US 20080243140 A1
The invention relates to a spacing device (stent) for use in fenestrations of the paranasal sinus. Said device consists of a sheath which forms a hollow body, surrounding an internal cavity. An active substance, which is released in a controlled manner by the spacing device, is contained in the sheath or in at least one layer of the sheath. The relationship q of the external diameter of the hollow body to the internal diameter of the hollow body is expressed by 1.2≦q≦3.0.
1. A method for treating a disorder that affects a paranasal sinus, middle ear or trachea, said method comprising the steps of:
A) providing a substance delivering device that is implantable in an opening of a paranasal sinus, middle ear or trachea, said device comprising a tubular body having a wall, a lumen, first and second open ends, an outer surface, an inner surface and a substance containing layer, the substance containing layer comprising a matrix that contains therapeutic substance such that a therapeutically effective amount of the substance will elute from the device while implanted, wherein said therapeutic substance comprises at least one steroid; and
B) implanting the device in an opening of a paranasal sinus, middle ear or trachea such that a therapeutic amount of the therapeutic substance is delivered to the paranasal sinus, middle ear or trachea in which the device is implanted.
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C) removing the device.
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This patent application is a division of copending U.S. patent application Ser. No. 10/470,881 filed Feb. 4, 2004 which is a national stage filing under 35 U.S.C. § 371 of PCT/EP02/01228 filed Feb. 6, 2004, which claims priority to German Patent Application No. DE10105592.7 filed Feb. 6, 2001, the entire disclosure of each such application being expressly incorporated herein by reference.
The present invention relates to a spacing device (stent) for use in fenestrations of the paranasal sinus.
About 5% of our population suffer from a chronic mucous membrane inflammation of the paranasal sinuses. In the course of an inflammation of this type, nasal polyps occur in every fifth patient. If corresponding symptoms occur and an attempt at medicinal treatment remains unsuccessful, the chronic sinusitis is approached surgically.
The paranasal sinus system consists of a series of cavities lined with mucous membrane and filled with air. The interruption of the natural secretion drainage from the remote paranasal sinus portions and the removal of natural ventilation are important in the occurrence of chronic sinusitis. The remote, diseased paranasal sinus portions are accordingly reventilated during cleaning-up interventions through newly created or extended accesses (“windows”). After healing, the natural secretion drainage of these reventilated compartments reappears.
Surgical treatment of chronic sinusitis has been transformed after the introduction of modern optical aids (rigid endoscopes, microscope). Nowadays, the “minimally invasive” clearing exclusively of those mucous membrane parts which have undergone an obviously irreversible change owing to the inflammation process predominates. Other reversibly changed or unaffected mucous membrane areas are spared as far as possible (Hosemann W G, Weber R K, Keerl R E, Lund V J: Minimally invasive endonasal sinus surgery. Thieme, Stuttgart, New York 2000).
If the frontal sinus mucous membrane is involved in the inflammatory modification of the sinus a surgical fenestration takes place towards the nose. This is carried out with special instruments (bent sharp spoons, special stamps, drills). Accesses of about 5 to a maximum of 10 mm in diameter are produced by routine “fenestration” of the frontal sinus. During healing of the wound these accesses narrow by about 1.5 mm.
If certain health factors are present, such as, for example intolerance of analgesics, a disproportionate tendency to scarred narrowing has to be taken into account (Hosemann W, Th. Kuhnel, P. Held, W. Wagner, A. Felderhoff: Endonasal frontal sinusotomy in surgical management of chronic sinusitis—a critical evaluation. Am. J. Rhinology 11: 1-9 (1997)). In such cases it is advised to maximise the surgical access as a precaution. This “widened frontal sinus surgery” is subdivided into specific types (Draf W: Endonasal micro-endoscopic frontal sinus surgery: the Fulda concept. Op Tech Otolaryngol Head Neck Surg 2: 234-240 (1991); May M, Schaitkin B: Frontal sinus surgery: endonasal drainage instead of an external osteopolstic approach. Op Tech Otolaryngo Head Neck Surg 6: 184-192 (1995)).
As stated, the neo-ostium to the front sinus narrows to a greater or lesser extent, according to experience. To prevent this scarred stenosis it was already proposed at the start of the last century, i.e. long before the introduction of minimally invasive endoscopic surgery to insert a spacing device (stent). These spacing devices usually had the form of a small tube and were made of various materials: at the beginning rolled metal or metal braided in wires was used (Fletscher Ingals E: New operation and instruments for draining the frontal sinus. Ann Otol Rhinol Laryngol 14: 515-519 (1905), Good R H: An intranasal method for opening the frontal sinus establishing the largest possible drainage. Laryngoscope 18: 266-274 (1908)). In the last two decades silicone tubes were preferred (Stammberger H: Komplikationen entzundlicher Nasennebenhohlenerkrankungen eischlie.beta.lich iatrogen bedingter Komplikationen. Eur Arch Oto-Rhino-Laryngol Suppl 1993/1: 61-186).
Experience with spacing devices for stabilising the newly created frontal sinus access was not always, however, encouraging, apart from individual reports (Jacobs J B: 100 years of frontal sinus surgery. Laryngoscope 107: 1-36 (1997); Weber, R, W. Hosemann, W. Draf, R. Keerl, B. Schick, S. Schinzel: Denonasale Stirnhohlenchirugie mit Langzeiteinlage eines Platzhalters. Laryngol. Rhinol. Otol. 76: 728-734 (1997).
Initially it remained unclear as to how long a spacing device of this type was required in the area of the operation. From animal experiments on wound healing, it became clear that a scarred narrowing of the frontal sinus access for a post-operative period of at least three months has to be assumed (Hosemann, M. E. Wigand, U. Gode, F. Lnger, I. Dunker: Normal wound healing of the paranasal sinuses—clinical and experimental investigations, Eur. Arch, Otorhinolarylgol. 248: 390-394 (1991)). Accordingly, the spacing device would have to be used over eight to twelve weeks. Even with the correct duration in position a spacing device will often only delay and possibly reduce in scope the undesired scarred narrowing, without being able to prevent it completely. An additional medicinal treatment to reduce excessive wound reactions would have to take place here.
According to the present level of knowledge about wound healing processes in the nose the administration of medicinal substances such as, for example, corticosteroids, seems to be in a position to counteract, with a certain reliability, this tendency to regenerating mucous membrane for scarred stricture of the front sinus nose passage (Hosemann, M. E. Wigand, U. Gode, F. Lnger, I. Dunker: Normal wound healing of the paranasal sinuses—clinical and experimental investigations. Eur. Arch. Otorhinolaryngol. 248: 390-394 (1991); Hosemann W, Gode U, Langer F, Wigan M E: Experimentelle Untersuchungen zur Wundheilung in den Nasennebenhohlen. II. Spontaner Wundschluss und medikamentose Effekte im standardisierten Wundmodell. HNO 39″48-54 (1991); Hosemann W, Kuhnel Th, Allert M H. Weiterbehandlung nach Nasennebenhohleneingriffen, part 2: Theapeutische Maβnahmen, HNO aktuell 7: 291-302 (1999).
Unfortunately, conventional medicine forms such as salves or sprays do not reach into the problem region of the transition of frontal sinus and nose during routine application (Prince M E P, Lemckert R J: Analysis of the intranasal distribution of ointment. J Otolaryngol 26: 357-360 (1997); Weber R. Keerl R, Radziwill R, Schick B, Haspersen D, Dshambazov K, Mlynski G, Draf W: Videoendoscopic analysis of nasal steroid distribution. Rhinology 37: 69-73 (1999)).
Postoperative systemic administration of corticosteroids is certainly usual in rhinosurgery (Bumm P: Hals-Nasen-Ohrenkrankheiten. In: Kaiser H, Kley H K (Hrsg.) Cortizontherapie, Corticoide in Klinik und Praxis. Thieme, Stuttgart 1992, pages 390-401), but the treatment plans do not usually extend over the required duration of 8 weeks. Moreover, with longer-term systemic corticosteroid administration side effects of the treatment have to be increasingly taken into account.
The presently described problems show the need for systems which can in a controlled manner dispense the active substances such as, for example, corticosteroids over a longer period directly to the operation site.
A series of systems have been proposed for the controlled release of medicinal substances such as, for example implants of polymers loaded with a medicinal substance. U.S. Pat. No. 5,633,000 thus describes implants for the release of pain killers. The polymers used there release the active substance via diffusion. U.S. Pat. No. 5,019,372 describes that this release can be modulated by incorporation of magnetic particles and by application of alternating magnetic fields. If this formed body is designed with a correspondingly defined geometry the release of the active substances can be optimised such that they are released over the application period at a constant speed (U.S. Pat. No. 4,803,076).
The polymers used for such applications include, apart from biodegradable materials, non-biodegradable materials, i.e. those which do not decompose on contact with body fluids. Examples of such polymers are silicone, polyacrylate and ethylene vinyl acetate copolymer (U.S. Pat. No. 4,069,307). The last polymer group, in particular, was used for a series of systems for controlled release of active substances.
U.S. Pat. No. 3,393,073 thus describes a so-called reservoir system consisting of a medicinal substance reservoir which is surrounded by a polymer sheath regulating the release rate of the medicinal substance. Such systems were successfully used for the development of “intra-uterine devices” which release the active substance in the uterus (U.S. Pat. No. 3,967,618 and U.S. Pat. No. 4,016,251) and for producing therapeutic systems which release medicinal substances to the eye (U.S. Pat. No. 4,052,505).
Such systems were also described, as carrier systems with a microporous membrane controlling the discharge of the active substance, for introduction into various body cavities, such as for example, the ear, nose or the rectum (U.S. Pat. No. 3,948,254).
Those made of plastics are described in the area of “stents” for the treatment of paranasal sinuses, such as, for example in U.S. Pat. No. 5,693,065 or U.S. Pat. No. 5,336,163. U.S. Pat. No. 5,693,065 describes a stent for the nose area made of silicone rubber having a cylindrical shaft of which the leading end to be inserted into the nose is designed in the shape of the point of a spear, the base of the point connected to the shaft having a wider diameter than the shaft. The point is closed at the front and laterally has ribs with slits therebetween, the ribs expanding in the inserted state and thus ensuring the hold of the stent in the nose area.
An external diameter of 0.157 inches and an internal diameter of 0.118 inches is given as the dimensions for the shaft. The firm seat of the stent in the nose passage is only ensured, however, by the spreading of the spear-shaped point.
U.S. Pat. No. 5,336,163 relates to a stent for the nose area formed from a porous material and having a non-adhering, but slightly porous outer surface. The stent is formed from a material here which expands on contact with liquid.
U.S. Pat. No. 5,601,594 describes a stent for insertion into a nose aperture, the stent having a bent shape and being formed from a compressible material.
However, these are systems which are free of medicinal substances and the action of which only aims to keep open the accesses to the frontal sinus by physical/mechanical effects.
Despite this progress in the area of controlled release of active substances there has previously not been any indications that this technology could be usable for the post-operative care of sinus systems after minimally invasive clearing. Although so-called “stents” which prevent a tissue reconstruction are known these are described exclusively for the treatment of blood vessels and are accordingly geared to other biological needs.
U.S. Pat. No. 5,980,551 describes a stent for blood vessels, the stent having an inner support structure which may be formed from a wire and the support structure is surrounded by a biodegradable resorbable substrate. Biologically active microparticles which release active substances in a controlled manner can be embedded into this substrate.
Stents for suppressing the restenosis of coronary arteries have design features which clearly differ from the subject of the invention and therefore also make them unsuitable for application in the frontal sinus.
In many cases the “coronary stents” also require application aids. Such application aids are described in combination with a stent in U.S. Pat. No. 6,080,190 and U.S. Pat. No. 5,843,089. A serious problem of coronary stents to release active substances is the construction of the medicinal substance release system. Coronary stents generally consist of a stent body such as, for example, a wire braiding covered with medicinal substance-carrying polymers or sheathed in thin polymer films (U.S. Pat. No. 5,824,048, U.S. Pat. No. 5,700,286, U.S. Pat. No. 5,837,313, U.S. Pat. No. 5,679,400). The mechanical stability of these stents is geared to the needs of arteries and makes them unsuitable for application in the nasal sinus, as they are not mechanically stable enough.
Coronary stents are rotationally symmetrical hollow bodies and preferably have the geometry of a hollow cylinder. They can therefore not be fixed via thickenings at the cylinder end in a fenestration of the paranasal sinus. Moreover, a fenestration of the paranasal sinus is generally not uniformly round, but more or less irregular which creates additional problems with respect to anchoring. In general, coronary stents cannot have large wall thicknesses so as not to impede the blood flow.
Moreover, coronary stents differ from spacing devices for paranasal sinuses due to their function. The coronary stent is intended to expand the vessel in many cases. The front sinus spacing device, on the other hand, is inserted in a surgically applied passage which has bony (stable) walls. This passage was surgically newly formed; the coronary artery, on the other hand is left as a tube, but expanded.
A coronary stent is a permanent implant, it is completely absorbed by the body. The frontal sinus spacing device, on the other hand, is removed after a period of about 8 weeks.
The coronary stent is completely absorbed by the body. Blood flows in the interior of the coronary stent; the wall is completely colonised in the most favourable case by the body's own cells (endothelial cells). With the frontal sinus spacing device, complete absorption into the body is not desirable. Secretion from the mucous membrane surface should drain in the interior of the frontal sinus spacing device and ventilation should simultaneously be ensured. Colonisation of the interior of the spacing device with the body's own cells is neither anticipated nor desired.
On the other hand, the mucous membrane should widen at the outside of the frontal sinus spacing device. In this manner, once the spacing device has been removed, a passage lined with intact mucous membrane should remain.
A problem in the coronary stent is the formation of a clot with the risk of an occlusion which has to be suppressed by the administration of special medication. The frontal sinus spacing device does not require the administration of special medication.
It has been proposed to produce medical devices used in the body from a material loaded with active substance or to coat them therewith.
WO 96/29071 describes medical devices such as catheters or stents, on the surface of which antibacterial means are applied, the antibacterial means adhering to the surface owing to adhesive forces, without further aids being required.
It is proposed in general in WO 92/15286 to form medical devices from a polymer loaded with medicinal substance or to provide them with a coating thereof, stents also being mentioned for use in the nasal area, without more detail about the configuration of a stent of this type.
It was the object of the invention to provide a spacing device suitable, in particular, for use in the paranasal sinus having not only adequate stability and a firm hold but simultaneously able to release in situ a desired active substance in a controlled manner, a controlled release of the required amount of active substance with the desired time course also being ensured over an adequately long period for the treatment.
In addition, the spacing device according to the invention allows an adequately large quantity of active substance to be received and stored, without impairment of the controlled release owing to interactions of the active substance contents.
According to the invention, this object is achieved by a spacing device as described in the independent claims 1 and 2. Advantageous developments are the subject of the sub-claims.
To do justice to the above-mentioned requirements the ratio q of the external diameter ra to the internal diameter ri of the stent body is a value of 1.2 and more.
According to the invention the ratio q is selected in a range of 1.2≦q≦3.0, in particular of 1.2≦q≦2.8, preferably of 1.5≦q≦2.5 and particularly preferably 1.8≦q≦2.2.
In contrast to this, for coronary stents the value q is typically in a range of less than 1.2.
It has been shown, however, that with the smaller wall thicknesses of the coronary stent in comparison to the stent according to the invention for the paranasal sinus, the controlled release of active substance as desired according to the invention cannot be achieved.
The quotient q can thus serve as the calculation basis here. For example, for a hollow cylinder the volume V can be calculated from the height h, the internal diameter ri and q:
Formula I makes it clear that the volume of a coronary stent (with q=1.2), with the same internal diameter ri and the same height h is a maximum of about 15% of the volume of a paranasal sinus spacing device according to the invention (with q=2). It follows from this that stents with q=1.2 or less can receive a maximum of 1/7 of the active substance dose of a paranasal sinus spacing device according to the invention.
The quotient q has serious consequences for the release periods over which active substances can be released. To estimate the release duration t as a function of the thickness of a material I and the diffusion coefficients D, in the literature the dimensionless expression:
is used (Cussler, E. L.; Diffusion: Mass Transfer in Fluid Systems, Cambridge Univ. Press, 1996). The diffusion section in a hollow cylinder can be estimated as half the difference between external diameter ra and external diameter ri. In a stent with a constant internal diameter ri the release duration is reduced to 4% when q is reduced from 2 to 1.2. For the above-mentioned reasons, for the described paranasal sinus spacing device the value q is preferably above 1.2 and in particular in a range 1.2≦q≦2.8, particularly preferably 1.5≦q≦2.5 and particularly preferably the range is 1.8≦q≦2.2.
According to a further aspect, the invention relates to a spacing device for the paranasal sinus in which the layer or layers loaded with active substance are separated towards the inner cavity by a layer consisting of a material which is impermeable or at least virtually impermeable for the active substance. Active substance losses are thus avoided and the duration over which the active substance is released is simultaneously increased.
Serious differences also exist with respect to the mechanical properties. Coronary stents which are introduced via a catheter into the blood vessels have to be plastically, i.e. irreversibly deformable. Owing to an irreversible widening of the stent, they have to be fixed to the vessel wall.
The spacing device developed in the course of this invention for use in the paranasal sinus, in contrast thereto, is distinguished by elastic properties and therefore reversible deformability; the paranasal sinus spacing device can be fixed simply in the apertures to the paranasal sinus, inter alia owing to this elasticity.
It is possible with the spacing device (stent) loaded with active substance according to the invention to keep the frontal sinus accesses open not only by a physical/mechanical mechanism, but also by a pharmacological mechanism. These spacing devices are adapted to the surgically created accesses to the paranasal sinus and fulfil two functions:
1. They keep physically open the newly created “fenestration” of the front sinus in the course of the minimally invasive clearing. On the one hand, this is achieved by the application of the spacing device to the surgically changed tissue and assisted by the encouragement of the secretion drainage from the sinus.
2. The developed spacing devices may release active substances such as medicinal substances such as, for example corticosteroids which suppress tissue formation or overshooting wound healing and therefore keep open the surgically newly created fenestration.
In order to be able to fulfil both functions in an optimal manner, the “stent” has some design features which will be described in more detail hereinafter with the aid of the figures.
The spacing device according to the invention is a hollow body which is composed of a sheath surrounding an inner cavity and having a respective aperture at two opposing ends.
The hollow body is preferably based on a cylindrical shape wherein it can deviate from the ideal cylindrical form with an in particular uniform diameter along the shaft.
The external diameter along the cylinder shaft may thus vary, for example the external diameter in the end regions close to the apertures may be selected to be larger than in the central shaft region.
Starting from the end regions, the external diameter may continuously reduce in the direction of the central shaft region, may be reduced in the manner of an hourglass in the central region, wherein the specific shape of the cylindrical basic body can be adapted in any way as necessary.
The wall thickness of the cylinder may also be selected to be variable.
Thus, in the drawings:
The geometry of the spacing device is preferably that of a hollow cylinder as can be seen in
The length of the cylinder is preferably selected here in a range of 5 to 30 mm and its external diameter in a range of 1 to 30 mm. The wall thickness is to be selected according to need as a function of the physical properties of the polymer materials used and the active substances used and the desired release profile within the above-mentioned ranges for the ratio q of external diameter to internal diameter.
The at least two inner apertures 2 typically have a diameter in a range of 0.5 to 25 mm.
The release-controlling material forming the cavity, for example a reservoir 4 is surrounded by an outer membrane 3 which preferably consists of a polymer material through which the active substance can diffuse.
The cavity forming the reservoir 4 is preferably separated on the inside to the inner cavity 3 by an inner wall 4 preferably consisting of a material which is impermeable or virtually impermeable to the active substance.
An inner layer (inner wall 4) which is as impermeable as possible to the active substance is suitable in principle for any active substance-carrying systems for avoiding active substance losses in the direction of the inner cavity 3.
The inner wall 4 may consist here of a corresponding polymer material but also of an inorganic material such as a metal etc.
The sheath 1 may have perforations 7, as shown in
The form and number of perforations 7 can be freely selected here as required.
A configuration according to the invention with a varying external diameter is shown in
As shown here, the wall thickness may also vary, wherein it decreases in this case towards the end regions.
The wall thickness, in other words the ratio q of external diameter to internal diameter may, as required, in particular in the end regions or else in short central sections be outside the value to be adjusted according to the invention for q, if the usability of the stent is not impaired. Thus, at least in the wound regions q should be within the above-mentioned value range according to the invention of 1.2≦q≦3.0. In the event that in individual regions of the hollow body the wall thickness has a value q outside the value range according to the invention, these regions or this range should not be more than 30% of the hollow body.
The stent according to the invention may be formed from one or more layers, wherein the layers may consist of the identical and/or different polymers. Individual regions of a layer, for example the end regions close to the apertures 2 may be manufactured from a material which is different from the material for the remaining layer regions. In other words one layer may contain at least one region which is formed from a different material than the remaining layer.
In addition, the stent according to the invention may have layers which are free of active substance in addition to layers which are loaded with active substance.
If necessary, the stent according to the invention may be surrounded by a suitable outer coating.
In contrast to coronary stents, the spacing device according to the invention does not necessarily lie homogenously and in a planar manner on the tissue. This circumstance requires a particular construction so that, for example, secretion cannot build up in the long term between the spacing device and the sinus wall. Secretion drainage can be facilitated by perforations 7 in the wall of the spacing device (see cross-section shown in
According to a further configuration, the space holder may have irregularities such as humps etc. on its outer surface. In this case, contact with the nasal wall is via these irregularities, wherein, on the one hand, the contact face can be reduced and an adequately firm hold is nevertheless ensured. The developing cavities between the outer surface of the stent and nasal wall simultaneously encourage secretion drainage.
The spacing device is moreover advantageously provided such that suction of the paranasal sinus remains possible owing to the spacing device. This is made possible owing to a relatively small length. The spacing device is therefore preferably constructed such that it can be cut to the desired length directly prior to application.
The spacing device must be “anchored” counter to gravity in the frontal sinus entry. This anchoring can be achieved by a “ballooning” of the implant, i.e. a widening of the spacing device end in the frontal sinus or fixing by means of a seam on the nasal septum. Moreover, the stent may consist of materials which favour anchoring and shape adaptation. In this context “shape memory polymers” (for example U.S. Pat. No. 5,139,832, U.S. Pat. No. 5,189,110) or swelling polymers can be used (for example DE 4 032 096).
While the former change their shape at body temperature, with swelling substances there is a volume increase of the material owing to water absorption and therefore an increase in the stent diameter after its application. The materials adapt optimally here to the defect and thus prevent slipping of the stent. Owing to their good permeability to water, swelling polymers prevent a build up of secretion at the contact face to the tissue.
An example of this is shown in
The spacing device in the nose, in contrast to spacing devices in vessels, is exposed to a bacteria-loaded environment (mucous membrane wounds with free contact to the outside air). Owing to corresponding shaping, scab formation and bacterial contamination is delayed. This may, for example, be achieved by an adequately large internal diameter of the spacing device encouraging secretion drainage. The materials used may moreover be modified at the surface in such a way that secretion drainage is encouraged and bacterial contamination is avoided. An example is the hydrophilising of the surface. For this purpose the interior of the hollow body can be lined with a polymer layer which is highly wettable and preferably has water contact angles <45°.
As an alternative thereto, polymers can be used, the surface of which has been chemically modified, such as, for example, by the chemical bonding of hydrophilic substances or by treatment with gas plasma.
To avoid any bacterial contamination the spacing device may also be loaded with bactericidally or bacteriostatically active substances.
In order to ensure the diverse functions of the stent, the design of the matrix system may above all consist of a plurality of polymer layers as the cross-section in
The spacing device may also be already preformed prior to application or else be shaped to its final geometry by processing a precursor. Methods, such as, for example, extrusion or injection moulding are excellently suited to producing preformed spacing devices. For production from precursors polymer films may for example be rolled to form hollow bodies and fixed by a seam.
The materials from which the spacing device can be produced may be biodegradable or else non-biodegradable materials or a combination thereof.
Examples of possible biodegradable materials are polymers of lactic acid or glycolic acid and their copolymers. Further suitable examples are to be found in the literature (K. Park, W. S. W. Shalaby, H. Park, Biodegradable Hydrogels for Medicinal substance Delivery, Technomic Publishing Inc. Lancaster 1993; A. Domb, J. Kost, D. M. Wiseman, Handbook of Biodegradable Polymers, Harwood Academic Publishers, 1997).
While biodegradable materials have the advantage of not having to be removed after application, non-biodegradable materials can be better fixed in the region of use of the spacing device. Examples of such materials are silicones, polyacrylates and polymethacrylates and the copolymers thereof (Eudragit®)), poly(ethylene vinyl acetate) copolymer and other compositions as described in the polymer literature and known for medical applications.
The polymers should preferably be flexible so that they adapt to the wound area. Moreover, they should be elastic enough to remain in the fenestration and should be biocompatible, in other words have good tolerability with respect to cells and tissues. To ensure the mechanical adherence of the spacing device to the fenestration, the polymers mentioned can be combined with other materials, such as for example metals to ensure a reliable seat of the “stent” with smaller wall thicknesses. These metals can be incorporated into the wall of the cylinder.
The polymers can be processed by various industrial methods to form the spacing devices shown in
The casting of polymer solutions is a simple production method (solvent casting). For this purpose the polymers are dissolved in organic solvents and the solution is poured or sprayed onto an inert surface. After evaporation of the solvent dry polymer films loaded with active substance are obtained which can be cut into any, for example rectangular forms.
While tubes are directly obtained by extrusion or injection moulding, small individually adapted tubes can be formed from rectangular polymer films directly before insertion into the patient. This may take place by repeated rolling of the polymer film or by mechanical adhesion or sticking of opposing film edges.
Owing to the type of production, the polymer properties can be controlled such that either smooth or porous surfaces are produced. This influences the rate of active substance administration and optionally the interaction between the spacing device and wound edges.
The surfaces of the spacing device towards the tissue and the secretion side may also be changed such that they optimally do justice to the requirements of their functions. The inside of the cylinder to the cavity of the spacing device may, for example be physico-chemically changed on its surface such that there can be improved wetting with secretion and therefore improved secretion drainage. Examples are the above-mentioned hydrophilising of surfaces or the covalent bonding of hydrophilic substances to the polymer surfaces.
The surface to the tissue side may be chemically changed such that the tissue compatibility is improved. This can be achieved by a coating with materials in the form of thin films or connection or application of functional groups or whole molecules which interact with the biological system. Thus the anchoring of polyethylene glycol chains to the surface leads to a reduced cell attachment and this facilitates the removal of the spacing device and increases it compatibility with the wound tissue.
The active substances can be selected according to need, application, desired property etc. They can also be used in combination. In particular, the stents according to the invention are loaded with medicinal substances.
Substances are generally used as medicinal substances which may influence the behaviour of cells and tissues, in particular they should prevent uncontrolled tissue growth. For this purpose, representatives of the group of glycocorticosteroids are suitable, such as for example cortisol, corisone, prednisone, prednisolone, 6-methylprednisolone, dexamethasone, fludrocortisone, desoxycorticoacetate. Further examples are proteins from the area of cytokines and growth factors which are also said to have some cell growth-inhibiting properties. Moreover, tyrosine kinase inhibitors, antisense-oligonucleotides and mitosis inhibitors such as mitomycin are suitable for eliminating the proliferative influence of growth factors during wound healing.
The active substances can be released from the spacing device over a long time period. Depending on the design and the material used, releases can be carried out for up to several years. Release preferably extends over a time period of 2 to 12 weeks. Principles controlling the release include, apart from the wall thickness expressed as the ratio q, primarily diffusion and polymer swelling for non-biodegradable polymers. When using biodegradable materials, i.e. those which dissolve during use, polymer erosion also plays an important part (Gopferich, Polymer Degradation and Erosion: Mechanismus and Applications, Eur. J. Pharm. Biopharm., 42 (1996) 1-11).
If the spacing device is produced from the preferred non-degradable materials, the active substance is preferably released from the reservoir or a matrix system. In both cases, the active substance is released in the process by diffusion. The release of active substance can be influence by a plurality of factors. By changing the geometry the active substance can be released over different lengths of time. Furthermore, it is possible to control the kinetics of the active substance release by the degree of loading.
The loading, in particular in the embodiment as a matrix system, is preferably in a range up to 30% by weight based on the total system. The minimum loading depends inter alia on the potency of the active substance and on the desired duration of release.
To further influence diffusion additives can be added to the polymer matrix or the polymers. Inert inorganic materials such as, for example silicone dioxide thus lead to a reduction in the rate of release. Depending on the type of polymer the rate of release can be increased by plasticiser additives. During polymer swelling, swelling can be increased by osmotic additives into the polymer and the rate of release can therefore be increased depending on the active substance properties.
To control the active substance release by erosion, the type of biodegradable polymer can be geared to the application. Thus, for example, it is known with poly(D,L-lactide-co-glycolide) that the rate of release and the rate of erosion can be controlled by the increase in the glycolide content.
The subject of the invention is a spacing device (stent) which after surgical opening of the paranasal sinus (mainly the frontal sinus) is inserted into the created fenestration to the nose. The newly developed spacing device prevents a post-operative scarred narrowing in that it combines two conventional treatment attempts for the surgically newly created frontal sinus access:
1. The spacing device acts as a physical barrier which mechanically keeps the access to the frontal sinus open.
2. The spacing device releases medicinal substances which control the growth of the tissue around the newly created access to the front sinus.
The material of the spacing device preferably has the mechanical properties of an elastomer such as, for example silicone, a proven material in ENT surgery for spacing devices. Owing to the preferred geometry which corresponds substantially to that of a hollow cylinder, secretion can drain from the sinuses. Moreover, the material acts as a local release system for medicinal substances such as for example corticosteroids. Owing to the shape and function the stent ensures a firm seat and simultaneously allows optimum secretion drainage. The continuous release of a defined quantity of medicinal substance is preferably ensured over a period of 8 weeks. The anticipated duration in position of the implant is preferably also 8 weeks. For production, films loaded with medicinal material, for example, can be rolled to form a cylinder and stabilised with a surgical seam. The spacing device is inserted intra operationem into the newly created frontal sinus access. If necessary, it is fixed in the operation area by its particular form, the materials used, its construction and/or by a surgical seam to prevent displacement. Apart from the use in fenestrations to the paranasal sinus, use is possible in the middle ear and the trachea.
Production of a Dexamethasone-Loaded Polymer Film
The film has the following composition:
The polymer used, a poly(ethylene-vinyl acetate) copolymer is initially freed of additives which were added during the production of Evatane 40-55. 50 g of Evatane 40-55 are also weighed out into a 500 ml iodine measuring cylinder with a magnetic stirring rod. 250 ml acetone p.a. are measured with a measuring cylinder and added to the polymer. The batch is stirred on the magnetic stirrer for about a week and the acetone is then decanted. The polymer is washed 3 times with 80 ml acetone p.a. and the washing liquid discarded. The extraction and washing procedure is repeated once with acetone and twice with ethanol using the same volumes. The polymer is then dried in a crystallising dish in a laminar airflow box for 48 h and then in a desiccator under vacuum.
17.955 g Evatane 40-55 are then weighed out into a 250 ml iodine value vessel. The dichloromethane is added thereto and stirred on the magnetic stirrer over 12 h. The dexamethasone is dissolved in acetone and added to the polymer solution. The batch is then left to stand for 10 min without stirring to remove air bubbles. The solution is poured into a planar Teflon mould with an area of 15 cm2 and dried in a laminar airflow box over 4 days.
The dried film is drawn from the Teflon mould and cut into pieces of any size. The film thickness is about 0.8 to 1 mm. The polymer films are rolled to form a hollow cylinder and preferably fixed by a seam with a biocompatible seam material at the contact points in such a way that the cylinder does not unwind owing to the elasticity of the material. The small tube formed in this way is then inserted into the fenestration to the paranasal sinus.
Round pieces with a diameter of 1.2 cm in diameter were cut from the film described in Example 1 and the release determined in vitro. The polymer platelets loaded with 0.25% dexamethasone were also stored in closable glass vessels in 10 ml phosphate buffer at 37° C. Samples were removed from the batch at regular intervals and replaced by fresh buffer. The dexamethasone content was determined per HPLC.