Multi-scale analysis of the toraymyxin adsorption cartridge. Part II: computational fluid-dynamic study.

Extracorporeal endotoxin removal by means of the Toraymyxin device is based on the ability of polymyxin B to bind endotoxins with a high specificity. The endotoxins/polymyxin molecular interactions were computationally analyzed in a parallel work (Part I). In this paper we investigate with a multi-scale approach the phenomena involving blood and plasma fluid dynamics inside the device. The macro- and mesoscale phenomena were studied by means of 3D models using computational fluid dynamics. The flow behavior in the sorbent material was focused, modeling the sorbent as a homogeneous porous medium at the macroscale level, or accounting for the realistic geometry of its knitted fibers at the mesoscale level. A microscale model was then developed to analyze the behavior of endotoxin molecules subjected to the competition of flow drag and molecular attraction by fiber-grafted polymyxin B. The macroscale results showed that a very regular flow field develops in the sorbent, furthermore supplying the peak velocity to be input in the lower-scale model. The mesoscale analysis yielded the realistic range for wall shear stresses (WSSs) acting on fiber walls. With WSS values in the entire range, the results of the microscale analysis demonstrated that the capability of polymyxin B to capture endotoxin molecules from the flow extends at distances one order of magnitude greater than the characteristic distance of the stable intermolecular bond. We conclude that the use of an integrated, multi-scale analysis allows for a comprehensive understanding of the complex mechanisms involved in endotoxin sorption phenomena with immobilized polymyxin B.

Multi-scale analysis of the toraymyxin adsorption cartridge. Part I: molecular interaction of polymyxin B with endotoxins.

Endotoxins or lipopolysaccharides are the main constituents of the outer leaflet of Gram-negative bacteria membrane and play a central role in the pathogenesis of the septic shock. Polymyxin B has both antibacterial and antiendotoxin capability; indeed it is able to destroy the bacterial outer membrane and bind endotoxin neutralizing its toxic effects. Cartridges containing polymyxin B-immobilized fibers (Toraymyxin PMX-F, Toray Industries, Japan) are used in extracorporeal hemoperfusion to remove circulating endotoxin. The aim of this study is the characterization of the polymyxin B-endotoxin system at the molecular level, thus providing quantitative evaluation of the binding forces exerted in the molecular complex. Polymyxin B was interfaced with five molecular models of lipopolysaccharides differing in their structure and molecular mechanics simulations were performed at different intermolecular distances aimed at calculating the interaction energies of the complex. Binding forces were calculated by fitting interaction energies data. Results show that in the short range the polymyxin B-endotoxin complex is mediated by hydrophobic forces and in the long range the complex is driven by ionic forces only. From a mechanical standpoint, polymyxin B-endotoxin complex is characterized by maximum binding forces ranging between 1.39 nN to 3.79 nN. The knowledge of the binding force behavior at different intermolecular distances allows further investigations at higher scale level (Part II).

Biological performances of collagen-based scaffolds for vascular tissue engineering.

Collagen is widely used for biomedical applications and it could represent a valid alternative scaffold material for vascular tissue engineering. In this work, reconstituted collagen films were prepared from neutralized acid-soluble solutions for subsequent haemocompatibility and cell viability performance assays. First, haemoglobin-free, thrombelastography and platelet adhesion tests were performed in order to investigate the blood contact performance. Secondly, specimens were seeded with endothelial cells and smooth muscle cells, and cell viability tests were carried out by MTT and SEM. Results show that neutralized acid-soluble type I collagen films do not enhance blood coagulation, do not alter normal viscoelastic properties of blood and slightly activate platelet adhesion and aggregation. Cell culture shows that the samples are adequate substrates to support the adhesion and proliferation of endothelial and smooth muscle cells.

Endothelial cell adhesion force estimation at the nanoscale.

Endothelial cell adhesion to a synthetic surface includes a definite set of molecular interactions. Cell adhesion is managed by fibronectin and vitronectin in extracellular matrix (ECM) that binds the receptor site of the trans-membrane protein dimers, the integrins. These proteins contain one of the binding sites (I-like domain receptor) for the Arg-Gly-Asp (RGD) peptides that are the established adhesion receptor sites in the ECM. A molecular approach can quantify the adhesion strength by ligand-receptor force computation. The molecular interaction energy between a polyethylene (PE) surface covalently grafted with the adhesion sites (RGD-containing) and trans-membrane integrin receptor (I-domain) was evaluated through a molecular model of a single ligand-receptor complex. The aims of this work were: (i) the generation of the receptor molecular model: the I-like domain; (ii) the evaluation of the greatest binding chemical affinity between the I-like domain and three RGD-containing peptides; (iii) the development of the molecular model of crystalline lamellae of PE; and (iv) the evaluation of the interac-tion energies and the interaction force between the I-like domain and the grafted biomaterial. The calculation of the interaction energies can provide an estimation of the adhesion force of the ligand-receptor complex and, finally, of the endothelial cell adhesion force. The calculated cell adhesion force is in agreement with experimental data.(Journal of Applied Biomaterials and Biomechanics 2005; 3: 42-9).

Possible role of decorin glycosaminoglycans in fibril to fibril force transfer in relative mature tendons--a computational study from molecular to microstructural level.

Experimental studies on immature tendons have shown that the collagen fibril net is discontinuous. Manifold evidences, despite not being conclusive, indicate that mature tissue is discontinuous as well. According to composite theory, there is no requirement that the fibrils should extend from one end of the tissue to the other; indeed, an interfibrillar matrix with a low elastic modulus would be sufficient to guarantee the mechanical properties of the tendon. Possible mechanisms for the stress-transfer involve the interfibrillar proteoglycans and can be related to the matrix shear stress and to electrostatic non-covalent forces. Recent studies have shown that the glycosaminoglycans (GAGs) bound to decorin act like bridges between contiguous fibrils connecting adjacent fibril every 64-68 nm; this architecture would suggest their possible role in providing the mechanical integrity of the tendon structure. The present paper investigates the ability of decorin GAGs to transfer forces between adjacent fibrils. In order to test this hypothesis the stiffness of chondroitin-6-sulphate, a typical GAG associated to decorin, has been evaluated through the molecular mechanics approach. The obtained GAG stiffness is piecewise linear with an initial plateau at low strains (<800%) and a high stiffness region (3.1 x 10(-11)N/nm) afterwards. By introducing the calculated GAG stiffness in a multi-fibril model, miming the relative mature tendon architecture, the stress-strain behaviour of the collagen fibre was determined. The fibre incremental elastic modulus obtained ranges between 100 and 475 MPa for strains between 2% and 6%. The elastic modulus value depends directly on the fibril length, diameter and inversely on the interfibrillar distance. In particular, according to the obtained results, the length of the fibril is likely to play the major role in determining stiffness in mature tendons.

[Distal termino-lateral spleno-renal anastomosis, using the Warren technic]. / L'anastomosi spleno-renale termino-laterale distale sec. Warren.

The authors describe 23 cases of distal splenorenal derivation after Warren. Of these patients, 17 received a complete followup clinical hematological and angiographic examination at an average remove of 10 months after surgery. The authors discuss their results and submit that the Warren operation, while really selcetive in most cases when performed, in the long run tends to shung rather too much blood away from the liver; in other words, the effectiveness of the shunt tends to exceed the intended drainage,which should be restricted to the gastro-esophageal vascular bed.

[Gastric metastasis of melanoma (report of a clinical case)]. / Metastasi gastrica da melanoma (presentazione di un caso clinico).

The Authors report a case of gastric metastasis from melanoma of the skin, occurring 6 years after removal of the primary neoplasm. The metastasis, which was characterized by conspicuous alimentary tract haemorrhage, called for emergency surgery consisting in a total gastrectomy with oesophago-jejunal anastomosis according to Roux. The Authors then go on to review the literature on the subject, stressing the frequency of gastrointestinal metastases in skin melanomas with an incidence affecting up to 60% of cases in autopsy series. After examining the main clinical aspects, endoscopic appearances and r-ray findings, the Authors deal at some length with prognosis, pointing out that isolated metastases may constitute a surgical indication in view of the cases of fairly good long-term survival reported in the literature.

[Benign pathology of the breast. Diagnostic protocol and therapeutic indications]. / La patologia benigna della mammella. Protocollo diagnostico ed indicazioni terapeutiche.

The frequency of benign mammary disease and the need to differentiate between benign and malignant tumors without the indiscriminate use of instrumental examinations and biopsies have prompted the Cooperative Interdisciplinary Group on Mammary Neoplasms to adopt the diagnostic protocol and propose a number of therapeutic indications. Though involving a progressive reduction in biopsies, the use of the protocol has not led to failure to recognize carcinomas, the number of identified malignancies being maintained within the anticipated limits.

[Retroperitoneal neurilemmoma (considerations on 4 cases)]. / Il neurilemmoma retroperitoneale (considerazioni su 4 casi).

The authors show 4 cases of retroperitoneal neurilemmoma, surgically treated by simple excision of the tumour. From the general observations, as well as from the analysis of the literature, they can remark the rareness of the location in such anatomical region. The clinical symptoms are common to those of the region retroperitoneal tumours, and are due to the compressive effect developed by the tumour on the contiguous structures. As regards the diagnostic procedures, they emphasize the primary value of axial computed tomography in the evaluation of the retroperitoneal pathology. The diagnosis cannot be but histologic, and is based upon the presence of the typical histologic pictures according to Antoni A and B types.

[Pancreas transplant today: review of the literature]. / Il trapianto di pancreas oggi: revisione della letteratura.

The authors, after analysing the world literature concerning the pancreatic transplantation, dwell in considering the problems involved in the indications and techniques of the transplantation itself. Among the several problems expecting an ultimate solution, the improvement of prophylaxis, diagnosis and treatment of rejection seems to heavily affect the future of this surgery.

[A case of duodenal duplication in the adult]. / Su di un caso di duplicazione duodenale dell'adulto.

The authors describe a rare case of duodenal duplication presenting in adult life; the complete preoperative investigations did not substantiate. The diagnosis which can be accomplished in most cases only intraoperatively. The diagnosis is mainly based upon knowledge of the condition and upon pathologic examination.

[Endobronchial lipomas]. / I lipomi endobronchiali.

The authors report three cases of endobronchial lipoma, and study the etiopathogenesis and the main clinical and therapeutical aspects of such neoplasiae. Both diagnosis and treatment should be timely, in order to prevent irreversible damages to lung parenchyma, compelling surgeons to mutilating operations making the function of the apparatus heavier.

[Segmental transplantation of the pancreas in juvenile diabetes: clinical experience at the Munich Transplantation Center]. / Il trapianto segmentale pancreatico nel diabete giovanile: esperienza clinica del centro trapianti di Monaco di Baviera.

The authors report their data relating to the first combined kidney-pancreas transplants performed at the Munich University Transplant Centre in the years 82-84 and discuss the main technical aspects of explantation and implantation surgery in these cases as well as the results obtained.

[Clinical results after proximal selective vagotomy (considerations on 42 cases)]. / Risultati clinici dopo vagotomia selettiva prossimale (considerazioni su 42 casi).

The authors report the results of a 6-8 year follow-up of 42 patients treated by selective proximal vagotomy with pyloroplasty for gastric or duodenal ulcer disease. On the basis of Visick's classification, the patients broke down into the following categories: Cat. 1: 66.6%; Cat. 2: 26.1%; Cat. 3: 2.3%; Cat. 4: 4.7%, with 92.7% belonging to the first two categories. These data are in agreement with other data reported in the literature, and show no significant differences as compared to follow-up one year after surgery.

[Update in transplant surgery with special reference to the problem of organ donation]. / Attualità in chirurgia dei trapianti con particolare riguardo al problema della donazione d'organo.

The authors analyze the advances made and the current state of the art in transplant medicine and surgery, dealing at some length with the problems relating to organ donation. Particular attention is devoted to the provisions of law currently applicable in this field and those aspects currently under debate, comparing the situation in Italy with that obtaining elsewhere in Europe. The authors also focus on the need to make medical practitioners fully aware of the problem so as to achieve practical collaboration of the type possible today in West Germany.

[Epithelial splenic cysts]. / Cisti splenica epiteliale.

The authors describe a case of an epithelial cyst of the spleen treated successfully by splenectomy. Diagnostic techniques and the principles adopted in treatment this rare disease are discussed.

[Esophago-gastro-enteric manifestations of scleroderma. Apropos of a clinical case]. / Le manifestazioni esofago-gastro-enteriche nella sclerodermia. A proposito di un caso clinico.

Starting from the observation of a case of scleroderma with oesophageal location, the Authors study the digestive troubles of such disease, and remark that, in some cases, the treatment with cimetidin can give good results as to symptomatology, in spite of the chronic evolution of the disease.

The cancer of the papilla of Vater. Diagnosis, treatment and long term results.

Survey of 18 cases of cancer in the Papilla of Vater, which were observed during the years between 1971 and 1979 at the Surgical Clinic of Padua University - Seat of Verona - with particular regard to the diagnostic means and their reliability. The histological investigations gave the following results: All lesions were found to be adenocarcinomas; 6 cases well differentiated, 4 cases fairly well differentiated, 2 cases little differentiated, 3 cases indifferentiated. The following operations were carried out: 15 Duodenopancreatectomies, 3 Internal derivations of the biliary flow, one of which associated with gastroenteroanastomy. Of all the patients who underwent to the radical operation, 1 survived 3 years after the operation, and then was lost to the follow-up, 2 were surviving 19 months after the operation, 2 were surviving 12 months after the operation, 1 was surviving 10 months after the operation, 1 died 18 months after the operation, 7 died between the 2nd and the 12th month after the operation, 1 died in the postoperative period. Of those patients who underwent the palliative operation, none survived longer than one year.

[Hepatic cystadenocarcinoma: presentation of a clinical case and review of the literature]. / Cistoadenocarcinoma epatico: presentazione di un caso clinico e revisione della letteratura.

The finding of a case of cystadenocarcinoma supplies the opportunity for a reviewing of the literature concerning this rare liver neoplasm. From a diagnostical standpoint, the instrumental tests result non-specific. Only the needle-biopsy of papillary formations set forth through the echography within hepatic formations of cystic type is able to supply diagnoses of cystadenocarcinoma. Yet, the procedure is not exempt from risks. Decisive may be the peroperative histologic testing on fragments of the cyst wall. In consideration of the better prognosis of cystadenocarcinoma in respect of hepatocarcinoma and cholangiocarcinoma, and the risk of relapse, the election surgical treatment should be represented by hepatectomy.

Mechanisms of polymyxin B endotoxin removal from extracorporeal blood flow: molecular interactions.

The outer leaflet of Gram-negative bacteria membrane contains a great amount of lipopolysaccharides, also known as endotoxins, which play a central role in the pathogenesis of septic shock. It has been demonstrated that the polymyxin B (PMB) molecule has both antibacterial and antiendotoxin capabilities; in fact, it is able to compromise the bacterial outer membrane and bind lipopolysaccharides, thereby neutralizing its toxic effects. Extracorporeal hemoperfusion treatments based on cartridges containing PMB-immobilized fibers (Toraymyxin PMX-F; Toray Industries, Tokyo, Japan) are used to remove endotoxins circulating in the blood flow. In this study, we focused on the characterization of the interactions occurring in the formation of the PMB-endotoxin complex at the molecular level. In particular, the molecular mechanics approach was used to evaluate the interaction energy and eventually the interaction force between the two molecules. PMB was faced with five molecular portions of lipopolysaccharides differing in their structure. The interaction energy occurring for each molecular complex was calculated at different intermolecular distances and the binding forces were estimated by fitting interaction energy data. Results show that the short-range interactions between PMB and endotoxins are mediated mainly by hydrophobic forces, while in the long term, the complex formation is driven by ionic forces only. Maximum binding forces calculated via molecular mechanics for the PMB-endotoxin complex are in the range of 1.39-3.79 nN. Understanding the interaction mechanism of the single molecular complex is useful both in order to figure out the molecular features of such interaction and to perform higher scale level analysis, where such nanoscale detail is impractical but could be used to account for molecular behavior at a coarse level of discretization.