Bioreactors are important inevitable part of any tissue engineering (TE) strategy as they aid the construction of three-dimensional functional tissues. Since the ultimate aim of a bioreactor is to create a biological product, the engineering parameters, for example, internal and external mass transfer, fluid velocity, shear stress, electrical current distribution, and so forth, are worth to be thoroughly investigated. The effects of such engineering parameters on biological cultures have been addressed in only a few preceding studies. Furthermore, it would be highly inefficient to determine the optimal engineering parameters by trial and error method. A solution is provided by emerging modeling and computational tools and by analyzing oxygen, carbon dioxide, and nutrient and metabolism waste material transports, which can simulate and predict the experimental results. Discovering the optimal engineering parameters is crucial not only to reduce the cost and time of experiments, but also to enhance efficacy and functionality of the tissue construct. This review intends to provide an inclusive package of the engineering parameters together with their calculation procedure in addition to the modeling techniques in TE bioreactors.

Intravaginal rings (IVRs) are minimally invasive polymeric devices specifically designed to be used for the sustained and prolonged release of various type of drugs such as hormones. One of the benefits of using topical drug delivery systems (e.g., IVRs) is the fact that systemic drug delivery may cause drug resistance due to elevated drug levels. Topical drug delivery also provides higher concentrations of the drug to the target site and has fewer side effects. In addition, when a drug is administered vaginally, the hepatic first-pass effect is avoided, resulting in higher absorption. Contraception and treatments for specific diseases such as endometriosis and hormone deficiencies can be improved by the administration of hormones via an IVR. This article aims to classify and compare various designs of commercially available and non-commercial hormonal IVRs and to analyze their performance. Current challenges affecting the development of IVRs are investigated, and proposed solutions are discussed. A comprehensive search of publications in MEDLINE/PubMed and of commercial product data of IVRs was performed, and the materials, designs, performance, and applications (e.g., contraception, endometriosis, estrogen deficiency and urogenital atrophy) of hormonal IVRs were thoroughly evaluated. Most hormonal IVRs administer female sex hormones, i.e., estrogen and progestogens. In terms of material, IVRs are divided into 3 main groups: silicone, polyurethane, and polyethylene-co-vinyl acetate IVRs. As regards their design, there are 4 major designs for IVRs which strongly affect their performance and the timing and rate of hormone release. Important challenges include reducing the burst release and maintaining the bioavailability of hormones at their site of action over a prolonged period of administration as well as lowering production costs. Hormonal IVRs are a promising method which could be used to facilitate combination therapies by administering multiple drugs in a single IVR while eliminating the side effects of conventional drug administration methods. IVRs could considerably improve womenʼs quality of life all over the world within a short period of time.