Category Archives: Engineering

Nano biomechanical engineering of agent delivery to cells

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figure 1 from [1] with text explanationWhile many of us are being jabbed in the arm to deliver an agent that stimulates our immune system to recognize the coronavirus SARS-CoV-2 as a threat and destroy it, my research group has been working, in collaboration with colleagues at the European Commission Joint Research Centre, on the dynamics of nanoparticles [1] [see ‘Size matters‘ on October 23rd, 2019] which could be used as carriers for the targeted delivery of therapeutic, diagnostic and imaging agents in the human body [2].  The use of nanoparticles to mechanically stimulate stem cells to activate signalling pathways and modulate their differentiation also has some potential [3]. In studies of the efficacy of nanoparticles in these biomedical applications, the concentration of nanoparticles interacting with the cell is a primary factor influencing both the positive and negative effects.  Such studies often involve exposing a monolayer of cultured cells adhered to the bottom of container to a dose of nanoparticles and monitoring the response over a period of time.  Often, the nominal concentration of the nanoparticles in biological medium supporting the cells is reported and used as the basis for determining the dose-response relationships.  However, we have shown that this approach is inaccurate and leads to misleading results because the nanoparticles in solution are subject to sedimentation due to gravity, Brownian motion [see ‘Slow moving nanoparticles‘ on December 13th, 2017] and inter-particle forces [see ‘ Going against the flow‘ on February 3rd, 2021] which affect their transport within the medium [see graphic] and the resultant concentration adjacent to the monolayer of cells.  Our experimental results using the optical method of caustics [see ‘Holes in fluids‘ on October 22nd, 2014] have shown that nanoparticle size, colloidal stability and solution temperature influence the distribution of nanoparticles in solution.  For particles larger than 60 nm in diameter (about one thousandth of the diameter of a human hair) the nominal dose differs significantly from the dose experienced by the cells.  We have developed and tested a theoretical model that accurately describes the settling dynamics and concentration profile of nanoparticles in solution which can be used to design in vitro experiments and compute dose-response relationships.

References

[1] Giorgi F, Macko P, Curran JM, Whelan M, Worth A & Patterson EA. 2021 Settling dynamics of nanoparticles in simple and biological media. Royal Society Open Science, 8:210068.

[2] Daraee H, Eatemadi A, Abbasi E, Aval SF, Kouhi M, & Akbarzadeh A. 2016 Application of gold nanoparticles in biomedical and drug delivery. Artif. Cells Nanomed. Biotechnol. 44, 410–422. (doi:10.3109/21691401.2014.955107)

[3] Wei M, Li S, & Le W. 2017 Nanomaterials modulate stem cell differentiation: biological
interaction and underlying mechanisms. J. Nanobiotechnol. 15, 75. (doi:10.1186/s12951-
017-0310-5)

Bringing an end to thermodynamic whoopee

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Two weeks ago I used two infographics to illustrate the dominant role of energy use in generating greenhouse gas emissions and the disportionate production of greenhouse gas emission by the rich [see ‘Where we are and what we have‘ on November 24th, 2021].  Energy use is responsible for 73% of global greenhouse gas emissions and 16% of the world’s population are responsible for 38% of global CO2 emissions.  Today’s infographics illustrate the energy flows from source to consumption for the USA (above), UK and Europe (thumbnails below).  In the USA fossil fuels (coal, natural gas and petroleum) are the source of nearly 80% of their energy, in the UK it is a little more than 80% and the chart for Europe is less detailed but the proportion looks similar. COP 26 committed countries to ending ‘support for the international unabated fossil fuel energy sector by the end of 2022’ and recognised ‘investing in unabated fossil-related energy projects increasingly entails both social and economic risks, especially through the form of stranded assets, and has ensuing negative impacts on government revenue, local employment, taxpayers, utility ratepayers and public health.’  However, to reduce our dependency on fossil fuels we need a strategy, a plan of action for a fundamental change in how we power industry, heat our homes and propel our vehicles.  A hydrogen economy requires the production of hydrogen without using fossil fuels, electric cars and electric domestic heating requires our electricity generating capacity to be at least trebled by 2050 in order to hit the net zero target. This scale and speed of  transition to zero-carbon sources is such that it will have to be achieved using an integrated blend of green energy sources, including solar, wind and nuclear energy.  For example, in the UK our current electricity generating capacity is about 76 GW and 1 GW is equivalent to 3.1 million photovoltaic (PV) panels, or 364 utility scale wind turbines [www.energy.gov/eere/articles/how-much-power-1-gigawatt] so trebling capacity from one of these sources alone would imply more than 700 million PV panels, or one wind turbine every square mile.  It is easy to write policies but it is much harder to implement them and make things happen especially when transformational change is required.  We cannot expect things to happen simply because our leaders have signed agreements and made statements.  Now, national plans are required to ween us from our addiction to fossil fuels – it will be difficult but the alternative is that global warming might cause the planet to become uninhabitable for us.  It is time to stop ‘making thermodynamic whoopee with fossil fuels’ to quote Kurt Vonnegut [see ‘And then we discovered thermodynamics‘ on February 3rd, 2016].

 

 

 

 

 

 

 

 

 

Sources:

Kurt Vonnegut, A Man without a Country, New York: Seven Stories Press, 2005.  He wrote ‘we have now all but destroyed this once salubrious planet as a life-support system in fewer than two hundred years, mainly by making thermodynamic whoopee with fossil fuels’.

US Energy flow chart: https://flowcharts.llnl.gov/commodities/energy

EU Energy flow chart: https://ec.europa.eu/eurostat/web/energy/energy-flow-diagrams

UK Energy flow chart: https://www.gov.uk/government/collections/energy-flow-charts#2020

Where we are and what we have

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Pie chart showing green house gas emissions by sectorIn his closing statement at COP26 in Glasgow earlier this month, António Guterres, the Secretary-General of the UN stated that ‘Science tells us that the absolute priority must be rapid, deep and sustained emissions reductions in this decade. Specifically – a 45% cut by 2030 compared to 2010 levels.’   About three-quarters of global green house gas emissions are carbon dioxide (30.4 billions tons in 2010 according to the IEA). A reduction in carbon emissions of 45% by 2030 would reduce this to 16.7 billion tons or an average of about 2 tons per person per year (tCO2/person/yr) allowing for the predicted 9% growth in the global population to 8.5 billion people by 2030. This requires the average resident of Asia, Europe and North America to reduce their carbon emissions to about a half, a quarter and a tenth respectively of their current levels (3.8, 7.6 & 17.6 tCO2/person/yr respectively, see the graphic below and ‘Two Earths‘ on August 13th, 2012).  These are massive reductions to achieve in a very short timescale, less than a decade.  Lots of people are talking about global and national targets; however, very few people have any idea at all about how to achieve the massive reductions in emissions being talked about at COP26 and elsewhere.  The graphic above shows global greenhouse gas emissions by sector with almost three-quarters arising from our use of energy to make stuff (energy use in industry: 24%), to move stuff and us (transport: 16%), and to use stuff and keep us comfortable (energy use in building: 17.5%).  Hence, to achieve the target reductions in emissions and prevent the temperature of the planet rising more than 1.5 degrees compared to pre-industrial levels, we need to stop making, buying, moving and consuming stuff.  We need to learn to live with our local climate because cooling and heating buildings consumes energy and heats the planet.  And, we need to use public transport, a bicycle or walk.  By the way, for stuff read all matter, materials, articles, i.e., everything!  We will need to be satisfied with where we are and what we have, to learn to love old but serviceable belongings [see ‘Loving the daily current of existence‘ on August 11th, 2021 and ‘Old is beautiful‘ on May 1st, 2013].

Infographic showing CO2 emission by region and wealth

Follow your gut

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Decorative image of a fruit fly nervous system Albert Cardona HHMI Janelia Research Campus Welcome Image Awards 2015Data centres worldwide consume about 1% of global electricity generation, that’s 200-250 TWh (Masenet et al, 2020), and if you add in mining of cryptocurrencies then consumption jumps by about 50% (Gallersdörfer et al, 2020). Data transmission consumes about 260-340 TWh or at least another 1% of global energy consumption (IEA, 2020).  The energy efficiency of modern computers has been improving; however, their consumption is still many millions times greater than the theoretical limit defined by Landauer’s principle which was verified in 2012 by Bérut et al.  According to Landauer’s principle, a computer operating at room temperature would only need 3 zJ (300 billion billionths of a Joule) to erase a bit of information.  The quantity of energy used by modern computers is many millions times the Landauer limit.  Of course, progress is being made almost continuously, for example a team at EPFL in Lausanne and ETH Zurich recently described a new technology that uses only a tenth of the energy of current transistors (Oliva et al 2020).  Perhaps we need turn to biomimetics because Escherichia Coli, which are bacteria that live in our gut and have to process information to reproduce, have been found to use ten thousand times less energy to process a bit of information than the average human-built device for processing information (Zhirnov & Cavin, 2013).  So, E.coli are still some way from the Landauer limit but demonstrate that there is considerable potential for improvement in engineered devices.

References

Bérut A, Arakelyan A, Petrosyan A, Ciliberto S, Dillenschneider R & Lutz E. Experimental verification of Landauer’s principle linking information and thermodynamics. Nature, 483: 187–189, 2012.

IEA (2021), Data Centres and Data Transmission Networks, IEA, Paris https://www.iea.org/reports/data-centres-and-data-transmission-networks

Gallersdörfer U, Klaaßen L, Stoll C. Energy consumption of cryptocurrencies beyond bitcoin. Joule. 4(9):1843-6, 2020.

Masanet E, Shehabi A, Lei N, Smith S, Koomey J. Recalibrating global data center energy-use estimates. Science. 367(6481):984-6, 2020.

Oliva N, Backman J, Capua L, Cavalieri M, Luisier M, Ionescu AM. WSe 2/SnSe 2 vdW heterojunction Tunnel FET with subthermionic characteristic and MOSFET co-integrated on same WSe 2 flake. npj 2D Materials and Applications. 4(1):1-8, 2020.

Zhirnov VV, Cavin RK. Future microsystems for information processing: limits and lessons from the living systems. IEEE Journal of the Electron Devices Society. 1(2):29-47, 2013.