Life-like Materials
We are building chemical systems that are capable to pick up signals from their environment and process these, like a “chemical soft-ware program”, into behavior at micro- and mesoscopic length scales. By combining molecular self-assembly to physicochemical phenomena such as osmosis, diffusion and surface tension, we aim at fundamentally new principles that further expand the potential of information processing smart materials.
KEYWORDS: systems chemistry | molecular self-assembly | out-of-equilibrium | self-organization | hydrogels | active matter | surfactants | Marangoni flow
Living organisms display an enormous diversity of mechanisms to sense environmental information and process this into appropriate behavior. For example, social amoeba cells communicate through oscillating chemical reactions that resonate beyond a critical density of signal molecules, such that the cells can count each other prior to self-organization into multicellular bodies. Slime molds exemplify self-organization at an even larger length scale and grow long wires that form networks to explore surfaces and find nutrients.
Importantly, the underlying mechanisms are all based on chemistry: living matter is constructed via molecular assembly and regulation mechanisms that rely on chemical circuitries.
In the artificial systems we develop in our lab, we employ molecular self-assembly as well: the reversible associations involved in molecular self-assembly enable us to arrive at structures that can be formed, disassembled and re-formed again. Their dynamic behavior allows these systems to adapt and reorganize in response to stimuli from the environment.
Self-organization
We have developed self-assembling structures that organize themselves into wire-like structures at the centimeter length scale – in a (primitive) analogy to the growth of slime mold wires. Our system combines the self-assembly of a linear amphiphile with surfactant release/depletion dynamics at air-water interfaces that result in sustained Marangoni flows. Whereas the Marangoni flows generate repulsive forces that push the source and drain droplets apart, the filaments that originate from the source tether to the drain droplets, resulting in attractive forces. A controlled balance between these repulsive and attractive forces enables an out-of-equilibrium positioning of complex dynamic assemblies at air-water interfaces.
Read our paper in Nature Communications about the self-organizing system that we have developed, based on amphiphile self-assembly, Marangoni flow and self-sustained gradients. Or check out this article by NEMO Kennislink (in Dutch).
Or, check our paper in Langmuir, with more mechanistic insights, and a demonstration how we can use the filaments to attract selected droplets, based on their chemical content.
Currently, we are exploring how the growth of these wires, and the self-organization of the network they form, can be directed. To this end, we aim to integrate chemical reactions, polymer chemistry, hydrogels and physicochemical phenomena such as surface tension, reaction-diffusion, osmosis and feedback in the system. At the same time, we are working on methods to introduce behavior such as motion, self-repair, adaptation, memory and quorum sensing in these systems.
We aim to employ this assembly process to create an autonomous self-organizing system that transfers chemical signals via a network of wires that form and re-wire connections over 2D substrates. Ultimately, this may open new possibilities in e.g. adaptive microfluidics or electronics-free diagnostics where analytes are transferred over a substrate along different reagents.
Non-equilibrium hydrogels
Additionally, we enable hydrogels: 3D polymer networks that contain water and are capable to swell and contract in response to stimuli such as pH- or temperature changes. Typically, hydrogels are designed to continuously equilibrate to their surroundings (e.g. changes in pH or temperature). However, in order to extract information from a dynamic environment, this equilibrium approach is insufficient and a broader repertoire of complex signal extraction and processing is required.
Read here our paper in Nature Communications, together with the group of Joanna Aizenberg (Harvard), and Nadir Kaplan (Virginia Tech). Here, we introduce the idea that hydrogels, previously just thought to shrink and swell in time with the presence or absence of a specific stimulus, can generate fascinating new classes of non-equilibrium responses. Thereby, hydrogels can act as complex chemical signal integrators – a universal feature of living materials but currently absent from synthetic systems. Find more background on the paper in this Nature Research Chemistry Community blog post, or in this article by NEMO Kennislink (in Dutch).
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