Dehydration improves biomechanical strength of bioartificial vascular graft material and allows its long-term storage.

INTRODUCTION: We have recently reported about a novel technique for the generation of bioartificial vascular grafts based on the use of a compacted fibrin matrix. In this study, we evaluated the effects of a dehydration process on the biomechanical properties of compacted fibrin tubes and whether it allows for their long-term storage. MATERIALS AND METHODS: Fibrin was precipitated from fresh frozen plasma by means of cryoprecipitation and simultaneously with a thrombin solution applied in a high-speed rotating casting mold. Subsequent dehydration of the fibrin tubes (29/38) was performed in dry air with a dilator inside the tube to prevent the collapse of the lumen. Dehydrated fibrin tubes were stored for six (n=9) and 12 months (n=10) at room temperature. Comparative analysis was done on initially generated and dehydrated fibrin tubes before and after storage to evaluate the effects of the dehydration process and storage on the biomechanical properties and structure of the tubes. RESULTS: Thirty-eight fibrin tubes were generated by high-speed rotation-molding from 142±3 mg fibrinogen with an inner diameter of 5.8±0.1 mm and a length of 100 mm. A centrifugal force of nearly 900×g compacted applied fibrin, while fluid was pressed out of the matrix and drained from the mold via holes resulting in a 16-fold compaction of the fibrin matrix. Dehydration was characterized by shrinkage of the tubes to a diameter of 3.2±0.2 mm, while the length remained at 100 mm equivalent to a further two-fold compaction. The biomechanical strength of the dehydrated fibrin tubes significantly increased to values comparable to that of native ovine carotid arteries and maintained during the first 6 months of storage. After 12 months of storage, only five of 10 tubes were intact, and only one showed maintained biomechanical strength. DISCUSSION: Compaction of a fibrin matrix in high-speed rotation-moulding and subsequent dehydration enables for the construction of small-caliber fibrin grafts. Over and above, the dehydration process allows their storage and stockpiling as a prerequisite for clinical use.

MicroRNA 628-5p as a Novel Biomarker for Cardiac Allograft Vasculopathy.

BACKGROUND: Cardiac allograft vasculopathy (CAV) remains the leading cause of morbidity and mortality after orthotopic heart transplantation (OHT). Because of its clinically silent progression and lack of symptoms, detection is often difficult and invasive coronary angiography is performed routinely. To date, there are no established noninvasive biomarkers available for prediction of CAV in transplanted patients.MicroRNAs (miRNAs) are highly conserved, small noncoding RNA molecules that negatively regulate gene expression. As they are detectable in peripheral blood, recent studies have suggested miRNAs as biomarkers for various cardiovascular diseases. Thus, we hypothesized that circulating miRNAs may serve as noninvasive biomarkers for CAV. METHODS: To determine the regulation of circulating miRNAs, we performed miRNA profiling studies in plasma samples of OHT patients with confirmed high-degree CAV and a matched control group consisting of patients without any signs of CAV at least 5 years after OHT. Candidate miRNAs were verified by quantitative reverse transcriptase polymerase chain reaction. RESULTS: Microarray analysis revealed 5 candidate miRNAs (miR-34a, miR-98, miR-155, miR-204, miR-628-5p) that were differentially regulated in plasma samples of patients with CAV and therefore were selected for verification by quantitative reverse transcriptase polymerase chain reaction. In CAV patients, plasma levels of miR-628-5p and miR-155 were significantly increased (P = 0.001 and P = 0.028, respectively). A miR628-5p value above 1.336 was able to predict CAV with a sensitivity of 72% and a specificity of 83%. CONCLUSIONS: For the first time, the present study identifies the circulating miRNA miR-628-5p as a novel potential biomarker of CAV in patients after OHT.

Novel method for the generation of tissue-engineered vascular grafts based on a highly compacted fibrin matrix.

The generation of tissue-engineered blood vessel substitutes remains an ongoing challenge for cardiovascular tissue engineering. Full biocompatibility and immediate availability have emerged as central issues for clinical use. To address these issues, we developed a technique that allows the generation of highly stable tubular fibrin segments. The process is based on the compaction of fibrin in a custom-made high-speed rotation mold. In an automated process, fibrin is precipitated from plasma by means of the Vivostat® system. Following application to the rotating mold, the fibrin was compacted by centrifugal force and excess fluid was pressed out. This compaction results in increasing cross-links between the fibrin fibrils and a corresponding significant increase of biomechanical stability up to a burst strength of 230mm of mercury. The molding process allows for a simultaneous seeding procedure. In a first in vivo evaluation in a sheep model, segments of the carotid artery were replaced by tissue-engineered vascular grafts, generated immediately prior to implantation (n=6). Following subjection to the body's remodeling mechanisms, the segments showed a high structural similarity to a native artery after explantation at 6months. Thus, this technique may represent a powerful tool for the generation of biomechanically stable vascular grafts immediately prior to implantation. STATEMENT OF SIGNIFICANCE: Fibrin has previously been shown to be suitable as a matrix for the seeding of different celltypes and for that reason was widely used as scaffold in different fields of tissue engineering. Nevertheless, fibrin's lack of stability has strongly limited its application. Our study describes a novel moulding technique for the generation of a highly compacted fibrin matrix. Using this approach, it was possible to optimize the engineering process of tubular fibrin segments to provide bioartificial vascular grafts within one hour with sufficient stability for immediate implantation in the arterial system. Thus, this technique may represent a powerful tool to get closer to the ultimate aim of an optimal bioartificial vascular graft.