Characterization of drug delivery vehicles using atomic force microscopy: current status

ABSTRACT

Introduction: The field of nanomedicine, utilizing nano-sized vehicles (nanoparticles and nanofibers) for targeted local drug delivery, has a promising future. This is dependent on the ability to analyze the chemical and physical properties of these drug carriers at the nanoscale and hence atomic force microscopy (AFM), a high-resolution imaging and local force-measurement technique, is ideally suited.

Areas covered: Following a brief introduction to the technique, the review describes how AFM has been used in selected publications from 2015 to 2018 to characterize nanoparticles and nanofibers as drug delivery vehicles. These sections are ordered into areas of increasing AFM complexity: imaging/particle sizing, surface roughness/quantitative analysis of images, and analysis of force curves (to extract nanoindentation and adhesion data).

Expert opinion: AFM imaging/sizing is used extensively for the characterization of nanoparticle and nanofiber drug delivery vehicles, with surface roughness and nanomechanical/adhesion data acquisition being less common. The field is progressing into combining AFM with other techniques, notably SEM, ToF-SIMS, Raman, Confocal, and UV. Current limitations include a 50 nm resolution limit of nanoparticles imaged within live cells and AFM tip-induced activation of cytoskeleton proteins. Following drug release real-time with AFM-spectroscopic techniques and studying drug interactions on cell receptors appear to be on the horizon.

KEYWORDS:

• Atomic force microscopy
• AFM
• drug delivery
• drug delivery vehicles
• review

Article highlights

• Atomic force microscopy (AFM), a high-resolution imaging and local force measurement technique, is becoming increasing established as a tool for characterizing drug delivery vehicles.

• The majority of AFM studies of nanoparticles and nanofibers are focused on imaging and particle sizing, the latter of which is in close-agreement with measurements obtained from dynamic light scattering and electron microscopy.

• Surface roughness and data have been obtained from AFM images of nano-sized drug delivery systems; the acquisition of nanomechanical properties (nanoindentation and adhesion) from AFM force curves of such systems have also been reported, although to a lesser extent.

• The field is progressing into combining AFM with other techniques (such as SEM, ToF-SIMS, Raman, Confocal, and UV). Many of these promise the potential to follow drug release real-time and for studying drug interactions on cell receptors.

This box summarizes key points contained in the article.

Declaration of interest

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Additional information

Funding

This paper was not funded.