A review of experimental techniques to produce a nacre-like structure

The performance of man-made materials can be improved by exploring new structures inspired by the architecture of biological materials. Natural materials, such as nacre (mother-of-pearl), can have outstanding mechanical properties due to their complicated architecture and hierarchical structure at the nano-, micro- and meso-levels which have evolved over millions of years. This review describes the numerous experimental methods explored to date to produce composites with structures and mechanical properties similar to those of natural nacre. The materials produced have sizes ranging from nanometres to centimetres, processing times varying from a few minutes to several months and a different range of mechanical properties that render them suitable for various applications. For the first time, these techniques have been divided into those producing bulk materials, coatings and free-standing films. This is due to the fact that the material's application strongly depends on its dimensions and different results have been reported by applying the same technique to produce materials with different sizes. The limitations and capabilities of these methodologies have been also described.

Fluorescence microscopy techniques for quantitative evaluation of organic biocide distribution in antifouling paint coatings: application to model antifouling coatings

A test matrix of antifouling (AF) coatings including pMMA, an erodible binder and a novel trityl copolymer incorporating Cu₂O and a furan derivative (FD) natural product, were subjected to pontoon immersion and accelerated rotor tests. Fluorescence and optical microscopy techniques were applied to these coatings for quantification of organic biocide and pigment distribution. Total leaching of the biocide from the novel copolymer binder was observed within 6 months of rotor immersion, compared to 35% from the pMMA coating. In pontoon immersions, 61% of the additive was lost from the pMMA coating, and 53% from the erodible binder. Profiles of FD content in the binders revealed an accelerated loss of additive from the surface of the CDP resulting from rosin degradation, compared to even depletion from pMMA. In all samples, release of the biocide was inhibited beyond the Cu₂O front, corresponding to the leached layer in samples where Cu₂O release occurred.

Biliary intervention by means of percutaneous puncture of the antecolic jejunal loop

PURPOSE

To evaluate the safety and efficacy of biliary intervention performed by means of percutaneous transjejunal access.

MATERIALS AND METHODS

In 28 patients with conventional antecolic Roux-en-Y choledochojejunostomy or hepaticojejunostomy loops, 41 attempts were made at direct percutaneous entry into the jejunal loop. Indications for previous surgery included sclerosing cholangitis, orthotopic liver transplantation, cholangiocarcinoma, bypass of benign iatrogenic strictures, and bypass of choledochal cyst. Roux-en-Y loops were directly accessed with single-wall, 19-gauge needles after localization by review of previous cholangiograms or computed tomographic (CT) scans and localization of surgical clips with fluoroscopy.

RESULTS

The transjejunal approach was successful in 36 of 41 attempts. In 30 cases, transhepatic puncture was entirely avoided. There were four minor complications and one major complication of biliary sepsis. No procedure-related deaths occurred.

CONCLUSION

This transjejunal approach is an effective and safe route for a variety of percutaneous biliary procedures in patients with biliary-enteric anastomoses.

Hepatic arterial chemoembolization for metastatic neuroendocrine tumors

BACKGROUND

Patients with neuroendocrine neoplasma, even with metastases to the liver, often have indolent disease and are treated conservatively. However, when debilitating symptoms from hormonal syndromes or mass effect arise, more aggressive treatment may be warranted.

METHODS

Thirty-nine chemoembolization procedures were performed in 30 patients with significant symptoms, with carcinoids and islet cell tumors. An emulsification of intraarterial doxorubicin, iodized oil, and water-soluble contrast was followed by embolization with absorbable gelatin powder or pledgets.

RESULTS

Twenty-seven patients exhibited subjective improvement in clinical symptoms. Hormonal markers and/or tumor size decreased by at least 50% in 79% of patients. Inclusion of minor responses raises this to 92%. Seven complications were noted, and no procedure-related deaths occurred. Median survival was 24 months after chemoembolization or 53 months after diagnosis. Computed tomographic features of tumor vascularity, distribution of metastatic lesions, and distribution of ethiodized oil were not clearly correlated with outcome. Presence of a nonresected primary tumor had a negative effect on survival.

CONCLUSIONS

Compared with previously described treatments for neuroendocrine liver metastases, this technique appears to be more effective and to be associated with less morbidity, and is recommended for patients with significant symptoms who have failed to respond to more conservative therapy and who are not surgical candidates.

MR angiography as the sole method in evaluating abdominal aortic aneurysms: correlation with conventional techniques and surgery

PURPOSE

To compare magnetic resonance (MR) angiography with conventional preoperative imaging techniques and surgical findings in the evaluation of abdominal aortic aneurysms (AAAs).

MATERIALS AND METHODS

MR angiography was performed in 40 patients with an AAA. Two-dimensional time-of-flight MR angiography with maximum intensity projections was compared with conventional angiography, ultrasound, computed tomography, and surgery.

RESULTS

In 18 of 20 patients, MR angiography demonstrated more extensive disease than did angiography. MR angiography depicted 41 of 43 renal arteries and seven of eight renal artery stenoses (one false-negative finding of mild stenosis) identified at angiography. When iliac arteries were imaged (30 patients), good correlation with angiography was seen in all but one patient (resulting from surgical clip artifact). Ten iliac stenoses were seen at both studies. Angiography caused underestimation of the extent of seven iliac aneurysms.

CONCLUSION

MR angiography can provide all of the necessary preoperative information for evaluation of AAA and can replace conventional angiography in many cases.

Embolotherapy: agents, clinical applications, and techniques

For embolization to be successful, three factors must be addressed: embolic agent selection, clinical application, and technical skill. The major embolic agents used include stainless steel coils, absorbable gelatin pledgets and powder, polyvinyl alcohol foam, ethanol, and glues. Each of these agents acts at different levels in the arterial system; for example, coils are equivalent to surgical ligation and occlude medium to small arteries, whereas liquid agents and the smaller diameter particles occlude at the arteriolar level or the capillary bed. The type of agent selected should also be determined according to clinical application, which includes trauma, tumors, male infertility, impotence, and vascular malformations. It may be better to occlude an artery only temporarily, particularly in trauma patients, and absorbable gelatin material is preferred for this application. Conversely, permanent occlusion of arteries with either ethanol or polyvinyl alcohol foam particles may be necessary in the treatment of tumors. To use embolotherapy effectively, the interventional radiologist must be experienced, familiar with the underlying pathologic processes, and knowledgeable with regard to the role of other specialties in the treatment of the disease process presented.

[The role of magnetic resonance angiography prior to the transjugular placement of a portosystemic stent shunt (TIPS)]

The authors employed magnetic resonance angiography (MRA) to guide catheter placement for transjugular intrahepatic portosystemic stent shunt (TIPS) procedures in 14 of 24 patients, and compared the results to the 10 patients who did not have prior planning based on MRA. Two-dimensional time-of-flight venography was performed during breath holding, and projection venograms were formatted in sagittal, coronal and axial planes. MRA defined venous anatomy sufficiently well to shorten the procedure and helped to minimize invasiveness. With MRA guidance, intrahepatic needle punctures were significantly fewer (without MRA guidance: mean 12.1; with MRA guidance: mean 3.5, p < 0.001) and associated complications were absent (without MRA guidance: failed placement, N = 1; bleeding requiring blood transfusions, N = 2; death complicating intraperitoneal haemorrhage with haemobilia, N = 1, and hepatic capsular perforation, N = 1). The average time for the procedure was 2.8 hours without MRA guidance and 1.8 hours with MRA guidance (p < 0.0005). The authors conclude that MR angiography is a useful technique to define portal and hepatic venous anatomy prior to TIPS, and planning based on MRA may decrease the difficulty and length of the procedure.

MR angiographic guidance for transjugular intrahepatic portosystemic shunt procedures

The authors used magnetic resonance (MR) angiography to guide catheter placement in transjugular intrahepatic portosystemic shunt (TIPS) procedures in nine of 18 patients and compared the results with those of the nine patients for whom prior planning based on MR angiography was not done. Two-dimensional time-of-flight MR venography was performed during breath hold, and projection venograms were formatted in sagittal, coronal, and axial planes. MR angiography defined venous anatomy sufficiently to shorten the procedure and help minimize invasiveness. With MR angiographic guidance, intrahepatic needle punctures were significantly fewer (without MR guidance: mean, 12.1; with MR guidance: mean, 3.6; P < .001) and associated complications were absent (without MR guidance: failed placement, n = 1; bleeding requiring blood transfusions, n = 1; death due to intraperitoneal hemorrhage with hemobilia, n = 1; and death due to hepatic capsular perforation, n = 1). The average time for the procedure was 2.9 hours without MR angiographic guidance and 1.8 hours with MR angiographic guidance (P < .001). The authors conclude that MR angiography is a useful technique for defining portal and hepatic venous anatomy before the TIPS procedure and that planning based on MR angiography may decrease the difficulty and length of the procedure.

Hepatic arterial chemoembolization for metastatic neuroendocrine tumors

PURPOSE OF THE STUDY

To evaluate the effectiveness of chemoembolization of the liver with doxorubicin and iopamidol emulsified in ethiodized oil for the treatment of metastatic neuroendocrine tumors.

PATIENTS AND METHODS

Twenty patients with hepatic islet cell or carcinoid metastases were treated with selected hepatic arterial embolization consisting of an emulsion of doxorubicin and iopamidol emulsified in ethiodol followed by Gelfoam powder embolization. Fifteen patients had failed intravenous chemotherapy. Two of the patients with carcinoid tumors had three embolizations over 4 and one 6 years earlier with gelatin sponge only.

RESULTS

In 14 patients with hormonally active tumors, hormones secretion decreased 90% (range 69-98%) in 10 days with relief of symptoms in all patients. Average tumor size decrease was 84%. Average hospital stay was 8 days. Six patients are alive and asymptomatic at 14-33 months postembolization. Fourteen patients have died 2-16 months postembolization. Ten patients died 2-37 months postembolization from progressive liver disease. One of these patients was 103 months post-Gelfoam embolization and 13 months postchemoembolization. In 8 patients, the pancreas was the primary site: 5 were nonfunctioning islet cell carcinomas, 1 glucagonoma, 1 gastrinoma and 1 carcinoid. The primary site in 1 patient with carcinoid was the bronchus, and the primary site was unknown in 1 patient with gastrinoma. The remaining 4 patients died with liver disease under control from renal failure, peritonitis, carcinoid heart failure and generalized bone metastases. The response rate was 95% with median duration of response 8.5 months. The median survival was 24 months.

CONCLUSION

Chemoembolization with doxorubicin and iopamidol emulsified in ethiodized oil is less morbid than embolization with particulate matter alone, is more convenient and less costly, and it is less morbid than the effects of systemic chemotherapy. The median survival, duration and response compare favorably with other reported therapies.

Percutaneous intraarterial thrombolysis: analysis of factors affecting outcome

PURPOSE

The authors report results of high-dose thrombolytic therapy in native arteries and vein grafts and discuss the various factors affecting outcome.

PATIENTS AND METHODS

In a retrospective study, the outcome of 82 high-dose urokinase infusions in 76 patients was examined. Comorbid risk factors as they relate to outcome were studied extensively with log-linear analysis. Positive thrombolytic outcome (PTO) is defined as complete thrombolysis of a previously occluded segment with restoration of antegrade flow augmented by angioplasty or operative intervention to clear symptoms for 30 days.

RESULTS

The procedure resulted in a PTO in 63 of 82 instances (77%). The treatment was with urokinase alone in 39 cases (47%) and urokinase followed by surgery in 34 (41%), by angioplasty in four (5%), and by angioplasty in the proximal artery and peripheral vein grafting in five (6%). All stenoses associated with grafts were treated surgically. None of the following affected thrombolytic outcome: age of occlusion, heparin dose, catheter type, length or location of graft, or artery versus graft occlusion. The 30-day mortality was 6.1%, with a procedure-related mortality rate of 2.4%. Overall amputation rate was 18% (74% for patients in whom lysis failed by 30 days).

CONCLUSION

The presence of at least one runoff vessel was the most important factor affecting outcome (PTO, 95%; P = .00001, chi 2). The most important comorbid risk factor for failed thrombolysis was coronary artery disease (P = .03, chi 2).

In vivo and in vitro analysis of the effectiveness of doxorubicin combined with temporary arterial occlusion in liver tumors

PURPOSE

The authors evaluated the effects of daunomycin (daunorubicin)--an analogue of doxorubicin--ethiodized oil, and arterial occlusion on an in vitro hepatoma analogue and on in vivo rat liver tumors.

MATERIALS AND METHODS

A human Sk hepatoma cell monolayer sandwich system was used to determine uptake of 3H-daunomycin under normoxic/hypoxic conditions with use of autoradiography. Fluorescence microscopy was used to evaluate the biodistribution of doxorubicin in cell cultures (human Sk hepatoma and colon carcinoma). Microvascular flow adjacent to and within liver tumors and the intrahepatic effects of doxorubicin and ethiodized oil were studied with in vivo video microscopy on exteriorized rat livers containing peripheral hepatomas.

RESULTS

Increased uptake of 3H-daunomycin by hepatoma cells occurred under hypoxic conditions. Intrahepatic arterial administration of ethiodized oil caused temporary occlusion of peripheral sinusoids following passage through arterioportal anastomoses. Tumors received portal venous and neovascular blood supply and ethiodized oil occluded but did not enter the narrow neovasculature perfusing the tumors.

CONCLUSION

Hypoxia increases uptake of 3H-daunomycin by human Sk hepatoma and colon carcinoma cell cultures. Selective hepatic arterial occlusion (and perhaps the resultant hypoxia) may facilitate increased uptake of doxorubicin analogues into liver tumors. Hepatomas receive both arterial and portal venous blood supply, and ethiodized oil reaches the tumor via arterioportal anastomoses that perfuse the tumor periphery.

Chemoembolization for hepatocellular carcinoma: epinephrine followed by a doxorubicin-ethiodized oil emulsion and gelatin sponge powder

PURPOSE

This study evaluates chemoembolization (CE) of the liver with minimal vasoconstriction followed by selective intraarterial delivery of an emulsion of iopamidol, doxorubicin, and ethiodized oil and temporary occlusion of hepatic artery with gelatin sponge powder in patients with hepatocellular carcinoma.

PATIENTS AND METHODS

Since 1988, 30 patients with nonresectable hepatocellular carcinoma underwent CE with the above protocol. Intraarterial epinephrine (0.5-1 microgram diluted in 10 mL of saline) was rapidly injected directly into the proper hepatic artery or selectively into the right or left hepatic arteries and was followed by 40-60 mg of doxorubicin dissolved in 10 mL of iopamidol and emulsified in 20 mL of ethiodized oil. The chemoembolic mixture was injected at the rate of arterial flow. Liver function and clotting parameters were monitored three times a day until there was a downward trend toward preembolic levels. Computed tomography (CT) was performed immediately after embolization and at 1-3-month intervals. Embolization was repeated when CT demonstrated recurrent or progressive disease.

RESULTS

Disease recurred or progressed in 11 patients at 2-17 months after embolization. CE was repeated in four patients; one individual underwent three embolizations. Re-embolization was performed up to 14 months after initial embolization (median, 10 months). Five patients (16.7%) died within 1 month of embolization. Ten patients died at 3-33 months after CE. Two of these patients died of cirrhosis at 6 and 14 months, without evidence of recurrent tumor. Fifteen patients remain alive 5-28 months after CE. Kaplan-Meier estimation of probability of survival curves demonstrates a median survival of 14 months. Sixty-one percent of patients were alive at 1 year and 36% at 2 years after the procedure.

CONCLUSION

CE with use of the above technique is effective for palliating inoperable hepatocellular carcinoma. It causes a significant prolongation of survival over the expected 18-24 weeks in untreated patients; this may occur because high doses of chemotherapeutic agents are delivered and come in contact with the tumor for a longer period, followed by ischemia brought about by temporary arterial occlusion.

Hepatic arterial chemoembolization for metastatic endocrine tumors

PURPOSE

In patients with hepatic metastases from endocrine tumors, the safety and effectiveness of chemoembolization with ethiodized oil was determined and compared with those of embolization with particulate matter alone.

PATIENTS AND METHODS

Twenty patients with hepatic islet cell or carcinoid tumor metastases were treated with selective hepatic artery injection of doxorubicin and iopamidol emulsified in ethiodized oil, followed by gelatin foam powder embolization.

RESULTS

In 16 patients with hormonally active tumors, hormone secretion decreased 90% (range, 69%-98%) in 10 days, with relief of symptoms in all patients. Average tumor size decrease was 84%; average hospitalization was 8 days. Seventeen patients are alive 6-27 months after embolization, and all are asymptomatic. Three patients died within 1 year after embolization of progressive disease outside the liver.

CONCLUSION

Chemoembolization with doxorubicin emulsified in ethiodized oil and iopamidol is effective in the treatment of hepatic metastases from endocrine tumors. This technique appears to result in less morbidity than particulate embolization alone.

Central venous occlusion: MR angiography

The authors evaluated time-of-flight magnetic resonance (MR) angiography in 30 patients with suspected thoracic venous occlusion. The results of the MR studies were compared with results at contrast venography in 22 patients and at central venous cannulation in seven of the remaining eight patients. Twenty-eight patients had abnormalities on MR venograms; 21 of these abnormalities involved multiple veins. Eight patients had superior vena cava (SVC) occlusion with retrograde azygos blood flow, and two patients had nonocclusive SVC thrombus. Fifteen patients had thrombosis involving the brachiocephalic veins; 14, involving the subclavian veins; and eight, involving the internal jugular veins. Correlation was excellent between findings of venous obstruction and occlusion at contrast venography and MR angiography. MR imaging provided more comprehensive information than catheter venography on central venous anatomy and blood flow. For evaluation of central veins, MR angiography is an accurate and graphic technique that may succeed in cases in which other methods may give inadequate findings or may be impossible to perform.

Liver transplantation: MR angiography with surgical validation

Thirty patients (mean age, 45 years) were evaluated with magnetic resonance (MR) angiography before liver transplantation to assess the accuracy of MR angiography. A series of breath-hold, two-dimensional images were acquired and subsequently processed to form three-dimensional projection angiograms. Graphic information on blood flow in the portal vein was acquired by using presaturation bolus tracking. Correlative duplex ultrasound (US) was performed in 28 patients, and surgical or autopsy correlation was available in all cases. MR angiography demonstrated patency of the portal vein in 26 (96%) of 27 patients, made possible the diagnosis of portal venous occlusion in three of three patients, depicted reversed portal flow in one patient, and provided clear delineation of the extent of varices and specific portosystemic collateral vessels. When duplex US was successful, there was full agreement with MR angiographic results in assessing portal vein patency and flow direction. All of the MR findings were corroborated at surgical exploration or autopsy. The authors conclude that MR angiography is very accurate in the portal system and is valuable in preoperative assessment for liver transplantation.

Biliary duct stones: percutaneous transhepatic removal

Percutaneous transhepatic removal of common bile duct stones was performed 57 times in 53 patients with a success rate of 93%. All patients had contraindications to surgery or had undergone unsuccessful attempts at endoscopic retrograde cholangiopancreatography and papillotomy. A modified Dormia basket was inserted through a percutaneous transhepatic approach and the stones or fragments were advanced into the duodenum. Monooctanoin (26 patients) or methyl tertiary butyl ether (4 patients) was infused to reduce stone size or remove residual debris. The average time for complete stone removal was 8.5 days. Morbidity was 12% and mortality was 4%, results which compare favorably with those of surgery.

Five-year results of iliac and femoropopliteal angioplasty in diabetic patients

Results of 127 iliac and femoropopliteal transluminal angioplasties in 97 diabetic patients are presented. Patients who had undergone iliac (n = 70), femoral (n = 41), and popliteal (n = 16) angioplasties for stenoses up to 15 cm long were followed up for 6-60 months. In diabetic patients presenting with only claudication or adequate runoff, the 5-year iliac patency rate was 76% and the femoral patency rate was 60%; these results were comparable with those found in nondiabetic patients. For limb salvage, 3-year patency rates were 66% for iliac, 37% for femoral, and 37% for popliteal angioplasties, and 5-year patency rates were 29% for iliac, 7% for femoral, and 0% for popliteal angioplasties. Severe peripheral ischemia, poor runoff, and diffuse stenoses all had negative effects on angioplasty results.

Biliary duct stones: update on 54 cases after percutaneous transhepatic removal

Percutaneous transhepatic removal of common bile duct stones was performed 54 times in 50 patients with a success rate of 93%. In all patients, a modified Dormia basket was inserted through a percutaneous transhepatic catheter, and the stones or fragments were advanced into the duodenum. All patients had contraindications to surgery or had undergone unsuccessful attempts at endoscopic retrograde cholangiopancreatography and sphincterotomy. Monooctanoin (25 patients) or methyl tertiary-butyl ether (four patients) was infused to reduce stone size or remove residual debris. The average time for complete stone removal was 8.6 days. Morbidity was 13% and mortality was 4%, results which compare favorably with those of surgery.

A chicken transferrin gene in transgenic mice escapes X-chromosome inactivation

Mammalian X-chromosome inactivation involves a coordinate shutting down of physically linked genes. Several proposed models require the presence of specific sequences near genes to permit the spread of inactivation into these regions. If such models are correct, one might predict that heterologous genes transferred onto the X chromosome might lack the appropriate signal sequences and therefore escape inactivation. To determine whether a foreign gene inserted into the X chromosome is subject to inactivation, transgenic mice harboring 11 copies of the complete, 17-kilobase chicken transferrin gene on the X chromosome were used. Male mice hemizygous for this insert were bred with females bearing Searle's translocation, an X-chromosome rearrangement that is always active in heterozygous females (the unrearranged X chromosome is inactive). Female offspring bearing the Searle's translocation and the chicken transferrin gene had the same amount of chicken transferrin messenger RNA in liver as did transgenic male mice or transgenic female mice lacking the Searle's chromosome. This result shows that the inserted gene is not subject to X-chromosome inactivation and suggests that the inactivation process cannot spread over 187 kilobases of DNA in the absence of specific signal sequences required for inactivation.

Bile duct stones: percutaneous transhepatic removal

Percutaneous transhepatic intervention for transduodenal removal of biliary stones was performed 38 times in 34 patients with obstructive jaundice, biliary colic, and cholangitis. The technique entailed the percutaneous transhepatic placement of a modified Dormia basket in the common duct with the flexible tip in the duodenum. The stones were passed into the duodenum and were crushed, or were crushed in the common duct and passed as fragments into the duodenum. In addition to the snare procedure, monooctanoin was used 18 times to dissolve remaining fragments of stone and sludge that could not be snared and passed into the duodenum. The average time for completion of the procedure was 10 days. There were no deaths from the procedure. The complication rate was 21%--probably no greater than would occur with surgery in a similar patient population. The procedure can be performed when endoscopic retrograde cholangiopancreatography and sphincterotomy with stone removal is technically impossible or refused, and in patients who have previously undergone choledochojejunostomy.

Complications of transluminal angioplasty

Four hundred fifty-three percutaneous transluminal angioplasties in 352 patients were reviewed to determine the frequency, distribution, and cause of complications. The primary success rate was 89% (81%-82% for renal and distal runoff vessels, 91%-95% for the iliofemoral arteries). Fifty-nine complications occurred in 53 patients, including 20 puncture site complications, the most frequent being hematoma. The most important angioplasty complication was acute occlusion of the arterial lumen attributed to acute thrombosis (2%). Subintimal passage of the guide wire/catheter (2%) may also cause luminal compromise. Arterial dissection following balloon dilatation (1%) and distal emboli (1.5%) were less important clinically, and vessel wall rupture was rare (0.4%). Complications were two to four times more frequent for renal and distal popliteal/tibial compared with iliofemoral angioplasties; the lower success and higher complication rates are attributed to greater technical difficulty and the increased importance of spasm. Operator experience and technical refinements play an important role in reducing occurrence of serious complications. The frequency and severity of angioplasty complications compare favorably with the alternative surgical procedure.