In recent years, stimulus-sensitive drug delivery systems have been developed for parenteral administration as a depot system. In situ systems incorporate smart polymers that undergo a phase transition at the site of administration. All parenteral and ocular dosage forms must meet sterility requirements. Careful selection of the sterilization method is required for any type of stimuli-sensitive system. Current sterilization methods are capable of altering the conformation of polymers or APIs to a certain extent, ultimately causing the loss of pharmacological and technological properties of the drug. Unfortunately, the issues of risk assessment and resolution regarding the sterilization of stimuli-sensitive systems, along with ways to stabilize such compositions, are insufficiently described in the scientific literature to date. This review provides recommendations and approaches, formulated on the basis of published experimental data, that allow the effective management of risks arising during the development of in situ systems requiring sterility.

Stimuli-sensitive (in situ) drug delivery systems are a dynamically developing area of pharmaceutical research. Over the past decade, the number of studies on such systems has doubled. Among these, phase-inversion (or phase-sensitive) formulations, which were among the earliest proposed, offer significant advantages, including enhanced stability and stimuli-responsiveness. However, phase-inversion systems have remained relatively understudied. Despite the existence of three patented technologies (Atrigel^®, BEPO^®, FluidCrystal^®) for delivery systems utilizing phase inversion for various routes of administration, the absence of unified approaches to development and standardization has significantly impeded the introduction of novel, effective drugs into clinical practice. This review examined the main polymers and solvents used to create phase-inversion compositions and discussed the feasibility of introducing other excipients to modify the systems’ physicochemical properties. The most commonly used polymers included polylactide-co-glycolide, shellac, and polylactic acid. The most frequently used solvents were N-methylpyrrolidone and dimethyl sulfoxide. Following an analysis of clinical studies of phase-sensitive drugs conducted over the past 25 years, as well as original research indexed in PubMed, ScienceDirect, and Google Scholar, the main problems hindering the broader adoption of phase-inversion systems in clinical practice were identified, and recommendations for further development in this promising area were provided.

Due to their excellent mechanical properties and good biocompatibility, titanium (Ti) and its alloys are widely used as biomaterials. However, when implanted in the body, metallic materials may cause serious complications such as wear and infection, leading to patient discomfort and, in some cases, the need for revision surgery. Micro-arc oxidation (MAO) is a surface modification technique that offers a promising strategy to overcome these challenges. This study investigated the impact of the microstructure of Ti-25 Ta-xNb alloys (x = 10, 20, and 30 wt%) and the variation in applied voltage during the MAO process on the characteristics of the TiO₂ oxide coatings formed. The alloys were treated by MAO at 200, 250, and 300 V using a bioactive electrolyte containing Ca, P, Mg, and Ag. EDS, SEM, XRD, Raman spectroscopy, and adhesion tests performed characterization. Results indicated that Nb addition stabilized the β phase and anticipated the potentiostatic regime. Increasing the voltage supplied to the system provides greater energy, prolonging the galvanostatic regime and promoting the formation of larger and more uniform pores. The oxide coating thickness ranged from approximately 3 to 10 μm, with a tendency to decrease at higher voltages. The coatings exhibited low c, with anatase and rutile phases predominating, the applied voltage and Nb concentration influencing their relative proportions. Even in small amounts, all electrolyte elements (P, Mg, and Ag) were successfully incorporated into the coatings under all conditions. Raman and XRD analyses confirmed a decrease in anatase and an increase in rutile phases with increasing voltage and Nb content. Mechanical testing revealed good adhesion of the coatings in all samples, with the best results obtained at 200 V. The findings demonstrate that the developed coatings exhibit promising characteristics for future surface engineering strategies aimed at improving the performance of metallic biomaterials.

In the biodegradable metal class, Mg-based alloys are considered the most promising candidates for temporary implant manufacture. However, their high corrosion rate in physiological media is considered a main drawback for clinical translation. Conversion coatings address the limitations of Mg-based alloys and provide a strategy to control corrosion and improve surface biocompatibility. In this review paper, a detailed analysis of various conversion coating techniques, including ceramic conversion coatings based on metals, polymeric conversion coatings, bioactive conversion coatings, and hybrid conversion coatings, is performed. Attention is devoted to the corrosion process and parameters, as well as to the biological response in relation to bioactivity or biocompatibility. The main angiogenic and osteogenic signaling pathways are described based on the analyzed conversion coatings, and the evolution of the cellular response is estimated. Although significant progress has been made in the field, there are still challenges associated with synchronizing Mg alloy degradation with new bone formation and with precisely guiding cell signaling responses to achieve a desired biological response. An overall conclusion of the paper consists of the fact that conversion coatings are an important topic, as they can enhance the surface of Mg-based alloys, making them prone to clinical translation.