In our group it is important to define scientific terms, especially terms for fundamental material properties. It is our view that the establishment of clear definitions is an underestimated challenge in our time. Normally it should arise from essential importance that scientist understand each other, which requirs a clear understanding of the terms they are using. However, as scientists in many different fields share common research interests, they each bring the terms and systems of their unique disciplines, resulting in a soup of unconnected terms that need to be clearly defined and standardized.
To this end, our group recently suggested a new principle to better define and evaluate multifunctional nanomaterials by extending the idea of atom economy to create the “multifunctional efficiency concept” (Box 1). We suggest evaluating the synthesis of a functional material not only based on yield and product selectivity (e.g. atom economy) but also with regard to the speciﬁc tasks the material can fulﬁll (number of functional units) and the simplicity of the production process (number of process steps).
Box 1 | Defining the multifunctional efficiency of nanocarriers
Nanocarriers for drug delivery have to be multifunctional in order to comply with diverse requirements, so their synthesis can be quite complex and involved. Ideally, the production of these highly sophisticated materials should be simple, reproducible, cost effective, and technical feasible, even at large scales. Here we define the parameter ‘mulfifunctional efficiency’ for the assessment of nanocarriers with consideration of their ‘functionality ratio’ and ‘process efficiency’:
(1) A functional unit (FU) is defined as a distinct building unit (BU) of the nanomaterial providing properties necessary for its specific purpose as nanocarrier or which fulfils specific tasks within the drug delivery pathway. Examples include shielding domains, targeting ligands, endosomolytic elements, controlled release coatings or chemical valves, and therapeutic entities.
(2) A process step (PRS) is defined as a distinct step in the synthesis. Examples include the formation of nanoparticles in a one-step self-assembly reaction, post-modification by polymer conjugation or surface coating, and drug loading.
(3) The functionality ratio (FR) of a nanocarrier is defined according to formula (𝑖)
where nFU is the number of functional units and mBU is the total number of building units of the nanocarrier.
(4) The process efficiency (PE) of a nanocarrier production process is defined according to formula (𝑖𝑖)
where nFU is the number of functional units and rPRS is the number of process steps within the production process of the nanocarrier.
(5) The multifunctional efficiency (MFE) is defined according to formula (𝑖𝑖𝑖)
where FR is the functionality ratio, PE is the process efficiency, nFU is the number of functional units, mBU is the total number of building units and rPRS is the number of process steps within the production process of the nanocarrier.
R. Freund, U. Lächelt, T. Gruber, B. Rühle, S. Wuttke,* Multifunctional efficiency: extension of the concept of atom economy to functional nanomaterials, ACS Nano 2018, 12, 2094-2105. (DOI: 10.1021/acsnano.8b00932)
M. Peller,* K. Böll, A. Zimpel, S. Wuttke,* Metal-organic framework nanoparticles for magnetic resonance imaging, Inorg. Chem. Frontiers 2018, 5, 1760-1779. (DOI: 10.1002/adfm.201606314)
S. Wuttke,* D. D. Medina, J. M. Rotter, S. Begum, T. Stassin, R. Ameloot, M. Oschatz, M. Tsotsalas,* Bringing porous organic and carbon-based materials towards thin film applications, Adv. Funct. Mater. 2018, 1801545. (DOI: 10.1002/adfm.201801545)
M. Limont,* L. Dreesen, S. Wuttke,* Metal-organic framework nanoparticles in phodynamic therapy : Current status and perspectives, Adv. Funct. Mater. 2017, 27, 1606314. (DOI: 10.1002/adfm.201606314)
S. Wuttke,* M. Lismont, A. Escudero, B. Rungtaweevoranit,
W. J. Parak,* Positioning metal-organic framework nanoparticles within the context of drug delivery – A comparison with mesoporous silica nanoparticles and dendrimers, Biomaterials 2017, 123, 172-183. (DOI: 0.1016/j.biomaterials.2017.01.025)