Kin Foong Chan

High-resolution maskless lithography by the integration of micro-optics and point array technique

An innovative High Resolution Maskless Lithography System (Hi-Res MLS) was designed using Texas Instruments’ SVGA DMD, which employs additional micro-optics with a combination of low and high NA projection lens systems. A low power mercury-arc lamp filtered for G-line (λ = 435.8 nm) was used as the light source. Exposure experiments were performed using Ball patented Point Array scrolling or scanning method and proprietary data conversion, extraction and transfer software algorithms. In each scan, the field-width (W) was approximately 8.47 mm with the field-length (longitudinal field) only limited by memory capacity. DMD frame rates of up to 5 kHz (kframe/s) were achievable, which were synchronized to the stage motion. In this experiment, TSMR-8970XB10 photo-resist, diluted to 3.8 cP with PR thinner was employed. The photo-resist was spin-coated on a glass substrate to 1.0-μm thickness with 0.1-μm uniformity. A 0.4-μm step-size was used and 27000 DLP frames were extracted and transferred to the DMD driver. Results indicated consistent 1.8 μm L/S resolved across the entire field-width of 8.47 mm. At certain locales, 1.5-μm L/S was also resolved. The potential of this maskless lithography system is substantial. Even at the current level of performance, the system is sufficient for applications in MEMS, MOEMS, photomasking, high resolution LCD, high density PCB, etc. Higher productivity is predicted by lens system designed for H-line (λ = 405 nm), by using Ball’s violet diode laser systems, and the development of real-time driver.

Design and fabrication of microlens and spatial filter array by self-alignment

For typically small volume production of MEMS, MOEMS, fine feature PCB, high density chip packaging and display panels, especially for lab tests, low cost and the capability to change the original design easily and quickly are very important for customers and researchers. BALL Semiconductor Inc.s Maskless Lithography Systems (MLS) feature the Digital Mirror Device (DMD) as the pattern generator to replace photo-masks. This can remove masks from UV lithography, and dramatically reduce the running cost and save time for lab tests and small volume production. At Ball Semiconductor Inc, 1.5μm line/space, 10μm line/space, and 20μm line/space Maskless Lithography Systems were developed. In our MLS, an 848×600 microlens and spatial filter array (MLSFA) was used to focus the light and to filter the noise. In order to produce smaller line-space than 16μm the MLSFA was used to get smaller UV light pad (compared with the SVGA DMD’s micro-mirror: 17μm×17μm) and to filter the noise produced from the DMD, optical lens system, and micro lens array. This MLSFA is one of the key devices for our Maskless Lithography System, and determines the resolution and quality of maskless lithography. A novel design and fabrication process of a single-package MLSFA for our Maskless Lithography System will be introduced. To avoid problems produced by misalignment between a two-piece spatial filter and microlens array, MEMS processing is used to integrate the microlens array with the spatial filter array. In this paper, the self-alignment method used to fabricate exactly matched MLSFA will be presented.

Effects of endogenous fluorescence from ex vivo human facial skin specimens in the pharmacokinetic study of a topical minocycline gel using two-photon excitation fluorescence (2PEF) and fluorescence lifetime imaging microscopy (FLIM) (Conference Presentation)

The safety and efficacy of an investigational topical minocycline gel (BPX-01) has recently been studied in a Phase 2b trial for the treatment of acne vulgaris. As part of the drug development process, there was a need to determine if minocycline was delivered to the target tissue compartments, including the epidermis, hair follicle, and the sebaceous gland. While it was easier to demonstrate delivery on an ex vivo human skin model with an infinite dose, it was initially challenging to verify low-dose delivery with conventional fluorescence microscopy due to the high autofluorescence inherent to human skin. An integrating sphere screening approach was implemented along with conventional fluorescence microscopy to quantitatively and qualitatively assess endogenous fluorescence concurrently from numerous human facial skin specimens. Donor tissues were cut into 50-µm frozen sections, mounted onto microscope slides, and positioned on an inverted fluorescence microscope, sandwiched between the microscope’s 40x high NA objective lens and an external integrating sphere. The tissue sections were illuminated with UV excitation centered at 386 nm. For the first time, it was found that random samples from >40 human facial skin donors produced at least 5× differential in measurable autofluorescence. This observation has significant implications for the use of 2PEF microscopy and FLIM to visualize/quantify drug distribution; the endogenous autofluorescence may limit the detectability of the minocycline signature. Our studies indicated that a single daily dose of BPX-01 was detected in low autofluorescence skin specimens with FLIM, thus validating a novel imaging modality for future pharmacokinetic studies.

Phasor approach to fluorescence lifetime imaging microscopy for visualization and quantification of drug distribution of a topical minocycline gel in human facial skin (Conference Presentation)

Acne vulgaris is a common chronic skin disease in teenagers and young adults. Minocycline, an antibiotic, has thus far been widely utilized to treat acne, but only via oral administration. Recently, a topical minocycline gel (BPX-01) was developed to directly deliver minocycline to the epidermis and pilosebaceous unit to achieve localized treatment with lower doses of drug. In order to evaluate the effectiveness of topical drug delivery in terms of pharmacokinetics and pharmacodynamics, visualization and quantification of drug within a biological tissue is essential. As minocycline is a known fluorophore, we demonstrate a method for visualization and quantification of minocycline within human skin tissue by utilizing a phasor approach to fluorescence lifetime microscopy (FLIM). In phasor analysis of FLIM, the fluorescence decay trace from each pixel in the FLIM image is plotted as a single point in the phasor plot. Since every fluorophore has a specific decay trace, we can identify a specific molecule by its position in the phasor plot. To demonstrate the feasibility of this visualization and quantification method, the human facial skin samples treated with various concentrations of BPX-01 were investigated using the phasor approach to FLIM. The unique signature of minocycline in FLIM phasor analysis was successfully differentiated from the endogenous fluorescence of human tissue. Furthermore, by sorting the individual pixels of minocycline signature in FLIM image, the distribution of minocycline within human facial skin can be visualized and quantified. Based on these results, we believe that the visualization and quantification method using a phasor approach to FLIM can play an important role in future pharmacokinetics and pharmacodynamics analyses.

Fluorescence lifetime imaging microscopy (FLIM) for visualization of targeted drug delivery and local distribution in skin of a single daily dose of topical minocycline gel: an update on translational research from preclinical to clinical (Conference Presentation)

Oral minocycline has been the standard of care for the treatment of non-nodular moderate to severe inflammatory acne vulgaris due to its inhibitory effects on the acne-causing Propionibacterium acnes bacterium and its anti-inflammatory properties, Despite the availability of an oral dosage form since 1966, a commercial topical minocycline remains elusive because of the challenges in stabilizing the active pharmaceutical ingredient (API) in a liquid/semisolid while ensuring sufficient uptake into targeted lesions. Recently, an investigative topical minocycline gel (BPX-01) has been developed to address the unmet needs for localized and targeted delivery while minimizing the risks of systemic side effects. Earlier preclinical studies pertaining to transepidermal delivery of the API had depended on semi-infinite doses of the 1%, 2% and 4% formulations to elicit enough fluorescence yield. We have subsequently shown evidence of minocycline delivery of 1% and 4% BPX-01 into the pilosebaceous unit of ex vivo human facial skin specimens dosed with about 2.5× daily dose using two-photon excitation fluorescence microscopy. In this study, we demonstrated another novel approach to identifying minocycline fluorescence signature using fluorescence lifetime imaging microscopy (FLIM) with phasor analysis. It was found that for a single daily dose and with FLIM, minocycline was consistently noted in the epidermis and hair follicle, with some incidence in the sebaceous gland for both 1% and 2% BPX-01. These observations corroborated with the recent success of a Phase 2b dose-finding study, with 2% BPX-01 meeting the primary endpoint of lesion reduction at week 12 with statistical significance over the vehicle.

Visualizing and quantifying drug uptake in skin

The study of drug uptake, distribution, and activity within skin is a necessary but problematic requirement in the development and translation of compounds from the bench to the bedside. Drug delivery into the skin is highly complex, due in part to the natural barrier function of the stratum corneum in addition to the many different routes of transdermal entry of drugs. Moreover, skin is not uniform throughout the body or across age groups. For example, epidermal thickness changes 30-fold from the thick skin of the fingertips (485 m) to the thin skin of the face and eyelids (17 m).1 Transdermal delivery can occur over a wide range of timescales (from seconds to hours), and the number of potential cellular targets necessitates quantification on the micrometer scale.2 Optical imaging tools are well-suited to meet these challenges, in particular for the uptake of drugs within the first millimeter of skin. Fluorescence, Raman, and nonlinear optical imaging techniques offer subcellular resolution, rapid real-time 3D image acquisition, and the ability to quantitatively analyze imaging data for both pharmacokinetic and pharmacodynamic information. Optical tools are unique in that they also offer the ability to quantify drugs via phenomena that emerge from their structure, including light absorption, fluorescence, and molecular vibrations. This is particularly useful as most pharmaceuticals are small molecules, where modification to include a reporter can completely change the behavior and thus uptake of the compound. Fluorescence imaging methods can be particularly powerful in measuring the uptake and distribution of drugs. We have been developing a topical acne gel, BPX-01, that is currently in a clinical Phase 2b dose-finding study. BPX-01 is an anhydrous hydrophilic topical gel with solubilized minocycline for enhanced cutaneous delivery and bioavailability to target Figure 1. Conventional fluorescence microscopy images of ex vivo human facial skin specimens. (a) Control, and those treated with (b) 1% BPX-01 (a topical acne gel) and (c) 4% BPX-01 at 24 hours. Minocycline fluorescence is shown in red.

Front Matter: Volume 10046

This PDF file contains the front matter associated with SPIE Proceedings Volume 10046, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Front Matter: Volume 10038

This PDF file contains the front matter associated with SPIE Proceedings Volume 10038, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Temperature monitoring with FBG sensor during diffuser-assisted laser-induced interstitial thermotherapy (Conference Presentation)

Temperature variations are often monitored by using sensors operating at the site of treatment during Laser-induced Interstitial Thermotherapy (LITT). Currently, temperature measurements during LITT have been performed with thermocouples (TCs). However, TCs could directly absorb laser light and lead to self-heating (resulting in an over-estimation). Fiber Bragg grating (FBG) sensors can instead overcome this limitation of the TCs due to its insensitivity to electromagnetic interference. The aim of the current study was to quantitatively evaluate the FBG temperature sensor with a K-type thermocouple to real-time monitor temperature increase in ex vivo tissue during diffuser-assisted LITT. A 4-W 980-nm laser was employed to deliver optical energy in continuous mode through a 600-µm core-diameter diffusing applicator. A goniometric measurement validated the uniform light distribution in polar and longitudinal directions. The FBG sensor showed a linear relationship (R2 = 0.995) between wavelength shift and temperature change in air and tissue along with a sensitivity of ~ 0.0114 nm/˚C. Regardless of sensor type, the measured temperature increased with irradiation time and applied power but decreased with increasing distance from the diffuser surface. The temperature elevation augmented the degree of thermal coagulation in the tissue during LITT (4.0±0.3-mm at 99˚C after 120-s). The temperature elevation augmented the degree of thermal coagulation in the tissue during LITT s irradiation). The FBG-integrated diffuser was able to monitor the interstitial temperature in tubular tissue (porcine urethra) real-time during laser treatment. However, the thermal coagulation thickness of the porcine urethra was measured to be 1.5 mm that was slightly thicker (~20%) than that of the bovine liver after 4-W 980-nm laser for 48 s. The FBG temperature sensor can be a feasible tool to real-time monitor the temporal development of the temperature during the diffuser-assisted LITT to treat urethral disease.

One to one correlation of needle based optical coherence tomography with histopathology: a qualitative and quantitative analysis in 20 prostatectomy specimens (Conference Presentation)

Prostate cancer treatment is shifting from radical to focal therapy. Instant tumor visualization on a microscopic level is crucial for clinical application of focal therapy. Optical coherence tomography (OCT) produces instant tissue visualization on a µm scale and the attenuation of OCT signal as a measure of tissue organization. The objective is to correlate qualitative and quantitative OCT analysis with histopathology. Twenty prostates were analyzed by needle based OCT after radical prostatectomy. For precise correlation, whole mount histology slides were cut through the OCT trajectory. OCT images were classified in eight histological categories. Two reviewers independently performed assessment of the OCT images into these categories. Quantitative attenuation coefficient was used to discriminate stroma and malignant tissue. Sensitivity and specificity for detection of malignancy on OCT was calculated. Visual analyses showed that OCT can reliably differentiate between fat, cystic and regular atrophy and benign glands. Differentiation of benign stroma and inflammation and also malignancy Gleason 3 and 4 is more difficult. Sensitivity and specificity for detection of malignancy on OCT were calculated at 77% and 75%. Quantitative analysis by means of the attenuation coefficient for differentiation between stroma and malignancy showed no significant difference (4.39 mm-1 vs. 5.31 mm-1). Precise correlation of histology and OCT is possible and helps us to understand what we see and measure on OCT. Visual malignancy detection shows reasonable sensitivity and specificity. Our future studies focus on improving discrimination of malignancy with OCT for example by combining an extra imaging modality.