Long term performance of polycaprolactone vascular grafts in a rat abdominal aorta replacement model

In the active field of vascular graft research, polycaprolactone is often used because of its good mechanical strength and its biocompatibility. It is easily processed into micro and nano-fibers by electrospinning to form a porous, cell-friendly scaffold. However, long term in vivo performance of polycaprolactone vascular grafts had yet to be investigated. In this study, polycaprolactone micro and nano-fiber based vascular grafts were evaluated in the rat abdominal aorta replacement model for 1.5, 3, 6, 12, and 18 months (n = 3 for each time point). The grafts were evaluated for patency, thrombosis, compliance, tissue regeneration, and material degradation. Results show excellent structural integrity throughout the study, with no aneurysmal dilation, and perfect patency with no thrombosis and limited intimal hyperplasia. Endothelialization, cell invasion, and neovascularization of the graft wall rapidly increased until 6 months, but at 12 and 18 months, a cellular regression is observed. On the medium term, chondroid metaplasia takes place in the intimal hyperplasia layers, which contributes to calcification of the grafts. This study presents issues with degradable vascular grafts that cannot be identified with short implantation times or in vitro studies. Such findings should allow for better design of next generation vascular grafts.     

Axonal regeneration into Schwann cell grafts within resorbable poly(alpha-hydroxyacid) guidance channels in the adult rat spinal cord

Axonal growth and myelination in a SC graft contained in a resorbable tubular scaffold made of poly(D,L-lactic acid) (PLA50) or high molecular weight poly(L-lactic acid) mixed with 10% poly(L-lactic acid) oligomers (PLA(100/10)) were studied for up to 4 months after implantation in the completely transected adult rat thoracic spinal cord. The PLA50 tubes collapsed soon after implantation and, consequently, compressed the graft inside, leading to only occasional thin cables with SCs and a low number of myelinated axons: 17 +/- 6 at 1 and 158 +/- 11 at 2 months post-grafting. The cable contained 32 +/- 23 blood vessels at 2 weeks, 55 +/- 33 at 1 month and 46 +/- 30 at 2 months after implantation. PLA(100/10) tubes, on the other hand, were found to break up into large pieces, which compressed and sometimes protruded into the tissue cable inside. At all time points studied, however, cables contained SCs and were well vascularized with 414 +/- 47 blood vessels at 2 weeks, 437 +/- 139 at 1, 609 +/- 134 at 2 and 396 +/- 95 at 4 months post-grafting. The number of myelinated axons was 712 +/- 509 at 1 month, 1819 +/- 837 at 2 months and 609 +/- 132 at 4 months post implantation. These results demonstrated that fiber growth and myelination into a SC graft contained in a resorbable PLA(100/10) tube increases over the first 2 months post-implantation but decreases thereafter. Changes in geometry of both types of polymer tubes were detrimental to axonal regeneration. Future research should explore the use of polymers that better retain the appropriate mechanical, geometrical and permeability properties over time.     

Valvular interstitial cell seeded poly(glycerol sebacate) scaffolds: Toward a biomimetic in vitro model for heart valve tissue engineering

Tissue engineered replacement heart valves may be capable of overcoming the lack of growth potential intrinsic to current non-viable prosthetics, and thus could potentially serve as permanent replacements in the surgical repair of pediatric valvular lesions. However, the evaluation of candidate combinations of cells and scaffolds lacks a biomimetic in vitro model with broadly tunable, anisotropic and elastomeric structural–mechanical properties. Toward establishing such an in vitro model, in the current study, porcine aortic and pulmonary valvular interstitial cells (i.e. biomimetic cells) were cultivated on anisotropic, micromolded poly(glycerol sebacate) scaffolds (i.e. biomimetic scaffolds). Following 14 and 28 days of static culture, cell-seeded scaffolds and unseeded controls were assessed for their mechanical properties, and cell-seeded scaffolds were further characterized by confocal fluorescence and scanning electron microscopy, and by collagen and DNA assays. Poly(glycerol sebacate) micromolding yielded scaffolds with anisotropic stiffnesses resembling those of native valvular tissues in the low stress–strain ranges characteristic of physiologic valvular function. Scaffold anisotropy was largely retained upon cultivation with valvular interstitial cells; while the mechanical properties of unseeded scaffolds progressively diminished, cell-seeded scaffolds either retained or exceeded initial mechanical properties. Retention of mechanical properties in cell-seeded scaffolds paralleled the accretion of collagen, which increased significantly from 14 to 28 days. This study demonstrates that valvular interstitial cells can be cultivated on anisotropic poly(glycerol sebacate) scaffolds to yield biomimetic in vitro models with which clinically relevant cells and future scaffold designs can be evaluated.     

A novel hyaluronan-based biomaterial (Hyaff-11) as a scaffold for endothelial cells in tissue engineered vascular grafts

Current prosthetic small diameter vascular grafts show poor long-term patency rates, leading to the pursuit of a biological alternative. Hyaff-11 is a hyaluronan-based biodegradable polymer developed for tissue-engineering applications. This study aimed to determine whether human vascular endothelial cells attach to Hyaff-11 scaffolds and produce a subendothelial matrix. Two forms of fibrous, non-woven Hyaff-11 scaffolds: unpressed and pressed felts, were analysed. Attachment of human venous endothelial cells was investigated after 1, 5, 10 and 20 days in culture using SEM and confocal microscopy. The deposition of subendothelial matrix components was investigated by immunofluorescent staining.

We demonstrate that endothelial cells adhere to the individual fibres of both unpressed and pressed scaffolds: with a seeding density of 1×10⁶ cells/cm², 94% of the cells attached to Hyaff-11 fibres after 24 h. The pressed material provided the best environment for cell growth, allowing the formation of a complete endothelial monolayer after 20 days. Furthermore, endothelial cells on Hyaff-11 pressed felts deposited an organised subendothelial matrix containing laminin, fibronectin, type IV and type VIII collagen. This work indicates Hyaff-11 based biopolymers as suitable scaffolds to promote endothelialisation within the next generation of vascular grafts.     

In vitro and in vivo comparisons of staphylococcal biofilm formation on a cross-linked poly(ethylene glycol)-based polymer coating

Poly(ethylene glycol) (PEG) coatings are known to reduce microbial adhesion in terms of numbers and binding strength. However, bacterial adhesion remains of the order of 10⁴ cm^?2. It is unknown whether this density of bacteria will eventually grow into a biofilm. This study investigates the kinetics of staphylococcal biofilm formation on a commercially produced, robust, cross-linked PEG-based polymer coating (OptiChem^®) in vitro and in vivo. OptiChem^® inhibits biofilm formation in vitro, and although adsorption of plasma proteins encourages biofilm formation, microbial growth kinetics are still strongly delayed compared to uncoated glass. In vivo, OptiChem^®-coated and bare silicone rubber samples were inserted into an infected murine subcutaneous pocket model. In contrast to bare silicone rubber, OptiChem^® samples did not become colonized upon reimplantation despite the fact that surrounding tissues were always culture-positive. We conclude that the commercial OptiChem^® coating considerably slows down bacterial biofilm formation both in vitro and in vivo, making it an attractive candidate for biomaterials implant coating.     

Safety and biodegradability of a synthetic dural sealant patch (Liqoseal) in a porcine cranial model

BackgroundLiqoseal consists of a watertight layer of poly(ester)ether urethane and an adhesive layer containing polyethylene glycol‐N‐hydroxysuccinimide (PEG‐NHS). It is designed to prevent cerebrospinal fluid (CSF) leakage after intradural surgery. This study assessed the safety and biodegradability of Liqoseal in a porcine craniotomy model.MethodsIn 32 pigs a craniotomy plus durotomy was performed. In 15 pigs Liqoseal was implanted, in 11 control pigs no sealant was implanted and in 6 control pigs a control dural sealant (Duraseal or Tachosil) was implanted. The safety of Liqoseal was evaluated by clinical, MRI and histological assessment. The degradation of Liqoseal was histologically estimated.ResultsLiqoseal, 2 mm thick before application, did not swell and significantly was at maximum mean thickness of 2.14 (±0.37) mm at one month. The foreign body reaction induced by Liqoseal, Duraseal and Tachosil were comparable. Liqoseal showed no adherence to the arachnoid layer and was completely resorbed between 6 and 12 months postoperatively. In one animal with Liqoseal, an epidural fluid collection containing CSF could not be excluded.ConclusionLiqoseal seems to be safe for intracranial use and is biodegradable. The safety and performance in humans needs to be further assessed in clinical trials.     

In vitro and in vivo degradability and cytocompatibility of poly(l-lactic acid) scaffold fabricated by a gelatin particle leaching method

Porous poly(l-lactic acid) (PLLA) scaffolds fabricated by a gelatin particle-leaching technique have good mechanical property and cytocompatibility, as demonstrated by a previous in vitro study. Here we investigate further the in vitro degradation of the scaffolds in terms of weight loss, water uptake, weight-average molecular weight, thermal behavior and morphology during a 39 week period in phosphate-buffered saline. The water uptake decreased dramatically during the initial stage due to release of the remaining gelatin, and then increased slightly with degradation time. The weight-average molecular weight decreased linearly as a function of time, while the crystallinity steadily increased with slightly decreased melting temperature. After degradation, many defects and big holes were seen in the scaffolds by scanning electron microscopy. Cartilage regeneration and scaffold disappearance in vivo were compared by implanting the construct into nude mice for 30-120 days. While the scaffolds maintained their intact pore structure after 23 weeks of degradation in vitro, they almost disappeared in vivo at the same time, implying a faster degradation rate in vivo. By 120 days after implantation, the scaffolds were hardly seen in the newly formed cartilage-like tissue. The regenerated cartilages could not maintain their predesigned shape after a long period of in vivo culture due to the weakening of the mechanical strength of the constructs as a result of PLLA degradation. The regions occupied initially by PLLA scaffold were filled later by collagen type II secreted by the chondrocytes, but with no evident basophilic proteoglycan.     

Quantitative measurement of telomerase activity and localization of its catalytic subunit (hTERT) in chronic inflammation of capsule formation around various model implants and in sarcomas in a rat model

Telomerase is upregulated in some preneoplastic lesions and overexpressed in the majority of malignant tumors, but absent in most nonneoplastic somatic tissues. We analyzed telomerase activity using TRAP-assay in capsule tissues in a rat model with chronic inflammation and in tumor, and visualized the catalytic subunit of telomerase (hTERT) by immunhistochemistry. Significant elevated telomerase activity was found in tumor tissue compared with nonneoplastic tissue (p = 0.047). Cases with a strong inflammation in capsule tissue showed a specific telomerase activity. In these cases, there were no significant differences in telomerase activities compared with malignant tumor tissue. We demonstrate elevated telomerase activity and its diagnostic limits around model implants in a rat model, and visualize its expression not only in malignant tissue but also in inflammatory cells. So the quantitative measurement of telomerase activity should not be applied in general as a marker for malignancy in capsule tissue.     

The american alligator (Alligator mississipiensis): a new model for investigating developmental mechanisms in normal and abnormal palate formation

Despite numerous investigations, there are still many unsolved problems concerning normal and abnormal palatal development. The American Alligator is here put forward as a new model for the investigation of a variety of developmental phenomena associated with palatogenesis. The structure of the palate of the adult Alligator is reported. This animal exhibits a unique combination of reptilian and mammalian features in its craniofacial anatomy and so its craniofacial development should be of considerable interest.     

Vessel size index measurements in a rat model of glioma: comparison of the dynamic (Gd) and steady-state (iron-oxide) susceptibility contrast MRI approaches

Vessel size index (VSI), a parameter related to the distribution of vessel diameters, may be estimated using two MRI approaches: (i) dynamic susceptibility contrast (DSC) MRI following the injection of a bolus of Gd‐chelate. This technique is routinely applied in the clinic to assess intracranial tissue perfusion in patients; (ii) steady‐state susceptibility contrast with USPIO contrast agents, which is considered here as the standard method. Such agents are not available for human yet and the steady‐state approach is currently limited to animal studies. The aim is to compare VSI estimates obtained with these two approaches on rats bearing C6 glioma (n = 7). In a first session, VSI was estimated from two consecutive injections of Gd‐Chelate (Gd₁ and Gd₂). In a second session (4 hours later), VSI was estimated using USPIO. Our findings indicate that both approaches yield comparable VSI estimates both in contralateral (VSI{USPIO} = 7.5 ± 2.0 µm, VSI{Gd₁} = 6.5 ± 0.7 µm) and in brain tumour tissues (VSI{USPIO} = 19.4 ± 7.1 µm, VSI{Gd₁} = 16.6 ± 4.5 µm). We also observed that, in the presence of BBB leakage (as it occurs typically in brain tumours), applying a preload of Gd‐chelate improves the VSI estimate with the DSC approach both in contralateral (VSI{Gd₂} = 7.1 ± 0.4 µm) and in brain tumour tissues (VSI{Gd₂} = 18.5 ± 4.3 µm) but is not mandatory. VSI estimates do not appear to be sensitive to T₁ changes related to Gd extravasation. These results suggest that robust VSI estimates may be obtained in patients at 3 T or higher magnetic fields with the DSC approach. Copyright © 2011 John Wiley & Sons, Ltd.     

Establishment of efficacy and safety assessment of human adipose tissue-derived mesenchymal stem cells (hATMSCs) in a nude rat femoral segmental defect model

Human adipose tissue-derived mesenchymal stem cell (hATMSC) have emerged as a potentially powerful tool for bone repair, but an appropriate evaluation system has not been established. The purpose of this study was to establish a preclinical assessment system to evaluate the efficacy and safety of cell therapies in a nude rat bone defect model. Segmental defects (5 mm) were created in the femoral diaphyses and transplanted with cell media (control), hydroxyapatite/tricalcium phosphate scaffolds (HA/TCP, Group I), hATMSCs (Group II), or three cell-loading density of hATMSC-loaded HA/TCP (Group III-V). Healing response was evaluated by serial radiography, micro-computed tomography and histology at 16 weeks. To address safety-concerns, we conducted a GLP-compliant toxicity study. Scanning electron microscopy studies showed that hATMSCs filled the pores/surfaces of scaffolds in a cell-loading density-dependent manner. We detected significant increases in bone formation in the hATMSC-loaded HA/TCP groups compared with other groups. The amount of new bone formation increased with increases in loaded cell number. In a toxicity study, no significant hATMSC-related changes were found in body weights, clinical signs, hematological/biochemical values, organ weights, or histopathological findings. In conclusion, hATMSCs loaded on HA/TCP enhance the repair of bone defects and was found to be safe under our preclinical efficacy/safety hybrid assessment system.     

Characteristics of synovial fluid effusion in collagen-induced arthritis (CIA) in the DA rat; a comparison of histology and antibody reactivities in an experimental chronic arthritis model and rheumatoid arthritis (RA)

We have characterized the cellular content and some antibody reactivities in synovial fluid (SF) from DA rats with CIA. Since CIA is widely used as a model for RA, in which many studies concerning immune responses are performed on SF samples, we considered it important to describe the local, disease-causing immune reactions in CIA. At the peak of disease (day 22 after immunization), the major cell population in CIA SF was granulocytes (72%), but macrophages (17.9%), plasma cells (2.6%) and lymphocytes (7.7%) were also present. The CIA synovial membrane (SM) obtained at the same time was mainly infiltrated by monocytes, with granulocytes, lymphocytes and plasma cells also present. Cell populations in blood did not differ between arthritic and normal DA rats. Equally, high anti-collagen type II (CII) and rheumatoid factor (RF) levels could be detected both in SF and in sera. Notably, RF levels were also increased in normal DA rats. Moderate levels of anti-heat shock protein 65 kD (hsp) antibodies were recorded systemically in both normal and diseased animals. In conclusion, the cellular composition in SF and in SM are similar in rat CIA and in RA. The morphological differences between SF and SM that are characteristic for RA could also be demonstrated in CIA. The antibody data indicate systemic production of anti-CII and anti-hsp antibodies as well as RF, but they give no support for local production of these antibodies in the joints, which is the case in RA.     

The decrease in hippocampal transient receptor potential M2 (TRPM2) channel and muscarinic acetylcholine receptor 1 (CHRM1) is associated with memory loss in a surgical menopause rat model

IntroductionThe aim of the study was to investigate the association of transient receptor potential M2 (TRPM2) channel and muscarinic acetylcholine receptor 1 (CHRM1) activity with the memorial functions that are deteriorated in surgical menopause.Material and methodsA total of 14 female rats were randomly divided into 2 groups: group (G)1: sham group; group (G)2: surgical menopause group, the group in which bilateral ovariectomy was performed. Fourteen days after the surgical procedure, learning and memorial tests were performed in G1 and G2 for a totally 13 days. The time required for the rats to find the cheese in the labyrinth was recorded and statistical evaluation of it was performed between groups. On the 14^th day of the memory test, the rats were decapitated and the brain tissues were fixed in 10% formalin. Hippocampal TRPM2 and CHRM1 gene expression was evaluated with RNA isolation, complementary DNA (cDNA) synthesis and quantitative real-time PCR (qRT-PCR) analysis. TRPM2 and CHRM1 immunoreactivity was evaluated in hippocampal tissue with the immunohistochemical method. Histo-score was calculated regarding the diffuseness of and severity of the staining; and statistical analyses were performed.ResultsIn the ovariectomized group, the mean time required for the rats to find the cheese was statistically significantly elongated (39.29 ±4.0 s vs. 29.86 ±2.6 s). When the hippocampal TRPM2 and CHRM1 gene expression and immunoreactivity were compared with the sham group, there was a statistically significant decrease in the surgical menopause group (p < 0.05).ConclusionsIn surgical menopause, in deterioration of memorial functions, hippocampal TRPM2 channel and CHRM1 activity plays an important role.     

MRI and quantitative autoradiographic studies following bolus injections of unlabeled and (14)C-labeled gadolinium-diethylenetriaminepentaacetic acid in a rat model of stroke yield similar distribution volumes and blood-to-brain influx rate constants

In previous studies on a rat model of transient cerebral ischemia, the blood and brain concentrations of gadolinium‐diethylenetriaminepentaacetic acid (Gd‐DTPA) following intravenous bolus injection were repeatedly assessed by dynamic contrast‐enhanced (DCE)‐MRI, and blood‐to‐brain influx rate constants (K_i) were calculated from Patlak plots of the data in areas with blood–brain barrier (BBB) opening. For concurrent validation of these findings, after completing the DCE‐MRI study, radiolabeled sucrose or α‐aminoisobutyric acid was injected intravenously, and the brain disposition and K_i values were calculated by quantitative autoradiography (QAR) assay employing the single‐time equation. To overcome two of the shortcomings of this comparison, the present experiments were carried out with a radiotracer virtually identical to Gd‐DTPA, Gd‐[¹⁴C]DTPA, and K_i was calculated from both sets of data by the single‐time equation. The protocol included 3 h of middle cerebral artery occlusion and 2.5 h of reperfusion in male Wistar rats (n = 15) preceding the DCE‐MRI Gd‐DTPA and QAR Gd‐[¹⁴C]DTPA measurements. In addition to K_i, the tissue‐to‐blood concentration ratios, or volumes of distribution (V_R), were calculated. The regions of BBB opening were similar on the MRI maps and autoradiograms. Within them, V_R was nearly identical for Gd‐DTPA and Gd‐[¹⁴C]DTPA, and K_i was slightly, but not significantly, higher for Gd‐DTPA than for Gd‐[¹⁴C]DTPA. The K_i values were well correlated (r = 0.67; p = 0.001). When the arterial concentration–time curve of Gd‐DTPA was adjusted to match that of Gd‐[¹⁴C]DTPA, the two sets of K_i values were equal and statistically comparable with those obtained previously by Patlak plots (the preferred, less model‐dependent, approach) of the same data (p = 0.2–0.5). These findings demonstrate that this DCE‐MRI technique accurately measures the Gd‐DTPA concentration in blood and brain, and that K_i estimates based on such data are good quantitative indicators of BBB injury. Copyright © 2010 John Wiley & Sons, Ltd.     

Collateralization of frontal eye field (medial precentral/anterior cingulate) neurons projecting to the paraoculomotor region,superior colliculus,and medial pontine reticular formation in the rat: a fluorescent double-labeling study

Summary Paired injections of fluorescent tracers (True Blue, Diamidino-Yellow) were made into the oculomotor complex (OMC) and medial pontine reticular formation (mPRF), and superior colliculus (SC) and mPRF, in adult rats to retrogradely label the cortical cells of origin of projections to these oculomotor-related brainstem structures. While large numbers of single-labeled cells in the medial frontal cortex projected only to the mPRF, the presence of many double-labeled cells in the dorsomedial shoulder cortex (medial precentral/anterior cingulate areas), the rat frontal eye field (FEF), indicated that this cortical region contains lamina V pyramid neurons whose axons collateralize to project to the region of the OMC, SC, and mPRF. The similarities of rat and monkey FEF connections, and their relevance to the control of eye movement, are discussed.Abbreviations AC anterior commissure - ACd anterior cingulate area, dorsal - ACv anterior cingulate area, ventral - AId anterior insular area, dorsal - AIv anterior insular area, ventral - BC brachium conjunctivum (superior cerebellar peduncle) - CP caudoputamen - DY Diamidino Yellow - IL infralimbic area - MAB medial accessory nucleus of Bechterew - MLF medial longitudinal fasciculus - mPRF medial pontine reticular formation - MO medial orbital area - OMC oculomotor complex - PAG periaqueductal gray - PrCl lateral precentral cortex - PrCm medial precentral cortex - PL prelimbic area - RN red nucleus - riMLF rostral interstitial nucleus of the MLF - rs rhinal sulcus - SC superior colliculus - TB True Blue - VLO ventrolateral orbital area