Monoblock Acetabular cup with Trabecular-like Coating

Final Report Summary - MATCH (Monoblock Acetabular cup with Trabecular-like Coating)

Executive Summary:

The project aim is to enhance the research and innovation of three SMEs working in different sectors, namely glass production, coatings fabrication and software on demand. These SMEs will commercially exploit the project findings on osteoinductive coatings and scaffolds. Without this project the 3 SMEs would not be in a position to provide into this market area.
One person out of 150 people reading this document will likely need a hip prosthesis in the following 30 years.
Therefore, to meet this ever increasing demand, MATCh aims to deliver a MONOBLOCK ceramic acetabular cup prototype during the project period.
At present, non-cemented acetabular elements are characterized by a configuration comprising a cup housed in a metal back for the implant osteointegration. This configuration has drawbacks of high risk of relative mobility, wear of the cup and potential damage to the pelvis bone.
To overcome these drawbacks, three different prototypes of an innovative MONOBLOCK ceramic cup had been developed based on the patent demand no. WO2008/146322A2, which describes a cup anchored to the bone through a bioactive trabecular coating, glazed on its surface and able to promote both primary and long term osteointegration. In this monoblock cup, there is no metal back and it allows a ceramic-on-ceramic coupling with very low wear rate. In addition, this configuration allows a wider range of prostheses sizes and less trauma during surgical implantation.
MATCh had developed three different prototypes that should be able to accelerate osteointegration and to avoid aseptic loosening due to wear, relative mobility and bone damage and that could be used for a wider range of patients.
The project goals had been achieved within the project duration thanks to the RTD partners background and work (AIMEN, FCIM, ICI, POLITO) and to the continuous support and monitoring of the SMEs partners.
Technologies for glazing glasses on ceramic substrates and for the production of scaffolds and trabecular-like coatings had been developed and optimized.
The SMEs partners (FAME-MED, GTS and EXEMPLAR) had worked on the production of coatings, industrial glass synthesis and biomechanical modeling.

MATCh has a public website:
http://match-euproject.com

Project Context and Objectives:
MATCh project objective aims to work out the recent need of the market offering new designs in
the field of orthopaedic devices. The SMEs (FAME MED, GTS, EXEMPLAR) will provide their skills in order to design new and reliable macroporous glass-ceramic coatings for the surface modification of commercial ceramic acetabular cup, leading to the delivery of a new generation of
hip prostheses with enhanced functionalities, currently not available on the market. Although extensive research is carried out regarding surface modification of biomedical implants, the
translational approach from lab bench to industry is lacking. One out 150 of the people reading this
text will likely need an hip prosthesis in the next 30 years and it is obvious that improving implant technology in an aging world is important.
MATCh aims at increasing the quality of patient’s life increasing the prostheses life time, enhancing their degree of osteointegration and allowing the use of a long-lasting ceramic-on ceramic coupling also to patients that normally could not benefit of it for technological constraints.
In fact it is becoming normal to implant hip prostheses in patients below 50 and even below 40 years old, and in such cases ceramic-on-ceramic coupling, due to its very low wear rate, is a real need.
Avoiding the metal-back with a surface modification of the ceramic cup will allow to reduce the cup thickness and to increase the ceramic ball size of the prostheses in accordance to most recent trends.
There are several specific scientific/technological needs that the SME participants will try to solve, together with the RTD performers:

Ceramic Processing (FCIM)
The world of Advanced Technical Ceramics (ATC) is in the hands of multinationals, since the necessity of resources drives it away from SMEs. But SMEs outwin multinationals in niche markets, where flexibility and imagination are essential.
Ceramic processing is long since it is constituted of many intermediate steps that cannot be avoided.
This is compensated by serial manufacturing with intermediate semi stocks, that while increasing the cost, enable faster delivery.
Getting functional prototypes using Rapid Prototyping techniques have a vital importance in making the ATCs, because apart from being able to reduce launch costs would reduce the time to availability of prototype.

New materials synthesis (POLITO, AIMEN)
Bioceramics have been widely investigated as bone graft materials with a wide range of applications including bone defects filling, fracture fixation, trauma, tumours, maxillofacial and spinal surgery, drug delivery systems. Among the ceramic materials, calcium and phosphate salts as well as hydroxyapatite (HA) are usually used for these applications. Besides, a wide range of glasses and glass-ceramics have been proposed. Their main property, which makes them very challenging in comparison to other synthetic materials, is their bioactivity, i.e. the implant is not only osteoconductive, but also induces osteoblasts to differentiate and to deposit bone matrix.
However, very few of these materials have been successfully used for load bearing applications
This drawback can be reasonably solved in the case of glasses and glass-ceramics because of their very peculiar compositional versatility.
A new, bioactive, macroporous glass-ceramic coating for ceramic surfaces as the one proposed within this project would be of primary importance in bone surgery market.
POLITO experience in the field of bioactive glasses and glass-ceramics, coatings on ceramic substrates and macroporous 3D scaffolds for tissue engineering, is widely documented (e.g. C.
Vitale Brovarone et al., Acta Biomater. (2007);3:199-208; C. Vitale-Brovarone et al. J Mater Sci:Mater Med (2009);20:643-653; S.Scheiner et al. Biomater (2009); 30(12):2411-2419; F. Baino et al. Mater Sci and Eng C. (2009); 29:2055-2062; C. Vitale-Brovarone et al. J Biomater Appl,(2010);24:693-711, Baino et Al. (2011);97:514-535, Vitale-Brovarone et al. J Mater Sci Mat Med (2012); 23:2369-2380).
This long experience will be of great importance in view of the optimization of innovative formulations for the specific field of application.
Laser cladding is a rapid prototyping technique that will be proposed by AIMEN to fabricate the trabecular part of the ceramic cup and will also be tuned in order to tailor the degree of crystallinity of the glass-ceramic aiming to modulate its mechanical strength and osteoinductive behaviour.
It is normally used to produce full 3D structures, but will be exploited in an innovative way to prepare a tailored trabecular-like surface with a controlled degree of cristallinity on the already produced part, in a fast and productive process when compared with traditional rapid prototyping approaches.
Laser Ablation is a surface processing technique based on high power short laser pulses able to directly vaporize (ablate) the irradiated material, that can be used to tailor the texture and surface topography of virtually any material by creating a controlled microscale structure.

GTS is a SME who is highly interested in the developing of new bioactive glass and glass-ceramic formulations on a pre-industrial and industrial scale to supply them to manufactures.

New medical devices
FAME – MED is interested in getting into the market of medical devices with the production of new bioactive coatings on ceramic medical devices that are one of the MATCh prototypes but it is also interested in extending the acquired know-how to metallic implants.
The main problem associated with the production of glass and glass-ceramic coatings on alumina and zirconia substrates is the mismatch in their thermal expansion coefficients: a considerable residual tensile stress is induced in the glass coating, resulting in crack formation and insufficient adhesion at the interface if the glass composition is not carefully optimized, taking into account also the compositional ranges for bioactivity. Additional challenges can be associated to the production of bioactive coating with a trabecular-like morphology and to the preparation of ceramic surfaces with suitable roughness.
Macroporous glasses and glass-ceramics can be prepared by using different methods; the most promising ones are sponge replication and freeform fabrication through laser cladding.
The skills of participant SMEs (FAME-MED, GTS and EXEMPLAR) together with the RTD performers (POLITO, FCIM, AIMEN, ICI) will be focused on the optimisation of the ceramic surface properties, the glass composition and the coating procedure, in order to engineer a process
transferable to the production line able to provide a dense ceramic cup covered by an adherent and
sound trabecular bioactive coatings. MATCh efforts are focused on the INNOVATION of existing products.

Modeling
EXEMPLAR is a dynamic SME with experience in software for biomedical applications that will get benefits from the development of an automatic process methodology that could take into account new material data and laws, geometrical models, and so on. The aim is the validation of components and the methodology altogether in a two steps process.
In the first step, a virtual environment (complete automatic process) will be created; this model will
be validated by testing data provided by other SMEs and/or RTDs and in particular ICI and POLITO. In a second phase, virtual model could be extended for further and more complex mechanical and thermal testing. In addition every variation of the model (material properties, constraints, loads and every boundary conditions) will be taken into account in order to optimize the
PROTOTYPES features and performance.
All the topics described above have in common the need for new, versatile materials and technologies aiming to develop innovative glass-ceramic layers suitable to be applied on ceramic or
ceramic-matrix composite surfaces. The involved SMEs have a limited access to research facilities
and the outsourcing of research activities to RTD performers was essential at this point.

Project Results:
As reported in the summary of the Project, the final aim of MATCh Project is to obtain a prototype of an innovative ceramic cup with a trabecular-like coating (Fig. 1) to be used for hip prosthesis in ceramic-on-ceramic couplings.

PRODUCT SPECIFICATIONS

As described in Annex I, at the beginning of the project, the consortium, with the active support of the SMEs, had defined the materials and products specification in order to properly address and define the project intermediate and final objectives.
More specifically, the ceramic cup feature had been examined and defined thoroughly also enlarging the discussion to several orthopaedic surgeons (one of which is directly involved in the consortium as a SME: FAME-MED).The discussion had been supported by an extensive market search with the objective of verifying the commercial products already available (already done during the project preparation) but eventual recent innovations had been searched thoroughly.
The discussion was at the end focused on the realisation of a ceramic cup with a hemispherical shape and with dimensions referring to the most commonly implanted ceramic cups.
At the end of this activity, the ceramic cup features were defined as reported in Fig. 2.
The composition of the ceramic cup was defined taking into account the most widespread commercial product that had been taken as a reference material (Biolox® Delta, http://www.scribd-com/doc/44989493/Biolox-Delta-Book-Chapter-2009) and an analogous composition (apart from minor components) was set as part of the project specifications.

NEW BIOMEDICAL GLASSES

A great attention was also devoted to the overview of bioactive glass commercial products as well to the standard specifications applied to these materials. In particular, it was agreed among the consortium to use ASTM F1538-03 “Standard Specification for Glass and Glass Ceramic Biomaterials for Implantation”, as the glasses that will be developed in the frame of the Project are supposed entering the biomedical device field of application. At this purpose, the involved SME (GTS) had selected suitable sources for the different oxides, taking into account the limitation of the relative ASTM standard (see Fig. 3 as a summary), with a careful eye on the commercial costs, that are essential to be competitive on the market.
A set of 8 purposely developed compositions was provided and they have all been tested at the laboratory scale at Politecnico di Torino.
After an extensive characterisation phase, on the basis of considerations related mainly to their thermal expansion coefficient, bioactivity and bioresorbability and, most importantly, sintering behaviour, two out of 8 compositions had been selected in order to realize the dense coating (code 3-C glass) and both the dense coating and the trabecular-like layer (3-U). On the two selected glasses, the involved SME (GTS) had intensively worked in tandem with POLITO, in order to develop a suitable strategy to obtain the tuned formulation within the limits imposed by ASTM F1538-03. Being this an important industrial foreground, the decision of making public the developed compositions had not been taken yet, so they will not be reported in this document.
The selection and mixing of raw materials are surely key issues to be taken into account in order to produce a homogenous batch and glass melt, but homogeneity of glass melt is also ensured by stirring and gas bubbling through the melt. The suitable industrial process was successfully developed at GTS (UK) for the two of the selected glasses and it is considered confidential.
Fig. 4 reports the interior of one of GTS furnaces used to produce the biomedical glasses and Figs. 5a and 5b show the glass frits and the glass powders after suitable machining and sieving.

COMPOSITE CERAMIC CUP FABRICATION

Impressive results have been obtained in the machining of the composite ceramic cup using the subtractive technology, as can be seen from the details reported in this section. A series of technical procedures and processing parameters had been developed in the frame of a dedicated WP (WP3) and the optimised method is reported at the end of this section.
At the beginning of the process, the raw ceramic material (75%wt. Al2O3-25%wt. Y-ZrO2) is prepared in the shape of a powder of homogeneous grains. The two elements of the final ceramic material are mixed together to obtain the final powder. In this regard, there are two different steps to undertake: shredding and mixing. The first one is used in order to obtain a homogeneously mixed powder. This step is performed in an automatic mixer and requires 24 hours. If the step is not performed until the completion, there is a risk that the two components are poorly distributed in the material and that the “green” ceramic cylinder (that will be prodiced later) behaves randomly. Then, there is a second step of atomizing the powder, to obtain a fine powder, comparable to a fluid. The first step of the machining process is to create a machinable solid part; this part is a cylinder of external dimensions of 50 mm diameter and 35 mm length, as defined for a minimum material waste and an optimal machining. In order to create the geometry needed, the ceramic powder is pressed into a special mould and then the cylinder is pre‐sintered in order to increase the bonds between the ceramic grains making the part stronger and denser and thus able to be machined. In order to machine the ceramic cylinder, it has to be fixed to an aluminum support that will be affected by the stress constraints related of the subjection method instead of the fragile ceramic part. To achieve the bond between the two parts, a two component Epoxy resin is used. The fragility of this material and the geometrical requirements of the design imposed the development of subjection systems that could allow the machining processes of the internal and external sides of the cup. For simplicity, the first process was the machining of the outer side of the cup that was divided in three distinct operations: the blank sphere machining, the finished sphere machining and then the planar surface (see Fig. 6).
The hemispherical geometry of the outer face and the fragility of the ceramic compound used in the cup made impossible the utilization of a conventional subjection system for the machining of the inner face of the cup. In this sense, an innovative solution for the immobilization of the ceramic was designed and implemented; this system consisted of a tailored plastic holder for the accommodation of the hemispherical cup and, in order to provide immobilization and rigidity, an adapted metallic box containing the plastic holder. With this solution the ceramic cup could be machined without damage; the metallic box used for supporting the plastic holder was closed with a lid screwed on the metallic box, therefore immobilizing the ceramic cup. In order to allow the subsequent machining of the ceramic cup the lid was drilled.
A ring was added to this subjection system between the lid and the ceramic cup in order to avoid the possible scratching of the fragile ceramic part when clamping the lid, and also to guarantee the correct adaptability of the system for different cup dimensions (small and large size).
For maximizing the contact surface between the box and the plastic holder, making the liaison safer and optimizing the subjection system by preventing from internal movements during the machining operations, a conical shape for the inside of metallic box and the plastic holder was proposed. The plastic holder was fabricated by stereolithography (Fig. 7). The metallic support designed for the subjection of the ceramic cup during the machining of its internal side consisted of a box, a lid and a ring (Fig. 8). The box used to enclose the system, shown in Fig. 8a, was made of steel, preparing first the base of the cylinder and then machining its exterior side, the external thread and the inner cone. These operations were realized using a CNC turning machine in a three-jaw chuck subjection device.
As in the case of the box, the base material used for the lid (Fig. 8b) was a steel cylinder. In a first step the lid was machined and drilled using a CNC lathe, making the hole for the subsequent machining of the inner face of the ceramic cup, and then the lid was threaded using a M90 standard so that it could be screwed on the metallic support. In a second step, the top edge of the lid was rounded with a 5-radius machine. For the ring (Fig. 8c) a standard CNC turning machine was used for the machining of the entire ring, after which its two sides were subjected to an abrasive treatment through a grinding machine to achieve a fine finished surface. In the same stage of the process, a drill was used to perforate a bore in the center of the ring as in the case of the lid. Then, the grinding machine was used to provide the ring its final finish suitable for the contact with the ceramic cup without damaging it.
Once the subjection system was manufactured and mounted wrapping the ceramic cup (see Fig. 9), the inner part of the cup could be successfully machined as shown in Fig. 10.
The stages constituting the whole manufacturing process of the ceramic cups are summarized in Fig. 9.

As a conclusion, the work done to obtain a tailored hemispherical cup with biomedical applications enabled the development of a fully customized subjection system for the machining of the internal and external faces of the ceramic cup in such a manner that the stress caused during the machining steps did not cause any damage to the ceramic part. The mechanical properties of the ceramic used and the complexity of the geometry of the part, together with its functional requirements, demanded the design and development of a tailored subjection mechanism for the different machining steps of the ceramic cups. In this sense, the system conceived for the machining of the external face of the cup consisted of an aluminum cylinder attached to the ceramic. This aluminum support absorbed the stress generated in the process, preventing any possible damage to the ceramic material. For the machining of the internal part of the cups, a tailored system was designed consisting of a plastic holder whose geometry was adapted to hold the external face of the cup. This plastic device was introduced into a metallic box that enclosed the system, permitting the machining of the internal face of the ceramic cup without damaging it.
As a summary, the manufacturing comprises 13 different phases, differentiated in Fig. 11 by a colour coding. The red colour corresponds to the heat treatment applied on the ceramic material, such as pre-sintering and sintering. The blue colour is used for the machining phases applied to the parts, such as the outer and inner sphere machining, the crosscutting and the laser ablation. The phases in green are the different metrology or roughness assessments which result in the metrology or roughness reports. The rest of phases in grey are the preparation phase, about the material or about the machining support and tooling.

DENSE COATING FABRICATION

The aim was to obtain a dense intermediate layer well adherent to the composite ceramic cup obtained with subtractive methodology in the frame of the first months of the Project.
At this purpose several technologies had been addressed:

*Air-Brushing
*Spin coating
*Dipping
*Laser cladding

After a series of tests and coatings fabrication, the strategy had been focused on dipping and laser cladding technologies, obtaining in both cases reproducible and significant results.

AIRBRUSHING

For sake of completeness, the airbrushing system used at Politecnico di Torino (POLITO) in the frame of MATCh Project is reported in Figs. 12 and 13 and curved coated samples as well as a micrograph of a cross-section of the realized coating is reported in Fig. 14.
The technique was abandoned due to issues related to the block of the nozzle by the glass powders and to the intrinsic limitation of obtaining a uniform thickness with the necessary slurry that is characterised by a limited solid loading needed to reduce as much as possible clotting of particles and nozzle obstruction.

SPIN COATING

The spin coating technique was proposed and tested at FAME-MED (SME-Turkey) using glass powders supplied by GTS. The glass powders were carefully ground in ethanol in a planetary ball mill using zirconia balls as grinding bodies. The slurry was then used in a spin coater (Fig. 15) for different coating steps, at suitable rpm for time periods in the order of tenths of minutes.
The obtained coatings are shown in Fig. 16 and are only a few microns thick, thereby resulting unsuitable for the application envisaged for MATCh Project; for this reason this technique had been abandoned.

DIPPING METHOD

Dip coating was proposed and tested by POLITO, with the support of GTS and FCIM in supplying the raw materials/products (glass powders and alumina/zirconia composite cups, respectively).
From a conceptual viewpoint, this technique is quite easy and analogous to traditional enamelling of ceramic products, which has been used by skilled craftsmen for producing coated vessels and, more generally, pottery since the ancient times.

It is interesting to underline that, in developing MATCh project activity, the researchers moved from flat substrates to curved ones. By following this logical rationale, coating techniques able to be applied first to a plane surface and then to a non-planar one were selected. Therefore, this is the reason why airbrushing was investigated as first technique and considered potentially suitable for the intended goals – it could be applied to both plane surfaces in the preliminary embodiment and afterwards to the curved surface of the cup. On the contrary, dip coating seemed not to be particularly suitable for flat substrates – problems of coating homogeneity and thickness uniformity would occur, apart from technological problems on how to deposit the coating with such geometries – but quite promising to coat products exhibiting particular symmetries, like rotational symmetry or even better axial-symmetry.

The typical processing schedule applied for the dip coating of the alumina/zirconia composite cups supplied by FCIM can be summarized in 4 stages (slurry preparation, dipping, drying and firing), as listed below. The feasibility study for this method was carried out at a Lab-scale; some suggestions for industrial up-scaling of the process were also provided in the frame of a confidential report to the interested SMEs.

A 3-component slurry was prepared mixing glass particles, distilled water and poly(vinylalcohol) (PVA) used as a binding agent; the two selected compositions (3-C and 3-U) were both used.
The water-based slurry prepared for dip coating had a high solid load and the slurry preparation involved the following stages:
 preparation of PVA/water batch in a beaker;
 PVA dissolution under continuous magnetic stirring at around 80 °C;
 glass powder addition to the PVA/water solution;
 re-addition of the water evaporated during PVA dissolution to maintain the original ratio among the constituents;
 further stirring at room temperature to ensure homogeneity of the slurry.

The rotation should be sufficiently vigorous to avoid sedimentation of the glass particles at the bottom of the beaker but, at the same time, not too excessive in order to avoid air incorporation in the slurry, with the consequent unwanted formation of bubbles. The cup was manipulated by means of an ad-hoc designed sample-holder system, constituted by a plastic tube hosting a peg and a ring (Fig. 17). This supporting system is centred coaxially with the main rotational axis of the cup. This approach is valuable to avoid any unwanted contact between the green glass coating deposited on the cup and the operator’s fingers or other surfaces, that might damage or accidentally remove the coating.
The plastic disk at one of the peg’s ends not only supports the cup, but also prevents the slurry from percolating into the cup cavity during the immersion. In view of the development of a production line, an automatic system of “grasping” and transportation – for instance, a bearing line with many “small arms” – will be implemented for this purpose.
The cup was slowly dipped into the slurry till its external surface was completely submerged by the suspension (Fig. 18) and maintained there for few seconds; both small and large ceramic cups were used. The thickness of the intermediate layer was tuned on the basis of a series of suitable dipping cycles.
After drying, the green layer underwent a suitable glazing treatment which allowed the glass softening and the firm attachment of the coating to the ceramic cup as can be seen in Fig. 19, in which a green coated small cup and a small and a large coated cups after the thermal treatment are shown. Fig. 20 reports a micro-CT reconstruction of the ceramic cup coated with the dense intermediate layer whereas Fig. 21 shows the uniformity of the coating obtained by dipping.
Ceramic materials typically have a brittle behavior, i.e. when subjected to compressive and tensile loads exhibit almost exclusively elastic deformation up to the breaking point. The absence of plastic deformation justifies the high compressive strength, up to 10 times greater than that in tension. A high mechanical strength of adhesion between the layers constituting the monoblock cup studied in the project (alumina/zirconia substrate cup + glass-ceramic intermediate layer + glass-ceramic trabecular coating) is a fundamental requirement in order to obtain a good clinical outcome.
In an in vivo scenario, the porous layer will be involved as an active player in the bone in-growth processes. The strength of an implanted porous biomaterial can significantly increase in vivo due to tissue in-growth: in fact, the cells adherent on scaffold, the newly formed tissue and the scaffold itself create a biocomposite in situ, thereby increasing the time-dependent scaffold strength.
Therefore, maybe the most critical interface is that between the intermediate glass-derived layer and the ceramic substrate, since the adhesion between these two elements has to adequately withstand the stresses to which the device will be subjected postoperatively without originating any detachment between coating and substrate – which would represent the failure of the cup.
For this reason, the glass-derived intermediate coatings were tested under tensile loads to assess the adhesion strength to the substrate from a quantitative viewpoint and value of sigmat of 27.4 ± 18.6 MPa were obtained. If we refer to international standards, a tensile stress of at least 15 MPa is recommended, for instance, in the case of hydroxyapatite coatings on titanium alloys for prosthetic applications and so the obtained values are well above the standard limits.

LASER CLADDING

The bioactive glass powder provided by GTS were placed in a powder feeder from Medicoat (Fig. 22a), which delivered the powder transported by an argon (Ar) stream to a powder coaxial nozzle COAX 8 (Fraunhofer IWS). This nozzle was attached to the laser processing optics (Fig. 22b), a parabolic Cu mirror able to focus the laser beam to a laser spot diameter of 200 um. Therefore, the powder was injected coaxially with the laser beam, so that it was blown onto the substrate at the same laser beam incidence point. In this way, the powder was melted and joined to the ceramic cup substrate.
Both the laser optics, with the attached powder nozzle, and the ceramic cup were manipulated by a 5-axis CNC machine from LANTEC. The relative movement between powder nozzle and ceramic substrate allowed obtaining a laser cladded track on the substrate surface. By overlapping several laser cladded tracks a dense coating can be produced.
The study was carried out using a low laser power (peak power 350 W) due to the high absorbance of glass at the CO2 laser wavelength (10.6 um), in both continuous wave and pulsed mode (5000 Hz repetition rate and duty cycle from 20 to 40%). The laser spot diameter on the substrate surface was varied from 200 um to 2 mm. The powder flow was slightly changed between 2 and 3 g.min-1 using 3 l.min-1 of Ar as carrier gas and 9 l.min-1 as shielding gas. The processing speed was also changed from 60 to 70 mm.s-1.
A uniform, completely amorphous glass layer was finally obtained on flat substrates (Fig. 23). The technique showed to be effective and highly reproducible and was then applied to the ceramic cup as can be seen in Figs. 24 and 25.
The technique can be also applied to substrates different from ceramics.
At this purpose, one of the involved SMEs is evaluating the possibility of applying the generated foreground to metallic implants.

TRABECULAR-LIKE COATING FABRICATION

The trabecular-like coating in the outer layer of the proposed monoblock ceramic cup and it is the one that should go directly in contact with the patient pelvis bone.
It should be highly porous, bioactive and its morphology should mimic as much as possible the one of the natural spongious bone tissue, in other word it would be a 3D-scaffold firmly attached to the ceramic cup coated by the dense layer (as can be seen in Fig.1).
One of the main challenges of bone scaffolds manufacturing still remains the attempt to set up a technologically easy, ideally inexpensive and highly reproducible method of fabrication able to lead to 3-D glass-derived structures effectively mimicking the 3-D trabecular architecture, morphology and biomechanical behaviour of natural cancellous bone.
Many experimental evidences demonstrate that the sponge replication technique fulfils these requirements. Briefly, this method involves the impregnation of a polymeric template (e.g. an open-cells sponge) with a glass slurry, followed by the removal of the organic phase (burning-out) and the sintering of the inorganic particles via a thermal treatment. In this way, it is possible to obtain a glass or glass-ceramic porous scaffold that closely mimics the trabecular architecture of natural bone.
The features of the final scaffold are dependent on many parameters, e.g. the starting polymeric template, the chosen glass, the slurry characteristics (e.g. ratio among the components, viscosity), the processing parameters and the sintering conditions.
The easiest, less expensive approach involves the use of a commercially available polymeric sponge; the pores morphology, size and interconnectivity of the final scaffold are closely dependent on the analogous features of the starting porous polymer. The sponge should be easily and completely removable at relatively low temperature (below 500 °C) to avoid any organic contamination of the scaffold (on the contrary, the glass phase will sinter at higher temperature); an open-cells polyurethane (PU) sponge is very suitable for this purpose. After choosing the sacrificial polymeric template, it is necessary to tailor the sponge according to the final shape and size required for the final scaffold. The sponge can be shaped by manual cutting or by using automated/semi-automated processes depending on the geometry complexity; in MATCh Project the cup size were obtained by applying a semi-automated thermal pre-forming strategy. Usually, the slurry is a homogeneous water-based suspension of glass powders used to uniformly coat the walls/struts of the porous polymeric template. A typical recipe for slurry preparation includes fine glass powders, water and other additives as binding or dispersant agents. A key parameter that should be carefully considered is the solid load, i.e. the fraction of glass particles over the liquid (water). In fact, if it is too high, the slurry viscosity will become excessive, thereby preventing the glass particles from penetrating the inner part of the template. On the contrary, if the solid load is too low, the slurry viscosity becomes too low and, therefore, the glass particles will not stick to the polymer and will be “washed away” from the sponge structure. In order to improve the adhesion of the inorganic particles to the sponge struts, the use of a binder is very appropriate. For instance, poly(vinyl alcohol) (PVA) is helpful to stick the glass particles together as well as on the sponge walls and to strengthen the impregnated sponge after drying, thereby avoiding damages of the glass particles layer.
The components have to be carefully mixed together, which is usually performed by magnetic stirring, to allow the complete solubilisation of the binder(s) and the homogeneous dispersion of the glass particles. The porous polymer is soaked into the slurry, wherein it can expand freely. The glass slurry infiltrates the pores and coats the sponge struts; by carefully setting the impregnation time, it is possible to obtain thicker or thinner glass particles coatings. After sponge infiltration, the exceeding slurry entrapped within the foam pores could lead to a final scaffold with many closed pores and, consequently, with a too low and non-interconnected porosity. Therefore, the impregnated foam has to be compressed to re-open the clotted pores of the structure; this step is crucial for the whole process and a ad hoc procedure (not reported here for confidentiality had been developed purposely). It is possible to control the final scaffold porosity by optimizing the number and features of impregnation/compression cycles, in order to have a scaffold pore content comparable to that of cancellous bone. The impregnated sponge is dried to promote structure consolidation. The dried sponge is thermally treated, in air or in inert atmosphere, to remove both the residual slurry additives and the polymeric template. The final stage involves the densification of the ceramic skeleton; the sintering temperature usually ranges within 700-1200 °C and must be chosen depending on the features of the used glass material and on the desired properties for the final scaffold. It is worth mentioning that the final scaffolds, derived from glasses, is often glass-ceramic, as the nucleation of crystalline phases usually occurs during the sintering treatment. The most important stages of the sponge replication process (as used in this project) are illustrated in Fig. 26.
Fig. 27 reports the impregnation procedure of the ceramic cup and Fig. 28 show the monoblock acetabular cup prototype obtained at Politecnico di Torino (detail about the processing parameters and the ad hoc procedure are not disclosed due to confidentiality).

TRABECULAR-LIKE COATING OBTAINED BY LASER CLADDING

Previous to obtain 3D structured, some flat samples have been coated with a dense coating by laser cladding. Over this coating, a 3D structure has been growing using single laser cladding tracks.
Different strategies have been followed and two different prototypes had been obtained (the details of the processing parameters are not reported for confidentiality issues)
Figure 29 reports the second embodiments of the monoblock acetabular cup obtained in the frame of MATCh Project at AIMEN, whereas Fig. 30 reports the third one.

Potential Impact:
The project provided a unique opportunity for all the involved SMEs, as they were able to increase their competitiveness by defining and establishing the basis of a new commercial and industrial approach, by strengthening their industrial network capabilities and by acquiring a specific know-how that could be of benefit for enlarging their potential market.

The proposed acetabular component is expected to have a significant impact in the field of orthopaedic surgery, as it could potentially overcome the postoperative complications of existing cemented and cementless prostheses. More than 60% of implanted total hip joint prostheses are characterized by a modular geometry, involving a metal or ceramic femoral head coupled with a UHMWPE cup housed in the so-called metal-back. However, one of the major drawbacks of such implants is the risk, after assembly, of mobility of some components, which may cause severe wear phenomena eventually leading to implant failure. Furthermore, the modular geometry does not allow to achieve small-sized implants – which are useful, for instance, to children, women or undersized people – due to the need of using the metal-back. For these reasons, surgeons usually prefer to implant cemented ceramic acetabular cups in young and active patients, but the cement carries problems of potential toxicity at the implant site and of osteolysis due to debris formation over time. Therefore, debris release and implant fixation issues are crucial points affecting the performance and duration of the prosthesis.
The average age of patients who require a primary total hip arthroplasty is decreasing and today ever younger, more active patients require hip implants that will last for decades. As the bioactive trabecular coating is able to create a strong and “physiological” fixation between patient’s bone and implant, it would significantly promote the osteointegration of the acetabular prosthetic device.
Furthermore, the monoblock implant developed in the project can find application both as acetabular cup for hip prosthesis and as femur or tibial component for knee prosthesis, to which can be adapted.

The monoblock acetabular cup that had been developed at the lab scale during the project is expected to achieve the following features:
- excellent wear resistance, as it allows ceramic/ceramic coupling;
- “physiological” osteointegration of the implant, thanks to the presence of the highly bioactive
trabecular coating that bonds to patient’s bone;

The introduction of such a device on the market would also introduce significant advances in the context of innovative manufacturing of medical devices, in the view of working out effective and low-cost processing techniques. For instance, manufacturing of small series of prosthetic components with high added value is of great interest for the partners involved in the project. The concept of obtaining small series of parts on ceramic biocompatible materials is increasingly being an object of study due to the multiple applications and because of the challenges and implications on their manufacturing processes. In fact, technical ceramics are much difficult to machine than other materials due to their special characteristics such as fragility, dustiness and abrasive behaviour.
The feasibility of the utilisation of subtractive methods to green ceramic materials has been successfully proven by researchers in FCIM in recent years and their know-how had been increased in the frame of MATCh Project leading to impressive results.
The confirmation of the extension of the green machining methodologies taking into account the shape deformation foreseen during the post-machining sintering is going to have a great impact in the machine-tool manufacturing industry and will set a new milestone for it.

Bioactive glasses, such as Hench’s 45S5 Bioglass, are already on the market for dental restoration materials and as coating for metallic implants; the design and development of new glassformulations having superior properties (mechanical strength, bioactivity, controllable degradation kinetics) compared to the existing ones is going to widen the market of these biomaterials with potential benefit ending directly on one of the SME involved in MATCh Project (GTS-UK).
Another versatile manufacturing method, of great interest for AIMEN and two of the involved SMEs (GTS and FAME-MED), concerns the application of the laser cladding technology to produce dense or porous ceramic bodies. The results obtained in the frame of MATCh Project had also opened the scenario for further biomedical applications which are under evaluation and might have great impact on the biomedical field of metal implants.

The use of a glass-derived scaffolds as a bioactive trabecular coating on prosthetic devices had proven to be feasible and transferrable to the industrial line and would represent a significant advance in the application of biocompatible glasses in the clinical practice.
At present Bioglass®, BoneAlive®, TheraGlass® and StronBone® has been used mainly in form of powders, granules or dense blocks for filling small bone defects in dentistry and orthopaedics or are still under approval. Literature concerning macroporous scaffolds based on commercial bioactive glass composition reports very poor mechanical properties, unsuitable for load-bearing applications like the object of MATCh project.
The impressive results obtained during MATCh Project will then open both the use of mechanically competent 3D-scaffolds for bone substitution as well as completely new applications for these materials (e.g. trabecular-like coatings for ceramic elements), enlarging their market and increasing the competitiveness of the involved SMEs and more generally of the EU competitors.
An unplanned application of the realized trabecular-like coatings might also appear on the market due to the acquired know-know and to the possibility of transferring it also to metallic implants.
Apart from the obtained biomaterials and prototypes, the project gave the involved SMEs as well as the biomedical scientific community in the broadest sense inputs for the rational development of new testing methodologies. For instance, during the project there was the need of performing tensile tests on the trabecular-like coatings; although no pre-developed standard methodologies or guidelines were available, some experimental attempts have been made for this purpose. Therefore, the project findings and the achievement of these results posed new challenges and created new needs, that will act as a stimulus for further research.

From a clinical viewpoint, the proposed implant, obtained at the prototype scale in two different embodiments, will offer a wide range of benefits to patients, including the following:

- overcoming the problems associated to cement toxicity and the risk of related osteolysis, as the cement will not be used;
- overcoming the problems associated to the traumatic fixation through the metal-back (bone drilling by screws, pegs or pins) avoiding its use;
- application, at least to a great extent, to every kind of patients (adult, children, women, active people) without size limitations.

Since the anchorage between patient’s host bone and implant is direct and obtained by press-fitting, the time needed for surgery is expected to be shorter than in the case of cemented prostheses, for which the cement must be prepared by surgeon intraoperatively, and modular implants, that require preoperatively a careful assembly of the two components.
It is worth underlining that the system of anchorage through glass-derived trabecular coating can also be suitable to other implantable devices different from acetabular cups, such as the femoral or tibial component of knee prosthesis thus increasing the final MATCh Project impact.
The produced trabecular-like structure could also be commercialised as such (porous scaffolds of custom-made size and shape) for bone substitution application for dental or orthopaedics applications strengthening the EU competitors and possibly taking one of the involved SMEs close to the biomedical market.

From technological, business and market viewpoints, significant benefits had been reached for the SMEs, including the following:
- improvement of their innovation ability, benefitting by an integrate approach to problems thanks to a profound synergy between researchers having different skills and expertise in materials/biomaterials science, mechanical/biomechanical engineering, theoretical/computational modelling, materials/implants processing;
- establishing collaborations with well-recognized and highly-reputed academic partners and
RTD performers;
- increasing their possibility of widening their market share;
- opening new potential market applications and challenges.

MATCh Consortium believes that the ideas and the achievements gained during this project will ensue in significant advances in several areas of the biomedical field, leading to new knowledge on biomaterials design/processing, structural/functional biomechanics and performance of biomaterials and implants. In order to extend the potential benefits of this idea to other fields in the wide world of arthroprostheses, a robust activity of dissemination and exploitation had been carried out.

The list of all the dissemination activities in reported under section A.

Two dissemination activities are reported below as particularly worth noting.

A two days workshop “Glasses and Ceramics for Biomedical Application” (24th-25th October 2012) that collected more than 100 participants and that was organized at Politecnico di Torino by Prof. Chiara Vitale-Brovarone (Project Coordinator).

A special session “Bioceramics for the future” was organized in the frame of the 25th International Conference of the European Society for Biomaterials held in Madrid (11th September 2013) in collaboration with other three EU funded Projects (MATCh, LONGLIFE, RESTORATION and Bio-BONE).

List of Websites:

Project website: www.match-euproject.com

Project coordinator: Prof. Vitale -Brovarone Chiara- Politecnico di Torino, Applied Science and Technology Department (www.composites.polito.it)

Final Report Summary - MATCH (Monoblock Acetabular cup with Trabecular-like Coating)

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