The ability to generate 3D angiogenesis models is central for tissue engineering and drug screening applications. However, existing bio-fabrication technologies have yet to attain precise guidance of capillary networks in 3D. Here, we present our latest results in fabricating capillary networks using a novel laser-assisted bioprinting technique named Laser Induced Side Transfer (LIST). We found that LIST-printed human umbilical vein endothelial cells (HUVECs) present negligible loss of viability and maintain their abilities to migrate, proliferate and form intercellular junctions. Furthermore, we showed that LIST enabled the formation of capillary-like networks in 3D with high spatial precision (50 μm) over a large volume (1 cm3). Those networks were validated as angiogenesis assays for pro- and anti-angiogenic compounds. LIST could be widely adapted for applications requiring multiscale bioprinting capabilities, like the development of 3D drug screening models and artificial tissues.
The effect of the laser and the optomechanical parameters in the micromachining process of the complex geometry is the challenging part in the manufacturing industry due to wide range of materials. There are limited ways to find the best process parameters for machining and texturing with specific depth, thickness and roughness. The COMSOL software was used to model all the laser parameters like laser power, sampling rate, and optomechanical parameters like pulse overlap. Presented simulation demonstrates the roughness, depth and thickness of machined path. In addition, from the simulation point of view, the laser and optomechanical parameters can be optimized for the specific depth and thickness. To validate the numerical model, experiments are conducted for different process parameters by changing the laser power, varying the sampling rate of the laser and data acquisition card, changing the pulse overlap and the results are tabulated. Also the same input parameters are given to numerical simulation and the results are in good agreement with experimental outcomes. In conclusion, the simulated model can be used to estimate the effect of the process parameters before the machining. So that the presented model has the control over the machined surface quality and the process can be optimized by giving different material properties in the simulation.
Laser micro machining is one of the micro manufacturing processes. Since it has wide range of applications in Microelectronics, medical device, aerospace etc., the accuracy of the process is the most significant factor. In this study, the challenges and corresponding possible solutions that are encountered in machining complex geometries are addressed. Furthermore, the effect of process parameters on the overall quality of the manufacturing are discussed. The paper proposes mathematical function based and image processing based algorithms to find the machining coordinates. The former calculates the first and second derivatives of the functions to find the essential coordinates and the latter converts pixels of the image into coordinates. Achieving required overlap is one of the difficulty in the curved shapes, which can be solved by using both the algorithms. However, the function-based approach is more efficient as the image processing approach depends on the image resolution. Lower resolution results in reduction in smoothness of the extracted coordinates and higher resolution leads to increased computational cost. By changing the different laser parameters such as laser power and mechanical parameters like sampling rate of data acquisition card; different roughness, depth and overlaps can be attained. The study demonstrates precision micromachining and it establishes optimal relation between the process parameters and quality of the machined surface.
The parameters of an off-axis cylindrical mirror-focused line-scanning system were studied to optimize the flatness of the 2 mm scan field. The scanning system parameters included the beam size, the distance between the scanning and the focusing mirror, the angle between the incident beam and the reflected beam, the optical scan angle, and the effective focal length of the cylindrical mirror. Because of the off-axis line-scanning system configuration, the scanning could be carried out either in the tangential (Y-scan) or in the sagittal (X-scan) plane. A 53 nm spectral bandwidth light source was used to evaluate the imaging performance of the scanning system. Since reflective optics is employed in this work for focusing, the scanning system could be used with a higher spectral bandwidth light source for optical coherence tomography applications. The effect of the angle between of the incident and reflected beams, the distance between the mirrors, the focal length of the cylindrical mirror and the scanning directions, on the flatness of the scan field were studied. It was proved that the sagittal scanning is least sensitive to variations in scanning system parameters and thus provides maximum flexibility in design.
The quality of the spectrometer affects the sensitivity fall-off, axial resolution, and depth scan range, therefore overall
performance of the spectral domain optical coherence tomography (SD-OCT) imaging. Chromatic aberration, optical
resolution, and detector array resolution are the key design consideration for high-quality OCT spectrometer.
Traditionally refractive optics spectrometer is used in SD-OCT. In the present work, the optical design of the reflective
optics spectrometer and of the refractive optics spectrometers is reported for high-speed line field optical coherence
tomography imaging. The performance of the spectrometers was compared by using the ZEMAX optical design
software. The ZEMAX optical modeling analysis shows that the reflective optics spectrometer provides better
performance by comparison with the refractive optics spectrometer.
Optical design of a spectrometer for all-reflective optics based line scan Fourier domain optical coherence tomography
(FD-OCT) imaging has been reported in this work for high-speed scanning. FD-OCT imaging data acquisition offers
significantly improved imaging speed in the depth direction compared to conventional time domain optical coherence
tomography (TD-OCT). On the other hand, line focused scanning improve imaging speed in the transverse direction
compare to commonly used flying spot scanning. Combination of FD-OCT acquisition and line focused scanner can give
higher imaging speed. Spectrometer is a critical submodule in FD-OCT system. Apart from the spectrometer optical
resolution, and detector array resolution, the chromatic aberration should be considered to design a high-quality FD-OCT
imaging spectrometer. The proposed imaging spectrometer consists of a planer reflective grating, off-axis parabolic
cylindrical mirror and a CCD array detector. Mirror focusing reduces the chromatic aberration because of its insensitivity
to the wavelength of the laser beam, therefore the spectrometer image quality enhanced by the reflective optics focusing.
Spot profile fall-off characteristic was analyzed by using ZEMAX optical design software.
The optical and analytical modeling of a line-scan optical coherence tomography (LS-OCT) system for high-speed three-dimensional
(3D) endoscopic imaging is reported. To avoid complex lens system and image distortion error, an off-axis
cylindrical mirror is used for focusing the line illumination on the sample surface and a micro mirror scanner is
integrated with the proposed configuration for transverse scanning. The beams are swept on the cylindrical mirror by the
micro mirror rotation and finally focused on the sample surface for transverse scanning. A 2mm by 3.2mm en-face
scanning is configured with a 2mm focused line and ±3° scanning mirror rotation. The proposed configuration also has
the capability of dynamic focusing by the movement of the cylindrical mirror without changing the transverse resolution.
The cylindrical mirror enhances the image quality by reducing the aberration. The system is capable of real-time 3D
imaging with 5μm and 10 μm axial and transverse resolutions, respectively.
Temporal phase shifting method, which is commonly used for characterization of the microstructures, requiring phaseshifter
has inherent errors due to non-linearity. To overcome this, an Acoustic-Optic Modulated Stroboscopic
Interferometer (AOMSI) was developed using the principle of Stroboscopic Interferometer. The technique utilizes the
advantage of stroboscopy to create phase shifted images without requiring any component for phase shifting.
Using Carré algorithm and developed AOMSI the curvature of microstructures due to residual stress was extracted.
Experiments were performed on a silicon wafer to demonstrate the feasibility of the presented technique. Further,
experiments were performed on a designed micro cantilever to extract surface-height information using the proposed
method. To verify the accuracy of the presented method, the same micro cantilever was characterized using a WYKO
surface profiler and the comparison was found to be in good agreement.
Optical Fiber Bragg Gratings (FBG) sensors have seen significant development in recent years. Such sensor
technology developed initially for the civil infrastructure is currently attracting the aerospace industry due to
the potential versatility of this technology and its measurement capability. The structural health monitoring
and the diagnostics and prognostics health management communities are excited about such development and
ready to embrace such capability. Sensors reliability and accuracy, however, continue to be two parameters
critical to the eventual implementation of the technology in high value targets. Such parameters can be
improved by different manufacturing techniques as well as optimum grating's coating selection. This paper
presents an evaluation of the mechanical behavior of the FBG strain sensors. A simulated analysis, using
finite element modeling, revealed the impact of coating material selection, coating thickness selection, and
bonding effect on the strain transfer loss. Results illustrate that metallic fiber coatings are more suitable for
improved strain transfer than their polymeric counterparts and acrylic coatings are least effective with
adhesive layer as small as possible.
A requirement to advance consistency and predictability of Micro-Electro Mechanical System (MEMS) device has
triggered research to have precise measurements and visual means to characterize dynamic parameters. Time resolved
measurements of entire surface in a microdevice to nanometer level accuracy are difficult using conventional metrology
system such as optical interferometer and optical microscopy. Laser Doppler Vibrometer (LDV) has found their
applications to some extent. Due to Single point technique, scanning is a must in LDV which sets drawback for
characterization in Microsystems. In this paper we propose the use of Acousto Optic Modulator (AOM) as a strobing
device with a continuous wave laser to develop a stroboscopic interferometer for static and dynamic characterization of
out of plane motion. Due to high random access time (typical 150 nanoseconds) AOM improves the capability of the tool
to test MEMS devices of higher frequencies. Detail study is done on the strobe frequency to correlate the pulsating
frequency of the laser by the AOM and the driven frequency of the microdevice. Theoretical modeling of the
stroboscopic interferometer is carried out by formulating the understanding between strobe frequency and the MEMS
device.
In this paper, detection of system noise in the optical layout for instantaneous phase shifting interferometry is discussed. Experiments were carried out on a diamond turned aluminum surface on the developed interferometer. The results were then compared with results from a commercial profiler to ascertain the uncertainty in the developed system. The uncertainties in the developed system were attributed to the larger measurement area, compared to that of the commercial profiler, and the use of nonstandard reference surface for measurement.
This paper describes the design of a novel electrostatically actuated optical attenuator that uses the electrostatic actuation of a cylindrical waveguide. The optical MEMS device consists of an electrostatically actuated waveguide positioned in a V-groove and overhanging at the end to act as a cantilever. The optical fiber waveguide can be sputtered with a thin film of gold that acts as a good electrode. The electrostatic force between the electrodes actuates the input fiber under the application of a voltage and causes misalignment between the input and output fibers and thereby attenuates the amount of light transmitted to the output fiber. Electrostatic modeling of the system presented in this paper is simple and sufficiently accurate. The proposed analytical model takes into consideration the geometry of the cylindrical electrodes. The geometrical relationship of the cantilever beam to the range of the biasing voltage is also discussed. The paper presents the variation of deflection of the waveguide and the variation of power loss with respect to the applied voltages. The obtained results clearly demonstrate the efficient use of the proposed method and modeling approach.
Planar gratings have wide applications and, till date, many methods for the fabrication of gratings have been reported. Ultrashort pulse laser has been used for the machining of gratings primarily due to its ability of direct ablation and its capability to fabricate sub-wavelength structures. In this paper, we present a novel direct ablation technique for the fabrication of planar gratings by interfering ultrashort pulses in a novel optical configuration. This technique not only simplifies the optical setup, but also immunizes the system to extraneous and inherent vibrations, thus enabling planar gratings of good edge acuity. In addition, this technique ensures that gratings are formed only on the focal point. The grating line width can also be adjusted without much change to the optical configuration. With this technique, we have successfully fabricated planar grating of different line-widths on a silicon substrate. Effect of pulse number, and the laser threshold on the grating quality has been qualitatively studied using SEM analysis. This method offers a novel technique for the fabrication of surface relief profile on the metal surface by direct ablation. The optical setup is immune to vibration, at the same time cost effective and fast. Gratings have wide applications and this fabrication technique can be realized commercially.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.