Summary Platelets play a key role in (sub)acute thrombotic occlusion after stenting. We examined the possible differences between biodegradable polylactide (PLA) and stainless steel (SS) stents in platelet attachment and morphology after whole blood perfusion. PLA stents of different configurations (spiral/braided) and polycaprolactone-polylactide (PCL-PLA)-coatings, or SS stents were implanted into a PVC tube (Ø 3.2 mm), with or without precoating of the tube with type-I collagen. PPACK (30 µM)-anticoagulated blood with 3H-serotonin prelabeled platelets was perfused (flow rate: 30 ml/min, 90 s) over the stents. Platelet deposition was assessed by scintillation counting and morphology by scanning electron microscopy (SEM). To examine coagulation activation, plasma prothrombin fragments (F1+2) were measured before and after the perfusion. Protein deposition on PLA/SS stents was assessed at augmented shear forces mimicking coronary flow (rate: 60 ml/min, 60 s) under minimal anticoagulation (PPACK 1 µM). More platelets deposited on PLA stents than on SS stents under all study conditions (p <0.03). Under anticoagulation (PPACK 30 µM) the generation of F1+2 remained unaltered. Under higher flow rate and limited anticoagulation SS stents accumulated 3.27 ± 0.75 µg and PLA stents 5.25 ± 1.74 µg of protein (Mean ± SD, p <0.95). Among all biodegradable stents, the braided PLA stent coated with PCL-PLA-heparin accumulated the fewest platelets (p <0.02). In SEM, signs of platelet activation on braided heparin-coated PLA stents, when compared with uncoated braided PLA/SS stents, appeared modest. In conclusion, PCL-PLAheparin coating of biodegradable stents may enhance their hemocompatibility, expressed by less platelet deposition. Nevertheless, materials, design, and coating techniques of biodegradable stents must be further developed.
To evaluate, in a pilot study, the efficacy and safety of combining a braided poly(lactic-co-glycolic acid) (PLGA, a copolymer of l-lactide and glycolide) urethral stent and dutasteride in the treatment of acute urinary retention (AUR) due to benign prostatic enlargement (BPE).Ten men with AUR due to BPE were treated as outpatients. A biodegradable braided PLGA urethral stent was inserted into the prostatic urethra, using a specially designed insertion device under visual control. Dutasteride treatment was started and the patients were followed up for 3 months after insertion of the stents.In all patients the stents were placed successfully with the new insertion device. All men were able to void after inserting the stent. At 1 month five patients voided freely with a low residual urine volume (<150 mL), two voided but had a high residual urine volume and a suprapubic catheter was placed, and three needed a suprapubic or an indwelling catheter before 1 month, due to AUR or comorbidities. At 3 months five patients were voiding with no problems.We have developed a new and effective insertion device for biodegradable braided prostatic stents. The new braided-pattern stent overcomes the earlier problems of migration and sudden breakage into large particles associated with biodegradable spiral stents. However, the mechanical properties of the new stent need to be improved and tested in a longer follow-up. We consider that this new biodegradable braided-pattern urethral stent could provide a new option in the future treatment of AUR.
To investigate in vitro whether pH ranging between 6 and 9 has an effect on the degradation of stent fibers made of poly(l-lactide-co-glycolide) (PLGA) 80/20.The fibers were divided into three groups and immersed in sodium phosphate-buffered saline (Na-PBS) solution with three different pH values: 6, 7.4, and 9. The mechanical and thermal properties were studied, and scanning electron microscopy (SEM) images were taken at specific time points of hydrolysis.The tensile testing showed that the strength of the fibers decreased through hydrolysis and was lost at 8 weeks in all groups. The T(m) and T(g) of the PLGA fibers did not indicate any significant differences between the different groups. In SEM images taken at 4 weeks, there were no significant differences between the fibers immersed in Na-PBS solutions of different pH values. However, at 8 weeks the surface of the fiber immersed in saline with a pH of 6 seemed coarser than that of those immersed in neutral (pH 7.4) or alkaline (pH 9) Na-PBS.The studied pH values did not influence the degradation behavior of the PLGA 80/20 fibers. Therefore, rabbits can be used as model animals for human biodegradable urological devices even though the pH of their urine is different.
Purpose:To report results of an in vivo pilot study to evaluate the biocompatibility and delivery system of a new biodegradable vascular stent and validate the study design. Methods:Two self-expanding intravascular stents, a biodegradable poly-D/L-lactic acid (PLA) and a medical stainless steel stent (Wallstent) were implanted in the common iliac arteries of 2 postpuberal female pigs and 3 laboratory-bred beagle dogs. Specimens were harvested after 45 days in the dogs and 32 days in the pigs for histomorphometry of the stented iliac artery segments. Preliminary measurements were made to assess the reliability of the quantitative histomorphometric measurements before final measurements Results:Histomorphometry analyses showed that mean luminal diameter and area were decreased in the PLA stent group (1.97±0.48 mm and 14±6.4 mm2, respectively) compared to the control stent group (4.28±0.83 mm and 61±19 mm2, respectively). The intimal thickness was higher in the PLA stent group (0.65±0.07 mm) than in the control group (0.44±0.21 mm). The mean injury score was 0.19±0.12 in the PLA stent group and 0.78±0.39 in the controls. In the PLA stent group, the mean inflammation score was 1.46±0.78 compared to 0.58±0.40 in the control group. There were no differences observed between the animal models. Conclusions:The PLA stent showed increased neointimal formation and reduced patency during early follow-up. Mechanical properties of the new biodegradable vascular stents are still inadequate, and the stent and the delivery device require modifications. The study methods were assessed as reliable and reproducible.
This study was designed to evaluate the suitability of a novel bioabsorbable material in treating bone defects. A poly(desaminotyrosyl-tyrosine-ethyl ester carbonate) (PDTE carbonate) membrane (thickness 0.2–0.3 mm) was implanted into the mandibular angle of 20 New Zealand White rabbits to cover a through-and-through defect (12×6 mm). In group 1, the defects were left unfilled but covered with membrane and in group 2 the defects were filled with bioactive glass mesh and covered with membrane, too. Controls were left uncovered and unfilled. The animals were followed for 6, 12, 24 and 52 weeks, respectively. The material was evaluated by qualitative analysis of histological reactions and newly formed bone. We found that PDTE carbonate elicited a modest foreign body reaction in the tissues, which was uniform throughout the study. New bone formation was seen in all samples after six weeks. Group 1 had more new bone formation until 24 weeks and after this the difference settled. Based on findings of this study it was concluded that PDTE carbonate membranes have good biocompatibility and are sufficient to enhance bone growth without additional supportive matrix.
Purpose: To assess the reliability of quantitative histomorphometry measurements for the intimal reaction that occurs after intraluminal stenting in an animal model. Methods: Two self-expanding intravascular stents, a biodegradable poly-D/L-lactic acid (PLA) stent and a stainless steel Wallstent, were implanted in the common iliac arteries of a beagle dog. After 45 days, the histomorphometry of the stented iliac artery segments was quantitatively measured. The relative standard error (RSE) of the estimate was calculated, and the reliability of measurements for maximal (LD max ) and minimal (LD min ) luminal diameters and internal (IELT) and external (EELT) elastic lamina thicknesses was assessed. Results: The PLA stent required more measurements of variables from a single slide to ensure reliable (RSE<10%) results (1 for LD max , 1 for LD min , 8 for IELT, and 4 for EELT) compared to the Wallstent (1 for LD max , 1 for LD min , 2 for IELT, and 2 for EELT 2). The measured results were reliable for both stent materials when variables were measured from 2 slides of each segment (proximal/central/distal) of the stent. Conclusions: We conclude that these preliminary measurements to estimate the reliability of quantitative histomorphometry measurements should be made and reported before final results are given.
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