Design Considerations for a Successful Nanoparticle Delivery System

 Nanoparticles (NPs) are thought to have potential as novel intravascular probes for both diagnostic (e.g., imaging) and therapeutic purposes (e.g., drug delivery). 

Critical issues for successful nanoparticle delivery include the ability:

• To target specific tissues and cell types 
• Endocytosis (uptake into the cells)
• Targeting agent (address tags)
• To escape from the biological particulate filter 
• Mononuclear Phagocyte System (MPS; clearance of unwanted particulate material)
• Phagocytes and Nanoparticles
• Protection from Clearance by MPS 
• Main NP research question—how is particulate material recognized and cleared?

In this article, we will cover the above five highlighted areas.  Note that the below topics are parts of the design considerations, but will not discussed here.

• Reduction in toxicity while maintaining therapeutic effects
• Greater safety and biocompatibility

Figure 1.  Endocytosis (Created by Mariana Ruiz Villarreal LadyofHats)

Endocytosis—Uptake into the Cells

Nanoparticles enter the cells by endocytosis. Endocytosis is a process of the uptake substances into the cell.  It is a form of active transport which includes:^[92]

• Pinocytosis (cell drinking) 
• The uptake of small (<0.5 μm) particles into vesicles
• Phagocytosis (cell eating)
• The uptake of larger particles (>0.5 μm) by a process involving actin polymerization. 

Both can be receptor mediated. 

Figure 2.  Schematic representation of qdot targeting. (source: [95])
Intravenous delivery of qdots into specific tissues of the mouse. (Upper)
Design of peptide-coated qdots. (Lower)
Qdots were coated with either peptides only or with peptides and PEG.
PEG helps the qdots maintain solubility in aqueous solvents and minimize nonspecific binding.

Targeting Agent (Address Tags)

Biodegradable nanoparticles have been studied extensively for the fabrication of drug delivery systems.  The design considerations include controlling the release of drugs, stabilizing labile molecules (e.g., proteins, peptides, or DNA) from degradation, and site-specific drug targeting.

Nanoparticles (NPs) can be linked to biological molecules that can act as address tags.  Common address tags are:

• Monoclonal antibodies
• Aptamers
• Streptavidin 
• Peptides. 

Address tags can direct NPs to:

• Specific sites within the body^[90]
• Specific organelles within the cell^[95]
• Follow specifically the movement of individual protein or RNA molecules in living cells^[96]

For example, scientists were able to show that (See Figure 1):^[91]

ZnS-capped CdSe qdots coated with a lung-targeting peptide accumulate in the lungs of mice after i.v. injection, whereas two other peptides specifically direct qdots to blood vessels or lymphatic vessels in tumors. 

Adding polyethylene glycol (PEG) to the qdot coating prevents nonselective accumulation of qdots in reticuloendothelial tissues.

These targeting agents should ideally be covalently linked to the nanoparticle and should be present in a controlled number per nanoparticle:

• Multivalent nanoparticles
• Bearing multiple targeting groups, can cluster receptors, which can activate cellular signaling pathways, and give stronger anchoring
• Monovalent nanoparticles
• Bearing a single binding site,^[97-99] avoid clustering and so are preferable for tracking the behavior of individual proteins.

Figure 3.  Nanoparticle Uptake: The Phagocyte Problem (Source: [111])

Mononuclear Phagocyte System

Initially, Reticuloendothelial System (RES) denotes a system of specialized cells that effectively clear colloidal vital stains (so called because they stain living cells) from the blood circulation.  

The capture and clearance of unwanted particulate material from blood and lymph were considered to be the major function of the RES. 

As knowledge accumulated, the term RES was regarded as insufficient to describe resident phagocytes and their antecedents.  In 1969, a group of prominent pathologists/immunologists proposed the term Mononuclear Phagocyte System (MPS) as a more accurate term.^[100]

The MPS is part of both humoral and cell-mediated immunity.  The trinity of MPS include:

• Monocytes
• Macrophages
• Dendritic cells

which are distinguished on the basis of their morphology, function, and origin, yet collectively constitute the MPS.

Phagocytes and Nanoparticles

Issues plaguing nanomaterials circulation and targeting in humans can be attributed to:[104-110]

• Rapid vascular filtration and clearance of therapeutics and diagnostics
• Induction of host inflammatory responses due to non-specific recognition
• Uptake of nanoconstructs by macrophages in vivo

Phagocytes are key cellular participants determining important aspects of host exposure to nanomaterials, initiating clearance, biodistribution and the tenuous balance between host tolerance and adverse nanotoxicity.^[111] 

Macrophages in particular are believed to be among the first and primary cell types that process nanoparticles, mediating host inflammatory and immunological biological responses. 

These processes occur ubiquitously throughout tissues where nanomaterials are present, including the host mononuclear phagocytic system (MPS) residents in dedicated host filtration organs (i.e., liver, kidney spleen, and lung). 

Nanoparticle delivery vehicles designed to either avoid or specifically harness this host recognition system could improve payload delivery, reduce inflammatory effects and improve imaging and drug efficacy. 

Figure 4.  Adsorbed protein conformation can be affected by different particle surface properties.
Surface curvature, topography, hydrophilic/hydrophobic chemistry and
polymer coating steric barriers on nanoparticle surfaces are shown to
alter amounts and conformations of proteins adsorbed to surfaces. (Source: [111])

Protection from Clearance by MPS

The nanoparticle size and surface properties can be manipulated to avoid rapid clearance by phagocytic cells.  

Nanoparticle association with the host highly evolved mononuclear phagocytic system (MPS) is a function of particle opsonization upon contact with blood and rapid recognition of these opsonins via the MPS.^[113,115] 

Surface-adsorbed proteins (opsonins) influence macrophage recognition and uptake of nanoparticles.^[112-114]  Additionally, conformational protein rearrangements on nanoparticle surfaces alters protein epitope exposures to phagocytes.^[116,117]  Certain epitopes have the capacity to activate macrophages.^[113] 

Protein adsorption and subsequent phagocytic uptake appear dependent upon (see Figure 4):^[111] 

• Particle surface curvature^[118,119]
• Particle surface topography^[120]
• Particle surface energies (e.g., hydrophilicity/hydrophobicity)
• Polymer coating steric barriers on nanoparticle surfaces

For example, hydrophilic polyethylene glycol (PEG) has often been immobilized in many forms and approaches to provide a brush-like steric barrier that is shown to reduce protein adsorption and is correlated with increased blood circulation times for some particles.^[121] Dextran layers employed on commercial iron oxide MRI agent nanoparticles (i.e., Feridex™) may serve the same role.^[121] 

Surface modification of NPs with polyethylene glycol (PEG) have improved drug delivery properties and prolonged circulation life time with enhanced protection from clearance by mononuclear phagocytic systems.^[101-103]

References

1. Nanoparticles—a historical perspective
2. Preparation and Characterization of Cross-Linked Polymeric Nanoparticles for Enhanced Oil Recovery Applications (pdf)
3. Polyacrylamide and its deriv ylamide and its derivatives for oil r es for oil recovery (pdf)
4. Nanosizing of drugs: Effect on dissolution rate
5. Development and functional characterization of alginate dressing as potential protein delivery system for wound healing
6. Designing hydrogels for controlled drug delivery (good)
7. Novavax addresses urgent global public health needs with innovative technology
8. How the Novavax Vaccine Works
9. Widder KJ, Senyel AE, Scarpelli GD. Magnetic microspheres: a model system of site specific drug delivery in vivo. Proc Soc Exp Biol Med. 1978;158:141–6.
10. Nuclear molecular imaging with nanoparticles: radiochemistry, applications and translation
11. Methods for Synthesis of Nanoparticles and Fabrication of Nanocomposites
12. NANOPARTICULATE DRUG DELIVERY SYSTEM
13. Switchable Release of Entrapped Nanoparticles from Alginate Hydrogels.[Adv Healthc Mater. 2015]
14. Nanosized cationic hydrogels for drug delivery: preparation, properties and interactions with cells. Vinogradov SV, Bronich TK, Kabanov AV. Adv Drug Deliv Rev. 2002 Jan 17; 54(1):135-47.
15. Applications of Targeted Nano Drugs and Delivery Systems
16. Langer R. Drug delivery and targeting. Nature. 1998;392:5–10.
17. Hoare TR, Kohane DS. Hydrogels in drug delivery: Progress and challenges. Polymer. 2008;49:1993–2007.
18. Liechty WB, Kryscio DR, Slaughter BV, Peppas NA. Polymers for drug delivery systems. Ann Rev Chem Biomol Eng. 2010;1:149–173.
19. Cohen J. IL-12 deaths: explanation and a puzzle. Science. 1995;270:908–908.
20. Florence AT, Jani PU. Novel oral drug formulations. Drug Safety. 1994;10:233–266.
21. Ashley GW, Henise J, Reid R, Santi DV. Hydrogel drug delivery system with predictable and tunable drug release and degradation rates. Proc Natl Acad Sci USA. 2013;110:2318–2323.
22. Tiwari G, et al. Drug delivery systems: An updated review. Int J Pharm Investig. 2012;2:2–11.
23. Tibbitt MW, Dahlman JE, Langer R. Emerging frontiers in drug delivery. J Am Chem Soc.
24. Singh, BN; Prateeksha, Gupta VK; Chen, J; Atanasov, AG (2017). "Organic Nanoparticle-Based Combinatory Approaches for Gene Therapy". Trends Biotechnol. 35 (12): 1121–1124. 2016;138:704–717.
25. Wang, Zhenming; Wang, Zhefeng; Lu, William Weijia; Zhen, Wanxin; Yang, Dazhi; Peng, Songlin (October 2017). "Novel biomaterial strategies for controlled growth factor delivery for biomedical applications"
26. Mitragotri S, Lahann J. Physical approaches to biomaterial design. Nat Mater. 2009;8:15–23.
27. Euliss LE, DuPont JA, Gratton S, DeSimone J. Imparting size, shape, and composition control of materials for nanomedicine. Chem Soc Rev. 2006;35:1095–1104.
28. Gratton SE, et al. The effect of particle design on cellular internalization pathways. Proc Natl Acad Sci USA. 2008;105:11613–11618.
29. Geng H, Song H, Qi J, Cui D. Sustained release of VEGF from PLGA nanoparticles embedded thermo-sensitive hydrogel in full-thickness porcine bladder acellular matrix. Nanoscale Res Lett. 2011;6:1–8.
30. Oh JK, Drumright R, Siegwart DJ, Matyjaszewski K. The development of microgels/nanogels for drug delivery applications. Prog Polym Sci. 2008;33:448–477.
31. Crommelin DJ, Storm G. Liposomes: from the bench to the bed. J Liposome Res. 2003;13:33–6.
32. Metselaar JM, Storm G. Liposomes in the treatment of inflammatory disorders. Expert Opin Drug Deliv. 2005;2:465–76.
33. Noh SY, Nash A, Notman R (2020). "The aggregation of striped nanoparticles in mixed phospholipid bilayers". Nanoscale. 12 (8): 4868–81.
34. Nanotechnologies: 6. What are potential harmful effects of nanoparticles?
35. Thake, T.H.F; Webb, J.R; Nash, A.; Rappoport, J.Z.; Notman, R. (2013). "Permeation of polystyrene nanoparticles across model lipid bilayer membranes". Soft Matter. 9 (43): 10265 10274.
36. Greulich, C.; Diendorf, J.; Simon, T.; Eggeler, G.; Epple, M.; Köller, M. (January 2011). "Uptake and intracellular distribution of silver nanoparticles in human mesenchymal stem cells". Acta Biomaterialia. 7 (1): 347–354.
37. Compartmentalization Technologies via Self-Assembly and Cross-Linking of Amphiphilic Random Block Copolymers in Water
38. Drug delivery and nanoparticles: Applications and hazards (good)
39. The pKa Table Is Your Friend (important)
40. Nanoparticles as a Targeted Drug Delivery System
41. Self-Assembled Hydrogel Nanoparticles for Drug Delivery Applications
42. Gupta M, Gupta AK. In vitro cytotoxicity studies of hydrogel pullulan nanoparticles prepared by AOT/N-hexane micellar system. J Pharm Pharmaceut Sci. 2004;7:38–46.
43. Biocompatibility and drug delivery systems (good)
44. S. R. Little and D. S. Kohane, Polymers for intracellular delivery of nucleic acids, J. Mater. Chem., 2008, 18, 832–841
45. Polymeric Nucleic Acid Delivery for Immunoengineering
46. Dubernet C., Couvreur P. Nanoparticles in cancer therapy and diagnosis. Adv. Drug Delivery Rev. 2002;54:631–651.
47. Panyam J., Labhasetwar V. Biodegradable nanoparticles for drug and gene delivery to cells and tissue. Adv. Drug Delivery Rev. 2003;55:329–347.Moghimi S.M., Hunter A.C., Murray J.C. Long-circulating and target-specific nanoparticles: Theory to practice. Pharmacol. Rev. 2001;53:283–318.
48. Moghimi S.M., Hunter A.C., Murray J.C. Long-circulating and target-specific nanoparticles: Theory to practice. Pharmacol. Rev. 2001;53:283–318.
49. Sun T.-M., Du J.-Z., Yan L.-F., Mao H.-Q., Wang J. Self-assembled biodegradable micellar nanoparticles of amphiphilic and cationic block copolymer for siRNA delivery. Biomaterials. 2008;29:4348–4355.
50. Jain A.K., Goyal A.K., Gupta P.N., Khatri K., Mishra N., Mehta A., Mangal S., Vyas S.P. Synthesis, characterization and evaluation of novel triblock copolymer based nanoparticles for vaccine delivery against hepatitis B. J. Control. Release. 2009;136:161–169.
51. Niidome T, Yamagata M, Okamoto Y, et al. PEG-modified gold nanorods with a stealth character for in vivo applications. J Control Release. 2006;114:343–7.
52. M. Goldberg, R. Langer and X. Jia, Nanostructured materials for applications in drug delivery and tissue engineering, J. Biomater. Sci., Polym. Ed., 2007, 18, 241–268.
53. D. S. Kohane, Microparticles and nanoparticles for drug delivery, Biotechnol. Bioeng., 2007, 96, 203–209
54. What Are Lipid Nanoparticles in mRNA Vaccines? 
55. Plard J.P., Bazile D. Comparison of the safety profiles of PLA(50) and Me.PEG-PLA(50) nanoparticles after single dose intravenous administration to rat. Colloids Surf. B. 1999;16:173–183.
56. Peracchia M.T., Fattal E., Desmaele D., Besnard M., Noel J.P., Gomis J.M., Appel M., d'Angelo J., Couvreur P. Stealth PEGylated polycyanoacrylate nanoparticles for intravenous administration and splenic targeting. J. Control. Release. 1999;60:121–128.
57. Matsumura Y., Maeda H. A New Concept for macromolecular therapeutics in cancer chemotherapy: Mechanism of tumoritropic accumulation of proteins and the antitumor agent smancs1. Cancer Res. 1986;46:6387–6392.
58. Brannon-Peppas L., Blanchette J.O. Nanoparticle and targeted systems for cancer therapy. Adv. Drug Delivery Rev. 2004;56:1649–1659.
59. Moghimi S.M., Hunter A.C., Murray J.C. Nanomedicine: Current status and future prospects. FASEB J. 2005;19:311–330.
60. Fang C, Shi B, Pei YY, et al. In vivo tumor targeting of tumor necrosis factor-alpha-loaded stealth nanoparticles: Effect of MePEG molecular weight and particle size. Eur J Pharm Sci. 2006;27:27–36.
61. Shim J, Seok Kang H, Park WS, et al. Transdermal delivery of minoxidil with block copolymer nanoparticles. J Control Release. 2004;97:477–84.
62. Zhang L, Hu Y, Jiang X, et al. Camptothecin derivative-loaded poly(caprolactone-co-lactide)-b-PEG-b-poly(caprolactone-co-lactide) nanoparticles and their biodistribution in mice. J Control Release. 2004;96:135–48.
63. A programmable chemical switch based on triggerable Michael acceptors
64. SELF-IMMOLATIVE CHEMISTRY: Structural Features and Applications in Designing Smart Materials (pdf)
65. Measuring particle size distribution of nanoparticle enabled medicinal products, the joint view of EUNCL and NCI-NCL. A step by step approach combining orthogonal measurements with increasing complexity
66. D’Mello SR, Cruz CN, Chen ML, Kapoor M, Lee SL, Tyner KM. The evolving landscape of drug products containing nanomaterials in the United States. Nat. Nanotechnol. 12(6), 523–529 (2017).
67. US FDA. Guidance Document: Drug Products, Including Biological Products, that Contain Nanomaterials – Guidance for Industry.
68. EMA. Development of Block-Copolymer-Micelle Medicinal Products (Reference Number EMA/CHMP/130299/2013).
69. EMA (Committee for Medicinal Products for Human Use). Reflection Paper on the Data Requirements for Intravenous Iron-Based Nano-Colloidal Products Developed with Reference to an Innovator Medicinal Product (2012).
70. Committee for Human Medicinal Products. Reflection Paper on the Data Requirements for Intravenous Liposomal Products Developed with Reference to Aninnovator Liposomal Product (2013).
71. US FDA. Liposome Drug Products: Chemistry, Manufacturing, and Controls; Human Pharmacokinetics and Bioavailability; and Labeling Documentation (2018).
72. Nano-enabled medicinal products: time for an international advanced community?
73. El-Sayed, M. A. Some interesting properties of metals confined in time and nanometer space of different shapes. Accounts Chem. Res. 34, 257–264 (2001).
74. Trindade, T., O'Brien, P. & Pickett, N. L. Nanocrystalline semiconductors: synthesis, properties and perspectives. Chem. Mater. 13, 3843–3858 (2001).
75. Kelly, K. L., Coronado, E., Zhao, L. L. & Schatz, G. C. The optical properties of metal nanoparticles: the influence of size, shape, and dielectric environment. J. Phys. Chem. B. 107, 668–677 (2003).
76. Seo, W. S. et al. Size-dependent magnetic properties of colloidal Mn3O4 and MnO nanoparticles. Angew. Chem. Int. Ed. 43, 1115–1117 (2004).
77. Mohanty, A., Garg, N. & Jin, R. A universal approach to the synthesis of noble metal nanodendrites and their catalytic properties. Angew. Chem. Int. Ed. 49, 4962–4966 (2010).
78. Rao, C. N. R., Kulkarni, G. U., Thomas, P. J. & Edwards, P. P. Size-dependent chemistry: properties of nanocrystals. Chem. Eur. J. 8, 29–35 (2002).
79. Boal, A. K. et al. Self-assembly of nanoparticles into structured spherical and network aggregates. Nature 404, 746–748 (2000).
80. Li, P., Kaslan, M., Lee, S. H., Yao, J. & Gao, Z. Progress in exosome isolation techniques. Theranostics 7, 789 (2017).
81. Lane, R. E., Korbie, D., Anderson, W., Vaidyanathan, R. & Trau, M. Analysis of exosome purification methods using a model liposome system and tunable-resistive pulse sensing. Sci. Rep. 5, 7639 (2015).
82. Batrakova, E. V. & Kim, M. S. Using exosomes, naturally-equipped nanocarriers, for drug delivery. J. Control. Rel. 219, 396–405 (2015).
83. Prime, KL; Whitesides, GM (1991). "Self-assembled organic monolayers: model systems for studying adsorption of proteins at surfaces". Science. 252 (5009): 1164–7.
84. Liu, Wenhao; Greytak, Andrew B.; Lee, Jungmin; Wong, Cliff R.; Park, Jongnam; Marshall, Lisa F.; Jiang, Wen; Curtin, Peter N.; Ting, Alice Y.; Nocera, Daniel G.; Fukumura, Dai; Jain, Rakesh K.; Bawendi, Moungi G. (20 January 2010). 
85. "Compact Biocompatible Quantum Dots via RAFT-Mediated Synthesis of Imidazole-Based Random Copolymer Ligand". Journal of the American Chemical Society. 132 (2): 472–483.
86. Gupta AK, Gupta M. Synthesis and surface engineering of iron oxide nanoparticles for biomedical applications. Biomaterials. 2005;26:3995–4021.
87. "Nanoparticles play at being red blood cells". Archived from the original on 1 July 2011. Retrieved 1 July 2011.
88. Surface-Energy Control and Characterization of Nanoparticle Coatings
89. Core–shell nanostructures: perspectives towards drug delivery applications
90. Cancer Cell Membrane-Coated Nanoparticles for Anticancer Vaccination and Drug Delivery
91. Akerman ME, Chan WC, Laakkonen P, Bhatia SN, Ruoslahti E (2002). "Nanocrystal targeting in vivo". Proceedings of the National Academy of Sciences of the United States of America. 99(20): 12617–12621.
92. Praaning-van Dalen, DP; Brouwer, A; Knook, DL (December 1981). "Clearance capacity of rat liver Kupffer, Endothelial, and parenchymal cells". Gastroenterology. 81 (6): 1036–44.
93. Anderson, CL (December 2015). "The liver sinusoidal endothelium reappears after being eclipsed by the Kupffer cell: a 20th century biological delusion corrected". Journal of Leukocyte Biology. 98(6): 875–6.
94. Ganesan, LP; Mohanty, S; Kim, J; Clark, KR; Robinson, JM; Anderson, CL (September 2011). "Rapid and efficient clearance of blood-borne virus by liver sinusoidal endothelium". PLoS Pathogens. 7 (9): e1002281.
95. Hoshino, A; Fujioka, K; Oku, T; Nakamura, S; Suga, M; Yamaguchi, Y; Suzuki, K; Yasuhara, M; Yamamoto, K (2004). "Quantum dots targeted to the assigned organelle in living cells". Microbiology and Immunology. 48 (12): 985–94.
96. Suzuki, KG; Fujiwara, TK; Edidin, M; Kusumi, A (2007). "Dynamic recruitment of phospholipase C at transiently immobilized GPI-anchored receptor clusters induces IP3 Ca2+ signaling: single-molecule tracking study 2". The Journal of Cell Biology. 177 (4): 731–42.
97. Sung, KM; Mosley, DW; Peelle, BR; Zhang, S; Jacobson, JM (2004). "Synthesis of monofunctionalized gold nanoparticles by fmoc solid-phase reactions". Journal of the American Chemical Society. 126 (16): 5064–5.
98. Fu, A; Micheel, CM; Cha, J; Chang, H; Yang, H; Alivisatos, AP (2004). "Discrete nanostructures of quantum dots/Au with DNA". Journal of the American Chemical Society. 126 (35): 10832–3.
99. Howarth, M; Liu, W; Puthenveetil, S; Zheng, Y; Marshall, LF; Schmidt, MM; Wittrup, KD; Bawendi, MG; Ting, AY (2008). "Monovalent, reduced-size quantum dots for imaging receptors on living cells". Nature Methods. 5 (5): 397–9.
100. van Furth R, Cohn ZA, Hirsch JG, Humphrey JH, Spector WG, Langevoort HL. [Mononuclear phagocytic system: new classification of macrophages, monocytes and of their cell line]. Bull World Health Organ (1972) 47:651–8.
101. Jokerst, V. J.; Lobovkina, T.; Zare, N. R.; Gambhir, S. S. Nanoparticle PEGylation for imaging and therapy. Nanomedicine 2012, 6, 715– 728.
102. Hak, S.; Helgesen, E.; Hektoen, H. H.; Huuse, E. M.; Jarzyna, P. A.; Mulder, W. J. M.; Haraldseth, O.; de Lange Davies, C. L. The Effect of Nanoparticle Polyethylene Glycol Surface Density on Ligand-Directed Tumor Targeting Studied in Vivo by Dual Modality Imaging. ACS Nano 2012, 6, 5648– 5658.
103. Pelaz, B.; del Pino, P.; Maffre, P.; Hartmann, R.; Gallego, M.; Rivera-Fernández, S.; de la Fuente, J. M.; Nienhaus, G. U.; Parak, W. J. Surface Functionalization of Nanoparticles with Polyethylene Glycol: Effects on Protein Adsorption and Cellular Uptake. ACS Nano 2015, 9, 6996– 7008.
104. He X, Nie H, Wang K, Tan W, Wu X, Zhang P. Anal Chem. 2008;80:9597–9603. 
105. Huang X, Li L, Liu T, Hao N, Liu H, Chen D, Tang F. ACS Nano. 2011;5:5390–5399. 
106. Kumar R, Roy I, Ohulchanskky TY, Vathy LA, Bergey EJ, Sajjad M, Prasad PN. ACS Nano. 2010;4:699–708. 
107. Liu T, Li L, Teng X, Huang X, Liu H, Chen D, Ren J, He J, Tang F. Biomaterials. 2011;32:1657–1668. 
108. Liu Y, Hu Y, Huang L. Biomaterials. 2014;35:3027–3034. 
109. Ohno K, Akashi T, Tsujii Y, Yamamoto M, Tabata Y. Biomacromolecules. 2012;13:927–936. 
110. Owens DE, 3rd, Peppas NA. Int J Pharm. 2006;307:93–102.
111. Nanoparticle Uptake: The Phagocyte Problem.
112. Dobrovolskaia MA, Aggarwal P, Hall JB, McNeil SE. Mol Pharm. 2008;5:487–495.
113. Jenkin CR, Rowley D. J Exp Med. 1961;114:363–374.
114. Absolom DR. Methods Enzymol. 1986;132:281–318.
115. Mortimer GM, Butcher NJ, Musumeci AW, Deng ZJ, Martin DJ, Minchin RF. ACS Nano. 2014;8:3357–3366.
116. Andrade J, Hlady V. Biopolymers/Non-Exclusion HPLC. Springer; 1986. Protein adsorption and materials biocompatibility: a tutorial review and suggested hypotheses; pp. 1–63. 
117. Andrade JD, Hlady VL, Van Wagenen RA. Pure Appl Chem. 1984;56:1345–1350.
118. Vertegel AA, Siegel RW, Dordick JS. Langmuir. 2004;20:6800–6807. 
119. Davidson WS, Jonas A, Clayton DF, George JM. J Biol Chem. 1998;273:9443–9449.
120. Lord MS, Foss M, Besenbacher F. Nano Today. 2010;5:66–78. 
121. Walkey CD, Chan WC. Chem Soc Rev. 2012;41:2780–2799. 
122. Banda NK, Mehta G, Chao Y, Wang G, Inturi S, Fossati-Jimack L, Botto M, Wu L, Moghimi SM, Simberg D. Part Fibre Toxicol. 2014;11:64. 
123. Nano based drug delivery systems: recent developments and future prospects (good)
124. Chapter 31 - Advances in delivery of nanomedicines and theranostics for targeting breast cancer
125. Role of drug delivery technologies in the success of COVID-19 vaccines: a perspective

Long-Term Effects of Too Much Salt

Video 1.  Sodium and Arterial Function: A-salting our Endothelium (YouTube link)

The Western diet is rich in salt, which poses various health risks.  For example,  too much sodium in the diet can lead to high blood pressure, stomach cancer, kidney stones, bone loss, obesity and even cause direct damage to our kidneys, arteries, and heart.

According to the WHO’s recommendations, the maximum amount of salt individuals should consume every day is 5 grams, which is about 1 level teaspoon. In reality most of us are exceeding this amount considerably.

Long-Term Effects of Too Much Salt

• Bad for cardiovascular systems^[5]
• Consume one salty meal, and not only does our blood pressure go up, but our arteries literally stiffen
• Sodium in our blood stiffens the artery lining within minutes and reduces nitric oxide release
• Whereas potassium, concentrated in fruits and vegetables, softens the cells that line our arteries and increases the release of nitric oxide that allows our arteries to relax
• Bad for immune system^[6,8]
• Human volunteers consuming an extra 6 grams of salt a day experienced pronounced immune deficiencies. This amount is equivalent to the salt content of 2 fast food meals.
• A high-salt diet compromises antibacterial neutrophil responses through hormonal perturbation
• High salt diet → overactivation of Th17 cells → autoimmune diseases
• Salt appears to drive autoimmune disease by the induction of disease-causing Th17 cells, which includes but not limited to:
• Multiple sclerosis, psoriasis, type I diabetes, Sjögren’s syndrome, asthma, and rheumatoid arthritis
• It turns out there’s a salt-sensing enzyme which is responsible for triggering the formation of these Th17 cells.
• Bad for bone
• It can cause calcium losses, some of which may be pulled from bone.
• Higher stomach cancer risk
• The pickled foods (i.e., kimchi and the like) may explain why Korea appears to have the highest stomach cancer rates in the world.^[17]
• In a study, it showed that the importance of nitrate as risk factor for stomach cancer mortality increased markedly with higher sodium levels. However, the relationship of stomach cancer mortality with sodium was always stronger than with nitrate.^[15]

Some Salt-Rich Foods

Dietary salt intake is directly associated with the risk of stomach cancer.^[15]  And, the higher the intake, the higher the risks. In a meta-analysis study,  it went further looking at specific salt-rich foods: 

• Pickled foods
• Salted fish
• Processed meat
• Miso soup

to see their effect on the cancer rate.  Here are its findings:

• Habitual consumption of pickled foods, salted fish,  and processed meat were associated with about a 25% greater risk of stomach cancer. 
• But, there was no significant association with the consumption of miso soup.^[18] 
• This may be because the carcinogenic effects of the salt are counteracted by the anti-carcinogenic effects of the soy, effectively canceling out the risk. 
• And, if we made garlicky soup with some scallions thrown in, it may drop our cancer risk even lower.

Video 2.  Is miso health? (YouTube link)

References

1. Association Between Sodium Excretion and Cardiovascular Disease and Mortality in the Elderly: A Cohort Study
2. 老人吃盐太少，很危险，国外最新研究发现
3. Sodium & Arterial Function: A-Salting our Endothelium
4. Sodium Skeptics Try to Shake Up the Salt Debate
5. Why We Should Cut Down on Salt Independently of Blood Pressure (Dr. Greger)
6. A high-salt diet compromises antibacterial neutrophil responses through hormonal perturbation
7. Salt and Sodium 
8. Sodium and Autoimmune Disease: Rubbing Salt in the Wound?
9. Mickleborough TD, Lindley MR, Ray S. Dietary salt, airway inflammation, and diffusion capacity in exercise-induced asthma. Med Sci Sports Exerc. 2005 Jun;37(6):904-14.
10. Javaid A, Cushley MJ, Bone MF. Effect of dietary salt on bronchial reactivity to histamine in asthma. BMJ. 1988 Aug 13;297(6646):454.
11. van der Meer JW, Netea MG. A salty taste to autoimmunity. N Engl J Med. 2013 Jun 27;368(26):2520-1.
12. Zhou X, Zhang L, Ji WJ, Yuan F, Guo ZZ, Pang B, Luo T, Liu X, Zhang WC, Jiang TM, Zhang Z, Li YM. Variation in dietary salt intake induces coordinated dynamics of monocyte subsets and monocyte-platelet aggregates in humans: implications in end organ inflammation. PLoS One. 2013 Apr 4;8(4):e60332.
13. Wu C, Yosef N, Thalhamer T, Zhu C, Xiao S, Kishi Y, Regev A, Kuchroo VK. Induction of pathogenic TH17 cells by inducible salt-sensing kinase SGK1. Nature. 2013 Apr 25;496(7446):513-7.
14. Yi B, Titze J, Rykova M, Feuerecker M, Vassilieva G, Nichiporuk I, Schelling G, Morukov B, Choukèr A. Effects of dietary salt levels on monocytic cells and immune responses in healthy human subjects: a longitudinal study. Transl Res. 2015 Jul;166(1):103-10.
15. Joossens JV, Hill MJ, Elliott P, Stamler R, Lesaffre E, Dyer A, Nichols R, Kesteloot H. Dietary salt, nitrate and stomach cancer mortality in 24 countries. European Cancer Prevention (ECP) and the INTERSALT Cooperative Research Group. Int J Epidemiol. 1996 Jun;25(3):494-504.
16. Boutron-Ruault MC, Trichopoulou A, Psaltopoulou T, Roukos D, Lund E, Hemon B, Kaaks R, Norat T, Riboli E. Meat intake and risk of stomach and esophageal adenocarcinoma within the European Prospective Investigation Into Cancer and Nutrition (EPIC). J Natl Cancer Inst. 2006 Mar 1;98(5):345-54.
17. Stomach cancer statistics
18. Is Miso Healthy?
19. What Are the Best Foods for Kidney Health?
• A renal diet is a diet that becomes increasingly more restrictive as your kidney function declines. It starts out with having you limit your salt and the amount of protein you eat.

Characterization Techniques for Nanoparticles Enabled Medicinal Products

The number of innovative nanoparticles enabled medicinal products (NEMPs) being developed has been continually increasing.^[66] Multiple regulatory bodies^[67-71] implicitly demand product assessment in their quality, safety and efficacy in order to support their decision-making process, allowing effective translation toward a clinical application and subsequent commercialization.^[67-71]

With their small sizes, nanoparticles (NPs) present unique opportunities and challenges in both manufacturing and analysis:^[72]

If compared with ‘classical’ small molecule drugs, the assessment for NEMPs demands the investigation of many additional physico-chemical (PC) properties, including particle size distribution and polydispersity, dispersion stability, drug loading and drug release, particle shape, surface charge, surface coating, among many others.

To complicate matters, each NEMP is unique, imposing different methodological approaches to characterize its PC properties and to determine the critical quality attributes, which could impact its immunological effects, biodistribution, pharmacokinetics, metabolism and safety profile.

For example, measurements of particle size and zeta potential are routinely performed on the same instrument by dynamic light scattering (DLS) and laser Doppler electrophoresis (LDE), but require multiple experiments, and are challenged by polydisperse samples, for example, exosomes isolated from body fluids.

In this article, we will focus on three such characterization techniques for:

• Particle Size Distribution
• Surface Charge
• Surface Coating

Figure 1.  Antibody conjugated PLGA Nanoparticle

Properties of Nanoparticles

The reason why nanoparticles (NPs) are attractive for medical purposes is based on their important and unique features:

• Nanosize
• The small particle diameter allows the whole material to reach homogeneous equilibrium with respect to diffusion in a very short time.
• Small drugs may diffuse through the capillary walls into the tissues. Otherwise nanoparticles transport occurs through compromised endothelial barrier or mediated by specific transport systems.
• The small size not only makes them needle-injectable, but also enhance penetration through tissue barriers.
• Large area/volume ratio
• The high surface area of a material in nanoparticle form allows heat, molecules, and ions to diffuse into or out of the particles at very large rates.
• Offers a large surface area for bioconjugation and effortless natural clearance
• Ability to absorb and carry other compounds
• Drugs can be conjugated to nanoparticles surfaces via ionic or covalent bonding and physical absorption and NPs can deliver them and control their release through biological stimuli or other activations (see Figure 1).
• More subject to the brownian motion
• They usually do not sediment, like colloidal particles that conversely are usually understood to range from 1 to 1000 nm.
• Can easily pass through common filters (e.g., common ceramic candles)
• Separation from liquids requires special nanofiltration techniques.
• Cannot be seen with optical microscopes
• Being much smaller than the wavelengths of visible light (400-700 nm), nanoparticles require the use of electron microscopes or microscopes with laser.

With consistent efforts, researchers have strived to engineer these NPs by modifying their physical and chemical properties, referring to them as ‘smart’ or ‘intelligent’ NPs since they respond to external stimuli like temperature, pH, light, magnetic and electric fields, ionic strength, or enzymatic environment.

Particle Size Distribution

The particle size distribution (PSD) and the stability of NEMPs in complex biological environments are key attributes to assess their quality, safety and efficacy.

Nanoparticle's chemical, electronic, optical, magnetic and catalytic, properties, and self-assembly, inherently depend on their size and composition.^[73-79]

There are different methods to measure the nanoparticle size:

1. Dynamic light scattering
• Despite its low resolution, DLS is the most common sizing technique
2. Electron microscopy
3. Field flow fractionation coupled to online sizing detectors
4. Centrifugal techniques
• Ultracentrifugation, one of the most commonly used concentration methods, is time consuming and suffers from contamination.^[80,81]
• Size-based filtration through membranes can result in deformations or even break the particles.^[80,82]
5. Particle tracking analysis
6. Nanoparticle tracking analysis
7. Tunable Resistive Pulse Sensing

In a perspective article,^[65] it proposes a multi-step approach of incremental complexity to measure particle size distribution and size stability of NEMPs, consisting of:

1. A quick preliminary step to assess sample integrity and stability by low resolution techniques (pre-screening)
2. Followed by the combination of complementary high resolution sizing measurements performed both in simple buffers and in complex biological media

Surface Charge

The surface charge of nanoparticles is important as it determines its

• Stability
• Propensity to aggregate in the bloodstream
• Interacting with the cell membranes
• It has been revealed that cellular internalization is faster for nanogels of positive zeta potential or with high aspect ratios (for example, those with a rod-like shape).^[28]

Zeta potential is a measure of the surface charge of a nanoparticle. The magnitude of the zeta potential provides information about particle stability:

In a sense, the zeta potential represents an index for particle stability. For charged particles, as the zeta potential increases the repulsive interactions becomes larger, leading to stable particles, likely to have a more uniform size distribution.

The zeta potential of particles is typically measured by Electrophoretic Light Scattering (ELS).^[89] In contrast to streaming potential measurements no movement of the liquid is generated, but the movement of the particles is induced. Therefore, an electric field is applied and the electrophoretic mobility of particles is used to calculate the zeta potential. Due to the electric field particles will move at different speeds: highly charged particles will move faster than less charged particles. 

Figure 2. Core-shell nanoparticles: perspectives towards drug delivery applications (source: [88]).
In the review article,^[88] it explores state-of-the-art developments and advances in core–shell nanoparticle systems, the desired structure–property relationships, newly generated properties, the effects of parameter control, surface modification, and functionalization, and, last but not least, their promising applications in the fields of drug delivery, biomedical applications, and tissue engineering.

Surface Coating

Nanosystems have shown encouraging outcomes and substantial progress in the areas of drug delivery and biomedical applications. In this regard, core–shell type nanoparticles are promising nanocarrier systems for controlled and targeted drug delivery applications.

These functional nanoparticles are emerging as a particular class of nanosystems because of their unique advantages, including high surface area, and easy surface modification and functionalization. Such unique advantages can facilitate the use of core–shell nanoparticles for the selective mingling of two or more different functional properties in a single nanosystem to achieve the desired physicochemical properties that are essential for effective targeted drug delivery.

Several types of core–shell nanoparticles, such as metallic, magnetic, silica-based, upconversion, and carbon-based core–shell nanoparticles, have been designed and developed for drug delivery applications (see Figure 2).

Nanoparticles often develop or receive coatings of other substances, distinct from both the particle's material and of the surrounding medium. Even when only a single molecule thick, these coatings can radically change the particles' properties, such as and chemical reactivity, catalytic activity, and stability in suspension.

Many properties of nanoparticles, notably stability, solubility, and chemical or biological activity, can be radically altered by coating them with various substances — a process called functionalization.

For biological applications,

• Coatings that mimic those of red blood cells can help nanoparticles evade the immune system.^[86,90]
• Coating should be polar to give high aqueous solubility and prevent nanoparticle aggregation.
• In serum or on the cell surface, highly charged coatings promote non-specific binding, whereas polyethylene glycol linked to terminal hydroxyl or methoxy groups repel non-specific interactions.^[83,84]
• Coatings can be used to prevent agglomeration
• Which can keep the particles in colloidal suspension including various polymers like polyethylene glycol (PEG), poly(vinylpyrrolidone) (PVP) etc, natural polymers like dextran, chitosan, pullulan etc, and surfactants like sodium oleate, dodecylamine etc.^[85]

By consideration of surface energy, it is shown that these particles are expected to possess distinctly differing coating structures, with the polystyrene coating being incomplete. A comprehensive characterization of these systems can be done using a selection of complementary techniques including:

• Scanning electron microscopy (SEM)
• Scanning transmission electron microscopy (STEM)
• Thermal Gravimetric Analysis (TGA)
• Dynamic light scattering (DLS)
• Differential centrifugal sedimentation
• X-ray photoelectron spectroscopy

By combining the results provided by these techniques, it is possible to achieve superior characterization and understanding of the particle structure than could be obtained by considering results separately.^[87]

References

1. Nanoparticles—a historical perspective
2. Preparation and Characterization of Cross-Linked Polymeric Nanoparticles for Enhanced Oil Recovery Applications (pdf)
3. Polyacrylamide and its deriv ylamide and its derivatives for oil r es for oil recovery (pdf)
4. Nanosizing of drugs: Effect on dissolution rate
5. Development and functional characterization of alginate dressing as potential protein delivery system for wound healing
6. Designing hydrogels for controlled drug delivery (good)
7. Novavax addresses urgent global public health needs with innovative technology
8. How the Novavax Vaccine Works
9. Widder KJ, Senyel AE, Scarpelli GD. Magnetic microspheres: a model system of site specific drug delivery in vivo. Proc Soc Exp Biol Med. 1978;158:141–6.
10. Nuclear molecular imaging with nanoparticles: radiochemistry, applications and translation
11. Methods for Synthesis of Nanoparticles and Fabrication of Nanocomposites
12. NANOPARTICULATE DRUG DELIVERY SYSTEM
13. Switchable Release of Entrapped Nanoparticles from Alginate Hydrogels.[Adv Healthc Mater. 2015]
14. Nanosized cationic hydrogels for drug delivery: preparation, properties and interactions with cells. Vinogradov SV, Bronich TK, Kabanov AV. Adv Drug Deliv Rev. 2002 Jan 17; 54(1):135-47.
15. Applications of Targeted Nano Drugs and Delivery Systems
16. Langer R. Drug delivery and targeting. Nature. 1998;392:5–10.
17. Hoare TR, Kohane DS. Hydrogels in drug delivery: Progress and challenges. Polymer. 2008;49:1993–2007.
18. Liechty WB, Kryscio DR, Slaughter BV, Peppas NA. Polymers for drug delivery systems. Ann Rev Chem Biomol Eng. 2010;1:149–173.
19. Cohen J. IL-12 deaths: explanation and a puzzle. Science. 1995;270:908–908.
20. Florence AT, Jani PU. Novel oral drug formulations. Drug Safety. 1994;10:233–266.
21. Ashley GW, Henise J, Reid R, Santi DV. Hydrogel drug delivery system with predictable and tunable drug release and degradation rates. Proc Natl Acad Sci USA. 2013;110:2318–2323.
22. Tiwari G, et al. Drug delivery systems: An updated review. Int J Pharm Investig. 2012;2:2–11.
23. Tibbitt MW, Dahlman JE, Langer R. Emerging frontiers in drug delivery. J Am Chem Soc.
24. Singh, BN; Prateeksha, Gupta VK; Chen, J; Atanasov, AG (2017). "Organic Nanoparticle-Based Combinatory Approaches for Gene Therapy". Trends Biotechnol. 35 (12): 1121–1124. 2016;138:704–717.
25. Wang, Zhenming; Wang, Zhefeng; Lu, William Weijia; Zhen, Wanxin; Yang, Dazhi; Peng, Songlin (October 2017). "Novel biomaterial strategies for controlled growth factor delivery for biomedical applications"
26. Mitragotri S, Lahann J. Physical approaches to biomaterial design. Nat Mater. 2009;8:15–23.
27. Euliss LE, DuPont JA, Gratton S, DeSimone J. Imparting size, shape, and composition control of materials for nanomedicine. Chem Soc Rev. 2006;35:1095–1104.
28. Gratton SE, et al. The effect of particle design on cellular internalization pathways. Proc Natl Acad Sci USA. 2008;105:11613–11618.
29. Geng H, Song H, Qi J, Cui D. Sustained release of VEGF from PLGA nanoparticles embedded thermo-sensitive hydrogel in full-thickness porcine bladder acellular matrix. Nanoscale Res Lett. 2011;6:1–8.
30. Oh JK, Drumright R, Siegwart DJ, Matyjaszewski K. The development of microgels/nanogels for drug delivery applications. Prog Polym Sci. 2008;33:448–477.
31. Crommelin DJ, Storm G. Liposomes: from the bench to the bed. J Liposome Res. 2003;13:33–6.
32. Metselaar JM, Storm G. Liposomes in the treatment of inflammatory disorders. Expert Opin Drug Deliv. 2005;2:465–76.
33. Noh SY, Nash A, Notman R (2020). "The aggregation of striped nanoparticles in mixed phospholipid bilayers". Nanoscale. 12 (8): 4868–81.
34. Nanotechnologies: 6. What are potential harmful effects of nanoparticles?
35. Thake, T.H.F; Webb, J.R; Nash, A.; Rappoport, J.Z.; Notman, R. (2013). "Permeation of polystyrene nanoparticles across model lipid bilayer membranes". Soft Matter. 9 (43): 10265 10274.
36. Greulich, C.; Diendorf, J.; Simon, T.; Eggeler, G.; Epple, M.; Köller, M. (January 2011). "Uptake and intracellular distribution of silver nanoparticles in human mesenchymal stem cells". Acta Biomaterialia. 7 (1): 347–354.
37. Compartmentalization Technologies via Self-Assembly and Cross-Linking of Amphiphilic Random Block Copolymers in Water
38. Drug delivery and nanoparticles: Applications and hazards (good)
39. The pKa Table Is Your Friend (important)
40. Nanoparticles as a Targeted Drug Delivery System
41. Self-Assembled Hydrogel Nanoparticles for Drug Delivery Applications
42. Gupta M, Gupta AK. In vitro cytotoxicity studies of hydrogel pullulan nanoparticles prepared by AOT/N-hexane micellar system. J Pharm Pharmaceut Sci. 2004;7:38–46.
43. Biocompatibility and drug delivery systems (good)
44. S. R. Little and D. S. Kohane, Polymers for intracellular delivery of nucleic acids, J. Mater. Chem., 2008, 18, 832–841
45. Polymeric Nucleic Acid Delivery for Immunoengineering
46. Dubernet C., Couvreur P. Nanoparticles in cancer therapy and diagnosis. Adv. Drug Delivery Rev. 2002;54:631–651.
47. Panyam J., Labhasetwar V. Biodegradable nanoparticles for drug and gene delivery to cells and tissue. Adv. Drug Delivery Rev. 2003;55:329–347.Moghimi S.M., Hunter A.C., Murray J.C. Long-circulating and target-specific nanoparticles: Theory to practice. Pharmacol. Rev. 2001;53:283–318.
48. Moghimi S.M., Hunter A.C., Murray J.C. Long-circulating and target-specific nanoparticles: Theory to practice. Pharmacol. Rev. 2001;53:283–318.
49. Sun T.-M., Du J.-Z., Yan L.-F., Mao H.-Q., Wang J. Self-assembled biodegradable micellar nanoparticles of amphiphilic and cationic block copolymer for siRNA delivery. Biomaterials. 2008;29:4348–4355.
50. Jain A.K., Goyal A.K., Gupta P.N., Khatri K., Mishra N., Mehta A., Mangal S., Vyas S.P. Synthesis, characterization and evaluation of novel triblock copolymer based nanoparticles for vaccine delivery against hepatitis B. J. Control. Release. 2009;136:161–169.
51. Niidome T, Yamagata M, Okamoto Y, et al. PEG-modified gold nanorods with a stealth character for in vivo applications. J Control Release. 2006;114:343–7.
52. M. Goldberg, R. Langer and X. Jia, Nanostructured materials for applications in drug delivery and tissue engineering, J. Biomater. Sci., Polym. Ed., 2007, 18, 241–268.
53. D. S. Kohane, Microparticles and nanoparticles for drug delivery, Biotechnol. Bioeng., 2007, 96, 203–209
54. What Are Lipid Nanoparticles in mRNA Vaccines?
55. Plard J.P., Bazile D. Comparison of the safety profiles of PLA(50) and Me.PEG-PLA(50) nanoparticles after single dose intravenous administration to rat. Colloids Surf. B. 1999;16:173–183.
56. Peracchia M.T., Fattal E., Desmaele D., Besnard M., Noel J.P., Gomis J.M., Appel M., d'Angelo J., Couvreur P. Stealth PEGylated polycyanoacrylate nanoparticles for intravenous administration and splenic targeting. J. Control. Release. 1999;60:121–128.
57. Matsumura Y., Maeda H. A New Concept for macromolecular therapeutics in cancer chemotherapy: Mechanism of tumoritropic accumulation of proteins and the antitumor agent smancs1. Cancer Res. 1986;46:6387–6392.
58. Brannon-Peppas L., Blanchette J.O. Nanoparticle and targeted systems for cancer therapy. Adv. Drug Delivery Rev. 2004;56:1649–1659.
59. Moghimi S.M., Hunter A.C., Murray J.C. Nanomedicine: Current status and future prospects. FASEB J. 2005;19:311–330.
60. Fang C, Shi B, Pei YY, et al. In vivo tumor targeting of tumor necrosis factor-alpha-loaded stealth nanoparticles: Effect of MePEG molecular weight and particle size. Eur J Pharm Sci. 2006;27:27–36.
61. Shim J, Seok Kang H, Park WS, et al. Transdermal delivery of minoxidil with block copolymer nanoparticles. J Control Release. 2004;97:477–84.
62. Zhang L, Hu Y, Jiang X, et al. Camptothecin derivative-loaded poly(caprolactone-co-lactide)-b-PEG-b-poly(caprolactone-co-lactide) nanoparticles and their biodistribution in mice. J Control Release. 2004;96:135–48.
63. A programmable chemical switch based on triggerable Michael acceptors
64. SELF-IMMOLATIVE CHEMISTRY: Structural Features and Applications in Designing Smart Materials (pdf)
65. Measuring particle size distribution of nanoparticle enabled medicinal products, the joint view of EUNCL and NCI-NCL. A step by step approach combining orthogonal measurements with increasing complexity
66. D’Mello SR, Cruz CN, Chen ML, Kapoor M, Lee SL, Tyner KM. The evolving landscape of drug products containing nanomaterials in the United States. Nat. Nanotechnol. 12(6), 523–529 (2017).
67. US FDA. Guidance Document: Drug Products, Including Biological Products, that Contain Nanomaterials – Guidance for Industry.
68. EMA. Development of Block-Copolymer-Micelle Medicinal Products (Reference Number EMA/CHMP/130299/2013).
69. EMA (Committee for Medicinal Products for Human Use). Reflection Paper on the Data Requirements for Intravenous Iron-Based Nano-Colloidal Products Developed with Reference to an Innovator Medicinal Product (2012).
70. Committee for Human Medicinal Products. Reflection Paper on the Data Requirements for Intravenous Liposomal Products Developed with Reference to Aninnovator Liposomal Product (2013).
71. US FDA. Liposome Drug Products: Chemistry, Manufacturing, and Controls; Human Pharmacokinetics and Bioavailability; and Labeling Documentation (2018).
72. Nano-enabled medicinal products: time for an international advanced community?
73. El-Sayed, M. A. Some interesting properties of metals confined in time and nanometer space of different shapes. Accounts Chem. Res. 34, 257–264 (2001).
74. Trindade, T., O'Brien, P. & Pickett, N. L. Nanocrystalline semiconductors: synthesis, properties and perspectives. Chem. Mater. 13, 3843–3858 (2001).
75. Kelly, K. L., Coronado, E., Zhao, L. L. & Schatz, G. C. The optical properties of metal nanoparticles: the influence of size, shape, and dielectric environment. J. Phys. Chem. B. 107, 668–677 (2003).
76. Seo, W. S. et al. Size-dependent magnetic properties of colloidal Mn3O4 and MnO nanoparticles. Angew. Chem. Int. Ed. 43, 1115–1117 (2004).
77. Mohanty, A., Garg, N. & Jin, R. A universal approach to the synthesis of noble metal nanodendrites and their catalytic properties. Angew. Chem. Int. Ed. 49, 4962–4966 (2010).
78. Rao, C. N. R., Kulkarni, G. U., Thomas, P. J. & Edwards, P. P. Size-dependent chemistry: properties of nanocrystals. Chem. Eur. J. 8, 29–35 (2002).
79. Boal, A. K. et al. Self-assembly of nanoparticles into structured spherical and network aggregates. Nature 404, 746–748 (2000).
80. Li, P., Kaslan, M., Lee, S. H., Yao, J. & Gao, Z. Progress in exosome isolation techniques. Theranostics 7, 789 (2017).
81. Lane, R. E., Korbie, D., Anderson, W., Vaidyanathan, R. & Trau, M. Analysis of exosome purification methods using a model liposome system and tunable-resistive pulse sensing. Sci. Rep. 5, 7639 (2015).
82. Batrakova, E. V. & Kim, M. S. Using exosomes, naturally-equipped nanocarriers, for drug delivery. J. Control. Rel. 219, 396–405 (2015).
83. Prime, KL; Whitesides, GM (1991). "Self-assembled organic monolayers: model systems for studying adsorption of proteins at surfaces". Science. 252 (5009): 1164–7.
84. Liu, Wenhao; Greytak, Andrew B.; Lee, Jungmin; Wong, Cliff R.; Park, Jongnam; Marshall, Lisa F.; Jiang, Wen; Curtin, Peter N.; Ting, Alice Y.; Nocera, Daniel G.; Fukumura, Dai; Jain, Rakesh K.; Bawendi, Moungi G. (20 January 2010). "Compact Biocompatible Quantum Dots via RAFT-Mediated Synthesis of Imidazole-Based Random Copolymer Ligand". Journal of the American Chemical Society. 132 (2): 472–483.
85. Gupta AK, Gupta M. Synthesis and surface engineering of iron oxide nanoparticles for biomedical applications. Biomaterials. 2005;26:3995–4021.
86. "Nanoparticles play at being red blood cells". Archived from the original on 1 July 2011. Retrieved 1 July 2011.
87. Surface-Energy Control and Characterization of Nanoparticle Coatings
88. Core–shell nanostructures: perspectives towards drug delivery applications
89. Anton Paar. (n.d.) Faster, More Sensitive Zeta-Potential Measurements with cmPALS and the Litesizer™ 500. [January 24 2019]. Bellmann, C., Caspari, A., Moitzi, C., Fradler, C., Babick, F. (2018) DLS & ELS Guide. Luxbacher, T. (2014)
90. Cancer Cell Membrane-Coated Nanoparticles for Anticancer Vaccination and Drug Delivery