METHOD OF IMPLANTATION OF A MEDICAL DEVICE INTO NEURAL TISSUE

Abstract

A method of providing a channel in nervous tissue filled with an aqueous gel for implantation of a microelectrode or other medical device lacking sufficient physical stability for direct implantation by insertion, comprises providing an apparatus comprising an oblong rigid pin covered by a dry gel forming agent; locating a target in the tissue; defining a straight insertion path a desired tissue insertion point and the target; aligning the pin with its end foremost with the insertion path; inserting the pin into the tissue to a position near or at the target; allowing sufficient time to pass for a gel to be formed around the pin, withdrawing the pin. Also disclosed is a corresponding channel; a method of implantation of a microelectrode or microprobe into nervous tissue via the channel; a corresponding method of implantation of living cells; a corresponding apparatus for forming the channel.

Claims

1. A method of providing an oblong linear channel in nervous tissue of a person or a mammal for implantation of a medical device or other object into said tissue by insertion into the channel, the device being insufficiently physically stable for implantation by direct insertion into the tissue, the method comprising: providing a channel-forming apparatus comprising a rotationally symmetric, in particular cylindrical, rigid pin of a length exceeding the length of the channel to be provided and having a front end and a rear end, a section of the pin extending from its front end towards its rear end of a length corresponding to at least the length of the channel enclosed by a layer of gel forming agent or comprising gel forming agent, wherein a gel forming agent is a dry agent capable of forming an aqueous gel on contact with aqueous body fluid, the layer of gel forming agent or comprising gel forming agent comprising less than 20% by weight of water, preferably less than 10% by weight, in particular less than 5% or 2% by weight; inserting the pin into nervous tissue with its front end foremost; allowing aqueous gel to be formed around the pin by contact of gel forming agent with aqueous body fluid; withdrawing the pin from the gel; wherein the pin is sufficiently rigid to allow it to be inserted into nervous tissue in absence of the layer comprising or consisting of gel forming agent.

2. The method of claim 1, wherein the pin comprises two or more layers comprising or consisting of gel forming agent, wherein each of said two or more layers comprises a different gel forming agent.

3. The method of claim 1, wherein the pin is electrically conducting and/or comprises an axially extending electrical conductor and/or comprises an optical fiber.

4. The method of claim 1, wherein the pin is of a metal or comprises a metal conductor or an electrically conducting non-metallic material such as an electrically conducting polymer or electrically conducting carbon.

5. The method of claim 1, wherein the pin comprises a centrally disposed axially extending channel and optionally one or more channels extending radially from the axial channel.

6. The method of claim 1, wherein a gel forming agent comprises gel-forming protein or carbohydrate.

7. The method of claim 6, wherein the protein is selected from the group consisting of gelatin, hyaluronic acid and salts thereof, chemically modified gelatin, chemically modified hyaluronic acid and salts thereof.

8. The method of claim 7, wherein the protein is gelatin.

9. The method of claim 3, wherein a metallic lead is attached in an electrically conducting fashion to the pin or the metal conductor or the electrically conducting polymer at or near the rear end thereof.

10. The method of claim 9, wherein the lead is for connection with a voltage monitoring device or with a source of electric power.

11. The method of claim 3, wherein the pin is electrically insulated except for at its front end.

12. The method of claim 1, wherein a gel forming agent or a layer comprising a gel forming agent comprises a pharmacologically active agent, in particular a pharmacologically active agent selected from the group consisting of coagulant, anticoagulant, antibiotic, osmotic pressure adjusting agent, anti-inflammatory agent, nutrient, factor stimulating growth, factor stimulating cell differentiation, hormone, cytokine.

13. The method of claim 1, wherein the apparatus comprises a microelectrode and/or an optical fiber.

14. The method of claim 5, wherein said centrally disposed axially extending channel is designed for injection of aqueous fluid in an axial direction into the implantation channel.

15. The method of claim 14, wherein the axially extending channel is in fluid communication with one or more radially extending channels allowing injection of said fluid in a radial direction into the implantation channel.

16. A method of implantation of a microelectrode into nervous tissue, comprising: i) providing a microelectrode with a front end and a rear end, the microelectrode not being sufficiently rigid for insertion into nervous tissue; i) forming a linear implantation channel in the tissue by the method of claim 1; iii) inserting the microelectrode with its front end foremost into said channel to a desired depth.

17. A method for implantation of living cells into neural tissue, comprising: i) providing an aqueous suspension of living cells in a syringe with a needle or a pipette; ii) forming a linear implantation channel in the tissue filled with aqueous gel according to the method of claim 1; iii) inserting the syringe needle or pipette to a desired depth into the implantation channel; iv) injecting the aqueous suspension of living cells into the implantation channel; v) withdrawing the syringe needle or pipette; with the proviso that injection can be made prior to and/or during withdrawal.

18. A method for implantation of living cells into neural tissue, comprising: i) providing a frozen aqueous suspension of living cells attached to the tip of an insertion bar; ii) forming a linear implantation channel in the tissue filled with aqueous gel according to claim 1; ii) inserting the bar with its tip foremost to a desired depth into the implantation channel; iv) allowing the frozen suspension to thaw; v) withdrawing the bar.

19. Apparatus for forming a linear channel in nervous tissue for implantation of a medical device, comprising or consisting of an oblong rigid pin having a front end and a rear end and a layer comprising or consisting of dry gel forming agent disposed on a pin section extending from the front end in a distal direction and enclosing said section, wherein said layer or agent contains less than 20% by weight of water, preferably less than 10% by weight, most preferred less than 5% by weight, wherein the pin is sufficiently rigid to allow it to be inserted into nervous tissue in absence of its layer comprising or consisting of dry gel forming agent.

20. The apparatus of claim 19, wherein the pin is cylindrical.

21. The apparatus of claim 19, wherein the pin is of metal or comprises metal.

22. The apparatus of claim 21, wherein the metal is selected from steel, titanium, tungsten, hafnium, and iridium.

23. The apparatus of claim 19, wherein the pin is of a polymer material or comprises such material.

24. The apparatus of claim 23, wherein the polymer is acrylate or epoxy polymer.

25. The apparatus of claim 23, wherein the polymer is reinforced with fiber, in particular carbon fiber.

26. The apparatus of claim 19, comprising one or more means selected from electrode means, optical fiber means, sensor means.

27. The apparatus of claim 20, wherein the pin comprises an axially extending channel opening at the distal face thereof.

28. The apparatus of claim 27 comprising channel(s) extending radially from the axial channel.

29. The apparatus of claim 28, wherein the axially extending channel and/or a radially extending channel is plugged at its opening at the distal face or the cylindrical face, respectively, of the pin.

30. The apparatus of claim 29, wherein the plug is of a material dissolvable or degradable in an aqueous fluid.

31. The apparatus of claim 19, wherein the agent capable of forming a gel in contact with aqueous body fluid comprises a gel-forming protein or carbohydrate.

32. The apparatus of claim 31, wherein the protein is selected from a biocompatible gel forming agent, in particular an agent selected from the group consisting of gelatin, hyaluronic acid and salts thereof, chemically modified gelatin, chemically modified hyaluronic acid and salts thereof.

33. The apparatus of claim 19, wherein the layer comprises a pharmacologically active agent.

34. The apparatus of claim 33, wherein the pharmacologically active agent is selected from the group consisting of coagulant, anticoagulant, antibiotic, osmotic pressure adjusting agent, anti-inflammatory agent, nutrient, factor stimulating growth, factor stimulating cell differentiation, hormone.

35. The apparatus of claim 19, comprising a friction reducing layer disposed on the entire dry gel forming layer or a portion thereof.

36. The apparatus of claim 19, comprising a dissolution retarding layer disposed on the dry gel forming layer or a portion thereof.

37. The apparatus of claim 36, comprising a friction reducing layer disposed on the dissolution retarding layer.

38. A method of reducing microglia response to implantation of a medical device or other object into neural tissue, comprising providing a layer of a biocompatible aqueous gel surrounding the implanted device or object.

39. The method of claim 38, wherein the layer of biocompatible gel is provided in form of a channel extending from a surface of the nervous tissue.

40. The method of claim 39, wherein the medical device or other object is inserted into the tissue via the channel.

41. The method of claim 38, wherein the biocompatible gel is selected from the group consisting of gelatin gel, hyaluronic acid gel and gel of salts thereof, chemically modified gelatin gel, chemically modified hyaluronic acid gel and gel of salts thereof.

42. The method of claim 41, wherein the biocompatible gel is gelatin gel or chemically modified gelatin gel.

43. The method of claim 1, wherein a gel forming agent is selected from the group consisting of: arabinogalactan; arabinoxylan; galactan; galactomannan; lichenan; xylan; cellulose derivatives such as hydroxymethylpropyl cellulose; whey protein; soy protein; casein; hyaluronic acid; chitosan; gum Arabic; carboxyvinyl polymer; sodium polyacrylate; carboxymethyl cellulose; sodium carboxymethyl cellulose; pullulan; polyvinylpyrrolidone; karaya gum; pectin; xanthane gum; tragacanth; alginic acid; polyoxymethylene; polyimide; polyether; chitin; poly-glycolic acid; poly-lactic acid; co-polymer of poly-glycolic and poly-lactic acid; co-polymer of poly-lactic acid and polyethylene oxide; polyamide; polyanhydride; polycaprolactone; maleic anhydride copolymer; poly-hydroxybutyrate co-polymer; poly(1,3-bis(p-carbophenoxy)propane anhydride); polymer formed by co-polymerization with sebacic acid or with poly-terephthalic acid; poly(glycolide-co-trimethylene carbonate); polyethylene glycol; polydioxanone; polypropylene fumarate; poly(ethyl glutamate-co-glutamic acid); poly(tert-butyloxy carbonylmethyl glutamate); poly-caprolactone; poly(caprolactone-co-butylacrylate); poly-hydroxybutyrate and copolymers thereof; poly(phosphazene); poly(D,L-lactide-co-caprolactone); poly(glycolide-co-caprolactone); poly(phosphate ester); poly(amino acid); poly(hydroxybutyrate); polydepsidpeptide; maleic anhydride copolymer; polyphosphazene; polyiminocarbonate; poly[(7.5% dimethyl-trimethylene carbonate)-co-(2.5% trimethlyene carbonate)]; polyethylene oxide; hydroxypropylmethylcellulose, poly(ethylene-co-vinyl acetate); isobutylene-based copolymer of isobutylene and at least one other repeating unit such as butyl acrylate: butyl methacrylate; substituted styrene such as amino styrene, hydroxy styrene, carboxy styrene, sulfonated styrene; homopolymer of polyvinyl alcohol; co-polymer of polyvinyl alcohol and at least one other repeating unit such as a vinyl cyclohexyl ether; hydroxymethyl methacrylate; hydroxyl- or amino-terminated polyethylene glycol; acrylate-based copolymer such as methacrylic acid, methacrylamide, hydroxymethyl methacrylate; ethylene vinyl alcohol copolymer; silicone based copolymer of aryl or alkyl siloxane and at least one repeating unit; polyurethane; heparan sulfate; RGD peptide; polyethylene oxide; chrondroitin sulfate; YIGSR peptides; keratan sulfate; VEGF biomimetic peptide; perlecan (heparan sulfate proteoglycan 2); Ile-Lys-Val-Ala-Val (IKVAV) containing laminin alpha-1 chain peptide; modified heparin; fibrin fragments.

44. Linear channel in nervous tissue of a person or animal for implantation of a medical device, the channel filled with aqueous gel formed in situ by contact of body fluid with dry biocompatible gel forming agent provided on a solid support, in particular a member of the group consisting of gelatin, hyaluronic acid and salts thereof, chemically modified gelatin, chemically modified hyaluronic acid and salts thereof, wherein the support has been removed after forming the channel.

45. The linear nervous tissue channel of claim 44 filled with gel formed by contact of aqueous body fluid with one or more gel forming agents of the group consisting of: arabinogalactan; arabinoxylan; galactan; galactomannan; lichenan; xylan; cellulose derivatives such as hydroxymethylpropyl cellulose; whey protein; soy protein; casein; hyaluronic acid; chitosan; gum Arabic; carboxyvinyl polymer; sodium polyacrylate; carboxymethyl cellulose; sodium carboxymethyl cellulose; pullulan; polyvinylpyrrolidone; karaya gum; pectin; xanthane gum; tragacanth; alginic acid; polyoxymethylene; polyimide; polyether; chitin; poly-glycolic acid; poly-lactic acid; co-polymer of poly-glycolic and poly-lactic acid; co-polymer of poly-lactic acid and polyethylene oxide; polyamide; polyanhydride; polycaprolactone; maleic anhydride copolymer; poly-hydroxybutyrate co-polymer; poly(1,3-bis(p-carbophenoxy)propane anhydride); polymer formed by co-polymerization with sebacic acid or with poly-terephthalic acid; poly(glycolide-co-trimethylene carbonate); polyethylene glycol; polydioxanone; polypropylene fumarate; poly(ethyl glutamate-co-glutamic acid); poly(tert-butyloxy carbonylmethyl glutamate); poly-caprolactone; poly(caprolactone-co-butylacrylate); poly-hydroxybutyrate and copolymers thereof; poly(phosphazene); poly(D,L-lactide-co-caprolactone); poly(glycolide-co-caprolactone); poly(phosphate ester); poly(amino acid); poly(hydroxybutyrate); polydepsidpeptide; maleic anhydride copolymer; polyphosphazene; polyiminocarbonate; poly[(7.5% dimethyl-trimethylene carbonate)-co-(2.5% trimethlyene carbonate)]; polyethylene oxide; hydroxypropylmethylcellulose, poly(ethylene-co-vinyl acetate); isobutylene-based copolymer of isobutylene and at least one other repeating unit such as butyl acrylate: butyl methacrylate; substituted styrene such as amino styrene, hydroxy styrene, carboxy styrene, sulfonated styrene; homopolymer of polyvinyl alcohol; co-polymer of polyvinyl alcohol and at least one other repeating unit such as a vinyl cyclohexyl ether; hydroxymethyl methacrylate; hydroxyl- or amino-terminated polyethylene glycol; acrylate-based copolymer such as methacrylic acid, methacrylamide, hydroxymethyl methacrylate; ethylene vinyl alcohol copolymer; silicone based copolymer of aryl or alkyl siloxane and at least one repeating unit; polyurethane; heparan sulfate; RGD peptide; polyethylene oxide; chrondroitin sulfate; YIGSR peptides; keratan sulfate; VEGF biomimetic peptide; perlecan (heparan sulfate proteoglycan 2); Ile-Lys-Val-Ala-Val (IKVAV) containing laminin alpha-1 chain peptide; modified heparin; fibrin fragments.

46. The linear nervous tissue channel of claim 44 of cylindrical form.

47. The linear nervous tissue channel of claim 46, comprising two or more cylindrical layers of aqueous gel of same diameter as the channel.

48. The linear nervous tissue channel of claim 46, wherein a cylindrical central layer of aqueous gel is surrounded by a peripheral layer of aqueous gel.

49. The apparatus of claim 19, wherein a gel forming agent is selected from the group consisting of: arabinogalactan; arabinoxylan; galactan; galactomannan; lichenan; xylan; cellulose derivatives such as hydroxymethylpropyl cellulose; whey protein; soy protein; casein; hyaluronic acid; chitosan; gum Arabic; carboxyvinyl polymer; sodium polyacrylate; carboxymethyl cellulose; sodium carboxymethyl cellulose; pullulan; polyvinylpyrrolidone; karaya gum; pectin; xanthane gum; tragacanth; alginic acid; polyoxymethylene; polyimide; polyether; chitin; poly-glycolic acid; poly-lactic acid; co-polymer of poly-glycolic and poly-lactic acid; co-polymer of poly-lactic acid and polyethylene oxide; polyamide; polyanhydride; polycaprolactone; maleic anhydride copolymer; poly-hydroxybutyrate co-polymer; poly(1,3-bis(p-carbophenoxy)propane anhydride); polymer formed by co-polymerization with sebacic acid or with poly-terephthalic acid; poly(glycolide-co-trimethylene carbonate); polyethylene glycol; polydioxanone; polypropylene fumarate; poly(ethyl glutamate-co-glutamic acid); poly(tert-butyloxy carbonylmethyl glutamate); poly-caprolactone; poly(caprolactone-co-butylacrylate); poly-hydroxybutyrate and copolymers thereof; poly(phosphazene); poly(D,L-lactide-co-caprolactone); poly(glycolide-co-caprolactone); poly(phosphate ester); poly(amino acid); poly(hydroxybutyrate); polydepsidpeptide; maleic anhydride copolymer; polyphosphazene; polyiminocarbonate; poly[(7.5% dimethyl-trimethylene carbonate)-co-(2.5% trimethlyene carbonate)]; polyethylene oxide; hydroxypropylmethylcellulose, poly(ethylene-co-vinyl acetate); isobutylene-based copolymer of isobutylene and at least one other repeating unit such as butyl acrylate: butyl methacrylate; substituted styrene such as amino styrene, hydroxy styrene, carboxy styrene, sulfonated styrene; homopolymer of polyvinyl alcohol; co-polymer of polyvinyl alcohol and at least one other repeating unit such as a vinyl cyclohexyl ether; hydroxymethyl methacrylate; hydroxyl- or amino-terminated polyethylene glycol; acrylate-based copolymer such as methacrylic acid, methacrylamide, hydroxymethyl methacrylate; ethylene vinyl alcohol copolymer; silicone based copolymer of aryl or alkyl siloxane and at least one repeating unit; polyurethane; heparan sulfate; RGD peptide; polyethylene oxide; chrondroitin sulfate; YIGSR peptides; keratan sulfate; VEGF biomimetic peptide; perlecan (heparan sulfate proteoglycan 2); Ile-Lys-Val-Ala-Val (IKVAV) containing laminin alpha-1 chain peptide; modified heparin; fibrin fragments.

Description

DESCRIPTION OF THE FIGURES

[0076] FIGS. 1a-1f illustrate the method of the invention for providing a channel in nervous tissue of a person or a mammal for implantation of a medical device and a channel so produced, the method including identification of the position of a target in the nervous tissue in respect of which the front end of the channel is desired to be disposed; FIGS. 1c-1f illustrate a variation of the method of the invention in which the position of the target is not identified by radiation means;

[0077] FIGS. 1g, 1h illustrate the method of the invention for implanting a microelectrode into nervous tissue by inserting it into the channel provided by a method of the invention, and a microelectrode so implanted;

[0078] FIG. 2 illustrates a microelectrode implanted according to the method of the invention positionally fixed in neighboring osseous tissue;

[0079] FIG. 3 illustrates an apparatus according to the invention for forming a channel in nervous tissue for insertion of a microelectrode or other device;

[0080] FIG. 4 illustrates the microelectrode of FIGS. 1g-1j;

[0081] FIG. 5 illustrates an apparatus according to the invention for forming a channel in nervous tissue for insertion of a microelectrode or other device, the apparatus comprising an optical fiber;

[0082] FIG. 6 illustrates an apparatus according to the invention for forming a channel in nervous tissue for insertion of a microelectrode or other device, the apparatus comprising an optical fiber and an electrode;

[0083] FIGS. 7 and 7a illustrate an apparatus according to the invention for forming a channel in nervous tissue for insertion of a microelectrode or other device in axial A*-A* (FIG. 7; FIG. 7a showing an enlarged portion thereof) section, the apparatus comprising, in addition to a cylindrical pin covered with dry gelatin and comprising optical fiber and electrode means, an axially extending passage in the pin for injection of fluid material into the channel from the opening of the passage at the distal face of the apparatus;

[0084] FIGS. 8, 8a, 8b, 8c illustrate an apparatus according to the invention for forming a channel in nervous tissue for insertion of a microelectrode or other device in axial A**-A** (FIG. 8; 8a showing an enlarged portion thereof) and radial B-B (FIGS. 8b, 8c, further enlarged) section, the apparatus comprising, in addition to a cylindrical pin covered with dry gelatin and comprising optical fiber and electrode means, an axially extending passage in the pin for injection of fluid material into the channel from the opening of the passage at the distal face of the apparatus, and further comprising passages extending radially from the axially extending passage, the radially extending passages of a variety of the apparatus illustrated in dry FIG. 8c being plugged;

[0085] FIGS. 9, 9a, 9b, 9c illustrate an apparatus according to the invention corresponding to that of FIGS. 8, 8a, 8b, 8c, provided with a layer of friction reducing agent on the gelatin layer;

[0086] FIG. 10 illustrates a variety of the apparatus of FIG. 9 and in the same section, the gelatin layer being covered by a first, friction reducing layer extending from the distal end of the pin in a proximal direction and by a second layer comprising anticoagulant extending from the proximal end of the friction reducing layer in a proximal direction;

[0087] FIGS. 11, 11a, 11b, 11c illustrate four embodiments of cylindrical pins of the invention covered with one or more layers of dry gel forming agent used in the production of corresponding cylindrical channels in nervous tissue filled with aqueous gel, in an axial (channel axis) section;

[0088] FIG. 12, 12a, 12b, 12c illustrate four embodiments of the cylindrical channel of the invention in nervous tissue of filled with one or more layers of aqueous gel, produced by implantation of the pins of FIGS. 11, 11a, 11b, 11c, respectively, in an axial (channel axis) section.

DESCRIPTION OF PREFERRED EMBODIMENTS

Example 1. Determination of Position of Target, Front (Bottom) End of Channel, Rear (Top or Open) End of Channel, Providing Guiding Information for Insertion of Channel-Forming Apparatus

[0089] FIG. 1 is a rough representation of a section of a mammal brain 1 with adjacent portions of skull bone 2 and dura mater 3. A through bore 5 has been provided in the skull bone 2 through which a face 6 of the brain tissue 1 can be accessed after removal of a portion of the dura mater 3. In the brain tissue 1 a number of neural cells or rather cell clusters comprising 100 or more cells 4 are shown. One of them 4′ has been identified as a desired target for nervous cell potential with a microelectrode. The location of the target neural cell/cell cluster 4′ is determined by employing a combination of two imaging systems such as Computer Tomography (CT) 11 and Magnetic Resonance Imaging (MRI) 12 electrically connected with and controlled by a control unit 13. Based on the location information a microprocessor of the control unit 13 determines an insertion track 9 for a channel forming apparatus (20, FIG. 3), which is visualized by a laser 10 beam controlled by the control unit 13. The control unit 13 additionally determines a point 7 on the track near the target neural cell 4′ cluster corresponding to the distal end of a channel (23′, FIG. 2) to be formed defining the insertion depth of the channel forming apparatus (20, FIG. 3). The point 8 on the insertion track 9 where the laser beam hits the free face 6 of the brain tissue 4 is also determined. Point 8 represents the point of insertion into brain tissue 1 of the channel forming apparatus (20, FIG. 3).

Example 2. First Embodiment of a Channel-Forming Apparatus of the Invention and Manufacture Thereof

[0090] An embodiment of the channel forming apparatus 20 of the invention is shown in FIG. 3 in axial A-A section. The channel forming apparatus 20 comprises a stiff cylindrical pin 21 of a rigid material and a layer 22 of gelatin on a portion of the pin 21 extending from its front (distal) end 21′ in the direction of its rear (proximal) end 21″. The layer of gelatin 22 can be substituted by a corresponding layer of another agent capable of forming a gel on contact with body such as hyaluronic acid or PEG or a combination of such agents. The axial extension of the layer 22 corresponds to at least the depth of the channel to be formed. The diameter of the pin 21 is smaller than the diameter of the channel to be formed and should be kept as small as possible. The thickness of the layer 22 on the pin is determined by the desired width of the channel to be formed. The pin 21 should be tapering towards its distal end, such as by ending in a sharp or rounded tip, in particular a conically rounded tip. The material of the pin 21 is not critical but should provide good adherence for the layer of 22 of gelatin or other agent capable of forming a gel on contact with aqueous body fluid. On the other hand, the material of the pin or a material covering the surface of the pin should easily release the aqueous gel formed upon contact of the dry gel forming agent with aqueous body fluid, that is, should not provide good adherence for the so formed aqueous gel. The use of a poly-fluorinated material such as Teflon® covering the pin 21 constitutes an acceptable compromise. Other useful materials include silicones of various kind. Useful pin 21 materials include steel, aluminum, polycarbonate, polyester, glass, ceramics but also titanium, gold, platinum and alloys thereof. They may be covered by, for instance, a thin layer of poly-fluorinated material or a silicone or their surface may be silanized.

[0091] The channel forming apparatus 20 can be manufactured, for instance, by providing an aqueous solution of gelatin and a pin 21 of stainless steel. The viscosity of the gelatin solution is controlled by temperature and concentration so as to make it visibly viscous but not gelling. The pin 21 is dipped into the gelatin solution, then withdrawn, disposed horizontally, and rotated. Drying of the gelatin solution on the pin 21 can be accelerated by applying heat and/or vacuum.

[0092] The dipping step is repeated until a gelatin layer 22 of desired thickness has been formed on the pin 21. To avoid dissolution of dry gelatin the pin 21 is quickly withdrawn from the gelatin solution.

[0093] In another method of manufacture of the channel forming apparatus gelatin or other agent capable of forming a gel on contact with water is applied to the pin 21 by spraying with a corresponding aqueous solution.

[0094] In still another method of manufacture of the channel forming apparatus a mould of desired form is used for the manufactures of the channel forming apparatus. In a preferred embodiment two sheets of acrylic material (Plexiglass®) each comprising a hemi-cylindrical moulding section of same size constituting a cylindrical mould are mounted in an abutting disposition with their axes aligned around a cylindrical pin of the invention, the axis of which is centered in the mould. The sheets are kept in the abutting disposition by a number of screws disposed peripherally of the mould. The radial dimension of the mould is slightly larger than that of the pin. At one axial end of the mould a channel is provided through which a concentrated aqueous solution of the gel forming agent is injected into the space between the pin and the mould walls. Injection is made at a temperature at which the solution is not gelled. The sheets of the mould then are slowly released by loosening the screws to provide access of air for drying. After drying to a water content of about 2% by weight the pin covered with dry gelling agent is removed from the mould. The gelling agent can in turn be coated with a material such as Kollikoat® retarding contact of the dry gelling agent with aqueous body fluid and thus the onset of gelling as well as the end thereof.

Example 3. Forming an Implantation Channel

[0095] A preferred embodiment of forming an implantation channel of the invention is shown in FIGS. 1b through 1f.

[0096] A channel-forming apparatus 20 of the invention is positioned with its front end 21′ at insertion point 8 on the accessible brain tissue 4 surface 6 and with its axis A-A aligned with the insertion track line 9 (FIG. 1b). The apparatus 20 is then inserted into the tissue 4 along the track line 9 by applying pressure on its rear section lacking a gelatin layer 22. Application of pressure and insertion may be manually or by using an appropriate micromanipulator (not shown). The apparatus 20 is inserted into the desired depth, that is, until its front end has reached the front end 7 of the insertion track or path (FIG. 1c). Insertion should be as fast as possible to avoid dissolution of gelatin in the layer 22 by aqueous body fluid during insertion. Upon full insertion the apparatus 20 is left in the fully inserted position (FIG. 1c) until the gelatin layer 22 has been fully dissolved by aqueous body fluid and a tubiform layer of gelatin gel 23 formed around the pin 21 (FIG. 1d). The combination of pin 21 and tubiform layer of gelatin gel 23 constitute a pre-channel visualized in FIG. 1d by its contour 24. Since the axial length of the gelatin layer 22 exceeded the depth of insertion and thus the axial extension of its contact with aqueous body fluid, a proximal terminal portion 22′ of the gelatin layer 22 was not dissolved. In the following step the pin 21 is withdrawn (direction R) from the gel 23 along the insertion path 9. Withdrawal of the pin 21 reduces the volume of the pre-channel by the volume of the pin 21 so as to form a channel of the invention visualized in FIG. 1e by its contour 24′. FIG. 1f (enlarged) illustrates an initial phase of withdrawal of pin 21 in which a distal terminal portion of the gelatin gel 23′ has shrunken to the diameter of the channel 24′ and adopted cylindrical form while the adjacent portion of the gelatin gel 23 is still tubiform. Upon full withdrawal an implantation channel 24 filled with gelatin gel 23′ has been formed (FIG. 1e). The amount of gelatin for forming channel 24 can be reduced when using a physically stabilized microelectrode comprising a matrix dissolvable or degradable in aqueous body fluid.

[0097] By using cross-linked gelatin or other cross-linked gel-forming agent, it is possible to retain upon withdrawal of the pin a channel in the tissue filled with aqueous body fluid. The channel is surrounded by a cylindrical wall of cross-linked gel. It is particular useful for insertion of a not physically stabilized microelectrode or other probe or sensor of the invention into soft tissue.

Example 4. Second Embodiment of the Apparatus According to the Invention Additionally Comprising Optical Fiber Means

[0098] A second embodiment 50 of the apparatus according to the invention is shown in FIG. 5. Its pin 51 of polyacrylate encloses a centered (axis A′-A′) optical fiber 55 extending from the front end 51′ of the pin in a proximal direction leaving the pin near the other end thereof so as to emerge in a skew angle from the cylinder wall of the pin. Alternatively the optical fiber may extend through the entire pin in a centered disposition and leave the pin at its proximal end. The side wall of the pin 51 is covered by a layer 51 of dry gelatin extending from the distal end 51′ to a position distally of where the optical fiber 55 emerges from the cylinder wall. The front end face of the pin 51 is not covered by gelatin. This allows radiation to emerge from the front end of the optical fiber 55 unimpeded and/or inspection of tissue disposed in front of the pin's 51 front end.

Example 5. Third Embodiment of the Apparatus According to the Invention, Additionally Comprising Optical Fiber and Electrode Means

[0099] A third embodiment 60 of the apparatus of the invention is shown in FIG. 6. It is a modification of the second embodiment in that it further comprises an electrode function. The electrode function is provided by a conductive layer 66 of gold on the pin 61, which encloses an optical fiber 65 disposed centrally and which shares its central axis with that (A″-A″) of the pin 61. Except for a short portion near its distal end the gold layer 66 is electrically insulated by a lacquer 67. The gold layer 66 is electrically connected with a control unit (not shown) by an insulated lead 68 attached to the gold layer 66 at the proximal end thereof. A layer 62 of dry gelatin covers insulated and non-insulated portions of the gold layer 66.

Example 6. Microelectrodes

[0100] A wide assortment of microelectrodes can be used in the invention. Their design does not pertain to the invention other than that they should be oblong and generally suitable for implantation by the method of the invention. FIG. 4 illustrates such a microelectrode 30 consisting of a waveform thin metal wire 31 having a free front (distal) end and attached at its other (rear, proximal) end to a coupling element 32; the coupling element is preferably disposed at considerably distance from the skull. To the coupling element 32 may, for instance, be in turn attached a thin insulated metallic lead 33 in conducting relation with the wire 31, which may also be electrically insulated except for at its front end, which acts as an active electrode tip. The physical stability of the microelectrode 30 is insufficient to allow its direct insertion into brain tissue 1 due to deflection from its intended path of insertion caused by its flexibility and non-homogenous neural tissue. Diameters of microelectrodes for use in the invention preferably are in the sub-mm range, in particular in the sub-200 μm range. Lengths of microelectrodes for use in the invention are not critical and can be up to 100 mm and more.

Example 7. Microelectrode Implantation

[0101] Implantation of a microelectrode 30 into brain tissue is shown in FIGS. 1g and 1h. The microelectrode 30 is initially positioned above the channel 24′ (identified in the Figures by its contour) with its free front end adjacent to the open end of the channel 24′, approximately aligned with the central axis B-B (FIG. 1e) of the channel 24′, then inserted (direction F) into the channel 24′ partially (FIG. 1g) and, finally fully (FIG. 1h). Due to the nature of the gel 23′ radial errors of microelectrode 4 insertion can be corrected during insertion or by partial withdrawal and re-insertion. Other devices such as optical fibers can be implanted by the same method.

Example 8. Implanted and Positionally Fixed Microelectrode

[0102] For long-term use an implanted microelectrode 30 or other device can be positionally fixed. The principle of such fixation is shown in FIG. 2. With its electrode body 31 disposed in a desired position the coupling element 3 is held by a clamping holder 41 of resiliently flexible polymer mounted at a through bore in a lock 40 cemented to the skull bone 2 at the opening 5 thereof. This arrangement protects the wound in the skull from infection. Other devices can be fixed in a corresponding manner.

Example 9. Assessment of Implant Interaction with Neighboring Neural Cells

[0103] To evaluate the effect of gelatin surrounding implanted electrodes in the tissue, we compared the histological reactions 6 weeks in rat brains after implantation to an implanted flat (approximately 7 um thick, 140 um wide and 2.5 mm long) testing device made of SU-8 which was either embedded with a thin (5-10 μm) layer of gelatin or not.

Surgical Procedure.

[0104] All animal-related procedures were conducted in accordance with local and international ethical guidelines, with the permission of the Lund and Malmö Ethical Board, diary numbers M258-11. All implantations (n implantations=16) were made in female Sprague-Dawley rats (no. of rats=8, Taconic, Denmark) weighing 200-250 g. The animals were anaesthetized using intra-peritoneal injections of fentanyl (0.3 mg/kg body weight) and Domitor vet (medetomidin hydrochloride, 0.3 mg/kg) and placed in a stereotactic frame for surgery. A rostrocaudal incision in the skin was placed along the central suture of the skull to expose Bregma. An opening of about 2 mm diameter was made 1.0 mm caudally of Bregma and 2.3 mm laterally if the midline. The Dura mater was cut open using a forceps and a syringe. To facilitate handling and implantation, the testing device was mounted on a stainless steel guiding wire (length about 3 mm, diameter 50 μm) using a sucrose solution as an adhesive and then implanted into the cortex to a depth of 2.0 mm using a micromanipulator. Implantation of gelatin embedded testing devices in one hemisphere and non-embedded testing devices in the other hemisphere was made into rat (n=8) cerebral cortex. After rinsing the surface of the cortex with physiological saline to dissolve sucrose, the guides were retracted and removed and the openings in the skull filled using FujiChem silastic, tethering the implant to the skull. Afterwards the wounds were closed using surgical staples. The animals received subcutaneous injections of an antidote to the anesthesia (Antisedan, atipamezole hydrochloride, 0.5 mg/kg b.w.) as well as Temgesic (buprenorphine, 50 μg/kg b.w.) to reduce postoperative pain.

[0105] After six weeks the animals were anaesthetized with an overdose of pentobarbital (i.p) and trans-cardially perfused with 150-200 ml ice-cold 0.1 M phosphate buffer (PB), followed by 4% paraformaldehyde (PFA) in 0.1 M PB. The brains were postfixed in 4% PFA overnight and then soaked in 30% sucrose for at least 24 hours for cryopreservation. They were then serially sectioned in the horizontal plane at 30 μm, using a cryostat (Microm HM560). Sections were kept in antifreeze in a free-floating manner.

[0106] Astrocyte proliferation, recruitment of microglial cells and neuronal cell bodies were evaluated using standard free-floating immunohistochemical techniques (Lind et al 2013). In brief, the brain sections were reacted with primary antibodies overnight at room temperature. The primary antibodies used were rabbit polyclonal antibodies recognizing Glial Fibrillary Acidic Protein (GFAP, an astrocytic cytoskeleton protein 1:5000, Dako, Denmark) and mouse monoclonal antibodies recognizing either CD68/ED1 (expressed by activated microglia/macrophages, 1:100, Serotec, USA) or NeuN (expressed on neuronal nuclei 1:100, Millipore, USA). After repeated rinses with PBS, the brain sections were further incubated with Alexa488-conjugated antibodies for mouse IgG and Alexa594-conjugated antibodies for rabbit IgG (1:500, Invitrogen, USA) (2 h, dark, RT) and rinsed with PBS.

[0107] A DS-Ri1 Digital camera (Nikon Instruments, Japan) mounted on a Nikon Eclipse 80i microscope with a 10× objective (Nikon Instruments, Japan) was used for histological fluorescence image analysis. The images were acquired and analyzed using the NIS-Elements BR software 3.2 (NIS-elements, Nikon Instruments, Japan). Different evaluation methods were used for the different stainings. Manual counts were performed for neuronal NeuN stainings while fluorescence intensity measurements were used for the glial markers GFAP and ED1 as described previously (Lind et al, 2013). The regions of interest (ROIs) were set at 0-50 μm (inner ROI) and 50-200 μm (outer ROI) from where the testing device had been placed. Brain sections disposed adjacent to a central portion of the testing device, corresponding to cortical lamina 4, were analyzed. To analyze neuronal cell survival, matched NeuN-positive cells were also counted in identical ROIs placed in naïve areas of the cortex and served as controls.

Wilcoxon matched-pairs signed rank test was used. P-values<0.05 were considered significant. Analyses were performed using the GraphPad Prism 5.02 software (GraphPad Software Inc., USA).

[0108] Significant astrocyte reactions as well as significant microglia responses were restricted to the inner ROIs of the implanted testing devices. Embedding testing devices in gelatin produced a statistically significant (p<0.05) reduction in microglial (ED1) density as compared to the non-embedded experimental group. In contrast no differences in respect of astrocyte density were observed between embedded and non-embedded testing devices. In all experimental groups the neuronal density in the inner and outer ROIs was compared with the neural density in naïve tissue. A significant (P<0.05) decrease of neuronal density was found around non embedded testing devices in comparison with the respective controls (naïve brain). In contrast neuronal density was not decreased in tissue surrounding gelatin embedded testing devices. No differences were observed in neuronal densities in any of the outer ROIs when compared to control. In conclusion, gelatin embedding significantly reduced the microglia responses to the implanted testing devices. Moreover, there was no tendency for a reduction in neuronal density adjacent to a gelatin embedded implant, while the number of neurons in the adjacent tissue in non-embedded implants is significantly reduced, indicating that gelatin embedding is neuroprotective.

Example 10. Fourth Embodiment of the Apparatus According to the Invention, Comprising Fluid Passage Means for Distal Injection of Fluid

[0109] A fourth embodiment 70 of the apparatus of the invention having a proximal end 70″, a distal end 70′ and a lateral cylindrical face 78 is shown in FIGS. 7 and 7a. It is a modification of the third embodiment in that it further comprises fluid passage means in form of a centered (axis A′-A′) axially extending channel 75 in the pin 71. The substantially cylindrical channel 75 is formed by a flexible tube 73 disposed in an axial bore of the pin 71, the inner wall of the tube 73 being covered by a thin layer 74 of a metal of high conductivity, such as silver or gold. The layer 74 can serve as an electrode but can also be omitted. The flexible tube 73 is preferably of a transparent polymer material such as acrylate, and thus capable of conducting light and functioning as an optical fiber. At a short distance from the proximal end 70″ of the apparatus 70 the flexible tube 73 is bent away from the central axis A′-A′ so as to emerge from the lateral face 78 of the pin 71. A layer 72 of dry gelatin covers a portion of the lateral face 78 of the pin 71 extending from the frontal end 70′ towards near the distal end 70″ but does not cover the distal front face 77 of the pin 71 and thus not the distal opening of the channel 75.

[0110] The channel 75 can be used for injection of fluid material emerging at the distal end thereof. The fluid material can be, for instance, an aqueous solution of a pharmacologically active agent such as a neurotransmitter, for instance dopamine or acetylcholine or histamine. The axial channel 75 can also be used for sucking up fluid material, in particular during withdrawal of the pin 71 from tissue. The fluid material may also contain a nutrient such as glucose and be oxygenated to reduce local hypoglycemia and ischemia upon implantation.

Example 11. Fifth Embodiment of the Apparatus According to the Invention Comprising Fluid Passage Means for Lateral Injection of Fluid

[0111] A fifth embodiment 80 of the apparatus of the invention having a proximal end 80″, a distal end 80′ and a lateral cylindrical face 78 is shown in FIGS. 8, 8a, 8b. It is a modification of the fourth embodiment and comprises fluid passage means in form of a centrally disposed axially (axis A**-A**) extending channel 85 in the pin 81. The substantially cylindrical channel 85 is formed by a flexible tube 83 disposed in an axial bore of the pin 81, the inner wall of the tube 83 being covered by a thin layer 84 of a metal of high conductivity, such as silver or gold. The layer 84 can serve as an electrode but can also be omitted. The flexible tube 83 is preferably of a transparent polymer material such as acrylate, and thus capable of conducting light and functioning as an optical fiber. At a short distance from the proximal end 80″ of the apparatus 80 the flexible tube 83 is bent away from the central axis A**-A** so as to emerge at the lateral face 88 of the pin 81. A layer 82 of dry gelatin of a water content of about 2% by weight covers the pin 81 extending from the proximal end 80′ towards the distal end 80″ but does not cover the distal front face 87 of the pin 81 comprising the distal opening of the flexible tube 83. Radially extending channels 86 are branching out from axial channel 85. They can be used for injection of fluid material emerging at the lateral face thereof upon transformation of the dry gelatin layer 82 to an aqueous gel. The fluid material can be, for instance, an aqueous solution of an agent accelerating the transformation of the dry gelatin layer 82 to an aqueous gel but may also or additionally comprise a pharmacologically active agent such as a neurotransmitter, for instance dopamine or acetylcholine or histamine.

[0112] The lateral channels 86 can also be used for sucking up fluid material, in particular during withdrawal of the pin 81 from tissue. The axially disposed channel 85 may be open or plugged at its distal end, the plug (not shown) consisting of a permanent material or one which is dissolved or degraded over time, such as cross-linked gelatin. Varieties of the fifth embodiment lacking the metal layer 84 are also comprised by the invention as are varieties lacking the flexible tube 83 or a portion thereof extending from the distal end 80′ in a proximal direction; in such case the flexible tube 83 is substituted by a metal tube of high conductivity. The radially extending channels 86, such as four channels 86 disposed in a radial plane (FIG. 8b), extend from the axially disposed channel 85 through the flexible tube 83 and metal layer 84 walls but not through the dry gelatin layer 82. Peripheral terminal portions of the radially extending channels 86 may be plugged by plugs 87 (FIG. 8c) of a material dissolvable in an aqueous fluid; their provision facilitates covering the pin 81 with gelatin to form the dry gelatin layer 82 so as to avoid clogging the radially extending channels 86.

Example 12. First Modification of the Fifth Embodiment of the Apparatus According to the Invention Comprising a Friction Reducing Layer

[0113] The embodiment 90 of the apparatus of the invention shown in FIGS. 9, 9a, 9b, 9c corresponds to the embodiment 80 of FIGS. 8, 8a, 8b, 8c except for that it comprises a friction reducing layer 89 on the dry gelatin layer 82′ of same axial extension. Reference numbers 81′ and 83′ through 88′ designate features of same kind as features 81 and 83 through 88 of the embodiment of FIGS. 8, 8a, 8b, 8c. Central axis A+−A+corresponds to central axis A**-A** of FIG. 8. Reference numbers 90′ and 90″ designate the distal and proximal ends, respectively, of pin 81′. Section B+−B+corresponds to section B-B of FIG. 8a.

Example 13. Second Modification of the Fifth Embodiment of the Apparatus According to the Invention Comprising a Friction Reducing Layer

[0114] The embodiment 91 of the apparatus of the invention shown in FIG. 10 corresponds to the embodiment 80 of FIGS. 8, 8a, 8b, except for that it comprises two adjacent layers 92, 93 on the dry gelatin layer 82″ of same axial extension as the total extension of layers 92, 93. The proximally disposed layer 92 comprises a coagulant preventing bleeding from the channel formed by insertion of the apparatus 91 into nervous tissue, whereas the distally disposed layer 93 is a friction reducing layer to minimize tissue damage during insertion of the pin 81″. Reference numbers 82″, 86″ and 88″ designate features of same kind as features 82, 86 and 88 of the embodiment of FIGS. 8, 8a, 8b. Central axis A++−A++corresponds to central axis A**-A** of FIG. 8. Reference numbers 91′ and 91″ designate the distal and proximal ends, respectively, of pin 81″.

Example 14. Embodiments of the Apparatus of the Invention of which the Pin is Covered with One or More Layers of Gel Forming Agent

[0115] FIGS. 11, 11a, 11b, 11c illustrate, in a principal manner, an apparatus 100, 100a, 100b, 100c of the invention of which the cylindrical face of the pin 101, except for a portion extending for a short distance from the proximal end, is covered by of one or more layers of gel forming agent in varying disposition. In the embodiment 100 of FIG. 11 the pin 101 is covered by one layer 102 of gel forming agent. In the embodiment 100a of FIG. 11a, the pin 101 is covered by an inner layer 102 of gel forming agent covered by an outer layer 103 of gel forming agent. In the embodiment 100b of FIG. 11b the pin 101 is covered by a first layer 104 extending from the distal end thereof about halfway towards the proximal end, and by a second layer 102 abutting the proximal end of the first layer 104 and extending from there to near the proximal end of the pin 101. In the embodiment 100c of FIG. 11c, the pin 101 is covered by two inner layers 102, 104 disposed in the same manner as the layers of the embodiment of FIG. 11b, the inner layers 102, 104 being covered in turn by an outer layer 103.

Example 15. Embodiments of the Channel in Nervous Tissue of Invention Filled with One or More Layers of Aqueous Gel

[0116] FIGS. 12, 12a, 12b, 12c illustrate, in a principal manner, a channel in nervous tissue 105 of the invention filled with one or more layers of aqueous gel 102*, 103*, 104* formed from a corresponding layer of dry gel forming agent 102, 103, 104 on the pin 101 of the apparatus 100, 100a, 100b, 100c of the invention illustrated in FIGS. 11, 11a, 11b, 11c, respectively, by contact with aqueous body fluid exuded from nervous tissue 105. The channel of FIG. 12 is homogeneously filled with aqueous gel 102*. The channel of FIG. 12a is filled with a central gel cylinder 102* surrounded by a tubiform gel cylinder 103* abutting the cylindrical tissue wall of the channel. A section extending from the bottom of the cylindrical channel of FIG. 12b to about half its height is filled with a first aqueous gel 104*, the remaining upper portion of the channel being filled with a second aqueous gel 102*. A central cylindrical portion of the channel of FIG. 12c is filled with first 104* and second 102* aqueous gel in the same disposition as in FIG. 12b, and is surrounded by a tubiform layer 103* of aqueous gel extending over the combined height of layers 102*, 104*. By adapting the properties of a gel forming agent an aqueous gel of, for instance, desired viscosity or resistance to biological degradation, can be designed. It is also possible to incorporate non-gelling agents, such as pharmacologically active agent and nutrients in a dry gel forming layer to produce a corresponding aqueous gel comprising the non-gelling agent(s).