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PubMedDate not supplied

Genetic heterogeneity in northeastern India: reflection of Tribe-Caste continuum in the genetic structure.

We critically examined the gene frequency data for 11 genetic markers commonly available in the literature for 22 populations of northeastern India in the light of their geographic, linguistic, and ethnic affiliations. The markers investigated were three blood groups (A1A2BO, MNS, and Rh), four serum proteins (KM, Gc, Hp, and Tf), and four enzyme systems (AP, AK, EsD, and Hb). The neighbor-joining tree and multidimensional scaling of the distance matrix suggest relatively high genetic differentiation among the Mongoloid groups, with probably diverse origins when compared to the Caucasoid Indo-European populations, which had probably come from relatively more homogeneous backgrounds. Broadly speaking, the pattern of population affinities conforms to the ethno-historic, linguistic, and geographic backgrounds. An interesting and important feature that emerges from this analysis is the reflection of the effect of the sociological process of a Tribe-Caste continuum on genetic structure. While on one end we have the cluster of Caucasoid caste populations, the other end consists of Mongoloid tribal groups. In between are the populations which were originally tribes but now have become semi-Hinduized caste groups, viz., Rajbanshi, Chutiya, and Ahom. These groups have currently assumed caste status and speak Indo-European languages. Therefore, one may infer that what appears to be a purely sociological phenomenon of a Tribe-Caste continuum may well reflect in their genetic structure.

Blood Group Antigens↗

PubMed2002

Reflectance circular dichroism of solid-state chiral coordination compounds.

Solid-state diffuse reflectance circular dichroism (DRCD) spectra of some chiral lambda- and delta-M[(A--A)(n)](m+) coordination compounds [M(III) = Cr, Co; A--A = ethylendiamine (en), O,O'-2(R)3(R)dimethylethylene dithiophosphate ion, (R,R)bdtp(-), sepulchrate (Sep); n = 1, 3; m = 0, 3] were measured and compared with their solution, nujol mull, and KBr pellet spectra in the spectral region of 300-800 nm. The validity of the DRCD method to obtain reliable CD spectra which reflect a correct absolute configuration at the metal coordination center as well as subtle changes in the stereochemistry of the compound in the solid vs. solution states was proved. DRCD is the only spectroscopic method to examine randomly oriented chiral compounds without the effect of pressure, solvent, or diluting media such as KBr or nujol (which lends the sample irrecoverable and may interact with the sample), and directly relate to the structure that is revealed by X-ray diffractometry.

Journal Article↗

PubMed2005

Assessing outcomes through congruence of course objectives and reflective work.

INTRODUCTION: Course outcomes have been assessed by examining the congruence between statements of commitment to change (CTCs) and course objectives. Other forms of postcourse reflective exercises (for example, impact and unmet-needs statements) have not been examined for congruence with course objectives or their utility in assessing course outcomes. This study assessed the congruence of course objectives and statements of commitment to change, effects on practice, unmet-needs, and the utility of supplementing CTCs with other forms of reflective work in course evaluations. METHODS: A 3-module course on Alzheimer's disease and other dementias provided end-of-course CTC statements, follow-up data, and statements of effects on practice and unmet needs. Statements were aligned to module objectives and analyzed descriptively. RESULTS: Of the 932 physicians who registered for 1 of the 3 modules, 404 provided CTCs, 302 provided impact statements, and 265 provided unmet-needs statements. Sixty percent of the CTCs could be assigned to an objective for their module, and between 14% and 25% of CTCs were assigned to objectives for another module. Three-quarters of CTCs were fully or partially implemented. Physicians did not have an opportunity to implement the new content in 70% of nonimplemented CTCs. Fewer impact and unmet-needs statements were congruent with course objectives than CTCs. CONCLUSIONS: Commitment-to-change statements had more congruence with objectives than did impact or unmet-needs statements. These latter statements, particularly those that could not be assigned to an objective, may reinforce and supplement the information provided by CTC analyses.

Alzheimer Disease↗

PubMed2004

Using reflective learning to improve the impact of short courses and workshops.

For a variety of reasons, short courses and workshops often have no impact on workplace practice and are, therefore, a waste of money. The notion of "impact" on work practice is introduced, and it provides a focus toward which all elements on a short course should contribute (including the administrative processes). This article discusses the distinction between teaching and learning and some variables about the quality of the learning process that should be taken into account: the approach the learner takes and the learner's stage of conception of the structure of knowledge. The support of good-quality learning is a principal attribute of good teaching, and the nature of good teaching is discussed on this basis. Teaching and learning in a short course can usefully be structured by a framework to improve the impact of short courses and workshops. This also provides a structure for reflective activities. This article briefly discusses the definition of reflection and considers how it might be implemented. Finally, as another tactic in the focusing on impact, the components of short courses are analyzed on the basis that every component needs to work toward the improvement of the impact of the course.

Education, Medical, Continuing↗

PubMed2002

The World Health Organization histologic classification system reflects the oncologic behavior of thymoma: a clinical study of 273 patients.

BACKGROUND: Although the histologic classification of thymic epithelial tumors has been confusing and controversial, an agreement on the universal classification system for thymic epithelial tumors was achieved by the World Health Organization (WHO) in 1999. The authors previously reported that the WHO histologic classification system reflects invasiveness and immunologic function of thymic epithelial tumors. In this subsequent study, they examined the prognostic significance of this classification system. METHODS: Clinical features as well as postoperative survival of patients with thymoma, but not thymic carcinoma, were examined with reference to WHO histologic classification based on an experience with 273 patients over a 44-year period. RESULTS: There were 18 type A tumors, 77 type AB tumors, 55 type B1 tumors, 97 type B2 tumors, and 26 type B3 tumors. In patients with type A, AB, B1, B2, and B3 tumors, the respective proportions of invasive tumor were 11.1%, 41.6%, 47.3%, 69.1%, and 84.6%; the respective proportions of tumors with involvement of the great vessels were 0%, 3.9%, 7.3%, 17.5%, and 19.2%; and the respective 20-year survival rates were 100%, 87%, 91%, 59%, and 36%. According to the Masaoka staging system, the 20-year survival rates were 89%, 91%, 49%, 0%, and 0% in patients with Stage I, II, III, IVa, and IVb disease, respectively. By multivariate analysis, the Masaoka staging system and the WHO histologic classification system were significant independent prognostic factors, whereas age, gender, association with myasthenia gravis, completeness of resection, or involvement of the great vessels were not significant independent prognostic factors. CONCLUSIONS: This study showed that histologic appearance reflects the oncologic behavior of thymoma when the WHO classification system is adopted. The WHO classification system may be helpful in clinical practice for the assessment and treatment of patients with thymoma.

Adolescent↗

PubMed1993

Cortical hierarchy reflected in the organization of intrinsic connections in macaque monkey visual cortex.

Neuronal response properties vary markedly at increasing levels of the cortical hierarchy. At present it is unclear how these variations are reflected in the organization of the intrinsic cortical circuitry. Here we analyze patterns of intrinsic horizontal connections at different hierarchical levels in the visual cortex of the macaque monkey. The connections were studied in tangential sections of flattened cortices, which were injected with the anterograde tracer biocytin. We directly compared the organization of connections in four cortical areas representing four different levels in the cortical hierarchy. The areas were visual areas 1, 2, 4 and Brodman's area 7a (V1, V2, V4 and 7a, respectively). In all areas studied, injections labeled numerous horizontally coursing axons that formed dense halos around the injection sites. Further away, the fibers tended to form separate clusters. Many fibers could be traced along the way from the injection sites to the target clusters. At progressively higher order areas, there was a striking increase in the spread of intrinsic connections: from a measured distance of 2.1 mm in area V1 to 9.0 mm in area 7a. Average interpatch distance also increased from 0.61 mm in area V1 to 1.56 mm in area 7a. In contrast, patch size changed far less at higher order areas, from an average width of 230 micron(s) in area V1 to 310 micron(s) in area 7a. Analysis of synaptic bouton distribution along axons revealed that average interbouton distance remained constant at 6.4 micron(s) (median) in and out of the clusters and in the different cortical areas. Larger injections resulted in a marked increase in the number of labeled patches but only a minor increase in the spread of connections or in patch size. Thus, in line with the more global computational roles proposed for the higher order visual areas, the spread of intrinsic connections is increased with the hierarchy level. On the other hand, the clustered organization of the connections is preserved at higher order areas. These clusters may reflect the existence of cortical modules having blob-like dimensions throughout macaque monkey visual cortex.

Animals↗

PubMed2003

Reversible immobilization of peptides: surface modification and in situ detection by attenuated total reflection FTIR spectroscopy.

A generic method is described for the reversible immobilization of polyhistidine-bearing polypeptides and proteins on attenuated total reflecting (ATR) sensor surfaces for the detection of biomolecular interactions by FTIR spectroscopy. Nitrilotriacetic acid (NTA) groups are covalently attached to self-assembled monolayers of either thioalkanes on gold films or mercaptosilanes on silicon dioxide films deposited on germanium internal reflection elements. Complex formation between Ni2+ ions and NTA groups activates the ATR sensor surface for the selective binding of polyhistidine sequences. This approach not only allows a stable and reversible immobilization of histidine-tagged peptides (His-peptides) but also simultaneously allows the direct in situ quantification of surface-adsorbed molecules from their specific FTIR spectral bands. The surface concentrations of both NTA and His-peptide on silanized surfaces were determined to be 1.1 and 0.4 molecules nm-2, respectively, which means that the surface is densely covered. A comparison of experimental FTIR spectra with simulated spectra reveals a surface-enhancement effect of one order of magnitude for the gold surfaces. With the presented sensor surfaces, new ways are opened up to investigate, in situ and with high sensitivity and reproducibility, protein-ligand, protein-protein, protein-DNA interactions, and DNA hybridization by ATR-FTIR spectroscopy.

Adsorption↗

PubMed2006

The pattern of MyoD and contractile protein localization in primary epaxial myotome reflects the dynamic progression of nascent myoblast differentiation.

The localization of contractile and regulatory proteins in early stages of epaxial primary myotome development was analyzed by immunofluorescence microscopy. Contractile proteins that appear in an ordered sequence in the rostro-caudal axis of somite development were found to reiterate that sequence in the dorso-medial-to-ventro-lateral axis of primary epaxial myotome development. Pair-wise localization of MyoD-titin, desmin-titin, and desmin-myosin defined three zones extending from the dermomyotome dorso-medial lip (DML) into the primary myotome layer. Zones M1 and M2, which were positive for MyoD + titin and MyoD + titin + desmin, respectively, were restricted to the dorso-medial-most extremity of the myotome layer and did not expand during the course of myotome development. Zone M3 was positive for MyoD, desmin, titin, myosin, and cardiac troponin T and was the only zone that expanded during primary myotome development. Myotome fibers in zone M3 were unit-length, spanning the full rostro-caudal axis of the myotome while fibers in zones M1 and M2 were shorter than unit length. Anti-myoD immunofluorescence, when detected in cells lacking contractile-protein-positive cytoplasm, was restricted to the DML and nascent myotome cells immediately subjacent to the DML. These results demonstrate a dynamic spatio-temporal sequence in the differentiation program of nascent myotome cells as they emerge from the DML; zones M1 and M2 reflect standing waves of sequential contractile protein activation during the maturation of nascent myotomal myoblasts, while the expanding zone M3 reflects the accumulation of mature myotome fibers expressing a full cohort contractile proteins.

Animals↗

PubMed1986

The level of lambda 1 light chain expression in the mouse reflects the probability of rearrangement of the relevant gene.

The predominance of kappa over lambda light chain expression in mice can either reflect the probability of rearrangement of the relevant locus or be the result of antigen-driven clonal expansion. To discriminate between these two possibilities we determined, by limiting dilution analysis, the frequencies of kappa- and lambda-producing cells in B lymphocytes generated in vitro from bone marrow pre-B cells. The frequencies obtained in these cultures are not significantly different from those obtained with mature spleen cells. In addition, Southern blot analysis of bone marrow-derived and splenic cell DNA revealed that in both populations the extent of B lymphocytes having undergone lambda 1 gene rearrangement does not exceed 4%. These results, therefore, establish that in the mouse the low level of lambda light chain expression directly reflects the probability of rearrangement of the relevant locus.

Animals↗

PubMed1995

Interaction of B and T lymphocyte subsets with high endothelial venules in the rat: binding in vitro does not reflect homing in vivo.

Lymphocytes continuously migrate through the body, and their efficient extravasation from the blood via high endothelial venules (HEV) is essential for initiating an appropriate immune response. Most investigations have focused on the lymphocyte/HEV interaction in vitro. However, to what extent such systems reflect the situation in vivo is not known. It is also unclear whether lymphocyte subsets immigrate into the HEV in proportion to their presence in the blood, and whether import capacity is limited by the HEV. When rat mesenteric lymph node lymphocytes were incubated in vitro on cryostat sections, the well-known preferential binding of B lymphocytes to HEV of Peyer's patches (PP) and T cells to HEV of axillary lymph nodes (axLN) was observed (axLN vs. PP: B lymphocytes 21.2 +/- 5.0% vs. 40.6 +/- 11.0%, T lymphocytes 84.6 +/- 6.3% vs. 56.5 +/- 12.9%). However, when labeled mesenteric lymph node lymphocytes were injected and their location within the HEV was analyzed 15 min later, no preferential interaction was seen. After injection of labeled thoracic duct lymphocytes, the percentage of labeled cells among B and T lymphocytes in the blood was significantly different (4.4 +/- 0.9% vs. 8.9 +/- 3.6%), whereas that in HEV of axLN (19.0 +/- 6.4% vs. 16.6 +/- 6.0%) and PP (30.6 +/- 6.1% vs. 33.9 +/- 4.4%) was comparable. Although the number of injected lymphocytes was similar in magnitude to the total blood lymphocyte pool, after injection there was no increase in lymphocyte numbers in the HEV. Thus, the adhesion assay in vitro does not completely reflect immigration into HEV in vivo. In addition, our data suggest that both the availability of lymphocyte subsets in small venules and the immigration rate into HEV are actively regulated in vivo.

Animals↗

PubMedDate not supplied

Physiologic cholestasis II: serum bile acid levels reflect the development of the enterohepatic circulation in rats.

We have shown that serum bile acid concentrations are elevated in human infants reflecting physiologic immaturity of the enterohepatic circulation. To define further the ontogeny of bile acid metabolism in mammals, we examined maturational changes in the serum concentration of total cholate conjugates by radioimmunoassay in fetal, neonatal, suckling, and mature Sprague-Dawley rats. Fetal (21st day) levels were low (1.4 +/- 0.23 microM; X +/- S.E.), possibly due to minimal enterohepatic cycling in utero. The concentrations in samples obtained minutes after birth, prior to suckling were significantly elevated (12.6 +/- 2.37; p less than 0.001 vs. fetal); these high values persisted after feeding was initiated (6 hr = 13.5 +/- 0.99), but fell at 12 hr (5.2 +/- 0.81) and remained unchanged for the duration of the first day. Serum values fluctuated briefly, being 9.6 +/- 0.73 on Day 4, and the rose progressively through the suckling period (Day 10 = 7.2 +/- 9.57; Day 14 = 10.4 +/- 1.70; Day 21 = 16.8 +/- 1.93); there was a dramatic peak after weaning (Day 28 = 21.8 +/- 1.53). The serum concentration of cholate conjugates then fell (5.6 +/- 0.68 on Day 42) to achieve adult levels by 56 days (4.0 +/- 0.55), a value substantially different from that of all developing animals (p less than 0.025). These data corroborate studies which suggest that a period of physiologic cholestasis occurs in the developing rat. Serum cholate conjugate concentrations likely reflect interrelated morphologic alterations (bile canalicular structure and portal blood flow) and physiologic changes (bile acid synthesis, pool size, and transport) occurring in the enterohepatic circulation during early life.

Age Factors↗

PubMedDate not supplied

The aminopyrine breath test and serum bile acids reflect histologic severity in chronic hepatitis.

To determine whether the aminopyrine breath test (ABT) and serum bile acid concentrations reflect histologic severity of chronic hepatitis, 56 patients were prospectively evaluated with liver biopsies and ABTs, and the results were compared to results of standard liver chemistry tests; 44 of these patients also had fasting and 2-hr postprandial serum bile acid measurements. Mean values for the ABT were significantly lower, and serum bile acids were significantly higher in patients with chronic active hepatitis with bridging or cirrhosis than in patients with mild chronic active hepatitis or chronic persistent hepatitis. Thirty of 35 patients with bridging or cirrhosis had ABTs less than 5.7% (mean of controls -2 S.D.) and 21 of 25 with mild chronic active hepatitis or chronic persistent hepatitis had values greater than 5.7% (sensitivity 0.86, specificity 0.84). Fasting and 2-hr postprandial bile acids were also more sensitive than standard chemistries in identifying patients with bridging or cirrhosis. Thus, the ABT and serum bile acids reflect histologic severity in chronic hepatitis patients and may be helpful in selecting patients for liver biopsy.

Adolescent↗

PubMed1996

Serum hyaluronate reflects hepatic fibrogenesis in alcoholic liver disease and is useful as a marker of fibrosis.

The high levels of hyaluronic acid (HA), a glycosaminoglycan of the liver extracellular matrix, which is synthesized and degraded in the liver sinusoidal cells, have been related with a decreased function of the endothelial sinusoidal cells. The relevance of HA in alcoholic liver disease has not been sufficiently evaluated, and therefore the current study was addressed to assess whether serum HA reflects the severity of liver fibrosis and fibrogenesis as well as the potential usefulness of hyaluronic acid as a marker of early fibrosis in alcoholics with liver damage. Serum HA and aminoterminal propeptide of collagen III (PIIIP) levels, a marker of liver fibrogenesis in alcoholics with liver disease, were assessed in 45 chronic alcoholic patients (31 men and 14 women, age: 44.1 +/- 1.5 years) (normal liver = 7; fatty changes = 8; fibrosis = 7; alcoholic hepatitis = 6; cirrhosis = 6; and cirrhosis plus alcoholic hepatitis = 11). The severity of liver inflammation and fibrosis were scored in liver specimens as: 0, no lesion; 1+ mild; 2+ moderate; and 3+ severe. Twenty-seven patients (60%) had HA above normal values (1 patient with fatty changes, 3 patients with fibrosis, and all patients with alcoholic hepatitis or cirrhosis). Hyaluronic acid and (PIIIP) levels increased in parallel with the severity of liver damage. Hyaluronic acid levels were higher in those patients with more liver inflammation (0, 128 +/- 38; 1+, 553 +/- 141; 2+, 668 +/- 259; 3+, and 1,073 +/- 419 microg/L; P = .004) and of fibrosis (0, 79 +/- 32; 1+, 156 +/- 70; 2+, 219 +/- 105; and 3+, 695 +/- 114 microg/L; P < .001). Procollagen III peptide levels were related with fibrosis (0, 17 +/- 1; 1+, 25 +/- 6; 2+, 47 +/- 13; 3+, and 55 +/- 9 ng/mL; P = .002) but not with inflammation (0, 29 +/- 7; 1+, 45 +/- 7; 2+, 54 +/- 9; 3+, and 66 +/- 30 ng/mL, P: not significant). Moreover, a direct linear correlation was observed between HA and PIIIP (r = .72, P < .001). A receiver operating characteristic (ROC) curve analysis revealed that HA was similar to PIIIP levels in discriminating between alcoholics without fibrosis and those with fibrosis (area under the ROC curves) .913 +/- .042 vs. .867 +/- .054; P: n.s). In conclusion, serum HA reflects the severity of liver inflammation, fibrosis, and fibrogenesis in patients with alcoholic liver disease and is useful as a marker of precirrhotic and cirrhotic stages.

Adult↗

PubMed2002

Extracellular matrix building marked by the N-terminal propeptide of procollagen type I reflect aggressiveness of recurrent breast cancer.

The purpose of our study was to examine the association between extracellular matrix homeostasis and aggressive breast cancer as reflected by the synthesis of type I collagen marked by circulating concentration of the aminoterminal propeptide of type I procollagen (PINP). Pre-therapeutic serum PINP concentrations were measured in 154 healthy women and 100 patients referred with their first metastatic manifestation of breast cancer and correlated to the metastatic pattern, response to therapy, time to progression and survival with a minimal follow-up of 5 years. Fifty-four percent of the patients had serum PINP concentrations greater than the 95th percentile of the healthy controls and 38% were high PINP level patients with values clearly outside normal range (>125 ng/ml). Patients with high PINP levels were more sick (p = 0.002), had a higher tumor burden (p = 0.013) and revealed a lower responsiveness to anthracycline-based therapy (p = 0.0002) as well as an accelerated time to disease progression (p = 0.00001) and death (p = 0.0006). Median survival in the high serum PINP level group was less than half of that in the group with low PINP level (14.5 vs. 32 months). The lowest PINP levels were seen when the cancer was restricted to the lymph node and skin and increasing PINP levels were found if the cancer had spread to the lungs, the bones, the bone marrow and the liver. High PINP level at recurrence and lack of estrogen receptors (ER) independently reflected aggressive tumor behavior after recurrence with an equal great impact on time to progression and survival. Patients with a high PINP level and primarily ER-negative tumors survived a median of only 6 months with no one alive after 22 months. By contrast patients with a low PINP level and ER-positive tumors had a median survival of 37 months and 23% were still alive after 5 years. Aggressive breast cancer induces a strong fibroproliferative response with synthesis of type I collagen. Serum PINP levels may be a diagnostic and prognostic tool that indicate breast cancer activity, aggressiveness, expansion and metastasis and a predictor of outcome after anthracycline-based chemotherapy.

Adult↗

PubMed1981

In vitro motility of cells from human epidermoid carcinomas. A study by phase-contrast and reflection-contrast cinematography.

The motile behavior of six cell lines derived from human squamous carcinomas (two from the larynx, four from the tongue) was studied by cinematography under phase- and reflection-contrast illumination. The recorded cell activities consist in spreading, stationary and translocation motility, and aggregate formation. Within this common pattern, quantitative modifications ("sub-pattern") are stable properties of the individual cells lines. Such modifications are particularly evident with regard to the dynamic texture of the aggregates which ranges from loose, netlike structures to compact islands with smooth borders. Accordingly, the intensity of cell traffic within and around the aggregates varies considerably. It is discussed to what extent the in vitro motility of the carcinoma cell populations reflects their behavior in the organism and thus the significance of cell movements for invasion.

Carcinoma, Squamous Cell↗

PubMed1988

Interferon-gamma treatment of B16 melanoma cells: opposing effects for non-adaptive and adaptive immune defense and its reflection by metastatic spread.

The impact of interferon-gamma (IFN) treatment of tumor cells on non-adaptive and adaptive immune defense and its reflection by metastatic spread were evaluated using a weakly metastasizing variant of B16 melanoma (B16-FI). Treatment of B16-FI with IFN resulted in a decrease in binding structures for NK cells and concomitantly in augmented metastasizing capacity. In line with this, activation of NK cells and Mo, which led to reduction of metastatic nodes, was less efficient with IFN-treated B16-FI, while after elimination of non-adaptive immune defense, the number of metastases increased significantly, but irrespective of IFN treatment. On the other hand, IFN-treated B16-FI cells become more prone to killing by cytotoxic T-cells (CTL). This was due to increased lysability by CTL and to increased immunogenicity; i.e., a higher frequency of B16-specific CTL was observed after immunization with IFN-treated than with untreated B16-FI. The reverse phenomenon was observed with anomalous and/or lymphokine-activated killer cells (AK/LAK). The common cause of increased antigenicity and immunogenicity may reside in increased expression of class-I and de novo expression of class-II MHC antigens after IFN treatment. Increased antigenicity and immunogenicity of IFN-treated B16-FI was reflected by significant reduction of metastatic nodes, prolonged survival and increased TD100 in animals immunized with IFN-treated vs. untreated melanoma cells. Comparison of the divergent effects of IFN treatment on B16-FI melanoma cells showed that the benefit of increased antigenicity/immunogenicity clearly outweighed the disadvantage of reduced susceptibility to non-adaptive immune defense.

Animals↗

PubMedDate not supplied

The revision of a workload measurement tool to reflect the nursing needs of patients with traumatic brain injury.

Rehabilitation for persons with head injuries is a multifaceted process that requires structure, consistency, and predictability. This article discusses the process followed by nurses on one rehabilitation unit to revise a standard nursing workload measurement tool to reflect the physical, cognitive, behavioral, and psychosocial needs of patients with traumatic brain injury (TBI). Family education and support, a critical component of care, was also addressed. The flexibility of the tool, known as GRASP, allowed the incorporation of neurobehavioral items based on the Rancho Los Amigos cognitive functioning scale and the inclusion of important therapeutic nursing interventions. The revised tool reflects the time required to deliver comprehensive nursing care to TBI patients and, thus, promotes the desired rehabilitation outcomes for patients and their families.

Brain Injuries↗

PubMed1978

Surface chemical analysis of Avcothane and Biomer by Fourier transform IR internal reflection spectroscopy.

During the solvent casting process, one side of the polymer film is exposed to air while the other side is in contact with a substrate, used as a mold. We have studied the effect of this difference in exposure during casting on the chemical composition of two types of segmented polyurethane, Biomer and Avcothane, by using Fourier transform IR internal reflection spectroscopy. Also, a depth-composition profile was obtained by placing a thin barrier film between the reflection plate and the polymer film. In Avcothane, the air side, which is the blood-contact side, contains a greater amount of the soft segment than the substrate side, and this is more pronounced in the layer closer to the surface. The anisotropy in composition is more drastic when the silicone content is compared. In a layer about 1.5 mu thick, one can detect a greater amount of silicone in the substrate side than in the air side. However, when one averages the concentration in a layer of about 0.8 microns the trend in reversed; i.e., the greater amount of silicone is now present in the air side than in the substrate side. In Biomer films, the anisotropy in chemical composition is less pronounced. Only a modest increase in the relative content of the soft segment/hard segment is observed in the air side when a depth-composition profile is obtained.

Biocompatible Materials↗