Recent Advances in the Development of Intravaginal Ring Drug Delivery Systems: Formulation Strategies and Therapeutic Applications

Because of unique anatomical and physiological characteristics, the vaginal route has developed as a popular site for drug administration for both local and systemic therapeutic objectives. One significant advantage of this method is that it avoids hepatic first-pass metabolism, which increases medication bioavailability while reducing gastrointestinal degradation and variability associated with oral administration. The vaginal mucosa has dense vascularization, high permeability to low-molecular-weight medicines, and a large absorptive surface area, all of which contribute to efficient drug absorption and therapeutic efficacy. ^[1–3]

Because of these unique physiological and pharmacokinetic properties, interest in vaginal medication administration has grown dramatically in recent years. A wide range of dosage forms have been created for vaginal delivery, including microemulsions, foams, semisolid preparations, vaginal rings, pills, and medicated tampons. Semisolid formulations, such as gels, have long been regarded as the most suitable for vaginal medication delivery due to their simplicity of application, capacity to produce localized drug action, and high patient acceptability ^[3]. Comparison between IVRs and conventional vaginal formulations is given in table 1.

However, despite these benefits, traditional formulations frequently suffer from limitations such as leakage, short retention time, and the need for frequent administration, prompting the development of advanced controlled-release systems such as intravaginal rings and other long-acting delivery platforms.^[4]

INTRAVAGINAL RINGS (IVRs)

Vaginal rings are flexible, donut-shaped devices designed to provide sustained or controlled drug release within the vagina, producing either local or systemic therapeutic effects. They are mainly used for the prevention or management of disorders related to women’s sexual and reproductive health. However, their application could also extend to other medical conditions, especially those requiring long-term, low-dose systemic therapy where patient adherence may be a concern.^[1,5,6] The daily administration of pills may be substituted by IVR.^[7]

The active principle, which will be released, is contained in this substance. Simply inserting the ring into the vagina allows for a controlled release of the medication. For proper insertion, contact with the vaginal epithelium is the only prerequisite. A number of variables, including the tissue-material partitioning, the initial load of the active principle, the presence of excipients, and the connection between the characteristic dimensions, influence the rate of release.^[1]

Benefits of IVR

• IVRs enable controlled and sustained drug release, eliminating the need for daily dosing.
• They allow the administration of lower drug doses while maintaining therapeutic effectiveness.
• A single device can be designed to deliver multiple drugs simultaneously.
• IVRs are user-controlled, meaning the patient can insert and remove them when required.
• Their use generally does not interfere with sexual intercourse, improving acceptability.
• These devices provide continuous vaginal drug delivery over a predetermined duration following a single application
• IVRs are made from biocompatible polymeric materials, ensuring safety during use.
• They offer advantages such as localized drug action, minimal systemic adverse effects, and predictable release profiles.
• Because they require one-time insertion for extended treatment periods, IVRs demonstrate high patient compliance and convenience.^[1,8]

Disadvantages

• Use of the device may lead to an increase in vaginal secretions in some individuals.
• There is a risk of accidental expulsion or displacement during use.^[1]

Table 1. Comparison between IVRs and conventional vaginal formulations ^[1,8]

Types of IVR

Different categories of IVRs include:

• Matrix type
• Reservoir type
• Sandwich type
• Pod type
• Tablet insert rings
• Hybrid rings

Matrix type IVRs

The most basic vaginal ring design distributes solid pharmaceutical particles, usually in a micronized form, throughout the whole polymeric matrix (Fig 1.A). The permeation mechanism that controls the drug-release yield from these so-called "homogeneous" or "matrix" rings depends on mainly four factors:

1. Solubility of the medication in the polymer
2. The diffusion capability of the dissolved drug through the polymer matrix
3. Drug-loading into the device.
4. Surface area of the ring ^[6,9].

This can be either soluble or insoluble.^[10]

Insoluble:  With insoluble matrix IVRs, the medicine integrated into the polymer is more soluble than the polymer itself, which does not dissolve in vaginal fluid. This characteristic allows the medicine to be released gradually through diffusion from the polymer matrix while the ring keeps its structural integrity. Drug release is possible along the entire ring surface of matrix IVRs because the entire outer surface of the device makes direct touch with vaginal fluid and surrounding tissue. These systems can be designed to deliver either a single drug or multiple drugs simultaneously. When multiple drugs are included in an insoluble matrix IVR, the device may be manufactured as: Continuous and Segmented systems ^[10,11].

Drug permeation in a matrix ring begins with dissolution of the drug in the polymer, followed by diffusion through the elastomeric network. The drug near the surface is released first, forming a depleted layer that inner drug molecules must cross before release. Over time, this depletion layer thickens and moves inward, reducing the effective surface area and causing a gradual decline in the drug-release rate.^[6]

Soluble: In order to enhance medication delivery performance, researchers have investigated the use of biocompatible and biodegradable (bio-soluble) polymers in the creation of IVRs. Through polymer degradation or erosion mechanisms, biodegradable polymers allow for regulated medication release, in contrast to traditional non-degradable polymer systems where drug release is predominantly dependent on diffusion.

The integrated medicine is released predictably and continuously as the polymer matrix slowly degrades in the vaginal environment. This approach is particularly advantageous for delivering drugs with diverse properties, including high-molecular-weight, hydrophilic, and hydrophobic compounds, while also potentially eliminating the need to remove the device after treatment.^[10,11]

Reservoir type

It contains the drug containing center zone which is enclosed by a drug free rate controlling polymeric membrane (RCM) (Fig1.B) ^[10]. Delivery of numerous actives at predefined and independent release rates is made possible by the incorporation of multiple separate drug-loaded cores of different lengths into a single core ring ^[6].

The drug molecules must first separate from the core crystal lattice, diffuse into the drug-free RCM, and then spread across the IVR's surrounding media. Until the medication's concentration at the core is exhausted, the drug is continuously released ^[12].

By altering the thickness of the rate-controlling outer membrane, the release rates of the can be further adjusted ^[6].

Sandwich type

The sandwich design comprises a thin, drug-loaded polymer layer placed between a non-medicated inner core and a non-medicated outer membrane (Fig 1.C) ^[6].

Positioning the drug layer close to the surface enhances the delivery efficiency of drugs that exhibit poor diffusion through polymers. Because the drug-containing layer lies only a fraction of a millimeter beneath the surface, this type of IVR is particularly suitable for compounds with limited polymer permeability. Additionally, sandwich IVRs provide a more consistent drug-release profile, which may help reduce side effects compared with matrix and core-type IVRs ^[6,11,13].

Tablet / Rod inserts

These IVRs are made of non-medicated polymeric rings with chambers that hold many vaginal rods or tablets laden with drugs (Fig1.D). There are several methods for preparing the rods themselves. For example, a plastic syringe can be used to inject a homogeneous mixture of medicine and polymer into PVC tubing. Following solidification, the tubing is taken out, and the resulting polymeric rod is cut to the proper lengths before being placed into the ring's chambers ^[10,14].

Pod inserts

Single or multi-drug release is achievable using IVRs with several small drug-containing sectors, called pods, which can be loaded with the same or different drugs. Pods are made from polymers containing homogeneously dispersed drugs coated with a layer of polymer to create a drug pod. These pods, which can have identical or different geometries, are then incorporated in a nonmedicated continuous or segmented IVR. The release rate of pod IVRs is controlled by their nonmedicated polymeric membrane, the characteristics of the sectors, and the number of pods in each IVR ^[10,15].

Hybrid IVRs

One innovative strategy recommended by recent study is the use of an IVR that combines many common IVR forms, such as matrix, reservoir, or insert. One could think of it as a hybrid IVR. A core embedded in a hot-melt extruded polymer carrying the active ingredient has been suggested as a method of producing core-matrix hybrid IVRs. An insert-matrix IVR, which consists of a medicated polymeric body with cavities for the insertion of vaginal rods, tablets, or pods, is another potential hybrid IVR design ^[10,16].

Fig 1: A) Matrix type B) Reservoir type C) Sandwich type D) Pod/Rod/Tablet insert E) Segmented

Polymeric materials used

The need for good drug permeability, flexibility, and biocompatibility restricts the variety of materials that can be utilized to make vaginal rings. PEVA or silicone (polydimethylsiloxane) elastomer are used to make commercial ring items. More recently, there has been research on the manufacture of rings using thermoplastic polyurethane materials. Biodegradable polymers are also being used these days ^[6,17].

• Silicone elastomers

Synthetic polymers known as silicones are made up of an alternating silicon and oxygen atom backbone with organic substituent groups bonded to the silicon ^[6,18].

Polydimethylsiloxane (PDMS) is the most widely utilized silicone in the creation of intravaginal rings (IVRs), while additional substituents including phenyl, vinyl, and trifluoropropyl can also be added to change the material's characteristics. Because of silicone elastomers' superior biocompatibility, flexibility, and long-term stability, they are frequently utilized in medical and drug delivery systems ^[6,10].

Even with their benefits, silicon polymers have drawbacks, such as the need for high temperatures, the possibility of drug deterioration, the inability to be reprocessed, increased production costs, and environmental issues because they are not biodegradable ^[1].

The silicone elastomers used in IVRs are primarily divided into condensation-cure and addition-cure systems according to their curing chemistry^[18]. Condensation-cure silicones can be treated at comparatively lower temperatures, while addition-cure systems need higher curing temperatures (between 120°C and 180 °C) and work with a wider variety of medications. The finished ring's mechanical characteristics and clinical performance are affected by variations in formulation factors, such as filler content and cross-link density ^[18–20].

Medical-grade silicone elastomers are available as restricted grades for short-term use (≤ 29 days) and unrestricted grades for long-term implantation (> 29 days)^[11].

• Ethylene vinyl acetate copolymers

The rate-controlling characteristics of elastomeric polymers, including ethylene-vinyl acetate copolymers (EVA), make them an excellent material for IVRs. Ethylene and Vinyl Acetate (VA) monomers combine to form the transparent copolymer known as EVA. The copolymer's mechanical characteristics, ease of manufacturing, and drug release rates are all significantly influenced by the amount of vinyl acetate present. ^[10,11,21]

Higher VA content → more amorphous polymer → higher drug permeability → faster release^[10]

Lower VA content → more crystalline polymer → slower diffusion → sustained release^[10]

Commercial hormonal devices, such as implants and contraceptive rings, have successfully used EVA matrices^[22].

• Advantages: Controlled drug release, adjustable mechanical properties, biocompatible, non-toxic, no curing step, less complex manufacturing via co-extrusion and versatile properties, greater adhesion ^[1,10,23,24].
• Limitations: Lower elasticity compared with silicone elastomers, limited permeability for certain drugs, hydrophobic which restricts the incorporation and release of hydrophilic drug^[25].
• Examples: An EVA-based device, that is available on the market, is the contraceptive IVR NuvaRing®^[26].

• Polyurethane

They belong to a class of condensed polymers whose molecular backbone is made up of urethanes. In the presence of a catalyst or UV light activation, isocyanates and polyols undergo a polymerization reaction to create polyurethanes. ^[6,10,27]

Segmented polymeric properties, or hard and soft sections, are present in polyurethanes. Isocyanate components make up the hard part, while polyol makes up the soft part. The hard portion of the polymer determines its mechanical strength, while the weight percentage of the soft section determines its flexibility. Numerous biological devices, such as catheters, pacemakers, wound dressings, medication implants, and vaginal rings, contain PU.^[6,27–29]

• Advantages: Tunable mechanical properties, versatile, good elasticity and flexibility, controlled and sustained drug release.^[6,30]
• Limitations: Susceptibility to hydrolytic and oxidative degradation, complex manufacturing and processing requirements.^[27,28]
• Example: Ornibel is an intravaginal ring made of polyurethane that is sold commercially and used for contraception.^[10]

• Polycaprolactone (PCL)

PCL has been investigated as a potential matrix carrier for extended-release intravaginal dosage forms among several biodegradable polymeric excipients because it is biocompatible, has been shown to be non-toxic to humans, and can be entirely eliminated from the body after being bioabsorbed ^[11,31,32]. PCL is a hydrophobic, semicrystalline polyester that is usually made via ring-opening polymerization of ε-caprolactone. The rate of biodegradation of PCL is extremely sluggish in comparison to other hydrophilic polyesters.^[31]

Limitations include due to hydrophobic nature it provides poor release of hydrophilic drugs, slow degradation (may be too slow for some therapies), low mechanical strength compared with some elastomers.

The use of PCL has been extensively studied in the delivery of antiretroviral agents, contraceptive drugs, antimicrobials, hormonal drugs.^[32–35]

Manufacturing strategies

• Hot melt extrusion

One of the most popular solvent-free manufacturing processes is hot-melt extrusion (HME), which is a continuous process that turns raw materials into products with a specific shape consistently by manipulating materials via various dies in a controlled environment under particular conditions involving temperature, humidity, pressure, feeding rate, and the extrusion screws' rotation speed^[5,34,36].

Steps:

1. Feeding of Formulation Components: Polymeric materials, active pharmaceutical ingredients (APIs), and optional excipients are accurately fed into the extruder through a hopper. Pre-blending is typically performed to ensure uniform drug distribution and consistent drug loading.
2. Melting and Homogenization: Inside the heated barrel, rotating screws generate thermal and mechanical energy, causing the polymer to melt and mix thoroughly with the drug. Venting systems may remove air or moisture to prevent defects.
3. Extrusion through the die: The homogeneous molten mass is forced through an annular die to form a continuous rod or tubular structure with defined dimensions.
4. Cooling and ring formation: The extrudate is cooled, cut into required lengths, and the ends are joined to form a closed intravaginal ring, followed by finishing and quality control.^[37,38]

Benefits: include increased solubility and bioavailability of poorly water-soluble medicines, solvent-free processes, continuous and scalable production, controlled drug release.^[37,38]

Limitations: not suitable for heat sensitive drugs and polymers, requires huge input of money and energy, raw materials with good flow properties are required.^[38]

• Co-extrusion

A popular technique for producing thermoplastic reservoir VRs is co-extrusion. An extra extruder produces a secondary stream of non-medicated polymer that is compatible with the polymer utilized in the active stream, while an extruder compounds API to provide a homogenous output of API and polymer. The die's shape determines the core's diameter and thickness. The API-loaded stream forms a rod that is coated with the non-medicated stream to produce a core/sheath arrangement. After being cut into predetermined lengths, the rod is put into a jig that bends it into a toroid and then butt-welded to create a seam^[6,37,39,40]

• Injection molding

Injection molding is a widely used technique for the fabrication of intravaginal rings, particularly silicone-based systems. In this process, a polymer–drug blend is melted and conveyed by a series of temperature-controlled screws and under pressure, injected into a ring-shaped mold cavity. After cooling and solidification, the molded ring is ejected and subjected to finishing operations. This method enables precise control of device geometry and is suitable for matrix-type IVRs. However, this method is not suitable for thermosensitive drugs and multilayer reservoir designs^{[36,36,41–43]}.

• Solvent casting

Solvent casting is a laboratory-scale fabrication method for intravaginal rings in which a polymer–drug solution is prepared using a volatile organic solvent and cast into a ring-shaped mold. Following solvent evaporation under controlled conditions, a solid matrix-type IVR is obtained. This method is particularly advantageous for thermosensitive drugs since it avoids high processing temperatures. However, concerns related to residual solvent toxicity, extended drying times, and challenges in large-scale production limit its industrial applicability^[44].

Numerous benefits of the solvent casting process include enhanced physicochemical characteristics, ease of use, inexpensive processing, and sufficient thickness consistency^[45].

• 3D Printing technology

The use of 3D printing in pharmaceutical research has grown significantly in recent years. For the production of IVRs, Additive manufacturing (AM) has several advantages over IM, including the ability to create intricate shapes without the need for a mold, a wider selection of materials, and a greater number of compatible APIs.^[36]

An additive manufacturing technique called fused deposition modeling (FDM) 3D printing creates 3D objects by layer-by-layer fusing or depositing materials. The printing head of an FDM printer is similar to that of an inkjet printer. But instead of ink, the item is constructed in tiny layers by extruding heated thermoplastic polymers from the print head as they melt at the right temperature. The volume and placement of each deposit can be precisely controlled to form each layer through repeated use of this method. It fuses or bonds to the earlier layers because the material is heated during the extrusion process. The solid form is created as the layers accumulate because each polymeric layer solidifies as it cools.^[37]

Only heat-stable APIs can be incorporated into the polymeric filament due to the high extrusion temperatures utilized in FDM (above 120 ?C) and hot-melt extrusion (above 150 ?C)^[46]

Computer-aided design (CAD) is used in the production of three-dimensional printed goods, allowing for the incorporation of designs into IVRs during construction. By doing so, the solid cross-section can be removed, changing the drug's surface area and diffusion distance to provide full and regulated API release.

For IVR manufacture, 3D printing can provide an infinite design space for fine-tuning API release to meet exact medication delivery goals. Furthermore, 3D printing might lessen the exposure of APIs to the high temperatures and pressures that are frequently associated with IM manufacture, enabling the consideration of more delicate APIs for vaginal delivery via IVRs and extending their usage for additional indications^[43].

IVRs are 3D printed using digital light synthesis (DLSTM) or continuous liquid interface production (CLIPTM). By adding oxygen to the fabrication process, CLIP stops solidification and polymerization. Therefore, an area of uncured resin known as the "dead zone" is created in oxygen-dominated places, such as close to the window where oxygen is fed. This area enables the continuous and layer less manufacture of smooth and monolithic parts..^[5,43]

Applications

Contraceptive Vaginal ring

Table 2: Hormonal contraceptives

• The main endogenous estrogen in premenopausal women, 17β-estradiol (E2), which is mostly produced by the ovaries, is being considered as a substitute for EE in a number of novel CVR products^[5,10].
• The Population Council is working with the National Institute of Child Health and Human Development to assess a contraceptive ring that releases the progesterone receptor modulator ulipristal acetate (UPA). When administered at the appropriate dosage and timing throughout a menstrual cycle, this 19-norprogesterone derivative successfully suppresses ovulation and causes amenorrhea^[5].

• Non hormonal contraception

Release of non-hormonal spermicides such as:

• Nonoxynol-9 (surfactant)
• Novel antimicrobial/spermicidal agents
• use membrane disruption of sperm cells, preventing fertilization^[5,10].

Ovaprene: This monthly ring is made of a silicone elastomer ring body that contains ferrous gluconate, a spermicidal agent, and ascorbic acid, which keeps iron in the ferrous state by lowering vaginal pH and preventing ferrous oxidation of serum iron. Sheep treated with an Ovaprene ring showed similar results to a sham-treated animal. Of the roughly 512 mg of ferrous gluconate that were allegedly put into the rings, Ovaprene discharged an average of 175 mg during the course of the 29-day use period ^[5,51,52].

Glycerol monolaurate (GML, also known as monolaurin) and lactic acid (LA) were chosen by Howard et al. as two possible nonhormonal contraceptive substances.  The vaginal environment can be acidified by using lactic acid, an endogenous substance found in the female reproductive tract and an active component of the FDA-approved nonhormonal contraception gel Phexxi^[51].

The goal of using LA to keep the vaginal environment acidic is to keep the pH of the vagina unsuitable for sperm. Ball et al. showed that GML could also have a contraceptive effect by preventing the motility and viability of sperm^[51]. Therefore, GML and LA together in our nonhormonal IVR may have a synergistic impact to support the effectiveness of two contraceptive mechanisms^[51].

• Endometriosis

IVRs are the perfect way to cure endometriosis in women. Though research is being done on the use of hormonal IVRs to treat endometriosis, there are presently no IVRs available to treat this condition. To treat recurring endometriosis in women of reproductive age, an IVR combining progestin and the aromatase inhibitor anastrozole has been created. In another study, women with endometriosis, dysmenorrhea, and polycystic ovarian syndrome were found to respond well to an IVR loaded with ethinylestradiol and etonogestrel, which prevents ovulation. An appealing and useful approach for treating endometriosis with concurrent hormonal contraception is the combination of anastrozole with a low-dose progestin in a sustained/controlled release vaginal ring device^[5,10,52,53].

• HIV Prevention

Numerous review articles detailing vaginal ring technologies for HIV prevention have been published during the past few years (table 3).

Table 3: IVRs for HIV prevention

• Cervical cancer

Vaginal delivery of chemotherapeutic agents represents a promising strategy for the localized management of cervical cancer. This approach can minimize the need for high systemic doses and thereby reduce the adverse effects commonly associated with oral or parenteral chemotherapy. Intravaginal rings (IVRs), in particular, provide sustained and controlled drug release over extended periods.^[5,59]

Their placement in close proximity to the cervix enables targeted drug exposure, making them especially suitable for the treatment of cervical intraepithelial neoplasia (CIN). CIN is a precancerous lesion confined to the epithelium. Since CIN does not initially invade deeper tissues, localized sustained therapy through IVRs can deliver cytotoxic or immunomodulatory agents directly to abnormal cells and potentially reduce the need for surgical procedures^[5,59].

Matrix-type, disc-shaped, cisplatin-releasing EVA devices made by the solvent casting and evaporation process have been described by Keskar et al. as model vaginal rings. A circular device with a diameter of 4 mm that contained up to 37.5 mg of cisplatin was created. With release rates (and apparent diffusion coefficients) rising with drug loading, biphasic drug release was seen, consisting of an initial burst (2–7 days) followed by much lower zero-order release out to 90 days^[5,59,60].

According to Tayyar et al., alisertib (MLN8237), a strong and specific Aurora A kinase inhibitor that destroys HPV-positive cervical cancer cells, is released from a matrix-type silicone elastomer ring. The produced rings showed the "burst effect" with root time kinetics over a prolonged length of time and attained comparatively respectable release kinetics over a 21-day timeframe. Finally, they demonstrated that Alisertib is a good option for vaginal delivery with intravaginal rings^[5,61].

Matrix-type EVA rings for the prolonged release of disulfiram, a cytotoxic thiocarbamate medication that causes apoptosis in a variety of tumor cell lines, including HeLa cells, were reported by Boyd et al^[5,62].

• Bacterial vaginosis (BV)

Drug-releasing vaginal rings might be a very useful therapeutic approach for better localized treatment of BV^[5].

Malcolm et al. developed a silicone matrix intravaginal ring for the sustained release of metronidazole intended for the treatment of BV. The formulation demonstrated controlled diffusion-driven drug release over extended periods, achieving therapeutically relevant concentrations while potentially minimizing systemic exposure. This study highlighted the potential of IVRs as an alternative to conventional oral and topical therapies for vaginal infections^[63].

Pathak et al. investigated polycaprolactone (PCL) matrices as a sustained-release system for intravaginal delivery of metronidazole in BV. The formulation provided controlled drug release in simulated vaginal fluid and preserved antibacterial activity against Gardnerella vaginalis, indicating that biodegradable vaginal devices could offer an effective and convenient alternative to conventional BV therapy with reduced systemic exposure^[64].

Zhao et al. evaluated the formulation and physicochemical aspects of silicone elastomer vaginal rings designed for sustained delivery of 5-nitroimidazole drugs in BV. Injection-molded rings containing 250 mg of metronidazole, tinidazole, secnidazole, and ornidazole demonstrated diffusion-controlled drug release over 28 days, with release rates dependent on each drug’s physicochemical properties^[20].

Li et al. formulated polycaprolactone (PCL)-based metronidazole delivery systems for prolonged intravaginal therapy. By incorporating metronidazole into therapeutic deep eutectic systems (THEDES), they modified its physicochemical properties to enable sustained release from PCL matrices. The study demonstrated controlled, extended drug release, suggesting this approach as a promising strategy for improving local treatment of BV^[34].

• Antifungal therapy

Tiboni et al. developed 3D-printed clotrimazole-loaded intravaginal rings using fused deposition modelling for the treatment of recurrent vulvovaginal candidiasis. The rings demonstrated sustained antifungal drug release over several days and effectively inhibited Candida albicans in vitro. This study highlights the potential of additive manufacturing to produce customizable, long-acting vaginal drug delivery systems for local infection management^[30].

Moroni et al. (2023) explored the fabrication of ethylene-vinyl acetate (EVA)–based intravaginal rings using 3D printing technology for sustained antifungal therapy. The researchers demonstrated that additive manufacturing can produce flexible and customizable vaginal rings capable of delivering drugs in a controlled manner over an extended period. By enabling sustained local drug delivery, these EVA-based rings  improve vaginal residence time, reduce dosing frequency, enhance patient adherence, and provide a promising alternative to conventional topical antifungal treatments^[26].

For antifungal treatment, Krishnan et al. (2025) assessed an intravaginal ring coated with a copper(I) complex based on quinazoline. Strong antifungal and antibiofilm activity against Candida species was shown by the coated ring, which considerably decreased biofilm development and pathogenicity. The results imply that metal-complex-modified IVRs may be used as novel long-acting treatments for vulvovaginal candidiasis^[65].

• Next generation IVRs

In order to detect the drop in core body temperature that takes place 24 to 48 hours before ovulation, two temperature-responsive vaginal rings are presently being studied. Priya, a vaginal ring with an integrated sensor that periodically detects vaginal temperature (as a proxy for core body temperature) and transmits the data wirelessly to a linked smartphone, is being developed by the US business Prima-Temp. VivoSensMedical is working on OvulaRing, a comparable temperature-recording ring^[5,66,67].

A vaginal ring device for four days of continuous in situ vaginal pH monitoring has been published by Paghi et al. for the diagnosis and treatment of BV^[5,68].

• Multipurpose IVRs

Table 4: Examples for multipurpose IVRs