Activities and future challenges of soft matter and biological physics education

The interactive teaching of soft matter and biological physics‡ promotes the high standing of both fields in modern day science. It is a paradigm for the successful co-education of students from different fields, including physics, physical chemistry, chemical engineering, biology and materials sciences.

The necessity of common teaching in soft matter and biological physics is best exemplified by looking back to the early development of biological physics. About 60 years ago, physicists working in life sciences were mainly involved in structural biology and generally worked at institutes for biochemistry and molecular biology, such as the world leading Cambridge Laboratory of Molecular Biology. Another branch of life science that fascinated physicists was neuroscience, starting after the groundbreaking work of Huxley and Hodgkin. The physicists concentrated on Onsager's theory of irreversible processes, and nonlinear dynamics (such as the Nagumo model of nerve conduction or the Van der Pol oscillator) and neural networks. Some theoretical physicists laid the groundwork for present theories of morphogenesis by extending Turing's model of biological pattern generation by chemical reaction–diffusion processes in tissue. Despite these promising developments, these pioneers had a hard time convincing physics faculties that biological physics was a sound and promising field for the future. Consequently it was not established in physics curricula.

The situation started to change when the close analogy between the physics of liquid crystals and biological membranes was recognized. The Frank continuum elasticity theory of liquid crystals stimulated the introduction of the bending elasticity concept of shape changes of cells between 1970 and 1973. The discovery of thermotropic phase transitions of artificial and biological membranes and of the elastic and electrostatic mechanisms of selective lipid protein interaction paved the way for our present understanding of the self-organisation and function of bio-membranes on the basis of physical concepts. Attracted by these discoveries, many brilliant young physicists working on the statistical mechanics of soft matter entered the field, which finally broke the ice.

Another powerful stimulus came some ten years later with the discovery that nature provides many new types of materials, such as semi-flexible macromolecules (actin, DNA), which linked biomaterial research to modern polymer physics and extended the scope of this field. This stimulated the development of more advanced theories of polyelectrolytes, which is expected to revolutionize our understanding of the chromatin structure and dynamics. Eventually, the physics community realized that biological physics of living matter is a highly sophisticated and sound branch of physics with a bright future. Physics faculties finally saw that they have to enter life science, to ensure that physics remains a leading science in the 21st century. Owing to the growing enthusiasm of many brilliant physics students for life sciences and thanks to the symbiosis with soft matter physics and statistical mechanics, courses in biological physics were eventually implemented in physics curricula.

Should we have common interdisciplinary courses on soft matter physics and biological physics?

The answer is definitely yes, provided they are complemented by high level courses in experimental and theoretical biological physics. The co-education of physicists, engineers, chemists, biochemists and biologists in introductory lectures and practical laboratory courses and seminars is an essential step towards the education of a new generation of scientists who are accustomed to cooperate with colleagues from neighboring scientific fields. In the author’s experience, about 10% of biology students and 20% of biochemistry students are open minded about physics. Their participation in the basic courses is highly recognized by physicists who realize that they can learn new ways of thinking.

Ideally, teaching should be accompanied by seminars given by students and, even more importantly, by laboratory courses, where students of different disciplines learn how beneficial interdisciplinary cooperation in the laboratory can be. Many biological themes, such as genetic expression, translation and transcription, can be treated in student seminars. In the writer’s long standing experience, students of different disciplines become most enthusiastic if they have a chance to work together in a biochemistry laboratory performing combined biochemical and physical experiments.

It is also mandatory to have special courses for students specializing in theoretical physics. Biological physics and soft matter physics have to compete with other popular fields, such as cosmology or field theory. To avoid losing the most brilliant students to these fields, the cutting edge courses on statistical physics of soft and biological matter have to be offered, ideally including introductions into the statistical physics of systems outside thermodynamic equilibrium and bioinformatics (see below).

On the balance of teaching fundamental concepts and biological systems

In the basic course, biological and physical concepts should be introduced interactively by showing how nature uses physical concepts to control the self-assembly and biological functions of living material (e.g. cellular organelles, tissues and chromatin) and systems (e.g. muscles and photosynthetic reaction centers).

Physics students are generally repelled by biology and biochemistry courses that involve learning many details by heart. Therefore the first introduction of biochemistry and biology should be ideally given by physicists. It is sufficient to introduce the few major classes of biomolecules (lipids, amino acids, sugar molecules, poly nucleotides, porphyrins) and elementary reactions (acid–base equilibrium, amino acid condensation, Michaelis–Menten model). The introductory lectures should be guided by examples where biochemistry and physics meet. An example appealing to biologists and physicists equally is ATP production in the electron transfer chain of mitochondria through protomotoric forces, generated by irreversible charge separation, and the analogy with electron–hole separation in photovoltaic cells. In the author’s experience, more sophisticated biological concepts, such as an introduction into genetic expression and cell division, can be best treated in accompanying seminars.

Conversely, biologists, biochemists and engineers become interested in physics if the concepts are also introduced through examples. One attractive way is to show how nature managed to generate a sheer infinite manifold of living beings from a relatively small number of molecular building blocks by the interplay of physics and genetics. The role of physics can be exemplified by showing how the evolution of a new design concept was guided by scaling laws of physics. This can be introduced stepwise by starting with Galilei's explanation of the limit of growth. Physicists and engineers become most fascinated if they learn how hydrodynamic scaling laws guided the development of different principles of swimming at low (such as bacteria and sandfish§) and high Reynolds numbers (such as fish).

The concept of Brownian motion becomes most appealing to students by showing them that important physical properties (such as viscoelastic parameters of cell envelopes and bio-macromolecular networks) can be determined by the mean square displacement-versus-time measurements using the Einstein–Stokes law. This paves the way for later introduction into the concept of viscoelasticity and the correlation between mechanical impedance spectra and molecular motion processes.

Concepts of photo-physics (such as fast physical and chemical reactions of excited molecules, energy and electron transfer reactions) can be smoothly introduced by considering the function of photosynthetic reaction centers and light harvesting complexes, where biology and quantum mechanics meet. Students become impressed if they learn how nature invented new concepts to overcome evolutionary crises, such as the proton pump to optimize reactions via pH gradients across cells, the generation of soft energy by water splitting, which triggered the evolution of the plant and animal kingdoms.

Ideally, modern courses on experimental biological physics should also deal with more challenging questions, outside the scope of soft matter physics. Appealing examples include: the adoption of senses (such as dark adoption of the eye or of the sensitivity of directional sensing by bacteria); the Huxley–Hodgkin model of the generation and propagation of action potentials along axons; and heart rhythm as an example of non-linear dynamics in biology. Given the limited time, these questions will be best treated in courses of theoretical biological physics.

Students are also interested in how scientific concepts developed historically. Examples are the introduction of the concept of viscoelasticity by Maxwell or the ingenious experiment invented by the young Helmholtz to measure the speed of nerve conduction in frog nerves (at a time when people believed in Newton's postulate that nerve pulses move with velocity of light). The work of Huxley and Hodgkin is another appealing example, showing how one can solve problems without big computers by thinking.

On the teaching of complex biological systems outside soft matter physics

To inspire students to continue studies of living matter or to point out the leading edge of research, some complex biological systems can be addressed in the basic course. A provoking field is the physics of hearing. Several physical and engineering concepts, which evolved during the development of higher animals, can be introduced via this topic. The exciting discovery of the travelling wave concept by Bekesy (around 1930), followed by the discovery of the signal pre-amplification at the organ of Corti by the electromotility of the outer hair cells (50 years later) is ideally suited to stimulate students for further studies. Here they can learn how nature managed to extend the dynamic range of hearing of vertebrates from 1 kHz (the limit of amphibians) to several tens of kHz. Topics of applied biomaterial research, such as medical imaging, structural research by scattering techniques and NMR spectroscopy, should be left to special courses and student seminars.

Another future challenge to be addressed in general courses is “Learning from Nature”: the living systems as they exist today are the products of evolution, which was often guided by the interplay of physics and genetics. Evolution of new biological systems and concepts (such as photosynthesis) were often triggered by evolutional crises (such as the solution of the energy crisis by the evolution of photosynthesis and soft energy production by proto-motoric forces). More insight into these processes may help to develop new renewable energy sources, for instance by mimicking nature's trick of water splitting.§

To render biological physics competitive in physics faculties theoretical biological physics courses are mandatory

Today biological physics and soft matter physics have to compete with other popular fields of physics, such as cosmology and quantum field theory. To avoid the escape of the most brilliant students into these attractive fields, advanced courses on statistical physics of soft matter, biological processes and systems have to be offered. Important themes could be: (i) statistical mechanics of passive and molecular motor-driven quasi-random motion in complex or fractal materials and cells; (ii) advanced theories of electrostatic interaction of bio-polyelectrolytes, such as supra-molecular DNA–protein complexes; (iii) pattern formation by chemical oscillators based on autocatalytic reaction cycles and chemical delay lines; (iv) population dynamics and biological evolution of species; (v) the sequential segmentation of an embryo’s body by oscillatory genetic networks; (vi) feed-forward mechanisms of biological regulatory cycles and analogies with technical control systems.

Connections of biological physics to other fields of materials science

There are astonishing links between biomaterials and hard matter, showing that, during evolution, nature utilized several concepts of solid state physics. These links show that biological physics is at eye level with other fields of physics and should be treated in advanced courses or special seminars. To understand the formation of functional domains in multicomponent lipid–protein mixtures, it is often most helpful to make use of the advanced concepts of the thermodynamics of mixtures and the dynamics of phase separation developed during the last 100 years in metal physics. They help us to understand how functional domains can form in multi-component lipid–protein alloys by heterogeneous nucleation and growth or uphill diffusion. Other appealing examples are the generation of high ductility biominerals (ceramics) by biopolymer-guided epitactic growth, and the minimization of friction at the nano-scale (nano-tribology), enabling the Sahara sandfish to swim beneath the sand.§ The generation of elastic shells (such as virus envelopes) from 2D crystals by minimizing the elastic energy through the introduction of dislocations and disclinations is another fascinating example of solid state stimulated biological physics. Another example is the fast switching of bacteria between directed and random motion on a time scale of 0.1 s by shape changes of the flagella driven by a Martensitic transition.§ The highly sophisticated theories of the elasticity of heterogeneous solid materials are extremely helpful for the development of novel theoretical models of elasticity of cells needed for understanding of the control of cell–tissue interactions by stress homeostasis.

Biological physics teaching beyond classical soft matter physics

We have to realize that biological physics is still considered with suspicion by many biologists. It is therefore mandatory to generate our own signature in the broad field of life sciences by linking it to other branches of physics, besides classical soft matter physics. Formulated to the extreme, we should make clear to the public that understanding living matter or biological evolution on the basis of physics is as fascinating and important for the future of mankind as the physics of fundamental forces and quantum field theory. This means that in the future we have to go beyond teaching classical soft matter physics and attack more fundamental questions of life sciences that are presently still a matter of research. However, in the near future, these questions (some of which are mentioned below) should be addressed in advanced courses, seminars and workshops. It is also expected to open new fields of soft matter physics.

Biological systems are far outside the chemical equilibrium, and the micro-anatomy of living matter (cells or tissue) is constantly reorganized by fluctuating mechanical forces, chemical fluxes and affinities, which are often triggered by changes of composition through genetic expression. This requires the extension of the classical theories of statistical thermodynamics, elasticity and viscoelasticity, hydrodynamics and even electrodynamics. To understand fast biochemical processes at charged interfaces, the classical Debye–Hückel theory may have to be extended, by accounting for the dynamic conductivity of electrolytes (similar to the dynamic Debye–Falkenhagen theory of electrical double layers).

The composition and structure of cellular organelles (such as biological membranes coupled to the intracellular scaffold) are constantly adapted to various biological needs by a confusing number of interactive cell signaling pathways. These genetic and enzymatic networks are presently intensively studied by bio-informaticians. However, for deeper insight into life processes it is absolutely necessary to also understand the manipulation of the material properties of cells or tissue by the biochemical and genetic networks, which is a domain of physics. Material properties, cell signaling and biological functions (such as cell proliferation) appear to be interrelated by a magic triangle. The cell proliferation goes out of control, causing cancer, if one of the three elements of the cycle does not function properly.

These complex questions are certainly not suited for the teaching of general courses. However, they should be addressed in specialized lectures and student seminars. Here students could learn from nature how to design novel materials by self-assembly of smart molecules, such as bio-analogue ceramics combining unique elastic properties with minimal surface abrasion.

Promotion of soft matter and biological physics in the undergraduate education of physicists, chemists and bioengineers

To promote the fields of soft matter and biological physics, one should try to implement introductory courses on soft and living matter in undergraduate courses and physics courses for chemists and biologists. It would make physics more attractive to pupils with a major interest in chemistry and biology if they realize how nature utilizes physical concepts to design materials of outstanding properties (such as red blood cells) or to control evolution by the interplay of genetics and physics. Some readers may remember how boring continuum mechanics could be when it focused on tensor calculus and made us believe that problems can be calculated analytically. Today we can show undergraduate students how beautiful Hook’s law works in the biology of soft shells (say erythrocytes) or how one can understand complex mechanical problems be applying Saint-Venant's principle of solving boundary value problems.

On what personal experience is this editorial based?

The author's experience is based on 40 years of teaching biological physics courses to physicists, biochemists and engineers. His obligation as an academic teacher was to educate excellent students, not only for scientific institutions but also for research and development departments in industry. When he switched from photophysics of organic material to biological physics he was strongly encouraged by short discussions with Aharon Katchalsky, Max Delbrück and Linus Pauling. He started to switch from model systems to living cells when he realized, to his great surprise, that the students working on the physics of cells and biological systems were offered excellent jobs in German industrial companies, where personal managers search for physicists who are accustomed to working in multidisciplinary teams with engineers, chemists and biologists. Several students in the author’s institute, developing micro-optical methods and fast image processing techniques, obtained excellent offers from German car companies from Mercedes to BMW. Some of them became successful entrepreneurs.

Erich Sackman, Technical University Munich, Germany

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Footnotes

† This article is part of a collection of editorials on Soft Matter Education.

‡ I use the notation “biological physics” to emphasize that the central aim of this new area of physics is to search for classical and new physical concepts controlling the self-assembly and function of living materials and biological processes. “Biophysics” denotes the application and adoption of physical tools to study biological materials without scrutinizing the role of physical laws in biology.

§ Information on the evolution of new concepts can be found in E. Sackmann: Biomimetic Physics: Nature as nano-material designer and engineer. Lecture Notes on Biophysics www.biophy.de

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