Comparison of All Solid Cancer Mortality and Incidence Dose-Response in the Life Span Study of Atomic Bomb Survivors, 1958-2009.

Recent analysis of all solid cancer incidence (1958-2009) in the Life Span Study (LSS) revealed evidence of upward curvature in the radiation dose response among males but not females. Upward curvature in sex-averaged excess relative risk (ERR) for all solid cancer mortality (1950-2003) was also observed in the 0-2 Gy dose range. As reasons for non-linearity in the LSS are not completely understood, we conducted dose-response analyses for all solid cancer mortality and incidence applying similar methods [1958-2009 follow-up, DS02R1 doses, including subjects not-in-city (NIC) at the time of the bombing] and statistical models. Incident cancers were ascertained from Hiroshima and Nagasaki cancer registries, while cause of death was ascertained from death certificates throughout Japan. The study included 105,444 LSS subjects who were alive and not known to have cancer before January 1, 1958 (80,205 with dose estimates and 25,239 NIC subjects). Between 1958 and 2009, there were 3.1 million person-years (PY) and 22,538 solid cancers for incidence analysis and 3.8 million PY and 15,419 solid cancer deaths for mortality analysis. We fitted sex-specific ERR models adjusted for smoking to both types of data. Over the entire range of doses, solid cancer mortality dose-response exhibited a borderline significant upward curvature among males (P = 0.062) and significant upward curvature among females (P = 0.010); for solid cancer incidence, as before, we found a significant upward curvature among males (P = 0.001) but not among females (P = 0.624). The sex difference in magnitude of dose-response curvature was statistically significant for cancer incidence (P = 0.017) but not for cancer mortality (P = 0.781). The results of analyses in the 0-2 Gy range and restricted lower dose ranges generally supported inferences made about the sex-specific dose-response shape over the entire range of doses for each outcome. Patterns of sex-specific curvature by calendar period (1958-1987 vs. 1988-2009) and age at exposure (0-19 vs. 20-83) varied between mortality and incidence data, particularly among females, although for each outcome there was an indication of curvature among 0-19-year-old male survivors in both calendar periods and among 0-19-year-old female survivors in the recent period. Collectively, our findings indicate that the upward curvature in all solid cancer dose response in the LSS is neither specific to males nor to incidence data; its evidence appears to depend on the composition of sites comprising all solid cancer group and age at exposure or time. Further follow up and site-specific analyses of cancer mortality and incidence will be important to confirm the emerging trend in dose-response curvature among young survivors and unveil the contributing factors and sites.

THYROID SCREENING AND RELIABILITY OF RADIATION THYROID DOSES FOR THE BELARUSIAN IN UTERO COHORT.

OBJECTIVE: To describe the status and results of thyroid disease screening and assessment of reliability of radiationthyroid doses in the Belarusian in utero cohort of 2,965 individuals exposed to Chernobyl (Chornobyl) fallout. MATERIALS AND METHODS: Thyroid screening examinations are currently underway including thyroid palpation by anendocrinologist, ultrasonographic examination by an ultrasonographer and analysis of blood samples for diagnosisof hypo- and hyperthyroidism, autoimmune thyroiditis, thyroid function tests (thyroid-stimulating hormone [TSH],thyroxine [T4], thyroid peroxidase antibody [anti-TPO], and thyroglobulin antibodies [anti-TG]). Reliability of (i)information from 780 pairs of questionnaires obtained during the first and second interviews of the mothers and (ii)thyroid doses, which were calculated for the cohort members using this information, is evaluated. RESULTS: As of 15 August 2021, 1,267 in utero exposed study subjects had been screened. A single thyroid nodule wasdiagnosed in 167 persons (13.2 % of the total) and multiple thyroid nodules in 101 persons (8.0 %): 189 (14.9 %)persons had nodules detected for the first time at the screening while 79 (6.2 %) persons had nodules detected pre-viously (pre-screening nodules). Fifty-nine out of 268 subjects (22.0 %) with a suspicious thyroid nodule werereferred to fine needle aspiration biopsy, and among them 33 (55.9 %) were biopsied. Reasonable agreement wasobserved for modelqbased doses calculated for the Belarusian in utero cohort members using data from the two inter-views (Spearman's rank-correlation coefficient rs = 0.74, p < 0.001), while measurementqbased doses yielded almost per-fect agreement (rs = 0.99, p < 0.001). CONCLUSIONS: During the thyroid screening, at least one thyroid nodule was identified in 268 of 1,267 (21.2 %) inutero exposed cohort members. Seven thyroid cancer cases were identified in the cohort, including 5 pre-screeningcases and 2 cases detected during the screening. Ongoing research on this unique cohort will provide importantinformation on adverse health effects following prenatal and postnatal exposure to radioiodine and radiocesium iso-topes, for which available epidemiological data are scant.

Morphological features of an endangered Japanese strain of Cyprinus carpio: reconstruction based on seven SNP markers.

Morphological analyses of 183 specimens of Japanese common carp Cyprinus carpio (171 from Lake Biwa and 12 from nursery ponds) using genetic hybrid indices demonstrated that the typical native Japanese strain of C. carpio has a more elongate body, more branched dorsal-fin rays, fewer and shorter gill rakers, more developed pneumatic bulb, more coiled pneumatic duct, longer posterior swimbladder and shorter intestine than the typical introduced C. carpio. These results provide a basis for a better understanding of the ecological characteristics and taxonomic status of the endangered Japanese strain of C. carpio.

Non-radiation risk factors for leukemia: A case-control study among chornobyl cleanup workers in Ukraine.

BACKGROUND: Occupational and environmental exposure to chemicals such as benzene has been linked to increased risk of leukemia. Cigarette smoking and alcohol consumption have also been found to affect leukemia risk. Previous analyses in a large cohort of Chornobyl clean-up workers in Ukraine found significant radiation-related increased risk for all leukemia types. We investigated the potential for additional effects of occupational and lifestyle factors on leukemia risk in this radiation-exposed cohort. METHODS: In a case-control study of chronic lymphocytic and other leukemias among Chornobyl cleanup workers, we collected data on a range of non-radiation exposures. We evaluated these and other potential risk factors in analyses adjusting for estimated bone marrow radiation dose. We calculated Odds Ratios and 95% Confidence Intervals in relation to lifestyle factors and occupational hazards. RESULTS: After adjusting for radiation, we found no clear association of leukemia risk with smoking or alcohol but identified a two-fold elevated risk for non-CLL leukemia with occupational exposure to petroleum (OR=2.28; 95% Confidence Interval 1.13, 6.79). Risks were particularly high for myeloid leukemias. No associations with risk factors other than radiation were found for chronic lymphocytic leukemia. CONCLUSIONS: These data - the first from a working population in Ukraine - add to evidence from several previous reports of excess leukemia morbidity in groups exposed environmentally or occupationally to petroleum or its products.

Non-thyroid cancer in Northern Ukraine in the post-Chernobyl period: Short report.

The Chernobyl nuclear power plant accident in Ukraine in 1986 led to widespread radioactive releases into the environment - primarily of radioiodines and cesium - heavily affecting the northern portions of the country, with settlement-averaged thyroid doses estimated to range from 10 mGy to more than 10 Gy. The increased risk of thyroid cancer among exposed children and adolescents is well established but the impact of radioactive contamination on the risk of other types of cancer is much less certain. To provide data on a public health issue of major importance, we have analyzed the incidence of non-thyroid cancers during the post-Chernobyl period in a well-defined cohort of 13,203 individuals who were <18 years of age at the time of the accident. The report is based on standardized incidence ratio (SIR) analysis of 43 non-thyroid cancers identified through linkage with the National Cancer Registry of Ukraine for the period 1998 through 2009. We compared the observed and expected number of cases in three cancer groupings: all solid cancers excluding thyroid, leukemia, and lymphoma. Our analyses found no evidence of a statistically significant elevation in cancer risks in this cohort exposed at radiosensitive ages, although the cancer trends, particularly for leukemia (SIR=1.92, 95% confidence interval: 0.69; 4.13), should continue to be monitored.

Iodine-131 dose-dependent gene expression: alterations in both normal and tumour thyroid tissues of post-Chernobyl thyroid cancers.

BACKGROUND: A strong, consistent association between childhood irradiation and subsequent thyroid cancer provides an excellent model for studying radiation carcinogenesis. METHODS: We evaluated gene expression in 63 paired RNA specimens from frozen normal and tumour thyroid tissues with individual iodine-131 (I-131) doses (0.008-8.6 Gy, no unirradiated controls) received from Chernobyl fallout during childhood (Ukrainian-American cohort). Approximately half of these randomly selected samples (32 tumour/normal tissue RNA specimens) were hybridised on 64 whole-genome microarrays (Agilent, 4 × 44 K). Associations between I-131 dose and gene expression were assessed separately in normal and tumour tissues using Kruskal-Wallis and linear trend tests. Of 155 genes significantly associated with I-131 after Bonferroni correction and with ≥2-fold increase per dose category, we selected 95 genes. On the remaining 31 RNA samples these genes were used for validation purposes using qRT-PCR. RESULTS: Expression of eight genes (ABCC3, C1orf9, C6orf62, FGFR1OP2, HEY2, NDOR1, STAT3, and UCP3) in normal tissue and six genes (ANKRD46, CD47, HNRNPH1, NDOR1, SCEL, and SERPINA1) in tumour tissue was significantly associated with I-131. PANTHER/DAVID pathway analyses demonstrated significant over-representation of genes coding for nucleic acid binding in normal and tumour tissues, and for p53, EGF, and FGF signalling pathways in tumour tissue. CONCLUSION: The multistep process of radiation carcinogenesis begins in histologically normal thyroid tissue and may involve dose-dependent gene expression changes.

ICRP publication 118: ICRP statement on tissue reactions and early and late effects of radiation in normal tissues and organs--threshold doses for tissue reactions in a radiation protection context.

This report provides a review of early and late effects of radiation in normal tissues and organs with respect to radiation protection. It was instigated following a recommendation in Publication 103 (ICRP, 2007), and it provides updated estimates of 'practical' threshold doses for tissue injury defined at the level of 1% incidence. Estimates are given for morbidity and mortality endpoints in all organ systems following acute, fractionated, or chronic exposure. The organ systems comprise the haematopoietic, immune, reproductive, circulatory, respiratory, musculoskeletal, endocrine, and nervous systems; the digestive and urinary tracts; the skin; and the eye. Particular attention is paid to circulatory disease and cataracts because of recent evidence of higher incidences of injury than expected after lower doses; hence, threshold doses appear to be lower than previously considered. This is largely because of the increasing incidences with increasing times after exposure. In the context of protection, it is the threshold doses for very long follow-up times that are the most relevant for workers and the public; for example, the atomic bomb survivors with 40-50years of follow-up. Radiotherapy data generally apply for shorter follow-up times because of competing causes of death in cancer patients, and hence the risks of radiation-induced circulatory disease at those earlier times are lower. A variety of biological response modifiers have been used to help reduce late reactions in many tissues. These include antioxidants, radical scavengers, inhibitors of apoptosis, anti-inflammatory drugs, angiotensin-converting enzyme inhibitors, growth factors, and cytokines. In many cases, these give dose modification factors of 1.1-1.2, and in a few cases 1.5-2, indicating the potential for increasing threshold doses in known exposure cases. In contrast, there are agents that enhance radiation responses, notably other cytotoxic agents such as antimetabolites, alkylating agents, anti-angiogenic drugs, and antibiotics, as well as genetic and comorbidity factors. Most tissues show a sparing effect of dose fractionation, so that total doses for a given endpoint are higher if the dose is fractionated rather than when given as a single dose. However, for reactions manifesting very late after low total doses, particularly for cataracts and circulatory disease, it appears that the rate of dose delivery does not modify the low incidence. This implies that the injury in these cases and at these low dose levels is caused by single-hit irreparable-type events. For these two tissues, a threshold dose of 0.5Gy is proposed herein for practical purposes, irrespective of the rate of dose delivery, and future studies may elucidate this judgement further.

The utility of focus group interviews to capture dietary consumption data in the distant past: dairy consumption in Kazakhstan villages 50 years ago.

From 1949 to 1962, residents of several villages in Kazakhstan received substantial doses of radiation to the thyroid gland resulting from nuclear tests conducted at the Semipalatinsk Nuclear Test Site. The primary source of radiation was internal from an intake of radioactive iodine by consumption of contaminated dairy products. A previous research study of childhood exposure and thyroid disease in this region gathered limited data on study participants' dairy intake at the time of the fallout for the purpose of estimating past radiation doses. As many participants were too young at the time of the nuclear tests to recall dietary consumption and existing sources of archival data are limited, it was necessary to interview parents and other village residents who cared for children during this time - older adults ranging in age from 75 to 90 years. Results from 11 focus group interviews conducted in 2007 with 82 women from 4 villages in Kazakhstan yielded group-level estimates of age-, gender-, ethnicity- and village-specific dairy consumption patterns in rural Kazakhstan during the 1950s. Children typically consumed cow's milk with limited consumption of mare, goat and sheep milk; and consumed dairy products such as sour milk (airan), soft cottage cheese (tvorog) and fermented mare milk (koumiss) with the greatest amounts of koumiss reported at ages 15-21 years. The consumption patterns differed by age, and between Kazakh and Russian children, which should lead to different estimates of radiation exposure to the thyroid. This study showed the utility of focus groups to obtain quantitative estimates for dietary intake in the distant past.

Behavioural and morphological differences between feral and domesticated strains of common carp Cyprinus carpio.

Morphological and behavioural traits of a feral strain of the common carp Cyprinus carpio from Lake Biwa in Japan were compared with those of two domesticated strains reared in Japan (one commercial strain and one ornamental koi). To compare genetically inherited traits, all fish were reared from eggs under similar environmental conditions. Using these fish, the following five traits were compared among the three strains: body shape, consumption rate of two types of free-swimming shrimp, medaka Oryzias latipes and bottom-dwelling chironomid larvae prey items, preference for a bottom habitat, feeding skills in detecting prey and escape response to predator attack. The feral strain of fish had more streamlined bodies, higher consumption rates for free-swimming prey, a greater preference for a bottom habitat, possessed greater skill in detecting prey and were more cautious of predator attacks, compared with the fish of the two domesticated strains. These characteristics shown by the feral fish are probably adaptive to the natural environment. A genetic analysis based on five nuclear single nucleotide polymorphism markers, however, suggested that the feral strain was relatively recently derived from domesticated stocks. Considering this, the present results appear to indicate the possibility that domesticated C. carpio could re-adapt to the wild environment during a short evolutionary period, although further research using more feral strains is required.

Mitochondrial DNA analysis reveals cryptic large-scale invasion of non-native genotypes of common carp (Cyprinus carpio) in Japan.

Wild common carp (Cyprinus carpio) are probably suffering from biological invasions of conspecific domesticated strains. However, such invasions may be largely camouflaged by morphological similarities between introduced and native strains. We conducted a large survey of mitochondrial DNA sequences (complete D-loop region) from 11 localities in Japan. From a total of 166 individuals, 28 haplotypes were determined to fit into six divergent clades. One of the six clades included 19 closely related haplotypes with moderate nucleotide differences; however, the remaining five clades each included either a single haplotype or two almost identical haplotypes. Phylogenetic analysis together with the previously published Eurasian haplotypes further demonstrated that the 'monotypic' clades were sisters to various Eurasian lineages, whereas the 19 related haplotypes formed a monophyletic group apart from the whole Eurasian clade. Given their monophyly and genetic diversity, the 19 related haplotypes were thought to originate from the Japanese native strain. Conversely, their phylogenetic affinities to Eurasian lineages and unnaturally low genetic diversities caused the haplotypes of the five monotypic clades to be considered as domesticated strains introduced from Eurasia. These hypotheses were supported by further evidences; i.e. the probable non-native haplotypes were frequently found from Japanese domesticated strains, and the probable native population structure was rescued when the probable non-native haplotypes were excluded from the analyses. This study revealed that almost half or more of the haplotypes in all of the locations studied originated from domesticated strains introduced from Eurasia.

Morphologic differences of the distal femur between Caucasian and Japanese women.

PURPOSE: To compare the morphology of the distal femur between Caucasian and Japanese women. METHODS: 30 Caucasian women aged 41 to 84 (mean, 67) years and 70 Japanese women aged 54 to 86 (mean, 70) years who underwent total knee arthroplasty for osteoarthritis were randomly selected. Morphologic measurements of the distal femur were compared using lateral radiographs. Both race and height influenced the morphology. To adjust for the influence of height on morphology, each measurement was divided by the patient's height and the ratios were compared. RESULTS: Caucasian women were generally taller and heavier (p<0.001) and had higher body mass index (p=0.03) than the Japanese women. Each morphologic measurement of the distal femur was significantly longer in the Caucasian women. In both groups, anteroposterior width of the condyle correlated more with height than weight. In women of equal height, the anteroposterior and metaphyseal widths of the femur and the anterior and resected condyles were longer in Caucasian women, but the posterior condyle was longer in Japanese women. CONCLUSION: Both the size of the femur and the anterior and posterior condyles are significantly larger in Caucasian than Japanese women.

Comparison of the cytokine-induced migratory response between primary and subcultured populations of rat mesenchymal bone marrow cells.

BACKGROUND: The aim of this study was to investigate the phenotypic differences of primary rat mesenchymal bone marrow cells (MBMCs) and subcultured cells, the influence of subculture and cell density on the cellular phenotypes, and the difference in the migratory responses of these cells to cytokines. METHODS: MBMCs were isolated from 8-week-old Wistar rats, and the cells were cultured for 1 week (passage 0, P0) or 3 weeks (P0-3W). P0 cells were subcultured for 1 week (P1). P1 cells were subcultured at several cell densities for 1 week (P2). Cell size and granularity were analyzed by flow cytometry. The gene expression characteristics of these cells were analyzed by reverse transcription polymerase chain reaction. Cell migration to bone morphogenetic protein-2 (BMP-2), fibroblast growth factor-2 (FGF-2), and platelet-derived growth factor-bb (PDGF-bb) was evaluated using a Boyden chamber. RESULTS: Three morphologically distinct populations in P0 and two in P2 were detected. The levels of human rapidly self-renewing cell-related marker genes in P0 were more highly expressed than in P2. Mesenchymal stem cell-associated markers were expressed at the same level in P0 and P2. The gene expression levels of immature oligodendrocyte precursor cell markers in P0 were higher than those in P2, whereas those of smooth muscle cell markers and osteoblastic cell markers in P0 were lower than those in P2. Subculture decreased the gene expression levels of human rapidly self-renewing cell-associated markers. Cell migration of P0 cells was stimulated by PDGF-bb but not by BMP-2 or FGF-2. In contrast, PDGF-bb, BMP-2, and FGF-2 all stimulated cell migration of P2. CONCLUSION: The types of cells in populations of primary and subcultured rat MBMCs were different, and the distribution of each cell population appeared to be changed by the culture conditions. The cell migration effect by PDGF-bb, BMP-2, and FGF-2 differed between the primary and subcultured MBMCs.

Solid cancer incidence in atomic bomb survivors: 1958-1998.

This is the second general report on radiation effects on the incidence of solid cancers (cancers other than malignancies of the blood or blood-forming organs) among members of the Life Span Study (LSS) cohort of Hiroshima and Nagasaki atomic bomb survivors. The analyses were based on 17,448 first primary cancers (including non-melanoma skin cancer) diagnosed from 1958 through 1998 among 105,427 cohort members with individual dose estimates who were alive and not known to have had cancer prior to 1958. Radiation-associated relative risks and excess rates were considered for all solid cancers as a group, for 19 specific cancer sites or groups of sites, and for five histology groups. Poisson regression methods were used to investigate the magnitude of the radiation-associated risks, the shape of the dose response, how these risks vary with gender, age at exposure, and attained age, and the evidence for inter-site variation in the levels and patterns of the excess risk. For all solid cancers as a group, it was estimated that about 850 (about 11%) of the cases among cohort members with colon doses in excess of 0.005 Gy were associated with atomic bomb radiation exposure. The data were consistent with a linear dose response over the 0- to 2-Gy range, while there was some flattening of the dose response at higher doses. Furthermore, there is a statistically significant dose response when analyses were limited to cohort members with doses of 0.15 Gy or less. The excess risks for all solid cancers as a group and many individual sites exhibit significant variation with gender, attained age, and age at exposure. It was estimated that, at age 70 after exposure at age 30, solid cancer rates increase by about 35% per Gy (90% CI 28%; 43%) for men and 58% per Gy (43%; 69%) for women. For all solid cancers as a group, the excess relative risk (ERR per Gy) decreases by about 17% per decade increase in age at exposure (90% CI 7%; 25%) after allowing for attained-age effects, while the ERR decreased in proportion to attained age to the power 1.65 (90% CI 2.1; 1.2) after allowing for age at exposure. Despite the decline in the ERR with attained age, excess absolute rates appeared to increase throughout the study period, providing further evidence that radiation-associated increases in cancer rates persist throughout life regardless of age at exposure. For all solid cancers as a group, women had somewhat higher excess absolute rates than men (F:M ratio 1.4; 90% CI 1.1; 1.8), but this difference disappears when the analysis was restricted to non-gender-specific cancers. Significant radiation-associated increases in risk were seen for most sites, including oral cavity, esophagus, stomach, colon, liver, lung, non-melanoma skin, breast, ovary, bladder, nervous system and thyroid. Although there was no indication of a statistically significant dose response for cancers of the pancreas, prostate and kidney, the excess relative risks for these sites were also consistent with that for all solid cancers as a group. Dose-response estimates for cancers of the rectum, gallbladder and uterus were not statistically significant, and there were suggestions that the risks for these sites may be lower than those for all solid cancers combined. However, there was emerging evidence from the present data that exposure as a child may increase risks of cancer of the body of the uterus. Elevated risks were seen for all of the five broadly classified histological groups considered, including squamous cell carcinoma, adenocarcinoma, other epithelial cancers, sarcomas and other non-epithelial cancers. Although the data were limited, there was a significant radiation-associated increase in the risk of cancer occurring in adolescence and young adulthood. In view of the persisting increase in solid cancer risks, the LSS should continue to provide important new information on radiation exposure and solid cancer risks for at least another 15 to 20 years.

A new multi-electrode array design for chronic neural recording, with independent and automatic hydraulic positioning.

We report on a new microdrive design, which enables the construction of multi-electrode arrays capable of chronically recording the multi-unit neural activity of waking animals. Our principal motivation for inventing this device was to simplify the task of positioning electrodes, which consumes a considerable amount of time and requires a high level of skill. With the new microdrives, each electrode is independently and automatically driven into place. A hydraulic drive system is adopted to reduce the size, weight, and cost of the structure. The hydraulic fluid is also used as a part of the electrical circuit, and facilitates the wiring of the electrodes. A routing system has been attached to reduce the number of tube connections. The microdrive is cylindrical, has a diameter of 23.5 mm, a height of 37 mm, and a weight of 15 g. It allows for up to 22 electrodes, which are arranged on a 0.35 mm grid. Each electrode can be positioned at any depth up to approximately 4mm. The microdrive was evaluated under acute and chronic recording experiments, and is shown to be capable of automatically positioning each electrode and successfully recording the neural signals of waking rats.

Incidence of haematopoietic malignancies in US radiologic technologists.

BACKGROUND: There are limited data on risks of haematopoietic malignancies associated with protracted low-to-moderate dose radiation. AIMS: To contribute the first incidence risk estimates for haematopoietic malignancies in relation to work history, procedures, practices, and protective measures in a large population of mostly female medical radiation workers. METHODS: The investigators followed up 71,894 (77.9% female) US radiologic technologists, first certified during 1926-80, from completion of a baseline questionnaire (1983-89) to return of a second questionnaire (1994-98), diagnosis of a first cancer, death, or 31 August 1998 (731,306 person-years), whichever occurred first. Cox proportional hazards regression was used to compute risks. RESULTS: Relative risks (RR) for leukaemias other than chronic lymphocytic leukaemia (non-CLL, 41 cases) were increased among technologists working five or more years before 1950 (RR = 6.6, 95% CI 1.0 to 41.9, based on seven cases) or holding patients 50 or more times for x ray examination (RR = 2.6, 95% CI 1.3 to 5.4). Risks of non-CLL leukaemias were not significantly related to the number of years subjects worked in more recent periods, the year or age first worked, the total years worked, specific procedures or equipment used, or personal radiotherapy. Working as a radiologic technologist was not significantly linked with risk of multiple myeloma (28 cases), non-Hodgkin's lymphoma (118 cases), Hodgkin's lymphoma (31 cases), or chronic lymphocytic leukaemia (23 cases). CONCLUSION: Similar to results for single acute dose and fractionated high dose radiation exposures, there was increased risk for non-CLL leukaemias decades after initial protracted radiation exposure that likely cumulated to low-to-moderate doses.

Parylene flexible neural probes integrated with microfluidic channels.

The fluidic channel in the flexible probe has three functions: (i) to inject chemicals into the tissues, (ii) to measure the neural activities from the tissues, and (iii) to improve the mechanical stiffness of the probe by filling the channel with a solid material. A 10-microm-thick microfluidic channel was embedded into the probe by using sacrificial photoresist patterns. Polyethylene glycol (PEG), which is solid at room temperature and dissolves when in contact with water, was used to fill the channel and increase the stiffness of the probe before insertion into the tissue. The impedance of the electrode inside the fluidic channel was around 100 kOmega at 1 kHz when the channel was filled with saline solution. We were able to insert the probe into a rat's brain and measure the neural signals with the electrode.

Micro-thermocouple probe for measurement of cellular thermal responses.

We have produced micro-thermocouple probes for the measurement of cellular thermal responses. Cells generate heat with their metabolisms and more heat with reactions to a certain physical or chemical stimulation. Therefore, the analysis of the cellular thermal responses would provide new physiological information. However, a real-time thermal measurement technique on a target of a single cell has not been established. In this study, glass micropipettes, which are widely used in bioengineering and medicine, are used for the base of the thermocouple probes. Using microfabrication techniques, the junction of two different metal films is formed at the micropipette tip with a diameter of 1 μm. This probe can inject a chemical substance into a cell and to detect its subsequent temperature changes simultaneously.

Diamond-like carbon coating on micropipettes.

Based on glass micropipettes which are widely used in bioengineering and medicine, various microsensor probes could be produced by recent microfabrication techniques. Conductive surfaces of these sensor probes mostly need electrical insulating films coated on them, but it has been difficult to coat a high-quality and strong insulating film on a microacute probe such as a micropipette, especially on its tip. Therefore, we have employed diamond-like carbon (DLC) as an insulating film and developed a DLC coating method based on plasma chemical vapor deposition method. In the deposition apparatus, the cathode is the micropipette itself and the anode is a mesh cylinder with a central focus on the micropipette. In order to prevent the growing films from transformation due to high temperature at the tip, the voltage between the pair of electrodes is impressed intermittently. Raman spectrum and electrical resistivity measured here indicate that the deposited film is DLC and it can be worked well as an insulating film. The DLC coating method could be useful in microprobe fabrications.