This year 3D printing technology will be celebrating its 37 years of existence, although it is somehow surprising that most of us have come across this term in recent years. There are lots of researches going on across the world for improving this technology and make it cheaper and more effective. This has brought down the cost of a 3D printer to nearly USD 700, (industrial grade 3D printers).

However, in February 2013, TEDx professor Skylar Tibbits first coined the term 4D printing in his speech at the MIT Conference.

Let’s see what exactly 4D printing is:

4D printing technology is an upgradation of the 3D printing technology that allows objects to be printed in 3D which can self-transform themselves in shape and material property when triggered by a pre-set stimulus like water submersion, heat exposure, current, UV light or other sources of energy.

During the manufacturing, materials are coded with instructions which trigger the material to respond and reshape/adapt it according to environmental factors making them smart materials.

In simple terms we can say, we are adding the 4th dimension to the already existing 3D printed material.

The difference between 4D printing and 3D printing is mainly because of the material. Smart design and smart materials make 4D printed to transform itself in shape or function.

Material used:

Let’s discuss the materials used in 4D printing and why they have come to be known as smart materials:

4D printing uses two main active polymers which are Hydrogel inks and Shape memory polymer (SMP).

Let’s get to know both of them one by one. 

Hydrogel

A hydrogel is a network of cross-linked polymer chains that are hydrophilic, sometimes found as a colloidal gel in which water is the dispersion medium. Hydrogels are highly absorbent (they can contain over 90% water) natural or synthetic polymeric networks.

The ability of hydrogels to absorb water arises from hydrophilic functional groups attached to the polymeric backbone, while their resistance to dissolution arises from cross-links between network chains. Many materials, both naturally occurring and synthetic, fit the definition of hydrogels.

Hydrogel when integrated with a non-swelling polymer or filament and immersed in a solvent, swells and creates mismatch strains between the two materials. The material undergoes an overall shape change. 4D printing that uses hydrogels does not require programming after printing. However, 4D printing with hydrogel have lower stiffness and lower actuation speed.

Shape Memory Polymer (SMP)

SMP can change their shape in a predefined way because of the coded instructions when exposed to an appropriate stimulus. The shape B is given by the initial processing step while the shape A is determined by applying a process called programming. 

Three most common shape memory polymers are Polytetrafluoroethylene (PFTE), polylactide (PLA), and ethylene-vinyl acetate (EVA).

4D printing with SMPs offer relatively high actuation speed and relatively stiff final structure than those obtained with printed hydrogels. However, the 4D printing with SMPs generally requires a series of steps and special jigs and fixtures to apply mechanical loads and a well-controlled thermal environment.

SMPs are also classified on the basis of the stimulus to which they respond such as temperature responsive, photo responsive.

Temperature-responsive SMPs are quite popular 4D materials. They have the ability to contract or expand in response to changes in temperature. When the temperature of a shape memory polymer is increased above the critical temperature for shape change, the deformed structure returns to its original structure.

Photo or light-responsive SMP on the other hand can be triggered by UV irradiation or sunlight. UV responsive polymer chains include azo compounds that can deform on exposure which leads to the deformation of the polymer chain structure, triggering a color change from white to purple.

The polymer returns to the original white when brought in a dark environment.

Not only color, but some light-responsive materials have been known to change their shapes or surface patterns via similar mechanisms. These light-responsive materials can be used in shopping bag packaging, aerospace structures, photovoltaic, and biomedical devices.

UV-responsive materials are available as ME filaments, and promising applications of UV-responsive materials exist in areas such as the fashion and entertainment industries.

Market Analysis

Several market reports have already predicted that 4D printing will be attracting large investment in this decade as various sectors have already set their eyes on this technology and looking to fully exploit this domain in order to take a big leap.

Analysis by some reports is cited below:

• According to a report by Mordor intelligence, the value of 4D Printing Market was estimated at USD 62.02 million in 2019 and is anticipated to cross USD 488.02 million by 2025, growing at a CAGR of approximately 42% over the forecast period 2020 – 2025 (from previous article).
• A newly released report called "4D Printing Market Analysis By Material (Programmable Carbon Fiber, Programmable Wood, Programmable Textiles), By End-use (Defense, Aerospace, Automotive, Textile, Healthcare), By Region, And Segment Forecasts, 2019 - 2025" by Grand View Research (GVR)⁹ reveals that the global market for 4D printing will touch $64.5 million in 2019.. Further report expected the global 4D printing market to grow at a CAGR of 42.95% between 2019 and 2025. The programmable carbon fiber segment is expected to be the leading contributor to the overall market, with a share of ~62% of the market, in 2019.
• Global 4D Printing Market 2019-2028 predicts growth of 4D printing market at a CAGR of 26.04% over the projected period 2019-2028.

The fastest growth is expected in North America for the 4D printing market in the coming years. The region is also likely to be the largest revenue generator in the world during the projected period as several major 3D printing players are present in this region.

Major Players

Some institutions and organizations that are majorly investing in R&D of 4D printing are:

• Massachusetts Institute of Technology
• Autodesk Inc
• Arc Centre of Excellence for Electromaterials Science (ACES)
• CT CoreTechnologie Group
• HP Development Company LP
• Organovo Holdings Inc
• ExOne and EnvisionTEC Inc.
• Stratasys is a global company providing applied additive technology solutions for different industries, including automotive, aerospace, healthcare and education.

Expected Products

• First 4D-printed water valve is created at the University of Wollongong in Australia. Valve shuts when exposed to hot water and re-opens when hot temperatures subside by using a hydrogel ink that responds rapidly to heat.
• The US Army Research center is planning on using the 4D printing technology for printing automatically camouflageable soldiers’ uniforms that can alter depending on the environment around them, and which can effectively protect against toxic gases.
• Aerospace industry will be using 4D printing technology for making self-deploying structures, for air ventilation, engine cooling and various other similar uses. Airbus S.A.S. is already working with 4D printing technology to develop a method to cool its engines depending on temperature.
• 4D printed biocompatible devices required for expansion/contraction of an object are also expected. These devices can find their use as cardiovascular stent that can increase its size for the purpose of keeping an artery open in order to reduce the chances of complications from traditional stent applications.
• Clothes and footwear which naturally adapt/change to the size/contours of the wearer.
• Shoes which become waterproof during rain or react to other external atmospheric conditions.
• Home appliances or products in the home, such as a chair, self-assembles through heat stimuli.
• Roads with self-healing potholes.

Patent Domain

There is not a better way to analyse the future of any technology than analysing the patent application filed for that technology in past few years. The patent shows the solutions identified for a given problem in a domain which new players haven’t encountered yet.

Patents solve the following issues:

• The existing ceramic precursors are not flexible and sufficiently stretchable to enable self-shaping assembly prior to polymer-to-ceramic transformation. A system and method of constructing a 4D-printed ceramic object, to allow the first elastic structure and second elastic structure to form a 4D-printed elastomeric object, and converting the 4D-printed elastomeric object into the 4D-printed ceramic object.
• Use of 4D printing for producing a three-dimensional (3D) composite structure with curved feature(s) from a substantially flat stack of composite layers without using a mould having a corresponding shape and without 3D printing of complex shapes. This may allow for a reduction in manufacturing cost and/or time.
• A design optimization and manufacturing approach for the creation of complex 3D curved rod structures with spatially variable material distributions that exhibit active deformation behaviour. The framework optimizes the cross-sectional properties of a rod structure, in particular the Young's modulus, such that under given loading conditions the rod structure may obtain one or more target shapes resulting from geometrically nonlinear deformation, from which the structure can then actively deform back to the original shape due to the shape memory effect. A novel algorithm is provided to generate physical realizations from the computational design model, which allows their direct fabrication via printing of shape memory composites with voxel-level compositional control with a multi-material 3D printer.
• A 4D printed component that uses the photo isomerization stimulus as a method of activation. Other 4D printing methods use heat, moisture, a combination of heat and stress, and the heat from a light source as methods of activation. The present invention takes advantage of 3D printing capability and adds the capability of providing a printable material that dynamically changes shape over time when exposed to an external stimulus. This characteristic reduces the amount of onboard weight of the 3D printed components by reducing the number of parts required to create motion. The invention removes the need for onboard sensors, processors, motors, power storage, etc. This characteristic will allow for manufacturing of, inter alia, novel medical devices, automated actuators, packaging, smart textiles, etc.
• Several polymeric bilayer actuators fabricated by 4D printing that can reversibly change their shape upon exposure to light. The photoactive layer includes a newly synthesized linear azobenzene polymer that is printed onto several different support layers to achieve bilayer actuators. An investigation of their optical and mechanical properties has allowed us to better understand the photomechanical behavior of these devices. The bilayer actuators provide the ability to design and fabricate more complex devices and extend their use to applications such as unmanned aerial vehicles, artificial muscles, and biomedical drug delivery platforms.
• Polymers having dynamic urea bonds and more specifically to polymers having hindered urea bonds (HUBs). The patent also relates to: (a) malleable, repairable, and reprogrammable shape memory polymers having HUBs, (b) reversible or degradable (e.g., via hydrolysis or aminolysis) linear, branched or network polymers having HUBs, and (c) to precursors for incorporation of HUBs into these polymers. The HUB technology can be applied to and integrated into a variety of polymers, such as polyureas, polyurethanes, polyesters, polyamides, polycarbonates, polyamines, and polysaccharides to make linear, branched, and cross-linked polymers. Polymers incorporating the HUBs can be used in a wide variety of applications including plastics, coatings, adhesives, biomedical applications, such as drug delivery systems and tissue engineering, environmentally compatible packaging materials, and 4D printing applications.
• A hearing device includes: an earpiece having a first end and a second end, wherein the first end of the earpiece is configured for insertion into an ear canal of a user, and wherein at least a part of the earpiece is configured for placement along a first bend of the ear canal; wherein the earpiece comprises a flexible member, at least a part of the flexible member located at the first end of the earpiece, wherein at least a part of the flexible member is configured for placement along a second bend of the ear canal located between the first bend and an eardrum. Flexible member can be 4D printed.

Patent Filing Trend in last 5years

Below table provides a data of number of patents filed and number of patents granted from 2015 to 2019 in 4D printing:

China has filed the maximum number of patents owing to fact that patent filing there took the least amount of time to get published.

Legal Status of patent

Below graph gives a general idea about the legal status of Intellectual Property  in 4D printing.

Conclusion:

4D printing will be majorly fruitful in applications where transformation due to external stimulus such as water submersion, heat exposure, etc. is required. China and US are the major contributors that are investing more in R&D of 4D printing. Thus, from market analysis and Intellectual Property trend of last 5 years, it can be concluded that 4D printing will grow in upcoming years.