Field of the Invention

The present invention relates to a powder suitable for use in the manufacture of glass articles via additive layer manufacturing. The present invention further relates to a process for making a glass article using the powder of the present invention.

Background of the Invention

Bioactive glasses have been widely used in biomedical applications. For example, bioactive glass has been employed in toothpastes for the treatment of hypersensitivity, in the manufacture of dental and orthopaedic implants, in bioactive coatings for metallic implants prostheses and in synthetic bone grafting materials.

The various uses of bioactive glass are discussed in Jones, Acta Biomaterialia, 23, (2015), S53-S82.

It has been recognised that porous bioactive glass might be a suitable material for use in the manufacture of three-dimensional (3D) scaffolds for tissue engineering applications, for example, bone grafting. Tissue engineering scaffolds are generally highly porous, 3-dimensional (3D) templates, exhibiting tailored porosity, pore size and controlled interconnectivity. In bone grafting applications, such a scaffold could be inserted into a bone defect cavity where it would act as a temporary template for bone growth in three dimensions.

To be suitable for tissue engineering applications, the 3D scaffold must have an interconnected porous structure that can allow fluid flow, cell migration and tissue ingrowth, whilst retaining adequate mechanical strength to provide structural support during healing. Further, such 3D scaffolds should be made from a material which is biocompatible and bioactive.

As used herein, the term "biocompatible" refers to a material that does not have a significant negative impact on tissue growth and viability.

As used herein the term "bioactive" refers to a material which exhibits a relatively high biocompatibility and bonding affinity to the host tissue of a

mammalian body. In particular, bioactive glasses are known to form a surface layer of hydroxyapatite (to which bone can bond) upon contact with physiological fluids.

Preferably, the material from which such 3D scaffolds are made is also osteogenic, chondrogenic and/or angiogenic. As used herein the term "osteogenic" refers to a material which promotes bone growth.

As used herein the term "chondrogenic" refers to a material which promotes cartilage growth.

As used herein, the term "angiogenic" refers to a material which promotes the formation of blood vessels.

Preferably, the material from which such 3D scaffolds are made should also be biodegradable, such that the scaffold is eventually absorbed by the surrounding tissues without the necessity of surgical removal. The rate at which degradation occurs should preferably coincide as much as possible with the rate of tissue formation.

Different techniques have been described for the fabrication of bioactive glass derived 3D scaffolds for tissue engineering, such as foam replication techniques, direct foaming techniques and freeze extrusion. However, scaffolds having sufficient porosity, pore interconnectivity and/or mechanical strength for tissue engineering applications have been difficult to achieve using such techniques.

The use of additive layer manufacturing (ALM) techniques for the production of 3D scaffolds from bioactive glass containing composite materials and other bioactive ceramic materials has been described.

Additive layer manufacturing (ALM) is a technique whereby 2-dimensional layers of material are sequentially laid down and fused or bound together to fabricate 3-dimensional solid objects. ALM processes are enabled by conventional 3D design computer packages that allow design of the shaped unit as a so-called "STL file" which is a simple mesh depiction of the 3D shape. Using the design software, the STL file is digitally cross- sectioned into multiple two-dimensional slices, which are the basis for the fabrication process. The fabrication equipment, reading the two- dimensional pattern, then sequentially deposits layer upon layer of material corresponding to the 2D slices. In order that the shaped unit has structural integrity, the material is bound, cured, or fused together as the layers are deposited. The process of layer deposition and binding or fusion is repeated until a robust shaped unit is generated.

The use of ALM for the production of 3D scaffolds for tissue engineering is desirable since it provides for regular geometric patterning of the layers that make up the scaffold. A number of ALM techniques are available, for example, binder-jetting ALM.

In binder-jetting, an inkjet print head moves across a bed of powder, selectively depositing a printing ink. The printing liquid may itself contain a binder material or may be a solvent for a binder material present in the powder. A thin layer of powder is spread across the completed section and the process is repeated with each layer adhering to the last. When the printing is complete, unbound powder is automatically and/or manually removed in a process called "de-powdering". The de- powdered, printed object typically requires further treatments, such as heat treatment.

Other ALM techniques include laser sintering, wherein a laser moves across a bed of powder, selectively melting a binder material present in the powder.

Winkel et al {Journal of the American Ceramic Society, 95 (2012) 3387-3393) describes the 3D printed composites of hydroxy apatite (HA) and a bioactive glass; and Bergmann et al, (J. European Ceramic Society, 30 (2010) 2563-2567), describes 3D printed composites of tricalcium phosphate (TCP) and bioactive glass (40wt% TCP, 60wt% bioactive glass). However, purer bioactive glasses are known to exhibit several advantages in comparison to composites and other bioactive ceramics in tissue engineering applications. For example, it is known that bioactive glasses may exhibit higher rates of osteogenesis compared to other bioactive materials, and may also exhibit angiogenic, antibacterial and antimicrobial behavior.

The use of additive layer manufacturing for the production of 3D scaffolds from bioactive glass has also been described.

Meszaros et al (Glass Technol.: Eur. J. Glass Sci. Technol. A, 52(4), 111-116) describes the three-dimensional printing of bioactive glass. In particular Meszaros et al describes the three dimensional printing of a powder composition comprising a bioactive glass powder of type 13-93 and 6wt% of a dextrin binder, using as a printing ink a 7: 1 water: glycerol solution.

In such processes, the printed body ("green body") is typically subjected to heat treatment in order to remove binder material and any organic components deriving from the printing ink, and also to sinter the bioactive glass particles such that they fuse together to form a glass article. However, it has been found that where relatively high amounts of binder and/or ink-derived organic components are present in a printed green body, prolonged heat treatment and or high temperatures are required for their removal. Prolonged heat treatment is undesirable since this may lead to crystallisation of the bioactive glass, which is known to reduce the bioactivity of bioactive glasses.

Summary of the Invention

According to the present invention, there is provided a powder, suitable for additive layer manufacturing, comprising:

a. at least 90wt% bioactive glass particles; and

b. less than 6wt% binder material.

The powder of the present invention is suitable for use in the additive layer manufacture of glass articles, for example, bioactive glass articles, such as 3D scaffolds for tissue engineering.

The powder of the present invention comprises a low binder content compared to known bioactive glass powders for additive layer manufacturing, this provides a number of advantages.

The reduced content of binder material allows for faster and/or lower temperature removal of binder material from green bodies produced in an ALM process. Where binder removal is carried out by heat treatment, faster removal of binder material may prevent crystallisation of the bioactive glass, which is known to reduce the bioactivity of bioactive glasses.

Surprisingly, green bodies produced by ALM using a powder according to the present invention have sufficient green strength that they may be handled without damage for the application of post-printing steps, such as heat treatment.

Further, the reduced binder content may result in a reduction in organic impurities in the final bioactive glass article.

According to a second aspect of the present invention there is provided a process for making a glass article comprising the steps of:

a) providing a powder comprising at least 90wt% bioactive glass particles and less than 6wt% binder material;

b) forming a layer of the powder;

c) activating the binder material at one or more selected regions of said layer, such that powder becomes bonded at said one or more selected regions; d) repeating steps b) and c) a selected number of times to produce a selected number of successive layers, said activation of step c) also causing the selected regions of successive layers to become bonded to each other, thereby forming a shaped unit;

e) removing unbonded powder which is not at said one or more selected

regions to provide a de -powdered shaped unit;

f) subjecting the de-powdered shaped unit to heat treatment to provide the article.

As used herein, the term "binder material" means a material which, on activation (for example contact with a printing ink, a laser, or UV radiation), is capable of bonding (adhering) powder particles together.

As used herein, the term "green body" refers to a shaped unit after it is printed but before binder removal and sintering.

As used herein, the term "green strength" refers to the structural integrity of a green body (shaped unit) prior to undergoing heat treatment. Detailed Description

The powder of the present invention comprises at least 90wt% bioactive glass particles. The bioactive glass may be any glass which exhibits bioactivity, or a mixture of such glasses. In particular, the bioactive glass employed in the powder of the present invention may be silicate bioactive glass, borate bioactive glass, borosilicate bioactive glass or phosphate bioactive glass. Preferably the bioactive glass is a silicate bioactive glass, such as 45S5, S53P4 and 1393. Silicate bioactive glass generally has a composition comprising sodium oxide, calcium oxide, phosphorus pentoxide and silica, such as a glass composition having about 45-60 mol % silica and a molar ratio of calcium to phosphate of 2-10: 1. Glass materials having this or a similar composition, demonstrate the formation of a hydroxyapatite film on the materials surface that readily bonds the glass material to bone. Compositional variations can be made, through the addition of compositions such as magnesia, potassium oxide, boric oxide, and other compounds.

A suitable bioactive glass composition comprises 0-60 wt% S1O2, 0-60 wt% B2O3, 0-30 wt% Na ₂ 0, 5-30 wt% CaO, 0-20 wt% K ₂ 0, 0-10 wt% MgO and 0-15 wt% P2O5.

A particularly preferred silicate bioactive glass composition comprises 40-70 wt% S1O2, 5-30 wt% Na ₂ 0, 5-30 wt% CaO, 10-20 wt% K ₂ 0, 2-10 wt% MgO and 2- 15 wt% P2O5. Alternatively, a suitable phosphate bioactive glass composition comprises 40- 75wt% P2O5, 5-40wt% Na ₂ 0, 5-40wt% CaO.

Preferably, the bioactive glass forms a surface layer of hydroxyapatite upon contact with physiological fluids.

Preferably, the bioactive glass is osteogenic, chondrogenic and/or angiogenic, and is biodegradable.

Bioactive glass particles may be prepared by mixing together the raw materials, melting them to form a molten glass mixture, and then quenching to form a glass. Alternatively, the bioactive glass may be prepared by sol-gel or flame spray pyrolysis techniques. The bioactive glass may then be milled to provide the desired particle size.

The bioactive glass particles may be spherical or non-spherical. If the particles are non-spherical, the particles may have an irregular shape. Further, the bioactive glass particles may be dense or porous.

Bioactive glass particles for use in the present invention may optionally be surface funtionalised in order to bind biocompatible organic species onto the glass surface. Such organic species may include, for example, enzymes, growth factors, and/or pharmaceutical agents. In one embodiment, bioactive glass particles may undergo silanisation before incorporation into the powder of the present invention.

The powder of the present invention comprises particles of bioactive glass in an amount of at least 90wt%. Preferably, the powder of the present invention comprises particles of bioactive glass in an amount of at least 94wt%, more preferably at least 95wt% (based on total weight of the powder).

The maximum particle size of the bioactive glass particles may be up to 100 microns, preferably in the range 50 to 90 microns. As used herein, "particle size" refers to volume-based particle size, i.e. the particle size of a given particle is equal to the diameter of a sphere that has the same volume as the particle.

Preferably, the bioactive glass particles have a particle size distribution in which the D10 particle size is at least 1 micron; the D50 particle size is at least 10 microns, more preferably at least 15 microns; and the D90 particle size is preferably at least 50 microns and less than 100 microns.

In one embodiment, the bioactive glass particles may have a bimodal particle size distribution. It has been found that such a bimodal particle size distribution may provide improved particle packing in shaped units directly formed by an ALM method using the powder of the present invention. Improved particle packing may allow for lower temperatures to be employed in heat-treatment (e.g. sintering) of the shaped units.

The particle sizes and distributions described herein may be determined using a dry dispersion laser diffraction method (e.g. using a Malvern Mastersizer 3000).

The powder of the present invention also contains a binder material. The binder material is a material which, on activation, acts to bond (adhere) powder particles together. Such activation may be effected, for example, by contact with a printing ink comprising a solvent for the binder material, or by contact with a laser or UV radiation to melt the polymeric binder material.

The bonding provided by the binder material should be sufficient that a shaped unit (green body) directly formed by an ALM method using the powder of the present invention may be handled without damage in order that heat treatment or other post- printing steps may be applied - i.e. the shaped unit must have sufficient "green strength".

The binder material is preferably water soluble, for use with an aqueous printing ink.

The binder material is preferably a polymeric binder material. Suitable polymeric binder materials may include water soluble polymeric compounds having a molecular weight in the range of 200-175,000 g/mol. Such polymeric compounds may be natural or synthetic biocompatible polymers.

The binder material may be provided as a coating on the bioactive glass particles. Examples of suitable polymeric binder materials which may be provided as such a coating include poly-vinyl alcohol (PVA), dextran, dextrin, starch, cellulose and sucrose.

Alternatively, the binder material may be provided as discrete particles in the powder of the present invention. In this embodiment, it is preferred that the binder material is a polymeric binder material having a glass transition temperature of at least 30°C.

Polymeric compounds conventionally used as binder materials for ALM applications, such as binder-jetting, tend to have a relatively low glass transition temperature, and therefore cannot be milled since they soften and flow easily under normal milling conditions; i.e. rather than breaking up into smaller pieces on milling, they would deform. Milling of such polymeric compounds has sometimes been performed at cryogenic temperatures (i.e. at or below -150°C) to increase the brittleness of the polymer being milled. However, such processes are laborious, time consuming and very energy intensive.

Advantageously, by using a polymeric binder material having a glass transition temperature of at least 30°C, pre-milled particles of binder material may be provided without the need for energy intensive techniques such as cryogenic milling.

Further, the provision of pre-milled particles of binder material, allows for the powder of the present invention to be prepared by dry-mixing of the binder material particles and the bioactive glass particles.

As used herein, the term "dry-mixing" refers to the mixing of components in the substantial absence of any liquid, i.e. no liquid is deliberately added as part of the mixing process. The term is not intended to exclude the presence of minor amounts of environmental vapour, such as atmospheric water vapour.

Dry-mixing of the powder components is desirable since wet processing of bioactive glass may result in reduced bioactivity of the glass due to leaching effects, i.e. the dissolution of the bioactive glass and the release of ions on contact with a solvent. Further, wet processing may cause agglomeration of particles which in turn results in reduced control over particle size distribution.

In this embodiment, the polymeric binder material preferably has a glass transition temperature of greater than 60°C, more preferably greater than 100°C, most preferably greater than 150°C. Preferably, the polymeric binder material has a glass transition temperature of less than 200°C, more preferably less than 180°C. Thus, the polymeric binder material may have a glass transition temperature in the range 30 to 200°C, preferably 60 to 200°C, more preferably, 100 to 180°C, most preferably 150 to 180°C.

Suitable polymeric binder materials having a glass transition of at least 30°C include biocompatible polymeric compounds such as polyvinylpyrrolidone, chitosan, gelatin, carrageenan, xanthan gum, acacia gum, alginate, polyvinyl alcohol (PVA), dextran, maltodextrin, starch, cellulose and sucrose.

Alternatively, such a polymeric compound may comprise a co-polymer. One co-polymer particularly suitable for use as a polymeric binder material is a copolymer of maleic anhydride and isobutylene. Co-polymers of isobutylene and maleic anhydride can be prepared using any suitable method. Such co-polymers are also commercially available, for example, Isobam 104 and Isobam 110 available from Kuraray.

The binder material is present in the powder of the present invention in an amount of less than 6wt%, preferably less than 5.5wt%. Preferably, the binder material is present in the powder in an amount of at least lwt%, preferably at least 2 wt%.

Where the binder material is present in the powder in the form of discrete particles, the maximum particle size of the particles of binder material is preferably less than 100 microns. In one embodiment, the maximum particle size of the particles of polymeric binder material may be similar to the maximum particle size of the bioactive glass particles. In an alternative embodiment, the maximum particle size of the particles of polymeric binder material is smaller than the maximum particle size of the bioactive glass.

Advantageously, it has been found that where the maximum particle size of the particles of polymeric binder material is smaller than the maximum particle size of the bioactive glass particles, a powder having a more even distribution of binder particles and bioactive glass particles may be achieved. A more even distribution of binder particles and bioactive glass particles may allow for lower amounts of binder material to be employed.

In this embodiment, the particles of polymeric binder material preferably have a particle size distribution in which the D10 particle size is less than or equal to 5 microns, more preferably less than or equal to 2 microns; the D50 particle size is less than or equal to 25 microns, more preferably less than or equal to 15 microns; and the D90 particle size is preferably less than 100 microns and more preferably less than 70 microns.

The powder of the present invention may further comprise additional biocompatible components useful in the tissue engineering applications, for example, additives, pharmaceutical agents, antibacterial agents, ceramic additives, such as calcium phosphate compounds, metal particles and/or metal oxides.

The powder of the present invention may be employed in processes employing

ALM to produce glass articles, for example, in the process according to the second aspect of the present invention.

In step a) of the process according to the second aspect of the present invention, a powder comprising at least 90wt% bioactive glass particles and less than 6wt% binder material is provided. Preferably, the powder is a powder according to any embodiment of the first aspect of the present invention.

Preferably, step a) comprises dry-mixing particles of bioactive glass with particles of a polymeric binder material. The particles of bioactive glass and the particles of a polymeric binder material may be dry-mixed using, for example, a turbula mixer, a roller mixer or a rotary mixer. Preferably, the particles of both the bioactive glass and the polymeric binder have the desired particle size prior to mixing. In order to achieve the desired particle size, the components may require preprocessing, such as milling and sieving.

Milling of bioactive glass and polymeric binder components is preferably carried out under dry conditions. Milling may be carried out at ambient temperature, or at reduced temperature, for example -20°C. Preferably, the components are milled separately, prior to mixing.

In step b) of the process of the present invention, a layer of powder is formed. Step b) may be carried out by spreading a thin layer of powder over the surface of a build platform. The build platform may be height-adjustable such that the platform may be lowered before a successive layer of powder is spread. The powder layer may be spread over the surface of the build platform using a spreader bar, preferably a vibrating spreader bar. Suitably, the layer of powder has a thickness in the range 90 to 200 microns. Preferably, the layer of powder has a thickness of approximately 100 microns.

In step c) of the process of the present invention the binder material is activated at one or more selected regions of the powder layer, such that powder becomes bonded at said one or more selected regions, i.e. bioactive glass particles at the selected regions are bonded (adhered) together by the activated binder material.

Activation of the binder material is preferably carried out by applying a suitable printing ink to the one or more selected regions of the layer of powder. The printing ink, on contact with the powder, interacts with the binder material, in a manner that results in the bonding of particles within the powder layer. Preferably, the printing ink is a solvent for the binder material. Preferred printing inks include aqueous solutions of a surfactant. The surfactant may include at least one of the following materials: glycerol, polyethylene oxide modified acetylenic diols, secondary ethoxylated alcohols, ethoxylated nonylphenols, ethoxylated silicones, ethoxylated fluorinated surfactants, ethoxylated tetramethyldecynediol, ethoxylated tetramethyldodecynediol, polyethermodified polysiloxanes, ethoxylated sorbitan monolaurate, octyl phenoxypolyethoxy-polypropoxy-propanol, sulfonated fatty acids, zwitterionic betaines, sodium di-octyl sulfosuccinate, dimethyl

dodecylammoniopropane sulfonate, sodium lauryl sulfate, sodium lauryl benzene sulfonate, sodium p-toluene sulfonate, sodium benzoate, sodium benzene sulfonate, potassium sorbate, sodium 2-ethylhexyl sulfonate, and combinations thereof.

Preferred surfactants include glycerol and ethoxylated acetylenic diols. A particularly preferred surfactant is ethoxylated 2,4,7, 9-Tetramethyl-dec-5-yne-4,7-diol

(commercially available from Air Products as Surfynol ^® 465).

Preferably, the printing ink is an aqueous solution comprising less than 5% w/w surfactant, more preferably less than 3% w/w, more preferably less than 2%w/w of surfactant. A suitable printing ink is a 1.5% w/w solution of glycerol in water. A preferred printing ink is a 1.5% w/w solution of ethoxylated 2,4,7,9-Tetramethyl-dec- 5-yne-4,7-diol in water.

The printing ink may be applied to the layer of powder via inkjet printing. In some embodiments, for example, where the polymeric binder material is only water soluble at elevated temperatures, the printing ink may be heated prior to printing.

In step d) of the process of the present invention, steps b) and c) are repeated a selected number of times to produce the selected number of successive layers. The number of successive layers is dependent on the design of the final article. The activation of the polymeric binder material carried out in step c) also causes the selected regions of successive layers to become bonded to each other, thereby providing a shaped unit.

Step e) involves the removal of unbonded powder which is not at the one or more regions at which activation of the polymeric binding material was applied (referred to as "de-powdering"). De-powdering may be carried out by gently agitating the shaped unit, by vacuum or by using a stream of compressed air in an extraction hood.

The de-powdered shaped unit comprises bioactive glass particles bound together by binder material.

Optionally, the shaped unit is subjected to a drying step. The drying step may take place prior to the depowdering of step e), or subsequent to step e) but prior to step f).

In step f) of the process of the present invention, the de -powdered shaped unit is subjected to heat treatment. In a preferred embodiment, the heat treatment of step f) removes polymeric binder material and, if present, organic components deriving from a printing ink, and also sinters the bioactive glass particles such that they fuse together to form the glass article.

In this embodiment, the heat treatment of step f) may be carried out in two stages, where the shaped unit is first subjected to a lower temperature treatment for removal of binder material and ink-derived organics (if present), and subsequently subjected to a higher temperature treatment for sintering of bioactive glass particles.

The exact conditions of the heat treatment will depend on the composition of the glass, the binder material employed and the size and shape of the green body. It is well within the capabilities of the skilled person to determine the ideal conditions for heat treatment.

For removal of binder material and, if present, any organic components deriving from a printing ink, heat treatment is preferably carried out in a furnace at a temperature in the range 250 to 450°C. For sintering of the bioactive glass particles, heat treatment is preferably carried out in a furnace at a temperature in the range 650 to 1200°C, preferably 650 to 1000°C, more preferably 650 to 900°C, most preferably 650 to 750°C. Preferably, the heat treatment is applied for as short a period as possible in order to avoid crystallisation of the bioactive glass, but still achieve sufficient binder removal and sintering. The skilled person would be able to determine an appropriate treatment time.

In a particularly preferred embodiment, the heat treatment is carried out by heating the shaped unit in a furnace according to a multistage heating profile.

Alternatively, the heat treatment of step f) may be carried out in a microwave oven.

In an alternative embodiment, binder material and, if present, organic components deriving from a printing ink may be removed from the de -powdered shaped unit prior to the heat treatment of step f) by a suitable oxidative treatment, for example, by contacting the shaped unit with ozone. Subsequent to such an oxidative treatment step, the shaped unit then undergoes the heat treatment of step f) to sinter the bioactive glass particles.

On removal of the binder and sintering of the glass, the printed article becomes densified. On densification, the printed article may undergo shrinkage, that is, the final glass article is reduced in size compared to the printed shaped unit (green body). The amount of shrinkage observed will depend on the type of binder material employed and the particle size distribution of the powder.

The process according to the second aspect of the present invention may be carried out using any suitable ALM apparatus. For example, suitable equipment includes the S-Print or S-Max™ 3D Printing Systems available from ExOne, VX series available from Voxeljet, and RAM260™ 3D Printing System from Viridis3D™.

The process of the present invention may be employed to produce 3D scaffolds suitable for use in tissue engineering. Alternatively, the process of the present invention may be used to produce other bioactive glass articles useful in other medical or dental applications, for example, drug delivery systems or dental implants.

Examples

The invention will now be further described with reference to the following examples, which are illustrative, but not limiting of the invention.

Example 1: Preparation of bioactive glass particles

A bioactive glass having the composition specified in Table 1 was prepared using the melt derived route according to the following procedure. Raw materials Na ₂ C03, CaC0 ₃ , K ₂ C0 ₃ , Si0 ₂ , MgO, Mg(H ₂ P0 ₄ ) ₂ were mixed in the respective proportions, homogenised and melted. The resulting melt was quenched in water and dried. The resulting bioactive glass was subjected to dry milling using a ball mill equipped with A1 ₂ 0 ₃ grinding media and an A1 ₂ 0 ₃ grinding jar to produce bioactive glass particles having a particle size distribution as shown in Table 2.

Table 1

Table 2

Example 2: Preparation of binder material particles

A commercially available co-polymer of isobutylene and maleic anhydride, Isobam ^® 104, was obtained from Kuraray, for use as the binder material. The glass transition temperature of Isobam ^® 104 according to differential scanning calorimetry is 165°C. Properties of the polymeric binder material are shown in Table 3.

The Isobam ^® 104 was subjected to dry-milling using a ball mill equipped with a ceramic milling vessel and corundum milling media. The resulting powder was sieved to provide particles of binder having a particle size distribution as shown in Table 4.

Table 3

Table 4 Example 3: Preparation of a powder according to the present invention

The bioactive glass particles prepared according to Example 1 and particles of polymeric binder material were combined by dry-mixing using a roller mixer. The composition of the resulting powder is given in Table 5.

Table 5

Example 4: Additive Layer Manufacturing

The powder prepared according to Example 3 was employed in an ALM process to produce 3-dimensional bioactive glass articles using a Voxeljet VX200 binder-jet 3D printer employing a 1.5% w/w solution of Surfynol ^® 465 (available from Air Products) in water as a printing ink.

A layer of the powder having a thickness of 100 microns was deposited onto a height- adjustable build platform using a vibrating spreader bar. Printing ink was then applied to the layer of powder via an inkjet print head at selected regions of the powder layer, according to instructions generated by a conventional computer-aided design package for 3D printing. The height-adjustable build platform was lowered and a second layer of the powder having a thickness of 100 microns deposited, followed by application of printing ink at selected regions. The steps of depositing a layer of powder, applying printing ink and lowering the height-adjustable build platform were repeated until the preselected number of successive layers were deposited.

After printing, the resulting shaped units (green bodies) were dried in an oven at 55°C for 8 hours. The bodies were manually depowdered by gentle agitation and then manually transferred to a furnace. The printed green bodies had sufficient green strength that they could be manually handled without damage.

The green bodies were then subjected to heat-treatment in the furnace, wherein they were exposed to a multistage heating profile in order to burnout the polymeric binder and organics deriving from the printing ink and to sinter the bioactive glass particles. The furnace was heated to 350°C at a heating rate of 5°C min ^"1 and held for 1 hour. Following the hold at 350°C the parts were heated to 720°C at a rate of 10°C min ^"1 and held for 1 hour. The furnace was then cooled to room temperature at a rate of 10°C min ^"1 .

The resulting bioactive glass articles had interconnected porosity, and structural integrity. Linear shrinkage of the bioactive articles compared with the printed green bodies was approximately 34%.