Lidocaine permeation from a lidocaine NaCMC/gel microgel formulation in microneedle-pierced skin: vertical (depth averaged) and horizontal permeation profiles

Lateral Dermal Penetration is Dependent on the Lipophilicity of Active Ingredients

INTRODUCTION

With its large surface area skin facilitates a topical administration of active ingredients, and thus percutaneous delivery to a specific target site. Due to its high barrier function and different diffusion characteristics skin governs the efficacy of these active ingredients and a bioavailability in the epidermal and dermal tissue.

OBJECTIVE

In order to characterize the vertical and lateral movement of molecules into and inside the skin the diffusivity of active ingredients with different physico-chemical properties and their penetration ability in different dermal skin layers was investigated.

METHODS

A novel lateral dermal microdialysis (MD) penetration setup was used to compare the diffusion characteristics of active ingredients into superficial and deep implanted MD membranes in porcine skin. The corresponding membrane depth was determined via ultrasound and the active ingredients concentration via high-pressure liquid chromatography (HPLC) measurement.

RESULTS

The depth depended penetration of superficial and deep implanted MD membranes and the quantitative diffusivity of two active ingredients was compared. An experimental lateral MD setup was used to determine the influence of percutaneous skin penetration characteristics of an active ingredient with different lipophilic and hydrophilic characteristics. Therefore, hydrophilic caffeine and lipophilic LIP1, which have an identical molecular weight, but different lipophilic characteristics were tested for their penetration ability inside a propylene glycol (PG) and oleic acid (OA) formulation.

CONCLUSION

The vertical and lateral penetration movement of caffeine was found to exceed that of LIP1 through the hydrophilic dermal environment. The findings of this study show that the lipophilicity of active ingredients influence the penetration movement and that skin enables a conical increasing lateral diffusivity and transdermal delivery.

A high-dosage microneedle for programmable lidocaine delivery and enhanced local long-lasting analgesia

Considering the staggering global prevalence of local pain affecting hundreds of million individuals, it is of great significance to develop advanced dosage forms or delivery systems for analgesic therapy to fulfill clinical applicability. In this study, a hydrogel microneedles (MNs) system made out of gelatin-methacryloyl (GelMA) was designed to deliver lidocaine hydrochloride (LiH) in a sustained manner, and the drug loading capacity of the GelMA MNs was increased considerably by using the backing layer reservoir. The in vitro and in vivo tests showed that the fabricated GelMA MNs are strong enough for reliable skin application, and achieve high drug delivery efficiency as compared with the commercial lidocaine patches. The Spared-nerve injury (SNI) model of rats was also prepared to test behavioral pain sensitivity in response to mechanical stimuli, which proved that the LiH/GelMA MNs can enhance and prolong the anesthetic effect of LiH. In addition, with biosafety evaluation in rats, the MNs treated site restored to normal appearance within several hours of application and no dermatosis-related side effects or behavior disorders were observed during the experiment. Together these results indicated that the use of GelMA MNs for transdermal delivery of LiH is an effective, safe and simple treatment method to provide a better choice for local long-lasting analgesia.

Amifostine-loaded armored dissolving microneedles for long-term prevention of ionizing radiation-induced injury

Amifostine is a cytoprotective agent against the hematopoietic damage induced by ionizing radiation, although the intravenous injection of amifostine is a unique administration method with strict dosing time limitation. Hence, the fields of application of amifostine are greatly limited. Here, we developed an amifostine-loaded armored microneedle (AAMN) with long-term prevention of hematopoietic injury induced by ionizing radiation. First, amifostine-loaded hyaluronic acid microneedles (AMNs) were fabricated, and the AMNs were then dipped in an N-vinyl-2-pyrrolidone (NVP) solution followed by ultraviolet (UV) photocuring to obtain AAMNs. AAMNs were nail-shaped with much higher mechanical strength compared to the conical shape and weak strength of AMNs, which was verified by their in silico simulation. In the in vitro release experiment, more than 55% of amifostine was released from AAMNs within 10 min, and 95% was released in 60 min. Drug skin permeation of AAMNs was also high, at twice that of AMNs. AAMNs provided long-term protection of the hematopoietic system from radiation within 3-7 h pre-radiation compared to the unique amifostine injection 0.5 h pre-radiation because topical application of AAMNs led to the long-term maintenance of the in vivo effective drug concentration. More importantly, AAMNs led to the survival of all irradiated mice due to intravenous amifostine. AAMNs are a promising transdermal delivery system of amifostine for long-term protection against ionizing radiation-induced injury. STATEMENT OF SIGNIFICANCE: An amifostine-loaded dissolving armored microneedle (AAMN) patch is developed for long-term prevention of ionizing radiation-induced injury. High drug loads in microneedles (MNs) with adequate mechanical strength is a challenge. We fabricated armors on the surface of high amifostine-loaded hyaluronic acid microneedles (AMNs) by dipping the tips of AMNs in N-vinyl-2-pyrrolidone (NVP) solutions and then subjecting them to UV irradiation, and high-strength armored AMNs (AAMNs) were obtained. AAMNs show deeper skin insertion and much higher drug permeation than AMNs. The controlled drug release from AAMNs in the mouse skins provides a long-term protection of radiation-induced injury with 3-7 h administration pre-radiation compared to the merely 0.5-h point of amifostine injection.

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.

Implantable polymeric microneedles with phototriggerable properties as a patient-controlled transdermal analgesia system

Adequate pain control can be achieved using a patient-controlled drug delivery system that can provide analgesia to patients as needed. To achieve this objective, we developed a phototriggered microneedle (MN) system that enables the on-demand delivery of pain medications to the skin under external near-infrared (NIR) light stimulation. In this system, polymeric MNs, containing NIR absorbers and analgesics, are combined with a poly(l-lactide-co-d,l-lactide) supporting array. A "removable design" of the supporting array enables the quick implantation of the MNs into the skin to act as a drug depot, thus shortening the patch application time. Upon irradiation with NIR light, the NIR absorbers in the implanted MNs can absorb light energy and induce a phase transition in the MNs to activate drug release. We demonstrated that lidocaine release can be modulated or repeatedly triggered by varying the duration of irradiation and controlling the on and off status of the laser. Lidocaine delivered by the implanted MNs can be rapidly absorbed into the blood circulation within 10 min and has a bioavailability of at least 95% relative to the subcutaneous injection, showing that the proposed system has the potential to provide a rapid onset of pain relief. Such an implantable device may allow pain sufferers receiving the painkiller without the need for multiple needle injections, and may enable controlling pain more conveniently and comfortably.

Spreading of a Lidocaine Formulation on Microneedle-Treated Skin

The spreadability of a liquid drug formulation on skin is an indication of it either remaining stationary or distributing (spreading) as a droplet. Factors determining droplet spreadability of the formulation are spreading area, diameter of the droplet base, viscosity of the liquid, contact angle, volume of droplet on skin and any others. The creation of microcavities from the application of microneedle (MN) has the potential to control droplet spreading, and hence, target specific areas of skin for drug delivery. However, there is little work that demonstrates spreading of liquid drug formulation on MN-treated skin. Below, spreading of a lidocaine hydrogel formulation and lidocaine solution (reference liquid) on porcine skin is investigated over MN-treated skin. Controlled spreadability was achieved with the lidocaine hydrogel on MN-treated skin as compared with lidocaine solution. It was observed that the droplet spreading parameters such as spreading radius, droplet height and dynamic contact angle were slightly lower for the lidocaine hydrogel than the lidocaine solution on skin. Also, the lidocaine hydrogel on MN-treated skin resulted in slower dynamic reduction of droplet height, contact angle and reduced time taken in attaining static advancing droplets because of the MN microcavities.