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Thiol-ene and Thiol-ene-epoxy Based Polymers for Biomedical Microdevices
KTH, School of Electrical Engineering (EES), Micro and Nanosystems.ORCID iD: 0000-0001-9651-4900
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Within healthcare there is a market pull for biomedical devices that can rapidly perform laboratory processes, such as diagnostic testing, in a hand-held format. For this reason, biomedical devices must become smaller, more sophisticated, and easier to use for a reasonable cost. However, despite the accelerating academic research on biomedical microdevices, and especially plastic-based microfluidic chips, there is still a gap between the inventions in academia and their benefit to society. To bridge this gap there is a need for new materials which both exhibit similar properties as industrial thermoplastics, and that enable rapid prototyping in academia.

In this thesis, thiol-ene and thiol-ene-epoxy thermosets are evaluated both in terms of their suitability for rapid prototyping of biomedical microdevices and their potential for industrial manufacturing of “lab-on-chips”.

The first part of the thesis focuses on material development of thiol-ene and thiol-ene-epoxy thermosets. Chemical and mechanical properties are studied, as well as in vitro biocompatibility with cells.

The second part of the thesis focuses on microfabrication methods for both thermosets. This includes reaction injection molding, photostructuring, and surface modification. It is demonstrated how thiol-ene and thiol-ene-epoxy both provide advantageous thermo-mechanical properties and versatile surface modifications via “thiol-click chemistry”.

In the end of the thesis, two applications for both polymer platforms are demonstrated. Firstly, thiol-ene is used for constructing nanoliter well arrays for liquid storage and on-demand electrochemical release. Secondly, thiol-ene-epoxy is used to enhance the biocompatibility of neural probes by tuning their flexibility.

It is concluded that both thiol-ene and thiol-ene-epoxy thermosets exhibit several properties that are highly suitable for rapid prototyping as well as for scalable manufacturing of biomedical microdevices.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. , p. 93
Series
TRITA-EE, ISSN 1653-5146 ; 2017:129
Keyword [en]
biomedical microdevices, lab-on-a-chip, off-stoichiometry thiol-ene, OSTE, thiol-ene-epoxy, hybrid polymer networks, reaction injection molding, photostructuring, surface modification, bonding, liquid encapsulation, biocompatibility
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Medical Engineering Medical Biotechnology Materials Engineering
Research subject
Electrical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-215110ISBN: 978-91-7729-530-3 (print)OAI: oai:DiVA.org:kth-215110DiVA, id: diva2:1146328
Public defence
2017-11-13, F3, Lindstedtsvägen 26, Stockholm, 10:15 (English)
Opponent
Supervisors
Funder
EU, European Research CouncilEU, FP7, Seventh Framework Programme
Note

QC 20171003

Available from: 2017-10-03 Created: 2017-10-02 Last updated: 2017-10-03Bibliographically approved
List of papers
1. Functional Off-Stoichiometry Thiol-ene-epoxy Thermosets Featuring Temporally Controlled Curing Stages via an UV/UV Dual Cure Process
Open this publication in new window or tab >>Functional Off-Stoichiometry Thiol-ene-epoxy Thermosets Featuring Temporally Controlled Curing Stages via an UV/UV Dual Cure Process
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2014 (English)In: Journal of Polymer Science Part A: Polymer Chemistry, ISSN 0887-624X, E-ISSN 1099-0518, Vol. 52, no 18, p. 2604-2615Article in journal (Refereed) Published
Abstract [en]

We present a facile two-stage UV/UV activation method for the polymerization of off-stoichiometry thiol-ene-epoxy, OSTE+, networks. We show that the handling and processing of these epoxy-based resins is made easier by introducing a material with a controlled curing technique based on two steps, where the first step offers excellent processing capabilities, and the second step yields a polymer with suitable end-properties. We investigate the sequential thiol-ene and thiol-epoxy reactions during these steps by studying the mechanical properties, functional group conversion, water absorption, hydrolytic stability, and thermal stability in several different thiol-ene-epoxy formulations. Finally, we conclude that the curing stages can be separated for up to 24 h, which is promising for the usefulness of this technique in industrial applications.

Place, publisher, year, edition, pages
John Wiley & Sons, 2014
Keyword
coatings, curing of polymers, initiators, mechanical properties, thermosets, thiol-ene-epoxy photopolymerization
National Category
Polymer Technologies
Research subject
Fibre and Polymer Science
Identifiers
urn:nbn:se:kth:diva-145658 (URN)10.1002/pola.27276 (DOI)000341189900006 ()2-s2.0-84905741353 (Scopus ID)
Projects
ROUTINEXMEMS
Funder
EU, FP7, Seventh Framework Programme, 304941EU, European Research Council, 267528
Note

Qc 20140911

Available from: 2014-05-26 Created: 2014-05-26 Last updated: 2017-12-05Bibliographically approved
2. Reaction injection molding and direct covalent bonding of OSTE+ polymer microfluidic devices
Open this publication in new window or tab >>Reaction injection molding and direct covalent bonding of OSTE+ polymer microfluidic devices
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2015 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 25, no 7Article in journal (Refereed) Published
Abstract [en]

In this article, we present OSTE+RIM, a novel reaction injection molding (RIM) process that combines the merits of off-stoichiometric thiol–ene epoxy (OSTE+) thermosetting polymers with the fabrication of high quality microstructured parts. The process relies on the dual polymerization reactions of OSTE+ polymers, where the first curing step is used in OSTE+RIM for molding intermediately polymerized parts with well-defined shapes and reactive surface chemistries. In the facile back-end processing, the replicated parts are directly and covalently bonded and become fully polymerized using the second curing step, generating complete microfluidic devices. To achieve unprecedented rapid processing, high replication fidelity and low residual stress, OSTE+RIM uniquely incorporates temperature stabilization and shrinkage compensation of the OSTE+ polymerization during molding. Two different OSTE+ formulations were characterized and used for the OSTE+RIM fabrication of optically transparent, warp-free and natively hydrophilic microscopy glass slide format microfluidic demonstrator devices, featuring a storage modulus of 2.3 GPa and tolerating pressures of at least 4 bars. 

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2015
Keyword
off-stoichiometric thiol–ene, epoxy, OSTE+, reaction injection molding, device fabrication, polymers, microfluidics
National Category
Nano Technology
Identifiers
urn:nbn:se:kth:diva-165616 (URN)10.1088/0960-1317/25/7/075002 (DOI)
Note

QC 201500618

Available from: 2015-04-29 Created: 2015-04-29 Last updated: 2017-12-04Bibliographically approved
3. Off-Stoichiometry Improves Photostructuring of Thiol-Enes Through Diffusion-Induced Monomer Depletion
Open this publication in new window or tab >>Off-Stoichiometry Improves Photostructuring of Thiol-Enes Through Diffusion-Induced Monomer Depletion
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2016 (English)In: Microsystems and Nanoengineering, ISSN 2055-7434, Vol. 2, article id 15043Article in journal (Refereed) Published
Abstract [en]

Thiol-enes are a group of alternating copolymers with highly ordered networks used in a wide range of applications. Here, “click” chemistry photostructuring in off-stoichiometric thiol-enes is shown to induce microscale polymeric compositional gradients due to species diffusion between non-illuminated and illuminated regions, creating two narrow zones with distinct composition on either side of the photomask feature boundary: a densely cross-linked zone in the illuminated region and a zone with an unpolymerized highly off-stoichiometric monomer composition in the non-illuminated region. By the use of confocal Raman microscopy, it is here explained how species diffusion causes such intricate compositional gradients in the polymer, and how off-stoichiometry results in improved image transfer accuracy in thiol-ene photostructuring. Furthermore, increasing the functional group off-stoichiometry and decreasing photomask feature size is shown to amplify the induced gradients, which potentially leads to a new methodology for microstructuring.

Place, publisher, year, edition, pages
Nature Publishing Group, 2016
Keyword
thiol-ene, oste, OSTEmer, polymer, photopatterning, photolithography, monomer diffusion, click chemistry, Raman confocal microscopy, microfluidics
National Category
Nano Technology Textile, Rubber and Polymeric Materials
Research subject
Electrical Engineering; Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-144992 (URN)10.1038/micronano.2015.43 (DOI)
Note

Updated from accepted to published.

QC 20160216

Available from: 2014-05-05 Created: 2014-05-05 Last updated: 2017-10-02
4. Polymer Nanoliter Well Arrays for Liquid Storage and Rapid On-demand Electrochemical Release
Open this publication in new window or tab >>Polymer Nanoliter Well Arrays for Liquid Storage and Rapid On-demand Electrochemical Release
2018 (English)In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 267, p. 111-118Article in journal (Refereed) Published
Abstract [en]

Polymer microfluidic systems are of increasing importance in several applications in biomedicine and biosensing. The integrated encapsulation, storage, and controlled release of small amounts of liquid in such systems remains an unresolved technical challenge. Here, we report two methods for the room-temperature and adhesive-free sealing of 1–330 nanoliter volumes of liquid in off-stoichiometry thiol-ene polymer well arrays by spontaneous bonding to 200 nm thin gold films. Sealed well arrays were stored for more than one month in a liquid environment with <10% liquid loss, and for more than one week in air with minimal loss. We demonstrated that controlling the electrical potential and polarity over encapsulated wells allowed for selecting one of two well opening mechanisms: slow anodic electrochemical etching, or rapid electrolytic gas pressure-induced bursting of the gold film. The results may find potential applications in diagnostic testing, in vivo drug delivery, or in spatio-temporal release of chemical compounds in biological assays.

Place, publisher, year, edition, pages
Elsevier, 2018
Keyword
nanoliter liquid encapsulation, nanoliter liquid storage, electrochemical liquid release, off-stoichiometry thiol-ene (OSTE) polymer, nanoliter well arrays
National Category
Polymer Technologies Medical Biotechnology Biomedical Laboratory Science/Technology Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-215017 (URN)10.1016/j.snb.2018.04.013 (DOI)2-s2.0-85045401734 (Scopus ID)
Note

QC 20180515

Available from: 2017-09-29 Created: 2017-09-29 Last updated: 2018-05-23Bibliographically approved
5. ROBUST MICRODEVICE MANUFACTURING BY DIRECT LITHOGRAPHY AND ADHESIVE-FREE BONDING OF OFF-STOICHIOMETRY THIOL-ENE-EPOXY (OSTE+) POLYMER
Open this publication in new window or tab >>ROBUST MICRODEVICE MANUFACTURING BY DIRECT LITHOGRAPHY AND ADHESIVE-FREE BONDING OF OFF-STOICHIOMETRY THIOL-ENE-EPOXY (OSTE+) POLYMER
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2013 (English)In: 17th IEEE International Conference on Solid-State Sensors, Actuators and Microsystems & EUROSENSORS XXVII (IEEE TRANSDUCERS 2013), IEEE conference proceedings, 2013, p. 408-411Conference paper, Published paper (Refereed)
Abstract [en]

We here demonstrate, for the first time, the use of direct lithography in off-stoichiometry thiol-ene-epoxy (OSTE+) to fabricate a microdevice. First, the photolithographic property of OSTE+ is shown by using a photomask to create micropillars with an aspect-ratio of 1:10 in a 2 mm thick layer. Secondly, a three-layer OSTE+ microdevice containing in-/outlet holes, channels, and pillars is fabricated by using a combination of direct lithography and adhesive-free dry bonding. The resulting microdevice shows desirable properties, such as leak-free filling and hydrophilic surfaces. This fabrication method enhances the microstructurability of OSTE+ beyond that of conventional soft lithography replica molding of other polymers, such as PDMS.

Place, publisher, year, edition, pages
IEEE conference proceedings, 2013
Keyword
Bonding, epoxy, microdevice fabrication, Microfluidics, OSTE+, photolithography, soft lithography, thiol, thiol-ene
National Category
Polymer Technologies Nano Technology
Identifiers
urn:nbn:se:kth:diva-124782 (URN)10.1109/Transducers.2013.6626789 (DOI)2-s2.0-84891691276 (Scopus ID)978-146735981-8 (ISBN)
Conference
17th IEEE International Conference on Solid-State Sensors, Actuators and Microsystems & EUROSENSORS XXVII (IEEE TRANSDUCERS 2013), Barcelona, Spain, 16-20 Jun, 2013
Projects
RoutineRappidXMEMS
Note

QC 20140212

Available from: 2013-07-31 Created: 2013-07-31 Last updated: 2017-11-22Bibliographically approved
6. Biocompatibility of OSTE polymers studied by cell growth experiments
Open this publication in new window or tab >>Biocompatibility of OSTE polymers studied by cell growth experiments
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2013 (English)In: Proceedings of the 17th Int. Conf. on Miniaturized Systems for Chemistry  and Life Sciences (microTAS), Freiburg, Germany, 2013Conference paper, Published paper (Refereed)
Abstract [en]

The recently introduced OSTE polymer technology has shown very useful features for microfluidics for lab-on-a-chip applications. However, no data has yet been published on cell viability on OSTE. In this work, we study the biocompatibility of three OSTE formulations by cell growth experiments. Moreover, we investigate the effect of varying thiol excess on cell viability on OSTE surfaces. The results show poor cell viability on one OSTE formulation, and viability comparable with polystyrene on a second formulation with thiol excess below 60%. In the third formulation, we observe cell proliferation. These results are promising for cell-based assays in OSTE microfluidic devices.

Place, publisher, year, edition, pages
Freiburg, Germany: , 2013
Keyword
loc OSTE lab-on-chip biocompatibility
National Category
Medical Materials
Identifiers
urn:nbn:se:kth:diva-129546 (URN)2-s2.0-84907370206 (Scopus ID)
Conference
The 17th International Conference on Miniaturized Systems for Chemistry and Life Sciences (MicroTAS 2013), Freiburg, 27-31 October 2013
Projects
CellRing
Funder
Swedish Research Council, B0460801EU, European Research Council, 267528
Note

QC 20131122

Available from: 2013-10-02 Created: 2013-10-02 Last updated: 2017-10-02Bibliographically approved
7. Rapid Fabrication Of OSTE+ Microfluidic Devices With Lithographically Defined Hydrophobic/ Hydrophilic Patterns And Biocompatible Chip Sealing
Open this publication in new window or tab >>Rapid Fabrication Of OSTE+ Microfluidic Devices With Lithographically Defined Hydrophobic/ Hydrophilic Patterns And Biocompatible Chip Sealing
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2013 (English)In: 17th International Conference on Miniaturized Systems for Chemistry and Life Sciences, MicroTAS 2013, Freiburg, Germany: NO , 2013, p. 134-136Conference paper, Published paper (Refereed)
Abstract [en]

Here we present an uncomplicated and robust method for rapid prototyping of microfluidic devices featuring: 1) lithographically defined, permanently surface modified hydrophilic and hydrophobic regions with contact angles varying from 18o to 118o, in which all four channel walls are surface modified in a single step using polymer chain grafting; 2) polymer chains grafted from open surfaces before bonding, making this method suitable for batch fabrication; 3) biomolecule-compatible, room temperature, dry, homogeneous chip-sealing, in which native as well as hydrophobic/hydrophilic modified OSTE+ surfaces allow for epoxy-epoxy and thiol-epoxy covalent bonding, hence greatly simplifying alignment and dramatically increasing device yields. We demonstrate the method with a functional microfluidic device. This represents a complete, simplified and robust method for batch-manufacturing compatible prototyping of microfluidic devices with tunable mechanical and surface properties. 

Place, publisher, year, edition, pages
Freiburg, Germany: NO, 2013
Keyword
Theracage, OSTE+, surface modification, lithography
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-124640 (URN)2-s2.0-84905743758 (Scopus ID)978-0-9798064-6-9 (ISBN)
Conference
The 17th International Conference on Miniaturized Systems for Chemistry and Life Sciences (MicroTAS), 27-31 October 2013, Freiburg, Germany
Projects
Theracage
Note

QC 20171122

Available from: 2013-07-23 Created: 2013-07-23 Last updated: 2017-11-22Bibliographically approved
8. A polymer neural probe with tunable flexibility
Open this publication in new window or tab >>A polymer neural probe with tunable flexibility
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2013 (English)In: 2013 6th International IEEE/EMBS Conference on Neural Engineering (NER), 2013, p. 691-694Conference paper, Published paper (Refereed)
Abstract [en]

A novel polymeric material, off stoichiometry thiol-ene-epoxy (OSTE+), has been evaluated for the fabrication of neural implants. OSTE+ is easily photo-structurable and exhibits mechanical properties suitable for stable implantation of the probe into brain tissue, while being sufficiently soft at physiological temperatures to reduce living tissue damage. The facile processing of OSTE+ allows use in applications where SU-8 or polyimide currently are the materials of choice. Uniquely, OSTE+ has a Young’s modulus of 1.9 GPa at 10 °C decreasing almost two orders of magnitude to 30 MPa at 40 °C, which can be compared to the Young’s modulus of 2.1 GPa for SU-8. We show a probe, with nine gold electrode sites, implanted into 0.5% agar at 40 °C using active cooling during the implantation.

Series
International IEEE/EMBS Conference on Neural Engineering, ISSN 1948-3546
Keyword
Implantable neural probes, Biocompatibility, Thiol-ene-epoxy, OSTE+
National Category
Medical Engineering Materials Engineering Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-125010 (URN)10.1109/NER.2013.6696028 (DOI)2-s2.0-84897675358 (Scopus ID)978-1-4673-1969-0 (ISBN)
Conference
2013 6th International IEEE/EMBS Conference on Neural Engineering (NER); San Diego, CA, USA, 6-8 November 2013
Note

QC 20140214

Available from: 2013-08-02 Created: 2013-08-02 Last updated: 2017-10-02Bibliographically approved

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