The present invention relates to a ceramic acetabular cup which is devoid of a liner for receiving a natural or prosthetic femoral head, the cup being partly hollow. The present invention further discloses a ceramic acetabular cup formed of a ceramic material during an additive manufacturing process. A light-weight ceramic prosthetic component formed via additive manufacturing is also provided. The present invention also relates to a ball-and-socket prosthetic system formed from ceramic material in which the ball is captively held. There is also disclosed a method of forming a ceramic prosthetic component, such as a ceramic acetabular cup, via additive manufacture.

A hip replacement involves inserting one or both an acetabular cup and a prosthetic femoral component during surgery. Typically a two-part acetabular cup, comprising a bearing or articulation liner and an outer shell, is used to enable a secure fit whilst providing sufficient strength and interoperative surgeon options of bearing size and material type. However, a two- part cup has known clinical issues such as potential liner misalignment and subsequent liner dissociation that can cause early failure.

In large patients, a thick and large two-part acetabular cup is used due to the required difference in the internal bearing diameter to accept the hip ball and the outer bone contacting surface, which is the hip socket. Such an acetabular cup is heavy and requires excessive material to manufacture. This adds much waste to the manufacturing process and cost to the prosthesis.

Furthermore, acetabular cup components are commonly at least partly formed of metal, such as stainless steel, titanium alloys, or cobalt chrome molybdenum alloys. Such metallic components may release particles and metal ions. Metal particles and metal ions have been linked to potential allergic reactions, carcinogenesis, aneuploidy, soft tissue necrosis, pseudotumours, or other adverse health effects for the patient. The use of metals to form the acetabular cup is therefore less biologically preferable than ceramic materials.

Ceramic cups are typically formed via heating ceramic material in powdered form to a high temperature within a mould, a process known as sintering a green body. The range of available ceramic cups is, however, restricted to the range of moulds available.

The present invention seeks to provide a solution to these problems.

According to a first aspect of the present invention, there is provided a ceramic acetabular cup devoid of a separate liner and comprising: an inner wall having a part-spherical articulating surface for non-captively receiving a femoral head; an outer wall having an outer surface for enabling bone fixation; and a cavity between an interior surface of the inner wall and an interior surface of the outer wall, wherein the cavity is sealed and wherein the acetabular cup is formed using a ceramic composition in an additive manufacturing process.

The advantage is that, for a given size, the acetabular cup is lighter by virtue of being at least partly hollow due to having at least one cavity. Ceramic is biocompatible and does not shed metal ions and particles.

The cup may be custom-made to a specific patient via three-dimensional printing. The fit may therefore be improved. Waste may be reduced. The cavity being sealed or closed may prevent or inhibit ingress of foreign objects into the acetabular cup, before or after insertion of the acetabular cup into the patient.

The term “additive manufacture” used herein and throughout is intended to mean an manufacturing process involving forming an initial layer/quantity of material then adding further layers/quantities of material sequentially to the initial layer in order to build up and produce a component.

Advantageously, the ceramic composition may comprise a binding agent and ceramic particles suspendable or suspended in the binding agent. The ceramic cup may be formed via binder jetting and/or photopolymerisation.

Furthermore, the binding agent may comprise a photocurable substance. The use of light to cure the binding agent may increase the precision when adding a layer of ceramic composition to the component during manufacture. This may, in turn, enable a prosthetic component to be manufactured with finer detail than can be achieved by traditional manufacture of ceramics parts. Beneficially, the inner wall and the outer wall may be formed as a one-piece, directly or indirectly. A monobloc design does not require assembly of two or more parts, thereby reducing the complexity and length of the surgery.

Furthermore, the rim may be planar. This may facilitate gripping and/or orienting the cup during impaction. Optionally, the cavity may extend at or adjacent to a pole of the cup. Advantageously, the inner wall may have a thickness which may be constant. Additionally or alternatively, the outer wall may have a thickness which may be constant. Furthermore, the inner wall may have a thickness which may be the same or substantially the same as the thickness of the outer wall. Constant thickness of a wall and/or equal wall thicknesses may prevent or inhibit the formation of a stress raiser, stress riser or stress concentration. The forces acting upon the cup in-use may be more distributed.

Optionally, the interior surface of the inner wall may be at least partly convex. Additionally or alternatively, the interior surface of the outer wall may be at least partly concave. Furthermore, the interior surface of the inner wall may be part-spherical. Optionally, the interior surface of the outer wall may be part-spherical. These shapes may match the articular surface and/or a receiving cavity in the acetabulum. This may provide an inner wall and/or an outer wall of equal or substantially equal thickness. An equal wall thickness equates with there being no or no substantial thinning of the relevant wall. As such, the structural integrity of the acetabular cup is increased as a thinning may provide a structural weakness.

The inner wall and/or the outer wall may, however, have a variable thickness along at least part of their extent, as required. This may be advantageous in order to compensate for or accommodate an uneven force distribution on the acetabular cup.

Advantageously, the ceramic acetabular cup may further comprise at least one reinforcing element. Optionally, the or at least one of the reinforcing elements may be connected to the interior surface of the inner wall and/or to the interior surface of the outer wall. Although the reinforcing element may increase the weight of the acetabular cup, the structural integrity of the cup may also be increased. The forces acting on the cup may be increased without damage to the cup relative to a similar acetabular cup devoid of any reinforcing element. The reinforcing element preferably comprises ceramic but any non-ceramic, such as a metal, may be envisioned.

Furthermore, the or at least one of the reinforcing elements may be integrally formed with the interior surface of the inner wall and/or with the interior surface of the outer wall. By being integrally formed, the ease of manufacture may be improved. An additional advantage may be that being integrally formed prevents or inhibits any movement of the or each reinforcing element within the acetabular cup. The position of the centre of gravity may also be influenced during manufacture by selecting the positioning and/or the number of reinforcing elements. Additionally, at least one of the reinforcing elements may be a partitioning element which may partition the cavity into a plurality of sub-cavities. Optionally, a first said sub-cavity may be sealed from a second said sub-cavity. A plurality of sub-cavities may prevent or inhibit spread from one cavity to another of any foreign object which may have been accidentally introduced into the acetabular cup. If the sub-cavities are fluid-proof, the sub-cavities may be filled with a compressible or, preferably, incompressible fluid. The fluid provides an opposing force against any external forces acting on the acetabular cup.

Advantageously, at least one of the sub-cavities may extend along a plane parallel with an equatorial plane of the acetabular cup. The ease of manufacture may be increased.

Alternatively, at least one of the reinforcing elements may be a strut. A strut may be light-weight. Beneficially, the ceramic acetabular cup may further comprise at least part of the outer surface a porous ceramic coating for permitting bone ingrowth thereinto. The coating may improve the engagement with the bone. According to a second aspect of the present invention, there is provided a wall having a part- spherical articulating surface for receiving a femoral head; at least one bone-engagement portion; and wherein only part of the ceramic acetabular cup is formed via an additive manufacturing process. This permits additional features to be added via additive manufacture to customise a generic acetabular cup. The generic acetabular cup may be formed by additive manufacture or by traditional manufacture. The generic acetabular cup may be formed from a ceramic composition and/or a non-ceramic composition, such as a metal acetabular cup. The generic acetabular cup may optionally be encased in ceramic.

According to a third aspect of the present invention, there is provided a ceramic acetabular cup comprising: a wall having a part-spherical articulating surface for receiving a femoral head; and at least one bone-engagement portion; wherein the ceramic acetabular cup is formed from a ceramic material in an additive manufacturing process. The whole of the acetabular cup may be 3D printed, whether in one stage or in several stages. 3D printing enables a prosthetic component to be adapted to a specific patient, which may improve the fit and therefore stability and/or lifespan of the implant.

According to a fourth aspect of the present invention, there is provided a ball-and-socket prosthetic system comprising: a socket element; and a ball element captively held for articulation within the socket element, at least the socket element being formed from a ceramic material in an additive manufacturing process with the ball element in situ. The joint has a reduced likelihood of dislocation.

Beneficially, the ball element may comprise a ceramic material. This may reduce or eliminate the risk of releasing metal ions and/or particulates.

According to a fifth aspect of the present invention, there is provided a ceramic prosthetic component comprising: a first wall; a second wall, wherein the first wall is spaced-apart from the second wall to form a cavity therebetween and the prosthetic component is formed from ceramic material during an additive manufacturing process for providing a light-weight ceramic prosthetic component. A light-weight prosthetic implant for any joint may be provided. As the prosthetic implant is made by additive manufacture, the prosthetic implant may be tailored to the specific patient. This may therefore improve the stability of the implant. Additionally, a tailored implant means there is no need to stock a range of prosthetic implants. The cavity means that less material is required during manufacture, which reduces waste.

Beneficially, the prosthetic component may be formed as a one-piece. Optionally, the cavity may be sealed. The ease of manufacture and/or implant may be increased.

Additionally, the ceramic material of the ceramic acetabular cup, preferably in accordance with the first aspect of the invention, or a ball-and-socket prosthetic system, preferably in accordance with the fourth aspect of the invention, or a ceramic prosthetic component preferably in accordance with the fifth aspect of the invention, may comprise aluminium oxide and/or zirconium oxide. An intrinsic property of zirconium oxide is that zirconium oxide expands upon transitioning from one state, the tetragonal state, to another state, the monoclinic state. Thus, zirconium oxide may prevent or inhibit the formation and/or expansion of any fractures. If provided with aluminium oxide, the ceramic material may comprise Zirconium Toughened Alumina ZTA, or Alumina Toughened Zirconia or ATZ.

According to a sixth aspect of the present invention, there is provided a method of forming a ceramic acetabular cup having at least one cavity between an interior surface of an inner wall adapted to receive a femoral head and an interior surface of an outer wall adapted for bone fixation, the method comprising the step of using a ceramic composition in an additive manufacturing process. The acetabular cup is formed to measure via 3D printing. The ceramic composition is preferably delivered or produced by the additive manufacturing process. Bone fixation may be direct or indirect. Although bone fixation occurs in, on or adjacent the outer surface of the outer wall, it may be envisioned that additionally or alternatively, bone fixation may occur in or on the interior surface of the inner wall and/or of the outer wall. Bone fixation may also occur in or on any reinforcing element. For example, one or more apertures may be provided in the outer wall which enable bone to grow therethrough and into the cavity. Such a cavity may be open or non-sealed.

According to a seventh aspect of the present invention, there is provided a method of forming a ceramic prosthetic component having at least one cavity between an interior surface of an inner wall and an interior surface of an outer wall, the method comprising the step of using a ceramic composition in an additive manufacturing process. The prosthetic component is formed according to a design via 3D printing.

According to an eighth aspect of the present invention, there is provided a ceramic acetabular cup devoid of a separate liner and comprising: an inner wall having a part-spherical articulating surface for non-captively receiving a femoral head; an outer wall having an outer surface for enabling bone fixation; and a cavity between an interior surface of the inner wall and an interior surface of the outer wall.

Optionally, the cavity may be sealed, but non-sealed may be envisioned. Additionally or alternatively to the cavity being sealed or non-sealed, the acetabular cup may be formed using a ceramic composition in an additive manufacturing process, but a non-additive manufacturing process may be envisioned. For example, the acetabular cup may be formed using a traditional manufacturing process.

The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a perspective representation of a first embodiment of an acetabular cup, in accordance with the first and eighth aspects of the invention;

Figure 2 illustrates a part cut-away perspective representation of the acetabular cup of Figure 1;

Figure 3 is a side representation of the acetabular cup of Figure 2;

Figure 4 shows a part cut-away perspective representation of a second embodiment of an acetabular cup, in accordance with the first and eighth aspects of the invention; and

Figure 5 shows a side representation of the acetabular cup of Figure 4.

Referring firstly to Figure 1, there is shown a prosthetic component, which in the preferred, illustrated embodiment, is an acetabular cup, indicated generally at 10.

The acetabular cup 10 may comprise metals, plastics, ceramics, any other suitable material, or any combination thereof. More preferably, the acetabular cup 10 comprises a, preferably flowable, ceramic material, and most preferably the acetabular cup 10 is solely formed from a, preferably flowable, ceramic material. Thus, the acetabular cup may be referred to as a ceramic acetabular cup 10.

The acetabular cup 10 may optionally comprise zirconium oxide. Alternatively or additionally, the acetabular cup 10 may comprise aluminium oxide, and/or any other alternative oxide such as strontium oxide or other ceramic materials. Additionally or alternatively to any of the above, the acetabular cup 10 may comprise silicon nitride SiN or other suitable ceramics. Preferably, the acetabular cup 10 is formed via an additive manufacturing process, also referred to as three-dimensional printing.

The acetabular cup 10 has a first or inner wall 12, a second or outer wall 14 and a rim portion 16. These features are more clearly visible in Figures 2 and 3. The acetabular cup 10 is devoid of a separate liner, but this feature may be envisioned. Preferably, the acetabular cup 10 is hemispherical at most. This enables a femoral head to be non-captively received within the cup 10. The cup 10 also comprises a pole P and a centre C. The pole P and the centre C are represented as dots on Figures 1 to 3 but it is to be understood that they are virtual points. The cup 10 may further comprise an axis A, indicated as dashed lines. Preferably, axis A extends through the pole P and/or the centre C, more preferably both, but neither is an option.

For clarity, any plane which is normal to axis A is a transverse plane. An example of such a plane is an equatorial plane of the cup 10. Preferably, the centre C is contained within the equatorial plane, but non-contained within is an option. In other words, the centre C may be offset relative to the equatorial plane. This may occur, for example, in hip resurfacing implants. Any plane which contains or is parallel to axis A may be referred to as an axial or longitudinal plane. The inner wall 12 and the outer wall 14 are preferably connectable, connected or integrally formed with each other and/or with the rim portion 16 along at least part of their extent. In the preferred embodiment, the inner wall 12 is integrally formed with the rim portion 16. Alternatively or preferably additionally, the outer wall 14 is integrally formed with the rim portion 16. Most preferably, the inner wall 12 and the outer wall 14 are formed as a one-piece. In other words, the acetabular cup 10 is preferably a monobloc.

The inner wall 12 has an exterior or outer surface 18 and an interior surface 20, although the interior surface may be omitted. A plurality of exterior surfaces and/or interior surfaces may be provided, as required.

The exterior surface 18 or a part thereof may be referred to as an articular surface or an articulating surface. The exterior surface 18 of the inner wall 12 is preferably curved in axial and/or transverse cross-section but non-curved or part-curved are options. More preferably, the exterior surface 18 of the inner wall 12 is at least partly concave. Most preferably, the exterior surface 18 or a part thereof is a part-spherical articulating surface. The articulating surface may in-use receive a femoral head, captively or non-captively.

The interior surface 20 of the inner wall 12 is preferably curved in axial and/or transverse cross- section but non-curved or part-curved are options. More preferably, the interior surface 20 is at least partly convex in axial and/or transverse cross-section. Most preferably, at least part of the interior surface 20 of the inner wall 12 is part-spherical.

Similarly to the inner wall 12, the outer wall 14 has an exterior surface or outer surface 22 and preferably an interior surface 24. A plurality of exterior surfaces and/or interior surfaces may be provided, as required. The exterior surface 22 is preferably abuttable against bone as this may provide stability and/or enable bone fixation in-use, although non-abuttable against bone may be an option.

Optionally, the cup 10 may further comprise a porous or plasma-sprayed metal and/or ceramic outer coating, not shown, for permitting bone ingrowth thereinto. The ceramic coating may optionally be provided on at least part of the outer surface. For example, the coating may comprise any or any combination of: titanium plasma and/or hydroxyapatite, Cobalt-Chrome- Molybdenum or CoCrMo.

Additionally or alternatively, the outer surface of the cup 10 may itself be formed to be porous, pitted or otherwise none-smooth or rough to again aid bone ingrowth. Such an outer surface may also then be coated with porous or plasma-sprayed metal and/or a ceramic outer coating for further promoting bone ingrowth.

The interior surface 24 and/or the outer surface 22 of the outer wall 14 are preferably curved in axial and/or transverse cross-section but non-curved or part-curved are options. More preferably, the interior surface 24 is at least partly concave. The outer surface 22 of the outer wall 14 may be at least partly convex. Most preferably, at least part of the interior surface 24 and/or at least part of the outer surface 22 of the outer wall 14 is part-spherical.

For clarity, the interior surface 20 and the exterior surface 18 of the inner wall 12 may be referred to as an inner-wall interior surface 20 and an inner-wall exterior surface 18, respectively. The corresponding surfaces of the outer wall 14 may be referred to as an outer- wall interior surface 24 and an outer-wall exterior surface 22 respectively.

The inner wall 12 is preferably at least partly spaced-apart from the outer wall 14. This may form at least one recess, hollow or cavity 26 therebetween such that the acetabular cup 10 may be at least partly hollow, although the cup may be devoid of a cavity. In this alternative embodiment, the interior surfaces may be omitted.

The inner wall 12 also has a thickness. The outer wall 14 has a thickness. The thickness of the inner wall 12 is preferably similar or identical to the thickness of the outer wall 14, but different thicknesses may be an option. Furthermore, the thickness of the inner wall 12 may be or be substantially constant or unvarying along all or a major extent of the cross-sectional length or of the area of the interior surface 20 of the inner wall 12, but a minor extent may be an option. Similarly, the thickness of the outer wall 14 may be or be substantially constant or unvarying along all or a major extent of the cross-sectional length or of the area of the interior surface 24 of the outer wall 14, but a minor extent may be an option.

The rim portion 16 has a bridging function as it spaces-apart the inner wall 12 from the outer wall 14. The rim portion or rim 16 is preferably at least partly planar in transverse cross-section but non-planar in transverse and/or longitudinal cross-section, such as curved or part-curved may be options. In the preferred embodiment, the rim portion 16 comprises an elongate wall 28 having an exterior surface 30 and an interior surface 32.

At least one of the exterior surface 30 and the interior surface 32 are at least partly planar, although neither may be planar. The exterior surface 30 of the rim portion 16 extends preferably in, at or adjacent the equatorial plane of the acetabular cup 10. As shown in Figure 3, the interior surface 32 is also at least partly curved in longitudinal cross-section.

The inner-wall exterior surface 18 meets or joins the exterior surface 30 of the rim 16 at a first edge 34. Similarly, the outer-wall exterior surface 22 meets or joins the exterior surface 30 of the rim 16 at a second edge 36. One or both edges 34,36 may be curved and/or chamfered as shown, but these features are optional.

The cavity 26 is provided between the inner-wall interior surface 20 and the outer-wall interior surface 24. The cavity 26 is sealable or sealed but non-sealed is an option. Preferably, the outer wall 14 and the inner wall 12 are devoid of any hole, aperture, or through-bore. This may be advantageous for structural integrity as an aperture may provide a local weakness. Additionally or alternatively, the absence of any opening may prevent or reduce ingress of materials into the cavity 26. Preferably, the cavity 26 extends between the inner wall 12 and the outer wall 14 along all or at least along a major extent of the cross-sectional length and/or all or at least along a major extent of a surface area of either or both the inner-wall interior surface 20 and the outer- wall interior surface 24, but a minor extent may be envisioned. Preferably, the cavity 26 extends at or adjacent to a pole P of the cup. In other words, the cup 10 is hollow at or adjacent the pole P. Additionally or alternatively, the cavity 26 may be at or extend to or towards the rim 16. The cavity 26 may be or be substantially hemispherical in shape.

In an alternative embodiment, no cavity may be provided at or adjacent the pole. For instance, the acetabular cup may be solid or non-hollow at or adjacent the pole. The cavity may still be provided between the inner and outer walls, for example away from the pole. The cavity may be or be substantially a torus, for example. In-use, the prosthetic component, which is an acetabular cup 10 in the preferred embodiment, needs to be manufactured. The acetabular cup 10 is formed using a flowable ceramic composition, although non-flowable is possible. In other words, the acetabular cup 10 is preferably formed via an additive manufacturing process.

If using an additive manufacturing process, the prosthetic component may be created before or, preferably, during the surgery. This enables a customised prosthetic component or implant to be created, specifically adapted or tailored to the patient. This advantageously improves the fit of the prosthetic implant, and may reduce the need for revision surgery. By having custom-made implants produced according to need, this may also reduce the stock that a hospital requires, further saving costs and reducing storage space required.

To create the prosthetic component, a three-dimensional printing process, also known as an additive manufacturing process, may be used. Any suitable additive manufacturing process for ceramics, and more preferably, any ISO_17296-2_2015 Additive manufacturing process may be used. Examples of additive manufacturing processes may include photo-polymerisation; binder jetting, fused filament fabrication or fused deposition modelling, and Selective Laser Sintering, although any other suitable additive manufacturing process may be envisioned.

To produce a component via photopolymerisation, the user obtains a photopolymerisation apparatus, and photocurable substance, bonding agent, or binding agent, such as a photocurable resin. The user also obtains ceramic particles, granules or powder. The ceramic powder is mixed with the binding agent to create a photocurable substance comprising suspended ceramic particles. The binding substance or agent with ceramic particles may alternatively be referred to as a liquid ceramic monomer suspension, a ceramic composition or a ceramic material. The ceramic material may be liquid, spreadable, flowable, deformable or malleable. In other words, the photocurable substance with suspended ceramic material may have a paste or slurry consistency. This may enable the ceramic material to be shaped, fashioned, or formed into the desired acetabular cup 10.

The photopolymerisation apparatus comprises a container or vat. The photocurable substance with ceramic material may be held in the vat during addition of layers to the prosthetic component. In this case, photo-polymerisation may be referred to as “vat photo-polymerisation”. To add a layer of ceramic material to a prosthetic component, there are at least two different techniques: vat photopolymerization by laser light source, and vat photopolymerization by controlled area light source.

In vat photopolymerisation by laser light source, the ceramic material is in a vat or container. The photopolymerisation apparatus further comprises a build platform, upon which the prosthetic component is built. The build platform is raisable and lowerable within the vat, by an elevator. The build platform may optionally be laterally displaceable, in other words, movable in a horizontal plane. A support structure may optionally be provided. The support structure may extend upwards from the build platform to support to the component being built.

Adjacent, and preferably above, the vat is provided a lighting arrangement. The lighting arrangement includes an energy light source. Preferably, the energy light source comprises a laser. Photopolymerisation typically relies on Digital Light Processing or DLP to harden the photocurable substance but any non-DLP light processing may be envisioned. The laser therefore may comprise UV light, white light, Infrared light, or any other suitable type of light. Optionally, the lighting arrangement also comprises at least one reflector. The reflector may comprise a mirror by way of example only. The at least one reflector redirects light, preferably towards the vat.

Upon the light emitted by the light source contacting the ceramic material, the ceramic material is cured. The photocurable substance within the ceramic material hardens, thereby adding a volume of cured ceramic material to the prosthetic component. At least one of: the reflector, the energy light source, and the build platform may be movable. This enables addition of a further volume of cured ceramic material in a different position to the prosthetic component. Optionally, a recoating and surface levelling mechanism may be provided. The mechanism recoats the upper layer of the component with ceramic material. The mechanism may ensure that the layer is uniform and/or that the surface of the ceramic material is level. The process is repeated until the whole prosthetic component has been formed.

Vat photopolymerization by controller area light source is similar to vat photopolymerization by laser light source, in that a vat or container is filled with the ceramic material. A build platform with elevator is preferably provided. A support structure is also preferably provided. Vat photopolymerization by controller area light source also has a lighting arrangement comprise at least an energy light source. Detailed description of the common features is omitted for brevity. The differences are detailed as follows.

In vat photopolymerization by laser light source, the build platform is generally lowered. However, in vat photopolymerization by controller area light source the build platform may be generally raised upwards and/or laterally as the component is formed. The vat or container comprises at least one transparent pane or wall. The transparent pane is provided at the bottom and/or in a side wall of the vat. Light is shone through the transparent pane. The reflector may optionally be omitted from the lighting arrangement. Similarly, the recoating and surface levelling mechanism may be omitted as the ceramic material flows automatically into the base of the vat under gravity. The lighting arrangement further comprises a mask, photo mask, or masking element. The mask is positionable along a light path between the transparent pane and the light source. The mask has an opening which lets through light. The opening dimensions may be selectably variable. This variability enables the shape and area of photocurable substance with suspended ceramic material which the light reaches through the transparent pane to be varied and selected. Upon light reaching the ceramic material, the photocurable substance is cured and hardens, thereby adding a layer to the component being built. This forms a green body.

In a variant embodiment, the prosthetic component may be formed by building layers of ceramic material positioned or injected via a nozzle of a printing device. Alternatively, a tape casting system or arrangement may be provided. The prosthetic component being formed may be repeatedly moved to temporarily contact a layer or bed of the ceramic material. The ceramic material being added to the prosthetic component is preferably in a flowable form. In other words, the ceramic material may be a paste or slurry. Contact between the prosthetic component being formed and the ceramic material adds a further layer of ceramic material to the prosthetic component being formed.

Optionally, if using a tape casting arrangement, the ceramic material which has not been incorporated into a specific layer of the prosthetic component may be recycled and/or reconditioned to be usable in a subsequent layer of the prosthetic component. This may reduce waste.

To produce a component via binder jetting, a binder jetting apparatus is required. The binder jetting apparatus comprises a container. Ceramic particles in powdered form are provided in the container, on a powder bed. Preferably, the particle size is uniform. The binder jetting apparatus also has a build platform, upon which the prosthetic component is built. The platform may be raisable and lowerable within the container, by an elevator. The build platform may optionally be laterally displaceable, in other words, movable in a horizontal plane. A support structure may optionally be provided. The support structure may extend upwards from the build platform to support to the component being built. The apparatus further comprises a liquid bonding agent dispenser which dispenses a liquid bonding or binding agent. The binding agent may be a photocurable binding agent, but preferably, the binding agent is non-photocurable.

At least one of the dispenser and the build platform is movable. This enables the binding agent to be selectively deposited on the ceramic powder. The selectable position enables the shape of each layer to be varied, as required. The ceramic particles may become suspended in the binding agent, thereby forming a ceramic material. Optionally, the binder jetting apparatus may comprise a powder spreading device. The device spreads a layer of powder on the component being built. The device additionally or alternatively ensures each powder layer has a constant or substantially constant thickness and/or levels the surface of the powder.

To produce a component via fused filament fabrication, the user obtains a filament having a binding agent, also referred to as a holding or suspending material. The filament also comprises ceramic particles, preferably in powder form. Most preferably, the ceramic particles are provided as a core of the filament, surrounded by a sheath. However, the ceramic particles may instead be suspended in a matrix. The sheath or matrix preferably comprise plastics, although non plastics are options.

The filament is threaded on, in or through a nozzle of a 3D printing device. At least part of the filament is heated such that the holding or suspending material is flowable, malleable or deformable. The nozzle is movable relative to a bed or surface. This enables the heated holding or suspending material to be laid down according to a design or pattern to form a shape. Once a layer of the prosthetic component being formed has been laid down, the surface is moved away from the nozzle or vice-versa. A further layer of heated holding or suspending material is applied to form a further layer. This process is repeated until at least a majority or all the prosthetic component has been formed via additive manufacturing.

Selective laser sintering involves using a laser to heat or sinter material, typically in powder form. Granules or particles are deposited in a layer. The laser is aimed at points in space which form the shape of the prosthetic component to be formed. The heating process results in the powder binding together to form a solid structure. A further layer of granules or particles is deposited, before being sintered. The process is repeated until the prosthetic component is complete.

During or after the additive manufacturing process, the ceramic material may harden without any further action but alternatively, a further step may be required, such as curing or altering the temperature of the component.

Optionally, the component undergoes a debinding process. Various techniques are known to the person skilled in the art, which may include using a solvent, a catalyst, thermolysis, or a combination of the above. The latter may involve heating the component to a sufficient temperature to remove the binding agent, for example via melting or burning the binding agent, the temperature and time being depending on the exact binding agent used and the desired properties of the ceramic material.

In any of the above additive manufacturing processes, the component may additionally undergo a sintering process. This may increase the density of the component. Sintering involves heating the component to at least 800°C, although less than 800°C may be envisioned. More preferably, the sintering temperature is at least 1000°C, and most preferably at least 1500°C. Furthermore, the sintering temperature may be less than 2000°C, although greater than 2000°C is an option. More preferably, the sintering temperature is less than 1800°C, and most preferably less than 1700°C. The component is heated at these temperatures for at least 10 minutes, although less than 10 minutes may be envisioned. More preferably, the prosthetic component is heated for at least 30 minutes and most preferably, for at least one hour.

The additive manufacturing process has the additional advantage that the acetabular cup 10 may be hollow to reduce the weight of the cup 10 whilst the cavity 26 can be sealed. Traditional manufacture of ceramics components involves inserting and compacting a ceramic powder into a mould to produce a green component with a density of generally 50% to 70%. Thereafter the green component is processed under high temperature and pressure. This processing is known as sintering the green body. Such traditional techniques do not enable ceramic products having one or more sealed cavities to be formed.

Thus, there is provided a method of forming a ceramic prosthetic component having at least one cavity between the interior surface of an inner wall and the interior surface of the outer wall. If the prosthetic component is an acetabular cup 10, the interior surface 20 of the inner wall 12 is adapted to receive a femoral head and the interior surface 24 of the outer wall 14, itself adapted for, indirect or preferably direct, bone fixation. The method optionally includes the step of using a flowable ceramic composition in an additive manufacturing process.

The acetabular cup 10 is inserted during surgery into a prepared acetabulum. The outer-wall exterior surface 22 engages with the bone and prevents or inhibits movement of the acetabular cup 10 relative to the bone. The outer-wall exterior surface 22 may optionally be at least partly covered with a coating to improve grip and/or enhance fixation. The coating may encourage natural bone growth in or on the coating.

Referring now to Figures 4 and 5, there is shown a second embodiment of a prosthetic component, which is also an acetabular cup 110.

Features of the second embodiment which are similar to features of the first embodiment have similar reference numerals, with the prefix “1” added. The acetabular cup 110 of the second embodiment has similar features to the acetabular cup 10 of the first embodiment, preferably having the same or similar material properties, inner wall 112, inner-wall exterior surface 118, inner-wall interior surface 120, outer wall 114, outer-wall interior surface 124, outer-wall exterior surface 122, rim portion 116, first edge 134, second edge 136 and cavity 126. Detailed description of the common features and caveats is omitted for brevity. The acetabular cup 110 is preferably at least partly or fully formed using a ceramic composition. The cup 110 may be at least in part and more preferably fully formed via an additive manufacturing process, but this is optional.

The acetabular cup 110 of the second embodiment is preferably formed from ceramics, similarly to the cup 10 of the first embodiment. More preferably, the acetabular cup 10 is formed using a ceramic composition. The cup 110 may optionally comprise zirconium oxide. Additionally or alternatively, the cup 110 may comprise aluminium oxide, and/or any other suitable oxide. Additionally or alternatively to any of the above, the acetabular cup 110 may comprise silicon nitride SiN or other suitable ceramic.

The second embodiment of the acetabular cup 110 further has at least one reinforcing element or reinforcement 128. The, each, or at least one of the reinforcing elements 128 may be provided in the cavity 126. Preferably, the or a said one reinforcing element 128 is connectable, connected, or integrally formed with the interior surface 118 of the inner wall 112. Alternatively or, preferably, additionally, the, each, or a said one reinforcing element 128 is connectable, connected, or integrally formed the interior surface 124 of the outer wall 114.

In the preferred embodiment, the or each reinforcing elements 128 is integrally formed with both the inner wall 112 and the outer wall 114. The or each reinforcing elements 128 may space- apart the inner wall 112 from the outer wall 114. The cavity 126 may be sealed, sealable or non- sealed. Preferably, the cavity 126 extends between the inner wall 112 and the outer wall 114 along all or at least along a major extent of the cross-sectional length and/or all or at least along a major extent of a surface area of either or both the inner-wall interior surface 120 and the outer-wall interior surface 124, but a minor extent may be envisioned. Preferably, the cavity 126 extends at or adjacent to a pole P of the cup. In other words, the cup 110 is hollow at or adjacent the pole P. Additionally or alternatively, the cavity 126 may be at or extend to or towards the rim 116.

In an alternative embodiment, the cavity may not be provided at or adjacent the pole. For instance, the acetabular cup may be solid or non-hollow at or adjacent the pole. The cavity may still be provided between the inner and outer walls, for example away from the pole. The cavity may be or be substantially a torus, for example. The, each, or at least one of the reinforcing elements 128 may comprise a partitioning element or partition which partitions the cavity 126 into a plurality of sub-cavities 138. There may be at least two sub-cavities 138. In the shown embodiment, there are five sub-cavities 138.

Optionally, a first said sub-cavity 138 may be sealable or sealed or fluidly-isolated from a second said sub-cavity 138. Preferably, all sub-cavities 138 are sealed or substantially sealed, but any number of sub-cavities may be non-sealed. At least one, and preferably all sub-cavities 138 extend or substantially extend circumferentially around the acetabular cup 110. Furthermore, at least one, and preferably all sub-cavities 138 extend or substantially extend in or along a transverse plane, parallel with the equatorial plane of the acetabular cup 110. Each sub-cavity 138 may be or be substantially a portion of a disk or a torus in transverse cross- section. Each sub-cavity 138 may be or be substantially a trapezium in longitudinal cross- section, as illustrated in Figure 5, but a non-trapezium may be envisioned. Preferably, at least one, and as shown, all corners of the trapezium are rounded and/or chamfered.

The term “trapezium” used herein and throughout is intended to mean a quadrilateral having a pair of parallel opposing sides.

The, each or at least one reinforcing element 128 may extend, in transverse and/or in longitudinal cross-section in a direction. The direction may be the same for at least two reinforcing elements. Additionally or alternatively, the direction may differ for at least two reinforcing elements 128. In the present embodiment, at least one, and preferably all reinforcing elements 128 may extend in different directions to each other in longitudinal cross-section. As best illustrated in Figure 5, all reinforcing elements 128 extend in a direction meeting at a common position, point, or location, but this feature is optional. The common position in the present embodiment is the centre C on the equatorial plane, and therefore the reinforcing elements extend radially, substantially radially, or generally in a radial direction. This is beneficial for improved strength of the cup in view of the typical forces imparted by a seated or received femoral ball head when in use. However, this preferred orientation may not be essential.

The uses of the second embodiment are the same or similar to those of the first embodiment. Detailed description of the common steps is omitted for brevity.

The acetabular cups of the first and second embodiments are examples of a prosthetic component.

Now referring to a third embodiment, there is provided a generalised prosthetic component, apparatus or device, not shown. The prosthetic component may be alternatively referred to as a prosthetic apparatus or device. A plurality of, preferably complementary, prosthetic components may be referred to as a prosthetic system, assembly, or arrangement. The prosthetic component may be any or any combination of: a ball, a neck, and a stem of a femoral component of a hip replacement, by way of example only. Other examples of a prosthetic component may include an implant for any joint, such as the knee, the ankle, the shoulder, the elbow, the wrist, the spine or one or more vertebrae thereof or any other joint.

The prosthetic component comprises a first wall and a second wall. Additional walls may be provided, as required.

The first wall optionally has an exterior surface and optionally, an interior surface. The first wall is similar to the inner wall 12; 112 in the first and second embodiments. Detailed description of the common features is omitted for brevity. The exterior surface or part thereof may or may not form an articular surface. Additionally or alternatively, the exterior surface may be abuttable against bone. The interior surface and/or the exterior surface of the first wall may be curved, although non-curved or part curved may be options. Furthermore, the interior surface and/or the exterior surface of the first wall may be part spherical, but non-part spherical may be envisioned, such as planar.

The second wall has an outer or exterior surface, and optionally, an interior surface. The second wall is similar to the outer wall 14; 114 in the first and second embodiments. Detailed description of the common features is, once again, omitted for brevity. Optionally, the exterior surface may be abuttable against bone for enabling bone fixation. Additionally or alternatively, the exterior surface or part thereof may form an articular surface. The interior surface and/or the exterior surface of the second wall may be curved, although non-curved or part curved may be options. Furthermore, the interior surface and/or the exterior surface of the first wall may be part spherical, but non-part spherical may be envisioned, such as planar.

The first wall is spaced-apart from the second wall for providing an at least partly hollow prosthetic component. Thus a cavity is provided between the interior face of the first wall and the interior face of the second wall. This may provide a light-weight ceramic prosthetic component the cavity is sealed or sealable but non-sealed or non-sealable are options.

The first wall may be integrally formed with the second wall, although connected or connectable are possibilities. The first wall meets or joins the second wall. Optionally, where the first wall and the second wall meet, a rim may be formed but this feature is optional. For example, the first wall may connect to the second wall without forming a rim. The first wall may transition into the second wall. It may not be possible to distinguish where the first wall ends and the second wall starts, and vice versa. For example, both walls may be convex or at least partly convex. By way of example only, a femoral prosthetic component may comprise two walls which are integrally formed, connected or connectable with each other along a longitudinal plane of the component. The two walls may form a cavity therebetween. The prosthetic component of the third embodiment may optionally comprise at least one reinforcing element, similar to the at least one reinforcing element of the second embodiment, but this feature is optional. Detailed description of the common features is omitted, once again, for brevity.

The prosthetic component preferably comprises ceramics, similar to the first and second embodiments, although non-ceramics, one or more polymers, and/or one or more composites may be included in addition to or instead of ceramics, for example. The prosthetic component may comprise any one or more of: a nitride, a carbide, an oxide, and combinations thereof. Examples of possible compounds include but are not limited to: silicon nitride; zirconium oxide; aluminium oxide. However, any suitable nitride, carbide, oxide or combination may be used. Any combination of the above may be envisioned. For example, the prosthetic component may comprise by weight or volume 0% or 100% or any percentage in between of any of: silicon nitride; zirconium oxide, and aluminium oxide, or any other compound. More preferably, the percentage may be in the range of 15% to 90%, more preferably within 20% to 85%, even more preferably between 25 % and 80%. More preferably yet, the range may be between 40% and 70% and even more preferably between 50% and 60%. The prosthetic component material may comprise an inorganic material or a material classed as such. However, it is also envisaged that the material may comprise any of organic, bioinorganic or organometallic elements or parts, for example. The prosthetic component material may be non-metallic or comprise non-metallic elements. For example, for a nitride, carbide or oxide, the ceramics may be non-metallic. However, in some cases, the prosthetic component material may be metallic or semi-metallic or comprise metallic or semi-metallic elements. The prosthetic component material may be crystalline. That is, the material may have a highly-ordered structure. The crystallinity of the material may be considered at the working temperature of the device in the body, which is typically about 37 degrees Celsius. Alternatively, the prosthetic component or part thereof may have a non-crystalline structure. That is, the material may be glassy or have an amorphous structure. If the prosthetic component comprises more than one material, then it is contemplated that all of the materials may be crystalline or non-crystalline, or that some materials are crystalline and others are non-crystalline.

Detailed description of the ceramic materials is omitted, once again, for brevity. More preferably, the prosthetic component is solely formed of ceramics but this feature may be omitted. The prosthetic component may be formed as a one-piece, but multiple parts may be envisioned.

The uses of the third embodiment are similar to the uses of the first two embodiments. The prosthetic component is optionally formed via an additive manufacturing process, as described for the first and second embodiments. Detailed description of the common features is omitted for brevity. Thus, the prosthetic component may be formed using a flowable ceramic material. The only different steps are that the shape of the prosthetic component may be different and that the prosthetic component may be inserted in another position and/or joint if the prosthetic component is not an acetabular cup and/or is for arthroplasty of another joint.

Referring now to a fourth embodiment of the invention, not shown, there is provided a ball-and- socket prosthetic system.

The system includes a socket element and a ball element. The socket element or socket may be similar to the acetabular cup of the first and/or second embodiments. The socket element may have at least one, and preferably two walls. Said walls may be spaced-apart, forming a cavity therebetween. The walls may optionally join at and form a rim. Optionally, one or more reinforcing elements may be provided. Detailed description of the common features is omitted for brevity.

The ball element or ball may be non-captively or, preferably, captively held for articulation within the socket element. This may reduce the likelihood of dislocation of the joint. To this effect, the socket element may optionally have a retaining portion.

The retaining portion may comprise a retaining ring, a protrusion, projection, such as a lip. The retaining portion may extend at least partly inwards relative to a rim of the socket element. Alternatively, the socket element may narrow or have a neck portion. This may occur, by way of example only, if the socket element has a part-spherical articular surface which is more than a hemisphere. The retaining portion may optionally be integrally formed, connected or connectable with the rim and/or a wall of the socket element, preferably at or adjacent the rim.

At least the socket element may be formed from ceramics, similar to the first embodiment. More preferably, the socket element is formed of a flowable ceramic material. Furthermore, the socket element and/or the ball element may optionally be formed via an additive manufacturing process. If the ball element is captively held within the socket element, the socket element is preferably formed of a flowable ceramic material via additive manufacture with the ball element in situ or received within the socket element. The ceramic material may comprise any or any combination of: zirconium oxide, aluminium oxide, and any other suitable oxide.

The ball element may comprise metals, plastics, ceramics, any other suitable material, or any combination of the above. Most preferably, the ball element consists essentially of ceramics. The ceramic material may be the same as or similar to the ceramic material of the first embodiment. Detailed description is omitted for brevity.

The ball element preferably has a recess but the recess may be omitted. Preferably the recess is suitably dimensioned and/or complementarily shaped to receive a portion of a stem and/or neck of a prosthetic component. The recess may therefore be referred to as a taper or taper portion. Optionally, the ball element may comprise at least one cavity. The uses of the fourth embodiment are similar to the first embodiment. Detailed description of the common steps is omitted for brevity.

The socket element may be formed via an additive manufacturing process, as described in the first embodiment. Preferably, the ball element is in situ prior to formation of the socket element and/or may be inserted during the formation of the socket element. In other words, the socket element may be formed around the ball element.

If desired, the socket element may be formed so as to captively hold the ball element. This is provided by forming a restraining element and/or shaping an opening of the socket element such that at least one of: a major dimension, a minor dimension, and a cross-sectional area of the opening is smaller than a relevant dimension and/or cross-sectional area of the ball element. This may be enabled by providing a narrowing or neck portion. Preferably, the opening of the socket element is circular or substantially circular, but non-circular is an option.

Before or during surgery, a stem or neck thereof of a prosthetic component is connected to the ball element. More preferably, the stem or neck thereof comprises a taper portion or a portion complementarily-shaped and/or dimensioned to engage with the recess of the ball element. The stem and/or neck portion may additionally comprise ceramics, but this feature may be omitted. The ball-and-socket prosthetic system may be suitable for any joint which traditionally comprises a ball and socket arrangement such as a hip or shoulder. However, it may even be envisioned that the ball-and-socket prosthetic system may be adapted for any other joint, such as a knee joint. In this case, the socket element may need to be adapted to limit, restrain, restrict, or prevent motion in certain directions. The opening of the socket element, in this case, may be non-circular. More preferably, the socket element opening may have an elongated shape. This non-circular shape may guide and/or constrain the movement of a prosthetic element connected to the ball element to a predetermined axis or direction.

The ball-and-socket prosthetic system together with the stem is implanted into the relevant joint of the patient.

In a slight modification to the above, the ball element of the ball-and-socket prosthetic system may optionally be integrally formed together with a stem of a prosthetic component. The socket element may be similarly formed around the ball element via additive manufacture.

Whilst the prosthetic component is preferably formed by additive manufacture, the prosthetic component may alternatively be formed via a traditional or non-additive manufacturing process. A traditional manufacturing process typically includes heating a ceramic material in powdered form in a mould, also known as sintering a green body, using usual techniques known to the person skilled in the art. Whilst the outer wall and the inner wall or first and second walls are preferably continuous and devoid of apertures, in an alternative embodiment, one or both walls may comprise at least one opening, through-bore, or aperture. This may facilitate fixation to the bone, for instance, by enabling a fastener to be receivable therethrough. An example of a fastener may be a screw. Although the or at least one of the reinforcing elements is a partitioning element, the or at least one further said reinforcing element may be a strut or strut-like element. Such a strut may not subdivide the cavity into sub-cavities. A strut may provide structural reinforcement and/or space- apart the inner and outer walls whilst remaining lightweight. Thus, the weight of the prosthetic component is minimised or reduced.

Further alternatives for a reinforcing element may include inserting into the cavity and/or into at least one sub-cavity any or any combination of: a fluid, such as a liquid and/or gas; a gel; and one or more ball bearings. If a fluid, the fluid may be at high pressure. The fluid may be compressible or incompressible. If a fluid, it may be preferable that the entire volume of the cavity and/or sub-cavity is filled so as to provide an opposing force to any force acting on the prosthetic.

Whilst the exterior surface of the outer wall or of at least one of the first and second walls is preferably directly abuttable against bone, indirect abutment or non-abuttable may be options. For example, an intermediate element or portion may be provided between the exterior surface. Such an intermediate element may be a liner, liner element, tissue, cartilage, artificial cartilage, bone cement, or any other suitable intermediary or combination thereof.

Although preferably a hemisphere at most, it may be envisioned that the acetabular cup may be a greater portion of a sphere than a hemisphere in an alternative embodiment. A smaller femoral head may be required in this alternative, in order to be insertable through the narrower rim portion.

Preferably, the inner wall or the first and second walls are devoid of any engagement-enhancing portions. However, these features may be envisioned for any wall, as required. An engagement enhancing portion may comprise one or more grooves, recesses, protrusions, projections, a non-smooth surface, a coating, such as a bone-growth enhancing coating, any suitable engagement-enhancing portion or combination thereof.

Although a trapezium with rounded corners is the preferred shape of a sub-cavity in longitudinal cross-section and a ring in transverse cross-section, any non-trapezium and/or non-ring, respectively, may be envisioned. Furthermore, although a preferred shape may be specified for the inner-wall interior surface, the inner-wall exterior surface, the outer-wall interior surface, the outer-wall exterior surface, the rim portion, or any above-described feature, it may be envisioned that the feature may have an alternative shape in transverse and/or longitudinal cross-section may be envisioned.

Any or any combination of: a sub-cavity, the inner-wall interior surface, the inner-wall exterior surface, the outer-wall interior surface, the outer-wall exterior surface, the rim portion, or any above feature may have an alternative longitudinal and/or cross-sectional shape. Said shape may be a polygon, such as a triangle, a square, a trapezoid, a rectangle, a pentagon, a hexagon, an octagon, or any other polygon; whether regular, irregular, optionally with one or more corners chamfered and/or rounded; any curved, part-curved, or non-curved shaped; a circle, an oval; or an ovoid; an ellipse; a line; periodic such as sinusoidal, saw-toothed, crenellated, or an abstract shape.

In all the above embodiments, a cavity is provided. However it could easily be envisioned that the cavity may be omitted in any of the embodiments. There may only be one wall in this embodiment.

Whilst in all the above embodiments, an outer surface of the wall or outer wall is abuttable against or engageable with bone, it may be envisioned that the outer surface of the wall or outer wall may not be abuttable or engageable with bone. The prosthetic component may instead comprise at least one bone-engagement portion. The, each or at least one bone-engagement portion or part thereof may be engageable with the bone instead. The or each bone- engagement portion may comprise a projection, spike, or protrusion. The, each or at least one bone-engagement portion may additional have a further function of reinforcing the prosthetic component. The cavity may be omitted. Alternatively, at least one secondary wall may be provided to form a cavity. The cavity may or may not sealed. The secondary wall may be positioned or recessed inwardly of an extremity or outer portion of the, each or at least one bone-engagement portion. The secondary wall thickness may be uniform and/or variable. The secondary wall may be thinner, thicker or of equal thickness relative to the first wall.

Although in all the above embodiments, the whole of the prosthetic component is formed via additive manufacture, it may alternatively be envisioned that in any embodiment, only part of the prosthetic component may be formed via additive manufacturing. By way of example only, a generic prosthetic component or a part may be formed via traditional manufacturing or via additive manufacture. In a further step, additional features may be added to the generic prosthetic component or part via additive manufacture. For example, a generic ceramic acetabular cup may be formed via traditional ceramic manufacture. In a further step, any or any combination of: a secondary wall, one or more reinforcing elements, and one or more bone- engagement portions may be added to the generic acetabular cup via additive manufacture. It is therefore possible to provide a light-weight acetabular cup by virtue of being hollow. As the acetabular cup is formed of ceramic, the cup does not release damaging particles and metal ions. It is therefore also possible to provide an acetabular cup formed via additive manufacture. As well as providing a custom-made prosthetic providing a better fit, this may advantageously reduce the number of prosthetic implants that need to stocked at the hospital, saving space, cost and reducing waste. There is also provided a prosthetic component, which may be an acetabular cup formed in multiple steps. A generic prosthetic component may be customised via addition of features via additive manufacture. There is also provided a ball-and- socket prosthetic system in which the ball is captively held within the socket. The risk of dislocation is reduced. It is also possible to provide a light-weight ceramic prosthetic component for any joint. A method of forming a ceramic prosthetic component, which may optionally be an acetabular cup, is also provided. As the method involves an additive manufacturing process, the prosthetic component may be customised to the patient for improved stability and/or durability. The words ‘comprises/comprising’ and the words ‘having/including’ when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components, but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

The embodiments described above are provided by way of examples only, and various other modifications will be apparent to persons skilled in the field without departing from the scope of the invention as defined herein.