Influence of salivary washout on drug delivery to the oral cavity using coated microneedles: An in vitro evaluation

Curcumin analogue AC17-loaded dissolvable microneedles activate FOXO3 and enhance localized drug delivery for oral squamous cell carcinoma treatment

Curcumin, a polyphenol extracted from turmeric, is a potential alternative for the treatment of oral squamous cell carcinoma (OSCC) due to its remarkable anticancer activity and low systemic toxicity. To further enhance the anticancer activity and bioavailability of curcumin, we synthesized a curcumin analogue, AC17, by modifying the benzene ring and methylene group of curcumin. A soluble hyaluronic acid microneedle patch (AC17@HAMN) was developed to ensure accurate and safe delivery of AC17 to tumor tissues. The inhibitory effect of AC17 on OSCC cells was stronger than that of curcumin and some common analogues. Transcriptome sequencing showed that the target genes of AC17 were mainly concentrated in apoptosis, cell cycle and cell senescence pathways. Among them, AC17 induces cell cycle arrest and inhibits cell proliferation mainly by activating FOXO3 signaling. With good penetration and dissolution properties, microneedles can deliver AC17 directly to the tumor site and show good anti-tumor effect. Moreover, AC17@HAMN showed good biosafety. In summary, AC17@HAMN offers high efficiency, minimal invasiveness, and few adverse reactions. This microneedle patch holds great promise for potential clinical applications, especially for the treatment of OSCC.

Rapid dissolution microneedle based on polyvinyl alcohol/chitosan for local oral anesthesia

At present, the main clinical methods of oral local anesthesia are direct injection of anesthetic and surface ointment. However, the pain and fear caused by the injection, the discomfort of topical anesthetic creams, and the scour and moist oral environment during the procedure pose great challenges to oral anesthesia. Herein, we designed a Lido-PVP/PVA DMNP microneedle (MN) for oral local anesthesia. The microneedle tip was consisted of Polyvinylpyrrolidone/Polyvinyl alcohol (PVP/PVA), which can quickly dissolve and release the lidocaine hydrochloride (Lido) drug within 5 min to achieve rapid anesthesia. The backing was composed of polyvinyl alcohol/chitosan (PVA/CS), and its excellent adhesion can overcome saliva erosion and anchor firmly to the oral mucosa, significantly improving the utilization rate of drugs, as well as the patient compliance. MNs have good mechanical properties for tissue insertion while possessing high drug loading (3 mg/MNs). Von Frey tests proved that MNs showed a faster and more effective local anesthetic effect (anesthesia takes effect at 5 min) compared to cream (anesthesia takes effect at 30 min). In addition, the excellent biocompatibility and no skin irritation endowed Lido-PVP/PVA DMNP MNs a great potential for oral local anesthesia in the oral cavity.

Intraoral medical devices for sustained drug delivery

OBJECTIVES

The oral cavity constitutes an attractive organ for the local and systemic application of drug substances. Oromucosal tablets, gels, or sprays are examples of the formulations applied. Due to the elution through the saliva, the residence time of the formulation at the application site is relatively short. Medical devices placed in the oral cavity, with a reservoir for an active substance, play an important role in solving this problem.

MATERIALS AND METHODS

In this review, we discuss the devices described in the literature that are designed to be used in the oral cavity, highlighting the advantages, disadvantages, and clinical applications of each of them.

RESULTS

Among the intraoral medical devices, special types are personalized 3D-printed devices, iontophoretic devices, and microneedle patches.

CONCLUSION

We anticipate that with the development of 3D printing and new polymers, the technology of flexible and comfortable devices for prolonged drug delivery in the oral cavity will develop intensively.

CLINICAL RELEVANCE

The presented review is therefore a useful summary of the current technological state, when in fact none of the existing devices has been widely accepted clinically.

Microneedle-enabled therapeutics delivery and biosensing in clinical trials

Microneedles (MNs) are micron-sized protrusions attached to a range of devices that are used in therapeutic delivery and diagnosis. Because MNs can be self-applied, are painless, and can carry multiple therapeutic agents, they have received extensive attention, and have been widely investigated, for local and systemic therapy. Many researchers are currently working to extend the use of MNs to clinical applications. In this review, we provide an update and analysis on MN-based clinical trials since their inception in 2007. The MNs in clinical trials are classified into five types based on their appearance and properties, including: hollow MNs, MN patches, radiofrequency MNs, MN rollers, and other MNs. The various aspects of MN trials are summarized, such as MN types, clinical trial time, and trial regions. This review aims to present an overview of MN development and provide insights for future research in this field. To our knowledge, this is the first review focused on MN clinical trials which showcases the latest applications of this advanced technology in medicine.

Microneedles for oral mucosal delivery - Current trends and perspective on future directions

INTRODUCTION

Oral cavity drug and vaccine delivery has the potential for local targeting, dose reduction, minimization of systemic side effects, and generation of mucosal immunity. To overcome current limitations of delivery into the oral cavity mucosa, microneedles (MNs) have emerged as a promising technology.

AREAS COVERED

We reviewed the literature on MN application in the oral cavity, including in vitro studies, in vivo animal studies, and human clinical trials.

EXPERT OPINION

MNs are sufficiently robust to cross the oral cavity epithelium and nearly painless when applied to different parts of the human oral mucosa including the lip, cheek, tongue, and palate. In recent years, MNs have been evaluated for different applications, including vaccination, topical anesthetic delivery, and treatment of local oral pathologies such as oral lesions or carcinomas. MNs are attractive because they have the potential to produce a better treatment outcome with reduced side effects. Over the coming years, we project a significant increase in research related to the development of MNs for use in dentistry and other medical conditions of the mouth.

Oral Mucosa Models to Evaluate Drug Permeability

Due to its numerous advantages, such as excellent drug accessibility, rapid absorption, and bypass of first-pass metabolism, the route of drug administration that involves crossing the oral mucosa is highly favored. As a result, there is significant interest in investigating the permeability of drugs through this region. The purpose of this review is to describe the various ex vivo and in vitro models used to study the permeability of conveyed and non-conveyed drugs through the oral mucosa, with a focus on the most effective models. Currently, there is a growing need for standardized models of this mucosa that can be used for developing new drug delivery systems. Oral Mucosa Equivalents (OMEs) may provide a promising future perspective as they are capable of overcoming limitations present in many existing models.

Microneedles: structure, classification, and application in oral cancer theranostics

Oral cancer is a malignant tumor that threatens the health of individuals on a global scale. Currently available clinical treatment methods, including surgery, radiotherapy, and chemotherapy, significantly impact the quality of life of patients with systemic side effects. In the treatment of oral cancer, local and efficient delivery of antineoplastic drugs or other substances (like photosensitizers) to improve the therapy effect is a potential way to optimize oral cancer treatments. As an emerging drug delivery system in recent years, microneedles (MNs) can be used for local drug delivery, offering the advantages of high efficiency, convenience, and noninvasiveness. This review briefly introduces the structures and characteristics of various types of MNs and summarizes MN preparation methods. An overview of the current research application of MNs in different cancer treatments is provided. Overall, MNs, as a means of transporting substances, demonstrate great potential in oral cancer treatments, and their promising future applications and perspectives of MNs are outlined in this review.

Oromucosal delivery of macromolecules: Challenges and recent developments to improve bioavailability

Owing to their biological diversity, high potency, good tolerability, low immunogenicity, site-specific activity, and great efficacy, macromolecular drugs (i.e., proteins and peptides, antibodies, hormones, nucleic acids, vaccines, etc.) are extensively used as diagnostics, prophylactics, and therapeutics in various diseases. To overcome drawbacks associated with parenteral (invasive) delivery of macromolecules as well as to preserve their therapeutic integrity, oromucosal route (sublingual and buccal) has been proven efficient alternate port of delivery. This review aims to summarize challenges associated with oromucosal route and overtime developments in conventional delivery systems with special emphasis on most recent delivery strategies. Over the past few decades, significant efforts have been made for improving the oromucosal absorption of macromolecules by employing chemical penetration enhancers (CPE), enzyme inhibitors, chemical modification of drug structure (i.e., lipidation, PEGylation, etc.), and mucoadhesive materials in the form of buccal tablets, films (or patches), sprays, fast disintegrating tablets, and microneedles. Adaptation of adjunct strategies (e.g., iontophoresis in conjunction with CPE) has shown significant improvement in oromucosal absorption of macromolecules; however, these approaches were also associated with many drawbacks. To overcome these shortcomings and to further improve therapeutic outcomes, specialized delivery devices called "hybrid nanosystems" have been designed in recent times. This newer intervention showed promising potential for promoting oromucosal absorption and absolute bioavailability of macromolecules along with improved thermostability (cold chain free storage), enabling self-administration, site-specific activity, improving therapeutic efficacy and patient compliance. We anticipate that tailoring of hybrid nanosystems to clinical trials as well as establishing their short- and long-term safety profile would substantiate their therapeutic value as pharmaceutical devices for oromucosal delivery of macromolecules.

Composite dissolvable microneedle patch for therapy of oral mucosal diseases

A composite microneedle patch (MN patch) is developed for oral transmucosal administration. To improve the oral transmucosal drug delivery efficiency, the composite MN patch is designed to consist of an array of 100 dissolvable microneedles (MNs) with drug-loaded tips and a backing layer. The MNs are composed of two parts, the hyaluronic acid (HA) tip part and the polyvinylpyrrolidone (PVP) base part. Due to the small size and sufficient mechanical strength, the HA-PVP MNs can painlessly penetrate the oral mucosa barrier and deliver drugs directly to the basal layer or submucosa. Betamethasone sodium phosphate (BSP), as the model drug, is concentrated in the HA tip parts to avoid the drug waste caused by mucosa elasticity. Considering the special moist environment and saliva flow in the mouth, a double-layer backing layer composed of a poly(vinyl alcohol) (PVA) adhesive layer and an ethyl cellulose (EC) waterproof layer is designed and constructed, which could reduce the saliva flow effects. The in vitro and in vivo results demonstrate that the MN patch could achieve rapid and efficient BSP release in oral mucosa due to the rapid dissolution of HA. The proposed MN patch provides a novel strategy for the therapy of oral mucosal diseases.

Lidocaine-Loaded Hyaluronic Acid Adhesive Microneedle Patch for Oral Mucosal Topical Anesthesia

The pain and fear caused by direct local injection of anesthetic or the poor experience with surface anesthetic cream increase the difficulty of clinical treatment for oral diseases. To address this problem, a hyaluronic acid microneedle patch (Li-HAMNs) that consists of fast-dissolving lidocaine hydrochloride (LDC)-loaded tips and a wet-adhesive backing layer made of polyvinyl alcohol (PVA)/carboxymethylcellulose sodium (CMC-Na) was fabricated to explore its potential use in dental topical anesthesia. Li-HAMNs could puncture the stratum corneum with an insertion depth of about 279 μm in the isolated porcine oral mucosal. The fast-dissolving tips could release LDC to improve the patients’ convenience and compliance. Importantly, the backing layer, which has good adhesion ability and water-absorbing properties, could surmount the contraction and extension of oral masticatory muscles and the saliva scour. In the tail flick test, the topical anesthesia efficacy of the Li-HAMNs group was much better than clinical lidocaine cream (EMLA cream, LDC, 1.2 mg) in spite of a relatively lower LDC dose with Li-HAMNs (LDC, 0.5 mg). It is believed that the proposed adhesive microneedle patch could enhance transmucosal delivery of anesthetics and thus open a new chapter in the painless treatment of oral diseases.

A Facile Low-Dose Photosensitizer-Incorporated Dissolving Microneedles-Based Composite System for Eliciting Antitumor Immunity and the Abscopal Effect

Nanomedicine-based photodynamic therapy (PDT) for melanoma treatment has attracted great attention. However, the complex design of polymer nanoparticles and high doses of photosensitizers used in intravenous injections (for sufficient accumulation of drugs in tumor lesions) pose a huge challenge to the commercialization and further clinical application. Herein, we fabricated the carrier-free nanoassemblies of a chlorin e6 (L-Ce6 NAs)-integrated fast-dissolving microneedles patch (L-Ce6 MNs) enriching only about 3 μg of Ce6 in the needle tips via a facile fabrication method. The L-Ce6 MNs had sufficient mechanical strength to penetrate the skin and facilitated the transportation of L-Ce6 NAs to a depth of 200-500 μm under the skin, thereby achieving efficient and accurate drug delivery to tumor lesions. In a xenograft mouse melanoma model, the L-Ce6 MNs-based PDT with low dose of Ce6 (0.12 mg/kg) exerted efficient ablation of the primary lesions in situ through reactive oxygen species (ROS) generation. More importantly, a significant abscopal effect was also elicited by activating immunogenic cell death (ICD) and releasing danger-associated molecular patterns (DAMPs), which in turn promoted dendritic cells (DCs) maturation and the subsequent antigen presentation, thereby facilitating the T-cell-mediated immune response without synergetic immunotherapies. Collectively, our findings indicate the facile, controllable, and fast-dissolving microneedles patch with a low dose of photosensitizers presented great therapeutic potential for enhanced photoimmunotherapy.

The enhancing effect and promoting mechanisms of the stereoisomeric monoterpene alcohol esters as enhancers for drugs with different physicochemical properties

To explore the structure-activity connections of amphiphilic permeation enhancers containing the length of the hydrophobic chains as well as the properties of the polar head, O-acylgeraniol and O-acylnerol derivatives were synthesized from geraniol/nerol (cis-isomer of geraniol) and pharmaceutical excipient acids in this research. Their promotion of the percutaneous absorption of three drugs as the model, flurbiprofen (FP), isosorbide dinitrate (ISDN) and donepezil (DNP), which were selected based on their physicochemical properties, was tested by in vitro skin penetration and in vivo. Molecular simulation, ATR-FTIR, CLSM and histological observation were implement to evaluate the mode of action of the enhancers. The results indicated that (E)-3,7-dimethyl-2,6-octadien-1-yl tetradecanoate (GER-C14, trans-) achieved the highest enhancement ability for the three drugs; additionally, the in vivo results obtained were in good correlation with the in vitro data. Molecular docking results suggested that enhancers loosen the hydrogen bonds between ceramides, and the results of molecular simulation indicated that GER-C14, NER-C14 could insert into the middle of the lipid bilayer to form an independent phase. According to ATR-FTIR and histological evaluation, the enhancers extracted lipids and influenced the protein region, thereby disturbing the skin array. In addition, CLSM described the dynamic effects of enhancers on lipids between stratum corneum (SC) cells. In conclusion, GER-C14 had a better penetration promotion effect, which broadened our understanding of stereoisomeric penetration enhancers.

In vitro evaluation of adhesion and mechanical properties of oral thin films

Oral drug delivery is often challenged with enzymatic degradation of drug molecules in the gastrointestinal tract and high first-pass metabolism, resulting in low bioavailability. Delivery of drug molecules via the oral cavity mucosa is considered a viable option to enhance bioavailability. One of the relatively new dosage forms for transmucosal drug delivery is the oral thin film (OTF) with mucoadhesive properties that offers several advantages over conventional dosage forms, including faster dissolution, higher patient compliance, and extended oral retention by reduced salivary washout. Mucoadhesive OTFs should have sufficient muco-adhesiveness as well as suitable mechanical properties for their best performance, thus such characterization is critical in the successful design and development of OTFs. However, there is currently no FDA or USP-recommended analytical procedure or standard available for evaluating adhesiveness and mechanical properties of mucoadhesive OTFs. Therefore, we aimed to develop a fast and reliable in vitro method capable of differentiating various OTFs in terms of their adhesive strengths using a texture analyzer. We found that an in vitro gel substrate composed of 4% w/v gellan gum and 2% w/v glycerin could be used to discriminate between the adhesive features of the tested film samples. Also, our studies show that the adhesion test parameters of 0.96 N target force, probe speed of 0.1 mm/s, holding time of 15 s, and conditioning medium volume of 200 μL while using the said substrate could successfully differentiate between the adhesion strength of the OTF samples. We further examined the film samples for their physicomechanical properties to obtain a tangible and practical range of mechanical values for pharmaceutical OTFs using the puncture test and folding endurance test. We found a breaking factor above 34.5 N/mm, elongation to puncture less than 5.55% and folding endurance of at least 50 folds can be used as a starting point when designing and manufacturing OTFs.

Resistivity Technique for the Evaluation of the Integrity of Buccal and Esophageal Epithelium Mucosa for In Vitro Permeation Studies: Swine Buccal and Esophageal Mucosa Barrier Models

Permeation assays are important for the development of topical formulations applied on buccal mucosa. Swine buccal and esophageal epithelia are usually used as barriers for these assays, while frozen epithelia have been used to optimize the experimental setup. However, there is no consensus on these methods. In transdermal studies, barrier integrity has been evaluated by measuring electrical resistance (ER) across the skin, which has been demonstrated to be a simple, fast, safe, and cost-effective method. Therefore, the aims here were to investigate whether ER might also be an effective method to evaluate buccal and esophageal epithelium mucosa integrity for in vitro permeation studies, and to establish a cut-off ER value for each epithelium mucosa model. We further investigated whether buccal epithelium could be substituted by esophageal epithelium in transbuccal permeation studies, and whether their permeability and integrity were affected by freezing at -20 °C for 3 weeks. Fresh and frozen swine buccal and esophageal epithelia were mounted in Franz diffusion cells and were then submitted to ER measurement. Permeation assays were performed using lidocaine hydrochloride as a hydrophilic drug model. ER was shown to be a reliable method for evaluating esophageal and buccal epithelia. The esophageal epithelium presented higher permeability compared to the buccal epithelium. For both epithelia, freezing and storage led to decreased electrical resistivity and increased permeability. We conclude that ER may be safely used to confirm tissue integrity when it is equal to or above 3 kΩ for fresh esophageal mucosa, but not for buccal epithelium mucosa. However, the use of esophageal epithelium in in vitro transmucosal studies could overestimate the absorption of hydrophilic drugs. In addition, fresh samples are recommended for these experiments, especially when hydrophilic drugs are involved.

Progress and perspective of microneedle system for anti-cancer drug delivery

Transdermal drug delivery exhibited encouraging prospects, especially through superficial drug administration routes. However, only a few limited lipophilic drug molecules could cross the skin barrier, those are with low molecular weight and rational Log P value. Microneedles (MNs) can overcome these limitations to deliver numerous drugs into the dermal layer by piercing the outermost skin layer of the body. In the case of superficial cancer treatments, topical drug administration faces severely low transfer efficiency, and systemic treatments are always associated with side effects and premature drug degradation. MN-based systems have achieved excellent technical capabilities and been tested for pre-clinical chemotherapy, photothermal therapy, photodynamic therapy, and immunotherapy. In this review, we will focus on the features, progress, and opportunities of MNs in the anticancer drug delivery system. Then, we will discuss the strategies and advantages in these works and summarize challenges, perspectives, and translational potential for future applications.

Ionic liquid-mediated delivery of insulin to buccal mucosa

Buccal drug delivery offers a potential non-invasive means of delivering therapeutics to patients. Despite the promise, the feasibility of transporting proteins and peptides into systemic circulation from buccal administration remains a daunting challenge. Here, we report the fabrication of a biodegradable polymeric patch for buccal delivery of insulin using chitosan as the mucoadhesive matrix and ionic liquids (ILs)/deep eutectic solvent (DES) as the transport facilitator. Insulin is mixed with ILs/DES made from Choline and Geranic acid (CAGE) to form a viscoelastic CAGE gel and sandwiched between two layers of a biodegradable polymer. The rheological properties of the CAGE gel were dominated by the elastic modulus and suggested a solid-like viscoelastic behavior. CAGE induced a 7-fold increase in the cumulative insulin transport across the ex vivo porcine buccal tissue (~26% of loaded insulin) which was also confirmed by confocal microscopy. The CAGE/insulin patches placed in the rat buccal pouch in vivo lowered blood glucose levels in a dose-dependent manner (up to 50% drop recorded) with no obvious tissue damage at the application site. The pharmacokinetic performance of the delivered insulin indicated a sustained profile as serum insulin levels plateaued after 3 h for the duration of study. The safety and efficacy of the polymeric patch using insulin as a model drug holds significant promise as a platform technology to deliver injectables through the buccal route.

Prolonged oral transmucosal delivery of highly lipophilic drug cannabidiol

Delivery of drugs through oral mucosa enables bypass of the gastrointestinal tract and "first pass" metabolism in the liver and the gut. Thus, a higher and less variable bioavailability can be obtained. Mechanisms of this administration route for cannabidiol were investigated in the current research in pigs. Results show that cannabidiol has substantially low permeability rate over 8 h through oral mucosa and accumulates significantly within it. Furthermore, following the removal of the delivery device, residual prolongation of release from the oral mucosa into systemic blood circulation continues for several hours. This method of delivery enabled acquisition of clinically relevant plasma levels of cannabidiol. The absorption profile indicates that cannabidiol, as well as other lipophilic molecules, should be delivered through oral mucosa for systemic absorption from a device that conceals the drug and prevents its washout by the saliva flow and subsequent ingestion into gastrointestinal tract.

Non-transdermal microneedles for advanced drug delivery

Microneedles (MNs) have been used to deliver drugs for over two decades. These platforms have been proven to increase transdermal drug delivery efficiency dramatically by penetrating restrictive tissue barriers in a minimally invasive manner. While much of the early development of MNs focused on transdermal drug delivery, this technology can be applied to a variety of other non-transdermal biomedical applications. Several variations, such as multi-layer or hollow MNs, have been developed to cater to the needs of specific applications. The heterogeneity in the design of MNs has demanded similar variety in their fabrication methods; the most common methods include micromolding and drawing lithography. Numerous materials have been explored for MN fabrication which range from biocompatible ceramics and metals to natural and synthetic biodegradable polymers. Recent advances in MN engineering have diversified MNs to include unique shapes, materials, and mechanical properties that can be tailored for organ-specific applications. In this review, we discuss the design and creation of modern MNs that aim to surpass the biological barriers of non-transdermal drug delivery in ocular, vascular, oral, and mucosal tissue.

Antimicrobial Efficacy Assessment of Human Derived Composite Amnion-Chorion Membrane

Human derived composite amnion-chorion membrane (ACM) has been used to facilitate wound healing due to reported anti-inflammatory properties and promotion of cell proliferation. This study aimed to assess the antimicrobial properties of the ACM using novel methods to visualize the antimicrobial efficacy of membranes in situ at different time points. Porcine Pericardium Collagen Membranes (PPCM) served as membrane controls. Circular pieces of the membranes were used in three different assays: insert, agar contact and glass-bottom well assays. Streptococcus gordonii were spotted onto the membranes and the plates were subsequently centrifuged to ensure direct bacterial contact with the membranes in the insert and agar contact assays, thus better mimicking bacterial adherence in the oral cavity. After incubation at 37 °C for 8, 24, and 48 hours, the membranes were dyed with the Live/Dead BacLight Bacterial Viability fluorescence stain and analyzed via confocal microscopy. The results demonstrated that the ACM completely inhibited bacterial growth at all time points, whereas the PPCM did not demonstrate any antimicrobial properties. Within the limits of this study, the ACM showed extremely high antimicrobial efficacy against oral streptococci. In addition, our methods may be useful in assessing antimicrobial properties for biomaterials with minimum diffusion ability, when traditional assessment methods are not applicable.

Microneedle Coating Methods: A Review with a Perspective

A coated microneedle array comprises sharp micrometer-sized needle shafts attached to a base substrate and coated with a drug on their surfaces. Coated microneedles are under investigation for drug delivery into the skin and other tissues, and a broad assortment of active materials, including small molecules, peptides, proteins, deoxyribonucleic acids, and viruses, have been coated onto microneedles. To coat the microneedles, different methods have been developed. Some coating methods achieve selective coating of just the microneedle shafts, whereas other methods coat not only microneedle shafts but also the array base substrate. Selective coating of just the microneedle shafts is more desirable since it provides control over drug dosage, prevents drug waste, and offers high delivery efficiency. Different excipients are added to the coating liquid to modulate its viscosity and surface tension in order to achieve uniform coatings on microneedles. Coated microneedles have been used in a broad range of biomedical applications. To highlight these different applications, a table summarizing the different active materials and the amounts coated on microneedles is provided. We also discuss factors that should be considered when deciding suitability of coated microneedles for new-drug delivery applications. In recent years, many coated microneedles have been investigated in human clinical trials, and there is now a strong effort to bring the first coated microneedle-based product to market.

Microneedles Coated with Tramadol Exhibit Antinociceptive Effect in a Rat Model of Temporomandibular Hypernociception

Coated microneedles have emerged as a promising drug delivery system for inflammatory pain treatment. We have previously shown that tramadol injection into the rat temporomandibular joint (TMJ) induces an antinociceptive and anti-inflammatory effect. In this study, microneedles coated with tramadol were investigated as a platform to treat TMJ pain. Male Wistar rats were administered tramadol using an intra-TMJ injection or with microneedles coated with tramadol, followed by 1.5% formalin nociceptive challenge administered 15 minutes later. The nociceptive behavior of rats was evaluated, and their periarticular tissues were removed after euthanasia for analysis. The duration of antinociceptive effect was determined by performing the formalin challenge at different time points extending up to 6 days post tramadol administration. Microneedles coated with tramadol produced an antinociceptive effect similar to injection of tramadol into the rat TMJ. Surprisingly, tramadol delivery using coated microneedles produced a more durable antinociceptive effect lasting as much as 2 days post tramadol delivery as compared with an antinociceptive effect lasting under 2 hours from intra-TMJ injection of tramadol. The proinflammatory cytokines tumor necrosis factor-α and interleukin-1β (IL-1β) were found to be reduced, whereas the anti-inflammatory cytokine IL-10 was found to be elevated in tramadol-treated groups. In conclusion, microneedles coated with tramadol can offer a therapeutic option for pain control of inflammatory disorders in the TMJ.

Microneedle-Mediated Vaccine Delivery to the Oral Mucosa

The oral mucosa is a minimally invasive and immunologically rich site that is underutilized for vaccination due to physiological and immunological barriers. To develop effective oral mucosal vaccines, key questions regarding vaccine residence time, uptake, adjuvant formulation, dose, and delivery location must be answered. However, currently available dosage forms are insufficient to address all these questions. An ideal oral mucosal vaccine delivery system would improve both residence time and epithelial permeation while enabling efficient delivery of physicochemically diverse vaccine formulations. Microneedles have demonstrated these capabilities for dermal vaccine delivery. Additionally, microneedles enable precise control over delivery properties like depth, uniformity, and dosing, making them an ideal tool to study oral mucosal vaccination. Select studies have demonstrated the feasibility of microneedle-mediated oral mucosal vaccination, but they have only begun to explore the broad functionality of microneedles. This review describes the physiological and immunological challenges related to oral mucosal vaccine delivery and provides specific examples of how microneedles can be used to address these challenges. It summarizes and compares the few existing oral mucosal microneedle vaccine studies and offers a perspective for the future of the field.

Full-Thickness Intraoral Mucosa Barrier Models for In Vitro Drug-Permeation Studies Using Microneedles

The use of permeation enhancers such as microneedles (MNs) to increase drug penetration across intraoral mucosa has increased in recent years. Permeation studies, commonly performed using vertical diffusion cells, are a well-established way to preview formulations and enhance their performance during the development stage. However, to our knowledge, the existing intraoral mucosa barrier models do not permit permeation using MN-pretreated mucosa due to their insufficient thickness. Therefore, the objective of this study was to develop a barrier model using thick palate tissues to perform in vitro permeation studies, with physical enhancement of the permeability of intraoral mucosa by pretreatment with MNs. The adapted Franz-type cells used in the permeation experiments were validated (cell dimensions and volume, sealing effectiveness, stirring and dissolution efficiency, temperature control, and establishment of uniaxial flux). Commercially available MNs were used in the palatal mucosa. Optical images of the mucosa were acquired to analyze the microperforations created. In vitro permeation studies were conducted with the MN-pretreated mucosa. This work presents a new in vitro method for the evaluation of MNs as permeation enhancers, with the aim of improving the absorption of drug formulations topically applied within the oral cavity.

Recent advances of controlled drug delivery using microfluidic platforms

Conventional systematically-administered drugs distribute evenly throughout the body, get degraded and excreted rapidly while crossing many biological barriers, leaving minimum amounts of the drugs at pathological sites. Controlled drug delivery aims to deliver drugs to the target sites at desired rates and time, thus enhancing the drug efficacy, pharmacokinetics, and bioavailability while maintaining minimal side effects. Due to a number of unique advantages of the recent microfluidic lab-on-a-chip technology, microfluidic lab-on-a-chip has provided unprecedented opportunities for controlled drug delivery. Drugs can be efficiently delivered to the target sites at desired rates in a well-controlled manner by microfluidic platforms via integration, implantation, localization, automation, and precise control of various microdevice parameters. These features accordingly make reproducible, on-demand, and tunable drug delivery become feasible. On-demand self-tuning dynamic drug delivery systems have shown great potential for personalized drug delivery. This review presents an overview of recent advances in controlled drug delivery using microfluidic platforms. The review first briefly introduces microfabrication techniques of microfluidic platforms, followed by detailed descriptions of numerous microfluidic drug delivery systems that have significantly advanced the field of controlled drug delivery. Those microfluidic systems can be separated into four major categories, namely drug carrier-free micro-reservoir-based drug delivery systems, highly integrated carrier-free microfluidic lab-on-a-chip systems, drug carrier-integrated microfluidic systems, and microneedles. Microneedles can be further categorized into five different types, i.e. solid, porous, hollow, coated, and biodegradable microneedles, for controlled transdermal drug delivery. At the end, we discuss current limitations and future prospects of microfluidic platforms for controlled drug delivery.