Silk microneedles deliver controlled-release drugs painlessly

December 21, 2011

MEDFORD/SOMERVILLE, Mass. -- Bioengineers at Tufts University School of Engineering have developed a new silk-based microneedle system able to deliver precise amounts of drugs over time and without need for refrigeration. The tiny needles can be fabricated under normal temperature and pressure and from water, so they can be loaded with sensitive biochemical compounds and maintain their activity prior to use. They are also biodegradable and biocompatible.

The research paper "Fabrication of Silk Microneedles for Controlled-Release Drug Delivery" appeared in Advanced Functional Materials December 2 online in advance of print.

The Tufts researchers successfully demonstrated the ability of the silk microneedles to deliver a large-molecule, enzymatic model drug, horseradish peroxidase (HRP), at controlled rates while maintaining bioactivity. In addition, silk microneedles loaded with tetracycline were found to inhibit the growth of Staphylococcus aureus, demonstrating the potential of the microneedles to prevent local infections while also delivering therapeutics.

"By adjusting the post-processing conditions of the silk protein and varying the drying time of the silk protein, we were able to precisely control the drug release rates in laboratory experiments," said Fiorenzo Omenetto, Ph.D., senior author on the paper. "The new system addresses long-standing drug delivery challenges, and we believe that the technology could also be applied to other biological storage applications."

The Drug Delivery Dilemma

While some drugs can be swallowed, others can't survive the gastrointestinal tract. Hypodermic injections can be painful and don't allow a slow release of medication. Only a limited number of small-molecule drugs can be transmitted through transdermal patches. Microneedles--no more than a micron in size and able to penetrate the upper layer of the skin without reaching nerves--are emerging as a painless new drug delivery mechanism. But their development has been limited by constraints ranging from harsh manufacturing requirements that destroy sensitive biochemicals, to the inability to precisely control drug release or deliver sufficient drug volume, to problems with infections due to the small skin punctures.

The process developed by the Tufts bioengineers addresses all of these limitations. The process involves ambient pressure and temperature and aqueous processing. Aluminum microneedle molding masters were fabricated into needle arrays of about 500 μm needle height and tip radii of less than 10 μm. The elastomer polydimethylsiloxane (PDMS) was cast over the master to create a negative mold; a drug-loaded silk protein solution was then cast over the mold. When the silk was dry, the drug-impregnated silk microneedles were removed. Further processing through water vapor annealing and various temperature, mechanical and electronic exposures provided control over the diffusity of the silk microneedles and drug release kinetics.

"Changing the structure of the secondary silk protein enables us to 'pre-program' the properties of the microneedles with great precision," said David L. Kaplan, Ph.D., coauthor of the study, chair of biomedical engineering at Tufts and a leading researcher on silk and other novel biomaterials. "This is a very flexible technology that can be scaled up or down, shipped and stored without refrigeration and administered as easily as a patch or bandage. We believe the potential is enormous."
-end-
Other co-authors on the paper, all associated with the Department of Biomedical Engineering, are Konstantinos Tsioris, doctoral student; Waseem Raja, post-doctoral associate; Eleanor Pritchard, post-doctoral associate; and Bruce Panilaitis, research assistant professor.

The research was based on work supported in part by the U.S. Army Research Laboratory, the U.S. Army Research Office, the Defense Advanced Research Projects Agency-Defense Sciences Office and the Air Force Office of Scientific Research.

Tsioris, K., Raja, W. K., Pritchard, E. M., Panilaitis, B., Kaplan, D. L. and Omenetto, F. G. (2011), Fabrication of Silk Microneedles for Controlled-Release Drug Delivery. Advanced Functional Materials. doi: 10.1002/adfm.201102012

Located on Tufts' Medford/Somerville campus, the School of Engineering offers a rigorous engineering education in a unique environment that blends the intellectual and technological resources of a world-class research university with the strengths of a top-ranked liberal arts college. Close partnerships with Tufts' undergraduate, graduate and professional schools, coupled with a long tradition of collaboration, provide a strong platform for interdisciplinary education and scholarship. The School of Engineering's mission is to educate engineers committed to the innovative and ethical application of science and technology in addressing the most pressing societal needs, to develop and nurture twenty-first century leadership qualities in its students, faculty, and alumni, and to create and disseminate transformational new knowledge and technologies that further the well-being and sustainability of society in such cross-cutting areas as human health, environmental sustainability, alternative energy, and the human-technology interface.

Tufts University

Related Engineering Articles from Brightsurf:

Re-engineering antibodies for COVID-19
Catholic University of America researcher uses 'in silico' analysis to fast-track passive immunity

Next frontier in bacterial engineering
A new technique overcomes a serious hurdle in the field of bacterial design and engineering.

COVID-19 and the role of tissue engineering
Tissue engineering has a unique set of tools and technologies for developing preventive strategies, diagnostics, and treatments that can play an important role during the ongoing COVID-19 pandemic.

Engineering the meniscus
Damage to the meniscus is common, but there remains an unmet need for improved restorative therapies that can overcome poor healing in the avascular regions.

Artificially engineering the intestine
Short bowel syndrome is a debilitating condition with few treatment options, and these treatments have limited efficacy.

Reverse engineering the fireworks of life
An interdisciplinary team of Princeton researchers has successfully reverse engineered the components and sequence of events that lead to microtubule branching.

New method for engineering metabolic pathways
Two approaches provide a faster way to create enzymes and analyze their reactions, leading to the design of more complex molecules.

Engineering for high-speed devices
A research team from the University of Delaware has developed cutting-edge technology for photonics devices that could enable faster communications between phones and computers.

Breakthrough in blood vessel engineering
Growing functional blood vessel networks is no easy task. Previously, other groups have made networks that span millimeters in size.

Next-gen batteries possible with new engineering approach
Dramatically longer-lasting, faster-charging and safer lithium metal batteries may be possible, according to Penn State research, recently published in Nature Energy.

Read More: Engineering News and Engineering Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.