Physicochemical Characterization

One of the major criticisms of early biomedical nanotechnology research was the general lack of physicochemical characterization that did not allow for the meaningful interpretation of resulting data or inter-laboratory comparisons. Traditional small molecule drugs are characterized by data that contribute to the chemistry, manufacturing and controls (CMC) section of the investigational new drug (IND) application with Food and Drug Administration (FDA), which include their molecular weight, chemical composition, identity, purity, solubility, and stability. The instrumentation to ascertain these properties has been well established, and the techniques are standardized. Engineered nanomaterials have dimensions between small molecules and bulk materials and often exhibit different physical and chemical properties than their counterparts. These physical and chemical

Physical

Characterization:

Size

Shape

Composition

Molecular weight

Surface chemistry

Identity

Purity

Stability

Solubility

In Vitro:

Pharmacology

Blood contact properties

Effects on immune cell function

Cytotoxicity

Mechanistic toxicology

Sterility

ADME Safety Efficacy

In Vivo:

FIGURE 7.1 An assay cascade for preclinical characterization of nanomaterials.

properties influence the biological activity of nanoparticles and may depend on parameters such as particle size, size distribution, surface area, surface charge, surface functionality, shape, and aggregation state. Additionally, because most nanoparticle concepts are multifunctional, the distribution of targeting, imaging, and therapeutic components can also have dramatic effects on nanoparticle biological activity. There is a need to establish and standardize techniques to define these nanoparticle attributes.

There is now ample evidence that size and surface characteristics can dramatically affect nanoparticle behavior in biological systems.1-4 For instance, a decrease in particle size leads to an exponential increase in surface area per unit mass, and an attendant increase in the availability of reactive groups on the surface. Nanoparticles with cationic surface character have a notably increased ability to cross the blood-brain barrier compared to nanoparticles with anionic surfaces.5 In general, surface area, rather than mass, provides a better fit of dose-response relationships in toxicity studies for particles of various sizes.6,7 Physicochemical characterization of properties, such as size, surface area, surface chemistry, and aggregation/agglomeration state, can provide the basis for better understanding of SARs.

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