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SPIE Professional April 2017

3D printing of ophthalmic lenses

A greener approach to making glasses?

By Mark Crawford

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There are many benefits to the 3D printing of lenses for glasses and contact lenses, once the technology is fully commercialized. Compared to the traditional, multi-step manufacturing process for lenses, 3D printing will be faster and less expensive.

Other advantages include a smaller manufacturing footprint, fewer processing steps, just-in-time manufacturing, and reduced inventory. Lenses and frames together will even be 3D-printed in a single step, saving more time and allowing customers to customize their look in creative ways.

As fantastic as this all sounds, however, don’t expect mass production any time soon.

Printing ophthalmic lenses with 3D technologies is an extremely challenging process, due largely to the critical requirements of precision, accuracy, and surface smoothness. To be commercially successful, 3D-printed eyeglasses must demonstrate satisfactory optical performance and reduced cost.

Although this combination is difficult to achieve, controlling this cost/performance ratio in the future could make 3D printing of ophthalmic lenses a reality. For example, Belgium-based Luxexcel, which has developed 3D-printed optics since 2009, announced that it would provide 3D-print technology to ophthalmic labs in 2017 that will produce lenses that meet all required industry standards.

CHALLENGES OF RESOLUTION AND SCALABILITY

Eyeglass lenses are some of the most challenging products to manufacture with 3D printing. Since eyeglasses are designed to manipulate the visible spectrum of the light with the wavelength ~ 500 nm, precision and surface smoothness need to be at the order of lambda/4, or preferably lambda/10. However, two major technological barriers stand in the way of achieving this: resolution and scalability.

“For the resolution challenge, let’s consider the more relaxed requirement for precision/resolution as lambda/4, which is around 100 nm,” says Cheng Sun, an associate professor of mechanical engineering at Northwestern University (USA) who is working in this field. “Of the leading additive manufacturing technologies — extrusion-based, laser/electron beam-induced melting/sintering, and photo-polymerization methods — low-energy, photo-polymerization provides the best potential for high-resolution 3D printing.”

There is a fundamental limit, though. Due to the diffraction-limit nature of the light, the resolution of the optical image is comparable with the wavelength of the light. “But at the same time, we want the precision to be lambda/4,” he says.

“Either we have to use much shorter wavelength for the 3D printing process, or utilize 2-photon absorption to control the resolution.” Both of these processes are being researched, but the equipment is very expensive and/or the fabrication process is very time-consuming.

Currently the only serious player in this space is Luxexcel, which won a 2015 Prism Award for Photonics Innovation for its 3D technology.

“We have made significant progress and have now achieved imaging quality,” states chief marketing officer Guido Groet. Luxexcel uses a propriety 3D print technology to achieve high resolution. Each lens is built from very small droplets of a proprietary, acrylic-like material; the droplets merge together and require no physical layering, which enhances smoothness.

With a refractive index of 1.53 and a specific weight of 1.15 g/cm3, this material is lighter than many ophthalmic materials. Luxexcel is also in the process of developing new materials with higher refractive indexes.

Scalability is the other inherent obstacle to the widespread use of 3D printing. “Now that we have proven lenses can be printed in high quality, we need to make sure we can make them on an industrial scale,” Groet adds.

UPDATE: See more developments from Luxexcel

Ideally, the goal is to fabricate the structure as large as possible, but also with as fine a resolution as possible. Even when this is attained, the next challenge is fabrication time.

A possible solution to this resolution/scalability/fabrication time obstacle is developing a high-throughput, high-resolution, 3D printing photo-polymerization process, a core research area for Sun.

Conventional 3D printing fabricates the 3D structure in point-by-point fashion. Instead, Sun developed a projection-based photo-polymerization method that fabricates a two-dimensional layer by projecting an optical image onto the photopolymer.

“The projected optical image determines the shape of the solidified 2D layer,” says Sun. “We can repeat the process in a layer-by-layer fashion to construct the 3D parts with significant time saving. In particular, the continuous liquid interface production (CLIP) process recently developed by Carbon3D further allows generation of monolithic polymeric parts to replace the discrete layered fabrication process.

“We are finding the projection process is orders of magnitude faster than other 3D printing methods, with the additional benefit of more homogenized materials properties and better surface finishing,” he says. “We are currently exploring how to use it as a way to 3D-print customized optical lenses.”


Michael McAlpine, an assistant professor of mechanical and aerospace engineering at Princeton, is leading a research team that uses 3D printing to create complex electronics devices such as this light-emitting diode, shown here printed on a contact lens.
Photo Princeton Univ. by Frank Wojciechowski
FUTURE POSSIBILITIES FOR 3D-PRINTED LENSES

3D printing of lenses is the first major technology disruption in the ophthalmic industry in many years. Gradient-index lenses can also be manufactured with 3D printing.

As part of a project demonstrating new 3D printing techniques, researchers at Princeton University have successfully embedded tiny light-emitting diodes (LEDs) into a standard contact lens, allowing the device to project beams of colored light. The process is an important step toward being able to 3D print electronics into complex shapes and materials, including “smart” ophthalmic lenses of the future.

“Electronics integrated into 3D-printed lenses, for example, could verify if a driver is falling asleep and sound an alarm,” Groet says.

Perhaps the greatest long-term benefit of 3D printing of eyeglass lenses will be helping the environment. About 2.9 billion eyeglasses were sold in 2014; this total is expected to climb to 3.77 billion units by 2022. Traditional manufacturing methods use blank lens that are then shaped and finished. About three-quarters of the material in the blank is removed through the cutting and grinding process. With the billions of eyeglasses produced every year, this represents a huge amount of waste from eyewear labs. The waste material contains hazardous materials such as lead, cadmium, indium, zirconium, sulfur, and styrene.

Other top concerns are excessive water and energy use.

These negative global environmental impacts would be eased significantly with widespread adoption of 3D printing of lenses. Less energy, water, and raw materials would be consumed and result in far less generated waste, “including chemicals or plastics that don’t degrade,” says Chen.

“Because 3D printing is a flexible manufacturing process, with a much smaller footprint, lenses can be manufactured at sites that are closer to individual markets,” he says, noting that 3D printing would also ease the burden for handling, transportation, and delivery, further reducing environmental impacts.

3D PRINTING at SPIE PHOTONICS WEST 

Cheng Sun and his research group at Northwestern University (USA) presented two papers on 3D printing of functional materials/devices at SPIE Photonics West in January.

Their paper on “Process development for high-resolution 3D-printing of bioresorbable vascular stents” can be found in the SPIE Digital Library.

–Mark Crawford is a freelance writer based in the USA.


DOI: 10.1117/2.4201704.16

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