Multiphoton Absorption Polymerization Research Articles

3D Printing of Resilin in Water by Multiphoton Absorption Polymerization (Adv. Funct. Mater. 39/2023)

3D Printing of Resilin in Water by Multiphoton Absorption Polymerization (Adv. Funct. Mater. 39/2023)

3D Printing of Resilin in Water by Multiphoton Absorption Polymerization

AbstractResilin is an elastic rubber‐like protein found in the cuticles of insects. It incorporates outstanding properties of high resilience and fatigue lifetime, where kinetic energy storage is needed for biological functions such as flight and jumps. Since resilin is rich in tyrosine groups, localized photopolymerization is enabled due to the ability to introduce di‐tyrosine bonds by a ruthenium‐based photoinitiator. Using Multiphoton Absorption Polymerization 3D printing process, objects containing 100% recombinant resilin protein are printed in water at a submicron length scale. Consequently, protein‐based hydrogels with complex structures are printed using space positioning voxel polymerization. The objects are characterized by dynamic mechanical analysis using nanoindentation. Printing parameters such as printing speed and laser power are found to enable tuning the mechanical properties of the printed objects. The printed objects are soft and resilient, similar to native resilin, while presenting the highest resolution of a structure made entirely of a protein and better mechanical properties of common hydrogels and poly(dimethylsiloxane). Moreover, topography and mechanical properties enable cell growth and alignment without cell adhesion primers, thus facilitating biological applications. The fabrication of 3D resilin‐based hydrogel will open the way for potential applications based on biomimicking and in creating new functional objects.

Thermal feature-size enhancement in multiphoton photoresists

We demonstrate a new approach for decreasing the feature size in multiphoton absorption polymerization (MAP). Acrylic photoresists containing the photoinitiator KL68 (bis-[4-(diphenylamino) stryl]-1-(2-ethylhexyloxy), 4-(methoxy)benzene) exhibit a proportional velocity (PROVE) dependence, yielding smaller feature sizes at lower fabrication speeds. The feature size in this photoresist decreases substantially with a temperature increase of less than 10°C when all other fabrication parameters are kept constant, suggesting that the PROVE behavior results from local heating. Although higher temperatures have previously been associated with decreased feature sizes in MAP, the effect observed here is considerably stronger than in previous work, and is shown to be a property of the photoinitiator. This discovery opens the door to exploiting thermal gradients to improve resolution in MAP lithography.

Elucidating complex triplet-state dynamics in the model system isopropylthioxanthone

SummaryWe introduce techniques for probing the dynamics of triplet states. We employ these tools, along with conventional techniques, to develop a detailed understanding of a complex chemical system: a negative-tone, radical photoresist for multiphoton absorption polymerization in which isopropylthioxanthone (ITX) is the photoinitiator. This work reveals that the same color of light used for the 2-photon excitation of ITX, leading to population of the triplet manifold through intersystem crossing, also depletes this triplet population via linear absorption followed by reverse intersystem crossing (RISC). Using spectroscopic tools and kinetic modeling, we identify the reactive triplet state and a non-reactive reservoir triplet state. We present compelling evidence that the deactivation channel involves RISC from an excited triplet state to a highly vibrationally excited level of the electronic ground state. The work described here offers the enticing possibility of understanding, and ultimately controlling, the photochemistry and photophysics of a broad range of triplet processes.

Methods for Determining the Effective Order of Absorption in Radical Multiphoton Photoresists: A Critical Analysis

AbstractThe accurate determination of the effective order of absorption (EOA) for multiphoton absorption polymerization in radical photoresists is critical for the development and characterization of new materials with improved sensitivity and/or resolution. However, reliable measurement of the EOA is a challenging problem. The accuracy of four techniques that have been developed to address this issue is analyzed in terms of the known kinetics of the radical polymerization of polyfunctional monomers. It is demonstrated that methods that are based upon full reciprocity, i.e., the concept that the chemical response of the photoresist depends on the exposure dose, but not on the period over which this dose is delivered, only enable reliable determination of the EOA under a highly constrained set of circumstances. Methods that depend on limited reciprocity, i.e., the concept that the chemical response of the photoresist is the same when the total exposure window is constant, even if the details of the exposure within that window are varied, can enable accurate determination of the EOA over a considerably broader range of operating conditions. This prediction is verified experimentally. The analysis presented here provides guidance for future experiments and a basis for clearer interpretation of previously published results.

The Characterization of Absorptive Nonlinearities

AbstractThe measurement of the order and magnitude of absorptive nonlinearities is essential to the development and improvement of a wide range of optical materials. This review presents and contrasts some of the most commonly used methods for making such measurements. As background, we introduce the history of, and the essential physics behind, multiphoton absorption (MPA) and phenomena that can interfere with its measurement. We review methods for the direct and indirect measurement of MPA. The direct methods covered include nonlinear transmission, absorption modulation, Z‐scan, and spectrally‐resolved, two‐beam coupling. The indirect methods reviewed, all of which rely on the measurement of multiphoton action cross sections, include nonlinear fluorescence excitation, thermal lensing, MPA‐induced photocurrent, and various techniques for determining the order of effective nonlinear absorption in multiphoton absorption polymerization.

In situ measurement of the effective nonlinear absorption order in multiphoton photoresists

AbstractKnowledge of the order of the effective nonlinear absorption in multiphoton photoresists is a key element in the development of improved materials for multiphoton absorption polymerization (MAP). The direct measurement of this nonlinearity has proven challenging. A new technique called 2‐beam initiation threshold (2‐BIT) is presented that allows for the unambiguous, in situ measurement of the order of the effective nonlinear absorption using a simple optical arrangement that can be employed with virtually any MAP setup. This technique is benchmarked using three common commercial photoinitiators that have been used previously in MAP and one common dye that acts as a photoinitiator. The linear absorption spectrum is demonstrated to be a poor predictor of the effective order of nonlinear absorption at a given wavelength. Surprisingly, for two of these initiators the effective nonlinear absorption process is dominated by 3‐photon absorption in the 800 nm wavelength range, suggesting that 2‐BIT is a valuable means of identifying initiators that can improve the resolution of MAP. image

Generating Nanostructures with Multiphoton Absorption Polymerization using Optical Trap Assisted Nanopatterning

The need to generate sub 100 nm features is of interest for a variety of applications including optics, optoelectronics, and plasmonics. To address this requirement, several advanced optical lithography techniques have been developed based on either multiphoton absorption polymerization or near-field effects. In this paper, we combine strengths from multiphoton absorption and near field using optical trap assisted nanopatterning (OTAN). A Gaussian beam is used to position a microsphere in a polymer precursor fluid near a substrate. An ultrafast laser is focused by that microsphere to induce multiphoton polymerization in the near field, leading additive direct-write nanoscale processing.

Metal-Enhanced Multiphoton Absorption Polymerization with Gold Nanowires

Metal-enhanced multiphoton absorption polymerization (MEMAP) is studied using gold nanowires with a set of three different photoresists. Photoresists that employ radical and cationic polymerization are investigated. In all cases, MEMAP is strongly correlated with multiphoton-absorption-induced luminescence (MAIL) of the nanowires. Wavelength-dependent studies indicate that the dominant mechanism for MEMAP is not field-enhanced two-photon absorption of the photoinitiator, but rather single-photon excitation of the photoinitiator by the broadband MAIL emission.

High-speed multiphoton absorption polymerization: fabrication of microfluidic channels with arbitrary cross-sections and high aspect ratios

We demonstrate the use of high-speed, multiphoton absorption polymerization (MAP) for the fabrication of large-area microfluidic master structures. High-speed fabrication in SU8 without laser-induced damage is made possible by the use of a novel photoacid generator with a high two-photon-absorption cross-section. Master structures fabricated with MAP can be used to produce polydimethylsiloxane microchannels with high aspect ratios and/or arbitrary cross-sections. Microchannels with different cross-sections and heights can be combined readily in a single device. This fabrication technique significantly increases the diversity of channel architectures available for microfluidic devices.

Self-polymerization of nano-fibres and nano-membranes induced by two-photon absorption

Laser Two-Photon Polymerization (LTPP) is a technique enabling formation of 3D nanostructures in photosensitive resins with sub-wavelength resolution and unmatched flexibility. However, controllable fabrication of sub-100 nm features by this technique is still a challenge. Self-polymerization, also known as non-local polymerization, is considered to be promising in this ultra-high resolution structure formation. Recent observation of fragile self-polymerized fibres with diameter within tens of nanometres (nano-fibres) encourages the use of self-polymerization to produce nanometre scale structures other than fibres and to define the conditions for controllable fabrication. “X”-shaped polymerized supports are used as rigid structures to produce suspended self-polymerized features of different nature (shape and dimensionality) in-between the walls of “X”. By laser writing lines parallel to the substrate and perpendicular to the long symmetry axis of “X” under different conditions, selfformation of periodic nano-fibres (diameter <100 nm) and nano-membranes is induced in acrylate photopolymer AKRE37. Depending on introduced exposure dose, spatial density threshold behaviour of non-structure, nano-fibre, nano-membrane, and laser written lines is deduced. Preliminary model including laser intensity, concentration of radicals, collapse force, and distance between supports as variables having threshold effect on final self-polymerized structure’s geometry is proposed to explain non-local self-polymerization. Keywords: femtosecond laser, multi-photon absorption polymerization, acrylate photopolymer, self-assembly, nanotechnology

Field-Enhanced Phenomena of Gold Nanoparticles

We investigate the connections between two field-enhanced phenomena of gold nanoparticles: multiphoton-absorption-induced luminescence (MAIL) and metal-enhanced multiphoton absorption polymerization (MEMAP). We observe a strong correlation between the nanoparticles and aggregates that have high efficiency for each process. The results of our studies indicate that for this system, MEMAP is driven not by field-enhanced two-photon absorption of the photoinitiator but rather by single-photon excitation of the photoinitiator by the MAIL emission.

High‐Performance Microring Resonators Fabricated with Multiphoton Absorption Polymerization

The fabrication of high-performance polymeric optical devices is demonstrated using multiphoton absorption polymerization (MAP). Supported waveguides with micrometer-scale diameters sustain high-quality modes with low loss. The performance of microring resonators created with MAP is comparable to that of devices created using more conventional lithographic techniques, but opens the door to the creation of devices with unique architectures.

Soft-lithographic replication of 3D microstructures with closed loops.

There is growing interest in lithographic technologies for creating 3D microstructures. Such techniques are generally serial in nature, prohibiting the mass production of devices. Soft-lithographic techniques show great promise for simple and rapid replication of arrays of microstructures but have heretofore not been capable of direct replication of structures with closed loops. We demonstrate that 3D microstructures created with multiphoton absorption polymerization can be replicated by using microtransfer molding to afford complex daughter structures containing closed loops. This method relieves many of the topological constraints of soft lithography, paving the way for the large-scale replication of true 3D microstructures.

Direct Laser Patterning of Conductive Wires on Three-Dimensional Polymeric Microstructures

We show that silver lines patterned on a substrate with multiphoton absorption can be rendered electrically conductive using electroless enhancement with copper. We demonstrate that this technique can be used to create metallic features on three-dimensional polymeric structures that have been fabricated with multiphoton absorption polymerization. This method makes it possible to use multiphoton absorption to create complete metal/polymer hybrid microstructures with a single fabrication setup.

Selective Functionalization of 3-D Polymer Microstructures

We demonstrate the selective functionalization of 3-D polymer microstructures that were created using multiphoton absorption polymerization. By fabricating different portions of the structures with acrylic and methacrylic polymers, we are able to take advantage of the differential reactivities of these materials to perform functionalization chemistry on a single polymeric component. We demonstrate the selective deposition of metal to create structures, such as a functional microinductor. Our strategy is quite general and can be extended readily to the deposition of materials, such as metal oxides and biomolecules.

Polymer microcantilevers fabricated via multiphoton absorption polymerization

We have used multiphoton absorption polymerization to fabricate a series of microscale polymer cantilevers. Atomic force microscopy has been used to characterize the mechanical properties of microcantilevers with spring constants that were found to span more than four decades. From these data, we extracted a Young’s modulus of E=0.44GPa for these microscale cantilevers. The wide stiffness range and relatively low elastic modulus of the microstructures make them attractive candidates for a range of microcantilever applications, including measurements on soft matter.

Replication of Two-Photon-Polymerized Structures with Extremely High Aspect Ratios and Large Overhangs

We demonstrate the replication of 3-D structures created with an acrylic polymer using multiphoton absorption polymerization. Microtransfer molding was used to replicate complex structures rapidly and with high fidelity, including structures that have high aspect ratios or reentrant features. It is also possible to replicate large numbers of structures simultaneously.

Three-Dimensional Micro- and Nanofabrication with Multiphoton Absorption

ABSTRACTMultiphoton absorption has become a powerful technique for the creation of three-dimensional micro- and nanostructures. Here we review some of our recent progress towards creating functional microdevices with multiphoton absorption. Specific thrusts of our research include development of new resins for multiphoton absorption polymerization, design of novel schemes for metal deposition, and post-fabrication ablation of polymeric structures.