Research based on the use of organs-on-chips is rapidly expanding and developing. These microengineered devices are microfluidic physiological models of tissues and organs. All sorts of organs-on-chips have been reported, including lung-on-a-chip, heart-on-a-chip and even blood-brain barrier-on-a-chip. See http://dx.doi.org/10.1039/C2LC40089H for a Frontier article by Ingber et. al., which focuses on advances in these microengineered organs.
The models have great potential in the field of pharmacology and toxicology, where they can be used to chart the effects of candidate drugs. But what if we could connect all these organs-on-chips together, and create an actual ‘human-on-a-chip’? Could such a model be used to replace the popular animal models? Could we soon be testing our drug candidates not on mouse or rat, but on the microHuman?
What would a microHuman look like? The answer is tiny. It would be a million times lighter than a regular human, giving it a mass of merely 70 mg. At such an incredible size, would the microHuman be functional, like you or I?
In a Critical Review by John Wikswo and colleagues (http://dx.doi.org/10.1039/C3LC50243K), the scaling requirements of a microHuman are discussed. It is concluded that a simple scaling system is not enough; a microhuman would be completely dysfunctional if we applied basic scaling laws to it. For example, its breathing rate would be approximately 10 breaths per second. In addition, its capillaries would be so small that any naturally-occurring blood cell would be too large to traverse them.
In response to these barriers, Wikswo and colleagues provide detailed discussion of scaling in a number of organ systems in the microHuman. Additionally, they give an overview of structural and functional parameters to guide the scaling of organs-on-chips in a microHuman, which are based upon human and animal data.
Interestingly, whilst the potential of a microengineered human-on-a-chip is huge, Wikswo et. al. point out that, like any model system, the microHuman will never be perfect: “It is important to realize that [these] systems reside in a niche of abstraction that will improve constantly with technology but will never exactly recreate a full human, which represents approx. 109 years of evolutionary engineering”.
Organs-on-chips, and their potential for the development into humans-on-chips, are currently an incredibly hot topic area. If you want to find out more, in addition to Wikswo’s excellent review you can read more about this exciting field in a paper by Shuichi Takayama and colleagues, published recently in the RSC Journal Integrative Biology (http://dx.doi.org/10.1039/C3IB40040A).