Adhesive backing foil interactions affecting the elasticity, adhesion strength of laminates, and how to interpret these properties of branded transdermal patches

Synthetic Pressure Sensitive Adhesives for Biomedical Applications

Pressure sensitive adhesives are components of everyday products found in homes, offices, industries, and hospitals. Serving the general purpose of fissure repair and object fixation, pressure sensitive adhesives indiscriminately bind surfaces, as long as contact pressure is administered at application. With that being said, the chemical and material properties of the adhesive formulation define the strength of a pressure sensitive adhesive to a particular surface. Given our increased understanding of the viscoelastic material requirements as well as the intermolecular interactions at the binding interface required for functional adhesives, pressure sensitive adhesives are now being explored for greater use. New polymer formulations impart functionality and degradability for both internal and external applications. This review highlights the structure-property relationships between polymer architecture and pressure sensitive adhesion, specifically for medicine. We discuss the rational, molecular-level design of synthetic polymers for durable, removable, and biocompatible adhesion to wet surfaces like tissue. Finally, we examine prevalent challenges in biomedical wound closure and the new, innovative strategies being employed to address them. We conclude by summarizing the progress of current research, identifying additional clinical opportunities, and discussing future prospects.

Preparation and Evaluation of Vitamin D3 Supplementation as Transdermal Film-Forming Solution

Vitamin D3 is available in oral and injectable dosage forms. Interest in the transdermal route as an alternative to the oral and parenteral routes has grown recently. In this study, several film-forming solutions for the transdermal delivery of vitamin D3 were prepared. They contained 6000 IU/mL of vitamin D3 that formed a dry and acceptable film in less than 5 min after application. The formulations consisted of ethanol and acetone 80:20, and one or more of the following ingredients: Eudragit L100-55, PVP, PG, limonene, oleic acid, camphor, and menthol. Vitamin D3 release was studied from both the film-forming solution and pre-dried films using a Franz diffusion cell. The film-forming solution released a significant amount of vitamin D3 compared to the dry film, which is attributed mostly to the saturation driving force due to the evaporation of volatile solvents. In vitro permeation studies through artificial skin Strat M^® membrane revealed that the cumulative amount of vitamin D3 permeated after 24 h under the experimental conditions was around 800 IU across 3.14 cm². The cumulative permeation curve showed faster permeation in earlier stages. Young's modulus, viscosity, and pH of the formulations were determined. Most of the formulations were stable for 3 weeks.

Antimicrobial adhesive polyurethane gel sheet with cetylpyridinium chloride-montmorillonite for facial and somato prosthesis fastening

PURPOSE

Existing options for attaching facial and somato prostheses, such as skin adhesives, are problematic because of microbial colonization and skin irritation. This study aims to evaluate the suitability of adhesive polyurethane gel sheets containing cetylpyridinium chloride (CPC)-montmorillonite (Mont) for prosthesis fastening.

METHODS

Adhesive gel sheets were fabricated as mixtures of base resin (99.6 wt% polyol) and hardening agent at a ratio of 3:1 with 0 (control), 2, 5, 10, or 15 wt% CPC-Mont. The controlled release of CPC, antimicrobial activity, in vitro skin irritation, and adhesive force against silicone and human skin at different blending ratios were determined. Statistical analyses of the data were performed using one-way analysis of variance (ANOVA), analysis of covariance (ANCOVA), Tukey's test, or single regression analysis, as appropriate.

RESULTS

The amount of CPC released increased with the CPC-Mont blending ratio and was linearly proportional to the surface occupation area ratio of CPC-Mont. The samples with >5 wt% CPC-Mont exhibited antimicrobial activity against Staphylococcus aureus at an exposure time of 0 d, and samples with >2 wt% CPC-Mont exhibited antimicrobial activity against Candida albicans at an exposure time of 1 d. All samples were classified as non-irritant based on an in vitro skin irritation test. The adhesive force on the silicone material and human skin decreased with increasing CPC-Mont blending ratio.

CONCLUSION

Samples with 5 wt% CPC-Mont are potential candidates as antimicrobial adhesive polyurethane gel sheets for fastening facial and somato prostheses.

Statistical considerations and impact of the FDA draft guidance for assessing adhesion with transdermal delivery systems and topical patches for ANDAs

Until 2016, a ratio of means (ROM) non-inferiority (NI) test was recommended in FDA product-specific guidances (PSGs) to evaluate adhesion performance for prospective generic transdermal delivery systems (TDS). However, the ROM NI test had low power for well-adhering TDS, which were becoming increasingly prevalent. Mathematical proof and simulation revealed that the low power wasn't because the non-normality of adhesion data violated the normality assumption of parametric methods; it was because the ROM NI test was coupled with an adhesion scale where scores approached 0 as adhesion got better. In June 2016, FDA published a draft general guidance on TDS adhesion and recommended a new statistical approach, replacing the ROM NI test with a difference-of-means (DOM) NI test, using the same scale and primary endpoint (mean adhesion scores). An analysis of 40 TDS adhesion studies submitted in ANDAs after the publication of the 2016 draft guidance suggests that, consistent with simulation results, the new statistical approach markedly improves the low power, and thereby reduces the sample size required by the old approach for moderately to well-adhering TDS, while retaining comparable power for poorly adhering TDS. The new statistical approach thus enhances the potential approvability and patient access to well-adhering generic TDS.

Gold Nanoparticle and Hydrophobic Nanodiamond Based Synergistic System: A Way to Overcome Skin Barrier Function

Gold nanoparticles (AuNP) have attracted ample attention as a transdermal (TND) drug delivery platform for improving the skin permeability of drug molecules. Herein a novel TND device formed from AuNP and oleylamine functionalized nanodiamond (AuD) has been developed successfully for the TND delivery of Ketoprofen (KP), a model drug. Poly(vinyl alcohol)/Polybutyl methacrylate (PVA/PBMA) film has been selected as the matrix of the TND device, as they furnish excellent skin adhesion properties. The PVA/PBMA membranes loaded with different concentrations of AuD have been characterized in terms of surface morphology, thermomechanical properties, water vapor permeability (WVP), optical transmittance, cosmetic attractiveness, skin adhesion behavior, and drug encapsulation efficiency (DEE). The matrix loaded with 3.0% AuD displayed enhanced thermomechanical and DEE due to the uniform distribution of nanofillers in the membrane. The in vitro skin permeation test proved that a higher amount of KP was delivered by AuD incorporated films, suggesting improved TND behavior. The synergistic management of AuNP and nanodiamonds (ND) has caused the enhanced skin permeation behavior of the device. The obtained results revealed that AuD may be employed as an effective carrier to substitute NDs for TND delivery. Additionally, while investigating the storage stability of the device we observed that the membrane kept at low temperature presented stability over time. More importantly, the results from cell viability assay and environmental fitness test revealed that the AuD based TND system is a high security device, as it is noncytotoxic and microbe-resistant. The developed device provides a novel and handy approach to the TND delivery of drug molecules.

Tuning the rheological properties of an ammonium methacrylate copolymer for the design of adhesives suitable for transdermal patches

Eudragit® RL (EuRL) matrices have been proposed to release a drug to the skin. However, no information is available on both viscoelastic and adhesive properties of such compositions. This work focuses on the evaluation of both rheological and texture properties of EuRL differently plasticized with tributyl citrate (TBC) or triacetin (TRI) in order to design a pressure sensitive adhesive suitable for transdermal patch preparation. The patch adhesive properties (i.e. tack, peel adhesion and shear adhesion) as well as its in vitro biopharmaceutical performances were determined after loading ibuprofen, ketoprofen or flurbiprofen. The addition of 40-60% w/w TBC or 40-50% w/w TRI to EuRL permitted to obtain matrices with the desired adhesive properties. Moreover, the increase of plasticizer content and loading of the drug reduced the relaxation time (τ_R). Consequently, the shear adhesion values decreased and the in vitro drug release constants (k) increased. Indeed, the k values from patches containing TBC were lower than the corresponding with TRI because of the lower fluidity of such matrices. In conclusion, the 60/40 EuRL/TBC binary blend is suitable for the design of transdermal patches since the in vitro permeability of the three selected drugs appeared comparable to those described in literature for marketed products.

Methacrylate-Stitched β-Cyclodextrin Embedded with Nanogold/Nanotitania: A Skin Adhesive Device for Enhanced Transdermal Drug Delivery

Transdermal (TD) drug delivery is a more attractive technique for drug delivery compared to oral and intravenous injection. However, the permeation of drug molecules across the skin is difficult due to the presence of highly ordered lipid barrier. This study details the development of a novel TD system, which has the potential to simultaneously enhance the skin permeability and adhesion behavior. Ibuprofen (IP) was selected as model drug. The ability of gold nanoparticle (AuNP) and hydrophobic titanium nanotube (TNT) to enhance the skin permeability was explored. Additionally, β-cyclodextrin (βCD), which can exceptionally encapsulate poorly water-soluble drugs, is grafted with methacrylates to improve the skin adhesion property. Finally, Au-TNT nanocomposite was deposited onto methacrylate-grafted βCD matrix. The developed material was characterized through NMR spectroscopy, infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. The characteristics of the film, including water vapor permeability (WVP), thermomechanical properties, etc., were examined in terms of Au-TNT content. The TD delivery of IP with different concentrations of Au-TNT was evaluated via an in vitro skin permeation study through rat skin. It is revealed that the prepared TD film exhibited an improved drug-delivery performance due to the synergistic action of AuNP and hydrophobic TNT. The cumulative percent of IP delivered across the skin is extremely depending on nanofiller content, lipophilicity, and thickness of the membrane, and the device incorporated with 4.0% Au-TNT displayed the best performance. In addition, a study on storage stability was performed by storing the films for 2 months at different temperatures. The study revealed that the device possessed excellent storage stability when stored at low temperature. The developed film offers excellent WVP, drug encapsulation efficiency, thermomechanical properties, and skin adhesion behavior. Moreover, the device was cosmetically attractive, noncytotoxic, and resistant to microbial growth and hence extremely reliable for skin application. The developed skin permeation strategy may open new avenues in TD drug delivery.

Validation of a fentanyl transdermal adhesion scoring tool for use in clinical practice

CONTEXT

The therapeutic efficacy of a transdermal system (TDS) is directly related to the adhesion of TDS, with partial adhesion resulting in lower plasma concentration. Currently there is no TDS adhesion scoring tool available for use in the clinical setting.

OBJECTIVES

To validate a U.S. Food and Drug Administration (FDA) scoring system for the adhesion of the fentanyl TDS in cancer patients.

METHODS

A library of images was created from photographs of fentanyl/placebo TDS placed on patients/volunteers. Thirty photographs, reflecting varying degrees of adhesion, were selected for each of series A and B, with 10 photographs common to both series. Each series was shown to 30 health professionals asked to score the photographs using the FDA scoring system. Validity was assessed using Spearman's rank correlation and reliability by Cohen's kappa (k). Photo editing software was used to assign control scores to each photograph.

RESULTS

Validity was high for both series (≥ 0.954). Inter-reliability (k) ranged from 0.327 to 0.858 (average, 0.547) and 0.433-0.910 (average, 0.620) in series A and B, respectively. The combined agreement across both series was 0.585. Intra-rater agreement (k) of the 10 common images was 0.605. No significant difference was observed between the scoring patterns for those with more than 10 years of working experience.

CONCLUSION

Overall, the TDS adhesion score determined by the participants visually in this study corresponded well to those generated by photo editing software, thus rendering the scoring system highly valid. The FDA scoring system is an adequate tool for assessing fentanyl TDS adhesion in clinical practice.

Investigations on the viscoelastic performance of pressure sensitive adhesives in drug-in-adhesive type transdermal films

Purpose

We aimed to investigate the effect of solubility parameter and drug concentration on the rheological behaviour of drug-in-adhesive films intended for transdermal application.

Methods

Films were prepared over a range of drug concentrations (5%, 10% and 20% w/w) using ibuprofen, benzoic acid, nicotinic acid and lidocaine as model drugs in acrylic (Duro-Tak 87-4287 and Duro-Tak 87900A) or silicone (Bio-PSA 7-4301 and Bio-PSA 7-4302) pressure sensitive adhesives (PSAs). Saturation status of films was determined using light microscopy. Viscoelastic parameters were measured in rheology tests at 32°C.

Results

Subsaturated films had lower viscoelastic moduli whereas saturated films had higher moduli than the placebo films and/or a concentration-dependent increase in their modulus. Saturation concentration of each drug in the films was reflected by decreasing/increasing viscoelastic patterns. The viscoelastic windows (VWs) of the adhesive and drug-in-adhesive films clearly depicted the effect of solubility parameter differences, molar concentration of drug in the adhesive film and differences in PSA chemistry.

Conclusions

Drug solubility parameters and molar drug concentrations have an impact on rheological patterns and thus on the adhesive performance of tested pressure sensitive adhesives intended for use in transdermal drug delivery systems. Use of the Flory equation in its limiting form was appropriate to predict drug solubility in the tested formulations.

Critical attributes of transdermal drug delivery system (TDDS)--a generic product development review

Bioequivalence testing of transdermal drug delivery systems (TDDS) has always been a subject of high concern for generic companies due to the formulation complexity and the fact that they are subtle to even minor manufacturing differences and hence should be clearly qualified in terms of quality, safety and efficacy. In recent times bioequivalence testing of transdermal patches has gained a global attention and many regulatory authorities worldwide have issued recommendations to set specific framework for demonstrating equivalence between two products. These current regulatory procedures demand a complete characterization of the generic formulation in terms of its physicochemical sameness, pharmacokinetics disposition, residual content and/or skin irritation/sensitization testing with respect to the reference formulation. This paper intends to highlight critical in vitro tests in assessing the therapeutic equivalence of products and also outlines their valuable applications in generic product success. Understanding these critical in vitro parameters can probably help to decode the complex bioequivalence outcomes, directing the generic companies to optimize the formulation design in reduced time intervals. It is difficult to summarize a common platform which covers all possible transdermal products; hence few case studies based on this approach has been presented in this review.

Adhesive properties: a critical issue in transdermal patch development

INTRODUCTION

Transdermal patches and medicated plasters (patch) represent well-established prolonged release dosage forms. Even if satisfactory adhesion to the skin is strictly linked to the efficacy and safety of the therapeutic treatment, nowadays numerous reports of in vivo 'adhesion lacking' are still addressed to regulatory agencies. The adhesive properties of a patch should be characterized considering i) the ability to form a bond with the surface of another material on brief contact and under light pressure (tack); ii) the resistance of the adhesive to flow (shear adhesion); and iii) the force required to peel away a patch from a surface (peel adhesion).

AREAS COVERED

In this manuscript, the most widely used methods to measure adhesive properties during development studies are described, along with the quality control of patches. The influence of formulative variables on patch adhesive properties, and their possible relationship with the in vivo adhesion performances, is also discussed.

EXPERT OPINION

The Pharmacopoeias should consider the opportunity of introducing compendial testing to assay the quality of adhesive patch properties, and regulatory agencies should issue proper guidelines to evaluate these features during development.