Fabrication of gradient porous microneedle array by modified hot embossing for transdermal drug delivery

Zero-order drug delivery: State of the art and future prospects

Pharmaceutical drugs are an important part of the global healthcare system, with some estimates suggesting over 50% of the world's population takes at least one medication per day. Most drugs are delivered as immediate-release formulations that lead to a rapid increase in systemic drug concentration. Although these formulations have historically played an important role, they can be limited by poor patient compliance, adverse side effects, low bioavailability, or undesirable pharmacokinetics. Drug delivery systems featuring first-order release kinetics have been able to improve pharmacokinetics but are not ideal for drugs with short biological half-lives or small therapeutic windows. Zero-order drug delivery systems have the potential to overcome the issues facing immediate-release and first-order systems by releasing drug at a constant rate, thereby maintaining drug concentrations within the therapeutic window for an extended period of time. This release profile can be used to limit adverse side effects, reduce dosing frequency, and potentially improve patient compliance. This review covers strategies being employed to attain zero-order release or alter traditionally first-order release kinetics to achieve more consistent release before discussing opportunities for improving device performance based on emerging materials and fabrication methods.

Noninvasive transdermal delivery of liposomes by weak electric current

Noninvasive transdermal drug delivery (NTDD) offers an exciting new method of administration relative to conventional routes, but is associated with some challenges. Liposomes are capable of encapsulating transdermally-unfavorable drugs. However, the horny layer of skin is a significant barrier that limits efficient transdermal delivery of liposomes. Iontophoresis using weak electric current (WEC) represents a NTDD technology. WEC treatment of liposomes applied to the skin surface improves transdermal penetration of encapsulated drugs by cooperative effects. In this review, we provide an overview of the application of WEC/liposomes for transdermal delivery of macromolecules and low molecular weight drugs. We compare the transdermal delivery and therapeutic efficiency of the combined system with conventional routes of administration and their individual use. We discuss a novel perspective on the mechanism of WEC-mediated transdermal delivery of liposomes, which suggests that WEC activates the intracellular signaling pathway for transdermal permeation and induces unique endocytosis in skin cells.

3D-MID Technology for Surface Modification of Polymer-Based Composites: A Comprehensive Review

The three-dimensional molded interconnected device (3D-MID) has received considerable attention because of the growing demand for greater functionality and miniaturization of electronic parts. Polymer based composite are the primary choice to be used as substrate. These materials enable flexibility in production from macro to micro-MID products, high fracture toughness when subjected to mechanical loading, and they are lightweight. This survey proposes a detailed review of different types of 3D-MID modules, also presents the requirement criteria for manufacture a polymer substrate and the main surface modification techniques used to enhance the polymer substrate. The findings presented here allow to fundamentally understand the concept of 3D-MID, which can be used to manufacture a novel polymer composite substrate.

Development of an Electromagnetic Actuator for the Hot-Embossing Process

Hot embossing is in the spotlight due to the development of electronic devices, wearable devices, microfluidic channels, and optical devices. The conventional hot-embossing process creates a pattern on polymer film by using a previously patterned stamp that applied heat and pressure. This method has a disadvantage because it depends on the shape of the patterned stamp. For this reason, this method requires a high cost and a lot of time when replacing the stamp for making a new pattern shape or for modifying the error of the pattern. To solve this problem, the impact print-type hot-embossing method was proposed to create arbitrary patterns, and equipment for this method was assembled. In addition, patterning experiments were conducted to imprint several tens of micrometer-sized patterns in real time. For this method, we proposed an electromagnetic actuator for making the hot-embossing print type and for reducing the size of the actuator compared to previous studies. Through the patterning experiment, we determined that the proposed device could engrave fine dot patterns ranging from 60 μm to 120 μm in diameter. We verified the size of the generated pattern by using a confocal microscope, and we found the proposed hot-embossing technology can realize the desired shape in any position by using the proposed technique.

Fabrication of Tip-Hollow and Tip-Dissolvable Microneedle Arrays for Transdermal Drug Delivery

We developed a modified micromolding method for the mass production of a novel tip-hollow microneedle array (MA). The tip-hollow MA was fabricated by tuning of the vacuum degree at -80 kPa for 60 s during the micromolding process. Subsequently, a tip-dissolvable MA encapsulated with drugs in the microcraters was fabricated from tip-hollow MA using repeated dipping and the freeze-drying process. Both the tip-hollow and tip-dissolvable MAs could easily penetrate in the rabbit skin without breakage, while the tip-hollow MA can just create a shallow loop hole in the skin. The drug-loaded tip-dissolvable MA can rapidly dissolve, releasing and diffusing the drug in the skin. The tip-dissolvable MA exhibited the best drug permeation ability in that the corresponding flux through the punctured skin using tip-dissolvable MA loaded with Rhodamine B is about 1.7- and 5.8-fold of that through the punctured skin using solid MA and the intact skin, respectively. The tip-dissolvable MA loaded with 5 IU insulin was fabricated to in vivo treat the type 1 diabetic SD rats. The tip-dissolvable MA had a good hypoglycemic effect and exhibited longer normoglycemic period in comparison with subcutaneous injection (5 IU). Therefore, our tip-dissolve MA is a promising medical device for transdermal drug delivery.

Engineering Microneedles for Therapy and Diagnosis: A Survey

Microneedle (MN) technology is a rising star in the point-of-care (POC) field, which has gained increasing attention from scientists and clinics. MN-based POC devices show great potential for detecting various analytes of clinical interests and transdermal drug delivery in a minimally invasive manner owing to MNs' micro-size sharp tips and ease of use. This review aims to go through the recent achievements in MN-based devices by investigating the selection of materials, fabrication techniques, classification, and application, respectively. We further highlight critical aspects of MN platforms for transdermal biofluids extraction, diagnosis, and drug delivery assisted disease therapy. Moreover, multifunctional MNs for stimulus-responsive drug delivery systems were discussed, which show incredible potential for accurate and efficient disease treatment in dynamic environments for a long period of time. In addition, we also discuss the remaining challenges and emerging trend of MN-based POC devices from the bench to the bedside.

Smart Microneedles for Therapy and Diagnosis

Microneedles represent a cutting-edge and idea-inspiring technology in biomedical engineering, which have attracted increasing attention of scientific researchers and medical staffs. Over the past decades, numerous great achievements have been made. The fabrication process of microneedles has been simplified and becomes more precise, easy-to-operate, and reusable. Besides, microneedles with various features have been developed and the microneedle materials have greatly expanded. In recent years, efforts have been focused on generating smart microneedles by endowing them with intriguing functions such as adhesion ability, responsiveness, and controllable drug release. Such improvements enable the microneedles to take an important step in practical applications including household drug delivery devices, wearable biosensors, biomedical assays, cell culture, and microfluidic chip analysis. In this review, the fabrication strategies, distinctive properties, and typical applications of the smart microneedles are discussed. Recent accomplishments, remaining challenges, and future prospects are also presented.

Microneedle System for Transdermal Drug and Vaccine Delivery: Devices, Safety, and Prospects

Microneedle (MN) delivery system has been greatly developed to deliver drugs into the skin painlessly, noninvasively, and safety. In the past several decades, various types of MNs have been developed by the newer producing techniques. Briefly, as for the morphologically, MNs can be classified into solid, coated, dissolved, and hollow MN, based on the transdermal drug delivery methods of "poke and patch," "coat and poke," "poke and release," and "poke and flow," respectively. Microneedles also have other characteristics based on the materials and structures. In addition, various manufacturing techniques have been well-developed based on the materials. In this review, the materials, structures, morphologies, and fabricating methods of MNs are summarized. A separate part of the review is used to illustrate the application of MNs to deliver vaccine, insulin, lidocaine, aspirin, and other drugs. Finally, the review ends up with a perspective on the challenges in research and development of MNs, envisioning the future development of MNs as the next generation of drug delivery system.