Lipid-coated microgels for the triggered release of doxorubicin

Explosomes: A new modality for DEB-TACE local delivery of sorafenib: In vivo proof of sustained release

The current medical practice in treating Hepatocellular carcinoma (HCC) using Drug Eluting Transarterial chemoembolization (DEB-TACE) technique is limited only to hydrophilic ionizable drugs, that can be attached ionically to the oppositely charged beads. This limitation has forced physicians to subscribe the more hydrophobic, first treatment option drugs, like sorafenib systemically via the oral route, thus flooding the patient system with a very powerful, non-specific, multiple-receptor tyrosine kinase inhibitor that is associated with notorious side effects. In this paper, a new modality is introduced, where highly charged, drug loaded liposomes are added to oppositely charged DEBs in a manner causing them to "explode" and the drug is eventually attached to the beads in the lipid patches covering their surfaces; therefore we call them "Explosomes". After fully describing the preparation process and in vitro characterization, this manuscript delves into an in vivo pharmacokinetic study over 50 New Zealand rabbits, where explosomal loading is challenged vs oral as well as current practice of emulsifying sorafenib in lipiodol. Over 14 days of follow up, and compared to other groups, explosomal loading of SRF on embolic beads proved to cause a slower release pattern with longer Tmax, lower Cmax and less washout to general circulation in healthy animals. This treatment modality opens a new untapped door for local sustained delivery of hydrophobic drugs in catheterized organs.

Using the Water Absorption Ability of Dried Hydrogels to Form Hydrogel-Supported Lipid Bilayers

The formation of supported lipid bilayers (SLBs) on hydrogels can act as a biocompatible anti-fouling interface. However, generating continuous and mobile SLBs on materials other than conventional glass or mica remains a significant challenge. The interaction between lipid membrane vesicles and a typical hydrogel is usually insufficient to induce membrane vesicle rupture and form a planar lipid membrane. In this study, we demonstrate that the water absorption ability of a dried polyacrylamide (PAAm) hydrogel could serve as a driving force to facilitate the formation of the hydrogel-SLBs. The absorption driving force vanishes after the hydrogels are fully hydrated, leaving no extra interaction hindering lipid lateral mobility in the formed SLBs. Our fluorescence recovery after photobleaching (FRAP) results show that SLBs only form on hydrogels with adequate absorption abilities. Moreover, we discovered that exposure to oxygen during drying could lead to the formation of an oxidized crust on the PAAm hydrogel surface, impeding SLB formation. Therefore, minimizing oxygen exposure during drying is crucial to achieving high-quality hydrogel surfaces for SLB formation. This water absorption method enables the straightforward fabrication of hydrogel-SLBs without the need for additional substrates or charges, thereby expanding their potential applications.

Design and applications of liposome-in-gel as carriers for cancer therapy

Cancer has long been a hot research topic, and recent years have witnessed the incidence of cancer trending toward younger individuals with great socioeconomic burden. Even with surgery, therapeutic agents serve as the mainstay to combat cancer in the clinic. Intensive research on nanomaterials can overcome the shortcomings of conventional drug delivery approaches, such as the lack of selectivity for targeted regions, poor stability against degradation, and uncontrolled drug release behavior. Over the years, different types of drug carriers have been developed for cancer therapy. One of these is liposome-in-gel (LP-Gel), which has combined the merits of both liposomes and hydrogels, and has emerged as a versatile carrier for cancer therapy. LP-Gel hybrids have addressed the lack of stability of conventional liposomes against pH and ionic strength while displaying higher efficiency of delivery hydrophilic drugs as compared to conventional gels. They can be classified into three types according to their assembled structure, are characterized by their nontoxicity, biodegradability, and flexibility for clinical use, and can be mainly categorized based on their controlled release, transmucosal delivery, and transdermal delivery properties for anticancer therapy. This review covers the recent progress on the applications of LP-Gel hybrids for anticancer therapy.

Effects of Lipid Shape and Interactions on the Conformation, Dynamics, and Curvature of Ultrasound-Responsive Liposomes

We perform coarse-grained molecular dynamics simulations of bilayers composed of various lipids and cholesterol at their different ratios. Simulations show that cholesterol-lipid interactions restrict the lateral dynamics of bilayers but also promote bilayer curvature, indicating that these opposite effects simultaneously occur and thus cannot significantly influence bilayer stability. In contrast, lyso-lipids effectively pack the vacancy in the bilayer composed of cone-shaped lipids and thus reduce bilayer dynamics and curvature, showing that bilayers are more significantly stabilized by lyso-lipids than by cholesterol, in agreement with experiments. In particular, the bilayer composed of cone-shaped lipids shows higher dynamics and curvature than does the bilayer composed of cylindrical-shaped lipids. To mimic ultrasound, a high external pressure was applied in the direction of bilayer normal, showing the formation of small pores that are surrounded by hydrophilic lipid headgroups, which can allow the release of drug molecules encapsulated into the liposome. These findings help to explain experimental observations regarding that liposomes are more significantly stabilized by lyso-lipids than by cholesterol, and that the liposome with cone-shaped lipids more effectively releases drug molecules upon applying ultrasound than does the liposome with cylindrical-shaped lipids.

Electrophoresis of dielectric and immiscible-liquid-layer-encapsulated colloids in aqueous media

In this paper we consider the electrophoresis of a functionalized nanoparticle in electrolyte solution. The undertaken particle is comprised of a rigid inner core encapsulated with a layer of dielectric liquid (e.g., oil or lipid layer), which is immiscible to the bulk aqueous medium. The peripheral liquid layer of the undertaken nanoparticle contains mobile charges due to presence of solubilized surfactants. The mobile electrolyte ions can penetrate across the peripheral layer depending on the difference in the Born energy of the both phases. Such types of nanoparticles have received substantial attention due to their widespread applications in biomedical research. The electric double layer (EDL) is governed by the linearized Poisson-Boltzmann equation under a low potential limit and the electroosmotic flow field is governed by modified Stokes equation. We adopt the flat-plate formalism to obtain the closed analytical expression for the electrophoretic mobility of the undertaken particle under a thin EDL approximation. The dependence of electrophoretic mobility on the pertinent parameters is also illustrated.

Self-Healing of Electrical Damage in Polymers

Polymers are widely used as dielectric components and electrical insulations in modern electronic devices and power systems in the industrial sector, transportation, and large appliances, among others, where electrical damage of the materials is one of the major factors threatening the reliability and service lifetime. Self-healing dielectric polymers, an emerging category of materials capable of recovering dielectric and insulating properties after electrical damage, are of promise to address this issue. This paper aims at summarizing the recent progress in the design and synthesis of self-healing dielectric polymers. The current understanding to the process of electrical degradation and damage in dielectric polymers is first introduced and the critical requirements in the self-healing of electrical damage are proposed. Then the feasibility of using self-healing strategies designed for repairing mechanical damage in the healing of electrical damage is evaluated, based on which the challenges and bottleneck issues are pointed out. The emerging self-healing methods specifically designed for healing electrical damage are highlighted and some useful mechanisms for developing novel self-healing dielectric polymers are proposed. It is concluded by providing a brief outlook and some potential directions in the future development toward practical applications in electronics and the electric power industry.

Sphere-Tubule Superstructures through Supramolecular and Supracolloidal Assembly Pathways

While colloids have been widely employed as models for atoms and molecules, the current study proposes to extend their use as building blocks for supracolloidal frameworks. Hereby, the self-assembly between highly anisotropic supramolecular microtubules and soft spherical fluorescent microgels is explored using confocal laser scanning microscopy. The influence of the particle size and charge with respect to the catanionic tubule composition, which consists of two oppositely charged bile salt derivatives, is investigated. Under certain conditions, microgel particles are found to specifically interact with the extremities of the tubular aggregates and hierarchically self-assemble into various superstructures varying from virus-like assemblies to supracolloidal networks. The reported approach is envisioned to open new self-assembly routes toward ordered hybrid superstructures where the spherical colloids act as responsive linkers of tubular structures.

Single bead investigation of a clinical drug delivery system - A novel release mechanism

Microgels, such as polymeric hydrogels, are currently used as drug delivery devices (DDSs) for chemotherapeutics and/or unstable drugs. The clinical DDS DC bead® was studied with respect to loading and release, measured as relative bead-volume, of six amphiphilic molecules in a micropipette-assisted microscopy method. Theoretical models for loading and release was used to increase the mechanistic understanding of the DDS. It was shown that equilibrium loading was independent of amphiphile concentration. The loading model showed that the rate-determining step was diffusion of the molecule from the bulk to the bead surface ('film control'). Calculations with the developed and applied release model on the release kinetics were consistent with the observations, as the amphiphiles distribute unevenly in the bead. The rate determining step of the release was the diffusion of the amphiphile molecule through the developed amphiphile-free depletion layer. The release rate is determined by the diffusivity and the tendency for aggregation of the amphiphile where a weak tendency for aggregation (i.e. a large cac_b) lead to faster release. Salt was necessary for the release to happen, but at physiological concentrations the entry of salt was not rate-determining. This study provides valuable insights into the loading to and release from the DDS. Also, a novel release mechanism of the clinically used DDS is suggested.

Manipulating Single Microdroplets of NaCl Solutions: Solvent Dissolution, Microcrystallization, and Crystal Morphology

A new "three-micropipette manipulation technique" for forming, dehydrating, crystallizing, and resolvating nanograms of salt material has been developed to study supersaturated single microdroplets and microcrystals. This is the first report of studies that have measured in situ both supersaturation (as homogeneous nucleation) and saturation (as microcrystal redissolution) for single microdroplets of NaCl solution using the micropipette technique. This work reports a measure of the critical supersaturation concentration for homogeneous nucleation of NaCl (10.3 ± 0.3 M) at a supersaturation fraction of S = 1.9, the saturation concentration of NaCl in aqueous solution as measured with nanograms of material (5.5 ± 0.1 M), the diffusion coefficient for water in octanol, D = (1.96 ± 0.10) × 10^-6 cm²/s, and the effect of the solvent's activity on dissolution kinetics. It is further shown that the same Epstein-Plesset (EP) model, which was originally developed for diffusion-controlled dissolution and uptake of gas, and successfully applied to liquid-in-liquid dissolution, can now also be applied to describe the diffusion-controlled uptake of water from a water-saturated environment using the extended activity-based model of Bitterfield et al. This aspect of the EP model has not previously been tested using single microdroplets. Finally, it is also reported how the water dissolution rate, rate of NaCl concentration change, resulting crystal structure, and the time frame of initial crystal growth are affected by changing the bathing medium from octanol to decane. A much slower loss of water-solvent and concomitant slower up-concentration of the NaCl solute resulted in a lower tendency to nucleate and slower crystal growth because much less excess material was available at the onset of nucleation in the decane system as compared to the octanol system. Thus, the crystal structure is reported to be dendritic for NaCl solution microdroplets dissolving rapidly and nucleating violently in octanol, while they are formed as single cubic crystals in a gentler way for solution-dissolution in decane. These new techniques and analyses can now also be used for any other system where all relevant parameters are known. An example of this is control of drug/hydrogel/emulsion particle size change due to solvent uptake.

Lipogels for Encapsulation of Hydrophilic Proteins and Hydrophobic Small Molecules

Lipid-polymer hybrid materials have the potential to exhibit enhanced stability and loading capabilities in comparison to parent liposome or polymer materials. However, complexities lie in formulating and characterizing such complex nanomaterials. Here we describe a lipid-coated polymer gel (lipogel) formulated using a single-pot methodology, where self-assembling liposomes template a UV-curable polymer gel core. Using fluorescently labeled lipids, protein, and hydrophobic molecules, we characterized their formation, purification, stability, and encapsulation efficiency via common instrumentation methods such as dynamic light scattering (DLS), matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS), UV-vis spectroscopy, fluorescence spectroscopy, and single-particle total internal reflection fluorescence (TIRF) microscopy. In addition, we confirmed that these dual-guest-loaded lipogels are stable in solution for several months. The simplicity of this complete aqueous formation and noncovalent dual-guest encapsulation holds potential as a tunable nanomaterial scaffold.

Synthesis of monodisperse core shell PVA@P(AMPS-co-NIPAm) nanogels structured for pre-concentration of Fe(III) ions

Core shell-structured poly(vinyl alcohol) @ poly(2-acrylamido-2-methyl-1-propane-sulfonic acid-co-N-isopropylacrylamide) PVA@P(AMPS-co-NIPAm) spheres are synthesized. The well-defined PVA@P(AMPS-co-NIPAm) core shell nanogels with diameter nearly 30 nm enriches Fe(III), and the nanogels are characterized by FT-IR, TEM, SEM and X-ray diffraction (XRD). The many factors affecting adsorption were successfully investigated. The maximum capacity of Fe(III) ions was 320 (mg/g) for PVA@P(90AMPS-co-10NIPAm) (wt.: wt%). The equilibrium data matching well with the Langmuir model and the pseudo-second-order form described the adsorption process better than the pseudo-first-order model. Findings of the present study highlight using a simple synthesis of PVA@P(AMPS-co-NIPAm) nanogels as superior and recyclable nanoadsorbents.

Cross-linked Pluronic-g-Polyacrylic acid microgel system for the controlled release of doxorubicin in pharmaceutical formulations

The binding of doxorubicin (DOX) to cross-linked Pluronic F127-g-PAA-EGDMA and L92-g-PAA-EGDMA microgels at different alpha (α) and salt concentrations was investigated using isothermal titration calorimetric (ITC), optical and scanning electron microscopic techniques (SEM). We seek to elucidate the mechanisms of interaction and the release of DOX from cross-linked microgels composed of Pluronic and poly(acrylic acid). The ITC results indicated a high binding affinity of DOX to the microgel, which is a function of salt concentrations due to the impact of electrostatic shielding on the DOX-binding process. Applying the polyelectrolyte theory allows the decoupling of the Gibbs free energy of binding that describes the role of non-electrostatic interaction of DOX and the microgel. The presence of DOX within the microgel resulted in the collapse of the microgel due to charge shielding, π-π interactions and self-association of polymer-bound DOX molecules. The diffusion of DOX through the microgel is controlled by the dissociation of COO^-/DOX⁺ coupling pairs.

Infrared and fluorescence spectroscopic studies of a phospholipid bilayer supported by a soft cationic hydrogel scaffold

Polarized attenuated total reflection (ATR-IR) spectroscopy and fluorescence microscopy techniques were used to characterize a 1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC) membrane supported on porous, cationic hydrogel beads. Fluorescence microscopy images showed that the DPhPC coated the external surface of the hydrogel scaffold. In addition, a fluorescence assay of the emission intensity of the Tb(3+)/dipicolinic acid complex demonstrated that the DPhPC coating acted as a barrier to Tb(3+) efflux from the scaffolded vesicle and successfully sealed the porous hydrogel bead. Fluorescence quenching and ATR-IR spectroscopic measurements revealed that the lipid coating has a bilayer structure. The phytanoyl chains were found to exhibit significant trans-gauche isomerization, characteristic of the fluid liquid phase. However, no lipid lateral mobility was observed by fluorescence recovery after photobleaching (FRAP) measurements. The phosphocholine headgroup was found to be well hydrated and oriented such that the cationic choline group tucked in behind the anionic phosphate group, consistent with an electrostatic attraction between the cationic scaffold and zwitterionic lipid. The absence of lipid lateral mobility may be due to the strength of this attraction.

Spectroscopic and permeation studies of phospholipid bilayers supported by a soft hydrogel scaffold

Polarized attenuated total reflection infrared (ATR-IR) spectroscopy, fluorescence microscopy, and fluorescence spectroscopy were used to characterize a lipid coating composed of 70 mol % 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 30 mol % cholesterol, supported on a spherical hydrogel scaffold. The fluorescence microscopy images show an association between the lipid coating and the hydrogel scaffold. Fluorescence permeability measurements revealed that the phospholipid coating acts as a permeability barrier, exhibiting characteristics of a lamellar bilayer coating structure. Variable evanescent wave penetration depth ATR-IR spectroscopy studies validated the determination of quantitative molecular orientation information for a lipid coating supported on a spherical scaffold. These polarized ATR-IR studies measured an average DMPC acyl chain tilt angle of ∼21-25°, with respect to the surface normal.

Construction of polyelectrolyte-responsive microgels, and polyelectrolyte concentration and chain length-dependent adsorption kinetics

We report on the construction of a polyelectrolyte-responsive system evolved from sterically stabilized protonated poly(2-vinylpyridine) (P2VPH(+)) microgels. Negatively charged sodium dodecylbenzenesulfonate (SDBS) surfactants could be readily internalized into the cationic microgels by means of electrostatic interactions, resulting in microgel collapse and concomitant formation of surfactant micellar domains (P2VPH(+)/SDBS)-contained electrostatic complexes. These internal hydrophobic domains conferred the opportunity of fluorescent dyes to be loaded. The obtained fluorescent microgel complexes could be further disintegrated in the presence of anionic polyelectrolyte, poly(sodium 4-styrenesulfonate) (PNaStS). The stronger electrostatic attraction between multivalent P2VPH(+) microgels and PNaStS polyelectrolyte than single-charged surfactant led to triggered release of the encapsulated pyrene dyes from the hydrophobic interiors into microgel dispersion. The process was confirmed by laser light scattering (LLS) and fluorescence measurements. Furthermore, the entire dynamic process of PNaStS adsorption into P2VPH(+) microgel interior was further studied by stopped-flow equipment as a function of polyelectrolyte concentration and degree of polymerization. The whole adsorption process could be well fitted with a double-exponential function, suggesting a fast (τ1) and a slow (τ2) relaxation time, respectively. The fast process (τ1) was correlated well with the approaching of PNaStS with P2VPH(+) microgel to form a nonequilibrium complex within the microgel shell, while the slow process (τ2) was consistent with the formation of equilibrium complexes in the microgel deeper inside. This simple yet feasible design augurs well for the promising applications in controlled release fields.

Lecithin-based nanostructured gels for skin delivery: an update on state of art and recent applications

Conventional carriers for skin delivery encounter obstacles of drug leakage, scanty permeation and low entrapment efficiency. Phospholipid nanogels have recently been recognized as prominent delivery systems to circumvent such obstacles and impart easier application. The current review provides an overview on different types of lecithin nanostructured gels, with particular emphasis on liposomal versus microemulsion gelled systems. Liposomal gels investigated encompassed classic liposomal hydrogel, modified liposomal gels (e.g. Transferosomal, Ethosomal, Pro-liposomal and Phytosomal gels), Microgel in liposomes (M-i-L) and Vesicular phospholipid gel (VPG). Microemulsion gelled systems encompassed Lecithin microemulsion-based organogels (LMBGs), Pluronic lecithin organogels (PLOs) and Lecithin-stabilized microemulsion-based hydrogels. All systems were reviewed regarding matrix composition, state of art, characterization and updated applications. Different classes of lecithin nanogels exhibited crucial impact on transdermal delivery regarding drug permeation, drug loading and stability aspects. Future perspectives of this theme issue are discussed based on current laboratory studies.

Tunable adsorption of soft colloids on model biomembranes

A simple procedure is developed to probe in situ the association between lipid bilayers and colloidal particles. Here, a one-step method is applied to generate giant unilamellar 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) vesicles (GUVs) by application of an alternating electric field directly in the presence of thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) microgels. We demonstrate that the soft PNIPAM microgel particles act as switchable stabilizers for lipid membranes. The change of the particle conformation from the swollen to the collapsed state enables the reversible control of the microgel adsorption as a function of temperature. At 20 °C, the swollen and hydrophilic soft microgel particles adsorb evenly and densely pack in 2D hexagonal arrays at the DOPC GUV surfaces. In contrast, at 40 °C, that is, above the volume phase transition temperature (TVPT = 32 °C) of the PNIPAM microgels, the collapsed and more hydrophobic particles partially desorb and self-organize into domains at the GUV/GUV interfaces. This study shows that thermoresponsive PNIPAM microgels can be used to increase and control the stability of lipid vesicles where the softness and deformability of these types of particles play a major role. The observed self-assembly, where the organization and position of the particles on the GUV surface can be controlled "on demand", opens new routes for the design of nanostructured materials.

A novel pulsatile drug delivery system based on the physiochemical reaction between acrylic copolymer and organic acid: in vitro and in vivo evaluation

Multilayer-coating technology is the traditional method to achieve pulsatile drug release with the drawbacks of time consuming, more materials demanding and lack of efficiency. The purpose of this study was to design a novel pulsatile drug delivery system based on the physiochemical interaction between acrylic copolymer and organic acid with relatively simpler formulation and manufacturing process. The Enalapril Maleate (EM) pulsatile release pellets were prepared using extruding granulation, spheronization and fluid-bed coating technology. The ion-exchange experiment, hydration study and determination of glass transition temperature were conducted to explore the related drug release mechanism. Bioavailability experiment was carried out by administering the pulsatile release pellets to rats compared with marketed rapid release tablets Yisu. An obvious 4h lag time period and rapid drug release was observed from in vitro dissolution profiles. The release mechanism was a combination of both disassociated and undisassociated forms of succinic acid physiochemically interacting with Eudragit RS. The AUC0-τ of the EM pulsatile pellets and the market tablets was 702.384 ± 96.89 1 hn g/mL and 810.817 ± 67.712 h ng/mL, while the relative bioavailability was 86.62%. These studies demonstrate this novel pulsatile release concept may be a promising strategy for oral pulsatile delivery system.

Merging the best of both worlds: hybrid lipid-enveloped matrix nanocomposites in drug delivery

The advent of nanotechnology has revolutionized drug delivery in terms of improving drug efficacy and safety. Both polymer-based and lipid-based drug-loaded nanocarriers have demonstrated clinical benefit to date. However, to address the multifaceted drug delivery challenges ahead and further expand the spectrum of therapeutic applications, hybrid lipid-polymer nanocomposites have been designed to merge the beneficial features of both polymeric drug delivery systems and liposomes in a single nanocarrier. This review focuses on different classes of nanohybrids characterized by a drug-loaded polymeric matrix core enclosed in a lipid shell. Various nanoengineering approaches to obtain lipid-polymer nanocomposites with a core-shell nanoarchitecture will be discussed as well as their predominant applications in drug delivery.

Adsorption and release of active species into and from multifunctional ionic microgel particles

We synthesize monodisperse ionic microgel particles which undergo a large change in volume in response to environmental stimuli such as pH and temperature. In addition, the study elucidates the effective uptake and release of rheology modifiers from these microgel particles to alter the bulk viscosity of a surrounding fluid. Moreover, we found that the prepared ionic microgel particles can demonstrate abilities to adsorb and repel iron oxide nanoparticles (Fe3O4-NPs) upon pH variation. The extent of the loading of Fe3O4-NPs within the colloidal particles and morphology can be manipulated by tunable interactions between the Fe3O4-NPs and ionic microgel particles.

Synthesis of monodisperse, covalently cross-linked, degradable "smart" microgels using microfluidics

The development of a robust method for the synthesis of highly monodisperse microgels cross-linked with degradable covalent bonds offers the potential for fabricating microgels with the highly controllable porosities, cell interactions, and degradation half-lives required for biomedical applications. A microfluidic chip is designed that enables the on-chip mixing and emulsification of two reactive polymer solutions (hydrazide and aldehyde-functionalized carbohydrates) to form monodisperse, hydrazone cross-linked microgels in the size range of ≈40-100 μm. The device can be run continuously for at least 30 h without a significant drift in particle size. The resulting microgels have a homogeneous bulk composition and can swell and deswell as the solvent conditions change in predictable ways based on the chemistry of the reactive polymers used, thereby enabling improved control over both the chemistry and morphology of the resulting microgels relative to other reported approaches. The in situ gelation chemistry used facilitates rapid microgel formation within the droplets without requiring the use of UV light or heating to initiate polymerization, thus making this approach of particular potential utility in cell encapsulation or drug delivery (as demonstrated).

Fabrication of microgel-in-liposome particles with improved water retention

Corneocytes represents the main water reservoir of stratum corneum, and that ability intimately arises from their architecture and total composition. Here we describe a novel method for fabricating a microgel-in-liposome (M-i-L) structure consisting of a sodium hyaluronate microgel and a lipid membrane envelop in order to mimic corneocyte cell structures. The essence of our approach is to use a lecithin-based microemulsion with a very low interfacial tension between the water droplet and oil continuous phase. Using this emulsion enables us to stabilize a dispersion of microgel particles without phase separation or aggregation. The addition of excess water produced single-core or multicore microgel particles enveloped in a lipid layer. To demonstrate the applicability of this unique vesicle system, we encapsulated a high concentration of natural moisturizing factor (NMF) in the microgel core and investigated how the M-i-L structure affected the water retention in comparison with other control systems. We have observed that our M-i-L particles with the NMF in the core, which mimicked the corneocyte cell structure, showed an excellent ability to retain water in the system. This experimental result inspired us to investigate how corneocyte cells, which feature a lipid-enveloped hydrogel structure, provide such long-lasting hydration to the skin.

Microgels and microcapsules in peptide and protein drug delivery

The present review focuses on the interaction of microgels and microcapsules with biological macromolecules, particularly peptides and proteins, as well as drug delivery applications of such systems. Results from recent studies on factors affecting peptide/protein binding to, and release from, microgels and related systems are discussed, including effects of network properties, as well as protein aggregation, peptide length, hydrophobicity and charge (distributions), secondary structure, and cyclization. Effects of ambient conditions (pH, ionic strength, temperature, etc.) are also discussed, all with focus on factors of importance for the performance of microgel and microcapsule delivery systems for biomacromolecular drugs.

Responsive micromolds for sequential patterning of hydrogel microstructures

Microscale hydrogels have been shown to be beneficial for various applications such as tissue engineering and drug delivery. A key aspect in these applications is the spatial organization of biological entities or chemical compounds within hydrogel microstructures. For this purpose, sequentially patterned microgels can be used to spatially organize either living materials to mimic biological complexity or multiple chemicals to design functional microparticles for drug delivery. Photolithographic methods are the most common way to pattern microscale hydrogels but are limited to photocrosslinkable polymers. So far, conventional micromolding approaches use static molds to fabricate structures, limiting the resulting shapes that can be generated. Herein, we describe a dynamic micromolding technique to fabricate sequentially patterned hydrogel microstructures by exploiting the thermoresponsiveness of poly(N-isopropylacrylamide)-based micromolds. These responsive micromolds exhibited shape changes under temperature variations, facilitating the sequential molding of microgels at two different temperatures. We fabricated multicompartmental striped, cylindrical, and cubic microgels that encapsulated fluorescent polymer microspheres or different cell types. These responsive micromolds can be used to immobilize living materials or chemicals into sequentially patterned hydrogel microstructures which may potentially be useful for a range of applications at the interface of chemistry, materials science and engineering, and biology.

Liquid-liquid two-phase systems for the production of porous hydrogels and hydrogel microspheres for biomedical applications: A tutorial review

Macroporous hydrogels may have direct applications in regenerative medicine as scaffolds to support tissue formation. Hydrogel microspheres may be used as drug-delivery vehicles or as building blocks to assemble modular scaffolds. A variety of techniques exist to produce macroporous hydrogels and hydrogel microspheres. A subset of these relies on liquid-liquid two-phase systems. Within this subset, vastly different types of polymerization processes are found. In this review, the history, terminology and classification of liquid-liquid two-phase polymerization and crosslinking are described. Instructive examples of hydrogel microsphere and macroporous scaffold formation by precipitation/dispersion, emulsion and suspension polymerizations are used to illustrate the nature of these processes. The role of the kinetics of phase separation in determining the morphology of scaffolds and microspheres is also delineated. Brief descriptions of miniemulsion, microemulsion polymerization and ionotropic gelation are also included.

Influence of architecture on the interaction of negatively charged multisensitive poly(N-isopropylacrylamide)-co-methacrylic acid microgels with oppositely charged polyelectrolyte: absorption vs adsorption

Two sets of core-shell microgels composed of temperature-sensitive poly(N-isopropylacrylamide) (PNiPAM) with different spatial distribution of pH-sensitive methacrylic acid (MAA) groups were prepared. The cores consist of either PNiPAM (neutral core; nc) or PNiPAM-co-MAA (charged core; cc). A charged shell existing of PNiPAM-co-MAA was added to the neutral core (yielding neutral core-charged shell; nccs), on the charged core, on the other hand, a neutral shell of PNiPAM was added (charged core-neutral shell; ccns). Complexes of these microgels with positively charged poly(diallyldimethylammonium chloride) (PDADMAC) of different molar masses were prepared. The amount of bound polyelectrolyte was quantified, and the microgel-polyelectrolyte complexes were characterized with respect to electrophoretic mobility and hydrodynamic radius. The penetration of polyelectrolyte into the microgel was also monitored by means of lifetime analysis of a fluorescent dye covalently bound to poly(L-lysine) providing information on the probe's local environment. The architecture of the microgel has a significant influence on the interaction with oppositely charged polyelectrolyte. Complexes with microgel with the charged shell tend to flocculate at charge ratios of 1 and are thus similar to polyelectrolyte complexes with rigid colloidal particles. Complexes with microgels that consist of a charged core and a neutral shell show very different properties: They are still temperature sensitive and reveal an influence of the polyelectrolyte's chain length. Low molecular weight PDADMAC can penetrate through the neutral shell into the charged core, and thus nearly no charge reversal occurs. The high-MW polyelectrolyte does not penetrate fully and leads to charge reversal. The results demonstrate that microgels are able to absorb or adsorb polyelectrolytes depending on the polyelectrolyte's chain length and the microgels architecture. Complexes with different surface properties and different colloidal stability can be prepared, and polyelectrolytes can be encapsulated in the microgel core. Thus, multisensitive core-shell microgels combine permeability and compartmentalization on a nanometer length scale and provide unique opportunities for applications in controlled uptake and release.

Uptake and distribution of labeled antibodies into pH-sensitive microgels

We investigated the uptake and release of labeled antibodies from pH-sensitive hydrogel microparticles (i.e. microgels) by means of fluorescence analysis of labeled biological samples. The poly(methacrylic acid) (PMAA) hydrogel is a carbon-based network having carboxylic groups on the surface that dissociate according to their acid-base equilibrium. The ability of the PMAA microgel to encapsulate and release anti-CD4 and anti-CD8 monoclonal antibodies (MAbs), differing for the isotype and labeled with highly photostable fluorophore, was studied in solution by photoluminescence spectroscopy. The experimental results indicated that the uptake and release of the tested antibodies were controlled by pH. Furthermore, confocal microscopy analysis in the solid state revealed that the distribution of the labeled antibodies either on the surface or in the core of the microgel matrix was related to the specific properties of these MAbs.

pH-sensitive immunoliposomes specific to the CD33 cell surface antigen of leukemic cells

A promising avenue in cancer therapy using liposomal formulations is the combination of site-specific delivery with triggered drug release. The use of trigger mechanisms in liposomes could be relevant for drugs susceptible to lysosomal hydrolytic/enzymatic degradation. Here, we propose a polymeric pH-sensitive liposome system that is designed to release its content inside the endosomes through a polymer structural change following receptor-mediated internalization. Specifically, pH-sensitive immunoliposomes (ILs) were obtained by including a terminally alkylated copolymer of N-isopropylacrylamide (NIPAM) in the liposome bilayer and by coupling the anti-CD33 monoclonal antibody to target leukemic cells. In vitro release of encapsulated fluorescent probes and cytosine arabinoside (ara-C) revealed that pH-sensitivity of the vector was retained in the presence of the antibody upon incubation in plasma. Flow cytometry and confocal microscopy analyses demonstrated that the pH-sensitive ILs were efficiently internalized by various CD33+ leukemic cell lines while limited interaction was found for liposomes decorated with an isotype-matched control antibody. Finally, the pH-sensitive ILs-CD33 formulation exhibited the highest cytotoxicity against HL60 cells, confirming the role of the NIPAM copolymer in promoting the escape of intact ara-C in the endosomes. These results suggest that this pH-sensitive liposomal formulation could be beneficial in the treatment of acute myeloid leukemia.