Two-photon Polymerization Research Articles

3D fiber-probe surface plasmon resonance microsensor towards small volume sensing

Integrating surface plasmon resonance (SPR) structures on fiber end facets enables the sensing system to be miniature, label-free, real-time, and remote detection. Yet, the wave vector matching condition for SPR excitation is hard to be satisfied by regulating the wave vector of light emitted from fiber ends. Here, we demonstrate a novel SPR microsensor realized by integrating a 3D micro waveguide onto the fiber tip. The mechanism of SPR excitation is illustrated by wave vector matching between the in-plane component of waveguide mode and surface plasmon polaritons. Using two-photon polymerization (2PP) and metallization process, the designed 3D waveguide probe with a length of 10 µm is fabricated on the fiber tip. Then, the microsensor was applied for the immune-sensing of anti-human IgG and human IgG interactions, and a LOD of 1.11 nM was achieved. The ultracompact structure endows with the capability for high-performance detection in the micrometre scale through a convenient “dip-and-read” manner. As a proof-of-concept for this “dip-and-read” small volume sensing, immunoassay detection in a small sample volume of 5 μL was also successfully demonstrated. The obtained results indicated that our 3D fiber-probe SPR microsensor may provide a powerful tool for small-volume biosensing applications.

Sustained Release Microneedles: Materials and Applications in Facial Rejuvenation.

Wrinkled and loose skin resulting from collagen degradation along with fibers decreasing reflects the youth diminishing. Microneedles (MNs) have opened up new avenues for the development of painless and noninvasive transdermal drug delivery systems for facial rejuvenation. Encapsulated drugs or molecules are transmitted to targeted tissues via percutaneous microchannels, which eliminate potential gastric stimulation or first-pass metabolic effects, as well as boost patient compliance. Although MNs are considered effective and feasible therapeutic alternatives to metals, silicon, and polymers, traditional procedures with reduction processes continue to encounter methodological limitations. In recent years, promising additive manufacturing processes such as three-dimensional printing and two-photon polymerization manufacturing have been developed with the aim of overcoming the limitations by traditional processes to facilitate an efficient and economic production mode. This review summarizes the design, material selection, and manufacturing method for recently advanced MN systems. Furthermore, we also highlight specific polymeric or natural microneedle products, like hyaluronan, plant derivates, and vitamins, for esthetic applications in this review. Impact Statement In this review, the materials and manufactural routes of microneedles (MNs) are detailed. Moreover, similar to the diagnostic or therapeutic MNs, the feature of dispensation with training and ready-to-use is perfect for beautification and anti-aging, which necessitate repeated and long-term usage. Furthermore, the specific polymeric or natural products for esthetic applications of MNs are highlighted in this review.

Two‐Photon Polymerization: Fundamentals, Materials, and Chemical Modification Strategies (Adv. Sci. 7/2023)

Two-Photon Polymerization In article number 2204072 by Andrew Kellett and co-workers, a series of two-photon printed microstructures used in optical, drug delivery, tissue engineering, and microfluidic devices are placed on the columns of the Giant-s Causeway, which is a natural phenomenon of interlocking basalt columns that resulted from ancient volcanic activity on the coast of county Antrim, Ireland.

A methodology for two-photon polymerization micro 3D printing of objects with long overhanging structures

A methodology for two-photon polymerization micro 3D printing of objects with long overhanging structures

Carbazole‐Based Anion Ionic Water‐Soluble Two‐Photon Initiator for Achieving 3D Hydrogel Structures

Abstract3D hydrogel structures fabricated by two‐photon polymerization (TPP) have become attractive in biomedical fields. Generally, conventional organic solvents are toxic and the residues left in the fabricated 3D structures are harmful to cells. Hence, anion ionic carbazole‐based water‐soluble two‐photon initiator (TPI) 3,6‐bis[2‐(1‐methylpyridinium)vinyl]‐9‐methylcarbazole ditosylate (BT) is proposed to construct arbitrary 3D hydrogel structures. Cucurbit[7]uril (CB7) and BT form a host‐guest complex (CB7/BT) with a binding ratio of 1:1, which further improves the water solubility, biocompatibility and nonlinear absorption property of TPI. A water‐soluble photoresist consisting of photoinitiator CB7/BT and monomer poly(ethylene glycol) diacrylate is prepared to explore the TPP fabrication capacity. The electron paramagnetic resonance measurement shows that CB7/BT initiates photopolymerization by alkyl radicals. The laser threshold power of the photoresist is 6.3 mW and the feature size is 127 nm in TPP at 780 nm. The initiator with p‐toluenesulfonate anion exhibits higher binding energy, larger two‐photon absorption cross‐section and two‐photon fabrication resolution compared with the previous work using iodide as an anion, indicating a promising way to improve the fabrication capacity of water‐soluble TPI through changing the anion ionic group. The proposed strategy will provide high potential for the further application in the biomedical field.

Bio-inspired Compact, High-resolution Snapshot Hyperspectral Imaging System with 3D Printed Glass Lightguide Array.

To address the major challenges to obtain high spatial resolution in snapshot hyperspectral imaging, 3D printed glass lightguide array has been developed to sample the intermediate image in high spatial resolution and redistribute the pixels in the output end to achieve high spectral resolution. Curved 3D printed lightguide array can significantly simplify the snapshot hyperspectral imaging system, achieve better imaging performance, and reduce the system complexity and cost. We have developed two-photon polymerization process to print glass lightguide array, and demonstrated the system performance with biological samples. This new snapshot technology will catalyze new hyperspectral imaging system development and open doors for new applications from UV to IR.

Colourful 3D anti-counterfeiting label using nanoscale additive manufacturing

ABSTRACT Microprinting is changing anti-counterfeit technology by producing complex micro-/nano-scale labels to increase the security level. However, the current microprinted anti-counterfeiting labels only contain 2D features, thought of as single coding (e.g. mostly in texts or graphs), unable to satisfy the high-end anti-counterfeiting demands of producing multi-coding, high-storage-density labels. Here, we introduce an approach for fluorescence printing to produce a 3D colourful, sophisticated anti-counterfeiting label. In the method, pre-synthetic QDs are printed with photoresists based on two-photon polymerisation, allowing for accurate regulation of fluorescence in both 2D and 3D. The fabricated photoresists exhibit immediate and postprocessing-free colour emissions under UV light. We demonstrated the ultra-high free design and accurate manufacturing capability of the approach by fabricating multi-colour, multi-layer patterns containing both texts and graphs on a 50μm × 50μm × 30μm portable label. The approach can also be applied to multi-dimensional optical data storage and colourful microdisplays.

Simultaneous measurement of humidity and temperature based on fiber-tip microcantilever cascaded with fiber Bragg grating.

We demonstrated a hybrid sensor of fiber Bragg grating (FBG) and Fabry-Perot interferometer (FPI) based on fiber-tip microcantilever for simultaneous measurement of temperature and humidity. The FPI was developed using femtosecond (fs) laser-induced two-photon polymerization to print the polymer microcantilever at the end of a single-mode fiber, achieving a humidity sensitivity of 0.348 nm/%RH (40% to 90%, when temperature = 25 °C ± 0.1 °C), and a temperature sensitivity of -0.356 nm/°C (25 to 70 °C, when RH% = 40% ± 1%). The FBG was line-by-line inscribed in the fiber core by fs laser micromachining, with a temperature sensitivity of 0.012 nm/ °C (25 to 70 °C, when RH% = 40% ± 1%). As the shift of FBG-peak on the reflection spectra is only sensitive to temperature rather than humidity, the ambient temperature can be directly measured by the FBG. The output of FBG can also be utilized as temperature compensation for FPI-based humidity measurement. Thus, the measured result of relative humidity can be decoupled from the total shift of FPI-dip, achieving the simultaneous measurement of humidity and temperature. Gaining the advantages of high sensitivity, compact size, easy packaging, and dual parameter measurement, this all-fiber sensing probe is anticipated to be applied as the key component for various applications involving the simultaneous measurement of temperature and humidity.

Highly conformable terahertz metasurface absorbers via two-photon polymerization on polymeric ultra-thin films

Highly conformable terahertz metasurface absorbers via two-photon polymerization on polymeric ultra-thin films

Highly conformable terahertz metasurface absorbers via two-photon polymerization on polymeric ultra-thin films

Abstract The continuously increasing interest in flexible and integrated photonics requires new strategies for device manufacturing on arbitrary complex surfaces and with smallest possible size, respectively. Terahertz (THz) technology can particularly benefit from this achievement to make compact systems for emission, detection and on-demand manipulation of THz radiation. Here, we present a novel fabrication method to realize conformable terahertz metasurfaces. The flexible and versatile character of polymeric nanomembranes is combined with direct laser writing via two-photon polymerization to develop free-standing ultra-thin quasi-perfect plasmonic absorbers with an unprecedentedly high level of conformability. Moreover, revealing new flexible dielectric materials presenting low absorption and permittivity in the THz range, this work paves the way for the realization of ultra-thin, conformable hybrid or all-dielectric devices to enhance and enlarge the application of THz technologies, and flexible photonics in general.

3D micro-structures for rarefied gas flow applications manufactured via two-photon-polymerization

In this work, the two-photon-polymerization (TPP) fabrication technique was employed to manufacture three-dimensional (3D) micro-structures suitable for confined rarefied gas flows. Four different micro-tubes of simple geometry have been tested in vacuum conditions. The geometry of the micro-tubes was characterized via a focus-variation 3D optical measurement microscope, a digital microscope and an X-ray μ-tomography. Mass flow rate measurements of pressure-driven rarefied gas flows of nitrogen in slip and transition regimes were compared to theoretical values obtained via the kinetic theory of gases. The experimental measurements were realized via the constant volume technique. The good agreement obtained between experimental and numerical results proves the feasibility of using this fabrication technique to create well controlled 3D shaped microsystems for rarefied gas flows applications.

Solid-State Crosslinkable, Shape-Memory Polyesters Serving Tissue Engineering.

Acrylate-endcapped urethane-based precursors constituting a poly(D,L-lactide)/poly(ε-caprolactone) (PDLLA/PCL) random copolymer backbone aresynthesized with linear and star-shaped architectures and various molar masses. It isshown that the glass transition and thus the actuation temperature couldbe tuned by varying the monomer content (0-8 wt% ε-caprolactone, Tg,crosslinked = 10-42 °C) in the polymers. The resulting polymers areanalyzed for their physico-chemical properties and viscoelastic behavior (G'max = 9.6-750kPa). The obtained polymers aresubsequently crosslinked and their shape-memory properties arefound to be excellent (Rr = 88-100%, Rf = 78-99.5%). Moreover, their potential toward processing via various additive manufacturing techniques (digital light processing, two-photon polymerization and direct powder extrusion) isevidenced with retention of their shape-memory effect. Additionally, all polymers arefound to be biocompatible in direct contact in vitrocell assays using primary human foreskin fibroblasts (HFFs) through MTS assay (up to ≈100% metabolic activity relative to TCP) and live/dead staining (>70% viability).

Two Photon Induced Pulsed Laser Polymerization with Near Infrared Light.

We introduce two-photon (2P) pulsed laser polymerization (PLP) at 800 nm, demonstrating its working principle even through biological tissue. We show that 2P PLP is reliable in determining propagation rate coefficients on the example of the free radical polymerization of methyl methacrylate (MMA) at frequencies ranging from 10 to 100 Hz.

3D printed fiber-optic nanomechanical bioprobe

Ultrasensitive nanomechanical instruments, e.g. atomic force microscopy (AFM), can be used to perform delicate biomechanical measurements and reveal the complex mechanical environment of biological processes. However, these instruments are limited because of their size and complex feedback system. In this study, we demonstrate a miniature fiber optical nanomechanical probe (FONP) that can be used to detect the mechanical properties of single cells and in vivo tissue measurements. A FONP that can operate in air and in liquids was developed by programming a microcantilever probe on the end face of a single-mode fiber using femtosecond laser two-photon polymerization nanolithography. To realize stiffness matching of the FONP and sample, a strategy of customizing the microcantilever’s spring constant according to the sample was proposed based on structure-correlated mechanics. As a proof-of concept, three FONPs with spring constants varying from 0.421 N m−1 to 52.6 N m−1 by more than two orders of magnitude were prepared. The highest microforce sensitivity was 54.5 nm μN−1 and the detection limit was 2.1 nN. The Young’s modulus of heterogeneous soft materials, such as polydimethylsiloxane, muscle tissue of living mice, onion cells, and MCF-7 cells, were successfully measured, which validating the broad applicability of this method. Our strategy provides a universal protocol for directly programming fiber-optic AFMs. Moreover, this method has no special requirements for the size and shape of living biological samples, which is infeasible when using commercial AFMs. FONP has made substantial progress in realizing basic biological discoveries, which may create new biomedical applications that cannot be realized by current AFMs.

Numerical and experimental investigation of gas flow field variations in three-dimensional printed gas-dynamic virtual nozzles

Gas-dynamic virtual nozzles (GDVNs) play a vital role in delivering biomolecular samples during diffraction measurements at X-ray free-electron laser facilities. Recently, submicrometer resolution capabilities of two-photon polymerization 3D printing techniques opened the possibility to quickly fabricate gas-dynamic virtual nozzles with practically any geometry. In our previous work, we exploited this capability to print asymmetric gas-dynamic virtual nozzles that outperformed conventional symmetric designs, which naturally leads to the question of how to identify the optimal gas-dynamic virtual nozzle geometry. In this work, we develop a 3D computational fluid dynamics pipeline to investigate how the characteristics of microjets are affected by gas-dynamic virtual nozzle geometry, which will allow for further geometry optimizations and explorations. We used open-source software (OpenFOAM) and an efficient geometric volume-of-fluid method (isoAdvector) to affordably and accurately predict jet properties for different nozzle geometries. Computational resources were minimized by utilizing adaptive mesh refinement. The numerical simulation results showed acceptable agreement with the experimental data, with a relative error of about 10% for our test cases that compared bell- and cone-shaped sheath-gas cavities. In these test cases, we used a relatively low sheath gas flow rate (6 mg/min), but future work including the implementation of compressible flows will enable the investigation of higher flow rates and the study of asymmetric drip-to-jet transitions.

Printing on Particles: Combining Two-Photon Nanolithography and Capillary Assembly to Fabricate Multimaterial Microstructures.

Additive manufacturing at the micro- and nanoscale has seen a recent upsurge to suit an increasing demand for more elaborate structures. However, the integration of multiple distinct materials at small scales remains challenging. To this end, capillarity-assisted particle assembly (CAPA) and two-photon polymerization direct laser writing (2PP-DLW) are combined to realize a new class of multimaterial microstructures. 2PP-DLW and CAPA both are used to fabricate 3D templates to guide the CAPA of soft- and hard colloids, and to link well-defined arrangements of functional microparticle arrays produced by CAPA, a process that is termed "printing on particles." The printing process uses automated particle recognition algorithms to connect colloids into 1D, 2D, and 3D tailored structures, via rigid, soft, or responsive polymer links. Once printed and developed, the structures can be easily re-dispersed in water. Particle clusters and lattices of varying symmetry and composition are reported, together with thermoresponsive microactuators, and magnetically driven "micromachines", which can efficiently move, capture, and release DNA-coated particles in solution. The flexibility of this method allows the combination of a wide range of functional materials into complex structures, which will boost the realization of new systems and devices for numerous fields, including microrobotics, micromanipulation, and metamaterials.

Monolayer heterojunction interactive hydrogels for high-freedom 4D shape reconfiguration by two-photon polymerization.

Mimicking natural botanical/zoological systems has revolutionarily inspired four-dimensional (4D) hydrogel robotics, interactive actuators/machines, automatic biomedical devices, and self-adaptive photonics. The controllable high-freedom shape reconfiguration holds the key to satisfying the ever-increasing demands. However, miniaturized biocompatible 4D hydrogels remain rigorously stifled due to current approach/material limits. In this research, we spatiotemporally program micro/nano (μ/n) hydrogels through a heterojunction geometric strategy in femtosecond laser direct writing (fsLDW). Polyethylene incorporated N-isopropylacrylamide as programmable interactive materials here. Dynamic chiral torsion, site-specific mutation, anisotropic deformation, selective structural coloration of hydrogel nanowire, and spontaneous self-repairing as reusable μ/n robotics were identified. Hydrogel-materialized monolayer nanowires operate as the most fundamental block at nanometric accuracy to promise high freedom reconfiguration and high force-to-weight ratio/bending curvature under tight topological control. Taking use of this biomimetic fsLDW, we spatiotemporally constructed several in/out-plane self-driven hydrogel grippers, diverse 2D-to-3D transforming from the same monolayer shape, responsive photonic crystal, and self-clenched fists at μ/n scale. Predictably, the geometry-modulable hydrogels would open new access to massively-reproducible robotics, actuators/sensors for microenvironments, or lab-on-chip devices.

Magnetically driven micro-optical choppers fabricated by two-photon polymerization.

In this Letter, a series of magnetically driven micro-optical choppers based on customized photoresist were fabricated by two-photon polymerization (TPP) technology. Synthetic Fe3O4 nanoparticles (NPs) were modified and dispersed in the original photoresist to achieve magnetic field response. After accurately formulating a magnetic photoresist containing Rhodamine B to reduce the light transmittance, four micro-optical choppers with different slot widths were printed using optimized processing parameters. The micro-optical choppers were remotely manipulated to rotate by the external magnetic field. More importantly, the function demonstration of the micro-optical choppers with an excellent chopping effect was achieved at a given light wavelength of 515 nm. The magnetically driven micro-optical choppers provide a new approach, to the best of our knowledge, for the fabrication of external field-responsive optical components.

Fabrication and performance evaluation of magnetically driven double curved conical ribbon micro-helical robot

In this research, a magnetically driven double curved conical ribbon micro-helical robot was proposed to improve the swimming stability and swimming performance. Its swimming performance as well as magnetization characteristics were analyzed by fluid dynamics simulation. Meanwhile, a transverse bidirectional fold-line scanning method was proposed to fabricate the designed microrobots via voxel-modulation two-photon polymerization microfabrication technology. After optimizing the machining parameters, the length dimension error of the double curved conical ribbon micro-helical robot could be further reduced to less than 1%. Furthermore, a conical rotating three-dimensional uniform magnetic field was established to drive the microrobots. Microrobot driven experiment of the conical rotating three-dimensional uniform magnetic field was conducted and compared with the planar uniform magnetic field. It is proved that the micro-helical robot driven by the conical rotating three-dimensional uniform magnetic field can achieve high stability and no swing swimming in the low-frequency spiral propulsion state. This work may provide a reference for the future application of micro-helical robots in the fields of drug delivery, cell sorting, sensing and environmental repair in vivo.

Innate immune cell instruction using micron-scale 3D objects of varied architecture and polymer chemistry: The ChemoArchiChip

<h2>Summary</h2> To design effective immunomodulatory implants, innate immune cell interactions at the surface of biomaterials need to be controlled and understood. The architectural design freedom of two-photon polymerization is used to produce arrays of surface-mounted, geometrically diverse 3D polymer objects. This reveals the importance of the interplay between architecture and materials chemistry in determining human macrophage fate <i>in vitro</i>. The ChemoArchiChip identifies key structure-function relationships and design rules from machine learning models to build a mechanistic understanding of cell attachment and polarization. Object shape, vertex/cone angle, and size are key drivers of attachment. Particular shapes are found to heavily modulate pro- or anti-inflammatory cell polarization, while triangular pyramids drastically reduce or even eliminate attachment. Caveola-dependent endocytosis is a principal mechanism by which cells respond to objects with sharp points; i.e., low vertex/cone angles. The discovery of these putative design rules points to surfaces decorated with architectures to augment implant performance.