Jaap den Toonder

Circulating tumor cells: the Grand Challenge

More than a century ago, in 1869, the Australian pathologist Thomas Ashworth noted that some cells present in the blood of a man with metastatic cancer did not look like normal blood cells. Rather, they appeared similar to those in the patient’s solid tumors. In the article Ashworth published about his discovery in the Australian Medical Journal, he wrote the visionary words: ‘‘cells identical with those of the cancer itself being seen in the blood may tend to throw some light upon the mode of origin of multiple tumours existing in the same person’’. With the advent of new technologies in the last decades, the work on these Circulating Tumor Cells (CTCs) has been revived and is growing fast. In my opinion, the field of CTCs defines one of the Grand Challenges for the microfluidics community. Indeed, nowadays we know that Circulating Tumor Cells are released into the blood from primary and metastatic tumors and that, aside from a functional role in establishing metastatic tumors, they have high clinical diagnostic potential in oncology. The possibility to isolate and characterize CTCs with respect to their biological properties is envisioned to no less than revolutionize cancer diagnosis and therapy. Treatment of cancer, namely, is expected to change dramatically in the coming years, as an increasing number of novel targeted drugs, directed at the biological mechanism in the tumor that is directly responsible for growth of the tumor, will become available and partly replace standard chemotherapy treatment. Since this biological mechanism is not identical in all patients with the same type of tumor, it is essential to identify the biological target prior to deciding on treatment with a targeted

Photo-Switchable Surface Topologies in Chiral Nematic Coatings†

An enlightening answer: Dynamic surface photo-responsive topologies of a polymer coating were realized by introducing azobenzene crosslinkers into liquid-crystal polymer networks (see picture). The principle of these coatings is based on breaking the molecular order in the liquid-crystal polymer networks. Under irradiation of UV light the azobenzene compound isomerizes from the trans to the cis conformation.

Fracture toughness and adhesion energy of sol-gel coatings on glass

The reliability of coatings that are used in industrial applications critically depends on their mechanical properties. Nanoindentation and scratch testing are well-established techniques to measure some of these properties, namely the elastic modulus and hardness of coatings. In this paper, we investigate the possibility of also assessing the coating fracture toughness and the energy of adhesion between the coating and the substrate using indentation and scratch testing. Various existing and new methods are discussed, and they are illustrated by measurements on particle-filled sol-gel coatings on glass. All methods are based on the occurrence of cracking, and they are therefore only applicable to coating systems that act like brittle materials and exhibit cracking during indentation and scratching. The methods for determining the fracture toughness give comparable results, but the values still differ to within about 50%. The values of the adhesion energy obtained from different measurements are consistent, but it remains uncertain to which extent the obtained values are quantitatively correct. The results show that the methods used are promising, but more research is needed to obtain reliable quantitative results.

Workshop meeting report Organs-on-Chips : human disease models

The concept of “Organs-on-Chips” has recently evolved and has been described as 3D (mini-) organs or tissues consisting of multiple and different cell types interacting with each other under closely controlled conditions, grown in a microfluidic chip, and mimicking the complex structures and cellular interactions in and between different cell types and organs in vivo, enabling the real time monitoring of cellular processes. In combination with the emerging iPSC (induced pluripotent stem cell) field this development offers unprecedented opportunities to develop human in vitro models for healthy and diseased organ tissues, enabling the investigation of fundamental mechanisms in disease development, drug toxicity screening, drug target discovery and drug development, and the replacement of animal testing. Capturing the genetic background of the iPSC donor in the organ or disease model carries the promise to move towards “in vitro clinical trials”, reducing costs for drug development and furthering the concept of personalized medicine and companion diagnostics. During the Lorentz workshop (Leiden, September 2012) an international multidisciplinary group of experts discussed the current state of the art, available and emerging technologies, applications and how to proceed in the field. Organ-on-a-chip platform technologies are expected to revolutionize cell biology in general and drug development in particular.

Microfluidics for cell-based high throughput screening platforms : a review

In the last decades, the basic techniques of microfluidics for the study of cells such as cell culture, cell separation, and cell lysis, have been well developed. Based on cell handling techniques, microfluidics has been widely applied in the field of PCR (Polymerase Chain Reaction), immunoassays, organ-on-chip, stem cell research, and analysis and identification of circulating tumor cells. As a major step in drug discovery, high-throughput screening allows rapid analysis of thousands of chemical, biochemical, genetic or pharmacological tests in parallel. In this review, we summarize the application of microfluidics in cell-based high throughput screening. The screening methods mentioned in this paper include approaches using the perfusion flow mode, the droplet mode, and the microarray mode. We also discuss the future development of microfluidic based high throughput screening platform for drug discovery.

Near-surface mechanical properties of amorphous polymers

Abstract Polymeric material near a free surface can have properties which deviate considerably from the bulk properties. Many researchers have reported a reduced glass transition temperature in thin polymeric films and attributed this effect to an enhanced segmental mobility near a free surface. It was also reported that sufficiently thin polymeric structures show a higher ductility than the bulk material. In this paper, we therefore investigate the hypothesis that the near-surface mechanical properties of amorphous polymers differ from the bulk properties owing to the presence of an absolute length scale. Microindentations and nanoindentations are performed on polystyrene, using a range of indenter sizes and indentation loads. In addition, numerical simulations are carried out with an advanced material model for polystyrene. A comparison between the experimental and numerical results indeed indicates that a length-scale effect is present near the surface. Simulations performed at an elevated temperature indicate that our results are consistent with the observations of a reduced T g.

Single-composition three-dimensionally morphing hydrogels

We describe an approach to create pH responsive films that can transform from a flat state to a pre-described deformation. Our approach to fabricate these films is based on the use of a monomeric mixture of acrylic acid and a diacrylate crosslinker. Upon UV initiated free-radical polymerization the different monomers have different reactivities, which enables polymerization induced diffusion during spatially modulated UV intensity gradients. By means of this process the crosslink density within the film can be tuned spatially both in-plane and over the film thickness. The crosslink density determines the degree of swelling upon actuation of the formed hydrogel by a pH change. We demonstrate this effect by pH-switchable systems which are either substrate-attached exhibiting surface topologies upon actuation or freestanding that can undergo geometrical changes in the form of bending, curling or morphing into even more complex shapes.

High-Q integrated RF passives and RF-MEMS on silicon

A technology platform is described for the integration of low-loss inductors, capacitors, and MEMS capacitors on a high-resistivity Si substrate. Using this platform the board space area taken up by e.g. a DCS PA output impedance matching circuit can be reduced by 50%. The losses of passive components that are induced by the semi-conducting Si substrate can effectively be suppressed using a combination of surface amorphisation and the use of poly crystalline Si substrates. A MEM switchable capacitor with a capacitance switching factor of 40 and an actuation voltage of 5V is demonstrated. A continuous tuneable dual-gap capacitor is demonstrated with a tuning ratio of 9 using actuation voltages below 15V.

Microfluidic cytometer based on dual photodiode detection for cell size and deformability analysis

Cellular mechanical properties play an important role in disease diagnosis. Distinguishing cells based on their mechanical properties provides a potential method for label-free diagnosis. In this work, a convenient and low-cost microfluidic cytometer was developed to study cell mechanical properties and cell size based on the change of transmission intensity, using a low-cost commercial laser as a light source and two photodiodes as detectors. The cells pass through a narrow microchannel with a width smaller than the cell dimension, integrated in a polydimethylsiloxane chip, below which the laser is focused. The transit time of individual cells is measured by the time difference detected by two photodiodes. This device was used to study the difference in cell mechanical properties between HL60 cells treated with and without Cytochalasin D. Furthermore, it was also applied to distinguish cells with different diameters, HL60 cells and red blood cells, by measuring the transmission intensity.

Determination of the relationship between collagen cross-links and the bone–tissue stiffness in the porcine mandibular condyle

Although bone-tissue stiffness is closely related to the degree to which bone has been mineralized, other determinants are yet to be identified. We, therefore, examined the extent to which the mineralization degree, collagen, and its cross-links are related to bone-tissue stiffness. A total of 50 cancellous and cortical bone samples were derived from the right mandibular condyles of five young and five adult female pigs. The degree of mineralization of bone (DMB) was assessed using micro-computed tomography. Using high-performance liquid chromatography, we quantified the collagen content and the number of cross-links per collagen molecule of two enzymatic cross-links: hydroxylysylpyridinoline (HP) and lysylpyridinoline (LP), and one non-enzymatic cross-link: pentosidine (Pen). Nanoindentation was used to assess bone-tissue stiffness in three directions, and multiple linear regressions were used to calculate the correlation between collagen properties and bone-tissue stiffness, with the DMB as first predictor. Whereas the bone-tissue stiffness of cancellous bone did not differ between the three directions of nanoindentation, or between the two age groups, cortical bone-tissue stiffness was higher in the adult tissue. After correction for DMB, the cross-links studied did not increase the explained variance. In the young group, however, LP significantly improved the explained variance in bone-tissue stiffness. Approximately half of the variation in bone-tissue stiffness in cancellous and cortical bone was explained by the DMB and the LP cross-links and thus they cannot be considered the sole determinants of the bone-tissue stiffness.