The role of carboxyl group of pressure sensitive adhesive in controlled release of propranolol in transdermal patch: Quantitative determination of ionic interaction and molecular mechanism characterization

Probing the mechanism of release process from metal coordination-based acrylic pressure-sensitive adhesives: Synergistic effect of coordination and hydrogen bonding for controlled drug release

Hydrogen bonding, ionic interactions, and dipole-dipole interactions have been extensively studied to control drug release from patches. However, metal coordination bonding has not been fully explored for the control of transdermal drug release. In this study, metal coordination-based acrylic pressure-sensitive adhesives (PSAs) were designed and synthesized in order to systemically elucidate the effect of metal coordination on drug release from acrylic PSAs. Ketoprofen (KET) and donepezil (DNP) were selected as model drugs. Results showed that the burst release rate of KET was controlled by N-[tris(hydroxymethyl)methyl]acrylamide (NAT) and Fe3+, while the DNP release rate had no significant changes. It was found that the PSA-drug interaction, rather than the molecular mobility of PSA, played a dominant role in the controlled release process of KET. The hydrogen bond interaction between NAT and KET controlled the release process, while the coordination bond interaction between Fe3+ and KET further slowed down the release of KET. In conclusion, it was found that the controlled release of KET was achieved by the synergistic effect of coordination bonding and hydrogen bonding, which opens up a facile but powerful avenue for the design of brand-new controlled release systems and new opportunities for their application in transdermal drug delivery.

Realizing zero-order controlled transdermal drug permeation through competing doubly ionic H-bond in patch

Transdermal drug delivery system (TDDS) was an effective way to realize controlled drug delivery. However, realizing zero-order controlled drug skin delivery was still challenging in the drug-in-adhesive patch. This study provided a strategy to accomplish this delivery form by stabilizing the drug concentration in adhesive through concentration-dependent competitive interaction. Clonidine (CLO) and Granisetron (GRA) were chosen as the model drugs which were of high skin permeability, and polydimethylaminoethyl acrylate (EA) as an excipient to interact with hydroxyphenyl adhesive (HP). Drug release, permeation and pharmacokinetic study were conducted to evaluate the controlled effect of HP-EA. The molecular interaction was characterized by FT-IR, 1H NMR and XPS. Dynamic simulation and molecular docking further clarified the competitive interaction involved in the release process. Both the drug skin permeation study of CLO and GRA patch based on the HP-EA adhesive showed good zero-order fitting with r of 0.994 and 0.998, compared with non-functional adhesive (0-PSA). Furthermore, the pharmacokinetic study of the CLO patch showed a plateau phase for around 52 h without influencing the area under concentration-time curve (AUC), indicating that the HP-EA could realize zero-order drug skin delivery. The mechanism study revealed that EA serving as a 'buffer component' promoted the conversion of the ionic CLO to the neutrals the as the neutrals released, which stabilized '1% neutrals CLO concentration'. In conclusion, the drug delivery system based on the concentration-dependent competitive interaction broadened our understanding of the molecular mechanisms involved in zero-order controlled release in transdermal patches which would promote the development of zero-order drug delivery in TDDS.

Eggshell membrane-incorporated cell friendly tough hydrogels with ultra-adhesive property

Adhesive and tough hydrogels have received increased attention for their potential biomedical applications. However, traditional hydrogels have limited utility in tissue engineering because they tend to exhibit low biocompatibility, low adhesiveness, and poor mechanical properties. Herein, the use of the eggshell membrane (ESM) for developing tough, cell-friendly, and ultra-adhesive hydrogels is described. The ESM enhances the performance of the hydrogel network in three ways. First, its covalent cross-linking with the polyacrylamide and alginate chains strengthens the hydrogel network. Second, it provides functional groups, such as amine and carboxyl moieties, which are well known for enhancing the surface adhesion of biomaterials, thereby increasing the adhesiveness of the hydrogel. Third, it is a bioactive agent and improves cell adhesion and proliferation on the constructed scaffold. In conclusion, this study proposes the unique design of ESM-incorporated hydrogels with high toughness, cell-friendly, and ultra-adhesive properties for various biomedical engineering applications.

High drug-loading and controlled-release hydroxyphenyl-polyacrylate adhesive for transdermal patch

Long-acting transdermal drug delivery system (TDDS) requires high drug-loading and drug controlled-release. To simultaneously improve drug-polymer miscibility and realize drug controlled-release, this work aimed to develop a new pressure sensitive adhesive modified with hydroxyphenyl (HP-PSA) by introducing doubly ionic H-bond into drug-PSA interaction. Eight model drugs divided into R₃N, R₂NH and no N type were chosen to understand the characteristics of the HP-PSA and inner mechanism. The results showed that the doubly ionic H-bond between R₃N and R₂NH type drugs and HP-PSA, differing from the ionic bond and neutral H-bond, was a reversible and relatively strong interaction. It could significantly enhance their drug-loading by 1.5 to 7 times and control drug release rate to its 1/5 to 1/2 without altering its total release properties, outperforming the commercial Duro-Tak® 87-2510 and Duro-Tak® 87-2852 adhesives. According to the pharmacokinetics results, the high drug-loading patches based on HP-PSA achieved a sustainable plasma drug concentration avoiding burst release, and over 2 times area under concentration-time curve (AUC) as well as 6 times mean residence time (MRT) revealed its potential to realize long-acting drug delivery. Additionally, its safety and mechanical features were satisfied. The mechanism study showed that the repulsion of the ionic drugs in HP-PSA increased drug-loading, and the relatively strong interaction could also control drug release. The incomplete H-bond transfer determined its reversibility, thus making the drug release percentage up to that of non-functional PSA. In conclusion, the high drug-loading efficiency and drug controlled-release capacity of HP-PSA, as well as its unique interaction, would contribute to the development of TDDS. Moreover, the construction of the doubly ionic H-bond would provide further inspiration for various drug delivery systems in the non-polar environment.

Mechanistic insights of different release behaviors dominated by drug physicochemical properties in polyisobutylene pressure sensitive adhesive

The purpose of this study was to investigate the effect of the physicochemical parameters of drugs on their own release behaviors in polyisobutylene pressure sensitive adhesive (PIB PSA), which provided a theoretical guidance for the application of PIB in transdermal drug delivery system (TDDS). Seven drugs with different physicochemical parameters including clonidine (CLO), flurbiprofen (FLU), diclofenac (DIC), ibuprofen (IBU), zolmitriptan (ZOL), lidocaine (LID), tulobuterol (TUL) and the mixed adhesive (7:3, w/w) of Oppanol® B 15 N (M.W. = 108,000 Da) and Oppanol® N 50 (M.W. = 565,000 Da) were selected for in vitro drug release and skin permeation studies. Regression analysis was used to study the relationship between physicochemical parameters and release behaviors. The release behaviors of drugs were a negative correlation with polarizability and dipole moment per molecular volume (μ/V), which represented van der Waals and dipole-dipole interaction, respectively. Fourier transform infrared spectroscopy (FT-IR), modulated temperature differential scanning calorimetry (MDSC) and molecular dynamics simulation were used to provide molecular details of the interaction between the drug and PIB. The free volume and molecular mobility of PIB were characterized using mechanical property tests, rheology study, MDSC and molecular dynamics simulation. Based on the above results, drugs with high polarizability and μ/V had stronger van der Waals and dipole-dipole interaction with PIB, reducing the free volume and molecular mobility of PIB, so that the drug struggled to release from PIB. In addition, the diffusion activation energy of the drug was calculated by using the variable temperature release study to characterize the ease of drug release from the kinetic aspect. And the trends of in vitro drug release and skin penetration profiles were basically similar. Thus, it was thought that the physicochemical parameters of the drug played a vital role in the drug release behavior of PIB PSAs and would affect the skin penetration process, which provided a reference for the design and application of patches based on PIB PSAs in TDDS.

The role of hydrophilic/hydrophobic group ratio of polyvinyl alcohol on the miscibility of amlodipine in orodispersible films: From molecular mechanism study to product attributes

The miscibility of the therapeutic drug in the polymer matrix is the key to the successful design and development of orodispersible films (ODFs). In the present study, four hydrolyzed polyvinyl alcohols (PVAs) with identical polymerization degree were investigated as carriers for Amlodipine (AML) ODFs systematically. The drug-polymer miscibility and the intermolecular interaction were investigated by Flory-Huggins theory, Gordon-Taylor theory, molecular simulation, FTIR, Raman and ¹H NMR. The product attributes of ODFs were also studied. A pharmacokinetic study in rats was then conducted using the film product of PVA5-72, the best performer tested. The results revealed that the drug-polymer miscibility decreased linearly with the increase of hydrolyzed degree of PVA. Hydrogen bonds formed between the drug and the hydrophilic and hydrophobic groups of PVAs were the main intermolecular interaction that caused the differences in drug-polymer miscibility. Furthermore, drug-polymer interaction influenced the product attributes of ODFs, including dissolution profile, mechanical properties and physical stability. The pharmacokinetic study showed the ODFs disintegrated rapidly, and the amorphous AML dissolved and absorbed in the gastrointestinal tract, which was comparable to the commercial product. The research offered a foundation for development scientists in designing and formulating PVA films.

Formulation and Evaluation of a Drug-in-Adhesive Patch for Transdermal Delivery of Colchicine

Gout is one of the most prevalent rheumatic diseases, globally. Colchicine (COL) is the first-line drug used for the treatment of acute gout. However, the oral administration of COL is restricted, owing to serious adverse reactions. Therefore, this study aimed to develop a drug-in-adhesive (DIA) patch to achieve transdermal delivery of COL. We investigated the solubility of COL in different pressure-sensitive adhesives (PSAs) using slide crystallization studies. The COL-DIA patches were optimized based on in vitro skin penetration studies and evaluated by in vivo pharmacokinetics and pharmacodynamics. The results showed that the optimized COL-DIA patch contained 10% COL, Duro-Tak 87-2516 as PSA, 5% oleic acid (OA) and 5% propylene glycol (PG) as permeation enhancer, exhibiting the highest in vitro cumulative penetration amount of COL (235.14 ± 14.47 μg∙cm^-2 over 48 h). Pharmacokinetic studies demonstrated that the maximum plasma drug concentration (C_max) was 2.65 ± 0.26 ng/L and the mean retention time (MRT) was 37.47 ± 7.64 h of the COL-DIA patch, effectively reducing the drug side effects and prolonging drug activity. In addition, pharmacodynamic studies showed the patch significantly decreased the expression levels of inflammatory factors of gouty rats and reduced pathological damage in the ankle joint of rats, making it an attractive alternative to the administration of COL for the treatment of gout.

Mechanistic Study of Release Characteristics of Two Active Ingredients in Transdermal Patch Containing Lidocaine-Flurbiprofen Ionic Liquid

Ionic liquids (ILs) have been proven to be an efficient technology for enhancing drug skin permeability. However, the question of whether the two components of ILs are released synchronously in transdermal preparations has remained unclear. Thus, this study aimed to investigate the release characteristics of two components of ILs and their underlying molecular mechanism. The ILs containing flurbiprofen (FLU) and lidocaine (LID) were synthesized and characterized. The four typical acrylates pressure sensitive adhesives (PSAs) with different functional groups were synthesized and characterized. The effects of PSAs on the release characteristics of two components of ILs were investigated by drug release tests and verified by skin permeation experiments. The action mechanisms were revealed by FTIR, Raman, dielectric spectrum, and molecular docking. The results showed that the average release amount of FLU (0.29 μmol/cm2) and LID (0.11 μmol/cm2) of ILs in the four PSAs was significantly different (p < 0.05), which illustrated that the two components did not release synchronously. The PSA−none and PSA−OH with low permittivity (7.37, 9.82) interacted with drugs mainly by dipole-dipole interactions and hydrogen bonds. The PSA−COOH and PSA−CONH2 with high permittivity (11.19, 15.32) interacted with drugs mainly by ionic bonds and ionic hydrogen bonds. Thus, this study provides scientific guidance for the application of ILs in transdermal preparations.

The Molecular Mechanism of Propylene Glycol Monocaprylate on Skin Retention: Probing the Dual Roles on the Molecular Mobility and Collagen Connection in Roflumilast Cream

The present work was to construct a roflumilast (ROF) cream for the treatment of psoriasis and clarify the dual roles of propylene glycol monocaprylate (PGM) in both molecular mobility of the cream, and drug-skin miscibility via drug-PGM-ceramide and drug-PGM-collagen intermolecular interaction. The cream formulation was screened through the stability study and in vitro skin administration study, optimized by Plackett-Burman and Box-Behnken design, and finally verified by the in vivo tissue distribution study. PGM demonstrated a significant drug skin retention enhancement effect (R_{max in vivo} = 19.5 μg/g). It increased the molecular mobility of the oil phase of the cream by decreasing the molecular interaction of oil molecules proven by the rheology study (E_c = 3.73 × 10^-4 mJ·m^-3). More importantly, because of the good stratum corneum (SC) compatibility (∆H =  - 403.88 J/g), PGM promoted an orderly flow of SC lipids (X-ray scattering, ΔLPP = 1.18 nm) and entered the viable epidermis/dermis (VE/DE) in large quantities (R_PGM = 1186 μg/g), acting as a bridge to connect the drug to collagen through two H-bonds (Length_H-bond = 2.846 Å and 3.313 Å), thus increasing the miscibility of drug and VE/DE significantly (∆H =  - 310.10 J/g, E_mix = 21.66 kcal/mol). In this study, a ROF cream was developed successfully and the effect of PGM on the skin retention was clarified at molecular level.

Predicting transdermal fentanyl delivery using physics-based simulations for tailored therapy based on the age

Transdermal fentanyl patches are an effective alternative to the sustained release of oral morphine for chronic pain management. Due to the narrow therapeutic range of fentanyl, the concentration of fentanyl in the blood needs to be carefully monitored. Only then can effective pain relief be achieved while avoiding adverse effects such as respiratory depression. This study developed a physics-based digital twin of a patient by implementing drug uptake, pharmacokinetics, and pharmacodynamics models. The twin was employed to predict the in-silico effect of conventional fentanyl transdermal in a 20–80-year-old virtual patient. The results show that, with increasing age, the maximum transdermal fentanyl flux and maximum concentration of fentanyl in the blood decreased by 11.4% and 7.0%, respectively. However, the results also show that as the patient's age increases, the pain relief increases by 45.2%. Furthermore, the digital twin was used to propose a tailored therapy based on the patient's age. This predesigned therapy customized the duration of applying the commercialized fentanyl patches. According to this therapy, a 20-year-old patient needs to change the patch 2.1 times more frequently than conventional therapy, which leads to 30% more pain relief and 315% more time without pain. In addition, the digital twin was updated by the patient's pain intensity feedback. Such therapy increased the patient's breathing rate while providing effective pain relief, so a safer treatment. We quantified the added value of a patient's physics-based digital twin and sketched the future roadmap for implementing such twin-assisted treatment into the clinics.

Spatial-thermodynamic understanding of stabilization mechanism using computational approaches and molecular-level elucidation of the mechanism of crystal transformation in polymorphic irbesartan nanosuspensions

Irbesartan polymorphisms possess low solubility properties, nanosuspensions represent a method for improving the dissolution. Stabilizers are significant constituents of nanosuspensions. Herein we presented computational research on screening stabilizers and exploring stabilization mechanisms. The crystal transformation mechanism was also investigated. Soluplus-P407 and TPGS-HPMCE5 were screened by spatial conformation and thermodynamic energy analyses. The prepared nanosuspensions improved the dissolution properties of bulk drugs at pH 1.2, 4.5, 6.8. The nanosuspensions stabilization mechanism was analyzed by Molecular docking, Molecular dynamics simulations, Fourier transform infrared spectroscopy and Raman spectroscopy. It might be relate to the decreased enthalpy and Gibbs free energy which were determined by the synergy of external and internal energy factors. The X-ray powder diffraction, differential scanning calorimetry, scanning electron microscopy and transmission electron microscopy showed the crystal structures. The irbesartan B form was transformed in a Soluplus-P407-B/TPGS-HPMCE5-B physical mixture, but not in an SDS (-OH free)-B physical mixture. The intra-proton transfer induced by -OH on the stabilizer might be the transformation mechanism.

The effect of combination of functional and nonfunctional acrylic polymers on transdermal patches of : in vitro permeation, in vivo evaluation using biochemical parameters, and stability studies

Background

A double-layer transdermal drug-in-adhesive patch of carvedilol was developed using functional and nonfunctional grades of acrylic adhesives, DURO-TAK® 387-2051, DURO-TAK® 387-2510, and DURO-TAK® 87-4098. The patch was designed to provide adequate permeation of the drug up to 2 days, with effective adhesion attributes. An optimized formulation was selected, the effect of the combination was studied and a 180° peel strength test was performed to evaluate adhesive properties. Further, the patch was assessed for in vivo studies on basis of biochemical parameters, skin irritation, and stability studies. The stability study was carried out on optimized fresh (S1) and 6 months old patches stored at room, and accelerated condition (40 ± 2 °C/75 ± 5% RH) using FTIR, DSC, and SEM techniques.

Result

It was studied that the steady-state flux (Jss) or permeation rate of the drug through excised rat skin has relied on the nature of acrylic and the combination of acrylic polymers. The TDDS containing –OH functional group DT 387-2510 with nonfunctional pressure-sensitive adhesives (PSAs) DT 87-4098, with Span 80 as penetration enhancer exhibited maximum flux (19.12 ± 0.64 μg/cm2/h) and form homogeneous and stable blends, controlling permeation of drug at a desired steady rate for 48 h. The data obtained from in vivo studies using biochemical parameters suggested that there were no statistical differences observed in results for the control and treated group while analyzing observations for serum creatinine, glucose test, sodium test, albumin, and potassium (p > 0.05). Also, the optimized formulation showed no sign of localized reactions and was confirmed by a skin histological study indicating the formulation was safe and compatible with the skin. A significant shift of peaks was not observed in FTIR spectra and DSC thermograms of the patches after the stability period.

Conclusion

The investigation reveals that the drug-in-adhesive patch of carvedilol, by a combination of functional and nonfunctional PSAs, provides a good and effective option for controlled delivery of carvedilol. From our findings, it has been concluded that drug in the adhesive patch has been able to provide satisfactory adhesion, drug uniformity, drug permeation, marked positive biochemical results, and good stability.

Development of long-acting rivastigmine drug-in-adhesive patch utilizing ion-pair strategy and characterization of controlled release mechanism

The purpose of present study was to develop a long-acting drug-in-adhesive patch of rivastigmine (RVS) to achieve controlled release under high drug loading. Formulation factors including ion-pair, pressure sensitive adhesive (PSA), drug-loading and permeation enhancers were investigated through in vitro skin permeation experiments. Optimized patch was evaluated by pharmacokinetic study. The mechanism of controlled release was studied by FTIR, Raman, DSC, rheology study and molecular modeling. The optimized patch composed of RVS-SA (equal to 30% RVS), 15% POCC as permeation enhancer and AAOH as PSA matrix. The RVS in optimized patch was basically permeated at a uniform rate, and the ratio of the skin permeation amount (2803.38 ± 153.85 μg/cm²) in 72 hours to that of the control group (1000.89 ± 62.45 μg/cm²) was 2.8. The plasma concentration of RVS was stable for 72 hours in vivo (AUC_optimized = 5721.30 ± 1994.87 h ng/mL, MRT_0-t = 29.55 ± 2.49 h), and C_max was significantly controlled. The results of the study on the controlled release mechanism showed that the addition of counter ion formed hydrogen bonds with RVS and PSA respectively, which reduced the fluidity and molecular mobility of PSA, and enhanced the interaction between RVS and PSA, thus achieving the purpose of long-acting effect. In conclusion, long-acting drug-in-adhesive patch of RVS was developed, and provided a new idea for the long term drug delivery of Alzheimer's disease.

A Data-Mining Approach for the Quantitative Assessment of Physicochemical Properties of Molecular Compounds in the Skin Flux

This paper aimed to provide an insight into the mechanism of transdermal penetration of drug molecules with respect to their physicochemical properties, such as solubility (S), the presence of enantiomer (ET) and logarithm of octanol-water partition coefficient (log P), molecular weight (MW), and melting point (MP). Propionic acid derivatives were evaluated for their flux through full-thickness skin excised from hairless mice upon being delivered from silicone-based pressure-sensitive adhesive (PSA) matrices in the presence or absence of various enhancers. The skin fluxes of model compounds were calculated based on the data obtained using the method engaged with the diffusion cell system. The statistical design of experiments (DoE) based on the factorial approach was used to find variables that have a significant impact on the outcomes. For the prediction of skin flux, a quantitative equation was derived using the data-mining approach on the relationship between skin permeation of model compounds (~125 mg/ml) and involved physicochemical variables. The most influential variables for the skin flux of propionic acid derivatives were the melting point (0.97) followed by the presence of enantiomer (0.95), molecular mass (0.93), log P values (0.86), and aqueous solubility (0.80). It was concluded that the skin flux of molecular compounds can be predicted based on the relationship between their physicochemical properties and the interaction with cofactors including additives and enhancers in the vehicles.

Enhanced Drug Loading in the Drug-in-Adhesive Transdermal Patch Utilizing a Drug-Ionic Liquid Strategy: Insight into the Role of Ionic Hydrogen Bonding

Though pharmaceutical polymers were widely used in inhibiting drug recrystallization via strong intermolecular hydrogen and ionic bonds, the improved drug stability was achieved at the cost of the drug release rate or amount in the drug-in-adhesive transdermal patch. To overcame the difficulty, this study aimed to increase drug loading utilizing a novel drug-ionic liquid (drug-IL) strategy and illustrate the underlying molecular mechanism. Here, naproxen (NPX) and triamylamine (TAA) were chosen as the model drug and corresponding counterion, respectively. In addiiton, carboxylic pressure-sensitive adhesive (PSA) was chosen as the model polymer. The drug-IL (NPX-TAA) was synthesized and characterized by differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FT-IR), and proton nuclear magnetic resonance. The miscibility between NPX-TAA and PSA was assessed using microscopy study, X-ray diffraction, fluorescence spectroscopy, and solubility parameter calculation. In addition, molecular mechanisms of crystallization inhibition were revealed by FT-IR, Raman spectroscopy, DSC, X-ray photoelectron spectroscopy (XPS), and molecular docking. Finally, the release pattern of the high load patch of NPX-TAA was evaluated using in vitro drug release and verified by a skin permeation experiment. The results showed that drug loading in PSA was increased by 5.0 times, which was caused by the synergistic effect of strong ionic hydrogen bonding (the decreased intensity and blue shift of the O-H peak of COOH in PSA) formed between NPX-TAA and PSA-COO^- and normal hydrogen bonding (red shift of the C═O peak in PSA) formed between NPX-TAA and the carbonyl group of PSA. In addition, -NH⁺ of TAA was confirmed as the molecular basis of ionic hydrogen bonding through new peak appearance (binding energy: 400.0 eV) in XPS spectra. Moreover, high drug release percent (80.8 ± 1.8%) was achieved even at high drug loading compared with the control group (72.4 ± 2.2%). Thus, this study introduced an effective drug-IL method to enhance drug loading capacity and illustrated the brand-new action mechanism, which provided a powerful instrument for the development of a high drug loading-high release patch.

Prediction of the physical stability of amorphous solid dispersions: relationship of aging and phase separation with the thermodynamic and kinetic models along with characterization techniques

Introduction: Solid dispersion has been considered to be one of the most promising methods for improving the solubility and bioavailability of insoluble drugs. However, the physical stability of solid dispersions (SDs), including its aging and recrystallization, or phase separation, has always been one of the most challenging problems in the process of formulation development and storage.Areas covered: The high energy state of SDs is one of the primary reasons for the poor physical stability. The factors affecting the physical stability of SDs have been described from the perspective of thermodynamics and kinetics, and the corresponding theoretical model is put forward. We briefly summarize several commonly used techniques to characterize the thermodynamic and kinetic properties of SDs. Specific measures to improve the physical stability of SDs have been proposed from the perspective of prescription screening, process parameters, and storage conditions.Expert opinion: The separation of the drug from the polymer, the formation, and migration of drug crystals will cause the SDs to shift toward the direction of energy reduction, which is the intrinsic cause of instability. Furthermore, computational simulation can be used for efficient and rapid screening suitable for the excipients to improve the physical stability of SDs.

Unconventional Passive Enhancement of Transdermal Drug Delivery: toward a Mechanistic Understanding of Penetration Enhancers Releasing from Acrylic Pressure-Sensitive Adhesive of Patches

PURPOSE

Penetration enhancers (PEs) enhancing efficacy depends on two processes: PEs release from patches and action on skin. Compared with their action on skin, PEs release process was poorly understood. Therefore, the purpose of this study was to make a mechanistic understanding of PEs release from acrylic pressure-sensitive adhesive of patches and propose an unconventional enhancement of PEs efficacy.

METHODS

PEs efficacy was evaluated both in drug permeation study and drug pharmacokinetic study. Confocal Raman spectroscopy was employed to observe PEs release behavior by mapping PEs dynamic distribution in skin. The mechanism of PEs release behavior was provided from molecular interaction and rheology using FT-IR, molecular docking, molecular dynamic simulation and rheometer, separately.

RESULTS

The release behavior of PEs themselves greatly restricted their efficacy. By using PEG 400, an improvement of oleic acid (OA) release behavior was achieved, and the efficacy of OA was significantly enhanced with enhancing ratio (ER) from 2.69 to 4.10 and AUC_last from 1574 ± 87 to 2664 ± 249 ng·h/mL, separately. The improvement of OA release behavior was primarily resulted from reduction of the interaction between OA and adhesive, which was caused by other small molecules with a strong ability in forming hydrogen bonds with adhesive. Also, the rigidity of adhesive was a factor in affecting PEs release behavior.

CONCLUSIONS

An unconventional passive enhancement of transdermal drug delivery was achieved via improving PEs themselves releasing from acrylic pressure-sensitive adhesive. Graphical abstract Influence of PEs release behavior on drug permeation through skin and molecular mechanism.

Change of Characterization and Film Morphology Based on Acrylic Pressure Sensitive Adhesives by Hydrophilic Derivative Ratio

Hydrophilic acrylic pressure-sensitive adhesives (PSAs) were synthesized by controlling the contents of 2-ethylhexyl acrylate (EHA), isobornyl acrylate (IBOA), and 2-hydroxyethyl acrylate (HEA); especially, the characteristic change of the HEA content was analyzed. Surface contact angle of acrylic PSA film decreased from 77.87° to 70.23° in the case of Acryl-2 to Acryl-8 (below HEA 10 wt %). However, the surface contact angle of Acryl-10 to Acryl-40 (HEA 10 wt % to 40 wt %) increased up to 92.29°, indicating hydrophobicity. All acrylic PSA films showed high adhesive force above 1800 gf/25 mm. According to X-ray diffraction (XRD) measurement, hydrophilic acrylic PSAs exhibited amorphous property and it was confirmed that the morphology of acrylic PSA film was significantly affected by the flexibility of the polymer chain and the strength of hydrogen bonding. The affinity with hydrophilic materials for acrylic PSA films was evaluated by T-type peel test, confirming that the affinity with hydrophilic materials is determined by the hydrophilicity of the acrylic PSA film. The synthesized acrylic PSA film is non-toxic regardless of the hydrophilicity.

Mechanistic insights of the controlled release capacity of polar functional group in transdermal drug delivery system: the relationship of hydrogen bonding strength and controlled release capacity

Background

Hydrogen bonding interaction was considered to play a critical role in controlling drug release from transdermal patch. However, the quantitative evaluation of hydrogen bonding strength between drug and polar functional group was rarely reported, and the relationship between hydrogen bonding strength and controlled release capacity of pressure sensitive adhesive (PSA) was not well understood. The present study shed light on this relationship.

Methods

Acrylate PSAs with amide group were synthesized by a free radical-initiated solution polymerization. Six drugs, i.e., etodolac, ketoprofen, gemfibrozil, zolmitriptan, propranolol and lidocaine, were selected as model drugs. In vitro drug release and skin permeation experiments and in vivo pharmacokinetic experiment were performed. Partial correlation analysis, fourier-transform infrared spectroscopy and molecular simulation were conducted to provide molecular details of drug-PSA interactions. Mechanical test, rheology study, and modulated differential scanning calorimetry study were performed to scrutinize the free volume and molecular mobility of PSAs.

Results

Release rate of all six drugs from amide PSAs decreased with the increase of amide group concentrations; however, only zolmitriptan and propranolol showed decreased skin permeation rate. It was found that drug release was controlled by amide group through hydrogen bonding, and controlled release extent was positively correlated with hydrogen bonding strength.

Conclusion

From these results, we concluded that drugs with strong hydrogen bond forming ability and high skin permeation were suitable to use amide PSAs to regulate their release rate from patch.

Mechanism and Improved Dissolution of Glycyrrhetinic Acid Solid Dispersion by Alkalizers

The purpose of this study was to increase the dissolution of glycyrrhetinic acid (GA) by preparing ternary solid dispersion (TSD) systems containing alkalizers, and to explore the modulating mechanism of alkalizers in solid dispersion systems. GA TSDs were prepared by hot melt extrusion (HME) with Kollidon^® VA64 as the carrier and L-arginine/meglumine as the alkalizers. The in vitro release of the TSD was investigated with a dissolution test, and the dissociation constant (pKa) was used to describe the ionization degree of the drug in different pH buffers. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-ray powder diffraction (XRPD), Fourier Transform Infrared Spectroscopy (FTIR), Raman spectra, X-ray photoelectron spectroscopy (XPS), and a molecular model were used for solid-state characterizations and to study the dissolution mechanism of the TSDs. It was evident that the dissolution of GA significantly increased as a result of the TSD compared to the pure drug and binary solid dispersion. SEM, DSC, and XPRD data showed that GA transformed into an amorphous form in TSD. As illustrated by FTIR, Raman, XPS, and molecular docking, high binding energy ion-pair complexes formed between GA and the alkalizers during the process of HME. These can destroy the H-bond between GA molecules. Further, intermolecular H-bonds formed between the alkalizers and Kollidon^® VA64, which can increase the wettability of the drug. Our results will significantly improve the solubility and dissolution of GA. In addition, the lower pKa value of TSD indicates that higher ionization is beneficial to the dissolution of the drug. This study should facilitate further developments of TSDs containing alkalizers to improve the dissolution of weakly acidic drugs and gain a richer understanding of the mechanism of dissolution.

Mechanistic Insights of the Critical Role of Hydrogen Donor in Controlling Drug Release From Acrylate Adhesive

In the present study, a pyrrolidone adhesive and an amide adhesive were synthesized, and their molecular mechanisms of controlled drug release were described. Using zolmitriptan as model drug, in vitro drug release and skin permeation experiments were performed. Adhesive properties were evaluated using modulated differential scanning calorimetry and rheology study. Free volume of polymer was directly obtained by positron annihilation lifetime spectroscopy. Intermolecular interactions between drugs and adhesives were determined by FTIR spectroscopic analysis and molecular simulation. Release percent (24 h) of zolmitriptan from pyrrolidone adhesive was about 55.8 ± 3.1% (w/w), while from amide adhesive, the release percent (24 h) was about 40.1 ± 1.6% (w/w). The free volume sizes of pyrrolidone adhesive and amide adhesive were about 2309.6 ų and 2854.5 ų, respectively, which were much larger than molecular volume of zolmitriptan (about 285.7 ų). Thus, the polymer networks might not hinder drug diffusion from the view of free volume. Comparing chemical structures of pyrrolidone group and primary amide group, the main difference was that primary amide group of amide adhesive possessed 2 hydrogen donors. It was proved that hydrogen bonding between zolmitriptan and hydrogen donor of primary amide group played a critical role in controlling drug release.