Rheology Applied to Microgels: Brief (Revision of the) State of the Art

Super-lubricous polyethylene glycol hydrogel microspheres for use in knee osteoarthritis treatments

Knee osteoarthritis (OA) is characterized by cartilage degeneration and significant reduction in lubrication. One strategy to recover the natural lubrication of the synovial fluid is the injection of hydrogel microspheres. Here, we have fabricated polyethylene glycol (PEG)-based hydrogel microspheres via a modified electrospraying setup. To improve throughout, crosslinking of PEG droplets was delayed until after droplet formation was complete. A custom-synthesized super-lubricious copolymer consisting of adhesive dopamine methacrylate (DMA), zwitterionic sulfobetaine methacrylate (SBMA), and fluorescent rhodamine B was used to dip-coat the PEG microspheres. Super-lubricious PEG microspheres coating reduced coefficient of friction by 57% compared to simulated synovial fluid, indicating beneficial lubrication properties. When injected into C57BL6 mice, PEG microspheres exhibited stability for up to 26 d and did not adversely affect mouse behavior. These super-lubricious PEG microspheres offer great promise to reduce the friction that is a hallmark of progressive OA, potentially mitigating the need for total knee arthroplasty.

Methods for determining the structure and physicochemical properties of hyaluronic acid and its derivatives: A review

Hyaluronic acid (HA) is a linear high molecular weight polymer ubiquitously distributed in humans and animals. The D-glucuronic acid and N-acetyl-D-glucosamine repeating disaccharide backbone along with variable secondary and tertiary structures endows HA with unique rheological characteristics as well as diverse biological functions such as maintaining tissue homeostasis and mediating cell functions. Due to its excellent biocompatibility, biodegradability, viscoelasticity and moisturizing properties, natural HA and its chemically modified derivatives are widely used in medical, pharmaceutical, food and cosmetic industries. For broad application purposes, abundant HA-based biochemical products have been developed, including the methodologies for characterization of these products. This review provides an overview focusing on the methods used for determining HA structure as well as the strategies for constructing its derivatives. Apart from the analytical approaches for defining the physicochemical properties of HA (e.g., molecular weight, rheology and swelling capacity), quantitative methods for assessing the purity of HA-based materials are discussed. In addition, the biological functions and potential applications of HA and its derivatives are briefly embarked and perspectives in methodological development are discussed.

Understanding the impact of formulation design on microstructure and drug release from porous microparticle-based tretinoin topical gels

For proportionally formulated intermediate strengths of a topical product, the relationship of drug release across multiple strengths of a given product is not always well understood. The current study aims to assess the proportionality of tretinoin release rates across multiple strengths of tretinoin topical gels when manufactured using two different methods to understand the impact of formulation design on drug product microstructure and tretinoin release rate. Two groups of tretinoin gels of 0.04 %, 0.06 %, 0.08 % and 0.1 % strengths were manufactured. Gels in Group I were prepared by incorporating 4-10 % g/g of 1 % w/w tretinoin-loaded microparticles into a gel base. Gels in Group II were manufactured using 10 % g/g of the microparticles that were loaded with increasing amounts (0.4-1 % w/w) of tretinoin. The two groups of gels were characterized by evaluating microstructure using a polarized microscope, rheology using an oscillatory rheometer, and drug release using Vison® Microette™ Hanson vertical diffusion cells. The microscopic images were used to discriminate between the two groups of gels based on the abundance of microparticles in the gel matrix observed in the images. This abundance increased across gels of Group I and was similar across gels of Group II. The rheology parameters, namely viscosity at a shear rate of 10 s-1, shear thinning rate, storage, and loss modulus, increased across gels of Group I, and were not significantly different across gels of Group II. The release rate of tretinoin from the drug products was proportional to the nominal strength of the drug product in both Group I and Group II, with a correlation coefficient of 0.95 in each case, although the absolute release rates differed. Overall, changing the formulation design of tretinoin topical gels containing porous microparticles may change the physicochemical and structural properties, as well as the drug release rate of the product. Further, keeping the formulation design consistent across all strengths of microparticle-based topical gels is important to achieve proportional release rates across multiple strengths of a given drug product.

Organogels: "GelVolution" in Topical Drug Delivery - Present and Beyond

Topical drug delivery holds immense significance in dermatological treatments due to its non-invasive nature and direct application to the target site. Organogels, a promising class of topical drug delivery systems, have acquired substantial attention for enhancing drug delivery efficiency. This review article aims to explore the advantages of organogels, including enhanced drug solubility, controlled release, improved skin penetration, non-greasy formulations, and ease of application. The mechanism of organogel permeation into the skin is discussed, along with formulation strategies, which encompass the selection of gelling agents, cogelling agents, and additives while considering the influence of temperature and pH on gel formation. Various types of organogelators and organogels and their properties, such as viscoelasticity, non-birefringence, thermal stability, and optical clarity, are presented. Moreover, the biomedical applications of organogels in targeting skin cancer, anti-inflammatory drug delivery, and antifungal drug delivery are discussed. Characterization parameters, biocompatibility, safety considerations, and future directions in optimizing skin permeation, ensuring long-term stability, addressing regulatory challenges, and exploring potential combination therapies are thoroughly examined. Overall, this review highlights the immense potential of organogels in redefining topical drug delivery and their significant impact on the field of dermatological treatments, thus paving the way for exciting prospects in the domain.

Viscoelasticity of Liposomal Dispersions

Janus-faced viscoelastic gelling agents-possessing both elastic and viscous characteristics-provide materials with unique features including strengthening ability under stress and a liquid-like character with lower viscosities under relaxed conditions. The mentioned multifunctional character is manifested in several body fluids such as human tears, synovial liquids, skin tissues and mucins, endowing the fluids with a special physical resistance property that can be analyzed by dynamic oscillatory rheology. Therefore, during the development of pharmaceutical or cosmetical formulations-with the intention of mimicking the physiological conditions-rheological studies on viscoelasticity are strongly recommended and the selection of viscoelastic preparations is highlighted. In our study, we aimed to determine the viscoelasticity of various liposomal dispersions. We intended to evaluate the impact of lipid concentration, the presence of cholesterol or 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and the gelling agents polyvinyl alcohol (PVA) and hydroxyethylcellulose (HEC) on the viscoelasticity of vesicular systems. Furthermore, the effect of two model drugs (phenyl salicylate and caffeine) on the viscoelastic behavior of liposomal systems was studied. Based on our measurements, the oscillation rheological properties of the liposomal formulations were influenced both by the composition and the lamellarity/size of the lipid vesicles.

Rheological Considerations of Pharmaceutical Formulations: Focus on Viscoelasticity

Controlling rheological properties offers the opportunity to gain insight into the physical characteristics, structure, stability and drug release rate of formulations. To better understand the physical properties of hydrogels, not only rotational but also oscillatory experiments should be performed. Viscoelastic properties, including elastic and viscous properties, are measured using oscillatory rheology. The gel strength and elasticity of hydrogels are of great importance for pharmaceutical development as the application of viscoelastic preparations has considerably expanded in recent decades. Viscosupplementation, ophthalmic surgery and tissue engineering are just a few examples from the wide range of possible applications of viscoelastic hydrogels. Hyaluronic acid, alginate, gellan gum, pectin and chitosan are remarkable representatives of gelling agents that attract great attention applied in biomedical fields. This review provides a brief summary of rheological properties, highlighting the viscoelasticity of hydrogels with great potential in biomedicine.