A guide to self-assembly
Imagine gently shaking a box of Lego building blocks, and then looking inside to find a series of complete structures.
Self-assembly doesn鈥檛 happen in the playroom, but Vinothan Manoharan, an assistant professor of chemical engineering and physics at Harvard鈥檚 School of Engineering and Applied Sciences (SEAS), wants to make it happen in the laboratory to treat life-threatening diseases or manufacture useful objects.
鈥淚t would be nice to make interesting stuff out of it,鈥� Manoharan said. 鈥淚t may also be useful to prevent self-assembly in diseases where it matters 鈥� and there are lots of diseases, like HIV, where it matters.鈥�
Manoharan explained the physics of self-assembly and its huge potential for the world of biology in a lecture 鈥� 鈥淭he New Science of Self-Assembly: From Living Things to New Technology鈥� 鈥� Friday night at the Science Center.
The hourlong talk was aimed at the nonscientist and came with a humorous series of disclaimers that 鈥渆verything was my own opinion鈥� and not that of his colleagues, that there was a 鈥渓ot of speculation,鈥� and that 鈥渁ny resemblance to established theories was coincidental.鈥�
Self-assembly, Manoharan explained, is when particles interact with one another and spontaneously arrange themselves into organized structures.
This happens in nature. Proteins self-assemble. So do viruses less lethal than HIV. Scientists such as Manoharan hope that by learning how self-assembly works they can stop deadly viruses in their tracks.
But Manoharan said that despite years of research his team is nowhere near copying the process.
鈥淣ature is doing something we don鈥檛 and that is learned through billions of years of evolution,鈥� Manoharan said. 鈥淲e haven鈥檛 been doing it nearly that long.鈥�
Indeed, Manoharan has only been at it 15 years.
His quest began accidentally in Santa Barbara, where his doctoral adviser at the University of California introduced the topic that is now his passion, asking him to create an opal from household paint.
Paint is made up of colloidal particles. So is milk, for that matter. The particles are tiny 鈥� 1,000 nanometers. Manoharan said if a colloidal particle were a tennis ball, a person would be the size of the Greater Boston area.
Under a microscope, they look like fat droplets and move in random directions 鈥� Brownian motion. That random motion is how self-assembly occurs, Manoharan said. Controlling that is key.
What got him wondering about self-assembly as a way of making things was thinking about the way cellphones are made. The chips inside are about 30 nm in size. As they get even tinier, sprawling factories have to be built to manufacture microscopic silicone chips. That seemed silly.
鈥淲ouldn鈥檛 it be great if you could take some silicone and put it into a beaker and shake it for a while and it spontaneously forms a microchip,鈥� Manoharan said. 鈥淚t seems crazy but that鈥檚 what self-assembly means to me.鈥�
After arriving at Harvard seven years ago, Manoharan began working on the problem.
A significant part of it was: Particles left alone crystallize, but they make mistakes and land in the wrong spot.
The trick is getting entropy to work for them. Entropy is a measure of disorder 鈥� the higher entropy, the more likely something will be ordered.
His team tried to introduce energy to increase entropy. Manoharan illustrated this by attaching Velcro (representing energy) to orange and yellow ping-pong balls in a clear box containing white balls and shaking it. The orange and yellow balls attached.
Manoharan鈥檚 team also has shown that polytetrahedrons have far greater vibrational entropy 鈥� 24 times more 鈥� than octahedrons. Again, this sheds light on how to make things stick.
鈥淚f you control the interactions, so you control which particles stick, you can beat entropy and get them to form,鈥� Manoharan said. 鈥淲e鈥檝e yet to do this.鈥�
Right now, HIV is treated with medicine that interferes with the virus鈥� mutations. But that requires multiple rounds of drugs switched rapidly to stay ahead with the mutations. If scientists could unlock self-assembly, Manoharan said, they could get ahead of HIV without drugs.
鈥淚f we understand it, we can treat HIV and get to the mutations,鈥� Manoharan said.
Provided by Harvard University
