Heidi Ottevaere

Heidi Ottevaere
Vrije Universiteit Brussel | VUB · Applied Physics and Photonics (TONA)

PhD

About

250
Publications
27,284
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
2,364
Citations
Introduction
Skills and Expertise

Publications

Publications (250)
Article
Full-text available
We demonstrate a miniaturized broadband spectrometer employing a reconstruction algorithm for resolution enhancement. We use an opto-digital co-design approach, by firstly designing an optical system with certain residual aberrations and then correcting these aberrations with a digital algorithm. The proposed optical design provides an optical reso...
Article
Full-text available
The pyro-electrohydrodynamic jet (p-jet) printing technology has been used for the fabrication of confined assemblies of gold nanoparticles with a round shape and a diameter ranging between 100 and 200 μm. The surface-enhanced Raman spectroscopy (SERS) performance of the p-jet substrate was evaluated by using Rhodamine 6G (R6G) as a reference. The...
Article
The continuous quest for chromatographic supports offering kinetic performance properties superior to that of the packed bed of spheres has pushed the field to consider alternative formats such as for example monolithic and pillar array columns. This quest seems bound to culminate in the use of 3D printing technology, as this intrinsically offers t...
Article
It is well known how the quantification of tiny amounts of molecular species in biological assays is a crucial issue. We present here a deep investigation on a pyro-electrohydrodynamic jet system at aim to demonstrate its capability to accumulate with high efficiency a large number of tiny aqueous droplets on the surface of a target slide. It makes...
Conference Paper
Flexible and compact beam shaping optical systems are gaining more attention due to their use in a broad range of applications. A monolithic freeform beam shaper for slanted, top-hat illumination is designed and fabricated, demonstrating a super-compact, flexible configuration.
Conference Paper
Freeform optics reveals many benefits for beam-shaping systems. We propose an approach by reproducible ray mapping functions and surface optimizations to significantly reduce the design complexity of freeform beam shaping optics.
Conference Paper
Materials play a key role in tissue engineering for the construction of 3-dimensional scaffolds that support the formation of a new extracellular matrix. They should be biocompatible, and for the fabrication of functional scaffolds, they should be mechanically robust, provide high resolution and printability factors to use in one-photon polymerizat...
Article
Full-text available
Recently, freeform optics has been widely used due to its unprecedented compactness and high performance, especially in the reflective designs for broad-wavelength imaging applications. Here, we present a generalized differentiable ray tracing approach suitable for most optical surfaces. The established automated freeform design framework simultane...
Article
Full-text available
(Attention for corrosion science, the abstract must not exceed more than 100 words) In this research, first a multi-analytical approach was carried out to propose a mechanistic model for the formation of the thermal oxide film on low Cr stainless steel. It describes the effects of kinetically and thermodynamically driven phenomena on the growth of...
Preprint
Reflective imaging systems form an important part of photonic devices such as spectrometers, telescopes, augmented and virtual reality headsets or lithography platforms. Reflective optics provide unparalleled spectral performance and can be used to reduce overall volume and weight. So far, most reflective designs have focused on two or three reflec...
Article
Compact and broadband spectrometers are very useful in various application domains such as agriculture, food, health and security. In minimally-invasive image-guided procedures spectral tissue sensing helps for screening and diagnostic purposes aiming at discriminating between healthy and tumorous tissue at point-of-care locations and outpatient ce...
Article
Full-text available
Various biopolymers including gelatin, have already been applied to serve a plethora of tissue engineering purposes. However, substantial concerns have arisen related to the safety and the reproducibility of these materials due to their animal origin and the risk associated with pathogen transmission as well as batch-to-batch variations. Therefore,...
Article
DOI: 10.1002/elps.202000001 The cover picture shows a radially elongated pillar array column fabricated in a glass substrate wherein capillary electrochromatography has been performed to separate small molecules (coumarins). By increasing the aspect ratio from 1 (cylinders) to 4 (rectangles), it could be demonstrated that the attainable performance...
Article
We present a Raman spectroscopy setup containing a conical beam shaper in combination with a freeform segmented reflector for surface enhanced Raman scattering (SERS) analysis. The freeform segmented reflector and the conical beam shaper are designed by numerical approaches and fabricated by means of ultra-precision diamond tooling. The segmented r...
Article
In the present study, cylindrical and laterally elongated pillar array columns were investigated for use in capillary electrochromatography. Minimal theoretical plate heights of H = 1.90 μm and H = 1.46 μm (in absence of sidewall effect) were obtained for coumarin C440 under unretained conditions for cylindrical and rectangular (laterally elongated...
Article
Full-text available
Improved chemical- and bio-sensing with Surface Enhanced Raman Spectroscopy (SERS) requires nanostuctures that can be flexibly designed and fabricated with different physical and optical properties. Here, we present nano-pillar arrays ranging from 200 nm to 600 nm as SERS substrates for mycotoxin detection that are fabricated by means of two-photon...
Article
Full-text available
We present a freeform-segmented reflector-based microfluidic system for conventional Raman and Surface-Enhanced Raman Scattering (SERS) analysis. The segmented reflector is directly designed by a numerical approach. The polymer-based Raman system strongly suppresses the undesirable background because it enables confocal detection of Raman scatterin...
Article
Full-text available
Adipose tissue engineering aims to provide solutions to patients who require tissue reconstruction following mastectomies or other soft tissue trauma. Mesenchymal stromal cells (MSCs) robustly differentiate into the adipogenic lineage and are attractive candidates for adipose tissue engineering. This work investigates whether pore size modulates ad...
Article
We present an optical signal coupling scheme for slab waveguide surface grating coupler sensors. The proposed solution is based on the use of polymer microlenses. In this work we analyze two types of compact polymer lenses: the aspheric plano-convex lenses and Fresnel lenses. The feasibility of the proposed scheme is demonstrated by the experimenta...
Article
In the present study, the peak capacity potential of ultra-long porous cylindrical pillar array columns is investigated. Coupling 4 columns of 2 m long allows to work near the minimal separation impedance of small molecules under retained conditions at a maximal pressure load of 250 bar. Minimal plate heights of H=5.0 µm, H=6.3 µm and H=7.7 µm were...
Article
Over the recent decades gelatin has proven to be very suitable as an extracellular matrix mimic for biofabrication and tissue engineering applications. However, gelatin is prone to dissolution at typical cell culture conditions and is therefore often chemically modified to introduce (photo-)crosslinkable functionalities. These modifications allow t...
Article
Gelatin is frequently used in various biomedical applications. However, gelatin is generally extracted from an animal source, which can result in issues with reproducibility as well as pathogen transmittance. Therefore, we have investigated the potential of a recombinant peptide based on collagen I (RCPhC1) for tissue engineering applications and m...
Article
Nanopatterned hyperbolic metamaterials (NPHMs) have proven to be efficient structures for enhancing the spontaneous emission rate (Γ) and quantum efficiency (η) of quantum emitters (QEs). However, many of the NPHM designs still rely on computationally costly 3D numerical simulations. In this context, we propose a fast, semianalytical method capable...
Article
There exists a clear clinical need for adipose tissue reconstruction strategies to repair soft tissue defects which outperform the currently available approaches. In this respect, additive manufacturing has shown to be a promising alternative for the development of larger constructs able to support adipose tissue engineering. In the present work, a...
Article
Full-text available
We report on the ability to change the layer properties of porous layered radially elongated pillar (PLREP) array columns and its relevance to the separation efficiency. The adjustment of the preparation condition resulted in the formation of a 1.2-fold thicker layer than the layer produced in the preceding study. The mesoporosity of the layer was...
Article
Full-text available
The performance of a porous-layered radially elongated pillar (PLREP) array column in a commercial nano-LC system was examined by performing separations of alkylphenones and peptides. The mesoporous silica layer was prepared by sol-gel processing of a mixture of tetramethoxysilane and metyltrimethoxysilane on REPs filling 16.5 cm long, 1 mm wide ch...
Conference Paper
We present the design and fabrication of a segmented freeform reflector for confocal Raman and SERS spectroscopic analysis in a microfluidic-based system. Further, we simulate the confocal performance and assess the results by experiments.
Conference Paper
Surface Plasmon Resonance devices have the promise to become the prevailing device technology for miniaturized point-of-care diagnosis. We have designed, fabricated and tested a disposable freeform SPR device outperforming traditional prism devices.
Article
Over the recent decades gelatin has proven to be very suitable as an extracellular matrix mimic for bio-fabrication and tissue engineering applications. However, gelatin is prone to dissolution at typical cell culture conditions and is therefore often chemically modified to introduce (photo-)crosslinkable functionalities. These modifications allow...
Article
Full-text available
In vascular tissue engineering, great attention is paid to the immobilization of biomolecules onto synthetic grafts to increase bio‐ and hemocompatibility—two critical milestones in the field. The surface modification field of poly(ethylene terephthalate) (PET), a well‐known vascular‐graft material, is matured and oversaturated. Nevertheless, most...
Article
We propose a semi-analytical method to model, both in two- and three-dimensions (2D and 3D, respectively), the radiation emission of quantum emitters (QEs) interacting with nano-patterned structures. We then investigate the emission from QEs near a hyperbolic metamaterial (HMM) with a metallic cylindrical grating on its top and a polymethylmethacry...
Article
Environmentally degradable polyesters offer an interesting perspective for a vast number of applications. However, current front-runners like poly(lactide), poly(glycolide) and poly(ε-caprolactone) are either semi-crystalline excluding applications for which optical transparency is desired, or exhibit low glass transition temperatures (Tg) resultin...
Book
This book offers a complete overview of photonic-enhanced materials from material development to a final photonic biomedical application. It includes fundamental, applied, and industrial photonics. The authors cover synthesis, the modification and the processing of a variety of (bio)polymers including thermoplasts (e.g. polyesters) and hydrogels (e...
Article
The joining of materials is essential to many industrial applications used today. However, it still lacks a reliable and true single step method to join different types of materials including polymers. Laser welding was primarily employed for metals until some decades ago, but with the rise of high power solid state lasers, applications have emerge...
Article
There is a clear and urgent clinical need to develop soft tissue fillers that outperform the materials currently used for adipose tissue reconstruction. Recently, extensive research has been performed within this field of adipose tissue engineering as the commercially available products and the currently existing techniques are concomitant with sev...
Article
Full-text available
The present paper describes the application of a sol-gel procedure on radially elongated pillars (REPs) using tetramethoxysilane and methyltrimethoxysilane. After octadecylsilylation, the quality of the porous layered REP (PLREP) columns was evaluated by in-situ determination of migration velocities and band broadening of coumarin dyes with fluores...
Article
Food quality and food safety are gaining more and more importance in recent decades. In particular, applications have included domains such as the identification of foreign bodies in solid food streams, the quality screening of vegetables and fruits, the recognition of food products inducing a health risk and the monitoring of the quality and authe...
Chapter
Photopolymerization of hydrogels in the presence of cells is a frequently applied technique to realize tissue engineering and regeneration due to the fact that the reaction can take place under cell-friendly physiological conditions. Photopolymerization can be subdivided into three modes, including radical, cationic, and anionic photopolymerization...
Conference Paper
Food quality and food safety are gaining the past decades more and more importance. In particular application domains such as the identification of foreign bodies in solid food streams, the quality screening of vegetables and fruits, the recognition of food products inducing a health risk and the monitoring of the quality and authentication of liqu...
Conference Paper
Raman spectroscopy is a powerful optical and non-destructive technique and a well-known method for analysis purposes, especially to determine the molecular fingerprint of substances. Traditionally, such analyses are done in a specialized lab, with considerable requirements in terms of equipment, time and manual sampling of substances of interest. I...
Conference Paper
We compare two algorithms to determine the radial profile of the photoelastic coefficient C in glass optical fibers. We first measure the retardance profile of a transversally illuminated fiber as a function of tensile load. The radial profile C(r) is obtained from the inverse Abel transform of this retardance profile. Our first algorithm expands t...
Conference Paper
Minimally-invasive image-guided procedures become increasingly used by physicians to obtain real-time characterization feedback from the tissue at the tip of their interventional device (needle, catheter, endoscopic or laparoscopic probes, etc…) which can significantly improve the outcome of diagnosis and treatment, and ultimately reduce cost of th...
Conference Paper
We present a microfluidic chip in Polymethyl methacrylate (PMMA) for optical trapping of particles in an 80μm wide microchannel using two counterpropagating single-mode beams. The trapping fibers are separated from the sample fluid by 70μm thick polymer walls. We calculate the optical forces that act on particles flowing in the microchannel using w...
Conference Paper
We determine the radial profile of the photoelastic constant C(r) in two single mode and one multimode polymer optical fibers (POFs), all fabricated from polymethylmethacrylate (PMMA). To determine C(r) we first determine the retardance of the laterally illuminated fiber submitted to a known tensile stress uniformly distributed over the fiber cross...
Article
Full-text available
In this work, the impact of the spacer features (interpillar distance and shape) on the membrane deflection, pressure difference across the membrane, and mass transfer was studied for a flat membrane microcontactor. It was demonstrated that decreasing the interpillar distance between the circular pillars reduced membrane deflection considerably. As...
Article
We show a detection system that simultaneously allows absorbance (ABS), laser-induced fluorescence (LIF) and scattering detection excited by two different laser sources at 405 nm and 450 nm. The heart of the system consists of a mass manufacturable polymer optofluidic chip. The chip is mounted in an optical detection assembly that aligns the chip t...
Article
We present an optofluidic chip in polymethyl methacrylate (PMMA) that combines optical trapping of single particles with confocal Raman spectroscopy. We introduce the design of the optofluidic chip and the ray-tracing simulations combined with mathematical calculations used to determine the optical forces exerted on the particles and to model the e...
Chapter
A selection of fourteen common and commercially available table-top artificial sweeteners was considered. The samples contained aspartame and saccharin as high-intensity sweeteners and dextrose, sorbitol, sucrose, and maltodextrin as low-intensity sweeteners. These were all examined both in powder form and as aqueous solutions. Raman spectra, excit...
Article
Full-text available
We present a microfluidic chip in Polymethyl methacrylate (PMMA) for optical trapping of particles in an 80μm wide microchannel using two counterpropagating single-mode beams. The trapping fibers are separated from the sample fluid by 70μm thick polymer walls. We calculate the optical forces that act on particles flowing in the microchannel using w...
Article
Despite its widespread application in the fields of ophthalmology, orthopedics and dentistry and the stringent need for polymer packagings that induce in vivo tissue integration, the full potential of poly(methyl methacrylate) (PMMA) and its derivatives as medical device packaging material has not been explored yet. We therefore elaborated on the d...
Article
In this paper we discuss the fabrication of lenses made out of multi-component oxide glasses by using double-sided hot embossing to allow low-cost, low-volume replication of these lenses. We focus on the choice of the glass for both the stamps as well as for the molded component and we discuss the various process parameters of the hot embossing pro...
Conference Paper
We show a proof-of-concept demonstration of a multi-parameter analysis low-cost optical detection system for the flowcytometric identification of vinegars. This multi-parameter analysis system can simultaneously measure laser induced fluorescence, absorption and scattering excited by two time-multiplexed lasers of different wavelengths. To our know...
Chapter
The 21st century offers vast challenges for researchers all around the globe, especially regarding the effective use of eco-friendly sustainable polymers and their materials for different applications. With this focus, sustainable polymers are now rising as one of the most feasible alternatives to traditional synthetic polymers/materials for a vari...
Conference Paper
Conventional multichannel imaging systems comprise of many optical channels having similar imaging properties, namely field-of-view (FOV) and angular resolution/magnification. We demonstrated that the different optical channels can be designed such that each optical channel captures a different FOV and angular resolution compared to its neighboring...
Article
e discuss two algorithms to determine the value and the radial profile of the photoelastic coefficient C in glass and polymer optical fibers. We conclude that C is constant over the fiber cross-sections, with exception of silica glass fibers containing a fluorine-doped depressed cladding. In the undoped and Ge-doped parts of these silica glass...
Article
We present an optofluidic lab-on-chip for confocal Raman spectroscopy, which can be used for the analysis of substances. The device strongly suppresses unwanted background signals because it enables confocal detection of Raman scattering thanks to a free-form reflector embedded in the optofluidic chip. We design the system using non-sequential ray-...
Article
Experimental and theoretical proof is provided for the fact that a microfabricated packed bed column which is uniformly filled with radially elongated pillars (REPs) can produce the same separation performance as non-packed, open-tubular columns. These are generally recognized as the best possible chromatographic column format, offering the highest...
Article
Full-text available
Raman spectroscopy excited at 1064 nm was used to measure a selection of artificial sweeteners that are commonly used in low-calorie diets. Aqueous solutions with different sweetener concentrations in the 5%-30% w/w range were analyzed, and a multivariate data processing of spectroscopic data was used to building a classification map. This map show...
Article
A mathematical procedure using the Matlab (R) PDE toolbox to calculate the numerical constant appearing in the general Taylor-Aris expression for the dispersion in a laminar flow through open-tubular conduits with a variety of quasi-rectangular cross-sectional shapes is described. The procedure has been applied to assess the effect of some of the m...
Article
An important bottleneck of pillar array columns designed for liquid chromatography is that small deviations of the target 'magical distance' at the sidewall region leads to detrimental sidewall effects, due to local differences of linear velocities at the sidewall region versus other locations in the pillar bed. In the present study, we demonstrate...