin-based constructs can potentially be modified by adjusting matrix density. Thus, as an attempt to optimize strength and elasticity of fibrin matrices for vascular tissue engineering applications, we developed a simple and reproducible method for transluminal compression of small-diameter fibrin-based vessels: After initial polymerization of high-concentration fibrin matrices in a vascular mold, vessels were compressed using an intraluminal angioplasty balloon. Vessels compacted with different pressures were compared for ultimate strength, elastic and structural properties and cellularization capacity. Transluminal compression increased fibrin network density and facilitated rapid production of homogenous vessels with a length of 10 cm. Compared to non-compressed controls, compacted fibrin vessels showed superior maximal burst pressure (199.8 mmHg vs. 94.0 mmHg), physiological elastic properties similar to the elastic behavior of natural arteries and higher luminal endothelial cell coverage (98.6% vs. 34.6%). Thus, transluminal compaction represents a suitable technique to enhance biomechanical properties of fibrin-based bioartificial vessels while preserving the biological advantages of this promising biomaterial.

A 3-Layered Bioartificial Blood Vessel with Physiological Wall Architecture Generated by Mechanical Stimulation.

The generation of cellularized bioartificial blood vessels resembling all three layers of the natural vessel wall with physiological morphology and cell alignment is a long pursued goal in vascular tissue engineering. Simultaneous culture of all three layers under physiological mechanical conditions requires highly sophisticated perfusion techniques and still today remains a key challenge. Here, three-layered bioartificial vessels based on fibrin matrices were generated using a stepwise molding technique. Adipose-derived stem cells (ASC) were differentiated to smooth muscle cells (SMC) and integrated in a compacted tubular fibrin matrix to resemble the tunica media. The tunica adventitia-equivalent containing human umbilical vein endothelial cells (HUVEC) and ASC in a low concentration fibrin matrix was molded around it. Luminal seeding with HUVEC resembled the tunica intima. Subsequently, constructs were exposed to physiological mechanical stimulation in a pulsatile bioreactor for 72 h. Compared to statically incubated controls, mechanical stimulation induced physiological cell alignment in each layer: Luminal endothelial cells showed longitudinal alignment, cells in the media-layer were aligned circumferentially and expressed characteristic SMC marker proteins. HUVEC in the adventitia-layer formed longitudinally aligned microvascular tubes resembling vasa vasorum capillaries. Thus, physiologically organized three-layered bioartificial vessels were successfully manufactured by stepwise fibrin molding with subsequent mechanical stimulation.

Chemically induced hypoxia by dimethyloxalylglycine (DMOG)-loaded nanoporous silica nanoparticles supports endothelial tube formation by sustained VEGF release from adipose tissue-derived stem cells.

Inadequate vascularization leading to insufficient oxygen and nutrient supply in deeper layers of bioartificial tissues remains a limitation in current tissue engineering approaches to which pre-vascularization offers a promising solution. Hypoxia triggering pre-vascularization by enhanced vascular endothelial growth factor (VEGF) expression can be induced chemically by dimethyloxalylglycine (DMOG). Nanoporous silica nanoparticles (NPSNPs, or mesoporous silica nanoparticles, MSNs) enable sustained delivery of molecules and potentially release DMOG allowing a durable capillarization of a construct. Here we evaluated the effects of soluble DMOG and DMOG-loaded NPSNPs on VEGF secretion of adipose tissue-derived stem cells (ASC) and on tube formation by human umbilical vein endothelial cells (HUVEC)-ASC co-cultures. Repeated doses of 100 µM and 500 µM soluble DMOG on ASC resulted in 3- to 7-fold increased VEGF levels on day 9 (P < 0.0001). Same doses of DMOG-NPSNPs enhanced VEGF secretion 7.7-fold (P < 0.0001) which could be maintained until day 12 with 500 µM DMOG-NPSNPs. In fibrin-based tube formation assays, 100 µM DMOG-NPSNPs had inhibitory effects whereas 50 µM significantly increased tube length, area and number of junctions transiently for 4 days. Thus, DMOG-NPSNPs supported endothelial tube formation by upregulated VEGF secretion from ASC and thus display a promising tool for pre-vascularization of tissue-engineered constructs. Further studies will evaluate their effect in hydrogels under perfusion.

Vascular procedures in patients with left ventricular assist devices: single-center experience.

OBJECTIVE: A growing number of patients suffering from heart failure is living with a left ventricular assist device (LVAD) and is in the need for non-cardiac surgery. Vascular procedures due to ischemia, bleeding, or other device-related complications may be required and pose a challenge to the caregivers in terms of monitoring and management of these patients. Therefore, we reviewed our experience with LVAD patients undergoing vascular surgery. METHODS: From January 2010 until March 2017, a total of 54 vascular procedures were performed on 41 LVAD patients at our institution. Patient records were reviewed retrospectively in terms of incidence of LVAD-related complications, including thrombosis, stroke, bleeding, wound healing, and survival associated with vascular surgery. The type of surgery was recorded, as well as various clinical demographic variables. RESULTS: Vascular procedures were performed in 35 men (85.4%) and 6 women (14.6%) with LVADs. There were no perioperative strokes, device thromboses, or device malfunctions. Thirty-day mortality overall was 26.8% (eleven patients), with most patients dying within 30 days after LVAD implantation due to multi-organ failure. In 25 procedures (46.3%), a blood transfusion was necessary. CONCLUSION: Patients on LVAD support are a complex cohort with a high risk for perioperative complications. In a setting where device function and anticoagulation are monitored closely, vascular surgery in these patients is feasible with an acceptable perioperative risk.

Perfusion promotes endothelialized pore formation in high concentration fibrin gels otherwise unsuitable for tube development.

Vascularization of tissue engineered implants is crucial for their survival and integration in the recipient's body. Pre-vascularized, fibrin-based implants offer a solution since low concentration fibrin hydrogels (1 mg/mL) have been shown to promote tube formation of endothelial cells in co-culture with adipogenic stem cells. However, higher fibrinogen concentrations (> 20 mg/mL) enabling the fabrication of stable implants are necessary.We here characterized fibrin gels of 1-30 mg/mL for their rheological properties and whether they support tube formation of endothelial cell-adipogenic stem cell co-cultures for up to 7 days. Moreover, 20 mg/mL gels containing preformed channels and endothelial cell-adipogenic stem cell co-culture were perfused continuously in a customized flow chamber with 3.9 dyn/cm2 for 12 days and analyzed for capillary formation.Rheology of fibrin gels showed increasing stability proportional to fibrinogen concentration with 20 mg/mL gels having a storage module of 465 Pa. Complex tube networks stable for 7 days were observed at 1-5 mg/mL gels whereas higher concentrations showed initial sprouting only. However, perfusion of 20 mg/mL fibrin gels resulted in endothelialized pore formation in several layers of the gel with endothelial cell-adipogenic stem cell co-culture.Thus, perfusion supports the formation of capillary-like structures in fibrin gels that are too dense for spontaneous tube formation under static conditions. Future studies are necessary to further increase pore density and to investigate proper nutrition of tissue-specific target cells in the scaffold.