Fabrication of topologically complex three-dimensional microfluidic systems in PDMS by rapid prototyping

This paper describes a procedure for making topologically complex three-dimensional microfluidic channel systems in poly(dimethylsiloxane) (PDMS). This procedure is called the "membrane sandwich" method to suggest the structure of the final system: a thin membrane having channel structures molded on each face (and with connections between the faces) sandwiched between two thicker, flat slabs that provide structural support. Two "masters" are fabricated by rapid prototyping using two-level photolithography and replica molding. They are aligned face to face, under pressure, with PDMS prepolymer between them. The PDMS is cured thermally. The masters have complementary alignment tracks, so registration is straightforward. The resulting, thin PDMS membrane can be transferred and sealed to another membrane or slab of PDMS by a sequence of steps in which the two masters are removed one at a time; these steps take place without distortion of the features. This method can fabricate a membrane containing a channel that crosses over and under itself, but does not intersect itself and, therefore, can be fabricated in the form of any knot. It follows that this method can generate topologically complex microfluidic systems; this capability is demonstrated by the fabrication of a "basketweave" structure. By filling the channels and removing the membrane, complex microstructures can be made. Stacking and sealing more than one membrane allows even more complicated geometries than are possible in one membrane. A square coiled channel that surrounds, but does not connect to, a straight channel illustrates this type of complexity.

Patient compliance is critical for equivalent clinical outcomes for breast cancer treated by breast-conservation therapy

OBJECTIVE

To determine the compliance with a standard breast-conservation therapy (BCT) program in a predominantly indigent, minority population of patients with early breast cancer (stage I and II) served by a rural state institution in the South; to compare the clinical outcomes of this group with those reported in clinical trials; and to examine the socioeconomic factors that may have contributed to the rate of compliance.

SUMMARY BACKGROUND DATA

Disease-free survival and overall survival in early breast cancer treated by BCT versus modified radical mastectomy are reported to be equivalent in prospective randomized trials. However, patients enrolled in clinical trials may not be representative of patients living in the various diverse communities that make up the United States. The authors' hypothesis is that patients enrolled in clinical trials at the national level may not be representative of indigent patients in the rural South and that clinical trial results may not be directly applicable.

METHODS

A retrospective review of 55 women with early-stage breast cancer treated from 1990 to 1995 was performed. Clinical data, compliance with treatment and clinical follow-up, and recurrence rates were examined. Statistical analysis performed include the Fisher exact test, Kaplan-Meier survival analysis, and log-rank test.

RESULTS

Full compliance (defined as completion of the entire course of radiation therapy and clinical follow-up) with the BCT program was observed in only 36% of patients. Fifteen of the 35 noncompliant patients did not complete radiation therapy. A significantly higher local failure rate was observed: 8 of these 15 patients (53%) have had local failure. In contrast, patients who were either in full compliance with the BCT program or were deficient only in that they missed part of their clinical follow-up had local failure rates of 5% (1/20) and 10% (2/20), respectively. Age, race, stage of cancer, economic status (measured by availability of medical insurance), distance of patient's residence from the hospital, and education level were evaluated as potential predictors of compliance. None predicted patient compliance, although a trend toward higher compliance was noted in patients with a higher education level, as determined by literacy testing.

CONCLUSIONS

Compliance with the BCT protocol at the authors' institution was worse than reported in clinical trials, and noncompliance translated into a significant increase in the local failure rate. Factors examined suggest that literacy may play a role in predicting compliance. Although BCT should be discussed with all breast cancer patients, the judicious application of clinical trial data to an institution's local population is warranted.

Diagnosis and management of a painful thyroid nodule in a patient with systemic sarcoidosis

Painful thyroid nodules caused by sarcoid are exceedingly rare. Painless involvement of the thyroid by sarcoid in patients with systemic sarcoidosis is not. Several autoimmune thyroid illnesses are closely linked to sarcoid. These illnesses may form thyroid nodules which may or may not be painful. We present only the second reported case of a painful thyroid nodule caused by direct sarcoid involvement. Fine needle aspiration may not provide a definitive diagnosis in patients whose appropriate therapy would vary greatly depending on this diagnosis. When an open surgical procedure is indicated, total unilateral thyroid lobectomy should be considered. Multi-centric involvement of a lobe with postoperative recurrence in remaining ipsi-lateral thyroid tissue would be very likely if the entire lobe is not removed.

Kinetics of P-selectin expression in regional vascular beds after resuscitation of hemorrhagic shock: a clue to the mechanism of multiple system organ failure

Leukocyte-endothelial cell interactions play an important role in mediating organ dysfunctions observed after hemorrhagic shock. P-selectin is the first endothelial cell adhesion molecule to be upregulated after an ischemic insult. The objective of this study was to define kinetics of P-selectin expression in different regional vascular beds of mice exposed to hemorrhagic shock. In-vivo P-selectin expressions were determined using dual radiolabeled monoclonal antibody technique in lungs, heart, liver, kidneys, intestinal mesentery, stomach, small bowel, and colon 0.5, 1, 2, 5, 10, and 24 h after resuscitation of 40 mmHg hemorrhagic shock. In another group, P-selectin expression was determined in same organs 5 h after resuscitation of 30 mmHg hemorrhagic shock. Hemorrhagic shock of 40 mmHg caused significant upregulation of P-selectin in lungs and liver at 30 min after resuscitation (P < 0.001). There was a second and more pronounced upregulation of P-selectin in lungs and liver at 5 h after resuscitation (P < 0.001). In heart, intestinal mesentery, stomach, small bowel, and colon, P-selectin was not upregulated until 5 h after resuscitation from 40 mmHg hemorrhagic shock (P < 0.001). While hemorrhagic shock of 40 mmHg did not cause P-selectin upregulation in kidneys, hemorrhage to 30 mmHg did elicit a significant increase at 5 h after resuscitation (P < 0.001). We conclude that P-selectin is upregulated after resuscitation of hemorrhagic shock in lungs, liver, heart, stomach, and intestines. P-selectin upregulation in kidneys only takes place after more severe hemorrhagic shock.

Both ischemic and pharmacological preconditioning decrease hepatic leukocyte/endothelial cell interactions

BACKGROUND

Ischemic preconditioning has been shown to protect some tissues from ischemia/reperfusion (I/R) injury. Adenosine is believed to play an important role by attenuating leukocyte-endothelial cell adhesive interactions. Dipyridamole increases adenosine bioavailability. The purpose of this study was to evaluate the effects of mechanical (MPC) and pharmacological preconditioning (PPC) on leukocyte endothelial cell interaction in hepatic I/R injury.

METHODS

C57BL6 mice were subjected to 30 min of ischemia to the left lobe of the liver. Groups tested at 30 min, 2, 5, 12, and 24 hr of reperfusion had 1) sham laparotomy (n = 10, 2) I/R (n = 25), 3) ischemic preconditioning with 5 min of ischemia and 10 min reperfusion before I/R (n = 25), and 4) (PPC) with dipyridamole (n = 25). Intravital microscopic examination was used to assess leukocyte/endothelial cell adhesion. Blood was drawn for leukocyte counts and liver function tests.

RESULTS

A significant decrease in leukocyte rolling was observed at 30-min and 5-hr reperfusion intervals in the PPC and ischemic preconditioning groups compared with the I/R group. A significant decrease in leukocyte saltation was also observed in the PPC and MPC groups at 2, 5, and 12 hr of reperfusion when compared with the I/R group. aspartate aminotransferase was significantly decreased in the 5-hr preconditioning groups. There was not a significant decrease in the white blood cell count because of PPC or MPC vs. I/R CONCLUSIONS: Preconditioning decreases endothelial/ leukocyte interaction and reduces liver damage as measured by aspartate aminotransferase. These data prove that IPC and PPC provide some degree of hepatic protection in I/R injury.

Fabrication of microfluidic systems in poly(dimethylsiloxane)

Microfluidic devices are finding increasing application as analytical systems, biomedical devices, tools for chemistry and biochemistry, and systems for fundamental research. Conventional methods of fabricating microfluidic devices have centered on etching in glass and silicon. Fabrication of microfluidic devices in poly(dimethylsiloxane) (PDMS) by soft lithography provides faster, less expensive routes than these conventional methods to devices that handle aqueous solutions. These soft-lithographic methods are based on rapid prototyping and replica molding and are more accessible to chemists and biologists working under benchtop conditions than are the microelectronics-derived methods because, in soft lithography, devices do not need to be fabricated in a cleanroom. This paper describes devices fabricated in PDMS for separations, patterning of biological and nonbiological material, and components for integrated systems.

Fabrication of microfluidic systems in poly(dimethylsiloxane)

Microfluidic devices are finding increasing application as analytical systems, biomedical devices, tools for chemistry and biochemistry, and systems for fundamental research. Conventional methods of fabricating microfluidic devices have centered on etching in glass and silicon. Fabrication of microfluidic devices in poly(dimethylsiloxane) (PDMS) by soft lithography provides faster, less expensive routes than these conventional methods to devices that handle aqueous solutions. These soft-lithographic methods are based on rapid prototyping and replica molding and are more accessible to chemists and biologists working under benchtop conditions than are the microelectronics-derived methods because, in soft lithography, devices do not need to be fabricated in a cleanroom. This paper describes devices fabricated in PDMS for separations, patterning of biological and nonbiological material, and components for integrated systems.

The use of FDG-positron emission tomography for the evaluation of colorectal metastases of the liver

Each year at least 130,000 people in the United States are diagnosed with colorectal carcinoma. Approximately 14,000 of these patients will have liver metastases, and 20 per cent of these patients will die from these metastases. Surgical resection is the only possible chance for cure in patients with only intrahepatic metastases, and extrahepatic disease is a contraindication to glucose metabolism. Positron emission tomography (PET) allows the in vivo study of the uptake and use of glucose in human cells. Here, we review our experience with the use of PET imaging for the diagnosis and management of colorectal metastases of the liver. We conducted a retrospective chart review of 14 patients undergoing PET imaging for known or suspected hepatic metastases from colorectal carcinoma. Results of CT, magnetic resonance imaging, and PET images were compared with pathological specimens. CT scan identified 7 lesions, and PET identified 31 intrahepatic lesions. Of the 6 patients who underwent surgery, CT identified 4 (20%) and PET identified 17 (85%) of the 20 intrahepatic metastases histologically confirmed. The accuracy (number of lesions) of CT and PET was 20 per cent and 85 per cent, respectively. CT scans had a sensitivity (number of patients) of 50 per cent, and PET had a sensitivity of 100 per cent in patients undergoing surgical resection. PET imaging altered the management in 49 per cent of patients. Twenty-one per cent of patients had their surgery cancelled due to previously undiagnosed extrahepatic metastases. Twenty-one per cent of patients had negative CT scans and underwent surgery on the basis of their PET images, and all had histologically proven disease. One patient avoided a second-look laparotomy when PET revealed a lesion seen on CT to be false positive. PET is an ideal imaging modality to detect intra- and extrahepatic metastases from colorectal carcinomas and would aid in the surgical management of these patients.

Effects of dextran and pentoxifylline on hemorrhagic shock-induced P-selectin expression

BACKGROUND

Dextran and pentoxifylline have been shown to prevent leukocyte-endothelium adherence encountered after hemorrhagic shock. P-Selectin is the first endothelial cell adhesion molecule to be upregulated after an ischemic insult. We investigated the effects of resuscitation with dextran 70 and administration of pentoxifylline during resuscitation on hemorrhagic shock-induced P-selectin expression.

MATERIAL AND METHODS

Hemorrhagic shock was induced in C57BL/6 mice by withdrawing blood to reduce mean arterial blood pressure to 30 mm Hg for 45 min. Animals were resuscitated by infusing one of the following solutions (each n:5): (1) Ringer's lactate, (2) 6% dextran 70, (3) Ringer's lactate plus 50 mg/kg pentoxifylline, (4) 5% human albumin. Afterward shed blood was infused. In vivo P-selectin expression was determined using dual-radiolabeled monoclonal antibody technique in lung, heart, liver, kidney, mesentery, stomach, small bowel, and colon 5 h after resuscitation.

RESULTS

P-Selectin was significantly upregulated in all of the organs studied in the Ringer's lactate resuscitation group (P < 0.001). Resuscitation with dextran 70 and administration of pentoxifylline during resuscitation prevented P-selectin upregulation. Resuscitation with human albumin caused significant attenuation but could not prevent P-selectin upregulation (p < 0.01).

CONCLUSION

Our study implies that the prevention of hemorrhagic shock-induced leukocyte-endothelium adherence by dextran 70 and pentoxifylline observed in other studies may be mediated by prevention of P-selectin expression by these agents.

SWORD '98: surveillance of work-related and occupational respiratory disease in the UK

The SWORD surveillance scheme, now 10 years old, uses systematic reporting from physicians to provide a picture of the incidence of occupational respiratory disease in the United Kingdom. An estimated total of 2966 incident cases was derived from reports by chest and occupational physicians during the 1998 calendar year. Occupational asthma continues to be the most-reported respiratory condition, with an estimated 822 cases (27% of total cases). The proportion of cases of mesothelioma (23%), benign pleural disease (21%) pneumoconiosis (7%) and inhalation injuries (6%) remain similar to those estimated in past years, although fewer cases overall were reported. The most commonly identified agents causing asthma in 1998 were enzymes, isocyanates, laboratory animals and insects, colophony and fluxes, flour, latex, and glutaraldehyde. An increased incidence of respiratory diseases of short latency was seen in mining, whilst cases in chemical, mineral products and motor vehicle manufacture remained high; lower rates were noted in wood products and textile manufacture when compared with 1997 figures. Inhalation accidents over the past 3 years were reviewed; gaseous agents and combustion products accounted for nearly half of cases. High rates for inhalation injuries were seen in coal miners, fuel production, motor vehicle manufacturing, water purification, and chemical manufacturing.

Chrysotile, tremolite and fibrogenicity

Recently published analyses have shown that the risks of mesothelioma and lung cancer in Quebec chrysotile miners and millers were related to estimated level of fibrous tremolite in the mines where they had worked. An analysis has therefore been made of radiographic changes in men who in 1965 were employed by companies in Thetford Mines where the same question could be examined for fibrogenicity. Of 294 men who met the necessary requirements, 129 had worked in six centrally located mines, where the tremolite content was thought to be high, 81 in 10 peripheral mines where it was thought to be low and 84 in both. The median prevalence of small parenchymal opacities (> or = 1/0) in chest radiographs read by six readers was higher among men ever than never employed in the central mines (13.6% against 7.4%), despite the fact that the mean cumulative exposure was lower in the former (430 mpcf.y vs 520 mpcf.y). After accounting by logistic regression for cigarette smoking, age, smoking-age interaction and cumulative exposure, the adjusted odds ratio for central mine employment was 2.44 (95% lower bound: 1.06). Together with other surveys of asbestos miners and millers, this study suggests that amphibole fibres, including tremolite, are more fibrogenic than chrysotile, perhaps to the same extent that they are carcinogenic, though the data available were not sufficient to address the latter question.

Cocaine-induced erythrocytosis and increase in von Willebrand factor: evidence for drug-related blood doping and prothrombotic effects

BACKGROUND

Mechanisms that mediate cocaine-induced cardiovascular events following vasoconstriction are incompletely understood.

OBJECTIVE

To examine the effects of cocaine in moderate doses on hematologic and hemostatic parameters that influence blood viscosity and thrombotic potential.

METHODS

Changes in hemoglobin concentration, hematocrit, and red blood cell counts were measured in human subjects who met Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition criteria for long-term cocaine abuse, before and sequentially after moderate intranasal and intravenous doses of cocaine. Hemostatic parameters, including von Willebrand factor, fibrinolytic activity, fibrinogen, plasminogen activator inhibitor antigen, and tissue-type plasminogen activator antigen, were sequentially measured after intravenous cocaine or saline placebo with cardiac troponin subunits T and I.

RESULTS

Hemoglobin level (P= .002), hematocrit (P =.01), and red blood cell counts (P = .04) significantly increased from 4% to 6% over baseline from 10 to 30 minutes after intranasal (n = 14) and intravenous (n = 7) cocaine administration in doses of 0.9 mg/kg and 0.4 mg/kg, respectively, with no change in white blood cell or platelet counts. There was a significant increase (P =.03) in von Willebrand factor from 30 to 240 minutes, peaking at 40% over baseline following intravenous cocaine administration in a dose of 0.4 mg/kg (n = 12), with no change after 0.2 mg/kg (n = 3) or placebo (n = 6). Other hemostatic factors, creatinine, blood urea nitrogen, and cardiac troponin subunits T and I showed no changes.

CONCLUSIONS

Cocaine induced a transient erythrocytosis that may increase blood viscosity while maintaining tissue oxygenation during vasoconstriction. An increase in von Willebrand factor without a compensatory change in endogenous fibrinolysis may trigger platelet adhesion, aggregation, and intravascular thrombosis.

P-selectin contributes to the initial recruitment of rolling and adherent leukocytes in hepatic venules after ischemia/reperfusion

We have recently reported that hepatic ischemia/reperfusion (I/R) is associated with a biphasic increase in the expression of P-selectin in the liver microvasculature, with peak expression levels observed at 20 min and 5 h after reperfusion. This I/R-induced upregulation of P-selectin expression is accompanied by leukocyte-endothelial cell adhesion in terminal hepatic venules (THV). The objective of this study was to determine whether the early expression of P-selectin contributes to the initial recruitment of rolling and adherent leukocytes in THV after liver I/R. Left hepatic lobe ischemia was induced for 30 min in anesthetized C57B1/6 and P-selectin knockout (KO) mice. The number of rolling, saltating, and adherent leukocytes in THV was measured at 0, 15, 30, 60, and 120 min after reperfusion using intravital video microscopy. Hepatic I/R elicited significant increases in the number of rolling, saltating, and adherent leukocytes, with peak values observed at 30 min after reperfusion. All of these responses were absent in P-selectin KO mice and in C57B1/6 mice treated with a blocking antibody to P-selectin. Our findings suggest that P-selectin is the primary determinant of leukocyte-endothelial cell adhesion observed in hepatic venules in the initial period after I/R. Hence, this adhesion molecule may represent a target for therapeutic intervention in liver transplantation and other conditions associated with hepatic I/R.

Are all successful renal transplants really successful?

We previously described a small group of renal transplant recipients considered to have successful allografts statistically, but who did not benefit clinically. These were patients in whom the grafts survived greater than 6 months but less than 3 years. This expanded study evaluates 179 consecutive renal transplant recipients divided into three groups. Group 1 (n = 18), group 2 (n = 41), and group 3 (n = 120) have patients with graft survival less than 6 months, between 6 months and 3 years, and greater than 3 years, respectively. Mean age, cause of renal failure, HLA match, and immunosuppressive regimen were not statistically different in any group. The number of acute rejection episodes, number of hospitalizations, and number and seriousness of complications were significantly greater in group 2 patients compared with the other groups. Patients in group 2 experienced five times the number of acute rejections (P < 0.0001), three times the number of hospitalizations (P < 0.0001), and two times the number of complications (P < 0.0001) compared with group 3 patients. In conclusion, those transplant recipients whose grafts survived longer than 6 months but less than 3 years were the most unfortunate. They experienced repeated and serious complications and spent many days in the hospital at great expense. A study with more sensitive methods of detecting presensitization might impact on graft performance in the future.

The role of ischemic preconditioning in the recruitment of rolling and adherent leukocytes in hepatic venules after ischemia/reperfusion

BACKGROUND

We have recently shown that hepatic ischemia/reperfusion (I/R) results in rolling and adherence of leukocytes in terminal hepatic venules (THV) followed by hepatic enzyme elevation and tissue destruction. The objective of this study was to determine the effect of ischemic preconditioning on the recruitment of leukocytes in THV after liver I/R.

METHODS

Left hepatic lobe ischemia was induced for 5 min (preconditioning) in anesthetized C57B1/6 mice followed by reperfusion for 10 min and then prolonged ischemia for 30 min. The number of rolling, saltating, and adherent leukocytes in THV was measured at 0.5, 2, 5, 12, and 24 h after reperfusion using intravital video microscopy. Matching sham groups were evaluated after 30 min of ischemia.

RESULTS

Hepatic I/R elicited significant increases in the number of rolling, saltating, and adherent leukocytes, with peak values observed at 30 min and 5 h after reperfusion. All of these responses were significantly attenuated in mice undergoing ischemic preconditioning. Rolling leukocytes in THV following I/R without preconditioning reached peak levels of 25.2 +/- 1.4 leuk/2 min (leukocytes/2 min) at 30 min reperfusion and 31.4 +/- 1.5 leuk/2 min at 5 h reperfusion. With ischemic preconditioning these values fell to 12.3 +/- 0.9 leuk/2 min and 14.4 +/- 1.0 leuk/2 min, respectively (P < 0.001). Similarly, adherent leukocytes in nonpreconditioned mice reached peak values of 4.8 +/- 1.3 leuk/2 min at 30 min reperfusion and 8.3 +/- 1.2 leuk/2 min at 5 h reperfusion compared with 2.0 +/- 1.5 leuk/2 min and 1.6 +/- 1.1 leuk/2 min in preconditioned mice, respectively (P < 0.001).

CONCLUSION

Ischemic preconditioning attenuates the initial events leading to leukocyte-mediated hepatic destruction following I/R injury. Delineating these mechanisms may play an important role in hepatic transplantation, resection, shock, and sepsis.

Can low volume liver transplant centers be successful? The Regional Transplant Center of Willis-Knighton & Louisiana State University Medical Center. The first 120 liver transplants

The development of orthotopic liver transplantation represents this century's most significant advance in the management of liver disease. In the 1980s the vast majority of liver transplants were performed at several large centers; however, in this decade, improvements in techniques and success rates have allowed live transplantation to expand to regional centers across the country, particularly in the southeast. This proliferation of regional centers and the widening disparity between organ availability and numbers of recipients have created tremendous controversy at the national level regarding the allocation scheme used to distribute livers to recipients. The large programs today are advocating change to a national waiting list which would eliminate local priority and jeopardize the existence of smaller regional centers. Furthermore, the large programs favor establishing a limited number of megacenters where all liver transplants would take place, arguing that low volume centers cannot perform liver transplants with acceptable complication and survival rates. At the Regional Transplant Center of Willis-Knighton Hospital and Louisiana State University Medical Center in Shreveport (WK/LSUMC) we performed 122 liver transplants between July 1, 1991 and December 31, 1997. The purpose of this study was to examine our complication and survival rates and compare them to national averages. The actuarial graft survival at 1, 2, and 3 years in this series compared to the national average respectively was 76% and 70%, 66% and 66%, 62% and 62%. The actuarial patient survival (WK/LSUMC vs National) at 1, 2, and 3 years was 80% and 80%, 75% and 75%, 70% and 74%. The rate of retransplantation was 8% with a national average of 10% to 20%. Our rate of graft primary non-function was 5% with the national average being 2% to 10%. The rate of vascular thrombosis of the graft in this series was 2% with a national rate of 5%. The differences in these results were not statistically significant (P < .05). Low volume transplant centers can perform liver transplant successfully, allowing the regionalization of the treatment of choice for end-stage liver disease.

Patterning cells and their environments using multiple laminar fluid flows in capillary networks

This paper describes the use of laminar flow of liquids in capillary systems to pattern the cell culture substrate, to perform patterned cell deposition, and to pattern the cell culture media. We demonstrate the patterning of the cell culture substrate with different proteins, the patterning of different types of cells adjacent to each other, the patterned delivery of chemicals to adhered cells, and performing enzymatic reactions over select cells or over a portion of a cell. This method offers a way to simultaneously control the characteristics of the surface to which cells are attached, the type of cells that are in their vicinity, and the kind of media that cells or part of a cell are exposed to. The method is experimentally simple, highly adaptable, and requires no special equipment except for an elastomeric relief that can be readily prepared by rapid prototyping.

Allergen exposure, atopy and smoking as determinants of allergy to rats in a cohort of laboratory employees

This study aimed to examine the relationship between exposure to rat urinary allergens, atopic status, smoking and the development of allergic symptoms and specific sensitization. It is a case-referent analysis of a cohort of 342 newly employed laboratory animal workers. Cases comprised persons developing symptoms of laboratory animal allergy or a positive skin prick test to rat urinary allergens; each was matched with up to two asymptomatic referents. Subjects were assigned to categories of exposure based on measurements of airborne rat urinary allergens. Of the cases, 80% reported that their symptoms started within 2 yrs of employment. The odds ratio (OR) for development of each symptom type (respiratory, eye or nose and skin) and of an immediate skin test reaction was increased in those with direct contact with rats. A gradient of increasing OR for the development of any such symptom across exposure categories was found; for respiratory symptoms and skin test reactions the OR for subjects in the highest exposure category were lower than those in intermediate categories, a pattern attenuated when the analysis was confined to outcomes developing within 2 yrs of first exposure. Atopy increased the OR of most outcomes as did cigarette smoking, although there was no evidence of a relationship between smoking and the development of a specific skin test reaction. In conclusion, allergen exposure was confirmed as the most important determinant of laboratory animal allergy; by implication, measures to reduce exposure may be the most effective means to reduce its incidence.

Role of P-selectin expression in hepatic ischemia and reperfusion injury

BACKGROUND

Researchers have shown that reperfusion of ischemic tissues initiates a complex series of reactions that paradoxically injure tissues. Although several mechanisms have been proposed to explain the pathobiology of ischemic/reperfusion (I/R) injury, much attention has focused on adhesion molecules. Our research is intended to show the kinetics of P-selectin in the liver in response to I/R injury.

METHODS

Left-lobar hepatic ischemia was induced for 30 min in 35 C57BL-6 mice and 20 P-selectin-deficient (K-O) mice. P-selectin expression was measured in these mice at 20 min, 2, 5, 12 and 24 h reperfusion times, as well as in control and sham animals. The animals were injected with radio-labeled P-selectin monoclonal antibody and the organs were harvested for counts/g tissue, expressed as the percentage injected dose. Serum liver enzymes were measured and pathological sections of ischemic and control livers were performed. The unpaired t-test was used for statistical analysis.

RESULTS

P-selectin expression showed two peaks in this animal model. The first peak was at 20 min and the second peak at 5 h of reperfusion (p < 0.001). We documented an 8-fold increase in aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactate dehydrogenase (LDH) levels 10 h following I/R injury. Pathological specimens showed periportal necrosis consistent with an ischemic event. P-selectin K-O mice showed no up-regulation as a separate control group, and the liver enzymes were significantly lower than the wild-type mice at 10 h (p < 0.001).

CONCLUSION

P-selectin has a bimodal expression following hepatic I/R injury. The first peak is attributed to the Weibel-Palade bodies and the second to new translational P-selectin. We noted no difference in the up-regulation of P-selectin in the ischemic and non-ischemic liver lobes in the same animal.

Rapid Prototyping of Microfluidic Systems in Poly(dimethylsiloxane)

This paper describes a procedure that makes it possible to design and fabricate (including sealing) microfluidic systems in an elastomeric material [Formula: see text] poly(dimethylsiloxane) (PDMS) [Formula: see text] in less than 24 h. A network of microfluidic channels (with width >20 μm) is designed in a CAD program. This design is converted into a transparency by a high-resolution printer; this transparency is used as a mask in photolithography to create a master in positive relief photoresist. PDMS cast against the master yields a polymeric replica containing a network of channels. The surface of this replica, and that of a flat slab of PDMS, are oxidized in an oxygen plasma. These oxidized surfaces seal tightly and irreversibly when brought into conformal contact. Oxidized PDMS also seals irreversibly to other materials used in microfluidic systems, such as glass, silicon, silicon oxide, and oxidized polystyrene; a number of substrates for devices are, therefore, practical options. Oxidation of the PDMS has the additional advantage that it yields channels whose walls are negatively charged when in contact with neutral and basic aqueous solutions; these channels support electroosmotic pumping and can be filled easily with liquids with high surface energies (especially water). The performance of microfluidic systems prepared using this rapid prototyping technique has been evaluated by fabricating a miniaturized capillary electrophoresis system. Amino acids, charge ladders of positively and negatively charged proteins, and DNA fragments were separated in aqueous solutions with this system with resolution comparable to that obtained using fused silica capillaries.

Spontaneous bacterial peritonitis in liver failure

Cirrhosis of the liver results from a variety of mechanisms that cause progressive hepatic injury. It is the sixth leading cause of death in all patients between the ages of 35 and 55. This study attempts to correlate the morbidity and mortality of spontaneous bacterial peritonitis in liver failure patients to numerous etiologic and clinical variables. A retrospective review of 26 patients with spontaneous bacterial peritonitis associated with chronic liver disease was performed in a university hospital. Demographics (age and gender), clinical variables (etiology of liver failure, Child's classification, prior history of ascites, fever, abdominal pain, encephalopathy, and upper gastrointestinal hemorrhage), and laboratory variables (ascitic polymorphonuclearcyte count and cultures, serum albumin, bilirubin, creatinine, and prothrombin time) were studied. All of the patients had Child's C liver disease. Mortality rate was 46 per cent. Alcohol (46%) and hepatitis (30%) were the most common etiologies. Escherichia coli and Klebsiella pneumoniae were the most common culture isolates. All of the infections were monomicrobial. The only significant predictor of mortality (P < 0.05) in this study was the peritoneal fluid polymorphonuclear (PMN) cell count. PMN count >1000 PMN/mm3 was associated with a mortality of 88 per cent. Few patients with spontaneous bacterial peritonitis are ultimately transplanted.