Search

Hot embossing with and without ultrasound are compared in this paper with respect to several properties of the fabricated samples. The same mold was employed for both processes and process parameters have been chosen adapted to each process such that to the best knowledge of the authors good moldings were achieved. Shrinkage is similar for both processes. Better mold filling is achieved without ultrasound and the polymer structures correspond better to the mold after demolding. Undesired sample curvature is also much less. With ultrasound required investment costs and energy consumption are significantly less, and the cycle time is reduced to seconds.

Strain : the journal of the British Society for Strain Measurement 12387 (2021). doi:10.1111/str.12387, Published by Wiley- Blackwell, Oxford [u.a.]

Ultrasonic welding of polymer micro structures is an economic and fast joining process but is also limited by the high need for geometrical accuracy required for tight and well-aligned joints. Melting of energy directors by ultrasound is nonhomogeneous especially when large parts are to be welded because the vibration amplitude is not the same everywhere under the sonotrode. This paper shows that the homogeneity of welding is improved by inserting metal parts between the joining partners.

Micro and nano structures and systems are generated in polymer surfaces with cycle times of a few seconds by ultrasonic processes such as ultrasonic hot embossing, welding and thermoforming paving the way for a variety of new products. However, measuring temperature and pressure during these processes is very difficult because the polymer is enclosed between an anvil and a sonotrode. Temperature and pressure distribution during ultrasonic processing now have been measured inside of a stack of thermoplastic polymer layers by sensor foils from polyvinylidene fluoride, 55 µm in thickness. The measurements are based on the piezoelectric and pyroelectric effect of polyvinylidene fluoride allowing to achieve resolutions in temperature and pressure of up to ± 1 °C and ± 0.5 kPa, respectively. The achieved resolutions in time and in normal and lateral direction are approximately 1 µs, 60 µm and 1 cm, respectively. The maximum temperature inside a foils stack that could be measured was 73 °C because the sensor foils lost sensitivity when heated up more. Every single oscillation of the polymer was measured as a pressure change. The difference in temperature change and ultrasonic pressure amplitude measured in lateral direction below a sonotrode with outer dimensions of 8 × 12 cm are approximately 12 °C and 4 kPa, 25 and 60%, respectively, indicating the width required for process windows of ultrasonic processing. Moreover, phase shifts are measurable and thus analysis of oscillation characteristics of sonotrodes were investigated.

Energy Harvesting and Systems 4(3), 137-141 (2017). doi:10.1515/ehs-2017-0004, Published by De Gruyter, Berlin ; Boston, Mass.

Microsystem technologies (2020). doi:10.1007/s00542-020-04818-5, Published by Springer, Berlin

Journal of magnetism and magnetic materials : MMM 506, 166694 (2020). doi:10.1016/j.jmmm.2020.166694, Published by North-Holland Publ. Co., Amsterdam

Microsystem technologies (2020). doi:10.1007/s00542-020-04834-5, Published by Springer, Berlin

Micro channels from polyether ether ketone (PEEK), 1 mm in width and depth and 1.6 cm in length, have been fabricated by ultrasonic hot embossing and ultrasonic welding. Micro channels from PEEK enable constructing chemically inert microfluidic systems suitable for applications at temperatures of more than 200 °C. Besides this, a new design can be realized within one working day, investment costs are only a few 10,000 €, and the cycle time of fabricating a microfluidic system is a few seconds. Maximum temperature and pressure difference over a micro channel are not limited by the material properties of semicrystalline PEEK but by difficulties in producing them and by their change of morphology during manufacturing. To ultrasonically fabricate a microchannel two ultrasonic processes need to be combined. The channel itself is fabricated in a first ultrasonic hot embossing process and then sealed with a lid foil in a second ultrasonic welding step. This paper shows that, PEEK changes its morphology when it is ultrasonically hot embossed to produce a microfluidic channel. Moreover the degree of crystallinity varies according to the local position in the micro channel. It turned out that successful sealing of a micro channel by ultrasonic welding is facilitated by energy directors from semicrystalline PEEK. Therefore, semi-finished PEEK channels need being exposed to a temperature of at least 170 °C for 30 min before ultrasonic welding. This way, the amorphous PEEK is recrystallized resulting in hardened polymer micro structures. Such a heat treatment is also necessary after welding to achieve the desired stability at high temperatures. Tests show that the PEEK channels remain tight at a pressure difference of up to 700 kPa at a temperature of up to 220 °C.

We present a polycarbonate-based microfluidic device that was rapidly manufactured by ultrasonic hot embossing and welding. The fabrication of microstructures using ultrasonic processing allowed the embossing of micrometer-sized structures in polymer films by molding from a master die; this process was completed within seconds. The short manufacturing time required using this process and its ease of reproducibility allows rapid prototyping of custom-made microfluidic devices. Through ultrasonic fabrication, disposable microfluidic devices were newly designed and manufactured within a working day. The feasibility of these devices was demonstrated by cultivating yeast cells. The cells remained viable within this system for at least 22 h. Enhanced green fluorescent protein (eGFP) expression was initiated by providing the cells with a supply of the inducer galactose. The present study not only shows the potential of microfluidic devices fabricated by ultrasonic processing but also discusses their capability for use in microbial analysis.

Microstructures are fabricated from polymer foils in seconds by a new process called ultrasonic hot embossing. This process allows to realize new designs within a day and is suitable both for large- and small-scale production. The required investment costs are in the order of some 10,000 ź. In this paper, heat generation and distribution in ultrasonic hot embossing is investigated with piezo-electric and pyro-electric foils from the polymer polyvinylidene fluoride (PVDF) placed into a stack of polymer layers. This way, the influence of pre-structures on and powders between polymer layers is revealed.

Calcification is a pathological accumulation of calcium phosphate in soft tissues including blood vessels [1] where it can cause cardiovascular morbidity and mortality e.g. heart attack [2] . Mixing blood serum with supersaturated calcium and phosphate results in colloidal calcium protein particles (CPPs) undergoing a typical ripening process. The conversion time can be optically determined by light scatter measurements of smaller primary and larger secondary CPPs (Fig 1). The half-maximal conversion time T 50 is a measure of the calcification risk in the patient. Here we report the miniaturization of the experimental setup on a polymer microchip fabricated by ultrasonic processing. Compared to the usual measurement of light scatter in a nephelometer, the analysis was accelerated by increasing the temperature. Furthermore, better reproducible results were obtained by using a staggered herringbone mixer to mix the reactants [3] . A Peltier element is employed to heat the chip. Using this setup, the analysis was shortened to 16.1 ± 1.1 min compared to 279 ± 9 min obtained in a nephelometer by increasing the temperature from 38 °C to 52 °C (Fig. 4).

Nozzles with circular cross-section and a diameter varying in axial direction have been fabricated in a microfluidic channel from polyvinylidene fluoride as chemically resistive thermoplastic polymer. Smallest diameter and length of the nozzle are approximately 150 µm and 3.4 mm, respectively. The nozzle and the entire channel system have been fabricated from two halves generated by ultrasonic hot embossing and bonded to each other by ultrasonic welding. Alignment during ultrasonic welding was assisted by a fit of energy directors and an accuracy of 35 and 10 µm in normal and lateral direction, respectively, was obtained. Thermoplastic molding of the two halves of the channel structures was performed by ultrasonic hot embossing with a cycle time of a few seconds. The development was significantly accelerated by milling the tools directly into aluminum plates. This way, new designs were realized within a day. The micro nozzles have been proven generating liquid/liquid dispersions of different flow patterns as a function of flow velocity and Capillary number.

Verkurzte Entwicklungszeiten chemischer Prozesse sind durch Laborexperimente und Erkenntnisse daraus moglich. Dies wird durch modulare Mikrosysteme und deren Standardisierung der Apparate vereinfacht. Kunststoffe bieten durch ihre variablen Materialeigenschaften die Anpassung an die jeweiligen Prozesse sowie kostengunstige Herstellung. Das modulare Konzept besteht aus ultraschallheisgepragten PVDF-Folien. Zwei mogliche Anordnungsvarianten werden bezuglich ihrer Charakteristiken und der Verbindungsarten einzelner Module diskutiert. Die Durchfuhrung einer Neutralisationsreaktion zeigt die Flexibilitat dieses modularen Systems hinsichtlich Prozessanforderungen. A reduction of developmental periods is possible by laboratory experiments and their insights. This is simplified by modular microsystems and the related standardization of equipment. Beside a more cost-effective fabrication, plastic materials as an alternative to commercial available systems made from glass and metals offer variable properties making an adaption on process demands possible. The modular system consists of ultrasonic hot embossed PVDF foils. Two arrangement concepts are discussed regarding their characteristics and connection techniques of single modules. Running a neutralization reaction shows the flexibility of this modular concept concerning process demands.

Current directions in biomedical engineering 4(1), 367-370 (2018). doi:10.1515/cdbme-2018-0088, Published by De Gruyter, Berlin

Ultrasonic fabrication of fiber reinforced plastics made from thermoplastic polymer films and carbon or glass fibers enables cycle times of a few seconds and requires investment costs of only some 10,000 &euro, Besides this, the raw materials can be stored at room temperature. A fiber content of 33 vol % and a tensile strength of approximately 1.2 GPa have been achieved by ultrasonic welding of nine layers of foils from polyamide, each 100 &micro, m in thickness, and eight layers of carbon fibers, each 100 &micro, m in thickness, in between. Besides unidirectional carbon fiber reinforced polymer composite (CFRP) samples, multi-directional CFRP plates, 116 mm, 64 mm and 1.2 mm in length, width and thickness respectively, were fabricated by processing three layers of carbon fiber canvas, each 300 &micro, m in thickness, and eight layers of polyamide foils, each 100 &micro, m in thickness. Furthermore, both the discontinuous and the continuous ultrasonic fabrication processes are described and the results are presented in this paper. Large-scale production still needs to be demonstrated.

Fabrication of micro devices from thermoplastic polymers by ultrasonic processing has become a promising new technology in recent years. Microstructures are generated on polymer surfaces with cycle times of a few seconds and are tightly sealed in even shorter times. Investment costs and energy consumption are comparatively low and processes are very flexible enabling economic fabrication even for small-scale production. For large-scale production role-to-role fabrication has been shown reducing costs even more. A variety of micro devices have been introduced up to now mostly for microfluidic applications. Besides this, electronic circuit boards are fabricated by ultrasonic processing.

Background Small-scale micro-bioreactors have become the cultivation vessel of choice during the first steps of bioprocess development. They combine high cultivation throughput with enhanced cost efficiency per cultivation. To gain the most possible information in the early phases of process development, online monitoring of important process parameters is highly advantageous. One of these important process parameters is the oxygen transfer rate (OTR). Measurement of the OTR, however, is only available for small-scale fermentations in shake flasks via the established RAMOS technology until now. A microtiter plate-based (MTP) μRAMOS device would enable significantly increased cultivation throughput and reduced resource consumption. Still, the requirements of miniaturization for valve and sensor solutions have prevented this transfer so far. This study reports the successful transfer of the established RAMOS technology from shake flasks to 48-well microtiter plates. The introduced μRAMOS device was validated by means of one bacterial, one plant cell suspension culture and two yeast cultures. Results A technical solution for the required miniaturized valve and sensor implementation for an MTP-based μRAMOS device is presented. A microfluidic cover contains in total 96 pneumatic valves and 48 optical fibers, providing two valves and one optical fiber for each well. To reduce costs, an optical multiplexer for eight oxygen measuring instruments and 48 optical fibers is introduced. This configuration still provides a reasonable number of measurements per time and well. The well-to-well deviation is investigated by 48 identical Escherichia coli cultivations showing standard deviations comparable to those of the shake flask RAMOS system. The yeast Hansenula polymorpha and parsley suspension culture were also investigated. Conclusions The introduced MTP-based μRAMOS device enables a sound and well resolved OTR monitoring for fast- and slow-growing organisms. It offers a quality similar to standard RAMOS in OTR determination combined with an easier handling. The experimental throughput is increased 6-fold and the media consumption per cultivation is decreased roughly 12.5-fold compared to the established eight shake flask RAMOS device. Electronic supplementary material The online version of this article (doi:10.1186/s13036-016-0034-3) contains supplementary material, which is available to authorized users.

A system of 96 micro valves has been developed and mounted on top of a 48-well micro titer plate providing two valves for each well controlling its air inlet and outlet. Testing of the valve system showed that all valves are working and are opened and closed reliably. A pneumatic system is switching inlet and outlet valves independently of each other. The geometry of the feed channels ensures an equal air flow through all wells, when the valves are open. Between the micro valves, one optical fibre was inserted through the lid of each well allowing measuring the oxygen partial pressure in the enclosed air volume by fluorescence sensor spots. Escherichia coli bacteria were grown inside the wells and their metabolism was observed by the oxygen partial pressure change due to respiration. In all 48 wells, the same oxygen transfer rate was observed within an averaged standard deviation of 1 mmol/L/h. The oxygen transfer rate differences compared to a macroscopic standard shake flask system were overall compatible within their uncertainties.