Neurosurgery Equipment

Abstract

A neurosurgical device for convection-enhanced delivery of infusate onto the brain parenchyma includes a guide tube for insertion into the brain, the guide tube having a proximal end, a distal end, and a through-hole for passage of a cannula. At least an outer layer (24) of the guide tube is formed of a hydrophobic material that is elastically deformable and porous to allow air to pass through. Also provided are a kit for convection-enhanced delivery of infusate onto the brain parenchyma and a surgical method for convection-enhanced delivery of infusate onto the brain parenchyma.

Description

[Technical field]

[0001] The present invention relates to devices for use in neurosurgery, in particular to devices used to deliver therapeutic agents by direct injection into the brain parenchyma. [Background technology]

[0002] Treatment of neurological disorders can be hindered by the presence of the blood-brain barrier. It is difficult to develop therapeutic agents that can be delivered from the systemic circulation into the brain parenchyma. It may be desirable to deliver therapeutic agents to specific regions of the brain ("brain volumes" or "target volumes"). To reduce undesirable side effects, it is desirable to obtain adequate concentrations of therapeutic agents within the target volume while minimizing exposure of the therapeutic agent outside of the specific region of the brain.

[0003] Convection-enhanced delivery (CED) is a method of targeted delivery of therapeutic agents to specific brain volumes using very small cannulas or tubes (often referred to in the art as microcatheters) for controlled infusion of therapeutic agents delivered into the brain parenchyma in fluid. The microcatheter has one or more ports at its tip that allow infusate containing the therapeutic agent to exit the catheter and enter the target brain volume. The achievement of a continuous pressure gradient at the ports overcomes the ambient pressure of the target brain volume and allows the infusate to flow effectively into the target brain volume.

[0004] There are challenges with the use of CED techniques because fluids flowing from the cannula ports follow the path of least resistance. Typically, the path of least resistance causes the fluid to flow back along the cannula-tissue interface rather than into the tissue as desired, a process known as backflow. To control backflow and ensure that the fluid is delivered into the target volume of tissue, CED cannulas typically have an abrupt change in diameter (a "step") toward the tip. For example, the tip of the cannula may be less than 1 mm in diameter for a short length at the tip, and the diameter increases stepwise to 1.5-2.5 mm for the remainder of the cannula. The small diameter tip forms a tissue seal around the cannula when inserted atraumatically, minimizing backflow along the interface. The change in diameter at the step compresses the tissue upon insertion into the brain, further preventing backflow.

[0005] Carefully controlled flow rates, typically in the range of 3-5 microliters per minute, promote flow of infusate into the tissue rather than backflow. Higher flow rates tend to increase the degree of backflow, and even in the wider diameter portion of the cannula, backflow infusate may cross a step and backflow along the cannula-brain tissue interface. Once over the step, the infusate enters a lower resistance path through the larger peripheral space around the larger diameter portion of the cannula, thereby reducing the intended distribution of infusate within the target volume.

[0006] The design of the anti-reflux step varies from CED cannula to CED cannula: EP 1 482 851 and US 2010 / 0217228 have a single step, WO 2007024841 discloses a cannula with multiple steps, and WO 2014-016591 has a recessed step.

[0007] In addition to the design of the step, the length the cannula extends beyond the step to its tip is also an important determinant of both the amount and shape of the infusate distributed to the brain tissue. Short stepped cannulas (i.e., short length, small diameter cannulas) have a small volume of distribution (Vd) that is roughly spherical. As the length of the small diameter segment increases, Vd becomes larger, more ovoid, and cylindrical, and pear-shaped with a bulbous tip.

[0008] When the radius of fluid convection into the brain exceeds that of the area of ​​tissue compressed by the step, the infusate will tend to follow the low resistance path along the larger diameter of the cannula and back out of the target volume, limiting Vd at the target.

[0009] Therefore, delivering therapy to clinically important tissue volumes using fixed step length configurations can be problematic. Using cannulas with short fixed step lengths requires sequential injections at different points along the trajectory into the brain to fill elongated tissue volumes. Similarly, multiple passes are required to fill larger, more spherical structures in the brain. Conversely, using catheters with relatively long step lengths to fill smaller targets can make it difficult to contain the therapeutic agent within the target. Therefore, being able to tailor the step length for each target provides a significant advantage.

[0010] The majority of CNS (central nervous system) disease treatment targets by CED require the implantation of several cannulas to reach the desired extent of the infusion fluid into the brain tissue. When the volume and shape of the desired target are clearly defined from MRI images, the number and orientation of cannulas required to fill that volume are determined by knowing the distribution shape and volume achievable with the placed cannulas. It is also important to confirm that the injected therapeutic fluid covers the prescribed therapeutic volume using MRI images during or immediately after injection. When using rigid cannulas, the cannulas are fixed in a stereotactic frame while the injection is being performed. In such an arrangement, the stereotactic frame needs to be MRI compatible and low-profile to fit the imaging coil. Usually, the insertion and injection of additional cannulas is required after the initial work is completed. Therefore, such procedures are relatively time-consuming and may endanger the patient by prolonged anesthesia and immobilization.

[0011] An alternative procedure using multiple cannula trajectories uses flexible cannulas that are embedded and fixed in the skull. The flexible cannula tubes that extend outside the skull can be attached to a low-profile skull fixation device. This facilitates safe transport to the MRI scanner and allows simultaneous injections to be performed with the patient awake for neurological evaluation. If flexible cannulas are used, a stereotactic frame is not required during injection. The flexible cannulas can be removed after the injection is completed or, in some cases, left in place for repeat injections days, weeks, or months later.

[0012] The use of flexible cannulas is described in EP 1482851, EP 13001067.1, EP 2819739 and WO 2014-016591. In these arrangements, the distance between the tip of the cannula and the reflux resistance step can be adjusted. In each case, the flexible cannula has a proximal hub and is cut to a desired length for insertion into the target point in the brain. Similarly cut to a desired length and inserted into an implanted guide tube, the hub of the cannula acts as a stop when it engages with the proximal head of the guide tube fixed to the skull. The cannula extends beyond the guide tube, and the step caused by the change in diameter from the cannula to the guide tube provides resistance to the reflux of the infusate.

[0013] In a typical procedure for implanting a flexible cannula, as described in EP 1482851, EP 13001067.1 and EP 2819739, a profile hole is formed in the skull along a selected trajectory, either by stereoguiding or by image-guided robotic guidance. A probe is then passed through the hole to the intended tip of the guide tube and withdrawn, leaving a trace in the brain tissue. A guide tube, cut to the appropriate length, is placed on the delivery probe so that the rounded tip of the probe extends slightly beyond its tip. The guide tube is inserted into the preformed trajectory until its proximal head fits into the hole formed in the skull. The probe is advanced to the intended location of the cannula target and then withdrawn, leaving a trajectory through the tissue adjacent to the guide tube hole.

[0014] A cannula, connected to an infusion pump and delivering infusate at a low flow rate, is inserted into the guide tube through a preformed trajectory in the tissue. The slow infusion rate through the cannula prevents perforation of the tissue during its passage. As the therapeutic fluid is delivered through the distal port of the cannula, it follows the path of least resistance and flows back along the cannula-tissue interface before reaching the tissue region compressed by the tip of the guide tube. Localized pressure at the interface acts to inhibit backflow, and the infusate is preferentially forced radially into the tissue.

[0015] The above-mentioned devices have potential drawbacks. The insertion method can cause microtrauma to the tissue, creating a low resistance path for the injectate and compromising reflux control at the guide tube-tissue interface. When the guide tube is inserted into a preformed trajectory in the brain, its distal cut end tends to shear the tissue and form a circumferential column of fragmented tissue. The force required to push the head of the guide tube into the preformed hole in the skull is also transferred to the tip of the guide tube, potentially increasing local tissue trauma in the area of ​​the step.

[0016] Furthermore, when the cannula is inserted into the guide tube, it acts as a piston and tends to push a column of air forward of the cannula. It is difficult to expel air from the narrow space between the cannula and the guide tube, even when suction is applied at the proximal end of the guide tube. As air is forced into the brain, it tears tissue and forms a space-occupying lesion adjacent to the reflux control step.

[0017] In the short term, this may disrupt the intended distribution pattern of the injectate, but as air is absorbed, the void left behind may form a low resistance path at the step, increasing undesirable reflux.

[0018] European Patent No. 3119310 describes a guide tube with an internal contour that creates a fluid return path for conveying fluid expelled from within the guide tube during catheter insertion. Such a path may also conduct or vent air during catheter insertion. However, creating a contour with an internal path of sufficient size to facilitate air evacuation increases the overall dimensions of the guide tube. A larger diameter guide tube may cause greater trauma during insertion. A narrow path between the guide tube and the cannula may be prone to air flow obstruction due to surface tension forces in the presence of fluid.

[0019] WO 2014 / 016591 discloses a concave step arrangement in which the guide tube has an internal recess that compresses the tissue inside. The internal recess has a step function intended to more effectively compress the tissue and limit the flow of infusate along the cannula-tissue interface. However, in such an arrangement, the guide tube scrapes off some of the brain tissue upon insertion. Localized tissue trauma can cause neurological damage or hemorrhage in eloquent parts of the brain.

[0020] A further potential problem with known CED devices, particularly those that are chronically implanted, is brain movement. Because the brain moves within the skull, fixation of the cannula and / or associated guide tube to the skull can result in movement of the tube or cannula relative to the brain tissue. This can cause localized tissue trauma, especially at reflux resistance steps, creating localized vacuolization and low resistance pathways that tend to increase reflux rather than resist it. Summary of the Invention [Problem to be solved by the invention]

[0021] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to overcome at least some of the problems mentioned above, and in particular to provide a CED device which has improved reflux resistance and reduced trauma during use. [Means for solving the problem]

[0022] According to a first aspect, the present invention provides a neurosurgical device for convection-enhanced delivery of infusate to brain parenchyma, the neurosurgical device comprising a guide tube for insertion into the brain, the guide tube having a proximal end, a distal end and a throughbore for passage of a cannula, at least an outer layer of the guide tube being a hydrophobic material that is elastically deformable and porous, allowing the passage of air.

[0023] According to a second aspect, the present invention provides a guide tube for use in the neurosurgical apparatus according to the first aspect. The guide tube is for insertion into the brain and has a proximal end, a distal end and a through hole for the passage of a cannula. At least an outer layer of the guide tube is a hydrophobic material that is elastically deformable and porous, allowing the passage of air.

[0024] By hydrophobicity is meant that the static contact angle θ at the liquid-vapor interface of a water droplet on the surface of the material used to form the guide tube is greater than 90°. Advantageously, at least the outer layer of the material of the guide tube disclosed herein is superhydrophobic, with θ>150°.

[0025] The use of neurosurgical devices, and in particular the guide tube of the present invention, will be described in detail with reference to a method for convection-enhanced delivery of infusate to the brain, however the guide tube can be used in any surgical procedure in which delivery of small instruments or tools to the brain (e.g., cannulas, in particular "microcatheters") is envisaged.

[0026] The porous and hydrophobic or superhydrophobic outer layer of the guide tube provides a venting path for air, as described in more detail below. The hydrophobic or superhydrophobic nature allows for the separation of air bubbles from the cerebrospinal fluid (CSF) and the patient's extracellular fluid or aqueous infusate at the interface with the material of the outer layer. Aqueous fluids are effectively repelled from the hydrophobic outer layer which prevents wetting of the material of the guide tube. This increases the effectiveness of the guide tube in repelling fluid from the interface of the guide tube and tissue and limiting reflux, as well as maintaining porosity to air. The use of a porous material to pass air also eliminates the need for special channels or similar structures in the wall of the guide tube to vent air, as used in some of the prior devices mentioned above. This allows the cross-sectional area of ​​the guide tube to be significantly reduced by 50% or more compared to some prior devices. This significantly reduces the trauma to the brain tissue and the possibility of undesirable complications.

[0027] At least the outer layer of the guide tube is elastically deformable. When the guide tube is in use, it can be fitted around the probe of the guide tube which passes through its through hole and inserted into a pre-made track in the brain. The pre-made track has a narrower diameter than the guide tube. The elastically deformable material has an advantage. The leading end of the guide tube, generally a square cut end, tends to deform into or towards a bullet shape. The bullet shape allows it to pass through the pre-made track more easily than conventional devices, where the square cut tube end tends to cause trauma by cutting brain tissue.

[0028] If the bullet-shaped leading edge is not inserted, it will tend to return to or towards its original configuration (e.g., a square cut). This leading edge can act as a physical barrier to reflux in a known manner. However, the effectiveness against reflux is enhanced by the use of a hydrophobic material and the resilience provided by the elastically deformable material.

[0029] When inserted into brain tissue, the guide tube is compressed radially inward from the brain tissue along its length as it passes through the track. Thus, when in place, the guide tube tends to expand radially outward toward its original diameter and press against the brain tissue, thereby providing a good sealing interface with the brain tissue. The guide tube acts within the brain to prevent backflow along its length, as will be described in more detail below.

[0030] To prevent undesired trauma to the brain tissue, the compression exerted on the brain tissue by the implantation of the guide tube should not be significantly greater than the generally expected elastic limit of the brain tissue. This can be achieved by appropriate selection of materials and diameters for the prefabricated tracks and guide tubes. The Young's modulus of elasticity of suitable materials can be, for example, in the range of 10 kPa to 1 MPa.

[0031] Suitable materials for at least the outer layer of the guide tube include ePTFE, silicone foam, polyurethane foam, shape memory polymers, polymers extruded as microporous hollow fibers or electrospun polymers. Electrospun polymers and polymers extruded as microporous hollow fibers include, but are not limited to, PTFE (polytetrafluoroethylene), PVDF (polyvinylidene fluoride), PU (polyurethane), polypropylene, or mixtures and / or copolymers thereof. Shape memory polymers can be used. When foams are used, at least some of the cells of the foam are open-celled, allowing the passage of air through the bulk material. All or substantially all of the outer layer of the foam structure or guide tube can be open-cell foam.

[0032] A further advantage of using a porous material for at least the outer layer of the guide tube is that there is an opportunity for integration with brain tissue over time, i.e., brain tissue can enter the porous structure of the guide tube. This can help secure the guide tube in a desired position even as the compressive force between the brain tissue and the guide tube decreases over time. Integration of the guide tube and brain tissue can eliminate a sharply defined cannula-tissue interface, thereby reducing the possibility of reflux.

[0033] At least the outer layer of the guide tube may be formed of a material that has been post-treated to improve its integration capabilities or other desirable properties. For example, the outer layer may include a coating and / or surface treatment configured to enhance lubricity and / or promote tissue integration. The surface treatment may include a plasma surface treatment. The coating may enhance its lubricity or increase its hydrophobicity. The coating may include a hydrophilic material.

[0034] The guide tube may further comprise an outermost layer axially outside the outer layer, the outermost layer comprising a hydrophilic material. The outermost layer of hydrophilic material may contribute to improving the lubricity of the guide tube. The outermost layer may comprise a mixture of hydrophilic and hydrophobic materials. Different cell types in the brain integrate more easily with hydrophobic or hydrophilic materials. For example, neural cells bind more easily to hydrophobic materials, while glial cells bind more easily to hydrophilic materials. An outermost layer comprising a mixture of these materials may improve tissue integration with multiple cell types.

[0035] At least the outer layer of the guide tube is elastically deformable to minimize trauma during insertion into brain tissue. If the guide tube is not sufficiently rigid, it may be distorted, particularly at a short length, when inserted into brain tissue, even with the aid of the guide tube's probe in the through-hole. Brain tissue is a relatively compliant (deformable) material. A guide tube made only of a material approaching the compliance of brain tissue would be difficult to insert well.

[0036] Thus, the guide tube can be constructed of non-homogeneous materials and / or materials with different properties to provide the desired combination of axial stiffness and radial compliance (elastically deformable behavior).

[0037] Where the guide tube is constructed of non-homogeneous materials and / or materials having different properties (particularly stiffness), the degree of stiffness provided may be along the entire length or substantially the entire length of the guide tube. In some embodiments of the invention, stiffness may vary along the length of the guide tube. For example, reduced stiffness or no additional stiffness may be provided at the proximal end of the guide tube, as described further below.

[0038] For example, the guide tube may be constructed of foam with increasing density radially inward from the outside towards the through-hole, or a region of increased density at or near the through-hole. The increased density provides increased stiffness and therefore support for the more compliant outer region.

[0039] Alternatively or additionally, the guide tube may have a laminated structure with a stiffer monolayer or multilayer at or near the through-hole, which provides support for the softer outer monolayer or multilayer. If the guide tube is laminated with a stiff monolayer or multilayer at or near the through-hole, the stiff monolayer or multilayer is preferably porous for the passage of air. This allows air appearing in the through-hole to pass through the porous material of the guide tube. If the stiff inner layer is not porous, air passing through the through-hole may be removed from the tip of the guide tube when it contacts the leading edge of the porous outer layer. The stiff monolayer or multilayer may be a hydrophobic or superhydrophobic material to help avoid liquid penetration through the guide tube structure. However, one or more layers may not have hydrophobic or superhydrophobic properties.

[0040] Thus, the inner layer, for example the layer providing the surface of the through holes, may be formed of a rigid material. An example of such a rigid material may be a polymer inner layer such as polyetheretherketone (PEEK) or copolymers thereof. More generally, the inner layer may be selected from the group consisting of polyetheretherketone (PEEK), nylon, polyurethane, polyester, fluoropolymers such as polytetrafluoroethylene (PTFE), perfluoroether polymers such as polyperfluoroalkoxyalkane (PFA), polyvinylidene fluoride (PVDF) and fluorinated ethylene propylene (FEP), liquid crystal polymers (LCP), and mixtures or copolymers thereof. The polymer layer may be a naturally non-porous material, but may be made porous in a variety of ways. For example, the inner layer is formed by micro-drilling the polymer material with a drill or laser. In a further example, a tube of porous polymeric sheet material is formed by weaving, braiding, or electrospinning polymer fibers around a cylindrical form. 3D printing may also be used to form the porous structure.

[0041] For example, an outer layer of ePTFE may be bonded to a relatively stiff inner layer formed as part of a (micro-perforated) PEEK tube. Bonding the relatively stiff inner layer to the outer layer may be accomplished by, for example, coating the inner layer with an adhesive prior to attaching the outer layer. Advantageously, the outer layer may be stretched over the inner layer prior to bonding. When such a tube is cut across its diameter, the stretched outer layer tends to contract at the cut end. This results in a "bullet shape" that can be used as a tip for insertion into the brain and has a relatively atraumatic tip shape.

[0042] In order to minimize trauma to the brain as much as possible, the guide tube should be as small as practical in outer diameter, at least when compressed and in place in the brain tissue. For example, the guide tube may have an outer diameter of 0.75 mm to 2.5 mm, preferably 1.2 mm to 1.7 mm. Thus, for example, the guide tube may have a diameter of 1.2 mm before compression for insertion into the brain, and a diameter of about 1 mm when inside.

[0043] In order to use cannulas (microcatheters) of the type used to deliver infusates into brain tissue in convection-enhanced delivery techniques, the through-hole of the guide tube may have a diameter of 0.4 mm to 0.7 mm, preferably 0.5 mm to 0.6 mm. Advantageously, the through-hole of the guide tube is sized to closely fit the outer surface of the cannula used. This close fit avoids the formation of a path for the infusate to return to the outside of the brain. The cannula itself may have a diameter of 0.5 mm to 0.6 mm, and the through-hole may have a diameter of 0.1 mm to 0.4 mm.

[0044] In use, the guide tube has a distal end that does not enter the brain but is fixed to or near the patient's skull to fix the position of the tube in the brain. Thus, the guide tube of the present invention can be enlarged at a proximal end that is sized and shaped for fixing in the thoracic bore of the skull, similar to conventional configurations. Typically, the enlarged proximal end is formed of a different material than the elastically deformable outer layer of the guide tube. The two portions of different materials can be integrally bonded, for example, by melting or gluing.

[0045] Advantageously, the guide tube can be inserted through a coronal hole in the skull already attached to a guide hub. A separate guide hub forms part of the neurosurgical device of the first aspect of the invention and is a third aspect of the invention. The guide hub has a passageway through which the guide tube passes. The guide hub can be secured to the skull in a separate procedure and the guide tube is then inserted through the passageway.

[0046] The guide hub provides a fixed reference point on the skull from which the probe, guide tube and cannula can be oriented and oriented. If a separate guide hub is used, the guide tube may have an enlarged proximal end for fixing in the guide hub in use. The enlarged proximal end of the guide tube can be placed in a correspondingly shaped seat in the passage of the guide hub. The enlarged proximal end may be, for example, cylindrical, partially spherical or conical ("flared"). The guide tube proximal end may then be fixed to the guide hub by a fitting, for example, a screw with a through hole, which is fastened to the enlarged proximal end of the guide tube and compresses on a correspondingly shaped seat in the guide hub. The enlarged proximal end may be made of a material different from that of the rest of the guide tube. For example, the enlarged diameter of the proximal end may be formed by an overmolding process in which a different polymer is applied to the end of the guide tube.

[0047] Advantageously, the flared proximal end of the guide tube can be compressed to form a fluid and gas seal between the guide tube and the hub and between the guide tube and the threaded joint. A deformable washer, such as a silicone washer, can be placed between the tip of the threaded joint with a central bore and the flared proximal end of the guide tube to radially compress and fix the cannula passing through the bore of the threaded joint and the guide tube relative to the hub. When compressed, the cannula, like a washer, can form a fluid and gas seal between the cannula and the guide tube. If the cannula has a proximal screw set with male threads, a fluid and gas seal can be formed between the cannula and the guide tube. The proximal screw set is threaded into a hub with a complementary female thread in the bore and forms a conical seal between the cone of the tip of the screw set, which is coaxial with the cannula, which engages in the bore of the flared proximal end of the guide tube.

[0048] The flared proximal end of the guide tube can also be compressed to form a fluid and gas seal between the guide tube and the hub, and between the guide tube and the cannula / screw joint attached by the elastically deformable outer layer of the guide tube. The flared proximal end of the guide tube can be made of a different material than the elastically deformable outer layer of the guide tube, but the outer layer can extend over and cover the flared proximal end. This can be accomplished, for example, when using an electrospun outer layer, by extending the area where the outer layer is electrospun. This avoids the need for one or more separate washers, which increases the complexity of the assembly and the size of the seal. The outer layer can extend over the flared proximal end of the guide tube. The guide tube can be configured such that the outer layer around the flared proximal end is compressed against the inner surface of the guide hub to secure the guide tube to the guide hub.

[0049] Convection-enhanced delivery techniques can be used for both acute (short-term) and chronic (long-term or repeated) delivery of therapy to brain tissue. For example, gene therapy is performed in a single treatment session, whereas therapy for other reasons, such as chemotherapy, may require repeated injections into the brain (chronic treatment regimes). In either case, it is highly desirable for the tip of the guide tube to remain located within the brain tissue, especially when a chronic treatment regime is employed. The tip of the guide tube is generally located at the proximal end of the cannula trajectory and serves to traverse the target volume and retain the injectate within the target by resisting reflux at the step formed between the diameters of the guide tube and the cannula. Fixing the proximal end of the guide tube to the skull or a guide hub fixed to the skull provides a relatively safe arrangement. However, the brain is movable relative to the skull. Thus, in use, the guide tube is subjected to axial or lateral forces as the brain moves. Such forces may cause the tip of the guide tube to repeatedly damage brain tissue. This can cause tissue to become vacuolated and create pathways of low resistance at the step that enhance rather than resist perfusion, resulting in loss of therapy from the target.

[0050] Advantageously, the guide tube is axially elastically stretchable and compressible, at least at the proximal end. Most advantageously, the material forming the base of the guide tube has a Poisson's ratio that is near zero or negative when stretched or compressed axially. Tubes made of ePTFE or polyurethane foam, for example, can exhibit this property, i.e., their wall thickness does not change substantially when compressed or stretched (under small strains). More generally, many polymer foams have a Poisson's ratio that is near zero because air tends to escape when the bubbles are compressed.

[0051] For example, the proximal end is located outside the brain in use. Such proximal end may extend from outside the brain to or toward the most proximal end of the guide tube. The guide tube is elastically expandable and compressible at its base, allowing it to expand and contract in response to changes in the distance between the brain and the proximal end of the guide tube that is fixed at the skull.

[0052] If the guide tube comprises a laminated structure with a stiff layer or layers at or near the through hole, stiffening may be reduced or absent at the proximal end. For example, the guide tube may have an inner tube of a stiff material (e.g., perforated PEEK) covered with an outer layer of a porous, elastically deformable material (e.g., electrospun PTFE or polyurethane). The inner tube may have an overmolding at its proximal end to form a flare or stop to limit insertion depth and facilitate fixation of the guide hub in the skull.

[0053] The base of the guide tube may be configured to be axially deformable. This can be achieved with the deformable portion of the inner tube configured to be axially deformable, for example by forming a helical cutout through the wall of the inner tube along the long axis to form it as a spring. The deformable portion of the inner tube can have a length of 5 to 30 mm, preferably 10 to 20 mm. By fixing the proximal end of the guide tube relative to the skull, for example by fixing within a guide hub, the deformable portion of the inner layer of the guide tube can accommodate movements of the brain relative to the skull. Meanwhile, the tip of the guide tube can remain fixed in position within the brain.

[0054] The outer layer of the guide tube is made of a more elastically deformable material and can be configured to accommodate the desired range of movement over this section. For example, the outer layer can be electrospun low-duty polyurethane to enhance axial compliance. This polyurethane has a high percentage of transversely oriented fibers. The outer layer can be poorly or non-adherent to the deformable portion of the inner layer of the guide tube to enhance compliance of the deformable portion of the guide tube. For example, electrospun polyurethane has poor adhesion to the smooth surface of PEEK, which can be overcome by immersing the PEEK in a polyurethane solution. When the inner tube of PEEK and this overmold are immersed in a polyurethane solution except for the deformable portion, the outer layer will have little or no adhesion to the deformable portion of the inner layer.

[0055] When a guide tube having the above-mentioned deformable portion is delivered into the brain via the guide tube probe, the axial force applied to the guide tube can compress the deformable portion so that the cylindrical strength of the guide tube is sufficient to deliver to the desired target. When the guide tube probe is removed and replaced with a cannula in situ, the tip of the guide tube remains fixed in position within the brain target, even though the cannula may move relatively. Relative movement of the cannula may increase reflux around the cannula. However, reflux will be limited to the target volume because the step formed by the guide tube tip, which is the primary control of reflux, is relatively fixed at the brain target.

[0056] An alternative to constructing a guide tube with a deformable base is to provide an inner tube that extends from the distal end of the guide tube but not to the proximal end. The base of the guide tube extends from the proximal end of the guide tube to the beginning of the inner tube, even without the inner tube. If the guide tube has an enlarged proximal end, the portion of the guide tube without the inner tube can extend from the distal end of the enlarged proximal end to the beginning of the inner tube. Thus, the enlarged proximal end still includes the inner tube. The base can be sized to extend from the patient's skull to or toward the outer layer of the brain in use. The base can be lengthened or shortened to allow the tip of the guide tube to remain in place within the brain tissue, since the relatively rigid inner tube is no longer present at the base.

[0057] In use, the guide tube is inserted into the brain when attached to a guide tube probe that passes through the through hole. To allow the guide tube probe to drive the guide tube, the guide tube probe can be shaped to engage the proximal end of the guide tube, for example, by forming a "step" of increasing diameter at the outer surface of the guide tube probe that engages the most proximal end of the guide tube. The guide tube can be attached to the guide tube probe using a friction fit. The guide tube probe can be configured such that when the guide tube is secured to the guide hub, the friction between the guide tube probe and the guide tube is less than the friction between the guide tube and the guide hub. This allows the guide tube probe to be easily withdrawn from the guide tube through hole once the guide tube is inserted into the intended location and secured to the guide hub.

[0058] As described above, when the guide tube has a base without an inner tube, the guide tube probe employed may have two steps. One engages the top of the inner tube to apply an insertion force, and the other engages and positions the very end of the base, generally compressing the base only slightly, for example, by 1 to 3 mm when the base has a length of about 1 to 1.5 cm. By applying a slight load to the base by compression during insertion, it can be easily lengthened when the distance from the skull to the brain is long.

[0059] As mentioned above, it may be necessary to cut the guide tube to a desired length before implanting it in the brain. The elastically deformable outer layer may make cutting the guide tube more difficult due to the tendency of the outer surface of the guide tube to deform when a cutting force is applied. To address this, the guide tube may be provided as part of a package. The package may include a guide tube and a wrapping tube, where the guide tube is provided within the wrapping tube. The wrapping tube may have a stiffness greater than the stiffness of the outer layer of the guide tube. The wrapping tube holds the guide tube in place and reduces the tendency to deform when a cutting force is applied, allowing the tip of the guide tube to be cleanly cut axially. Once the guide tube is cut to a length, it may be removed from the package immediately prior to insertion into the brain. The wrapping tube may also reduce direct handling of the outer surface of the guide tube prior to implantation, thereby reducing the chance of contamination of the guide tube, for example, by pathogens. The package may further include a stylet disposed within the through hole of the guide tube. The stylet further reduces deformation of the guide tube when cut.

[0060] The wrapping tube can be configured to compress the outer layer of the guide tube while the guide tube is within the wrapping tube. This helps prevent lateral deformation of the guide tube during cutting, but displacement of the distal end of the wrapping tube relative to the guide tube imparts an axial shear force to the outer layer of the guide tube. If, prior to cutting the guide tube, the wrapping tube is moved distally along the axis of the guide tube to impart a shear force to the outer layers moving them distally, then axial cutting of the guide tube can cause the distal end of the guide tube to have a bullet shape. When the wrapping tube is removed from the guide tube, proximal contraction of the outer layer results in a distal shape having a bullet shape after the shear force is removed.

[0061] As mentioned above, the guide tube is inserted into the brain on a pre-planned trajectory. The pre-planned trajectory is conventionally made using a relatively rigid probe with a rounded tip. However, the use of such probes is difficult in practice. A probe inserted into the brain must first pass through the pia mater, a tough outer membrane that covers the cortex. This is not easily accomplished with a rounded tip, which tends to displace the brain before substantially breaking the cortical surface. As the rounded probe moves to its target, the brain tends to deform around the probe depending on the conformity of the tissue through which the probe passes. This depends on whether it is gray or white matter and the orientation of the individual brain white matter tracts. Brain deformation during probe insertion can result in the probe deviating from the planned trajectory and causing target miss.

[0062] According to a fourth aspect, the present invention provides a probe for insertion into tissue, the probe comprising an axially extending rod with a rounded or conical tip and a thin spike with a tip for cutting tissue. The axially extending thin spike may comprise a rounded tip. The axially extending thin spike may be tapered from the rounded tip of the rod to the tip of the spike. The probe may be used for cannulation of brain tissue, but other applications and tissue types are also contemplated. For example, for inserting DBS (Deep Brain Stimulation) or recording electrodes. For each surgical indication, the diameter of the probe may be selected to form a trajectory with a diameter size equal to or smaller than the diameter of the device to be inserted. DBS electrodes typically have an outer diameter (OD) of 1.3 mm, and in this example, a probe with an OD of 1.3 mm or less, for example 1.2 mm, may be used. In the latter case, the rounded end of the DBS electrode lead will expand the trajectory created by the probe, which has a diameter of 1.2 mm, when inserted. The probe may be coated with a biocompatible lubricious material (e.g., parylene or PTFE), which reduces shear forces on the surrounding tissue and reduces microtrauma to the brain tissue when the probe is inserted.

[0063] The probe can be used when preparing a track (brain tissue) for the guide tube of the first aspect of the invention. The spike on the probe may generally have the same or slightly smaller diameter than the cannula used. The probe can therefore be provided as part of a kit for convection-enhanced delivery of infusate to brain parenchyma constituting the fifth aspect of the invention. The kit can include a probe for insertion into tissue to form a track for the cannula, e.g., a guide tube, a corresponding guide tube probe and a guide hub as just described. Here, the guide tube is not attached to an enlarged proximal end for fitting into the coronal saw hole.

[0064] According to a further aspect, the invention provides a cannula for insertion into the brain through a guide tube and for delivering infusate to a target brain volume. The cannula may be provided as part of the above kit for convection-enhanced delivery of infusate to the brain parenchyma. Once the cannula is attached through the guide tube, it can be used for delivery of infusate to the brain. It is important that air is not delivered into the brain through the cannula, and to reduce this risk, the cannula may have a bubble vent. The bubble vent is preferably provided at the proximal end of the cannula. The bubble vent is configured to prevent gas from entering the cannula. The bubble vent mitigates the risk of air bubbles entering the brain if they come out of solution in the infusate or are mixed into the infusate during connection and / or disconnection of the delivery system. A delivery system is used to deliver the infusate to the cannula, such as a dispenser, infusion line and / or pump. Air bubbles injected into the brain tissue can tear the tissue and impede the distribution of the therapeutic fluid / infusate. The bubble vent may be permanently coupled to the cannula or may be integrally formed with the cannula, further reducing the likelihood of introducing air bubbles when connecting the cannula to the delivery system. The bubble vent may additionally or alternatively be configured to prevent pathogens (e.g., microorganisms such as bacteria) from entering the cannula, thereby reducing the risk of treatment-emerging intracranial infection.

[0065] The bubble vent may have a low volume bubble filter made, for example, from expanded polytetrafluoroethylene (ePTFE). The bubble filter may have a hydrophobic (optionally superhydrophobic), gas permeable, microporous structure configured to remove air bubbles from the flowing treatment / infusate. The bubble filter is effective to remove air bubbles at flow rates of 30 μl / min or less. The bubble vent may further comprise a filter guard. The filter guard may have a distribution of multiple perforations (small holes) that facilitate degassing of the fluid / infusate as it flows through the bubble vent and into the cannula. The filter guard may also guard / protect the bubble filter against damage. The combination of the bubble filter and the filter guard facilitates the dispersion of contained air / bubbles from the fluid flow before the fluid enters the cannula.

[0066] The bubble vent may include a retaining cap that is connected to the filter guard to complete the assembly of the bubble vent and accommodate the bubble filter within the bubble vent. The retaining cap may include a septum stopper that provides a sealing unit until the septum is pierced by a hollow needle to make the fluid connection to the cannula. The septum stopper may be held in a compressed state by the septum cap. The retaining cap and filter guard may be connected by a snap fit connection. However, alternative configurations for these connections may be used, such as threaded connections, welded connections, adhesive connections, etc.

[0067] A bubble vent incorporating a bubble filter reduces the risk of air being delivered, for example to the brain, with a fluid containing a therapeutic / infusate. Fluid containing air / bubbles occupies space and can stretch or tear brain tissue while impeding the delivery / distribution of the therapeutic / infusate. The bubble vent can also act to filter out pathogens, including bacteria and other microorganisms, from the fluid.

[0068] In use, the spiked end of the probe can cut tissue with reduced trauma when inserted and can form a reduced resistance path for the rounded or conical end to expand the tissue to the larger diameter of the rod. To form a track for use with the guide tube of the present invention, the probe can have a diameter of 1.2 mm or less. The spike can have a length of 4-5 mm and can have a taper of 0.6 or 0.5 mm to 0.3 mm or 0.2 mm at its most distal end. For example, the spike can have a taper of 0.5 mm to 0.3 mm at its most distal end. If the probe has an outer diameter of 1.2 mm, the track formed in the brain tissue tends to have a slightly smaller diameter, for example 1.1 mm after the probe is removed. The probe can be formed from hardened stainless steel or tungsten carbide. In addition to providing a means for providing a track for the guide tube of the present invention, the spike of the probe can also provide a proximal track for a cannula that is inserted into the tissue beyond the end of the guide tube in the normal manner.

[0069] The present invention also provides methods of surgery using the devices described herein.

[0070] Thus, according to a sixth aspect, the present invention provides a surgical method for convection-enhanced delivery of an infusate to the brain parenchyma, the method comprising: a) Passing a guide tube into the brain parenchyma, where the guide tube is A base end and The tip and It has a through hole for the passage of the cannula. At least an outer layer of the guide tube is made of a hydrophobic material that is elastically deformable; It has holes that allow air to pass through. The guide tube is threaded into the brain with the aid of a guide tube probe passing through the through hole so that its tip is at or beyond the tip of the guide tube. b) When the guide tube tip is in the planned location, the guide tube probe is further advanced along the trajectory to form a trajectory that will accommodate the cannula through the brain tissue. c) Remove the guide tube probe. d) Passing the cannula through the hole along the trajectory into the brain. e) The infusion fluid is passed into the brain via the cannula.

[0071] Instead of steps b) and c) in the above method, the track for the cannula may be formed as follows. b1) When the guide tube tip is in the planned position, remove the guide tube probe. b2) A trajectory forming probe is inserted into the guide tube along the trajectory to form a trajectory to accommodate the cannula through the brain tissue. c1) Remove the orbit forming probe. Then, steps d) and e) are carried out.

[0072] The trajectory-forming probe used in step b2) may be the probe for insertion into tissue, according to the fourth aspect of the invention, as described herein.

[0073] More generally, each of the guide tube, the guide tube probe, the probe for forming a track for the cannula, and the cannula may include any of the features described herein with respect to other aspects of the invention.

[0074] The infusate may carry any suitable therapeutic, imaging or diagnostic agent that can be delivered into brain tissue via a suitable biologically inert fluid. [Brief description of the drawings]

[0075] Embodiments of the present invention will now be described with reference to the following schematic drawings.

[0076] [Figure 1] FIG. 1 illustrates a conventional neurosurgical assembly with reflux. [Figure 1a] FIG. 2 is an enlarged view of a portion of FIG. [Figure 2a] FIG. 2 is an enlarged view of a portion of a neurosurgical assembly according to the present invention. [Figure 2b] FIG. 2b shows a cross-section of the guide tube shown in FIG. 2a. [Figure 3a] 1 is a cross-sectional view of a portion of a neurosurgical assembly according to the present invention. [Figure 3b] 1 is a cross-sectional view of a portion of a neurosurgical assembly according to the present invention. [Figure 3c] FIG. 1 illustrates the neurosurgical assembly in use. [Figure 4a] FIG. 1 shows the end of a probe for forming a trajectory in brain tissue. [Figure 4b] FIG. 1 shows the end of a probe for forming a trajectory in brain tissue. [Diagram 5] FIG. 13 shows a bubble vent attached to the proximal end of the cannula. [Figure 6] FIG. 2 is an exploded view of the bubble vent. [Figure 7] FIG. 13 illustrates an alternative design of the bubble vent. [Figure 8] FIG. 8 is an exploded view of the bubble vent of FIG. [Figure 9] FIG. 9 shows a cross section of the bubble vent of FIGS. 7 and 8. [Figure 10] FIG. 10 is a close-up view of the bubble vent of FIG. 9 in use. [Figure 11] FIG. 2 shows a cross section of a guide tube having an outermost layer. [Figure 12] FIG. 1 shows the configuration of a kit for convection-enhanced delivery of infusate. [Figure 13] FIG. 1 shows the assembled neurosurgical device. [Figure 14] FIG. 13 illustrates a guide tube having a perforated inner tube running along nearly its entire length. [Figure 15] FIG. 2 is a close-up view of the proximal end of the assembled neurosurgical device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0077] 1 shows a conventional neurosurgical assembly 1 comprising an enlargement head 2 at the proximal end of a guide tube 4 and a cannula 6 extending from a source of infusate 8 through the guide tube 4 to a distal end 10. The enlargement head 2 is secured within a coronal bore (not shown) in the patient's skull and the distal end of the cannula 10 is positioned within brain tissue 12 to deliver infusate from the distal end 14 of the cannula 6 into a target volume of brain tissue, as shown by the dashed oval 16.

[0078] However, as shown in FIG. 1, infusate may backflow, and there is a low resistance path along the outer walls of the cannula 6 and guide tube 4 in an axial flow 20 (enlarged view 1a) extending from the leading edge 14 of the cannula 6 to the outside of the tip. Enlarged view 1a shows the axial flow 20 along the leading edges 10, 18 of the cannula 6 and guide tube 4, resulting in loss of infusate from the region of the target volume 16. A step (abrupt change in diameter) due to the change in diameter from the cannula 6 to the square cut leading edge 22 of the guide tube 4 can act against continued backflow in the direction indicated by arrow R. However, the step is overwhelmed by the fluid volume, and prevention of backflow along the outer surface of the guide tube 4 depends on the degree of sealing interaction between the guide tube 4 and the brain tissue 12. This sealing interaction may not be sufficient to prevent fluid from passing the step at the leading edge 22 of the guide tube 4.

[0079] 2a is an enlarged view of the tips 18, 14 of the guide tube 4 and cannula 6, where the guide tube 4 is in accordance with the present invention. The intended result of the infusate is to deliver the infusate to the target volume 16 of the brain tissue 12. In practice, successful delivery of the infusate resembles that indicated by a "tear drop" shape 24.

[0080] In the example of Fig. 2a, the guide tube 4 is elastically deformable, hydrophobic or superhydrophobic, and porous to air. Upon insertion into a pre-made track in the brain tissue 12, the guide tube 4 is compressed radially inward. As shown, the guide tube 4 exerts a pressure radially outward as it attempts to return to its natural (uncompressed) state. This pressure (indicated by arrow P) provides at least an initial sealing interaction with the brain tissue 12. Thus, the guide tube of the present invention exerts pressure along its length to help prevent backflow.

[0081] Furthermore, the porosity of at least the outer layer of the guide tube 4 enables it to integrate with the brain tissue 12 over time, and can block the return pathway.

[0082] FIG. 2b shows the entire length of the guide tube of FIG. 2a in schematic cross-section (not to scale). In this example, the guide tube has an outer layer 24 of ePTFE and an inner layer 26 of porous (micro-perforated) PEEK. The guide tube 4 has a flared proximal end 28 for seating in a guide hub as described below. A through hole 30 provides a passage for a cannula to deliver infusate. When the guide tube is inserted into the brain, the through hole 30 fits over a probe 32 as shown. The probe 32 has a step 34 of varying diameter that corresponds and engages the flared end 28 of the guide tube 4.

[0083] The outer layer 24 is porous and superhydrophobic. Thus, the outer layer is porous to air but not to aqueous fluids. The micro-perforated PEEK inner layer 26 has a water contact angle of 70°-90° and is relatively hydrophobic. When placed or operated within brain tissue 12, air present on the outside of the inner layer 4 or within the through holes 30 tends to enter the body of the guide tube as shown by arrow V and escape to the atmosphere.

[0084] FIG. 3a shows an alternative guide tube of FIG. 2b in schematic cross section, with similar parts numbered the same. In this example, the lower part of the outer layer 24, including the tip 18, is bonded to an inner layer of perforated PEEK 26 after expanding the (ePTFE) material. As a result, the leading edge 36 of the outer layer 24 is under tension and deforms into a rounded bullet shape. This can help to avoid trauma on insertion into brain tissue. The bullet shape may also be provided by cutting the end of the guide tube inside the package, as described above.

[0085] In this example, the inner perforated PEEK layer does not extend the entire length of the guide tube 4. The upper part (base 38) of the guide tube 4 is unlined. This part of the guide tube is elastically stretchable and axially compressible. The unlined base has a length L. This length may be relatively short, for example 1-1.5 cm in size, designed to be used at a distance from the patient's skull to the surface of the brain.

[0086] When used as described below with reference to Figures 3b and 3c, the base 38 can be compressed during insertion into the patient to act as a shock absorbing member and accommodate relative movement between the brain and skull. In this example, the base 38 is formed of ePTFE, which may vary in density but has a small change in diameter when stretched or compressed. Alternatively, the perforated inner layer 26 may extend substantially the entire length of the guide tube 4, as shown in Figure 14.

[0087] 3a also shows an ePTFE washer 40 and a PEEK washer 42 to aid in sealing against the seats in the guide hub (not shown in this view). The washers 40, 42 can also help to create a fluid and gas seal between the guide hub and the guide tube 4.

[0088] 15 shows a close-up view of the proximal end of the guide tube 4 in use when engaged with the guide hub 50, cannula 6, and cap 100. In this example, there are no washers. Fluid and gas seals between the guide tube 4 and the guide hub 50 and between the guide tube 4 and the cannula 6 are formed by compression of the elastically deformable outer layer at the flared proximal end 28 of the guide tube 4. Compression of the outer layer of the guide tube 4 forms a proximal seal 102 with a stopper 104 on the cannula 6. Compression of the outer layer of the guide tube 4 also forms a distal seal 108 with the guide hub 50.

[0089] FIG. 3b shows the arrangement of FIG. 3a, but inserted into the brain as indicated by arrow I. The insertion is performed by two coaxially arranged probes. A central probe 44 passes through the through hole 30 and extends down the distal end 18 of the guide tube 4. An outer probe 46 fits around the central probe 44 and has a step 34 for engaging the flared end 28 of the guide tube. The outer probe 46 also has a step 48 for engaging the upper end of the liner tube 26. When the guide tube 4 is inserted, the length L of the unlined proximal end of the guide tube 4 is shortened (compressed) as indicated by arrow I, so that the distance between the step 34 and the step 48 is shorter than the uncompressed length L. Instead of arranging two probes, a single probe can be employed that includes both steps 34, 48 within its outer contour and passes down the entire length of the through hole 30.

[0090] FIG. 3c shows the guide tube 4 of FIGS. 3a and 3b in use. The guide tube 4 is in place with the guide hub 50 fitted into a burr hole 52 in the patient's skull 54. The guide tube is threaded through the pia 56 of the patient's brain tissue 12. A cannula 6, supplied with infusate fluid from a source 8, passes down the guide tube through hole with the tip 10 extending beyond the guide tube 4. The unlined base 38 of the guide tube 4 is compressed as described above with respect to FIG. 3b. As the brain tissue 12 moves relative to the skull 54, the base 38 can move elastically to follow the displacement and avoid interference with the guide tube 4 inside the brain tissue 12. For example, the length L of the unlined base 38 when uncompressed can be 1.3 cm, and upon fitting in place, the length I is compressed to 1 cm.

[0091] FIG. 4a shows the end 58 of a hardened stainless steel probe 60. The end 58 has a rounded shape ("bullet shaped") and has a rod-shaped protruding spike 62 tapered from the bulbous end 58 to the tip 64 of the spike 62. An alternative end 58 is shown in FIG. 4b having a conical shape. In both examples, the tip 64 of the spike is itself rounded. The probe can be used to dissect tissue to form a trajectory, for example, through brain tissue prior to inserting a guide tube as shown in FIGS. 1-3 and described above.

[0092] FIG. 5 shows the proximal end of the cannula 6 with a bubble vent 74 disposed thereon. The structure and components of the bubble vent 74 are shown in FIG. 6 and described below. In summary, the bubble vent 74 mitigates the risk of air bubbles entering the brain if air bubbles are released from the solution in the infusate or are entrained in the infusate while the delivery system is connected and / or disconnected. A delivery system, such as a dispenser, infusion line and / or pump, is used to deliver the infusate to the cannula 6. The bubble vent 74 is preferably integral with the cannula 6 as shown in FIG. 5. This further reduces the possibility of air bubbles being entrained while the cannula 6 is connected to the delivery system. The bubble vent 74 may also be configured to prevent pathogens (e.g., microorganisms such as bacteria) from entering the cannula 6.

[0093] 6 shows an exploded view of a bubble vent 74 configured to attach to a cannula 6 or a fluid connector of a delivery system. Bubble vent 74 includes a perforated filter guard 80, a bubble filter 82, retaining rings 83A and 83B, a retaining cap 84, a septum stopper 86, and a septum cap 88.

[0094] In the illustrated example, bubble filter 82 is a low volume bubble filter fabricated from expanded polytetrafluoroethylene (ePTFE) that is superhydrophobic, gas permeable, and has a microporous structure configured to remove air bubbles from the flowing therapeutic agent. In the illustrated example, bubble filter 82 is effective to remove air bubbles at flow rates of 30 μl / min or less. Filter 82 is housed in perforated filter guard 80, which in the illustrated example is received on hollow post 85 and retained therein by retaining ring 83A, thereby positioning filter guard 80 concentrically.

[0095] In the illustrated example, the filter guard 80 is a hollow shell with a plurality of perforations (holes) 87 distributed around the periphery of the shell wall. The perforations 87 facilitate degassing of the fluid as it flows from the delivery system through the bubble filter 82 to the cannula 6. As the name suggests, the filter guard 80 also guards / protects the filter 82 from damage. The combination of the bubble filter 82 and the filter guard 80 facilitates the dispersion of any entrained air / bubbles from the dispenser fluid stream before the fluid enters the cannula 6.

[0096] The bubble vent 74 also has a retaining cap 84 which connects with the filter guard 80 to complete the assembly of the bubble vent 74 and house the bubble filter 82 within the bubble vent 74. The retaining cap 84 has hollow retention posts 89 and a retaining ring 83B which engage the bubble filter 82 to retain the bubble filter 82 in the correct position within the filter guard 80 and ensure efficient functioning of the bubble filter 82 during use.

[0097] In the illustrated example, the retaining cap 84 has a septum stopper 86 that provides a sealing unit until the septum 86 is pierced by a hollow needle to make a fluid connection to the cannula 6. The septum stopper 86 is held in compression by a septum cap 88.

[0098] In the illustrated example, the retaining cap 84 and the filter guard 80 are connected by a snap fit connection, however, alternative configurations for connecting them could be used, such as threaded connections, welded connections, adhesive connections, etc.

[0099] The bubble vent 74 incorporating a low volume bubble filter 82 reduces the risk of air being delivered by the therapeutic / infusate containing fluid, for example to the brain. Fluid containing air / bubbles occupies space and can stretch or tear brain tissue while impeding the delivery / distribution of the therapeutic / infusate. The bubble vent 74 can also act to filter pathogens, including bacteria and other microorganisms, from the fluid.

[0100] Figures 7-10 show an alternative design of bubble vent 174. Figure 7 shows bubble vent 174 in a ready-to-use assembly. Like bubble vent 74, bubble vent 174 includes a retaining cap 84. Retaining cap 84 includes a proximal connector 176, e.g., a threaded connector, for connecting to a fluid connector of a delivery system.

[0101] FIG. 8 shows an exploded view of the bubble vent 174, and FIG. 9 shows a cross-sectional view. The proximal connector 176 may have a septum 86 to seal the proximal connector 176 until the septum 86 is pierced, for example, by a hollow needle. The bubble vent 174 has a fluid passageway 140 that fluidly connects the proximal connector 176 and the cannula 6. In this design, the bubble vent has a first membrane 150 and a second membrane 152. The first membrane 150 and the second membrane 152 are disposed between the distal end of the fluid passageway 140 and the proximal end of the cannula 6. The first membrane 150 and the second membrane 152 may be substantially parallel to each other or substantially perpendicular to the axis of the fluid passageway 140. The first membrane 150 is disposed closer to the distal end of the fluid passageway 140 than the second membrane 152, such that fluid entering the bubble vent 174 through the septum 86 reaches the first membrane 150 before the second membrane 152. An annular washer 153 may be disposed between the first membrane 150 and the second membrane 152, forming a peripheral fluid seal between the membrane and the housing of the connector 174 and centrally separating the membranes to form a cylindrical gap therebetween. The cylindrical gap may have a diameter between 2 mm and 6 mm, with a most preferred diameter being 4 mm. The gap may separate the membranes 150, 152 by 0.05 mm to 0.2 mm, most preferably 0.1 mm. The first membrane 150 and the second membrane 152 may be connected to each other and to other components of the bubble vent 174 via a connecting surface 180. The connecting surface 180 may be connected by any suitable method, such as ultrasonic welding or the use of a layer of adhesive. The bubble vent 174 may have a support member 184 to support the tip of the second membrane 152 and to allow liquid passing through the second membrane 152 to more easily reach the cannula 70.

[0102] The first membrane 150 is hydrophobic and gas permeable. At the location where the fluid passage 140 faces the first membrane 150, a hole 154 is provided in the first membrane 150, allowing fluid from the fluid passage 140 to pass through the first membrane 150 through the hole 154. The septum seal connector 174 may have a support member that supports the proximal surface of the first membrane 150 and an annular connecting surface for attaching the membrane around its periphery and its central hole 154 (not shown in FIG. 8). The second membrane 152 is liquid permeable and preferably hydrophilic. The second membrane 152 does not need to be hydrophilic, but gas venting works most efficiently by using a combination of hydrophobic and hydrophilic membranes. If the hydrophobic first membrane 150 is used alone, air may be drawn from the atmosphere through the first membrane 150 into the infusate when the pressure in the line falls below atmospheric pressure. This may occur if the connector is elevated 10-25 cm above the head (depending on the intracranial pressure). Even in such a situation, the hydrophilic nature of the second membrane 152 prevents air from entering the brain. The second membrane 152 is impermeable to gas and bacteria. The second membrane 152 is not permeable to gases and bacteria, so that fluid from the fluid passage 140 must pass through the material of the second membrane 152 to reach the cannula 6. One or more air vents 160 (e.g., two air vents in the embodiment of FIG. 7) are provided in the bubble vent 174 on the proximal side of the first membrane 150. The first membrane 150 is not perforated where the air vent 160 faces the first membrane 150. This means that fluid from the fluid passage 140 must pass through the material of the first membrane 150 to reach the air vent 160.

[0103] The operation of the bubble vent 174 is shown in the enlarged view of FIG. 10. A mixture of liquid and gas (e.g., an infusate delivered to the patient's brain through the cannula 6, which contains gas bubbles) enters the bubble vent 174 through the septum 86 and the fluid passageway 140. The mixture passes through the first membrane 150 through the hole 154. The liquid is drawn into the hydrophilic second membrane 152 and is immersed in the cannula through the second membrane 152 (which is liquid permeable). The layer of liquid and the second membrane 152 form a barrier that prevents gas from passing through the cannula 6. The gas passes along the gap between the first membrane 150 and the second membrane 152 and can escape through the gas permeable first membrane 150 at the location of one of the vent holes 160. The hydrophobic nature of first membrane 150 repels liquids and prevents liquids from forming a barrier similar to that of second membrane 152, thereby allowing gas to migrate through vent 160 and out of bubble vent 174.

[0104] 11 shows a cross-sectional view perpendicular to the longitudinal axis of an example where the guide tube 4 includes an outermost layer 27 axially outboard of the outer layer 24, the outermost layer 27 including a hydrophilic material. The outermost layer 27 of hydrophilic material can contribute to improved lubricity and / or tissue integration of the guide tube 4, as described above. In this example, the inner layer is formed of PEEK having pores 25, the outer layer 24 is formed of electrospun hydrophobic polyurethane, and the outermost layer 27 is formed of hydrophilic polyurethane.

[0105] 12 shows kit configurations for convection-enhanced delivery of infusate to brain parenchyma. These configurations include a guide hub 50, a guide tube 4, a cannula 6, and a screw stopper 70 that is fastened to the guide hub 50.

[0106] FIG. 13 shows the assembled neurosurgical device with the cannula 6 threaded through the through hole of the guide tube 4 and the screw stop 70 fastened to the guide hub 50.

Claims

1. A cannula for insertion into the brain through a guide tube for delivering an infusion fluid to a target brain volume, the cannula having a bubble vent configured to prevent gas and / or microorganisms from entering the cannula.

2. The cannula according to claim 1, wherein the bubble vent is permanently connected to and / or integrally formed with the cannula.

3. The cannula according to claim 1, wherein the bubble vent is provided at a proximal end of the cannula.

4. The cannula according to claim 1, wherein the bubble vent has a microporous structure having hydrophobicity and gas permeability.

5. The cannula according to claim 1, wherein the bubble vent has a filter guard including a plurality of holes configured to degas a fluid passing through the bubble vent.

6. The cannula according to claim 1, wherein the bubble vent has a proximal connector with a partition wall.

7. The cannula according to claim 1, wherein the bubble vent has a first membrane and a second membrane.

8. The cannula according to claim 7, wherein the first membrane has hydrophobicity and gas permeability.

9. The cannula according to claim 7, wherein the second membrane has hydrophilicity and liquid permeability.

10. The cannula according to claim 7, wherein the first membrane and the second membrane are separated with a gap of 0.05 mm to 0.2 mm.

11. The cannula according to claim 7, wherein the first membrane and the second membrane are substantially parallel to each other.

12. The bubble vent has a fluid passage fluidly connecting a proximal connector of the bubble vent and the cannula, and the first membrane and the second membrane are substantially perpendicular to an axis of the fluid passage, according to claim 7 of the cannula.

13. The bubble vent has a fluid passage fluidly connecting a proximal connector of the bubble vent and the cannula, and the first membrane and the second membrane are disposed between a distal end of the fluid passage and a proximal end of the cannula, according to claim 7 of the cannula.

14. In the first membrane, holes are provided at locations where the fluid passage faces the first membrane, and the fluid from the fluid passage can pass through the first membrane through the holes, according to claim 13 of the cannula.

15. The cannula according to claim 13, wherein the fluid from the fluid passage passes through the material of the second membrane and reaches the cannula.

16. The bubble vent has one or more ventilation holes on the proximal end side of the first membrane, The cannula according to claim 13, wherein the fluid from the fluid passage passes through the material of the first membrane and reaches the ventilation holes.

17. A kit for convective enhanced delivery of an infusion fluid to the brain parenchyma, comprising: a) a guide tube for insertion into the brain, the guide tube having a proximal end, a distal end, and a through hole for passage of the cannula; b) a guide tube probe passing through the through hole of the guide tube to assist in insertion of the guide tube into the brain; c) a probe for forming a track for the cannula in the brain; d) a cannula according to any one of claims 1 to 16 for delivering an infusion fluid to the brain through the guide tube, wherein at least the outer layer of the guide tube is made of a hydrophobic material that is elastically deformable and has a porous structure allowing passage of air.

18. The kit according to claim 17, wherein the probe includes a rod having a circular or conical tip extending axially to form a track for the guide tube and the cannula in the brain, and a thin spike having an extreme end for incising tissue.

19. The kit according to claim 17, further comprising a guide hub that fits into a coronal saw hole in the skull and is connected to the proximal end of the guide tube.