Microneedle drug delivery carriers capable of achieving sustained and controlled release function.

Traditional injection methods such as subcutaneous (SC) and intramuscular (IM) injections are commonly used in clinical settings for their rapid therapeutic effects. However, these methods can cause additional pain to patients and may lead to infections and nerve damage. Oral administration and other forms of drug delivery are susceptible to the first-pass effect, resulting in low bioavailability and systemic side effects. In recent years, with the advancement of material and computer sciences, a novel drug delivery method known as microneedles has emerged. Microneedle drug delivery systems combine the efficiency of traditional injections with the safety of transdermal absorption, representing a new type of transdermal drug delivery systems (TDDs) formulation. Among these, microneedles with sustained and controlled release characteristics have garnered significant attention from researchers, as they facilitate optimal therapeutic effects, reduce the frequency of drug administration, enhance patient compliance, and minimize the toxic side effects of drugs. The application sites for microneedles are diverse and not limited to skin tissue. The controlled release characteristics of drugs can be easily manipulated. For instance, in hydrogel microneedles, this can be achieved by increasing the cross-linking degree of the hydrogel or by chemically modifying the polymers. This article provides a detailed description of the drug release mechanisms of sustained and controlled release microneedles, the impact of different materials on their release properties, recent research progress and application fields of sustained and controlled release microneedles, as well as their future prospects and challenges.