Abstract
This work demonstrates a simple approach for coating a porous polymer layer on stainless-steel (SS) microneedles characterized by a pH-responsive formulation for self-regulated drug delivery. For many drug-delivery applications, the release of therapeutic agents in an acidic microenvironment is desirable. Acid-sensitive polymers and hydrogels were extensively explored, but easily prepared polymeric microcarriers that combine acid sensitivity and biodegradability are rare. Here, we describe a simple and robust method of coating a porous polymer layer on SS microneedles (MNs) that release a model drug (lidocaine) in a pH-responsive fashion. It was constructed by packing the model drug and a pH-sensitive component (sodium bicarbonate) into the pores of the polymer layer. When this acid-sensitive formulation was exposed to the acidic microenvironment, the consequent reaction of protons (H+) with sodium bicarbonate (NaHCO3) yielded CO2. This effect generated pressure inside the pores of the coating and ruptured the thin polymer membrane, thereby releasing the encapsulated drug. Scanning electron micrographs showed that the pH-sensitive porous polymer-coated MNs exposed to phosphate-buffered saline (PBS) at pH 7.4 were characterized by closed pores. However, MNs exposed to PBS at pH 5.5 consisted of open pores and the thin membrane burst. The in vitro studies demonstrated the pH sensitivity of the drug release from porous polymer-coated MNs. Negligible release was observed for MNs in receiving media at pH 7.4. In contrast, significant release occurred when the MNs were exposed to acidic conditions (pH 5.5). Additionally, comparable results were obtained for drug release in vitro in porcine skin and in PBS. This revealed that our developed pH-responsive porous polymer-coated MNs could potentially be used for the controlled release of drug formulations in an acidic environment. Moreover, the stimuli-responsive drug carriers will enable on-demand controlled release profiles that may enhance therapeutic effectiveness and reduce systemic toxicity.
Highlights
Transdermal drug administration has the potential to improve therapeutic delivery, providing an approach that is safer and more convenient than traditional routes, such as oral administration and hypodermic injection
Scanning electron micrographs showed that the pH-sensitive porous polymer-coated MNs exposed to phosphate-buffered saline (PBS) at pH 7.4 were characterized by closed pores
Transcutaneous delivery systems may minimize the generation of dangerous medical waste and restrain the spread of disease known to occur through needle reuse and needle-based injury [5,6]
Summary
Transdermal drug administration has the potential to improve therapeutic delivery, providing an approach that is safer and more convenient than traditional routes, such as oral administration and hypodermic injection. This method offers the opportunity for improved therapeutic effectiveness through sustained and controlled drug release [1]. Compared with more traditional routes, transdermal drug delivery has the potential to provide many practical and clinical advantages [2]. Transdermal delivery is non-invasive, potentially allowing for rapid, pain-free administration either by minimally trained healthcare providers or through self-administration [3,4].
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