Editors' ChoiceBioengineering

Building Inner Strength

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Science Translational Medicine  11 Dec 2013:
Vol. 5, Issue 215, pp. 215ec204
DOI: 10.1126/scitranslmed.3008078

Microneedles are a promising modality of transdermal drug delivery because they promise less pain, better user safety and patient compliance, as well as the ability to target specific layers of skin. Dissolvable microneedle patches offer even better user safety and patient compliance because the device can be applied to deliver drugs or biomolecules with no subsequent patch removal or sharps disposal required. One factor that limits the use of dissolvable microneedles is the weak mechanical properties of the polymers that are used to fabricate them. Using heat or ultraviolet treatment to increase the strength of these microneedles can limit the loading of drugs and biomolecules and impair the rate at which the devices dissolve. Yan and colleagues have now demonstrated that reinforcement of room-temperature fabricated microneedles with nanoparticles can confer robust mechanical properties to a previously weak device without adversely affecting drug delivery and dissolving rate. Thus, this approach can help make more clinically relevant dissolvable microneedle devices a reality.

In order to strengthen dissolvable microneedles, layered double hydroxide (LDH) nanoparticles were incorporated into carboxymethylcellulose (CMC) polymer to create a nanoparticle-reinforced polymer (LDH-CMC) that had almost three times the elastic modulus and almost double the hardness of unmodified CMC. Microneedles made from LDH-CMC were capable of more uniform and deeper deposition of payload as compared to that of pure CMC microneedles when evaluated on pig and human skin. Furthermore, nanoparticle-reinforced microneedle delivery of ovalbumin (OVA) in mice elicited a stronger immune response than that of either subcutaneous injection or pure CMC microneedle delivery of OVA, while using 83.5% less antigen than does either subcutaneous or pure CMC microneedle delivery. Most importantly, the addition of LDH did not adversely affect CMC-based microneedle dissolving time of less than 1 minute.

Although preclinical data in mice suggest that LDH nanoparticles are biocompatible, further safety evaluations will be needed before LDH-CMC nanocomposite microneedles can be tested in the clinic. The work shown here, however, demonstrates the validity of this approach to strengthening dissolvable microneedles while retaining many of the properties that make them such an attractive drug delivery method.

L. Yan et al., Nanocomposite-strengthened dissolving microneedles for improved transdermal delivery to human skin. Adv. Healthc. Mater., published online 30 October 2013 (10.1002/adhm.201300312). [Abstract]

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