additive manufacturing

1. ME-353
Electronic Devices and their Applications
AUXETIC
LATTICE
STRUCTURE
FOR BIO
IMPLANTS
HEMANT KUMAR [B21294]
ABHISHEK [B21270]
PRESENTED BY

2. AUXETIC
MATERIAL
Auxetic structures:
→The word ‘auxetic’ derives from the Greek word ‘auxetikòs’, whose meaning
is ‘tending to increase’.
→Generally, materials are contracted in the direction orthogonal to load by
reducing their section.
→ Materials characterised from auxetic structures show an opposite behaviour
by revealing a complex flexure, which results as a whole in an increased
section in the direction orthogonal to load (Evans and Alderson, 2000).
→Auxetic behaviour is not related or specific to any particular material, being
purely a consequence of how the material itself is structured microscopically.
→ In engineering terms, Poisson’s ratio is the ratio between the transverse and
the longitudinal strain (εy / εx) produced by the application of a load F
orthogonal to its section.
→Auxetic materials show a negative Poisson’s ratio (NPR), ranging from 0 to –1,
while common materials, also defined as ‘Newtonian’, have a positive Poisson’s
ratio.

3. LATTICE
STRUCTURE
Lattice structures are a type of porous design
which are used in various fields
→Auxetic lattice structures are a type of lattice
structure that exhibits a negative Poisson's ratio.
→This means that when they are stretched, they get
thicker in the direction of the applied force.
→ This is in contrast to most materials, which get
thinner when they are stretched.

4. The negative Poisson's ratio of auxetic lattice structures is caused by their
unique geometry. The unit cell of an auxetic lattice structure is typically
shaped like a re-entrant honeycomb, which means that the edges of the
unit cell are bent inwards. When the unit cell is stretched, the edges rotate
outwards, causing the structure to get thicker.

5. Overview Advantages of Bioimplants
• Bioimplants are medical devices that are used to
replace or support a damaged biological
structure in the body.
• They play a vital role in enhancing the quality of
life for patients who have suffered from injuries
or ailments.
• In recent years, there has been a growing
interest in the use of lattice structures as an
alternative to traditional normal structures in
bioimplants.
• Lattice structures offer unique advantages that
make them a promising option for various
applications.
• Enhanced Quality of Life: Bioimplants restore
and improve bodily functions, allowing
individuals to regain their independence and
enjoy a higher quality of life.
• Biocompatibility: These devices are made from
materials that are compatible with the body,
reducing the risk of rejection or adverse
reactions.
• Long-term Durability: Bioimplants are designed
to withstand the test of time, providing long-
lasting benefits for patients.
WHAT ARE BIO
IMPLANTS

6. WHY AUXETIC LATTICE
STRUCTURE ARE PREFERRED
IN BIO-IMPLANTS ?
Auxetic lattice structures are more preferred in bio-implants than the normal lattice structures for several
reasons. First, auxetic lattice structures have a negative Poisson's ratio, which means that they expand when
stretched and contract when compressed. This property makes them ideal for bio-implants, as it mimics the
mechanical properties of natural bone. Natural bone is a porous material with a negative Poisson's ratio,
which allows it to absorb and dissipate stress. Auxetic lattice structures can also be designed to have a
porosity that is similar to that of natural bone, which can further promote bone ingrowth and
osseointegration

7. • Auxetic lattice structures are very tough and can withstand a lot of deformation before they break. This makes
them ideal for bio-implants, as they can withstand the stresses that are placed on them during movement.
Conventional lattice structures, on the other hand, are more brittle and can break more easily.
• Auxetic lattice structures can be designed to have a specific surface topography that can promote cell adhesion
and growth. This is important for bio-implants, as it allows cells to attach to the implant and form new bone.
Conventional lattice structures, on the other hand, typically have a smooth surface that is not as conducive to cell
adhesion and growth.
• Finally, auxetic lattice structures can be made from a variety of materials, including biocompatible metals,
polymers, and ceramics. This makes them versatile and allows them to be tailored to specific applications.
Conventional lattice structures, on the other hand, are typically made from a limited number of materials, which
can limit their use in bio-implants.
• Overall, auxetic lattice structures have a number of advantages over conventional lattice structures that make
them ideal for bio-implants. Their negative Poisson's ratio, toughness, surface topography, and versatility make
them a promising material for a variety of bio-implant applications.
WHY AUXETIC LATTICE
STRUCTURE ARE PREFERRED
IN BIO-IMPLANTS ?

8. FABRICATION OF AUXETIC BIO
MATERIALS
→The advancements in fabrication methods have enabled researchers and manufacturers to
produce complex structures with advanced materials.
→Techniques such as laser cutting and lithography are effective in creating 2D structures, but for 3D
auxetic materials, the most widely used method is additive manufacturing or 3D printing.
→This method allows for the fabrication of 3D structures at various scales using materials ranging
from polymers to metals.
→ The process involves creating a computer-aided design (CAD) of the desired structure, selecting the
materials, and then printing the geometry layer by layer.
→Additive manufacturing provides the flexibility to produce both low-cost prototypes and
sophisticated finished products, making it increasingly popular in the manufacturing industry.

9. Back to Agenda 08
Different techniques that are used for
manufacturing of auxetic bio materials:
1. Stereolithography (SLA) is a form of additive manufacturing (AM) that uses a laser to create three-dimensional objects
from a liquid photopolymer resin. The process works by hardening the resin layer by layer, using a UV laser to trace the
desired shape of the object.

10. working process Advantages
• The SLA process begins with a 3D model of the
desired object. This model is then sliced into thin
layers, typically 0.05-0.15mm thick. The laser then
traces the shape of each layer onto the surface of
the resin, hardening it in place. The platform then
lowers, and the laser cures the next layer of resin.
This process continues until the entire object has
been built
• High precision and accuracy, Fast and efficient,
variety of photopolymer resins available for SLA
printing, with different properties and
applications.
HOW
STEREOLITHOGRHY
WORKS

11. 2.DIGITAL LIGHT
PROCESSING
The DLP method improves upon SLA by offering sub-micron resolution and the ability to print various
materials, including polymers, resins, and even some metals. With DLP, the liquid polymer is exposed to
selected light from a projector through a system of lenses. This method is even faster than SLA and
supports continuous printing of multilayer structures due to the efficient curing or
photopolymerization step. The advancements in DLP technology have contributed to the rapid
development of 3D auxetic materials, providing enhanced resolution and material flexibility.
Working Principle:
3D Model Preparation: A 3D model of the desired object is generated.
Slicing: The 3D model is sliced into thin layers.
Photopolymer Resin Preparation: A photopolymer resin is placed under the DMD projector.
Light Projection and Curing: The DMD projects light patterns onto the resin, curing it layer by layer.
Layer-by-Layer Build: The build platform is lowered after each layer is cured, allowing the next layer to be projected and curedxt

12. 3.FUSED
DEPOSITION
MODELING
(FDM)
• Fused Deposition Modeling (FDM) is another widely used
additive manufacturing technique for fabricating auxetic
materials.
• FDM involves melting a thermoplastic filament and
depositing it in layers to create the desired structure.
• The flexibility and affordability of FDM printers make them
accessible for both prototyping and commercial production.
• By carefully controlling the deposition process and
optimizing the filament material, FDM can produce auxetic
materials with tailored properties, making it a valuable
method in the fabrication process.
Advantages of FDM:
Easy to use
Affordable
Versatile
High precision
Wide range of applications

13. CASE STUDIES AND
APPLICATIONS:
Studies by the research group of Mehmood et al. involved the manufacture of a polyurethane-based
auxetic polymeric bone plate, which can be used as an internal fixator for fractures of long bones.
The manufactured construction, in contrast to conventional implants the auxetic implants for the hip
stem , allows micromovement, which is of great importance in the process of bone healing. In this
case, according to references, micromovement is desirable for the formation of callus , facilitating the
connection of Bone fragments . The fabrication of the bone auxetic plate was performed using the
injection moulding technique discussed by Ali et al. The authors showed that the auxetic bone plate
has a potential use for fixing the bone in cases where protection against stress shielding and the
creation of micromotions is required. Arguably, manufacturing these solutions employing resorbable
materials may benefit from auxetic behaviour during healing and lead to a natural state after
resorption.
1.Fixation for Long Bones:

14. 2.SPINAL SURGERY:
Artificial intervertebral discs made of high-density auxetic polyethylene can bend and twist and may provide
improved biomechanical performance compared with traditional disc replacement solutions. Thanks to its
negative Poisson’s ratio, the disc prevents bulges that could injure the surrounding nerve endings. Importantly, the
disc perfectly mimics the behaviour of a natural lumbar intervertebral disc. Later, Baker put forward a theory on the
use of auxetic foams as a material for an artificial intervertebral disc. Auxetic foam has a re-entrant cellular structure
with a negative Poisson’s coefficient after heating by triaxial compression. Finite element analysis showed that the
use of an artificial intervertebral disc with a negative Poisson’s ratio would be a solution to the problem, as damage
to the surrounding nerves by the intervertebral disc is eliminated .
As another application linked to spinal surgery, Yan Yao et al. proposed an auxetic pedicle screw based on a Ti6Al4V
resin cell (DPR New Materials Technology Co., Ltd., Beijing, China) to improve the biomechanical interaction
between the surrounding bone and the screw, mainly for the spine. According to the results of the finite element
method (FEM), the correspondence between Young’s modulus of bone and screw is a necessary condition of pull-
out protection for a particular bone .

15. THANK YOU.....