Ultrasound-triggered delivery of paclitaxel encapsulated in an emulsion at low acoustic pressures

We investigated the in vitro ultrasound-triggered delivery of paclitaxel, a well known anti-cancerous drug, encapsulated in an emulsion and in the presence of CT26 tumor cells. The emulsion was made of nanodroplets, whose volume comprised 95% perfluoro-octyl bromide and 5% tributyl O-acetylcitrate, in which paclitaxel was solubilized. These nanodroplets, prepared using a high-pressure microfluidizer, were stabilized by a tailor-made and recently patented biocompatible fluorinated surfactant. The delivery investigations were performed at 37 °C using a high intensity focused ultrasound transducer at a frequency of 1.1 MHz. The ultrasonic pulse was made of 275 sinusoidal periods and the pulse repetition frequency was 200 Hz with a duty cycle of 5%. The measured viabilities of CT26 cells showed that paclitaxel delivery was achievable for peak-to-peak pressures of 0.4 and 3.5 MPa, without having to vaporize the perfluorocarbon part of the droplet or to induce inertial cavitation.

[Comparison between Stump Cylinder and custom mold, effect of the shape of the applicator on the dose distribution]

PURPOSE

The purpose of this study was to compare the efficacy of two applicators used in high dose rate vaginal brachytherapy. The first is the Stump Cylinder used in the "brachycenter" department at the Middle East Institute of Health in Lebanon and the second is the custom mold used in the radiotherapy department at Tenon Hospital in France.

MATERIALS AND METHOD

A comparison of the clinical target volume and the doses received by the rectum and bladder was performed in order to determine the best method of treatment and to optimize the dose distribution. 95 patients were treated in both departments.

RESULTS

The average values of the D95% dose received by the CTV were respectively 89.43% for the Stump Cylinder and 110.16% for the custom mold. The conformity index was 0.84 for the Stump Cylinder while it was 0.97 for the custom mold, which ensures a better dose distribution. For the rectum, the maximum dose D2cc taken by volume was 71.23% for the Stump Cylinder and 79.51% for the custom mold. The bladder was better protected with Stump Cylinder with a D2cc value of 65.81% against 94.88% for the custom mold.

CONCLUSION

The underdosing obtained using the Stump Cylinder was due to the shape of upper part of the cylinder which was not conform with the shape of the vaginal vault in women. A better protection of the organs at risk was observed with the Stump Cylinder since the dose taken by the rectum and bladder using a custom mold can reach the tolerance limits.

Development of a flow simulator to study haemodynamic behaviour of natural and artificial blood vessels under physiologic flow conditions

A new computer-controlled flow simulator has been designed to study the haemodynamic behaviour of natural and artificial blood vessels under physiologic flow conditions. The simulator can generate well characterized and fully developed laminar flow properties. It includes a unique perfusion case that imposes an axial tension on the vessel segment, and a commercial programmable pump to reproduce pulsatile flow rates. Response to high frequency commands was greatly attenuated and displayed a frequency dependent phase angle. Thus, for complex pulsating flow rates containing different frequency components, the system response was significantly distinct from the command. To reproduce physiologic waveforms, the transfer function of the whole system was determined for different amplitudes and frequencies of flow rate excitations. Each input command was compared to the measured flow rate, and the values of the gain and phase angle were evaluated. If the desired flow rate was composed of a sum of n sine wave components, each has a frequency fj and an amplitude Aj, a corrected command signal was then reconstructed by amplifying the attenuated components and advancing those lagged in time. The corrected signal was finally applied as the new command to the pump. The results showed an excellent agreement with physiologic waveforms. Examples of different pulsatile flow experiments to investigate the effects of frequency, pressure, and wall elasticity are presented.

Endothelial cells exposed to erythrocytes under shear stress: an in vitro study

After injury and vascular replacement, endothelial cell recovery is limited and could lead to thrombosis. Seeding small diameter vascular prosthesis with endothelial cells has been proposed to fulfil cell lining and improve surface hemocompatibility. However, detachment of seeded cells occurs following implantation. Previous in vitro studies have looked at the fluid shear stress as a major cause of cell detachment. To our knowledge, the role of erythrocyte collisions has not been investigated. The present in vitro study aims at investigating whether endothelial cell adhesion depends on (i) the presence of erythrocytes in flow and (ii) the latent culture period (1, 24 and 48 h) between seeding and exposure to flow. Endothelial cells were exposed to culture media containing different erythrocyte concentrations using a steady laminar flow of 1350 ml min(-1) in a parallel plate flow chamber. Endothelial cell morphology in dynamic conditions was quantified and compared to that in static conditions. The projected area of cells were mostly found smaller under dynamic than static conditions, particularly at a wall shear stress of 23 dyn cm(-2). Cells from the 1 h latent culture period were oriented parallel to the flow axis and were more elongated than under static conditions. Conversely, endothelial cell shape was slightly modified when either the latent period or the wall shear stress was increased. Disparate orientation was observed on confluent endothelial cells (24-48 h latent period) exposed to shear stress with or without erythrocytes. Increasing fluid viscous forces due to erythrocytes play a critical role on the behaviour of freshly seeded endothelial cells upon exposure to blood flow.

In vivo characterization of a fluoropassivated gelatin-impregnated polyester mesh for hernia repair

The present study was undertaken to evaluate a new prototype mesh that consists of a knitted polyester structure treated with a fluoropolymer and impregnated with gelatin. The Fluoropassiv mesh, as well as two controls, the Surgipro polypropylene mesh and the Gore-Tex expanded polytetrafluoroethylene patch, were used for the repair of experimentally induced abdominal hernias in piglets and followed for scheduled implantation periods of 4, 15, and 60 days. At the sacrifice the mesh and surrounding tissue were excised for histological assessment of the healing sequence, for the identification of changes in hematologic and immunological characteristics, and for the measurement of the mechanical properties. After cleaning to remove the encroaching tissue, the explanted devices were monitored for biostability by infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The present study has demonstrated that the Fluoropassiv mesh provides adequate mechanical strength and compares favorably with the two controls. No exacerbated systemic or in situ hematologic or immunological reactions were observed with either the meshes of the patch material. Histological studies revealed that thick collagenous and vascularized tissue were well anchored to the three biomaterials as early as 15 days after implantation. The degree of tissue penetration differed depending on the device. Chemically, they proved stable over time.

In vitro characterization of a fluoropassivated gelatin-impregnated polyester mesh for hernia repair

The surgical management of abdominal hernias requires prosthetic grafting in situations where the defect is too large or the surrounding tissue is not available for repair. Flat patches made of different biomaterials have been used in textile or microporous forms. The present work describes the results of an in vitro study comparing the morphological, mechanical, and chemical characteristics of a new textile prototype, Fluoropassiv, made of polyester fibers treated with a fluoropolymer and impregnated with gelatin to those of seven existing commercial meshes and patches made from polypropylene, polyester, polytetrafluoroethylene (PTFE) yarns, and expanded microporous PTFE graft. The morphological study revealed a diversity of structures having a minimal relative porosity of 70%, high bursting, and suture retention strengths in comparison with natural muscular tissue. Elasticmoduli proved to depend more on the direction of the textile the rigidity was higher for those materials having tight structure, like the Fluoropassiv and the Surgipro meshes (> 30 MPa), whereas those with more open structures, such as the Marlex, Trelex, Lars, Bard Teflon, and GoreTex structures, showed lower elastic modulus (10 mPa). In addition, chemical analyses confirmed no irregularities in the polymers used in all prostheses and demonstrated that the fluoropolymer coating of the Fluoropassiv was uniformly distributed. The innovative aspects in the construction of the knitted fabric Fluoropassiv appears to make it suitable for repairing hernias, and the inclusion of both continuous fluoropolymer surface treatment of polyester fibers and gelatin impregnation appears to improve the healing process.

Development of a parallel plate flow chamber for studying cell behavior under pulsatile flow

The design of a new parallel plate perfusion chamber for cell behavior studies involving pulsatile flowrates is presented. It was based on fluid mechanical considerations to ensure a region of regular and uniform shear stress at the wall. A numeric solution of the flow was performed to study the effect of pulsating flow on the entrance length. Dye injection investigations in the chamber showed laminar and uniform flow in the culture region under steady state conditions.

The influence of the number of endoclips and of mesh incorporation on the strength of an experimental hernia patch repair

The strength conferred to a mesh by fixing it with laparoscopic staples and the effects of tissue incorporation have never been quantified. Eighteen dogs were divided into three groups sacrificed at 2 days (5 dogs), 2 weeks (6 dogs), and 2 months (7 dogs). One 3.5- by 5-cm piece of abdominal wall was removed from each side through a median laparotomy, leaving the skin intact. A polypropylene mesh (5 by 7 cm) was fixed over one defect with four Endopath EMS staples (Ethicon Endo-surgery) and over the other with 16 EMS staples. At sacrifice, bursting strength (BS) was measured with an Instron tester and specimens were studied histologically. One-way analysis of variance and the Newmann-Keuls multiple-comparison test were used. BS tests showed that for each period studied, the strength of the repair performed with 16 staples was significantly higher than that obtained when four staples were applied. They also showed that tensile strength increased significantly in both groups as time elapsed. Light microscopy supported the conclusion that the initial strength of the repair was related to the number of clips and was significantly increased by cellular infiltration at 2 weeks and significantly more by collagen deposition at 2 months. At 2 months, BS was significantly higher in the 16-staples group, suggesting that initial fixation still plays a significant role.

Physical characterization of unimplanted gel filled breast implants. Should old standards be revisited?

Physical characterization of unimplanted gel filled mammary prostheses was undertaken using both destructive and non-destructive test methods. Physical properties measured included mass, volume, optical transmittance, coefficient of kinetic friction, mechanical stiffness, dynamic response to a stationary random vibration, bursting strength, elasticity of the envelopes, and nuclear magnetic resonance relaxation times. The data obtained from this study will provide reference points for quantifying the rate of degradation of prostheses in past and current clinical use. Some of the test methods are suitable for use as routine quality control procedures to improve the uniformity of the properties and performance of breast prostheses. This investigation also showed that some currently used prostheses do not comply with the relevant American Society for Testing and Materials standards, or even with the manufacturers' own stated claims or specifications.

Bursting strength evaluation. Comparison of 0-Prolene sutures and endoscopic staples in an experimental prosthetic patch repair of abdominal wall defect

Recently, titanium staples have been designed to stabilize a small prosthetic mesh used for laparoscopic herniorrhaphy. Unlike the giant prosthesis employed by Stoppa, the small mesh must be fixed to the surrounding musculo-aponeurotic defect. The strength of these titanium staples has never been evaluated and was compared to 0-Prolene sutures. In an ex vivo study, we evaluated the maximal stress (bursting strength [BS]) a repair performed with 0-Prolene sutures or staples can bear. Bilateral abdominal-wall defects were created in 16 piglets. A Prolene mesh was fixed preperitoneally on one side of the abdomen with 0-Prolene sutures and on the other side with the Endopath EMS stapler or the Endo Hernia stapler. The mean BS of meshes attached with 0-Prolene was 1,461.7 mmHg. The mean BS of meshes fixed with Endopath EMS staples was 885.5 mmHg and that of meshes fixed with Endo Hernia staples was 665.2 mmHg. A repair with 0-Prolene sutures is stronger (P < 0.05) than one with staples (Endopath EMS or Endo Hernia). Also, repair with an Endopath EMS stapler has a significantly higher BS (P < 0.05) than one with the Endo Hernia stapler. In the second part of the study, evaluation of the longitudinal tensile strength also showed that 0-Prolene sutures are stronger (P < 0.05) than staples. Endopath EMS staples are stronger (P < 0.05) than Endo Hernia staples.

Mechanical characterization of endoscopic surgical staples during an experimental hernia repair

Recent developments in laparoscopic hernia repair techniques have led to the design of titanium staples. In a laparoscopic hernia repair, a polypropylene mesh is stapled over the direct and indirect hernia sites in the inguinal region. The effectiveness of these staples in holding the prosthetic mesh, and therefore providing adequate strength to the abdominal wall, has not been yet investigated. We have characterized the bursting strength (BS) of an experimental hernia mesh repair fixed with Prolene suture, which is used extensively for this procedure, and the BS of repairs fixed with two currently available staplers, the Endopath EMS endoscopic multifeed stapler and the Endo Hernia stapler. We first simulated abdominal wall hernias in 16 piglets by creating incisions on both sides of the abdomen of each animal. Each defect was then covered with a polypropylene mesh, which was fixed on one side with Prolene sutures and on the other side using either the Endopath EMS (Group 1) or the Endo Hernia stapler (Group 2). The abdominal tissue with the mesh covering the defect was then excised and the BS evaluated using an Instron machine. Since many mechanical characteristics contribute to the BS of a repair, we investigated these characteristics in vitro, including tensile properties of the staples and the prosthetic mesh as well as the suture-tearing resistance of the mesh. Polypropylene mesh exhibits the same elongation in the three directions, i.e. 0 degrees , 45 degrees and 90 degrees . This elongation was estimated at 136% (SD = 130).(ABSTRACT TRUNCATED AT 250 WORDS)

Vascular access for hemodialysis: pathologic features of surgically excised ePTFE grafts

We analyzed 52 surgically excised ePTFE grafts used as secondary vascular access in chronic hemodialysis patients, structurally and histopathologically. Pseudoaneurysm formation at the site of repeated venipuncture was the main cause of surgical removal later than two years after implantation. Repeated needle punctures, twice per treatment, two or three times a week may result in a perigraft fibrous tissue capsule directly above areas where the graft was punctured. The delicate microporous structure of the graft wall was shown to be disrupted by needle punctures. The needle puncture sites were filled by surrounding connective tissue, and in one case, capillary formation was observed within the puncture sites. Examination by both light and scanning electron microscopy demonstrated identical patterns of pseudointima on the luminal surface. A thin pannus of endothelium-like cells, confined to the vicinity of the anastomoses, was noted in only four cases. On other areas of the luminal surface without endothelium, a red coagulum incorporating blood cells and fibrin was observed. Histological evidence of acute infection was absent in 61% of the cases and only 27% were considered to be clinically infected. Careful needle puncture technique, systematic rotation of puncture sites, and the use of rigorous aseptic technique are essential in preserving the long-term structural integrity of the vascular access, despite the good mechanical properties and reasonable good resistance to infection of ePTFE grafts.

A nonlinear analysis of pulsatile blood flow applied to investigate shear stress in arterial prostheses

Although the main function of an arterial graft is to restore distal blood flow, there is evidence that certain local parameters of blood flow, particularly wall shear stresses, are important in determining the graft's long-term patency. Wall shear stresses were associated with intimal hyperplasia, intimal proliferation, and endothelial cell development, morphology, and attachment. Here we present a detailed method which permits the investigation of the wall shear stress acting on arteries and prostheses in dogs. The theory takes into account the nonlinear terms of the Navier-Stokes equations as well as the nonlinear behaviour and large deformation of the arterial wall. It is based on the numerical resolution of the nonlinear equations by the Crank-Nicolson method which was selected for its unconditional stability. Through the locally measured values of the pressure, pressure gradient, radius and flow rate, the velocity distribution and wall shear stress at a given location along the artery or the prosthesis, can be determined. Complete results on the same dog are presented for the distal aorta and for the middle of a chemically processed prosthesis, implanted as substitute in the thoracic aorta.

Phonocardiogram spectral analysis simulator of mitral valve prostheses

Spectral analysis of sounds produced in vitro by mitral valve prostheses placed in a specially designed flow simulator has been carried out using a short-time Fourier representation of the recorded signal. Time variations of power spectra are displayed as a three-dimensional plot. Sounds produced by three types of valves, namely ball and cage, tilting disk and porcine valves, were analysed. Each valve type produced a characteristic spectrogram, and, for a given valve, spectrograms were reproducible to within a margin of 5 dB. The simulator may be used to detect structural deficiencies and functional abnormalities of prosthetic heart valves. In addition to quantifying the noise level of mechanical valves, the system may be used for quality control purposes to identify faulty valves.

An histo-morphological evaluation of ninety surgically excised human umbilical vein grafts

Morphological, histological, and scanning electron microscopy examinations were performed on 90 surgically excised human umbilical vein grafts. Most of the explanted grafts were removed because of thrombosis or infection and were removed typically from a patient in the mid 60s and after an average duration of implantation of 11 months. Multiple structural defects were found including deep folds, breaks on the luminal surface, and delamination. These areas as well as anastomotic sites represented potential areas for thrombotic accumulation. A higher incidence of infection was observed in grafts composed of 2 or 3 segments. Bacteria were often found in folds and could be seen invading the wall of the prosthesis. In addition, bacteremic colonization was often seen in noninfected grafts. The late aneurysmal formations were also of particular concern. The biodegradation of the wall and the disruption of the polyester mesh were the probable causes. The second generation Dardik Biograft aimed at reducing these formations. The success of this new processing remains to be evaluated.

Expanded polytetrafluoroethylene prostheses as secondary blood access sites for hemodialysis: pathological findings in 29 excised grafts

The popularity of expanded polytetrafluoroethylene (PTFE) arteriovenous fistulas for hemodialysis access is increasing. The low infection rate, low thrombogenicity and low body reactivity make it an important blood access for patients on routine hemodialysis. The authors examined 29 PTFE graft fistulas surgically excised from patients on hemodialysis for one or more of the following complications: infection 7, 2 with associated hemorrhage; thrombosis 9; aneurysm 11, 3 with associated thrombosis; stenosis 5, 3 with associated thrombosis; hemorrhage 4 and arterial steal 2. The explanted prostheses were reinforced Gore-tex in 20, Gore-tex thin wall in 1, Impra I in 4, Impra II in 3 and Vitagraft in 1. It was also noted that the implants failed in the short term mainly because of infection, in the medium term mainly because of thrombosis and stenosis, and in the long term usually because of aneurysm.

In vivo biostability of four types of arterial grafts with impervious walls; their haemodynamic and pathological characteristics

We describe the haemodynamic and pathological characteristics of four types of four impervious arterial prostheses, two alloplastic (Mitrathane and Gore-Tex), and two chemically processed bovine heterografts (Solcograft and Solco P). They were implanted in the thoracic aortae of dogs for durations of 24 hours, 48 hours, one week, two weeks, one month, three months and six months. Haemodynamic analyses showed no relation between the shear rate index, I.gamma, and compliance, CD. The observed shear rates are 6.5 times lower than those likely to damage the endothelial cell layer. Macroscopic and microscopic observations of explanted grafts showed the presence of obstructive thrombi at the anastomoses of Mitrathane grafts as early as one week. Gore-Tex grafts develop in the area of anastomoses parietal-thrombi which reorganize and become covered with pseudo-endothelial cells. The bovine heterografts show a similar behaviour. However, whereas Solcograft has an irregular thin wall, Solco P had improved characteristics except in the graft implanted for three months which demonstrated, some manufacturing weaknesses. Both types showed the development of anastomotic pannus covered with endothelial-like cells. All grafts, whether alloplastic or chemically processed, suffered from an absence of healing of the middle part of the prosthesis. The cause of this problem will be found in the analysis of the biochemical and enzymatic reactations between the material used and its physiological surrounding.

Biologic and structural evaluation of 80 surgically excised human umbilical vein grafts

Human umbilical vein is a valuable alternative to autogenous saphenous vein in lower-limb revascularization. However, the long-term patency is not as good. To understand better the reasons for this, the authors studied the biologic and structural changes occurring in 80 segments of human umbilical vein (HUV) grafts excised from 70 patients. Morphologic, histologic and scanning electron microscopy examinations were performed on each specimen. It was noted that increasing duration of implantation was associated with greater encapsulation and less surrounding inflammatory reaction. Twenty-six percent of clinically noninfected grafts were found to harbour bacteria. Bacteremic colonization was often in the folds of the luminal surface. As a result of these findings, the authors emphasize the need for complete excision of clinically infected grafts. Anastomoses between HUV segments are discouraged because they are associated with a high frequency of infection and a corresponding decrease in duration of implantation. Delamination of the wall was common, and such sites may represent areas at risk for further degradation. Continued surveillance of the biologic and structural changes occurring in excised grafts remains an important method in increasing our understanding of the evolutive complications of HUV grafts.

Quantitative characterization of blood rheological behavior in transient flow with a model including a structure parameter

Transient rheological behavior of blood which involves non newtonian viscosity, elasticity and thixotropy can be modelized with a Maxwell rheological state equation which depends on a structure parameter having dimension of a shear rate. Identification of the model parameters leads to use an exponential apparent shear rate step and to use recursive filters for taking into account the impulse response of the viscometer servo-control device. Typical results for a normal blood sample are given.