Gap Between Evidence and Patient Access: Policy Implications for Bariatric and Metabolic Surgery in the Treatment of Obesity and its Complications

Despite consistently supportive evidence of clinical effectiveness and economic advantages compared with currently available non-surgical obesity treatments, patient access to bariatric and metabolic surgery (BMS) is impeded. To address this gap and better understand the relationship between value and access, the objectives of this study were twofold: (i) identify the multidimensional barriers to adoption of BMS created by clinical guidelines, public policies, and health technology assessments; and, most importantly, (ii) develop recommendations for stakeholders to improve patient access to BMS. Updated public policies focused on treatment and clinical guidelines that reflect the demonstrated advantages of BMS, patient education on safety and effectiveness, updated reimbursement policies, and additional data on long-term BMS effectiveness are needed to improve patient access.

The effects of ambient lighting in chest radiology reading rooms

Under typical dark chest radiography reading room conditions, a radiologist's pupils contract and dilate as their visual focus intermittently shifts between the high luminance monitor and the darker background wall, resulting in increased visual fatigue and degradation of diagnostic performance. A controlled increase of ambient lighting may minimize these visual adjustments and potentially improve comfort and accuracy. This study was designed to determine the effect of a controlled increase of ambient lighting on chest radiologist nodule detection performance. Four chest radiologists read 100 radiographs (50 normal and 50 containing a subtle nodule) under low (E=1 lx) and elevated (E=50 lx) ambient lighting levels on a DICOM-calibrated, medical-grade liquid crystal display. Radiologists were asked to identify nodule locations and rate their detection confidence. A receiver operating characteristic (ROC) analysis of radiologist results was performed and area under ROC curve (AUC) values calculated for each ambient lighting level. Additionally, radiologist selection times under both illuminance conditions were determined. Average AUC values did not significantly differ (p>0.05) between ambient lighting levels (estimated mean difference=-0.03; 95% CI, (-0.08, 0.03)). Average selection times decreased or remained constant with increased illuminance. The most considerable decreases occurred for false positive identification times (35.4±18.8 to 26.2±14.9 s) and true positive identification times (29.7±18.3 to 24.5±15.5 s). No performance differences were statistically significant. Study findings suggest that a controlled increase of ambient lighting within darkly lit chest radiology reading rooms, to a level more suitable for performance of common radiological tasks, does not appear to have a statistically significant effect on nodule detection performance.

Optimized image acquisition for breast tomosynthesis in projection and reconstruction space

Breast tomosynthesis has been an exciting new development in the field of breast imaging. While the diagnostic improvement via tomosynthesis is notable, the full potential of tomosynthesis has not yet been realized. This may be attributed to the dependency of the diagnostic quality of tomosynthesis on multiple variables, each of which needs to be optimized. Those include dose, number of angular projections, and the total angular span of those projections. In this study, the authors investigated the effects of these acquisition parameters on the overall diagnostic image quality of breast tomosynthesis in both the projection and reconstruction space. Five mastectomy specimens were imaged using a prototype tomosynthesis system. 25 angular projections of each specimen were acquired at 6.2 times typical single-view clinical dose level. Images at lower dose levels were then simulated using a noise modification routine. Each projection image was supplemented with 84 simulated 3 mm 3D lesions embedded at the center of 84 nonoverlapping ROIs. The projection images were then reconstructed using a filtered backprojection algorithm at different combinations of acquisition parameters to investigate which of the many possible combinations maximizes the performance. Performance was evaluated in terms of a Laguerre-Gauss channelized Hotelling observer model-based measure of lesion detectability. The analysis was also performed without reconstruction by combining the model results from projection images using Bayesian decision fusion algorithm. The effect of acquisition parameters on projection images and reconstructed slices were then compared to derive an optimization rule for tomosynthesis. The results indicated that projection images yield comparable but higher performance than reconstructed images. Both modes, however, offered similar trends: Performance improved with an increase in the total acquisition dose level and the angular span. Using a constant dose level and angular span, the performance rolled off beyond a certain number of projections, indicating that simply increasing the number of projections in tomosynthesis may not necessarily improve its performance. The best performance for both projection images and tomosynthesis slices was obtained for 15-17 projections spanning an angular are of approximately 45 degrees--the maximum tested in our study, and for an acquisition dose equal to single-view mammography. The optimization framework developed in this framework is applicable to other reconstruction techniques and other multiprojection systems.

Towards optimized acquisition scheme for multiprojection correlation imaging of breast cancer

RATIONALE AND OBJECTIVES

Correlation imaging (CI) is a form of multiprojection imaging in which multiple images of a patient are acquired from slightly different angles. Information from these images is combined to make the final diagnosis. A critical factor affecting the performance of CI is its data acquisition scheme, because nonoptimized acquisition may distort pathologic indicators. The authors describe a computer-aided detection (CADe) methodology to optimize the acquisition scheme of CI for superior diagnostic accuracy.

MATERIALS AND METHODS

Images from 106 subjects were used. For each subject, 25 angular projections of a single breast were acquired. Projection images were supplemented with a simulated 3-mm three-dimensional lesion. Each projection was then processed using a traditional CADe algorithm at high sensitivity, followed by the reduction of false-positives by combining the geometric correlation information available from the multiple images. The performance of the CI system was determined in terms of free-response receiver-operating characteristic curves and the areas under receiver-operating characteristic curves. For optimization, the components of acquisition, such as the number of projections and their angular span, were systematically changed to investigate which of the many possible combinations maximized the obtainable CADe sensitivity and specificity.

RESULTS

The performance of the CI system was improved by increasing the angular span. Increasing the number of angular projections beyond a certain number did not improve performance. Maximum performance was obtained between 7 and 10 projections spanning a maximum angular arc of 45 degrees .

CONCLUSION

The findings suggest the existence of an optimum acquisition scheme for CI of the breast. CADe results confirmed earlier predictions on the basis of observer models. An optimized CI system may be an important diagnostic tool for improved breast cancer detection.

The influence of increased ambient lighting on mass detection in mammograms

RATIONALE AND OBJECTIVES

Recent research has provided evidence that in reading rooms equipped with liquid crystal displays (LCDs), a measured increase of ambient lighting may improve clinicians' detection performance. In agreement with this research, the American College of Radiology (ACR) has recommended a moderate increase of ambient lighting in mammography reading rooms. This study was designed to examine the effect of a controlled increase of ambient lighting in mammography reading rooms on the diagnostic performance of breast imaging radiologists.

MATERIALS AND METHODS

Four breast imaging radiologists read 86 mammograms (43 containing subtle cancerous masses and 43 normal) under low (E = 1 lux) and elevated (E = 50 lux) ambient lighting levels on a Digital Imaging and Communications in Medicine-calibrated, medical-grade LCD. Radiologists were asked to identify cancerous masses and to rate their detection confidence. Observer areas under the curve (AUCs) were calculated using a receiver-operating characteristic analysis of fully paired results. Additionally, average observer selection times under both ambient lighting levels were determined.

RESULTS

Average radiologist AUCs decreased with elevated ambient lighting (0.78 +/- 0.03 to 0.72 +/- 0.04). Observer performance differences, however, were of the same order of magnitude as interobserver variability and were not statistically significant. Average selection times under increased ambient lighting remained constant or decreased, with the greatest decrease occurring for false-positive (20.4 +/- 18.9 to 14.4 +/- 9.6 seconds) and true-positive (18.0 +/- 13.8 to 12.9 +/- 9.4 seconds) selections.

CONCLUSION

The results agree with those of previous studies in that observer performance differences under a controlled increase of ambient lighting are not statistically significant. On the basis of these findings and ACR guidelines, a moderate increase of ambient lighting in mammography reading rooms is still suggested, but further research with additional cases and observers should be considered.

Design and Development of a New Multi-Projection X-Ray System for Chest Imaging

Overlapping anatomical structures may confound the detection of abnormal pathology, including lung nodules, in conventional single-projection chest radiography. To minimize this fundamental limiting factor, a dedicated digital multi-projection system for chest imaging was recently developed at the Radiology Department of Duke University. We are reporting the design of the multi-projection imaging system and its initial performance in an ongoing clinical trial. The system is capable of acquiring multiple full-field projections of the same patient along both the horizontal and vertical axes at variable speeds and acquisition frame rates. These images acquired in rapid succession from slightly different angles about the posterior-anterior (PA) orientation can be correlated to minimize the influence of overlying anatomy. The developed system has been tested for repeatability and motion blur artifacts to investigate its robustness for clinical trials. Excellent geometrical consistency was found in the tube motion, with positional errors for clinical settings within 1%. The effect of tube-motion on the image quality measured in terms of impact on the Modulation Transfer Function (MTF) was found to be minimal. The system was deemed clinic-ready and a clinical trial was subsequently launched. The flexibility of image acquisition built into the system provides a unique opportunity to easily modify it for different clinical applications, including tomosynthesis, correlation imaging (CI), and stereoscopic imaging.

A mathematical model platform for optimizing a multiprojection breast imaging system

Multiprojection imaging is a technique in which a plurality of digital radiographic images of the same patient are acquired within a short interval of time from slightly different angles. Information from each image is combined to determine the final diagnosis. Projection data are either reconstructed into slices as in the case of tomosynthesis or analyzed directly as in the case of multiprojection correlation imaging technique, thereby avoiding reconstruction artifacts. In this study, the authors investigated the optimum geometry of acquisitions of a multiprojection breast correlation imaging system in terms of the number of projections and their total angular span that yield maximum performance in a task that models clinical decision. Twenty-five angular projections of each breast from 82 human subjects in our breast tomosynthesis database were each supplemented with a simulated 3 mm mass. An approach based on Laguerre-Gauss channelized Hotelling observer was developed to assess the detectability of the mass in terms of receiver operating characteristic (ROC) curves. Two methodologies were developed to integrate results from individual projections into one combined ROC curve as the overall figure of merit. To optimize the acquisition geometry, different components of acquisitions were changed to investigate which one of the many possible configurations maximized the area under the combined ROC curve. Optimization was investigated under two acquisition dose conditions corresponding to a fixed total dose delivered to the patient and a variable dose condition, based on the number of projections used. In either case, the detectability was dependent on the number of projections used, the total angular span of those projections, and the acquisition dose level. In the first case, the detectability approximately followed a bell curve as a function of the number of projections with the maximum between 8 and 16 projections spanning angular arcs of about 23 degrees-45 degrees, respectively. In the second case, the detectability increased with the number of projections approaching an asymptote at 11-17 projections for an angular span of about 45 degrees. These results indicate the inherent information content of the multi-projection image data reflecting the relative role of quantum and anatomical noise in multiprojection breast imaging. The optimization scheme presented here may be applied to any multiprojection imaging modalities and may be extended by including reconstruction in the case of digital breast tomosynthesis and breast computed tomography.

Effect of dose reduction on the detection of mammographic lesions: a mathematical observer model analysis

The effect of reduction in dose levels normally used in mammographic screening procedures on the detection of breast lesions were analyzed. Four types of breast lesions were simulated and inserted into clinically-acquired digital mammograms. Dose reduction by 50% and 75% of the original clinically-relevant exposure levels were simulated by adding corresponding simulated noise into the original mammograms. The mammograms were converted into luminance values corresponding to those displayed on a clinical soft-copy display station and subsequently analyzed by Laguerre-Gauss and Gabor channelized Hotelling observer models for differences in detectability performance with reduction in radiation dose. Performance was measured under a signal known exactly but variable detection task paradigm in terms of receiver operating characteristics (ROC) curves and area under the ROC curves. The results suggested that luminance mapping of digital mammograms affects performance of model observers. Reduction in dose levels by 50% lowered the detectability of masses with borderline statistical significance. Dose reduction did not have a statistically significant effect on detection of microcalcifications. The model results indicate that there is room for optimization of dose level in mammographic screening procedures.

Ambient illumination revisited: A new adaptation-based approach for optimizing medical imaging reading environments

Ambient lighting in soft-copy reading rooms is currently kept at low values to preserve contrast rendition in the dark regions of a medical image. Low illuminance levels, however, create inadequate viewing conditions and may also cause eye strain. This eye strain may be potentially attributed to notable variations in the luminance adaptation state of the reader's eyes when moving the gaze intermittently between the brighter display and darker surrounding surfaces. This paper presents a methodology to minimize this variation and optimize the lighting conditions of reading rooms by exploiting the properties of liquid crystal displays (LCDs) with low diffuse reflection coefficients and high luminance ratio. First, a computational model was developed to determine a global luminance adaptation value, Ladp, when viewing a medical image on display. The model is based on the diameter of the pupil size, which depends on the luminance of the observed object. Second, this value was compared with the luminance reflected off surrounding surfaces, Ls, under various conditions of room illuminance, E, different values of diffuse reflection coefficients of surrounding surfaces, Rs, and calibration settings of a typical LCD. The results suggest that for typical luminance settings of current LCDs, it is possible to raise ambient illumination to minimize differences in eye adaptation, potentially reducing visual fatigue while also complying with the TG18 specifications for controlled contrast rendition. Specifically, room illumination in the 75-150 lux range and surface diffuse reflection coefficients in the practical range of 0.13-0.22 sr(-1) provide an ideal setup for typical LCDs. Future LCDs with lower diffuse reflectivity and with higher inherent luminance ratios can provide further improvement of ergonomic viewing conditions in reading rooms.

Determining the MTF of medical imaging displays using edge techniques

The modulation transfer function (MTF) of a medical imaging display is typically determined by measuring its response to square waves (bar patterns), white noise, and/or line stimuli. However, square waves and white noise methods involve capture and analysis of multiple images and are thus quite tedious. Measurement of the line-spread function (LSF) offers a good alternative. However, as previously reported, low-frequency response obtained from the LSF method is not as good as that obtained from measurement of edge-spread function (ESF). In this paper, we present two methods for evaluating the MTF of a medical imaging display from its ESF. High degree of accuracy in the higher frequency region (near the Nyquist frequency of the system) was achieved by reducing the noise. In the first method, which is a variant of the Gans' original method, the periodic raster noise is reduced by subtracting a shifted ESF from the ESF. The second method employs a low-pass differentiator (LPD). A novel near maximally flat LPD with the desired cut-off frequency was designed for this purpose. Noise reduction in both the methods was also achieved by averaging over large portions of the image data to form the ESF. Experimental results show that the MTF obtained by these methods is comparable to that obtained from the square wave response. Furthermore, the MTFs of rising and falling edges of a cathode ray tube (CRT) were measured. The results show that the rising and falling vertical MTFs are practically the same, whereas the rising horizontal MTF is poorer than the falling horizontal MTF in the midfrequency region.

Effect of reuse on surface characteristics of balloon angioplasty catheters

Surfaces of reused angioplasty catheter balloons were characterized by scanning electron microscopy (SEM), image analysis, Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The surfaces were found to have longitudinal ridges, cracks, wrinkled regions and particulates. Most of the particles were carbon-based, and contained traces of Cl and Si. The average number of particles ranged between 11 and 38 per mm2, while the average particle size ranged from 14 micron to 28 micron. About 70%-90% of the particles were larger then 10 micron which is approximately the diameter of the fine blood capillaries. The particles appeared to be firmly attached to the outer surface of the balloon. FT-IR and XPS analysis revealed the presence of Si, the absence of proteins, and suggested that the surface of the reused balloon catheters was oxidized. The study highlights the large number of particles created and released during angioplasty.

Ascitic fluid cholesterol in differential diagnosis of ascites

Cholesterol was estimated in ascitic fluid of 89 patients (29 malignant and 60 non-malignant ascites). Mean ascitic cholesterol level was significantly higher in malignant ascites (89.52 mg/dl) as compared to non-malignant ascites (29.93 mg/dl). At a cut off value of 48 mg/dl, the sensitivity, specificity, positive and negative predictive value and overall diagnostic accuracy for diagnosing malignant ascites is 96.5%, 96.6%, 93.3%, 98.3% and 96.6% respectively. Ascitic fluid cholesterol estimation is an easy and reliable test for differentiating malignant ascites from non-malignant ascites.

Release of chemicals from polyurethane foam in the Même breast implant

Samples of polyurethane (PU) foam from the Même breast implant were incubated at 37 degrees C in either 0.3-3.0 N sodium hydroxide (NaOH) solutions, normal saline, or methanol. The chemicals released were analyzed by gas chromatography (GC), gas chromatography/mass spectrometry (GC/MS), and Fourier-transform infra-red (FT-IR) spectroscopy. The surfaces of the treated and untreated foam samples were studied by scanning electron microscopy (SEM). The NaOH solutions hydrolysed the foam, releasing toluene diamine (TDA). Incubating the foam in methanol washed out trace quantities of anti-oxidant, 2,4-dimethyl-6-t-butylphenol (DBP). When the foam was incubated in normal saline at 37 degrees C no TDA was detectable but another compound with a mass ion of 173 was detected. Further GC/MS studies confirmed that this compound was polyol, one of the reagents used to manufacture the PU foam. Repeatedly incubating or washing the foam in normal saline or methanol eliminated the release of polyol. SEM studies of the foam samples before and after incubation experiments, showed no evidence of polymer degradation. These findings indicated that polyol was present in the PU foam only as an impurity or residue and did not originate from the breakdown of the foam itself.

In vitro degradation of a poly(ether urethane) by trypsin

In vitro enzymatic degradation of non-porous films of segmented poly(ether urethane) (Pellethane 2363-80AE) was investigated by incubating the biomaterial in concentrated trypsin solutions for 5 months at room temperature. Chemical degradation of films was monitored by surface analysis techniques such as Fourier transform infrared spectroscopy-attenuated total reflectance and electron spectroscopy for chemical analysis. This latter technique proved to be much superior in detecting chemical changes. Extraction of films with methanol and characterization of the extracts by gel permeation chromatography revealed the presence of low-molecular-weight polymers. Results have shown that trypsin has the ability to induce degradation in PEU, the soft segment being most affected, particularly the CH2-O bond of the ether linkages.

Leaching of plasticizers from and surface characterization of PVC blood platelet bags

The leaching of phthalate plasticizers from four types of blood platelet bags was investigated. The anticoagulant solutions used in the blood collection bags had pH values of 5.64 +/- .04 and contained no detectable amounts of phthalates. Platelet bag materials from each bag were soaked in normal salines for up to 5 days. The salines were tested for the leached phthalates from the bags but none could be found. However, di-(2-ethylhexyl) phthalate (DEHP) leached out of the PL-146 and Terumo bags into bovine calf serum used for soaking the bag materials. There was an increase in the amount of DEHP leached from about 1.1 mg at the end of one day to about 3.3 mg per gm of bag material at the end of a five day extraction with the serum. In PL-732 sets, a platelet bag made of a specialty polyolefin, the amount of DEHP leached out was less than 0.02 mg per g of bag material. CLX bags, which contained tri-(2-ethylhexyl) trimelliate (TETM) as a plasticizer, showed a negligible amount of it leaching into the calf serum. Infra-red spectra showed that PL-146 bags had been coated with a layer of a fatty acid amide while the Terumo bags contained a layer of a silicone fluid on their inner surfaces. CLX bags showed a coating of stearates, which were probably soaps of calcium or zinc. Scanning electron microscopy (SEM) showed that the inner surfaces of each brand of the bag were distinctly different morphologically. The two PVC bags were very similar whereas the surfaces morphology of PL-732 was rougher. Terumo bag had a different surface morphology than those of the other bags whereas the CLX bags had a very regular surface pattern. The exact significance of the surface morphology is not certain but excessively rough surfaces may not be desirable for the bags.

Immobilization of enzymes on polypropylene bead surfaces by anhydrous ammonia gaseous plasma technique

Anhydrous ammonia gaseous plasma technique was used for the surface modification of polypropylene beads. Amino groups were added onto the surfaces of beads by exposing them to ammonia plasma. Through these amino groups covalent immobilization of glucose oxidase and peroxidase were carried out. The total amounts of immobilized glucose oxidase and immobilized peroxidase were found to be 52 and 43 micrograms/cm2, respectively. To assess the stability of enzyme-polypropylene linkage, beads with covalently immobilized glucose oxidase and peroxidase were washed with phosphate buffer. It was found that after the removal of the adsorbed enzymes, the concentration of covalently immobilized enzymes tended to reach a steady state. After additional washing with buffer for 5 to 6 h, 40-55% of the immobilized enzymes were found to be in the active form.

Degradation of explanted polyurethane cardiac pacing leads and of polyurethane

Polyurethane cardiac pacing leads explanted at autopsy and from reoperated patients were examined for degradation in the insulation. Scanning electron microscopy (SEM) analysis showed cracks on the polyurethane surface which were both parallel and perpendicular to the longitudinal axis of the lead. Surface analyses of leads were performed using Fourier-Transform Infra-red (FT-IR) spectrophotometry in the attenuated total reflectance mode. The FT-IR spectra of visibly deteriorated polyurethane from explanted lead sheaths were compared with that of unused polyurethane tubing used for such sheaths. Changes were most evident in the regions of 3000-2800, 1730 and 1368 cm-1. The observed alterations in the FT-IR spectra were consistent with a degradation mechanism involving oxidative chain cleavage in the polyurethane amorphous regions. New polyurethane tubing (Pellethane-Type 80A) was exposed to sodium hypochlorite to simulate a possible in-vivo process and generate reference material. Degradation with associated decreases in tensile strength and molecular weight was recorded. This study showed that polyurethane insulation used in pacing leads is susceptible to oxidative degradation.

Enhanced albumin binding to polypropylene beads via anhydrous ammonia gaseous plasma

Plasma surface modification technique was used to add amino groups onto the surfaces of polypropylene beads by exposing them to anhydrous ammonia plasma. Through these amino groups, albumin was attached to the polypropylene beads. Attached albumin was further stabilized by crosslinking with glutaraldehyde. The effect of washing albuminated polypropylene beads with saline and human plasma was investigated. It was found that after initial rapid removal of albumin, the concentration of attached albumin tended to reach a steady-state. After 52 h of washing, the amount of albumin retained on the beads varied between 125 and 171 micrograms/cm2.

Characterization of plasma polymerized polypropylene coatings

Propylene was polymerized at low pressure in a radio frequency plasma reactor. The plasma polymerized propylene (PPP) films were insoluble in toluene. Thermal analysis of PPP showed no phase transition took place up to 255 degrees C. From these results, it was concluded that PPP is a highly crosslinked polymer. To further characterize the deposited PPP, Fourier Transform infrared (FTIR) spectroscopy in the attenuated total reflection (ATR) mode was used. The deposited material was shown to be polymerized propylene as a spectrum of the material showed absorption bands characteristic of polypropylene.

Aggregation of insulin, containing surfactants, in contact with different materials

The aggregation of insulin and of insulin protected with surfactants was studied by shaking at 37 degrees C in glass, in polypropylene and polystyrene vials, and in CPI and Auto-Syringe insulin syringes and infusion sets. Surfactants such as Pluronic 17R8 and 25R5 hastened the aggregation, whereas Pluronic F68 was effective in preventing it. Furthermore, there was no change in the immunoreactivity of insulin containing Pluronic F68 even after 8 days of shaking. Unprotected insulin aggregated in all the vials. There appears to be little problem with the commercial syringes tested, but the infusion sets could cause aggregation of insulin if used over an extended period of time. Although Pluronic F68 prevented insulin aggregation in situ, it extracted more impurities from the contacting plastics. Further development in materials and design of insulin sets and insulin containers appears necessary.

In-vivo degradation of poly(lactic acid) of different molecular weights

Lactic acid was polymerized using tetraphenyl tin as a catalyst. The molecular weight of the resultant poly(lactic acid) varied between 0.89 X 10(6) and 2.94 X 10(6) depending upon the concentration of the catalyst used. In-vivo degradation of the poly(lactic acid) samples having 4 different molecular weights were studies by implanting these in Wistar rats. It was found that at the end of a 48-week implantation period lower molecular weight poly(lactic acid) samples were degraded at a faster rate than the higher molecular weight samples.

Characterization of plasma polymerized silicone coatings useful as biomaterials

Plasma polymerization techniques were used to deposit a layer of filler-free silicone rubber on a variety of substrate materials. The thickness of the deposited film was 0.5-0.8 micron. As it is the surface of the biomaterial that comes in direct contact with the body fluids, the surface of the biomaterial is of paramount importance. In this study, the plasma polymerized biomaterials were characterized. Thus, the scanning electron microscope (SEM) showed the surfaces to be smooth. To study the surface layer of the deposited polymer, Fourier-transform infrared spectrometry in the attenuated total reflection (ATR) mode was used. The deposited material was indeed silicone polymer with adsorption bands at 1262, 1020, and 802 cm-1 for the Si-CH3 bending, Si-0-Si stretching, and Si-CH3 bending, respectively. To find the bonding nature of the polymer, electron spectrometry for chemical analysis (ESCA) was used. The silicone polymer was shown to be highly cross-linked. To find the molecular weight between cross-links, swelling studies were done. Thus the results of the study show that the plasma polymerization could produce a filler-free silicone layer on a variety of substrate materials.

Toxicity evaluation of a novel filler free silicone rubber biomaterial by cell culture techniques

Cytotoxicity of a novel filler free silicone rubber (FFSR) was evaluated by studying its effect on mouse L929 cells. Silastic and a laboratory rubber tubing (RT) were used as control materials. Three different experimental methods were used. In method A, after six days of cell culturing in the sample extracts, there were 95, 80, and 50% of control viable cells for FFSR, Silastic, and RT, respectively. Similarly, in method B, after six days of direct contact between samples and the cells, there were 80, 40, and 20% of control viable cells for FFSR, Silastic, and RT, respectively. For the Agar Overlay Test, method C, the cells under the FFSR samples were normal and healthy compared to those under Silastic and RT. From these studies it was concluded that FFSR had the least cytotoxicity of the three materials studied.

Albuminated polymer surfaces for biomedical application

Amino groups were added on to the surfaces of Celgard-2400 membranes by exposing them to an ammonia plasma. The presence of amino groups on the surfaces was detected by an attenuated total reflection Fourier Transform infrared spectrometer and by the Auger electron spectrometer. Through these amino groups, albumin was attached to the membranes. In some experiments, the attached albumin was further stabilized by cross-linking with glutaraldehyde. The effect of washing the albuminated membranes with saline and with plasma was investigated. It was observed that after the initial wash-out of albumin, the concentration of attached albumin tends to level off. The amount of albumin retained on the membranes varied between 275 to 357 micrograms/cm2.

Evaluation of plasma polymerized hexamethylcyclotrisiloxane biomaterials towards adhesion of canine platelets and leucocytes

Silicone coated Celgard-2400 and Silastic membranes were prepared by plasma polymerization of hexamethylcyclotrisiloxane. The adhesion of canine platelets and leucocytes was tested by passing whole blood from the anaesthetized mongrel dog in an ex-vivo shunt system. The silicone control Celgard and silicone coated Silastic membranes had fewer platelets and fewer leucocytes compared to those on the control Silastic membranes. Furthermore, these blood cells underwent fewer morphological changes on the silicone coated Celgard and Silastic compared to those on the control Silastic. From these observations the silicone coated biomaterials were judged to be better than the Silastic as far as the adhesion of platelets and leucocytes are concerned.

Effect of gamma radiation on the molecular weight and the anticoagulant activity of heparin

4 g% aqueous solutions of heparin were irradiated with the gamma radiation doses of 4.6 x 10(5) or 9.2 x 10(5) rads. The irradiated and also the non-irradiated heparin samples were fractionated using a Sephadex G-200 column. With radiation, the peak of the molecular weight distribution curves shifted toward the lower molecular weight. Also, the number average molecular weight decreased by 8.2 and 11.5% with the doses of 4.6 x 10(5) and 9.2 x 10(5) rads, respectively. The anticoagulant activity depended on the molecular weight of the heparin fractions. For the heparin fractions with molecular weights below 7,900, the anticoagulant activity decreased with radiation. Thus, for a heparin fraction with a molecular weight of 6,200, the anticoagulant activity decreased from 211 to 198 IU/mg after 4 h of irradiation.

Use of plasma polymerization for preparing silicone-coated membranes for possible use in blood oxygenators

The plasma polymerization of hexamethylcyclotrisiloxane (D3) and octamethylcyclotetrasiloxane (D4) over the microporous polypropylene membrane Celgard 2400, over polypropylene filter membranes, and over glass slides was investigated. The rate of polymer deposition was dependent upon the location of the substrate materials in the reaction vessel. The increase in weight of all the substrates was linear with the time of reaction, indicating a uniform polymerization rate. The rate of polymer deposition over polypropylene filters was found to be 2.27 micrograms/cm(2)/min for both D3, and D4, whereas over the glass slides it was 1.53 and 1.87 microgram/cm(2)/min for D3 and D4, respectively. The coated Celgard membranes showed better blood compatibility that Silastic sheeting or glass.

A novel filler free silicone rubber biomaterial. II. Radiation chemical and physical evaluation

Hexamethylcyclotrisiloxane was polymerized at 60 degrees C by gamma radiation to yield filler free silicone rubber (FFSR). The G (crosslinking) value of 23.5 was found for the FFSR polymerized for 4 hours, compared to about 2 for the pure polydimethylsiloxane (PDMS). The sol fractions for both FFSR and cross-linked PDMS varied between 5-7%. The FFSR and the cross-linked PDMS both had tensile strength of about 1 kg per cm2 but FFSR was not brittle and could be extended as much as 500% before breaking. It is believed that the marked improvement in physical properties of FFSR is due to the formation of domains of highly cross-linked material which act as "internal filler".

In vivo interactions between novel filler free silicone rubber and blood

To evaluate the thrombogenicity of the novel filler free silicone rubber (FFSR) prepared in our laboratory, its interactions with blood were studied. The test samples (FFSR) along with control Silastic samples were placed in an extracorporeal shunt and primed with sterilized normal saline. The blood from an anaesthetized and systemically heparinized dog was passed over these samples for predetermined time intervals. After washing, fixing, etc., the platelets adhering to the samples were counted under light microscopy. To study the morphological changes of the platelets adhering to the samples, they were examined under scanning electron microscope. The number of platelets adhering to the FFSR samples was very small compared to the Silastic samples. For example, when the blood was passed over the samples for 10 min the number of platelets sticking per 0.14 mm2 surface area was 10 for FFSR samples compared to 380 for Silastic. Furthermore, there were no leukocytes on FFSR samples compared to 10 on Silastic. From these studies, the novel filler free silicone rubber prepared in our laboratory was judged to be more compatible with formed elements of blood compared to the Silastic material.

Investigation of Erythrina spp. VII. Chemical constituents of Erythrina variegata var. orientalis bark

The petroleum ether extractive of the bark of Erythrina variegata var. orientalis was fractionated and shown to be composed of wax alcohols and wax acids, alkyl ferulates, alkyl phenolates, stigmasterol, sitosterol, campesterol and possibly citrostadienol/24-methylenelophenol. The ethanol extractive yielded chloroform-soluble and water-soluble bases, identified as erysovine and stachydrine, respectively.