Claims:1. A polymerisable binder system for 3D powder printing; said system comprising –

a) aqueous solution of acrylamide monomer and accelerator; and

b) initiator, wherein the initiator is mixed with powder.

2. The polymerisable binder system as claimed in claim 1, wherein the accelerator is

selected from a group comprising N,N,N’,N’-tetramethylethane- 1,2-diamine (TMEDA or

TEMED), triethylenediamine (TEDA), tetrakis(hydroxymethyl)phosphonium chloride

(THPC) and the like.

3. The polymerisable binder system as claimed in claim 1, wherein the initiator is selected

from a group comprising ammonium persulphate, benzoyl peroxide, potassium

persulphate, sodium persulphate, azobisisobutyronitrile and the like.

4. The polymerisable binder system as claimed in claim 1, wherein the solution comprises

acrylamide monomer ranging from about 20% wt/vol to about 25% wt/vol; preferably

about 22% wt/vol added with accelerator ranging from about 0.2% to about 0.4%

preferably 0.3% vol/vol; the initiator concentration ranging from 2% wt/wt to about

8%wt/wt.

5. The polymerisable binder system as claimed in claim 1, wherein the binder static and

dynamic viscosity is ranging between 10mPa.s to about 20mPa.s and surface tension is

about 56 mN/m.

6. A system for three dimensional printing, said system comprising aqueous solution of

acrylamide monomer, N,N,N’,N’-tetramethylethane- 1,2-diamine, ammonium persulphate

and powder to be printed.

7. The system as claimed in claim 6, wherein the powder is selected from a group of

materials comprising alloys of metal, ceramic and polymers.

21

8. A method of preparation of polymerisable binder system for powder printing of claim 1,

said method comprising acts of;

a) preparing aqueous solution of monomer of acrylamide;

b) adding accelerator to the solution to form a homogeneous solution; and

c) mixing initiator with powder to be printed to obtain polymerisable binder system for

powder printing.

9. The method as claimed in claim 8, wherein the mixing is done in a planetary ball mill at

a speed of about 200 rpm to about 300 rpm for a period ranging from about 15min to

about 30min.

10. A method of powder printing, said method comprising acts of

a) mixing initiator with powder to be printed to form a mixture; and

b) contacting the mixture with aqueous solution of acrylamide monomer and accelerator

for powder printing.

11. The method of powder printing as claimed in claim 10, wherein the printing is through

inkjet powder printing. , Description:TECHNICAL FIELD:

The present invention is in relation to three dimensional powder printing. The invention provides

a methodology to formulate a novel binder system for 3D powder printing of a range of

materials. In particular, this methodology involves the use of monomer solution of acrylamide,

other components of the binder system, i.e. accelerator and an initiator to be mixed with the

powder to be printed. The system allows in-situ polymerization to facilitate intense physico-

chemical binding in the powder bed during the printing of objects. The printing process is

environment friendly as it involves aqueous medium and cost-effective to develop three

dimensional printed constructs with enhanced strength.

BACKGROUND:

The osseointegration of implantable biomaterials depends on the tailored porous architecture to

promote biocompatibility (angiogenesis, tissue in-growth) and bone mimicking physical

properties (elastic modulus, strength). To address such twin requirements, 3D powder printing,

an ambient temperature additive manufacturing method is successively employed to incorporate

designed volume fraction of porosities in scaffolds/implants. This technology relies on binder-

powder interaction during printing, wherein the powder physically gets adhered with adhesive

binder layer by layer to yield the full 3D construct. In general, the binders are powder chemistry

specific and the employability is limited towards the spectrum of FDA approved powder

materials.

The three dimensional printing is widely used in the medical field to develop patient-specific

three dimensional complex implants for tissue engineering applications with tailored mechanical

3

properties. Titanium alloy, commonly known as Ti-6Al- 4V is one of the clinically accepted and

widely used biomaterial in bone tissue engineering as well as limb salvage applications due to its

higher strength to weight ratio and biocompatibility. The most sensitive body implants for

example, total hip system, prosthetic cardiac valves, U shape inter laminar stabilization device

implantable in spine, locking bone plates, screws and the like are commercially manufactured

and used according to the specifications. Similarly, partially magnesia stabilized zirconia, porous

HDPE are other internationally approved biomaterials for surgical implants.

Additive manufacturing technique, commonly known as three dimensional printing is widely

used over conventional manufacturing methods to create aforesaid objects. It is well known that

layers of materials are deposited to develop a three dimensional object in the aforesaid process.

Although monolithic metallic implants of titanium and its alloys, stainless steel, cobalt-

chromium are frequently used in orthopedic and arthroplastic surgeries, porous designs are

necessary to avoid the failure due to stress shielding effect and to enhance the cell-material

interaction and bone ingrowth. It is to be noted that by controlling the porosity distribution and

architecture, mechanical properties of the implants can be tailored for the tissue-specific

applications. In general, interconnected pores of larger than 400 µm are found to be suitable for

vascularization, while the minimum pore size for osteogenesis is 100 µm. In this context,

interconnected pores facilitate the transportation of nutrients to and metabolic wastes from cells.

Additive manufacturing has multifaceted advantages over the conventional manufacturing

technologies. The patient-specificity and the addition of materials in contrast to conventional

machining are the major advantages. In addition, the manufacturing of complex shapes,

including intricate interior features added with the scope to incorporate biomedically relevant

porous architectures to match the elastic modulus with the host tissues can be achieved through

4

additive manufacturing. 3D powder printing is superior to the high energy laser or electron beam

based additive manufacturing as it can print ceramics and composite materials. The spine of 3D

powder printing is based on the development of powder-specific binder and tailoring post-

printing methodology.

However, the major limitation of 3D powder printing of biomaterials is the unavailability of

universal binder. The binder chemistry and properties need to be tuned for a given biomaterial.

The binder addition for three dimensional printing are used in two modes – indirect and direct.

The indirect mode involves the mixing of water soluble binder powder with the powder to be

printed and subsequently printing with distilled water. In contrast, direct mode involves the use

of a water soluble binder directly to print the scaffolds. The as-printed strength and print

resolution are limited in case of ‘indirect’ printing and the high viscosity of binder used in

‘direct’ mode of printing results in frequent clogging of micro-orifices of printhead.

This invention aims to provide a cost effective, ecofriendly novel system of a universal binder

for effective 3D powder printing of metal, ceramics and polymers that can be easily adopted for

printing three dimensional objects with high strength. The invention also aims to develop a

method of printing that desist the use of any high energy source like selective laser sintering

(SLS), electron beam melting (EBM) and the like.

STATEMENT OF INVENTION

A polymerisable binder system for 3D powder printing; said system comprising – a) aqueous

solution of acrylamide monomer and accelerator; and b) initiator, wherein the initiator is mixed

with powder; a system for three dimensional printing, said system comprising aqueous solution

of acrylamide monomer, N,N,N’,N’-tetramethylethane- 1,2-diamine, ammonium persulphate and

5

powder to be printed; a method of preparation of polymerisable binder system for powder

printing of present invention, said method comprising acts of;a) preparing aqueous solution of

monomer of acrylamide, b) adding accelerator to the solution to form a homogeneous solution,

and c) mixing initiator with powder to be printed to obtain polymerisable binder system for

powder printing and a method of powder printing, said method comprising acts of a) mixing

initiator with powder to be printed to form a mixture; and b) contacting the mixture with aqueous

solution of acrylamide monomer and accelerator for powder printing.

BRIEF DESCRIPTION OF FIGURES

The features of the present invention can be understood in detail with the aid of appended

figures. It is to be noted however, that the appended drawings illustrate only typical

embodiments of this invention and are therefore not to be considered limiting of its scope for the

invention.

Figure 1: Working principle of the binder system and the process methodology of 3D inkjet

powder printing. (a) powder containing APS (initiator); (b) aqueous binder comprising

acrylamide and TEMED; (c) binder shower from printhead according to ‘demand’of the CAD;

(d) binder droplet impact on powder bed and the polymerisation starts in the presence of

monomer solution, intiator and accelerator; (e) in-situ growth of viscous polyacrylamide chains

and inter-particles as well as inter-layers adhesion; (f) examples of as printed 3D bodies.

Figure 2: Macrostructures of as-printed and sintered prototypes/lab-scale test samples of metals

(Ti-6Al- 4V), ceramics (Mg-PSZ) and polymers (HDPE). (a) top: HDPE acetabular socket

prototype, middle: Ti-6Al- 4Vgreen cylinders, bottom: Mg-PSZ green cylinders; (b) sintered Ti-

6Al-4V cylinder; (c) Mg-PSZ acetabular socket (green and sintered)

6

Figure 3: (a) Constant static viscosity (independent of shear rate) indicating the nature of the binder

as Newtonian and (b) the range of the dynamic viscosity (10 – 20 mPa.s), showing the efficacy of

the binder as printable.

Figure 4: X-ray diffraction pattern of as received Ti-6Al- 4V powder and sintered scaffold

showing the presence of a-Ti and ß-Ti phases. Highest intensity peak in the starting powder is

contributed by (110) plane of ß-Ti. A shoulder peak right side of this peak corresponds to the

(101) plane of a-Ti at 2? value of 40°. In the sintered scaffold, the decrease in intensity of (110)

ß-Ti and hike in peak intensity of (101) plane of a-Ti is noticed

Figure 5: XRD pattern of Mg-PSZ (as received powder and sintered bodies). The high

temperature symmetric phase (tetragonal) is retained in room temperature even after sintering to

the presence of MgO as the partial stabiliser. (m – monoclinic, t – tetragonal).

Figure 6:. Compressive strength and modulus of both sintered Mg-PSZ and Ti-6Al- 4V

cylinders. This comparative representation of bar diagrams of compressive strength and modulus

of Ti-6Al- 4V and Mg-PSZ depict the reduction in strength and modulus (e.g. 110 GPa for

monolithic Ti) due to incorporation of microporosity in the structure. These microporosities get

incorporated in the 3D printed constructs during the process itself. This reduction in modulus

assists in avoiding ‘stress-shielding’ / ‘aseptic loosening’ of implants anchored with host bone in

vivo.

Figure 7: Overall low resolution X Ray scan (pixel size ~ 30-40 µm) of microporous acetabular

socket and femoral head prototypes (Mg-PSZ). (a) Front orthoslice (the tappering and the

interconnected porosity); (b) femoral ball head of Mg-PSZ; (c) front orthoslice of Mg-PSZ 3D

printed acetabular socket prototype; (d) low resolution overall scan of the acetabular prototype.

7

Figure 8: High resolution 3D reconstructed Micro-CT images of both as printed and printed-

sintered Ti-6Al- 4V and Mg-PSZ, to illustrate the effect of sintering in terms of reduction in

porosity and extent of pore-interconnectivity.

DETAILED DESCRIPTION OF INVENTION

The foregoing description of the embodiments of the invention has been presented for

the purpose of illustration. It is not intended to be exhaustive or to limit the invention to

the precise form disclosed as many modifications and variations are possible in light of

this disclosure for a person skilled in the art in view of the figures, description and

claims. It may further be noted that as used herein and in the appended claims, the

singular “a” “an” and “the” include plural reference unless the context clearly dictates

otherwise. Unless defined otherwise, all technical and scientific terms used herein have

the same meanings as commonly understood by person skilled in the art.

The present invention is in relation to a polymerisable binder system for 3D powder printing;

said system comprising –

a) aqueous solution of acrylamide monomer and accelerator; and

b) initiator, wherein the initiator is mixed with powder.

In an embodiment of the invention, the accelerator is selected from a group comprising

N,N,N’,N’-tetramethylethane- 1,2-diamine (TMEDA or TEMED), triethylenediamine (TEDA),

tetrakis(hydroxymethyl)phosphonium chloride (THPC) and the like.

In an embodiment of the invention, the initiator is selected from a group comprising ammonium

persulphate, benzoyl peroxide, potassium persulphate, sodium persulphate, azobisisobutyronitrile

and the like.

8

In another embodiment of the invention, the solution comprises acrylamide monomer ranging

from about 20% wt/vol to about 25% wt/vol; preferably about 22% wt/vol added with accelerator

ranging from about 0.2% to about 0.4% preferably 0.3% vol/vol; the initiator concentration

ranging from 2% wt/wt to about 8%wt/wt.

In still another embodiment of the invention, the binder static and dynamic viscosity is ranging

between 10mPa.s to about 20mPa.s and surface tension is about 56 mN/m.

The present invention is in relation to a system for three dimensional printing, said system

comprising aqueous solution of acrylamide monomer, N,N,N’,N’-tetramethylethane- 1,2-

diamine, ammonium persulphate and powder to be printed.

In another embodiment of the invention, the powder is selected from a group of materials

comprising alloys of metal, ceramic and polymers.

The present invention is also in relation to a method of preparation of polymerisable binder

system for powder printing of present invention, said method comprising acts of;

a) preparing aqueous solution of monomer of acrylamide;

b) adding accelerator to the solution to form a homogeneous solution; and

c) mixing initiator with powder to be printed to obtain polymerisable binder system for

powder printing.

In yet another embodiment of the invention, the mixing is done in a planetary ball mill at a

speed of about 200 rpm to about 300 rpm for a period ranging from about 15min to about 30min.

The present inventionis also in relation to a method of powder printing, said method comprising

acts of

9

a) mixing initiator with powder to be printed to form a mixture; and

b) contacting the mixture with aqueous solution of acrylamide monomer and accelerator

for powder printing.

In another embodiment of the invention, the printing is through inkjet powder printing.

An embodiment of the present invention provides a universal binder for three

dimensional powder printing to build 3D scaffolds of metal, ceramic, polymeric powders

with excellent print resolution and as printed strength. The system of the binder typically

comprises two parts- one part comprising aqueous solution of monomer of acrylamide and an

accelerator; the other part comprising initiator and powder that is to be printed.

An initiator is mixed with the powder, which is subsequently printed with a monomer solution

added with an accelerator. The polymer chains grow in the micro-area of droplet impact locally

and bind the powder particles intimately. Accordingly, the binding involves in situ room

temperature polymerization reaction in the powder bed itself. When the aqueous solution of

monomer of acrylamide and accelerator arrives in contact with the powder pre-mixed with the

initiator, the polymerisation initiates. Consequently, a viscous high molecular weight polymer

known as polyacrylamide or poly(2-propenamide) is synthesized in situ, in the micro-area of the

impact of the binder droplet in the powder bed. As a result, the powder particles get adhered

quickly with the polymer chains and gets hardened during drying (Figure 1).

As the monomer solution has low viscosity, issues relating to the printhead nozzle clogging does

not arise. The as-printed strength is appreciably high due to the intimate binding of the in situ

grown polymer chains and subsequent drying of the molecules along with the powder particles.

Typically, the binder system comprises aqueous solution of acrylamide monomer ranging from

about 20% wt/vol to about 25%wt/vol; preferably about 22% wt/vol; accelerator ranging from

10

about 0.2% to about 0.4% preferably 0.3%vol/vol; initiator ranging from 2% wt/wt to about

8%wt/wt of the printable powder. The initiator concentration will vary depending on the density,

as powder volume spreaded in each layer remains constant during printing, of which, weight can

vary as per the corresponding density.

The accelerator is selected from a group comprising N,N,N’,N’-tetramethylethane- 1,2-diamine

(TMEDA or TEMED), triethylenediamine (TEDA), tetrakis(hydroxymethyl)phosphonium

chloride (THPC) and the like and the initiator is chosen from a group of initiators for vinyl

polymerization, such as ammonium persulphate, benzoyl peroxide, potassium persulphate,

sodium persulohate, azobisisobutyronitrile and the like.

The binder preparation involves simple steps in two parts. In the first part, aqueous solution of

monomer of acrylamide as the base is prepared, accelerator is added and stirred to form a clear

solution. In the other part, initiator is mixed with the powder to be printed. The two parts of the

binder independently are extremely stable without any requirement of preservation and allow

three dimensional printing seamlessly. The three dimensional printing involving said system

relies on the principle of drop-on- demand (DOD), which involves the ejection of liquid binder

through a set of orifices, forming ink droplets.

Typically, the exemplified reaction of the present invention involves contacting N,N,N’,N’-

tetramethylethane-1,2- diamine with the initiator, ammonium persulphate. The ammonium

persulphate structure breaks down and gives rise to free radicals. Essentially, N,N,N’,N’-

tetramethylethane-1,2- diamine accelerates the formation of free radicals from persulfate. These

free radicals are extremely unstable and attack the double bond of acrylamide molecule and get

consumed by the molecule. After consuming the reactive electron from the free radical, the a -

center of the acrylamide monomer becomes unstable and extremely reactive. Thereafter, the

11

reactive molecules attack more vinyl sites of the monomer molecules one by one and add them in

the backbone. This continues as a chain reaction and the molecular weight as well as viscosity of

the chain continues to increase. As the system is inclusive of loose powder predominantly, they

get adhered quickly with the adhesive polymer and get bound.

The present disclosure demonstrates effective functionality of this binder in three classes of

biomaterials, metal (Ti-6Al- 4V), ceramic (Mg-PSZ) and HDPE (polymer).

A. Three dimensional printing and post processing-General procedure:

a) The pre-mixed powder (powder particle size in the range of 20 – 50 micron) is stacked in

the feed bed of the powder inkjet printer (Spectrum 510, Zcorp, USA) and the cartridge and the

printhead (HP™ no. 11 black printhead) are cleaned and filled with the binder. The saturation is

kept in the range of 100-150%. The x-y resolution of print is maintained at 600*540 dpi with z

resolution (single layer thickness) in the range of 80-100 µm. Cylindrical specimens having the

dimensions of (1: 1) height:diameter ratio are printed for Ti-6Al- 4V and Mg-PSZ.

The prototypes of human acetabular cup for total hip replacement are also printed with excellent

precision using HDPE and Mg-PSZ. Additionally, one human femoral ball head is also printed

using Mg-PSZ powder. The images of the as-printed bodies and sintered bodies are shown in

figure 2.

b) After printing, the print area is illuminated with an incandescent light bulb for 45 minutes

and then the excess supporting powder is roughly removed. The portable build plate along with

the powder covered as-printed bodies is taken out from printer and kept in an hot air oven at 70 –

75°C for further drying and hardening. The total setting time (stone hard) is observed to be 40

minutes to 1 hour. The setting time is identical for this binder as the reaction does not depend on

the powder chemistry.

12

After drying, the as-printed bodies appear to have sufficient handling strength, and the loose

powder is removed from the surface using a brush. To further enhance the final strength of the

as-printed bodies, high temperature heat treatment is often prioritized. For ceramics (Mg-PSZ in

this study), the as-printed bodies are sintered at 1450°C for 1 hour using 10°/min heating ramp.

In case of Ti-6Al- 4V, the first heating ramp (10°C/min) is limited up to 450°C and dwelled for 1

hour to remove the binder. The second heating ramp is started at the rate of 20°C/min, until it

reaches the final sintering temperature (1400°C). At 1400 °C, samples were kept for 2 hours and

furnace cooled.

B. Binder rheology, surface tension and pH

The flow behaviour of the binder is primarily governed by its static and dynamic viscosity,

which is characterized using a cone-plate viscometer (DHR3, TA instruments, USA). In static

viscosity measurement, the change in viscosity is monitored by changing the shear rate, while the

complex/dynamic viscosity is measured by varying the angular frequency. The static viscosity is

measured to be ~1.8 mPa.s, which is very less to be considered. Dynamic viscosity lies in the

range of 10 – 20 mPa.s and the prescribed value is below 30 mPa.s for best printability. These

values show clear indications of excellent binder physics under flow (Figure 3a and b).

The interfacial tension between liquid droplets and air, which is commonly known as surface

tension is measured using ‘pendant drop’ method in a contact angle goniometer (OCA 15EC,

Dataphysics®, Germany). The value is found to be ~56 mN/m. This value is less enough not to

form ligaments behind proceeding droplets and hence ensures good resolution.

The pH of the solution of acrylamide based binder lies in between 7.5 – 8 (little basic). This is

due to the presence of basic accelerator (TEMED) and such effect gets nullified after the

13

disintegration of TEMED during polymerization reaction in the powder bed. This pH value, in

turn, promotes the reaction, as the efficiency of reaction falls rapidly below pH 6.

C. Phase assemblage, mechanical and microstructural properties

Phase assemblage:

A diffractometer (X’ Pert Pro, PANalytical, Netherlands) is used to investigate the phase

assemblage in powder as well as in sintered scaffolds (both Mg-PSZ and Ti-6Al- 4V). For the

XRD (X-ray diffraction), samples are scanned for 2? in the range of 20° to 90° for Ti-6Al- 4V

and 20° to 70° with a scan rate of 0.06°/sec using Cu Ka radiation of wavelength 1.5418 Å.

Figure 4 represents the X-ray diffraction pattern of as received Ti-6Al- 4V powder and sintered

scaffold. In case of as-printed Ti-6Al- 4V, XRD pattern confirmed the presence of a-Ti (HCP) as

a predominant phase and metastable ß-Ti (BCC) as a minor phase due to the presence of ß

stabilizer (Vanadium). Importantly, no diffraction peak corresponding to oxide of Ti is found

within the detection limit, after sintering. An increase in intensity of diffraction peak

corresponding to (101) plane of a-Ti after sintering associated with a decreased intensity of

diffraction peak corresponding to (110) plane of ß-Ti. In the XRD pattern of Mg-PSZ,

monoclinic phases are predominant in the as received powder as expected. In contrast,

metastable tetragonal phases are observed in the sintered scaffolds due to the presence of the

magnesia as a partial stabiliser, which aids in retaining the high temperature phase (tetragonal) in

room temperature (Figure 5).

D. Mechanical properties:

Compressive stress – strain behaviours of the sintered cylinders of both Ti-6Al- 4V and Mg-PSZ

are measured in Universal Testing Machine (Zwick/Roell, USA) using 100 kN load cell with

crosshead speed of 0.5 mm/min. Compressive strength and modulus of the microporous sintered

14

Mg-PSZ cylinders (height ~ 13mm and diameter ~9 mm) are found to be in the order of 15

(±1.2) MPa and 6.6 (±0.9) GPa, respectively. On the other hand, compressive strength and

biomedically relevant modulus are found in the case of sintered Ti-6Al- 4V cylinders (both height

and diameter ~ 11 mm), where the values lie in the order of 222 (± 32) MPa and 4 (±0.3) GPa

respectively. The compressive strength and modulus of both sintered Mg-PSZ and Ti-6Al- 4V

cylinders are presented in Figure 6. This comparative representation of bar diagrams in figure 6

of compressive strength and modulus of Ti-6Al- 4V and Mg-PSZ depict the reduction in strength

and modulus (e.g. 110 GPa for monolithic Ti) due to incorporation of microporosity in the

structure. Also, a comparative analysis of mechanical properties of three dimensionally printed

object of present invention with the objects printed according to literature is provided in Table 1.

These microporosities get incorporated in the 3D printed constructs during the process itself.

This reduction in modulus assists in avoiding ‘stress-shielding’ / ‘aseptic loosening’ of implants

anchored with host bone in vivo.

Table 1: Comparative analysis of mechanical properties of three dimensionally printed

object of present invention with the objects printed according to literature.

Reported binders for

3D powder printing

of Ti and Ti6A14V

Sintering

temperature

(ºC)

Compression

Strength

(MPa)

Compressive

modulus (GPa)

Reference

Deionised water as

binder for Ti

premixed with PVA

powder

1300 107.2 0.86 Gagg et al. Materials

Science and

Engineering: C

2013;33(7):3858-3864.

Deionised water as

binder for Ti

premixed with PVA

powder

1350 455 13.2 Wiria et al.

Materials & Design

2010;31, Supplement

1(0):S101-S105

Deionised water as

binder fir Ti premixed

with PVA powder

1370 - 2.5 Hajje et al.

Journal of Materials

Science: Materials in

Medicine

2014;25(11):2471-

15

2480.

Deionised water as

binder for Ti

premixed with PVA

powder

1350 - 2.1 Maleksaeedi et al.

Procedia CIRP

2013;5(0):158-163

Aqueous

Maltodextrin solution

as binder for Ti-6A1-

4V powder

1400 200 4.0 Barui et al., Materials

Science and

Engineering: C, 70

(2017) 812-823

Novel in situ

polymerisable acrylic

binder for printable

biomaterials

1400 222.6 4.1 Present invention

E. Microstructural studies:

The finer scale 3D microstructure in terms of the internal porosity distributions in the as-printed

and sintered bodies of both Mg-PSZ and Ti-6Al- 4V are extensively studied using micro-

computed tomography (m-CT). The X-Ray scanning recipes for all components, including both

as-printed and sintered bodies, are shown in Table 2.

Table 2: X-Ray tomographic scan recipes for green and sintered cylinders and prototypes

Sample names X Ray

Energy (kV)

Power

(W)

Exposure

time (s)

Objectives

(X)

Pixel size

(µm)

Resolution

Ti-6Al- 4V as-printed

cylinder

120 10 2 4 3.15 High

Ti-6Al- 4V sintered

cylinder

140 10 2 4 3.18 High

Mg-PSZ as-printed

cylinder

140 10 2.5 4 4.3 High

Mg-PSZ sintered

cylinder

140 10 3.0 4 4.23 High

Mg-PSZ acetabular

socket (sintered)

140 10 7 0.39 38.32 Low

16

Mg-PSZ femoral head

(sintered)

140 10 7 0.39 29.8 Low

Figure 7 shows the overall low resolution X Ray scan (pixel size ~ 30-40 µm) of microporous

acetabular socket and femoral head prototypes (Mg-PSZ). High resolution scan (pixel size ~ 3-

4µm) of both as-printed and sintered Ti-6Al- 4V and Mg-PSZ cylinders were carried out to

critically quantify the volume fractions of material and pore phases as well as pore-

interconnectivity. Essentially, the single predominant color (green / blue) of a particular

parallelepiped pore phase in Figure 8 represents one single pore. Other colors, scattered

randomly as dots or small spheres, represent closed pores.

F. Experiment 1:

Method of preparation of the binder system for three dimensional printing.

22% (wt./vol.) aqueous solution of monomer of acrylamide is prepared as the base of the binder.

0.3% (vol./vol) N,N,N’,N’-tetramethylethane- 1,2-diamine is added and mixed by magnetic

stirring until a clear homogeneous solution is obtained. 2 -8% (wt./wt.) Ammonium persulphate

is mixed with the base powder (any powder to be printed) in a planetary ball mill at 300 rpm for

20 minutes. As Ammonium persulphate is extremely hygroscopic, attention is provided to keep

the pre-mixed powder in a tightly closed container and away from moisture.

Experiment 2: 3D powder printing of Mg-PSZ acetabular socket prototype:

a) Preparation of the powder:

500 gm spray dried Mg-PSZ powder is taken as the base material to be printed and 4% (wt/wt)

ammonium persulphate (APS) as the initiator is mixed in a planetary ball mill using agate jar and

agate balls. Ten batches of milling were carried out by taking 50 gm powder in each using 4:1

17

ball-powder ratio at 200 rpm for 20 minutes. The agate balls are separated and the powder is kept

in an airtight container as APS is extremely hygroscopic.

b) Preparation of binder:

The binder was prepared by dissolving 66 gm of acrylamide and 0.9 ml TEMED in 300 ml

distilled water (DI) under magnetic stirring for 15 minutes. The dissolution of acrylamide in

water is spontaneous and endothermic in nature. Once the entire acrylamide is dissolved, the

solution is filtered in Whatman 40 filter paper to ensure no presence of any solid particulate,

having the potential to clog the printhead micro-orifices (dia ~ 40-45 micron) during printing.

c) CAD modeling of acetabular socket:

A solid model of a standard acetabular socket is generated in a solid modeling software (viz.

Catia TM , Solidworks TM ) having the dimension of 56 mm and 32 mm as the OD and ID

respectively. The file is exported in *.stl format and fed in the slicing software (ZPrint TM ) which

subsequently sliced it in 260 layers keeping 0.1 mm layer thickness.

d) 3D powder printing of the Mg-PSZ acetabular socket prototype

The powder is stacked in the feed bed with sufficient height for the CAD (26 mm at least). The

cartridge is filled with binder and the ‘HP TM no. 11 black’ printhead is purged, cleaned and filled

with the binder. The binder line is ‘primed’ to remove existing air and the printhead is placed on

the septum firmly. The saturation is maintained at 150 % and the printing is carried out at 38°C

temperature (machine preset). After finishing the printing, the build area is illuminated with an

incandescent lamp (60-70°C) for ½ an hour and the loose powder is removed using a brush

superficially without touching the as-printed architecture. The portable build plate, containing

the powder covered architecture, is placed in a hot air oven at 70°C for 1 hour. After this, the

18

plate is taken out from oven and the loose powder is removed (‘depowdering’) using a

compressed air nozzle to reveal the geometry details intricately.

e). Post processing - high temperature heat treatment/sintering

The as printed acetabular socket is kept in an open air furnace (Carbolite TM ) and heated up to

1400°C using 10°C/min ramping and dwelled for 2 hours. The furnace is cooled normally and

the sintered prototype is taken out and the shrinkage is measured which was in the range of 20-

23%.

The present invention unveils a new horizon in 3D powder printing for various applications

including biomedical applications. The use of a universal binder satisfies several folds of

requirements. The system of the universal binder addresses the limitations of applicability of the

proprietary binder, which comes along with all commercial 3D powder printers. The binding

involves a room temperature polymerization reaction without any need of external energy

stimuli. The polymerization is rapid, a key requirement for 3D powder printing where the

viscous polymeric chains should form in between two layers pass. The polyacrylamide, formed

during 3D powder printing, is a biocompatible material with low setting time. Finally, the cost of

the chemicals is considerably less providing a economically viable, ecofriendly process and

product. This binder can be extensively used to fabricate patient specific implants for example

dental and orthopaedic implants in a cost-effective manner, thereby paving the way for

affordable healthcare.

The aforesaid description enables one to capture the nature of the invention. It is to be noted

however that the aforesaid description and the appended figures illustrate only a typical

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embodiment of the invention and therefore not to be considered limiting of its scope for the

invention may admit other equally effective embodiments.

It is an object of the appended claims to cover all such variations and modifications that can

come within the true spirit and scope of the invention.