(Nanowerk Spotlight) Adding gold nanoparticles to 3D printed materials has always faced a fundamental problem: the particles must either be mixed into the printing material beforehand or applied as a coating afterward. Both approaches limit device performance. Pre-mixing leads to particle clumping and uneven distribution. Coating only affects the surface. These constraints have prevented manufacturers from creating devices that need precisely placed nanoparticles throughout their structure.
Professor Haider Butt and team at Khalifa University have developed an elegant solution that turns this process inside out. Instead of adding pre-made nanoparticles, they print with materials that can create their own. Their method, published in an open access paper in Materials & Design (“Programmed polymeric integration of gold nanoparticles into multi-material 3D printed hydrogels”), uses leftover chemical bonds in standard printing materials to transform dissolved gold into nanoparticles exactly where needed.
The insight came from studying how 3D printers create solid objects from liquid resins. The printing process links molecules together into chains but never uses up all the available connection points. These remaining reactive sites – specifically carbon-carbon double bonds – can donate electrons to gold ions, converting them into nanoparticles.
The team developed a two-material printing process that exploits this chemistry. They combine a specialized hydrogel containing these reactive sites with standard printing resins that lack them. After printing an object, they immerse it in a solution containing gold salts. Within minutes, the hydrogel portions begin generating nanoparticles internally, while the rest stays unchanged. The particles form evenly throughout the material rather than clumping together.
This direct formation method solves multiple manufacturing challenges. The nanoparticles emerge precisely where needed without additional processing steps. They become permanently embedded in the material structure rather than washing out over time. The gold solution remains reusable since particles only form within the printed parts. The entire process takes just minutes compared to hours or days for traditional methods.
Reduction by polymers: a) Chemical reaction between gold chloride and the polymer (pHEMA hydrogel) in resin 1. Resin 2 was a commercial polymer (DentaCLEAR) with no pHEMA present. b) Experimental illustration that shows the actual process of immersing the 3D printed multi-material cylinder (upper half printed with pHEMA and lower half printed with DentaCLEAR) in gold precursor solution (final product shown). Upon boiling, the nanoparticles (in red) are only produced in the upper section, which contains pHEMA. (Image: Reprinted from DOI:10.1016/j.matdes.2025.113650, CC-BY) (click on image to enlarge)
The researchers demonstrated the technique’s precision by creating color-correcting contact lenses. These require specific concentrations of nanoparticles in exact locations to filter out problematic wavelengths of light while maintaining transparency. Tests showed the printed lenses matched the performance of commercial color blindness correction devices.
Detailed analysis revealed consistent nanoparticle sizes around 80 nanometers, ideal for optical applications. The particles produced a characteristic optical absorption at 550 nanometers wavelength, confirming their utility for color filtering. Testing showed no particle leaching even after extended water exposure, and the materials maintained appropriate flexibility and oxygen permeability for contact lens use.
The method works with standard 3D printers without modification. The innovation lies entirely in the material chemistry. The team successfully printed complex shapes with distinct nanoparticle-containing regions, demonstrating control in three dimensions. Cell testing confirmed the materials’ safety, while mechanical analysis showed the nanoparticle formation process didn’t compromise material strength.
This approach transforms nanoparticle integration from a limiting factor into a controlled feature of the printing process. Manufacturers can now print ordinary objects that generate their own nanoparticles in precisely defined regions. The speed and simplicity of the process make it practical for large-scale production of advanced optical devices, sensors, and medical implants.
By eliminating the need to handle pre-made nanoparticles, this method bridges the gap between laboratory demonstrations and practical manufacturing. The ability to grow nanoparticles directly within printed structures opens new possibilities for creating devices that take full advantage of nanoscale properties.
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