Monolithic microfabricated valves and pumps by multilayer soft lithography.
(41/1898)
Soft lithography is an alternative to silicon-based micromachining that uses replica molding of nontraditional elastomeric materials to fabricate stamps and microfluidic channels. We describe here an extension to the soft lithography paradigm, multilayer soft lithography, with which devices consisting of multiple layers may be fabricated from soft materials. We used this technique to build active microfluidic systems containing on-off valves, switching valves, and pumps entirely out of elastomer. The softness of these materials allows the device areas to be reduced by more than two orders of magnitude compared with silicon-based devices. The other advantages of soft lithography, such as rapid prototyping, ease of fabrication, and biocompatibility, are retained. (+info)
Tissue response to bioactive glass and autogenous bone in the rabbit spine.
(42/1898)
Bioactive glass S53P4 and autogenous bone were used as bone graft materials in an experimental rabbit model for spinal fusion. The study focused on differences in bone formation using bioactive glass and autogenous bone as bone graft materials. Bioactive glass, a mixture of bioactive glass and autogenous bone or autogenous bone was implanted for 4 and 12 weeks at the thoracolumbar level. Undecalcified sections were prepared for histological and histomorphometric evaluation. New bone formation was seen in all implanted areas, with the bone growing from the surface of the vertebrae enclosing both glass and autogenous bone in the bone fusion mass. During the observation period, the measured amount of bone remained at the same level in the autograft group, while in the glass and the glass/autograft bone groups it increased. By 12 weeks, no significant difference in bone formation between the three groups was observable. The bone formation in two selected standardized areas at 12 weeks was 21 and 24% in the glass group, 23 and 28% in the glass/autograft bone group and 27 and 26% in the autograft bone group. We consider bioactive glass as a potential bone graft material in experimental spinal fusion. (+info)
Evaluation of in vivo biocompatibility of different devices for interventional closure of the patent ductus arteriosus in an animal model.
(43/1898)
OBJECTIVE: To evaluate the in vivo biocompatibility of three different devices following interventional closure of a patent ductus arteriosus (PDA) in an animal model. MATERIALS AND METHODS: A medical grade stainless steel coil (n = 8), a nickel/titanium coil (n = 10), and a polyvinylalcohol foam plug knitted on a titanium wire frame (n = 11) were used for interventional closure of PDA in a neonatal lamb model. The PDA had been maintained by repetitive angioplasty. Between one and 278 days after implantation the animals were killed and the ductal block removed. In addition to standard histology and scanning electron microscopy, immunohistochemical staining for biocompatibility screening was also undertaken. RESULTS: Electron microscopy revealed the growth of a cellular layer in a cobblestone pattern on the implant surfaces with blood contact, which was completed as early as five weeks after implantation of all devices. Immunohistochemical staining of these superficial cells showed an endothelial cell phenotype. After initial thrombus formation causing occlusion of the PDA after implantation there was ingrowth of fibromuscular cells resembling smooth muscle cells. Transformation of thrombotic material was completed within six weeks in the polyvinylalcohol plug and around the nickel/titanium coil, and within six months after implantation of the stainless steel coil. An implant related foreign body reaction was seen in only one of the stainless steel coil specimens and in two of the nickel/titanium coil specimens. CONCLUSION: After implantation, organisation of thrombotic material with ingrowth of fibromuscular cells was demonstrated in a material dependent time pattern. The time it took for endothelium to cover the implants was independent of the type of implant. Little or no inflammatory reaction of the surrounding tissue was seen nine months after implantation. (+info)
Increasing age does not affect good outcome after lumbar disc replacement.
(44/1898)
From 1992 to 1998 fifteen Link-Charite SB III disc prostheses were implanted into 14 patients. The main indication was degenerative lumbar disc disease with segmental instability. With a mean follow-up of 48 months (18-68 months); 12 patients had a good (10) or fair (2) outcome regarding pain relief, return to employment and level of general physical activity. In contrast to previous publications we felt that age over 45 years did not appear to adversely affect the outcome. (+info)
Influence of atrial septal defect anatomy in patient selection and assessment of closure with the Cardioseal device; a three-dimensional transoesophageal echocardiographic reconstruction.
(45/1898)
BACKGROUND: The maximal diameter of the defect and the dimensions of the septal rims are essential parameters for the selection of optimal cases for device closure. Neither two-dimensional echocardiography nor balloon catheter sizing provide optimal data. Unique three-dimensional echocardiography might help to improve patient selection and assessment of results. Our aim was to optimize transcatheter closure of secundum type atrial septal defects using three-dimensional echocardiography. METHODS: Sixteen patients enrolled in a protocol for atrial septal defect transcatheter closure with the Cardioseal device underwent transoesophageal two- and three-dimensional echocardiography. Maximal diameter and tissue rim of the atrial septal defect were measured and compared by both methods. In the 12 patients selected for closure, the balloon stretched diameter was compared to three-dimensional echocardiography measurements. Device placement was assessed by two- and three-dimensional echocardiography. RESULTS: The shape of the atrial septal defect appeared variable on three-dimensional views: round in nine patients but complex (oval, raquet-shaped, multiple) in seven patients. The surface area of the atrial septal defect varied by 68+/-15% during the cardiac cycle. The correlation between atrial septal defect maximal diameters measured by two-dimensional transoesophageal echocardiography and three-dimensional echocardiography was better in round defects (y=1 x +1.6, r=0.99) than in complex defects (y=0.7 x -0.5, r=0.88). The antero-superior rim could only be properly assessed by three-dimensional echocardiography. In 12 patients the correlation between stretched diameter and three-dimensional echocardiography maximal diameter was poor (y=0.3 x +13, r=0.41). After placement of the device, three-dimensional echocardiography enabled the mechanism of residual shunting to be understood in three patients. CONCLUSIONS: Dynamic three-dimensional echocardiography enhances the understanding of the anatomy and physiology of atrial septal defect and should be an important process in future initiatives for device closures. (+info)
Transcatheter closure of multiple atrial septal defects. Initial results and value of two- and three-dimensional transoesophageal echocardiography.
(46/1898)
AIMS: To examine the feasibility of transcatheter closure of multiple atrial septal defects using two Amplatzer devices simultaneously and to describe the importance and the role of two- and three-dimensional transoesophageal echocardiography in the selection and closure of such defects. METHODS: Twenty-two patients with more than one atrial septal defect underwent an attempt at transcatheter closure of their atrial septal defects at a mean+/-SD age of 30. 8+/-18.6 years (range 3.7-65.9 years) and mean weight of 56.6+/-25.5 kg (range 12.9-99 kg) using two Amplatzer devices implanted simultaneously via two separate delivery systems. During catheterization, two dimensional transoesophageal echocardiography was performed in all but one patient, during and after transcatheter closure, while three dimensional transoesophageal echocardiography was performed in six patients before and after transcatheter closure. RESULTS: Forty-four devices were deployed in all patients to close 45 defects (one patient with three defects closed by two devices). Two dimensional transoesophageal echocardiography was helpful in selection and in guiding correct deployment of the devices. The mean size of the larger defect, as measured by transoesophageal echocardiography was 12.8+/-5.9 mm and the mean size of the smaller defect was 6.6+/-3.0 mm. The mean size of the larger devices was 15+/-7.5 mm, and 8.4+/-3.7 mm for the smaller. Three dimensional transoesophageal echocardiography provided superior imaging and demonstrated the number, shape and the surrounding structures of the atrial septal defects in one single view. The median fluoroscopy time was 28.7 min. Device embolization with successful catheter retrieval occurred in one patient. Forty-four devices were evaluated by colour Doppler transoesophageal echocardiography immediately after the catheterization with a successful closure rate of 97.7%. On follow-up colour Doppler transthoracic echocardiography demonstrated successful closure in 97.5% at 3 months. CONCLUSIONS: The use of more than one Amplatzer septal occluder to close multiple atrial septal defects is safe and effective. The use of two- and three-dimensional transoesophageal echocardiography provided useful information for transcatheter closure of multiple atrial septal defects using two devices. Three-dimensional transoesophageal echocardiography enhanced our ability to image and understand the spatial relationship of the atrial septal defect anatomy. (+info)
Shear stress-induced apoptosis of adherent neutrophils: a mechanism for persistence of cardiovascular device infections.
(47/1898)
The mechanisms underlying problematic cardiovascular device-associated infections are not understood. Because the outcome of the acute response to infection is largely dependent on the function of neutrophils, the persistence of these infections suggests that neutrophil function may be compromised because of cellular responses to shear stress. A rotating disk system was used to generate physiologically relevant shear stress levels (0-18 dynes/cm(2); 1 dyne = 10 microN) at the surface of a polyetherurethane urea film. We demonstrate that shear stress diminishes phagocytic ability in neutrophils adherent to a cardiovascular device material, and causes morphological and biochemical alterations that are consistent with those described for apoptosis. Complete neutrophil apoptosis occurred at shear stress levels above 6 dynes/cm(2) after only 1 h. Morphologically, these cells displayed irreversible cytoplasmic and nuclear condensation while maintaining intact membranes. Analysis of neutrophil area and filamentous actin content demonstrated concomitant decreases in both cell area and actin content with increasing levels of shear stress. Neutrophil phagocytosis of adherent bacteria decreased with increasing shear stress. Biochemical alterations included membrane phosphatidylserine exposure and DNA fragmentation, as evaluated by in situ annexin V and terminal deoxynucleotidyltransferase-mediated dUTP end labeling (TUNEL) assays, respectively. The potency of the shear-stress effect was emphasized by comparative inductive studies with adherent neutrophils under static conditions. The combination of tumor necrosis factor-alpha and cycloheximide was ineffective in inducing >21% apoptosis after 3 h. These findings suggest a mechanism through which shear stress plays an important role in the development of bacterial infections at the sites of cardiovascular device implantation. (+info)
Epithelialization of a synthetic polymer in the feline cornea: a preliminary study.
(48/1898)
PURPOSE: This study examined the potential of a synthetic polymer to support stable epithelial growth when implanted in the feline cornea. METHODS: A perfluoropolyether-based polymer was cast into lenticules that were coated with collagen I and implanted in four feline corneas. Epithelial growth onto the lenticules was monitored clinically for 6 weeks, after which time the animals were killed, and three corneas were evaluated histologically. Immunohistochemistry was used to identify proteins associated with the formation of a basement membrane (laminin) and adhesion complexes (bullous pemphigoid antigen and collagen VII). Electron microscopy was used to examine the tissue-polymer interface for evidence of the assembly of these adhesive structures. RESULTS: Postoperative epithelial growth began on days 2 to 3, and lenticules were fully epithelialized by days 5 to 9. Lenticules were clinically well tolerated and histology showed epithelium consisting of multiple layers adherent to the lenticule's surface. Laminin, bullous pemphigoid antigen and collagen VII were identified at the tissue-polymer interface using immunohistochemistry. Ultrastructural examination showed evidence of assembly of these proteins into a recognizable basement membrane and hemidesmosomal plaques. CONCLUSIONS: A perfluoropolyether-based polymer coated with collagen I was implanted in the feline cornea and supported epithelial growth that showed signs of persistent adhesion, both clinically and histologically. This polymer shows potential for ophthalmic applications that require sustained epithelialization. (+info)