Nanosurface

Abstract

The invention relates to a method for modification of a biocompatible component. The method of the invention includes the steps of a) providing a biocompatible component at least partly covered by metallic oxide; and b) treating at least a part of the component, which part is covered by the metallic oxide, with an aqueous composition that includes oxalic acid; whereby a modified metallic oxide, is obtained. The invention also relates to a biocompatible component-including a substrate having a surface with a) a microstructure including pits separated by plateus and/or ridges; and b) a primary nanostructure being superimposed on the microstructure, the primary nanostructure having depressions arranged in a wave-like formation.

Claims

1. A biocompatible component, comprising a substrate having a surface comprising a microstructure comprising pits separated by plateaus and/or ridges said pits, plateaus and/or ridges comprising a primary nanostructure and secondary nanostructure said primary nanostructure comprising a plurality of shallow depressions arranged in a wave-like continuous formation, wherein each shallow depression is defined by an edge, wherein said edge is an essentially circular or oval shape, and said secondary nanostructure comprises discrete projections having the shape of rounded peaks uniformly distributed on the surface structure, wherein said discrete projections comprise a metallic oxide, wherein the secondary nanostructure represents visualization using atomic force microscopy.

2. A biocompatible component according to claim 1, wherein said microstructure has a pit diameter in the range of from 0.5 to 15 m, a depth in the range of from 0.1 to 2.5 m, and a distance between mutually adjacent pits in the range of from 0 to 10 m.

3. The biocompatible component according to claim 1, wherein said shallow depressions of said primary nanostructure have a diameter in the range of from 10 nm to 1 m, and a depth in the range of from 10 nm to 300 nm.

4. The biocompatible component according to claim 1, wherein said diameter of a shallow depression of said primary nanostructure is smaller than the diameter of a pit of said microstructure on which said shallow depression is superimposed, and said depth of a shallow depression of said primary nanostructure is smaller than the depth of a pit of said microstructure on which said shallow depression is superimposed.

5. The biocompatible component according to claim 1, wherein at least part of said edge of a shallow depression of said primary nanostructure constitutes at least part of an edge of another shallow depression of said primary nanostructure.

6. The biocompatible component according to claim 1, wherein said component has been subjected to a mechanical surface treatment.

7. The biocompatible component according to claim 6, wherein said mechanical surface treatment comprises blasting.

8. The biocompatible component according to claim 1, wherein said substrate at least partly consists of titanium or a titanium alloy.

9. The biocompatible component according to claim 1, wherein said substrate consists of titanium.

10. The biocompatible component according to claim 1, wherein said peaks of the secondary nanostructure have a peak diameter in the range of from 20 to 550 nm, an average peak height in the range of from 5 to 200 nm, and a peak-to-peak distance in the range of from 10 to 450 nm.

11. The biocompatible component according to claim 1, wherein said peaks of the secondary nanostructure have a peak density in the range of from 15 to 150 peaks/m.sup.2.

12. The biocompatible component according to claim 1, wherein said discrete projections comprise titanium oxide.

13. A biocompatible component according to claim 1, wherein said surface further comprises a bone-growth enhancing material comprising metal ions or a salt thereof selected from the group consisting of titanium ions, magnesium ions, calcium ions, lithium ions, strontium ions, and any combination thereof.

14. The biocompatible component according to claim 13, wherein said bone-growth enhancing material comprises lithium ions.

15. The biocompatible component according to claim 13, wherein said bone-growth enhancing material comprises strontium ions.

16. The biocompatible component according to claim 1, further comprising a bone-growth enhancing material.

17. A method for implanting a biocompatible component into a human or animal body comprising the steps of i) providing a biocompatible component according to claim 1 or 13; and ii) implanting said biocompatible component into the body of a human or an animal.

18. The method according to claim 17, wherein said component is implanted into a periodontal area of said body of a human or an animal.

19. A biocompatible component, comprising a metal substrate having a surface of metal oxide, said surface having a hierarchical surface topography comprising a microstructure comprising pits separated by plateaus and/or ridges, said pits having a pit diameter x1 in the range of from 0.5 to 15 m, said microstructure further comprising; a primary nanostructure comprising shallow depressions arranged in a wave-like formation, said depressions having a diameter x2 in the range of from 10 nm to 1 m, wherein an individual pit of the microstructure comprises multiple depressions of the primary nanostructure; and a secondary nanostructure comprising discrete projections with peaks wherein the discrete projections comprise a metallic oxide and wherein said secondary nanostructure has an average peak height of from 5 to 200 nm and a peak density of from 15 to 150 peaks/m.sup.2.

20. The biocompatible component according to claim 19, wherein said secondary nanostructure has a peak-to-peak distance in the range of from 10 to 450 nm and said peaks have a diameter in the range of from 20 to 550 nm.

21. The biocompatible component according to claim 19, wherein said peaks have a diameter in the range of from 20 to 150 nm.

22. The biocompatible component according to claim 19, wherein said secondary nanostructure has an average peak height in the range of from 5 to 100 nm.

23. The biocompatible component according to claim 19, wherein said secondary nanostructure has a peak-to-peak distance is in the range of from 40 to 200 nm.

24. The biocompatible component according to claim 19, wherein said secondary nanostructure has a peak density is in the range of from 50 to 130 peaks/m.sup.2.

25. The biocompatible component according to claim 19, wherein said substrate at least partly consists of titanium or a titanium alloy.

26. The biocompatible component according to claim 19, wherein said substrate consists of titanium.

27. The biocompatible component according to claim 19, wherein said discrete projections comprise titanium oxide.

28. A method for implanting a biocompatible component into a human or animal body comprising the steps of: i) providing a biocompatible component according to claim 19; and ii) implanting said biocompatible component into the body of a human or animal.

29. The method according to claim 28, wherein said component is implanted into a periodontal area of said body of the human or animal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic illustration defining the parameters used in respect of the microstructure.

(2) FIG. 2 is a schematic illustration defining the parameters used in respect of the primary nanostructure.

(3) FIG. 3 is a schematic illustration defining the parameters used in respect of the secondary nanostructure.

(4) FIG. 4 is a schematic illustration defining the angles used in respect of the microstructure and the primary nanostructure, respectively.

(5) FIG. 5a is a scanning electron microscopy image of a titanium sample according to the invention.

(6) FIG. 5b is a scanning electron microscopy image of a titanium sample according to the invention, wherein diameters of the microstructure are marked.

(7) FIG. 6a is a scanning electron microscopy image of a titanium sample according to the invention, wherein depressions of the primary nanostructure are marked.

(8) FIG. 6b is a scanning electron microscopy image of a titanium sample according to the invention, wherein diameters of the primary nanostructure are marked.

(9) FIG. 7 is a is a scanning electron microscopy image of a titanium sample subjected to a conventional blasting technique.

(10) FIG. 8 is a scanning electron microscopy image of a blasted titanium sample according to the invention.

(11) FIG. 9 is a scanning electron microscopy image of a titanium sample according to the invention.

(12) FIG. 10 is an atomic force microscopy 3D image of a titanium sample according to the invention.

(13) FIG. 11 is a scanning electron microscopy image of a blasted titanium sample according to the invention, wherein elements of the microstructure are marked.

(14) FIG. 12a is a scanning electron microscopy image of a titanium reference sample treated for 5 minutes in a mixture of hydrofluoric acid and oxalic acid.

(15) FIG. 12b is a scanning electron microscopy image of a titanium reference sample treated for 30 minutes in a mixture of hydrofluoric acid and oxalic acid.

(16) FIG. 12c is a scanning electron microscopy image of a titanium sample treated in hydrofluoric acid and subsequently in oxalic acid.

(17) FIG. 13a is a graph showing the distribution of microstructure pit diameter of a titanium sample according to the invention.

(18) FIG. 13b is a graph showing the distribution of microstructure pit depth of a titanium sample according to the invention.

(19) FIG. 13c is a graph showing the distribution of distances between adjacent pits of the microstructure of a titanium sample according to the invention.

(20) FIG. 14a is a graph showing the distribution of microstructure pit diameter of a blasted titanium sample according to the invention.

(21) FIG. 14b is a graph showing the distribution pit depth of a blasted titanium sample according to the invention.

(22) FIG. 14c is a graph showing the distribution of distances between adjacent pits of the microstructure of a blasted titanium sample according to the invention.

(23) FIG. 15a is a graph showing the distribution of primary nanostructure depression diameter of a titanium sample according to the invention.

(24) FIG. 15b is a graph showing the distribution of primary nanostructure depression depth of a titanium sample according to the invention.

(25) FIG. 16a is a graph showing the distribution of primary nanostructure depression diameter of a blasted titanium sample according to the invention.

(26) FIG. 16b is a graph showing the distribution of primary nanostructure depression depth of a blasted titanium sample according to the invention.

(27) FIG. 17a is a graph showing the distribution of secondary nanostructure peak diameter of a titanium sample according to the invention.

(28) FIG. 17b is a graph showing the distribution of secondary nanostructure peak height of a titanium sample according to the invention.

(29) FIG. 17c is a graph showing the distribution of secondary nanostructure peak-to-peak distance of a titanium sample according to the invention.

(30) FIG. 18 is a graph showing the proliferation of cells grown for 7 days on a commercial titanium implant surface and on surfaces according to the invention, respectively.

(31) FIG. 19 is a graph showing the production of alkaline phosphatase after 7 days of cell cultivation on a commercial titanium implant surface and on surfaces according to the invention, respectively.

(32) FIG. 20a is a scanning electron microscopy image of cells grown for 36 hours centrally on a commercial implant surface.

(33) FIG. 20b is a scanning electron microscopy image of cells grown for 36 hours on a surface of a component according to the invention.

(34) FIG. 20c is a scanning electron microscopy image of cells grown for 36 hours on a surface of a component according to the invention.

(35) FIG. 21 is a graph showing the production of prostaglandin E2 after 7 and 14 days of cell cultivation on a commercial titanium implant surface and on surfaces according to the invention, respectively.

(36) FIG. 22 is a graph showing removal torque test results for implants according to the invention and a commercial titanium implant in a rabbit model.

(37) FIG. 23a is a histology section image of an implant according to the invention in a rabbit model six weeks after implantation.

(38) FIG. 23b is a histology section image of a commercial titanium implant in a rabbit model six weeks after implantation.

(39) FIG. 24a is a histology section image of an implant according to the present disclosure in a rabbit model six weeks after implantation.

(40) FIG. 24b is a histology section image of a commercial titanium implant in a rabbit model six weeks after implantation.

(41) FIG. 25a is a scanning electron microscopy image of a reference titanium sample representing the surface of a commercial titanium implant.

(42) FIG. 25b is a scanning electron microscopy image of the sample shown in FIG. 25a after immersion in simulated body fluid (SBF).

(43) FIG. 26a is a scanning electron microscopy image of a titanium sample treated according to step b of the invention.

(44) FIG. 26b is a scanning electron microscopy image of the sample shown in FIG. 26a after immersion in simulated body fluid (SBF).

(45) FIG. 27a is a scanning electron microscopy image of a titanium sample treated according to steps b and c of the invention.

(46) FIG. 27b is a scanning electron microscopy image of the sample shown in FIG. 27a after immersion in simulated body fluid (SBF).

(47) FIG. 28 is a graph Showing the residual titanium signal after apatite formation of a reference sample and of samples treated according to the invention as measured by energy dispersive spectroscopy.

(48) FIG. 29 is a graph presenting the calculated Ca/P ratios after apatite formation of a reference sample and of samples treated according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(49) As used herein, the term biocompatible component includes within its scope any component which is intended for long-term or short-term contact with living tissue and which, upon said contact, does not evoke significant adverse biological reaction of the tissue. One example of a biocompatible component is an implant, such as a dental implant.

(50) As used herein the term implant includes within its scope any device of which at least a part is intended to be implanted into the body of a vertebrate animal, in particular a mammal, such as a human. Implants may be used to replace anatomy and/or restore any function of the body.

(51) Generally, an implant is composed of one or several implant parts. For instance, a dental implant usually comprises a dental fixture coupled to secondary implant parts, such as an abutment and/or a restoration tooth. However, any device, such as a dental fixture, intended for implantation may alone be referred to as an implant even if other parts are to be connected thereto.

(52) As used herein, the term passivating (metallic) oxide refers to naturally formed oxide, also referred to as native oxide, which is stable, does not grow substantially thicker over time and which prevents any substantial chemical reaction of the underlying substrate with an external agent. Passivating titanium oxide formed on titanium in contact with atmospheric oxygen generally has a thickness of 2-5 nm.

(53) As used herein, the term bone-growth enhancing material includes within its scope any substance which is capable of promoting bone formation, (e.g., promoting adhesion, proliferation and differentiation of osteoblasts or pre-osteoblasts; promoting the production of bone matrix components, secretion of bone matrix components, mineralisation of bone matrix; and inhibition of osteoclast activity), either alone or in combination with other substances.

(54) As used herein, the term microstructure refers to a physical structure of dimensions generally ranging from 0.5 m to 100 m, and the term nanostructure refers to a physical structure of dimensions generally ranging from 0.1 nm to 500 nm.

(55) The biocompatible component of the invention may be a dental component, for example an implant, a fixture, an abutment, or combinations thereof, such as a one-piece implant. The biocompatible component may also be an orthopaedic component, such as a hip joint component intended for implantation into the neck of the femur of a patient.

(56) The biocompatible component of the invention may consist of any suitable material, such as a metal, e.g. titanium or an alloy thereof, zirconium or an alloy thereof, hafnium or an alloy thereof, niobium or an alloy thereof, tantalum or an alloy thereof, a chromium-vanadium alloy or any combination of these materials, or a non-metal. The biocompatible component may be provided with a metallic layer, for example an applied metallic surface layer covering a non-metallic body or a body partly consisting of a non-metallic material. Examples of non-metallic materials comprise a ceramic, a plastic and a composite material.

(57) The metallic oxide may be a naturally air-formed oxide, or it may be formed in any kind of treatment prior to the method according to the invention.

(58) The biocompatible component may be subjected to any kind of pretreatment in order to create a desired substrate surface for further modification according to the inventive method. For example, the component may be pretreated by a mechanical, chemical or thermal treatment, or any combination thereof, to obtain a desired initial surface composition or roughness. A mechanical treatment may for instance comprise a blasting process. A chemical treatment may for instance comprise a cleaning or degreasing process.

(59) In one aspect, the present invention relates to a method for modification of a biocompatible component.

(60) According to the inventive method, at least a part of the biocompatible component is subjected to treatment with an aqueous composition comprising oxalic acid, whereby a modified metallic oxide is obtained (referred to as step b). In this treatment, the modified metallic oxide is dissolved and the underlying substrate is etched while new oxide is formed on the biocompatible component. The oxide dissolution and reoxidation processes occur simultaneously.

(61) The part of the biocompatible component to be treated is at least partly covered by said metallic oxide. In embodiments of the invention, step b is performed by placing the component in an aqueous solution of oxalic acid at an elevated temperature under vigorous agitation for a period of time. Alternatively, only part of the component may be immersed in the composition, e.g. by dipping. A part of the component not intended to be treated may be masked during the treatment.

(62) The pH of the composition of step b should be acidic, such as pH 5 or below, pH 2 or below, or pH 0.7 or below. Preferably, the pH is as low as possible in view of processing convenience.

(63) The aqueous composition comprising oxalic acid may be an aqueous solution comprising oxalic acid at a concentration in the range of from about 0.001 to about 5 M, e.g., a solution of oxalic acid at a concentration within said range. Preferably, the concentration of oxalic acid in the composition is in the range of 0.01 to 2 M, more preferably in the range of fom 0.1 to 2 M and most preferably about 1 M.

(64) For the purpose of step b, at least a part of the biocompatible component may be immersed in the composition comprising oxalic acid for a period of time in the range of from about 5 to about 60 minutes, for example from 20 to 40 minutes. Typically, the duration of the treatment of step b is about 25 minutes or about 30 minutes. The treatment of step b is considered to be completed at the moment when the component is removed from the aqueous composition comprising oxalic acid.

(65) The temperature of the aqueous composition may be in the range of from about 20 C. to about 100 C. Typically, the temperature of the aqueous composition comprising oxalic acid may be in the range of from 60 C. to 90 C., for example about 80 C.

(66) As an example, the treatment of step b may be performed using an concentration of oxalic acid of about 1 M at a temperature of 80 C. for 30 minutes.

(67) When a titanium component is used, the modified oxide obtained in step b is more reactive than passivating titanium oxide formed in air, and it has a higher water content than passivating titanium oxide formed in air. Possibly, the modified titanium oxide of the invention is more amorphous than passivating titanium oxide formed in air or formed in a chemical cleaning pretreatment. The surface structure of the modified oxide obtained in step b comprises a microstructure and a primary nanostructure of which examples are shown in FIGS. 5 and 6, and which will be described in more detail below.

(68) The surface of the biocompatible component obtained in step b has a colour which is lighter and duller than the metallic grey colour of the surface of the component before treatment according to the method of the invention. However, there is a difference in colour between a component according to the invention which was pretreated by blasting, and a component according to the invention which was simply machine worked, the blasted component having a whiter colour than the machine worked component. The altered colour may be used as an indication that step b has been completed. However, the altered colour is more clearly seen after 2 minutes of washing in an ultrasonic bath.

(69) Following step b, at least a part of the modified oxide may be subjected to treatment with a second aqueous composition comprising at least one material selected from the group consisting of ionised fluorine and ionised chlorine, and at least one acid (referred to as step c). By step c, part of the modified metallic oxide formed in step b dissolves and subsequently precipitates to form a secondary nanostructure comprising uniformly distributed rounded projections of metallic oxide which are superimposed on said microstructure and primary nanostructure. Alternatively, any other compound which forms a complex with the metal of the dissolving metallic oxide may be used. Fluorine and chlorine are known titanium complexing agents.

(70) When the component is kept at a temperature of at least 0 C. at normal atmospheric pressure and in an oxygen-containing atmosphere such as air, step c should be performed within a relatively short period of time after the completion of step b. Step b is considered to be completed as soon as the component is removed from the aqueous composition of step b. More particularly, step c should be performed before the modified metallic oxide obtained in step b is covered by passivating oxide formed thereon. The passivating oxide is considered to be formed when it prevents any substantial chemical reaction of the underlying material with an external agent. The reactivity of the modified oxide obtained in step b is vital to achieving a uniform distribution of the rounded peaks of the secondary nanostructure. It is believed that during the step c treatment, the acid attacks the modified oxide at a multitude of active sites to dissolve the oxide. Hydrogen gas generated in this process increases the pH locally at each active site. The locally elevated pH causes metallic oxide to precipitate at the active site, provided that the aqueous composition has a sufficiently high concentration of metallic material. Dissolution of modified titanium oxide obtained in step b may provide a sufficiently high titanium concentration for the titanium oxide to precipitate. As a passivating oxide forms gradually over time in the presence of oxygen, a shorter time interval between step b and step c will improve the final result of step c when the component is kept at a temperature of at least 0 C., e.g., room temperature (15 to 25 C.), at normal atmospheric pressure and in an oxygen-containing atmosphere. Thus, under such conditions, the interval between step b and step c is preferably kept as short as possible. Step c may be perfomed up to within 180 hours after the completion of step b, for example 72 hours, 36 hours, 24 hours or 1 hour after step b. Preferably, step c is performed within 30 minutes or less after the completion of step b, more preferably within 10 minutes or less, and most preferably within 3 minutes or less after the completion of step b. However, if the component is kept in an inert atmosphere or otherwise prevented from forming a passivating oxide surface, the time interval between step b and step c may be considerably longer. To avoid the formation of a passivating oxide, any atmosphere having a reduced amount of reactive oxygen, compared to normal air, may be used. For example, following step b, the component may be placed in an inert gas such as nitrogen, helium, neon, argon, krypton, xenon or radon. Alternatively, the component may be placed in an atmosphere of reduced pressure or in vacuum. Alternatively, the component may be cooled or frozen. Any combination of the above strategies for partly or completely inhibiting the formation of a passivating oxide may also be used. For example, the component may be subjected to step b and subsequently frozen or placed in an inert gas for an extended period of time, and then restored to normal conditions (a temperature of at least 0 C. at normal atmospheric pressure) in an oxygen-containing atmosphere. In such cases, the time between step b and step c spent by the component under said normal conditions in an oxygen-containing atmosphere should be 180 hours or less, for example 72 hours or less, 36 hours or less, 24 hours or less, 1 hour or less, 30 minutes or less, 10 minutes or less, or 3 minutes or less.

(71) In embodiments of the invention, step c is performed by immersing the component in an aqueous solution of hydrofluoric acid. Alternatively, only part of the component may be immersed in the composition, e.g. by dipping. A part of the component not intended to be treated may be masked during the treatment.

(72) The aqueous composition comprises at least one material selected from the group consisting of ionised fluorine and ionised chlorine, and at least one acid. The aqueous composition may be an aqueous solution having a pH in the range of from 0.5 to 5, preferably from 1 to 3 M, and more preferably about 2. The concentration of ionised fluorine and/or chlorine may be in the range of from about 0.05 to 0.5 M. For example, the composition may be a solution of hydrofluoric acid (HF) having a concentration within said range. Preferably, a concentration of hydrofluoric acid in the range of from about 0.1 to 0.3 M, and more preferably about 0.1 M, is used.

(73) The step c treatment is considered to be starting when the acid may be observed to act on the substrate surface. This activity may be detected by the formation of hydrogen gas at the component surface, which usually takes place after about 20-30 seconds at room temperature. Thus, by the term active treatment is meant treatment which is performed starting with the formation of the first bubble of hydrogen gas. The active treatment time of step c is in the range of from 10 seconds to 60 minutes; such as from 10 seconds to 3 minutes, from 10 seconds to 2 minutes, from 10 to 60 seconds, from 10 to 50 seconds, from 10 to 40 seconds, and from 10 to 30 seconds.

(74) Step c may be performed at ambient temperature. Typically, the aqueous composition of step c may have a temperature in the range of from 15 to 25 C., e.g. a temperature in the range of from 18 to 23 C.

(75) As an example, the treatment of step c may be performed using hydrofluoric acid at a concentration of about 0.1 M at room temperature for an active treatment time of 40 seconds.

(76) It will be appreciated that the adjustment of any one of the parameters treatment time, temperature, pH and concentration may require appropriate adjustment of any other one of said pararametres within the above-mentioned ranges in order to obtain an acceptable result.

(77) By step c, the hierarchical surface structure obtained in step b is generally maintained, although its finer structures may be partly dissolved. The surface structure obtained after step c is shown in FIGS. 8 and 9 and will be described in more detail below. In embodiments of the invention, metallic oxide originating from the dissolution of modified metallic oxide obtained in step b precipitates to form a secondary nanostructure comprising uniformly distributed rounded peaks on top of the microstructure and the primary nanostructure. In embodiments of the invention, the peaks of the secondary nanostructure thus consist of metallic oxide. Soluble metal compounds may also be separately added to the aqueous composition of step c in order to increase the metal concentration of the step c composition.

(78) Optionally, the compositions used in step b and step c may comprise a bone-growth enhancing material. The bone-growth enhancing material may comprise metal ions, such as titanium ions, magnesium ions, calcium ions, litium ions and/or strontium ions, or a salt thereof. These ions may be separately added to the composition. For example, either the composition of step b or the composition of step c may comprise any of the above metal ions. Alternatively, both compositions may comprise metal ions. When both compositions comprise metal ions, they may comprise the same species or different species of metal ions. By incorporation of the above metal ions or any combination thereof, a modified surface may be obtained comprising said ions and/or salt(s) thereof, which has altered chemical properties. Thus the biocompatibility of the component may be improved and the osseointegration of the component may be stimulated.

(79) In particular, the inventors have found that lithium or strontium ions locally administered in bone tissue has a local effect on the bone formation and bone mass in said bone tissue. It has further been found that an implant comprising a surface containing and/or releasing ionised lithium or strontium provides an improved rate of bone formation, and thus an improved rate of attachment between bone tissue and the implant in comparison to an implant comprising a surface oxide containing, for instance, ionised calcium or magnesium. Thus, in embodiments of the invention, both the compositions of step b and step c, or the composition of step b only, comprise(s) ionised lithium or strontium or a combination thereof. Alternatively, only the composition of step c comprises ionised lithium or strontium or a combination thereof.

(80) Alternatively, a bone-growth enhancing material, such as ionised lithium or strontium, may be applied on the surface of the component after the performance of step b or step c according to the invention.

(81) In another aspect, the invention relates to a biocompatible component obtainable by the method described above, and to a method for implanting the biocompatible component into the body of a human or an animal. For example, the biocompatible component may be implanted into a periodontal area of the body of a human or an animal.

(82) In another aspect, the invention relates to a biocompatible component having a hierarchical surface structure comprising a microstructure, a primary nanostructure superimposed on said microstructure and optionally a secondary nanostructure superimposed on said primary nanostructure.

(83) The terms depth (h.sub.1), diameter (x.sub.1) and distance (D.sub.1) in respect of a profile of the microstructure are defined in FIG. 1. The depth (h.sub.1) of a pit is defined as the distance between an imaginary line drawn between two adjacent peaks and the intermediate surface at its lowest point. If no well-defined peaks are present, the imaginary line is drawn between those points where the surface profile starts to deviate from an essentially flat surface profile (a plateau). The diameter (x.sub.1) of a pit and the distance (D.sub.1) between adjacent pits are the distances between said adjacent points as defined in FIG. 1. In FIG. 1, a superimposed primary nanostructure is also schematically provided on the microstructure. The terms depth (h.sub.2) and diameter (x.sub.2) in respect of the primary nanostructure are correspondingly defined in FIG. 2.

(84) The terms height (h.sub.3), diameter (x.sub.3) and peak-to-peak distance in respect of the secondary nanostructure are defined in FIG. 3. The peak height is defined as the distance between an imaginary line drawn between two adjacent peaks and the intermediate surface at its lowest point. The peak diameter (x.sub.3) is measured between those points of the peak where the surface profile starts to deviate from an essentially flat surface profile.

(85) In FIG. 4, the angle in respect of a profile of the microstructure and the angle in respect of a profile of the primary nanostructure are defined. The angle is defined as the angle between two imaginary lines, one of which representing the slope of a wall of a pit of the microstructure at the point where the surface profile starts to deviate from an essentially flat surface profile (P.sub.1a), and one of which representing the slope of an adjacent wall of an adjacent pit of the microstructure at the point where the surface profile starts to deviate from an essentially flat surface profile (P.sub.1b). Said mutually adjacent pits may thus be separated by a plateau. Accordingly, in the case where two adjacent pits are separated by a peak, the imaginary lines represent the inclinations of the walls at said peak. The angle is defined as the angle between two imaginary lines representing the slope of a wall of a depression of the primary nanostructure at its inflection point (P.sub.2a) and the slope of an adjacent wall of an adjacent depression of the primary nanostructue at its inflection point (P.sub.2b), respectively. In the case where two concave depressions are separated by a peak, the inflection point is thus located at said peak.

(86) The microstructure and the primary nanostructure of the inventive component are essentially obtained in step b of the method described above. As described above, step b provides a modified oxide surface which is thickened, reactive, and has a white or whitish colour. FIG. 5a is a SEM image of a component after step b of the method of the invention showing said microstructure and said primary nanostructure. The component was pretreated by blasting. As is seen in this image, the microstructure comprises pore-like depressions or pits of different sizes. FIG. 5b is a SEM image of a component after step b according to the invention in which the diameters of some of the pits of the microstructure have been marked.

(87) FIGS. 13 and 14 present the distributions of pit diameter, pit depth and distance between mutually adjacent pits of the microstructure. For example, a pit of the microstructure may have a diameter x.sub.1 in the range of from 0.5 to 15 m, preferably from 1 to 10 m, and more preferably from 1 to 5 m; and a depth h.sub.1 in the range of 0.1 to 2.5 m, preferably from 0.1 to 1 m, and more preferably from 0.1 to 0.7 m. Adjacent pits are typically separated by a plateau or a ridge, which may have a diameter of up to 10 m, preferably up to 5 m, and more preferably up to 3 m. Thus, the distance D.sub.1 between adjacent pits may be up to 10 m, up to 5 m, or up to 3 m. However, as is often the case with a separating ridge, two adjacent pits may be considered not to be separated by any distance at all.

(88) As seen in FIG. 5, the general shape of an individual pit of the micro-structure may be roughly circular or oval, or it may be irregular. The micro-structure may also comprise undercuts. Furthermore, a pit of a larger diameter may comprise one or several pits of a smaller diameter.

(89) The microstructure may have an angle as defined above and in FIG. 4 in the range of from 20 to 130; preferably from 30 to 120, more preferably from 40 to 110, and most preferably from 50 to 100.

(90) On the above described microstructure, a superimposed primary nanostructure is provided. The primary nanostructure may be seen in FIG. 5, and is further illustrated in FIG. 6, in which elements of the primary nanostructure have been marked. The primary nanostructure may be described as a wave-like continuous structure. The primary nanostructure comprises a multitude of shallow depressions in the walls and bottoms of the pits of the microstructure and in the plateaus and/or ridges separating the pits of the microstructure. The diameter x.sub.2 of the depressions of the primary nano-structure may be in the range of from 10 nm to 1 m, preferably from 10 nm to 600 nm, and more preferably from 10 nm to 500 nm; and the depth h.sub.2 of the depressions of the primary nanostructure may be in the range of 10 to 300 nm, preferably from 30 to 150 nm. Typically the depressions are shallow, meaning that the diameter of a depression exceeds the depth thereof. The depressions of the primary nanostructure have an essentially circular or oval shape. FIGS. 15 and 16 present the diameter and depth distributions of the depressions of the primary nanostructure.

(91) The depressions of the primary nanostructure may have a distinct boundary or edge. However, a depression of the primary nanostructure may also have a wall which rises from the bottom of said depression and then softly passes into the next depression without forming a distinct boundary therebetween. In either of the above cases, however, there is no definable distance separating the boundary of a depression of the primary nano-structure from the boundary of another depression. Rather, the depressions are juxtaposed to form a wave-like pattern having a quite regular aspect. The primary nanostructure may have an angle as defined above and in FIG. 4 in the range of from 80 to 160; preferably from 90 to 150, more preferably from 100 to 140, and most preferably from 110 to 130.

(92) As mentioned above, the primary nanostructure is superimposed on the primary microstructure. Furthermore, the diameter and depth, respectively, of a primary nanostructure each is smaller than the corresponding dimension of an individual pit of the microstructure. Thus, an individual pit of the microstructure typically comprises multiple depressions of the primary nanostructure. For example, a pit of the microstructure may comprise from about 5 to about 50 of said depressions. Furthermore, a part of a boundary of a depression of the primary nanostructure typically constitutes a part of a boundary of another depression of the primary nanostructure.

(93) FIG. 8 and FIG. 9 are SEM images of a modified component according to the invention. In FIG. 8, the sample was pretreated by blasting, whereas in FIG. 9, the sample was simply machine worked. In these figures, a secondary nanostructure which is superimposed on the above-mentioned microstructure and primary nanostructure can be seen. FIG. 10 is an image taken by atomic force microscopy (AFM) further illustrating the secondary nanostructure. As is seen in FIG. 10, the secondary nanostructure comprises discrete projecting elements having the shape of rounded peaks. The nanopeaks are densely and uniformly distributed on the underlying surface structure. For example, the number of peaks per unit area may be in the range of from 15 to 150 peaks/m.sup.2, and preferably from 50 to 130 peaks/m.sup.2.

(94) FIG. 17 presents the peak diameter, the average peak height and the peak-to-peak distance distributions of the secondary nanostructure. Typically, the average peak height h.sub.3 of the secondary nanostructure is in the range of from 5 to 200 nm, and preferably from 5 to 100 nm. The diameter x.sub.3 of an individual peak of the secondary nanostructure typically is in the range of from 20 to 550 nm, and preferably from 20 to 150 nm. The peak-to-peak distance D.sub.3 typically is in the range of from 10 to 450 nm, and preferably from 40 to 200 nm. FIG. 11 presents a SEM image of a component comprising the microstructure, the primary nanostructure and the secondary nanostructure, wherein pits of the microstructure have been marked.

(95) In embodiments of the invention, in which a component of the invention has been subjected to blasting prior to the oxalic acid treatment, a superior surface structure exists on which the microstructure is superimposed. The surface structure of a component of the invention pretreated by blasting typically comprises large pits having a length in the range of from 10 to 70 m and a depth in the range of from 3 to 20 m. Typically, the large pits have a generally oval shape. The distance between adjacent pits may be in the range of from 1 to 20 m. Superimposed on this large pit structure is the microstructure mentioned above. Thus, the sides and bottoms of the large pits and the surfaces between the large pits comprise the pits and the separating plateaus and/or ridges of the above mentioned microstructure. A SEM image of a conventional blasted surface is presented in FIG. 7. A blasting pretreatment affects the dimensions of the subsequently formed microstructure, primary nanostructure and optional secondary nanostructure. In a component according to the invention which was subjected to blasting, the subsequently formed microstructure generally had somewhat larger dimensions than the microstructure of a component according to the invention which was simply machine worked, and the subsequently formed primary nanostructure generally had somewhat smaller dimensions than the primary nanostructure of a component according to the invention which was simply machine worked. Additionally, the diameters of both the microstructure and the primary nanostructure, and the depths of the microstructure were more uniform in a blasted component, as is demonstrated by the standard deviation values shown in Table 1, than the corresponding features of a machine worked component.

(96) In another aspect, the invention relates to a method for implanting a biocompatible component into the human or animal body. The method comprises the step of i) providing a biocompatible component as described above, and ii) implanting the component into the body of a human or an animal. For example, the biocompatible component may be implanted in a periodontal area of said body of a human or an animal.

EXAMPLES

Example 1

Surface Modification

(97) (i) Sample Preparation

(98) Titanium samples having the shape of a coin (machine worked and blasted, respectively), a fixture (blasted) and an abutment (machine worked) were cleaned by a conventional chemical treatment. The samples were immersed in an 1 M aqueous solution of oxalic acid and left at 80 C. for 30 minutes under vigorous agitation. After 30 minutes the samples were removed from the oxalic acid solution and rinsed in water followed by rinsing in water in an ultrasonic bath for 2 minutes. Approximately 10 minutes after rinsing, the samples were immersed in 0.1 M aqueous solution of hydrofluoric acid (HF) at room temperature and agitation until the start of active dissolution, followed by an additional active treatment time of 40 seconds. Next, the samples were removed from the HF solution and rinsed in water followed by rinsing in water in an ultrasonic bath for 5 minutes. The samples were dried in air at room temperature for about 60 minutes before sterilisation.

(99) (ii) Surface Topology Measurements

(100) Scanning electron microscopy (SEM) was perfomed using ESEM XL 30 (FEI) on samples after rinsing following step b and after drying following step c. Stereo images using magnifications between 500 and 15000 were taken and evaluated by the MeX 5.0 programme (Alicona). No filters were used. Depths and diameters of the pits of the microstructure and the depressions of the primary nanostructure and distances between adjacent pits of the microstructure were determined. The results are presented in FIG. 13a-c (machine worked sample) and FIG. 14a-c (blasted sample) for the primary microstructure and in FIG. 15 a-b (machine worked sample) and FIG. 16 a-b (blasted sample) for the primary nanostructure. SEM images taken after step b are presented in FIGS. 5a-b and 6a-b. SEM images taken after sterilisation are presented in FIGS. 8, 9 and 11.

(101) TappingMode atomic force microscopy (AFM) was performed using a Nanoscope IIIa instrument (Digital Instruments). The secondary nanostructure of three samples according to the invention (machine worked) were analysed at two points per sample, each point located approximately 1 mm from the sample edge. The area of analysis was 2 m2 m. Peak heights, peak diameters, peak-to-peak distances and the number of peaks/m.sup.2 were determined. Said dimensions were measured in mm and converted to nm using the scale provided in the profile plots obtained. The distributions of peak height, peak diameter and peak-to-peak distance, respectively, are presented in FIG. 17a-c.

(102) Table 1 summarizes the maximum, minimum and average values of the dimensions determined for the microstructure and primary nanostructure for blasted and machine worked components, respectively, determined by SEM/MeX 5.0. The maximum, minimum and average values determined for the secondary nanostructure of a machine worked component by AFM are also presented.

(103) TABLE-US-00001 TABLE 1 Surface structure dimensions for blasted and machine worked samples according to the invention. Machine Blasted sample worked sample Microstructure Diameter (x.sub.1) max 6.8 9.83 (m) min 0.9 3.74 average 2.97 2.24 SD 1.26 1.59 Depth (h.sub.1) max 2.1 1.27 (m) min 0.1 0.01 average 0.55 0.34 SD 0.45 0.25 Distance (D.sub.1) max 3.3 7.99 (m) min 0.4 0.0 average 1.60 1.54 SD 0.87 1.44 Primary nanostructure Diameter (x.sub.2) max 1130 890 (nm) min 9 231 average 353 506 SD 256 186 Depth (h.sub.2) max 220 295 (nm) min 9 33 average 74 117 SD 46 48 Secondary nanostructure Diameter (x.sub.3) max n/a 253.7 (nm) min n/a 14.9 average n/a 32.4 SD n/a 22.9 Height (h.sub.3) max n/a 129.4 (nm) min n/a 3.0 average n/a 32.4 SD n/a 22.9 Peak-to-peak max n/a 388.1 distance (D.sub.3) min n/a 29.9 (nm) average n/a 128.4 SD n/a 54.9

Comparative Example 1a

(104) Blasted titanium samples (coin-shaped) were immersed in an aqueous solution comprising 0.1 M hydrofluoric acid and 1 M oxalic acid at room temperature and agitation for 5, 15, 30 and 42 minutes, respectively. The samples were removed from the solution and rinsed in water followed by rinsing in water in an ultrasonic bath for 2 minutes. After drying of the samples, the surface topography was examined by scanning electron microscopy (ESEM XL 30, FEI).

(105) As a result, 5 minutes of the above treatment yielded samples having partly etched regions and non-uniformly distributed projecting elements. Samples taken after 15 minutes exhibited a relatively flat, etched surface structure comprising sparsely projecting elements. The surface of samples taken after 30 minutes had a striped appearance and comprised small projecting elements and also some unidentified particles. A SEM image of a dried sample treated for 5 minutes is presented in FIG. 12a, and a SEM image of a dried sample treated for 30 minutes is presented in FIG. 12b.

Comparative Example 1b

(106) Titanium samples were immersed in a 0.1 M aqueous solution of HF at room temperature and agitation until the start of active dissolution, followed by an additional treatment time of 40 s. Next, the samples were removed from the HF solution and rinsed in water followed by rinsing in water in an ultra-sonic bath for 5 minutes. Approximately 10 minutes after rinsing the samples were immersed in an 1 M aqueous solution of oxalic acid and left at 80 C. for 30 minutes under vigorous agitation. After 30 minutes the samples were removed from the oxalic acid solution and rinsed in water followed by rinsing in water in an ultrasonic bath for 2 minutes. The samples were allowed to dry for 1 hour at room temperature.

(107) An image were taken of a dried sample by scanning electron micro-scopy (ESEM XL 30, FEI). The result is presented in FIG. 12c.

Example 2

Cell Proliferation and Activity

(108) Cell proliferation and production of alkaline phosphatase (ALP) and prostaglandin E2 (PGE2), respectively, was investigated for human osteo-blast cells grown in vitro on titanium surfaces according to the invention in comparison to cells grown on a commercial implant surface (OsseoSpeed; Asta Tech Aft Sweden).

(109) (i) Cell Cultivation

(110) MG-63 is a human cell line conventionally used for in vitro studies of osteoblasts. In this study, MG-63 cells (MG-63, ATCC No CRL-1427, U.S.) were grown in 300 ml Falcon cell culture flasks (BD, WWR, Sweden) in Dulbecco's Minimum Essential Medium (D-MEM) (Gibco, UK) containing 5% fetal calf serum (FCS; Gibco, UK) and 1% penicillin-streptomycin (PEST; Gibco, UK) from second passage from an ampulla of frozen cells. When adherent cells had grown to confluency, they were passaged using 0.05% Trypsin-EDTA (Gibco, UK) for 3 passages. Cell viability was high (>98%) as counted using light microscopy.

(111) (ii) Cell Morphplogy (SEM)

(112) Three coin-shaped -sterilised titanium sample bodies, one of which had been subjected to step b according to the invention, one of which had been subjected to step b and step c according to the invention and one of which had a commercially available surface (OsseoSpeed; Asta Tech AB, Sweden) were each placed in a separate Falcon 24 well plate (BD, WWR, Sweden). To each well was added 1 ml D-MEM (Gibco, UK) containing 5% FCS (Gibco, UK) and 1% PEST (Gibco, UK) having a cell concentration of 20 000 cells/ml. The plates were incubated at 37 C., 5% CO.sub.2 and 100% humidity for 36 hours. Samples were fixed using glutaraldehyde at 4 C., followed by osmium tetroxide fixation, dehydration and gold sputtering according to a conventional SEM sample preparation procedure. Cell morphology was investigated by SEM (ESEM XL 30, FEI). SEM images of the cells are shown in FIG. 20a (cells grown on a conventional surface), FIG. 20b (cells grown on a component treated according to step b of the invention) and in FIG. 20c (cells grown on a component treated according to step b and step c of the invention).

(113) (iii) Evaluation of Cell Proliferation, ALP Activity and PGE2 Activity

(114) Three sets (n=6) of coin-shaped -sterilised titanium sample bodies, one set having been subjected to step b according to the invention (Inventive surface 1), one set having been subjected to step b and step c according to the invention (Inventive surface 2), and one set having a commercially available surface (OsseoSpeed; Asta Tech AB, Sweden), were each placed in a separate Falcon 24 well plate (BD, WWR, Sweden). To each well was added 1 ml D-MEM (Gibco, UK) containing 5% FCS (Gibco, UK) and 1% PEST (Gibco, UK) and having a MG-63 cell concentration of 20 000 cells/ml. The plates were incubated at 37 C., 5% CO.sub.2 and 100% humidity for 14 days.

(115) After 7 days of cultivation, a sample (50 l) from each well was analysed for exogeneous ALP. Adherent cells were analysed for endogeneous ALP by cell lysis followed by centrifugation and determination of supernatant and intracellular ALP content (ng/ml) using SenzoLyte pNPP Alkaline Phosphatase Assay Kit Colorimetric (BioSite, Sweden) according to the instructions of the manufacturer. After 7 days, the samples subjected to both step b and step c according to the invention (Inventive surface 2) had induced a markedly higher production of ALP per cell than the reference samples (OsseoSpeed). The results are presented in FIG. 19.

(116) After 7 and 14 days of cultivation, respectively, the total number of cells/well was determined using NucleoCassette, NucleoCounter (ChemoMetec A/S Denmark) according to the instructions of the manufacturer. The results are presented in FIG. 18.

(117) After 7 and 14 days of cultivation, respectively, 300 l of supernatant from each well was used for determination of PGE2 using ELISA kit R&D Systems PGE2 Immunoassay (R&D Systems, UK) according to the instructions of the manufacturer. After 7 days of cultivation, the production of PGE2 was slightly lower in the samples according to the invention compared to the reference. After 14 days, however, both sets of samples according to the invention had induced a markedly higher production of PGE2 per cell than the reference samples. The results after 7 and 14 days of cultivation, respectively, are presented in FIG. 21.

(118) In summary, it was found that the samples according to the invention induced a lower cell density and a lower number of adherent cells compared to reference surfaces. However, among the cells grown on the surfaces according to the invention, a higher number of cells were proliferative compared to cells grown on the reference surfaces. Cells grown on the surfaces according to the invention were also less apoptotic, more elongated and had many small projections indicating activity, as is seen in FIG. 20a-c.

(119) Cells grown on both surfaces according to the invention exhibited a significantly increased PGE2 production after 14 days of cultivation compared to that of cells grown on a conventional surface. Furthermore, cells grown on a surface according to the invention comprising a secondary nanostructure had a markedly higher ALP activity than cells grown on a conventional surface. An increase in ALP and/or PGE2 activity is related to an increased osteoblast activity, reduced osteoclast activity and an accelerated mineralization of the ECM. Thus, in conclusion, the invention provides a biocompatible component which is improved in respect of bone formation rate and osseointegration.

Example 3

Implantation

(120) The integration of implants according to the invention was tested in a rabbit model. The objective was to qualitatively and quantitatively study the in vivo bone tissue response to two implant surface modifications according to the invention compared to the response to commercially available reference implants.

(121) (i) Implants for Removal Torque Study

(122) Titanium torque fixtures (square headed removal torque design, 3.58.2 mm) prepared by immersion in oxalic acid and subsequently in HF as described in Example 1 (i.e., including steps b and c) were used (referred to as Test implant 2). Also, torque fixtures (3.58.2 mm) were used which were prepared by immersion in oxalic acid according to Example 1 (i.e., step c was omitted) (referred to as Test implant 1). Further, torque fixtures (3.58.2 mm) representing the commercially available OsseoSpeed oral implant were used as reference fixtures.

(123) (ii) Implants for Histological and Histomorphometrical Study

(124) Fixtures of human design of oral implants (3.58 mm) prepared as described in Example 1 above were used (Test implant 2). Also, fixtures were used (3.58 mm) which were prepared as described in Example 1, except that the HF treatment (i.e., step c) was omitted (Test implant 1). Further, fixtures (3.58 mm) representing the commercially available OsseoSpeed oral implant were used as reference fixtures.

(125) (iii) Implant Insertion

(126) Twelve mature male New Zealand white rabbits were scheduled for surgery. One rabbit died during initial anaesthesia (#8). The surgery went uneventful. Low speed drilling (1500 rpg for drilling the holes and 20 rpm for implant insertion) was done with continuous NaCl cooling.

(127) One implant (human design of oral implant; 3.58 mm) was inserted into each femur chondyle region and 3 implants (square headed removal torque design; 3.58.2 mm) were inserted into in each tuburositas tibia. The femur implants were scheduled for histomorphometrical analysis and the tibia implants for removal torque tests.

(128) (iv) Removal Torque Tests

(129) After six weeks the study was terminated and the rabbits were sacrificed. The implants and surrounding tissue were examined. The tibia implants were easy to locate and all of them showed signs of periosteal bone tissue up-growth. The biomechanical test of the implant-bone interface was performed with the removal torque test (RTQ). The RTQ instrument (Detektor AB Gteborg, Sweden) is an electronic equipment involving a strain gauge transducer used for testing the implant stability (the peak loosening torque in Ncm) in the bone bed and can thus be regarded as a three dimensional test roughly reflecting the interfacial shear strength between bone tissue and the implant (Johansson C. B., Albrektsson T., Clin Oral implants Res 1991; 2:24-9). A linear increasing torque was applied on the same axis of the implant until failure of integration was obtained, and the peak value was noted. The implants inserted in femur more often revealed a complete coverage of the implant head with bone tissue. The femur implants were immersed in fixative solution and further processed for histological and histomorphometrical investigations.

(130) The mean values of Test implants 1, Test implants 2 and reference implants for removal torque tests are presented in FIG. 22. Comparisons of all Test implants 1, Test implants 2 and reference implants revealed a 25% improvement in removal torque values for Test implants 2 compared to the reference implants. This difference was statistically significant (p<0.05; Student T-test). Moreover, the results suggested that the removal torque values of Test implants 1 were equal to or higher than those of the reference implants.

(131) (v) Histological Evaluation

(132) After six weeks the study was terminated and the rabbits were sacrificed. Selected samples of the femur implante site including bone tissue and implant from rabbits #1 and #5 were histomorphometrically evaluated in terms of bone to implant contact (BIC) and bone area inside the inner threads (inner area, ia) and in the corresponding mirror images (mi) in various regions around the implants retrieved from femur.

(133) Mean values for BIC and bone area of different regions of the implant as well as a total mean value for BIC and bone area for each implant are reported in Tables 2 and 3 below. The following implant regions were evaluated:

(134) (a) micro-threads;

(135) (b) macro-threads;

(136) (c) along the apical sides (without threads) in the marrow cavity; and

(137) (d) in the apical bottom of the implant (this region is reported for bone implant contact only)

(138) TABLE-US-00002 TABLE 2 Mean values for bone implant contact (BIC) (% of total contact) Total mean Micro- Macro- Apical Mean Apical value incl. Sample threads threads sides value bottom bottom Rabbit #1 14 30 15 20 30 22 Test implant 2 Rabbit #1 5 3 10 6 9 7 Reference Rabbit #5 15 7.5 23 15 7 13 Test implant 1 Rabbit #5 14 19 15 16 21 17 Reference

(139) TABLE-US-00003 TABLE 3 Mean values of bone area (% of total area) Micro- Macro- threads threads Apical sides Mean value Sample (ia/mi) (ia/mi) (ia/mi) (ia/mi) Rabbit #1 29/35 29/31 69/43 42/36 Test implant 2 Rabbit #1 13/26 10/8 29/10 17/15 Reference Rabbit #5 34/45 9/6 48/4 30/18 Test implant 1 Rabbit #5 36/35 25/17 6/10 22/31 Reference ia = inner area, mi = mirror image
For rabbit #5, reference implant, the section was accidentally made through the cut present in all implants. For this sample, the calculated bottom contact distance was based on an approximation of the total distance of that of rabbit #3, Test implant 1 (FIG. 24a).

(140) As can be seen in Tables 2 and 3, Test implant 2 showed higher bone implant contact and a larger bone area in the threads compared to the reference surface. Test implant 1 showed almost equal bone implant contact compared to the reference surface. Also, a larger inner bone area in the threads compared to that of the reference implant was observed (Table 2).

(141) Histology sections images qualitatively showing bone formation are presented in FIGS. 23-24, in which

(142) FIG. 23a represents rabbit #1, Test implant 2;

(143) FIG. 23b represents rabbit #1, reference implant;

(144) FIG. 24a represents rabbit #5, Test implant 1; and

(145) FIG. 24b represents rabbit #5, reference implant.

(146) Nearly all samples revealed more newly formed bone than old bone in close relation to the implant in the upper micro-threaded region. The bone tissue observed in the macro-threads, in the non threaded sides of the implant in the marrow cavity and in the apical bottom layer was also newly formed.

(147) In rabbit #1, a great amount of ongoing bone formation around Test implant 2 was observed compared to the reference implant. Osteoid seams with osteoblast rims of various shapes of the osteoblasts, were frequently observed (FIG. 23a, b).

(148) In rabbit #5, a great amount of ongoing bone formation around Test implant 1 compared to the reference implant was observed. Osteoblasts were frequently observed however not as pronounced as around Test implant 2 of rabbit #1 (FIG. 24a, b).

(149) The implant surfaces were in close connection to the fat cells of the marrow cavity irrespective of implant surface, indicating a high degree of biocompatibility of all surfaces with the sensitive bone marrow cells.

Example 4

Apatite Formation In Vitro

(150) One conventional in vitro model for studying bone formation is the immersion of biomaterials in simulated body fluids (SBFs). SBFs are solutions having ion concentrations approximately equal to those of human blood plasma (Kokubo T., Kushitani H., Sakka S., Kitsugi T., Yamamuro T., J Biomed Mater Res 1990; 24: 721-734; Oyane A., Kim H. K., Furuya T., Kokubo T., Miyazaki T., Nakamura T., J Biomed Mater Res 2003; 65A, 188-195). Depending on the nucleating capacity of the biomaterial., bone-like calcium phosphates will precipitate onto its surface. A quantitative correlation of apatite formation in SBF with in vivo bone bioactivity has been reported (Kokubo T., Takadama H., Biomaterials 2006; 27: 2907-2915). Today the SBF in vitro model is frequently used and is described by the international standard ISO 23317:2007 E.

(151) (i) SBF Immersion

(152) A revised SBF (Oyane A. et al., J Biomed Mater Res 2003; 65A, 188-195) having an electrolyte concentration very similar to that of human plasma (Vander A. J., Sherman J. H., Luciano D. S., Human physiology The mechanisms of body function, 5th ed. McGraw-Hill Publishing Company, New York, 1990: 349-400) was selected. The SBF was prepared by dissolving 10.806 g NaCl, 1.480 g NaHCO.sub.3, 4.092 g Na.sub.2CO.sub.3, 0.450 g KCl, 0.460 g K.sub.2HPO.sub.4.3H.sub.2O, 0.622 g MgCl.sub.2.6H.sub.2O, 23.856 g 2-(4-(2-hydroxyethyl)-1-piperazinyl)ethanesulfonic acid (HEPES), 0.776 g CaCl.sub.2, and 0.144 g Na.sub.2SO.sub.4 in 2000 ml deionised water. HEPES was dissolved in 200 ml deionised water before being added to the solution. The final pH was adjusted to 7.40 at 37 C. with 1.0 M NaOH. All chemicals were obtained from Merck (Sweden), except for NaCl and Na.sub.2SO.sub.4 which were obtained from Fluka (Sweden).

(153) Three sets of coin shaped sterilised titanium samples, one set having been subjected to step b according to the invention (referred to as Inventive surface 1), one set having been subjected to step b and step c according to the invention (Inventive surface 2), and one reference set representing a commercially available surface (OsseoSpeed; Astra Tech Aft Sweden), were immersed in 37 ml SBF in separate and sealed 50 ml polystyrene vials (VWR, Sweden) at 37 C. The samples were mounted hanging in the lid of the vials, allowing the side of the coin to be analysed to be oriented downwards without being contacted by any other objects. After three days the SBF immersion was interrupted and the samples were thoroughly rinsed with deionised water to remove any loosely attached calcium phosphate material. The samples were then dried at room temperature in a laminar air flow bench. Three samples of each set were not immersed in SBF, thus serving as controls.

(154) (ii) Morphology of Apatite Formed (SEM)

(155) Analyses of possible apatite formation were performed using an environmental scanning electron microscope (ESEM, XL 30, FEI). SEM images of the surface structures before SBF immersion are presented in FIGS. 25a (reference), 26a (Inventive surface 1) and 27a (Inventive surface 2). When the surface structures after SBF immersion were studied, it was concluded that a thin layer of calcium phosphate had been formed on all sets of samples; reference (FIG. 25b), Inventive surface 1 (FIG. 26b) and Inventive surface 2 (FIG. 27b).

(156) (iii) Chemical Evaluation of Apatite Formed (EDS)

(157) Energy dispersive spectroscopy (EDS, Apollo 40, EDAX) was used for chemical analysis of samples before and after apatite formation. By analysing the titanium signal, the degree of coverage of the samples by calcium phosphates could be assessed indirectly. Inventive surface 2 showed the largest decrease in titanium signal (FIG. 28) after SBF immersion, thus indicating the most extensive apatite formation among the sets of samples investigated.

(158) EDS was also used for calculation of the Ca/P ratio in order to estimate the relative prevalence of amorphous and crystalline calcium phosphates. The Ca/P ratios are presented in FIG. 29. The resulting Ca/P ratios indicate a higher degree of crystallinity of apatite formed on the Inventive surface 1 and Inventive surface 2 than on the reference surface. The stoichiometric Ca/P atomic ratios of tricalcium phosphate (Ca.sub.3(PO.sub.4).sub.2), and hydroxyapatite (Ca.sub.5(PO.sub.4).sub.3OH) are 1.5, and 1.67, respectively.

(159) In summary, early apatite formation was found on all sets of samples, Inventive surface 2 showing the highest degree of apatite coverage, as concluded by the titanium signal (FIG. 28).