Understanding the adhesion phenomena in carbohydrate-hydrogel-based systems: Water up-take, swelling and elastic detachment

Coupled Diffusion-Binding-Deformation Modelling for Phase-Transition Microneedles-Based Drug Delivery

Phase-transition microneedles (PTMNs)-based transdermal drug delivery (TDD) is gaining popularity due to its non-invasiveness and ability to deliver a wide range of drugs. PTMNs absorb interstitial skin fluid (ISF) and transport drugs from microneedle (MNs) domain to the skin without polymer dissolution. To establish PTMNs for practical use, one needs to understand and optimise the key parameters governing drug transport mechanisms to achieve controlled drug delivery. In addressing this point, we have developed a coupled diffusion-binding-deformation model to understand the effect of physicochemical parameters (e.g., swelling capacity, drug binding) of MN and skin mechanical properties on overall drug transport behaviour. The contact mechanics at the MN and skin interface is introduced to account for the resistive force exerted by the deformed skin to MN swelling. The model is validated with the reported data of in vitro insulin delivery using polyvinyl alcohol (PVA) MN. The drug binding parameters are estimated from the fitting of the cumulative release of insulin within 6 hours of MN insertion. To predict the in vivo data of insulin delivery using the PVA MN, one-compartment model of drug pharmacokinetics is incorporated. It is shown in the paper that the model is able to predict the final insulin concentration in blood and in good agreement with the reported experimental data. The proposed model is concluded to be a tool for the predictive design and development of PTMNs-based TDD systems.

Super-swelling Hydrogel-forming Microneedle based Transdermal Drug Delivery: Mathematical Modelling, Simulation and Experimental Validation

Super-swelling hydrogel-forming microneedles (HFMNs) based transdermal drug delivery (TDD) is gaining significant interest due to their non-invasiveness and ability to deliver a wide range of drugs. The HFMNs swell by imbibing interstitial skin fluid (ISF), and they facilitate drug transport from the reservoir attached at the base into the skin without polymer dissolution. To develop HFMNs for practical applications, a complete understanding of the drug transport mechanism is required, allowing for controlled TDD and geometrical optimisation. A three-phase system consisting of a reservoir, microneedle, and skin is considered. A mathematical model is developed to incorporate the drug binding within the matrix of the compartment, which was not considered earlier. Super-swelling nature of the HFMNs is incorporated through the swelling ratio obtained experimentally for a polymer. The results are validated with in vitro diffusion studies of ibuprofen sodium (IBU) across excised porcine skin, showing that around 20% of the loaded IBU in lyophilised wafer was delivered in 24 hours. It was observed that increasing IBU solubility in reservoir can achieve high drug transport across the skin. The developed model is shown to be in good agreement with the experimental data. It is concluded that the proposed model can be considered a tool with predictive design and development of super-swelling HFMNs based TDD systems.

Hydrogel-based commercial products for biomedical applications: A review

Hydrogels are hydrophilic polymer networks, able to absorb large amount of water, increasing their volume and showing a plethora of different material behaviors. Since their first practical application, dating from sixties of last century, they have been employed in several fields of biomedical sciences. After more than half a century of industrial uses, nowadays a lot of hydrogels are currently on the market for different purposes, and offering a wide spectra of features. In this review, even if it is virtually impossible to list all the commercial products based on hydrogels for biomedical applications, an extensive analysis of those materials that have reached the market has been carried out. The hydrogel-based materials used for drug delivery, wound dressing, tissue engineering, the building of contact lens, and hygiene products are enlisted and briefly described. A detailed snapshot of the set of these products that have reached the commercial maturity has been then obtained and presented. For each class of application, the basics of requirements are described, and then the materials are listed and classified on the basis of their chemical nature. For each product the commercial name, the producer, the chemical nature and the main characteristics are reported.

Mucoadhesive hydrogels for buccal drug delivery: In vitro-in vivo correlation study

AIM

It was the aim of this study to assess in vitro methods for the characterization of mucoadhesive hydrogels for their potential to predict the residence time on human buccal mucosa.

METHODS

Mixtures of hydrogels comprising hydroxyethyl cellulose (HEC), sodium carboxymethyl cellulose (CMC), xanthan gum (XTGM), hyaluronic acid sodium salt (HA), sodium alginate (ALG), carbopol (CP) as well as polycarbophil (PCP) and porcine mucus were analysed for relative rheological synergism. Furthermore, hydrogels were characterized for their texture and mechanical properties. For the assessment of mucoadhesive strength of formulations tensile studies were performed on porcine buccal mucosa. To facilitate a direct comparability of data the residence time of stained hydrogels was determined ex vivo on porcine buccal mucosa and in the oral cavity of volunteers.

RESULTS

The extent of relative rheological synergism was in good agreement with data from in vivo residence time studies. Results of tensile studies were further effected by textural properties of hydrogels leading to a restricted correlation with data from the in vivo experiment. The resistance towards removal by artificial saliva flow ex vivo revealed the highest correlation to the in vivo experiment with increasing mucosal residence time in the rank order CP < HEC, HA, ALG, PCP < CMC < XTGM.

CONCLUSIONS

This overview of measurement principles to predict the residence time of hydrogels for buccal application in humans may be a potent tool for the development of semisolid intraoral formulations.

Interfacial fluid transport is a key to hydrogel bioadhesion

Attaching hydrogels to soft internal tissues is a key to the development of a number of biomedical devices. Nevertheless, the wet nature of hydrogels and tissues renders this adhesion most difficult to achieve and control. Here, we show that the transport of fluids across hydrogel-tissue interfaces plays a central role in adhesion. Using ex vivo peeling experiments on porcine liver, we characterized the adhesion between model hydrogel membranes and the liver capsule and parenchyma. By varying the contact time, the tissue hydration, and the swelling ratio of the hydrogel membrane, a transition between two peeling regimes is found: a lubricated regime where a liquid layer wets the interface, yielding low adhesion energies (0.1 J/m2 to 1 J/m2), and an adhesive regime with a solid binding between hydrogel and tissues and higher adhesion energies (1 J/m2 to 10 J/m2). We show that this transition corresponds to a draining of the interface inducing a local dehydration of the tissues, which become intrinsically adhesive. A simple model taking into account the microanatomy of tissues captures the transition for both the liver capsule and parenchyma. In vivo experiments demonstrate that this effect still holds on actively hydrated tissues like the liver capsule and show that adhesion can be strongly enhanced when using superabsorbent hydrogel meshes. These results shed light on the design of predictive bioadhesion tests as well as on the development of improved bioadhesive strategies exploiting interfacial fluid transport.