Here, we performed photoinitiator-free two-photon polymerization (TPP) to fabricate 3D cell micro-scaffolds. By using a visible femtosecond pulsed laser as excitation, TPP is induced in deep UV-absorbing moieties without the use of photo-initiators. We fabricated 3D micro-structures of biocompatible materials and glycidyl methacrylate protein without photoinitiators. By using Raman/Brillouin spectroscopy, we quantitatively investigated the molecular and mechanical properties of the 3D structures, which are important factors for cell functions and growth on scaffolds. We seeded cells on the 3D scaffolds and observed their attachment and proliferation without causing numerous cell deaths due to the absence of potentially cytotoxic photoinitiators.
Multi-photon laser lithography (MPLL) is an economical maskless means for high resolution and intrinsic three-dimensional micro/nanostructures fabrication. Here, we report MPLL of AR-N 4340 photoresist, and a spatial resolution of 40 nm is obtained. The relationships between laser parameters and line morphologies are systematically investigated. In the MPLL process, standing wave interference generated by the reflected light from photoresist/air interface and the incident light could greatly influence the bonding capacity between the fabricated lines and glass substrate. Therefore, lines with width smaller than 150 nm can be easily taken away in the development process. In order to obtain line with higher resolution, two rectangular photoresist plates were fabricated for immobilization of the fabricated lines, and a nanoline with a feature size of 40 nm was achieved between them through carefully adjusting the incident laser power. This work is one of the evidences for high fabricating resolution characteristic of MPLL, and it exhibits the potential for fabricating high resolution semiconductor and electronic micro/nanostructures.
Here, we report a preparation method to fabricate 3D micro-cones with controllable morphology based on two-photon photolithography. Two-photon photolithography offers the unique ability to create arbitrarily complex 3D polymeric structures. The voxel shape of polymerization point is crucial for the topography of the micro-cone structure. Therefore, the relationship between focused voxel features of femtosecond laser and the shape of micro-cone were analyzed systematically, and a micro-cone structure with a cone height of 2 μm, cone tip of 50 nm, and a cone angle of 20° was successfully obtained in this study. In addition, 3D micro-cone structures with 10°, 20°, and 30° sharp corners have been fabricated by means of controlling the relative movement between laser focus and moving direction. Besides, the structures with a varied slope angle from 0° to 90° on the substrate surface can be obtained by controlling the post treatment process. Furthermore, a large array of 3D micro-cones has been achieved based on the proposed preparation method.
KEYWORDS: 3D printing, Printing, Two photon polymerization, 3D modeling, Photoresist materials, Additive manufacturing, Manufacturing, Polymers, Scanning electron microscopy, Surface roughness
In this work, we demonstrate a developed 3D printing based on two-photon polymerization for achieving millimeter-scale, micron-accuracy 3D structures (MM-3DS), which combines the femtosecond laser of 800 nm and low magnification objective lens of 10×. The commercial photoresist SU-8 is used in 3D printing system for improving mechanical strength and chemical stability of MM-3DS. The 3D microstructures are preprogrammed and optimized by considering the scanning mode and experiment parameters. During 3D printing process, micron features are written within the interior of SU-8 film via localized polymerization driven by nonlinear two-photon absorption process. By the 3D movement in ~1 mm scale of the focused beam, a customized MM-3DS can be produced. We have fabricated a customized MM-3DS with a size of 1.6 mm and an accuracy of 10 μm. The influence of volume for the printing structures Vs on the printing time T exhibits a linear behavior, indicating that the printing speed is 0.248 mm3/h under the current conditions. This technology offers a flexible and low-cost method of generating highly customizable, precisely controlled MM-3DS, which is promising for the manufacture of complex functional structures and devices for the microfluidics, microelectronics, photonics and so on.
Poly(ethylene) glycol diacrylate(PEGDA)-based hydrogel materials with the excellent biocompatibility are widely used not only for cell culturing and tissue engineering but also for damaged bone repairing. In order to guarantee the stability of PEGDA as cell scaffolds and the compatibility with the host tissue, a further knowledge of interaction between PEGDA micronanostructure and cells is indispensable. In this study, two kinds of three-dimensional PEGDA micronanostructures have been designed and fabricated by two-photon polymerization for fibroblasts culturing. The PEGDA (average molecular weight 700) used in our study can preferably reconcile with a quantitative crosslinker to enhance the mechanical strength of structures. The polymerized line width as a function of the experimental conditions such as laser power and scanning speed during the two-photon polymerization has been investigated. Through investigating the adhesion, proliferation, and spread of fibroblasts on PEGDA micronanostructures in vitro, a response between micro-structures and fibroblast has been investigated. This study would provide the potential application of PEGDA hydrogel in biophotonics and tissue engineering.
Luneburg lens is a fascinating gradient refractive index (GRIN) lens that can focus parallel light rays on a perfect geometrical point without aberration in geometrical optics, compared with conventional lens made of homogeneous dielectric materials with specially designed surfaces. Constructing a three dimensional (3D) Luneburg lens at optical frequencies is a challenging task due to the difficulty of fabricating the desired GRIN materials in the lab. Reported experimental realizations of Luneburg lens at optical frequencies are mainly based on two dimensional metamaterials structures, or plasmonic structures. Here, we present the first practical implementation of the 3D version of Luneburg lens at optical frequencies based on the effective medium approximation. The 3D Luneburg lens is designed with GRIN 3D simple cubic metamaterials (SCMs) structures, and fabricated with no-resonant dielectric metamaterials by laser direct writing method in the commercial negative photoresist IP-L. We have experimentally demonstrated the feasibility of tailoring inhomogeneous metamaterials structures to realize 3D Luneburg lens with the effective GRIN profiles. The effective refractive index has been spatially and gradually modified by tailoring the volume filling fraction of SCMs structures. Simulated and experimental results simultaneously exhibit interesting 3D ideal focusing performance of the 3D Luneburg lens for the infrared light at wavelengths of 6.25m. This study would provide the protocol for developing the 3D Luneburg lens with wide field-of-view and ideal focusing theoretically and experimentally, which would further prompt the potential applications in integrated light-coupled devices and lab-on-chip integrated biological sensors based on infrared light.
Hydrogels with the precise three-dimensional configuration (3D hydrogels) have played important roles in the fields of tissue engineering and drug delivery, which will help to mimic the behavior of bio-inspired systems. Thus, the improvement of the spatial resolution on both the microscopic and the nanometric scale has been urgently demanded. There are some developed techniques to fabricate the 3D microstructures, however, these techniques require either high energy, strict operation environment or expensive mask.
As a promising maskless and flexible photolithography technique, two-photon polymerization (TPP) is a promising protocol to achieve 3D hydrogels. However, TPP of 3D hydrogels has been hindered due to the lack of high efficient water-soluble photoinitiator. In this presentation, the development of water soluble TPP photoinitiator of high initiating efficiency, as well as its fabrication capability and the resolution will be illustrated. The high resolution of 92 nm has been achieved benefiting from the high efficency of the developed photoinitiators and the optimized optical parameters. Furthermore, the microstructures with high accuracy such as those simulating the morphology of adenovirus and red blood cell have been fabricated, demonstrating the promising fabrication capability for achieving arbitrary architectures. The design of the photoinitiators, and the TPP fabrication technique mentioned in this study would provide high potential for the futher application in the research fields of cell imaging and tissue engineering.
We focus on investigating the optical transmittance of silver grid transparent electrodes (SGTEs) in variable angle view theoretically and experimentally, rather than the optical transmittance under the normal incidence. The variable angle transmittance (VAT) values of SGTEs are measured on a home-made experimental setup. The experimental results about difference of the transmittance difference under different angles are small and negligible, although the measured angle is changed. Theoretically, the physical mechanism on nearly constant transmittance for different angle view can be well explained according to the theory of geometrical optics. This study provides an approach for investigating the VAT values of SGTEs in a controllable fashion and the influence of viewing angle of the touch screen.
The photonic band gap effect which originates from the translational invariance of the periodic lattice of dielectrics has been widely applied in the technical applications of microwave, telecommunication and visible wavelengths. Among the various examples, polymers based three dimensional (3D) photonic crystals (PhCs) have attracted considerable interest because they can be easily fabricated by femo-second (fs) ultrafast laser direct writing (DLW) method. However, it is difficult to realize complete band gap in polymers PhCs due to the low index contrast between polymers and air. Here, we report the design and experimental realization of light's nonreciprocal propagation in woodpile PhCs fabricated with DLW method. Firstly, we fabricated several polymers woodpile PhCs on glass substrate with different crystal planes. The Fourier transform infrared spectroscopy (FTIR) measurements are in agreement with the theoretical predictions, which proves the validity and the accuracy of our DLW method. Further measurements of the transmission spectra with respect to the incident angle reveal that the surface crystal planes and incident wave vectors play important roles in the optical response. Furthermore, we designed and fabricated a 30° PhC wedge. And we find nonreciprocal transmission effect between the forward and backward waves, resulting from the nonsymmetrical refraction of the light in different planes. Our results may find potential applications in future 3D photonic integrated circuits and pave the way for the fabrication of other photonic and optical devices with DLW method.
Considering the axially symmetric polarization and intensity distribution, radially polarized (RP) laser beam has comparatively higher axial component of electric field and smaller size of focal spot compared to linearly polarized (LP) laser. In this study, the effect of radial polarization on multiphoton fabrication has been studied, and polymer spots and lines are chosen as the study objects of 2D micro/nano structures of multiphoton lithography. These structures were fabricated with IP-L, a commercial negative photoresist, by RP fs-pulse laser beam which was tightly focused by an objective lens with high numerical aperture. Multiple experimental conditions, such as fabrication power, exposure time and scanning velocity, were verified in order to observe the structural variation of these polymer structures. On the basis of measurement from images of the scanning electron microscope, the transverse and longitudinal sizes of polymer spots and lines could be analyzed, and the relationship between the aspect ratio (AR) and the above experimental conditions could be acquired. The statistical results agree with our predictions that the RP laser beam can significantly reduce the AR, and the AR in RP laser fabrication has little correlation with conditions besides fabrication power, such as exposure time and scanning velocity.
In our study, two carbazole-based cyanines, 3,6-bis[2-(1-methylpyridinium)vinyl]-9-methyl carbazole diiodide (A) and 6,6'-bis[2-(1-methylpyridinium)vinyl]-bis(9-methyl-carbazol-3yl)methane diiodide (B) were synthesized and employed as light-up probes for DNA and cell imaging. Both of the cyanine probes possess a symmetric structure and bis-cationic center. The obvious induced circular dichroism signals in circular dichroism spectra reveal that the molecules can specifically interact with DNA. Strong fluorescence enhancement is observed when these two cyanines are bound to DNA. These cyanine probes show high binding affinity to oligonucleotides but different binding preferences to various secondary structures. Confocal microscopy images of fixed cell stained by the probes exhibit strong brightness and high contrast in nucleus with a very low cytoplasmic background.
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