Glaucoma is considered to be one of the biggest health problems in the world. It is the main cause of preventable blindness due to its asymptomatic nature in the early stages on the one hand and patients’ non-adherence on the other. There are several approaches in glaucoma treatment, whereby this has to be individually designed for each patient. The first-line treatment is medication therapy. However, taking into account numerous disadvantages of conventional ophthalmic dosage forms, intensive work has been carried out on the development of novel drug delivery systems for glaucoma. This review aims to provide an overview of formulation solutions and strategies in the development of in situ gel systems, nanosystems, ocular inserts, contact lenses, collagen corneal shields, ocular implants, microneedles, and iontophoretic devices. The results of studies confirming the effectiveness of the aforementioned drug delivery systems were also briefly presented.

Many different and innovative approaches have been investigated to reduce the barrier effects of the stratum corneum (SC) and one of those are microneedles. Microneedles (MNs) are micron-sized needles which assist drug delivery through skin by creating microchannels (micron-scale pores) in SC that are large enough to enable drugs, including macromolecules, to enter the skin while being small enough to avoid pain, irritation and needle phobia. They have the capacity to play a role in modern healthcare as they reduce pain, tissue damage and transmission of infection and have potential for selfadministration in comparison to traditional needles. MNs have been fabricated by a variety of methods, from a range of materials (including silicon, glass, metal, carbohydrates and polymers) and in varying geometries (Quinn et al., 2014). Additive manufacturing (AM), more commonly known as three-dimensional (3D) printing represents a new, cutting-edge technology of 3D objects fabricated from a digital model generated using computer-aided design (CAD) software by fusing or depositing proper material (e.g., ceramics, liquids, metal, plastic, powders or even living cells) in layers. Suitable thermoplastic material in the form of a filament is fed into the printer by rollers, where it is heated to just above its softening point (glass transition temperature, Tg) by heating elements into a molten state. The melted or softened material guided by gears is moved towards heat end where it is extruded from the printer’s head, through a nozzle and subsequently deposited layer-by-layer on a build plate, cooling and solidifying in under a second. The printer’s head moves within the xand y-axes, whereas the platform can move within the z-axis, thus creating 3D structures (Alhnan et al., 2016; Goole and Amighi, 2016; Jamróz, 2018; Prased and Smyth, 2016). The aim of this work was to fabricate biodegradable PLA microneedles using innovative FDM 3D-printing technology on two different 3D printers and then chemically etch their arrays to obtain ideally sized and shaped needles.

Although transdermal drug delivery systems (DDS) offer numerous benefits for patients, including the avoidance of both gastric irritation and first-pass metabolism effect, as well as improved patient compliance, only a limited number of active pharmaceutical ingredients (APIs) can be delivered accordingly. Microneedles (MNs) represent one of the most promising concepts for effective transdermal drug delivery that penetrate the protective skin barrier in a minimally invasive and painless manner. The first MNs were produced in the 90s, and since then, this field has been continually evolving. Therefore, different manufacturing methods, not only for MNs but also MN molds, are introduced, which allows for the cost-effective production of MNs for drug and vaccine delivery and even diagnostic/monitoring purposes. The focus of this review is to give a brief overview of MN characteristics, material composition, as well as the production and commercial development of MN-based systems.