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- Holtz, A, et al.
(author)
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Neuropathological changes and neurological function after spinal cord compression in the rat.
- 1990
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In: Journal of Neurotrauma. - : Mary Ann Liebert Inc. - 0897-7151 .- 1557-9042. ; 7:3, s. 155-67
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Journal article (peer-reviewed)abstract
- As part of a series of experimental investigations of the effects of various pharmacological agents on the outcome of compressive spinal cord trauma in the rat, the time course of the cell changes in the cord at the site of and distal to the compression was studied at the light microscopic level. The degree of compression used with the present model results in a transient paraparesis that recovers almost completely over a period of 3 weeks as judged by the inclined plane technique. The most significant morphological findings were as follows. Initially (1 and 24 h after the impact) there was pronounced swelling and hemorrhage at the compression site, chiefly in the gray matter of the cord. On day 4 there was severe necrosis in the same region, with numerous macrophages and leukocytes. Rats killed after 21 days showed either minor residual signs of necrosis or essentially normal tissue architecture. Surprisingly, necrosis with delayed onset also developed in the dorsal columns, involving the pyramidal tracts. This necrosis was detected in animals killed after 9 and 21 days but not in those observed after 4 days or earlier. The longitudinal tracts of the white matter showed reduced staining in paraffin sections of the compression site. Epon sections revealed splits in the myelin sheaths and enlarged periaxonal spaces as early as 1 h after the impact. The alterations in the longitudinal tracts persisted throughout the 21-day observation period and extended down to L2-L4. There was gradual functional recovery, documented by the inclined plane test. Preinjury values were almost reached on day 21, although the cord still showed some morphological damage. In individual animals, no relation was found between degree of function as tested by inclined plane and extent of morphologic injury. Additional functional and morphological methods obviously are needed in future investigations of the effects of treatments on the outcome of compressive spinal cord injury.
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- Larker, Rickard, et al.
(author)
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AEM investigation of ceramic/incology 909 diffusional reactions after joining by HIP
- 1994
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In: Journal of Materials Science. - 0022-2461 .- 1573-4803. ; 29:16, s. 4404-4414
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Journal article (peer-reviewed)abstract
- Diffusion bonding by hot isostatic pressing (HIP) was performed between Incoloy 909 and five different ceramics. Two of the ceramics were composites made from powder mixtures of Si3N4 and either 60 vol% TiN or 50 vol% TiB2, while three were monolithic materials, namely Si3N4 with 2.5 wt% Y2O3 as a sintering additive, Si3N4 without additives, and Si2 N2O without additives. A diffusion couple geometry was developed to facilitate the preparation of thin-foil specimens for examination by analytical electron microscopy (AEM). Diffusion bonding was performed by HIP at 927°C (1200K) and 200 MPa for 4 h. The formation of reaction layers was very limited, being less than 1 μm in total layer thickness. Two reaction products were found by AEM; a continuous, very thin, (≤100 nm) layer of fine TiN crystals at the initial ceramic/metal interface, and larger grains extending about 100–500 nm into the superalloy and forming a semi-continuous layer of a G-phase suicide containing mainly nickel, silicon and niobium.
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