a preferred embodiment of a brain probe or bio - probe assembly 10 , according to the present invention is composed of a probe core 12 and a handle core 14 . the probe core 12 is made of tungsten , chosen for its material stiffness and tensile strength . probe core 12 is preferably straight . to achieve this end , a straightening machine that pulls on core 12 , thereby creating tensile stress and annealing core 12 may be used . during further operations , a vacuum chuck may be used to hold core 12 in place . a tip or distal end 20 of probe core 12 has a diameter of 200 microns ( 8 . 0 mils ) and a base or proximal end 24 of core 12 has a diameter of 600 microns ( 24 mils ). in addition , core 12 is 89 mm ( 3 . 5 ″) long . the tip 20 is preferably formed by way of centerless grinding . probe core 12 should be electro polished so that the deposition of materials onto it ( see below ) can be accomplished efficiently and so that the finished assembly 10 can pass through brain tissue as smoothly as possible . alternatively , probe core 12 can be left in a comparatively rough state and coated with a coat of epoxy that is thick enough to minimize capacitance between core 12 and the traces 50 ( discussed below ). the comparatively rough state of the probe core actually helps to effect the binding of the epoxy to the probe core . one type of epoxy that can be used is the epoxy 377 discussed further below . for ease of assembly and so that operating personnel may more easily handle assembly 10 , the handle core 14 is expanded in cross - section relative to probe core 12 . although the handle core 14 is preferably a unitary piece of medical grade 304 stainless steel , it may be conceptually divided into a cylinder 15 , having a diameter of 4 . 826 mm ( 0 . 19 ″), and a frustum 17 . the frustum 17 tapers inwardly at 150 angle from the sides of cylinder 15 . a 600 μm ( 24 mil ) aperture ( not shown ) at the narrow end of frustum 17 permits introduction of the base of probe core 12 , after which probe core 12 is joined to handle core 14 , by way of an epoxy , to form joint core 26 . the epoxy used must be conductive , so that the probe core 12 is grounded to the base core 14 , and preferably heat resistant , so that it withstands the sterilization process that the probe 10 generally should undergo in use . it must also be able to withstand the different degrees of expansion that stainless steel and tungsten undergo during the sterilization process . an epoxy that is available from epoxy technology , inc . of billerica , mass ., under the designation e3084 appears to meet these requirements . in an alternative preferred embodiment , the probe core 12 is laser - welded to the base core 14 . after joint core 26 is produced , it is dip coated with a dielectric epoxy , which has been premixed with a surfactant to promote an even coating , to form an insulating coat 30 . the desirable characteristics for an epoxy to be used are biocompatibility , heat tolerance to withstand the sterilization process , low viscosity to produce a thin film , a heat accelerated cure and a high bulk resistivity and a low dielectric coefficient to avoid electrical losses and withstand electrostatic charges . one epoxy that appears to meet these requirements is the epoxy # 377 noted earlier . a suitable surfactant is available as fc - 430 from 3m of st . paul , minn . alternatively , acrylated epoxy could be used . for coat 30 , this material could have the composition , noted in table i , below , in parts per hundred resin ( phr ): table i substance proportion source , contact information photomer 3015 100 phr cognis corp ., http :// www . na . cognis . com / northamerica / nacognis . html tmpeota , 50 phr sartomer company , inc ., ( trimethylolpropane http :// www . sartomer . com triacrylate sr - 351 ) r - 812s ( fumed 10 phr degussa corp ., silica ) http :// www . degussa . com / en / home . html mibk ( methyl 20 phr aldrich corp ., isobutyl http :// www . sigmaaldrich . com / brands / keytone ) aldrich . html darocure 1173 2 . 6 phr em chemicals corp ., ( photoinitiator ) http :// www . emdchemicals . com / corporate / emd_corporate . asp in an additional preferred embodiment quartz crystal , glass or a similar dielectric material is vacuum deposited to form coat 30 . in this preferred embodiment , in order to gain adherence , however , a 200 å coat of chrome ( not shown ) is first applied , also through vacuum deposition on core 26 to promote the adhesion of coat 30 . the thickness of coat 30 is chosen to minimize the capacitance between core 26 and the conductive traces 50 ( see below ) deposited over it . on top of coat 30 , a 0 . 5 μm thick plate of conductive material ( not shown as such but later rendered into a set of traces 50 ) is , preferably , vacuum deposited . this plate 50 also may be adhered by way of a 200 å layer of vacuum deposited chrome ( not shown ). plating 50 must be highly conductive and , if vacuum coating is used , must be an element of the periodic table . accordingly , gold , platinum and iridium are among the materials that may be used . other deposition techniques , such as chemical deposition , may permit the application of other highly conductive materials , such as a conductive polymer . the material used to create plating 50 must also be susceptible to removal by laser ablating or an etching process . next , plate 50 is sectioned into 24 longitudinal traces 50 ( other numbers of traces 50 are possible ) extending from approximately the tip 20 to the proximal end of base core 14 . accordingly , near the tip 20 the traces 50 have a pitch of about 27 μm , near the base 24 have a pitch of about 80 μm at the proximal end of handle 14 have a pitch of about 630 μm . of particular utility for performing the task of sectioning the conductive plate into traces 50 is a frequency multiplied nd : yag laser , which can cut kerfs to separate the traces on the order of 5 – 10 μm width . in one preferred embodiment there are just four traces 50 . using this embodiment a compound probing device may be built that incorporates an array of probe assemblies 10 to sense and / or stimulate a number of neural sites separated not just in depth , but also transversely to probe assembly 10 longitudinal dimension . next , the conductive traces 50 are coated with an outer layer 60 of high coefficient dielectric material . an additional dip coat of epoxy # 377 is one way of accomplishing this . as an alternative , an acrylated epoxy urethane may be used , similar to the acrylated epoxy that my be used for layer 30 , and described by table ii , below : table ii substance proportion source , contact information photomer 3015 100 phr cognis corporation , http :// www . na . cognis . com / northamerica / nacognis . html tmpeota , 50 phr sartomer company , inc ., ( trimethylolpropane http :// www . sartomer . com triacrylate sr - 351 ) rx 03961 32 phr ucb radcure , inc ., ( acrylated urethane ) http :// www . chemicals . ucb - group . com / default2 . html r - 812s ( fumed 10 phr degussa corp ., silica ) http :// www . degussa . com / en / home . html mibk ( methyl 63 phr aldrich co ., isobutyl http :// www . sigmaaldrich . com / brands / keytone ) aldrich . html darocure 1173 2 . 6 phr em chemicals , ( photoinitiator ) http :// www . emdchemicals . com / corporate / emd_corporate . asp another method is a vacuum deposition of glass or quartz crystal placed , again over an intermediate 200 å layer of chrome . dielectric layer 60 preferably has a thickness of from 10 to 40 um to avoid damage by static electric discharge . a laser is used to ablate this outer layer to create several apertures extending through layer 60 , having a diameter of about 10 μm at each prospective microelectrode site . a platinum - iridium electrode or neural contact site 62 is built up , preferably by electroplating , at each of these sites . other materials that could be used for the neural contact sites 62 are platinum ( not mixed with iridium ), iridium , and oxidized iridium , which is also referred to as iridium black , and intrinsically conductive polymers , such as a doped polypyrrole . base 14 is attached to a plate 70 that includes outwardly extending conductive traces ( not shown ) that connect traces 50 to a set of connector pins 72 . in turn , a set of connectors 72 on plate 70 attach to a matching set of connectors 74 on a circuit card assembly 80 . assembly 80 includes a set of 24 circuit cards 82 , one for each trace , each bearing an identical amplification circuit for processing each signal from each trace 50 in an identical manner . the advantages of the above described preferred embodiment should now be apparent . probe assembly 10 is strong , smooth and sleek , for moving through brain tissue to the site of interest . the cross capacitance between traces 50 is minimized due to the shape of the traces 50 , which are curved solid rectangles , on the order of 0 . 5 um thick but varying between 10 um and 50 um wide . finally , identical circuits 82 ensure equal treatment for each trace signal . an alternative preferred embodiment of a bio - probe 110 according to the present invention is shown in fig5 and 6 . bio - probe 110 differs from bio - probe 10 in that it is made of flexible material and defines an inner lumen 112 , for accepting a rigid insert 114 . rigid insert 114 permits bio - probe 110 to be pushed through body tissue , for example brain tissue . insert 114 is then removed , so that as the probe recipient moves about with the probe installed , the flexible bio - probe 110 will not tear into brain tissue , as the brain moves about slightly in the brain pan . to manufacture bio - probe 110 , a mandrel , very similar in nature to insert 114 is used . a tube 116 of flexible dielectric material , for example , polyimide is provided and fit over mandrel 114 . tube 116 defines ten lumens 118 , the purpose of lumens 118 will be described later . the production of tube 116 may be effected by molding of polymeric resin . for example tube 116 could be produced by vacuum molding of polyimide resin . a layer of conductive material , for example gold , is then deposited by , for example , vapor deposition or sputtering . the original deposition of thin layer of conductive material may be followed by an electroplating stage , in which a thicker layer of conductive material is built up on the seed layer . next a set of kerfs 120 are created , thereby creating a set of separated conductive traces 122 . kerfs 120 may be formed by laser machining as noted above in reference to bio - probe 10 or through a photolithographic technique . the photolithographic technique could include a mask being pulled across a light source as bio - probe 10 , coated with photo resist , is rotated to expose different sections . other than this rotation technique , the photolithography would be relatively standard , with either positive or negative photo resist being used , and the metal being etched away in places where the developed photo resist has been removed . next , an additional layer 123 of dielectric material is coated over traces 122 . apertures 132 are created to lumens 118 and apertures 134 are created to traces 122 by the use of an nd : yag frequency multiplied laser . finally , platinum - iridium electrodes 124 are built up in apertures 134 . these electrodes are used to stimulate brain cells and sense brain activity . lumens 118 and apertures 132 are used in the delivery of substances , for example , a medicine or a stimulant to brain tissue . apertures 132 and electrodes 124 can be used in tandem with a liquid substance administered through apertures 132 and the resultant effect measured by electrodes 124 . the terms and expressions that have been employed in the foregoing specification are used as terms of description and not of limitation . there is no intention , in the use of such terms and expressions , of excluding equivalents of the features shown and described or portions thereof , it being recognized that the scope of the invention is defined and limited only by the claims which follow .
a bio - probe having a base and a tip , and comprising a longitudinal core of substantially rigid material . on the core , there is a first layer of dielectric material , supported by and substantially circumferentially surrounding the core . also , a set of conductors , each conductor extending longitudinally along the first layer of dielectric material and a second layer of dielectric material , substantially covering each of the set of conductors . for each of the conductors , an aperture is defined through the second layer of dielectric material to the conductor , thereby defining an electrode . in one preferred embodiment of this aspect , the first layer of insulative material is in the form of a tube and wherein the core is removable from the tube .