Manufacturing - Micro-/Nanotechnology

Effective Light Directed Assembly of Building Blocks with Microscale Control

Building blocks have to be brought together to form a larger structure. Nature has perfected this task, allowing the formation of complex hierarchies that determine the function of the larger system. To apply this approach in particle-supported tissue engineering, a biocompatible means of assembly is required, such as thermal convection. The challenge is to provide direction to the particle flow by locally controlling the convection. Light comes to mind because it offers high temporal and spatial resolution.

In their Full Paper in Small, Ngoc-Duy Dinh, Chia-Hung Chen from the National University of Singapore and their co-workers successfully use microconvection to assemble microparticles into a variety of patterns.

Chia-Hung Chen: “The idea is to introduce gold nanorods to generate sufficient microconvection by using low-power laser irradiation to move the micro-sized building blocks forming specific patterns for bottom-up tissue engineering”

Simulations on Gold nanorods show their ability to produce localized surface plasmon resonance that intensifies upon laser-light-triggered aggregation, causing a local temperature increase that in turn induces convection flow.

Suspensions of microparticles alone do not react to laser light, it is only upon the addition of gold nanorods that thermoplasmonic convection allows laser-light-controlled assembly. Precise spatiotemporal control is achieved at just 1/500 000th of the pulse laser power required for purely optical trapping, which even provides access even to multicomponent assemblies.

A programmable automated stage can aggregate more than 1000 particles within just two minutes. Also, complex structures are possible if post-assembly crosslinking is performed.

The suitability of the technique for tissue engineering is demonstrated by seeding mesenchymal stems onto sterilized hydrogel microparticles, obtaining excellent cell viability and proliferation at all applied laser intensities. The 3D structure of the resulting tissue can be revealed by confocal microscopy of immunohistochemistry staining.

Ngoc-Duy Dinh: “This light-guided assembly technique is expected to find a broad application such as bottom-up tissue engineering, 3D bioprinting and advanced biofabrication.”

To know more about this promising tissue engineering technique, please go to the Small homepage.

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