A team of researchers recently published a paper in the journal Demonstrating the feasibility of using three-dimensional ( 3D) printed polymer-based optical fibers for sensing applications.

Temperature sensors are widely used in a variety of applications such as medical diagnostics, generators, air conditioning, and the automotive industry to identify unexpected faults or failures and maintain optimal operating conditions.

While electrical sensors are commonly used for temperature sensing, they are less efficient in harsh environments and cannot provide accurate readings due to magnetic and electrical interference.

For example, white-light interferometers, glass fiber optic temperature sensors, and Fabery- Perot interferometers all exhibit high sensitivity. However, optical fibers have durability issues and are susceptible to small mechanical disturbances.

Polymer fiber-based sensors can be used to overcome these issues, as these sensors are immune to any environmental disturbances due to their excellent efficiency and robust strength. Although polymer-based fibers exhibit low sensitivity, they are reusable and relatively precise.

Sensors based on polymer fibers can be fabricated by molding or drawing. Additive manufacturing (AM)/ 3D printing processes have fundamentally changed the development of optical analysis and sensing devices by allowing the fabrication of customized optical devices or components of optical systems.

source 3D printers allow the use of custom materials that meet the requirements of the target application. Different 3D printing technologies such as digital light processing (DLP), stereolithography (SLA), masked stereolithography (MSLA), and fused filament fabrication (FFF) can be used to print polymer optical fibers .

Among these techniques, MSLA is more suitable because it is the fastest technique and has the highest resolution. Furthermore, various materials can be easily customized in MSLA with complex functions, enabling the possibility of different material compositions. Therefore, MSLA can be effectively used in the fabrication of functionalized polymer composites.

During or after resin synthesis, stimuli-responsive materials exhibiting sensitivity to specific external triggers (such as magnetic/electric fields, light, ions, temperature, or pH) can be incorporated into the resin to incorporate sensing capabilities or multifunctionality. added to 3D printed structures.

In this study, the researchers used an open-source MSLA 3D printer to fabricate thermochromic polymer optical fibers for temperature sensing applications . Reversible thermochromic micropowders were incorporated into 3D-printable polyethylene glycol diacrylate (peg da)/polyhydroxyethyl methacrylate ( pHEMA ) photocurable resin to add heat-sensing functionality to fabricated optical fibers .

of the fabricated 3D printed fibers were characterized, and the thermal sensing ability of the fibers was quantitatively analyzed in the temperature range of 25–32 °C . The researchers also established a correlation between light intensity and bending angle to demonstrate the strain-sensing capabilities of the fabricated fibers.

pHEMA was chosen due to its flexibility and good biocompatibility, while PEGDA, a flexible long-chain polymer suitable for making photopolymerizable polymers, was chosen to help crosslink HEMA. TPO can initiate photopolymerization in the presence of 385-420 nm ultraviolet (UV) light. Thermochromic pigments are non-toxic and temperature sensitive.

A photocurable resin of PEGDA/HEMA was synthesized for 3D printing of optical fibers based on PEGDA/HEMA copolymer by mixing the photoinitiator trimethylbenzoyldiphenylphosphine oxide (TPO), PEGDA , and HEMA at room temperature .

Functionalized polyethylene glycol monomethyl ether/HEMA copolymer-based thermochromic optical fibers for strain and temperature sensing applications were successfully fabricated using the MSLA 3D printing method . The manufactured fibers are extremely soft due to the flexible nature of the base polymer material used in its manufacture.

No morphological differences were observed between the colored powders used in the study. All pigments show a characteristic dip in their transmission spectra based on their color, and this dip was also observed in the two printed fibers containing these colors. Samples containing red and blue pigment powders showed greater impregnation due to the impregnation combination of the two powders.

Thermochromic powders are crystalline, while all 3D printed samples are amorphous. During the 3D printing process and the photocuring process, there is no reaction between the resin and the thermochromic powder.

After adding thermochromic powder, the strength of polymer-based optical fiber is reduced. The transparent PEGDA/ pHEMA sample exhibited the highest strength and elastic modulus, while the red/blue PEGDA/ pHEMA sample exhibited the lowest strength and elastic modulus due to the highest concentration of thermochromic powder.

Micron-sized spherical thermochromic particles are uniformly distributed throughout the polymer matrix with extremely low agglomeration. Even after dispersion, their shape and structure remained almost similar to the original powder. Furthermore, the 3D printed layers fused efficiently and no voids were observed between the layers, suggesting the successful fabrication of polymer-based thermochromic fibers.

Distinguishable color was observed at 25° C /room temperature for all samples. However, the samples became transparent and indistinguishable at 32 °C . The effect is reversible, as the color becomes visible again when the sample cools to room temperature. Even after undergoing multiple cooling and heating cycles, the fibers showed heat-sensitive properties.

The reflectivity of fibers increases with temperature and decreases at 32o because of their light absorption. Therefore, there is a linear relationship between temperature and reflection intensity.

The optical fibers remotely measure temperature changes in liquids with an accuracy of up to 25-32o. This demonstrates the feasibility of using these optical fibers for temperature measurement in a biomedical environment . In all samples, red, green, and blue (RGB) values increased with increasing temperature, indicating that the samples were transparent due to the thermochromic response.

When the polymer fibers were subjected to bending conditions, light intensity decreased significantly in all samples, with the highest reductions observed in green and blue fibers . In addition, the light intensity decreases with the increase of the bending angle. This effect can be used to sense bending or strain-related changes to predict structural deformation or failure.

great potential of flexible, cost-effective, and reusable stimuli-responsive polymer-based optical fibers for sensing applications. However, more development and testing is required before they can be used at scale in the real world