Current Challenges in Microcapsule Designs and Microencapsulation Processes: A Review

Microencapsulation is an advanced methodology for the protection, preservation, and/or delivery of active materials in a wide range of industrial sectors, such as pharmaceuticals, cosmetics, fragrances, paints, coatings, detergents, food products, and agrochemicals. Polymeric materials have been extensively used as microcapsule shells to provide appropriate barrier properties to achieve controlled release of the encapsulated active ingredient. However, significant limitations are associated with such capsules, including undesired leaching and the nonbiodegradable nature of the typically used polymers. In addition, the energy cost of manufacturing microcapsules is an important factor to be considered when designing microcapsule systems and the corresponding production processes. Recent factors linked to UN sustainability goals are modifying how such microencapsulation systems should be designed in pursuit of "ideal" microcapsules that are efficient, safe, cost-effective and environmentally friendly. This review provides an overview of advances in microencapsulation, with emphasis on sustainable microcapsule designs. The key evaluation techniques to assess the biodegradability of microcapsules, in compliance with recently evolving European Union requirements, are also described. Moreover, the most common methodologies for the fabrication of microcapsules are presented within the framework of their energy demand. Recent promising microcapsule designs are also highlighted for their suitability toward meeting current design requirements and stringent regulations, tackling the ongoing challenges, limitations, and opportunities.

3D Temperature-Controlled Interchangeable Pattern for Size-Selective Nanoparticle Capture

Patterned surfaces with distinct regularity and structured arrangements have attracted great interest due to their extensive promising applications. Although colloidal patterning has conventionally been used to create such surfaces, herein, we introduce a novel 3D patterned poly(N-isopropylacrylamide) (PNIPAM) surface, synthesized by using a combination of colloidal templating and surface-initiated photoinduced electron transfer-reversible addition-fragmentation chain transfer (SI-PET-RAFT) polymerization. In order to investigate the temperature-driven 3D morphological variations at a lower critical solution temperature (LCST) of ∼32 °C, multifaceted characterization techniques were employed. Atomic force microscopy confirmed the morphological transformations at 20 and 40 °C, while water contact angle measurements, upon heating, revealed distinct trends, offering insights into the correlation between surface wettability and topography adaptations. Moreover, quartz crystal microbalance with dissipation monitoring and electrochemical measurements were employed to detect the topographical adjustments of the unique hollow capsule structure within the LCST. Tests using different sizes of PSNPs shed light on the size-selective capture-release potential of the patterned PNIPAM, accentuating its biomimetic open-close behavior. Notably, our approach negates the necessity for expensive proteins, harnessing temperature adjustments to facilitate the noninvasive and efficient reversible capture and release of nanostructures. This advancement hopes to pave the way for future innovative cellular analysis platforms.

Design of Tailor-Made Biopolymer-Based Capsules for Biological Application by Combining Porous Particles and Polysaccharide Assembly

Various approaches have been described in the literature to demonstrate the possibility of designing biopolymer particles with well-defined characteristics, such as size, chemical composition or mechanical properties. From a biological point of view, the properties of particle have been related to their biodistribution and bioavailability. Among the reported core-shell nanoparticles, biopolymer-based capsules can be used as a versatile platform for drug delivery purposes. Among the known biopolymers, the present review focuses on polysaccharide-based capsules. We only report on biopolyelectrolyte capsules fabricated by combining porous particles as a template and using the layer-by-layer technique. The review focuses on the major steps of the capsule design, i.e., the fabrication and subsequent use of the sacrificial porous template, multilayer coating with polysaccharides, the removal of the porous template to obtain the capsules, capsule characterisation and the application of capsules in the biomedical field. In the last part, selected examples are presented to evidence the major benefits of using polysaccharide-based capsules for biological purposes.

Phenol release from pNIPAM hydrogels: scaling molecular dynamics simulations with dynamical density functional theory

We employed molecular dynamic simulations (MD) and the Bennett's acceptance ratio method to compute the free energy of transfer, ΔG_trans, of phenol, methane, and 5-fluorouracil (5-FU), between bulk water and water-pNIPAM mixtures of different polymer volume fractions, ϕ_p. For this purpose, we first calculate the solvation free energies in both media to obtain ΔG_trans. Phenol and 5-FU (a medication used to treat cancer) attach to the pNIPAM surface so that they show negative values of ΔG_trans irrespective of temperature (above or below the lower critical solution temperature of pNIPAM, T_c). Conversely, methane switches the ΔG_trans sign when considering temperatures below (positive) and above (negative) T_c. In all cases, and contrasting with some theoretical predictions, ΔG_trans maintains a linear behavior with the pNIPAM concentration up to large polymer densities. We have also employed MD to compute the diffusion coefficient, D, of phenol in water-pNIPAM mixtures as a function of ϕ_p in the diluted limit. Both ΔG_trans and D as a function of ϕ_p are required inputs to obtain the release halftime of hollow pNIPAM microgels through Dynamic Density Functional Theory (DDFT). Our scaling strategy captures the experimental value of 2200 s for 50 μm radius microgels with no cavity, for ϕ_p ≃ 0.83 at 315 K.

Bone tumors effective therapy through functionalized hydrogels: current developments and future expectations

Primary bone tumors especially, sarcomas affect adolescents the most because it originates from osteoblasts cells responsible for bone growth. Chemotherapy, surgery, and radiation therapy are the most often used clinical treatments. Regrettably, surgical resection frequently fails to entirely eradicate the tumor, which is the primary cause of metastasis and postoperative recurrence, leading to a high death rate. Additionally, bone tumors frequently penetrate significant regions of bone, rendering them incapable of self-repair, and impairing patients' quality of life. As a result, treating bone tumors and regenerating bone in the clinic is difficult. In recent decades, numerous sorts of alternative therapy approaches have been investigated due to a lack of approved treatments. Among the novel therapeutic approaches, hydrogel-based anticancer therapy has cleared the way for the development of new targeted techniques for treating bone cancer and bone regeneration. They include strategies such as co-delivery of several drug payloads, enhancing their biodistribution and transport capabilities, normalizing accumulation, and optimizing drug release profiles to decrease the limitations of current therapy. This review discusses current advances in functionalized hydrogels to develop a new technique for treating bone tumors by reducing postoperative tumor recurrence and promoting tissue repair.

Demonstrating the Interfacial Polymer Thermal Transition from Coil-to-Globule to Coil-to-Stretch under Shear Flow Using SFG and MD Simulation

Revealing interfacial shear-induced structural responsiveness has long been an important topic in that most fluids in nature and human life are in motion and cause interesting boundary phenomena. It is amazing how the polymer chain conformation or local structural features at a boundary change under the effective shear condition. In this study, microfluidic-assisted sum frequency generation (SFG) vibrational spectroscopy and all-atom molecular dynamics (MD) simulation are combined to reveal that the shear flow can effectively block the so-called thermal coil-to-globule transition of the poly(N-isopropylacrylamide) (PNIPAM) brushes on the solid substrate, and the normal coil-to-globule transition transfers to a coil-to-stretch one under shear flow with increasing ambient temperature. Such findings are attributed to the balance between the shear flow and the molecular interaction with respect to the polymer chains and adjacent water molecules, thus demonstrating the significant effect of the shear flow on the structural and dynamic behaviors of the polymer chains at the boundaries from the molecular level.

Construction of disulfide containing redox-responsive polymeric nanomedicine

Disulfide bonds (S-S) are widely found in chemistry, biology, and materials science. Polymer nanomaterials containing disulfide bonds with a variety of excellent properties have great potential as drug and gene delivery carriers. The disulfide bond can exist stably in extracellular environment, but upon entering cancer cells, it will undergo a sulfhydryl-disulfide bond exchange reaction with glutathione (GSH) in the cytoplasm, causing the disulfide bond cleavage. Therefore, polymeric nanomaterials containing disulfide bonds are promising in cancer treatment due to the elevated GSH concentration inside cancer cells. This review highlights various synthetic approaches to prepare disulfide containing redox-responsive polymeric nanomedicine, including synthesis of disulfide bonds containing polymers, construction of polymeric nanoparticle with shell or core crosslinked disulfide bonds, preparation of polymer-drug conjugates via disulfide linkers, and disulfide linked responsive payloads.

3D Printing of Thermoresponsive Hydrogel Laden with an Antimicrobial Agent towards Wound Healing Applications

Thermoresponsive hydrogel-based wound dressings with an incorporated antimicrobial agent can be fabricated employing 3D printing technology. A novel printable ink containing poly(N-isopropylacrylamide) (PNIPAAm) precursors, sodium alginate (ALG), methylcellulose (MC) that is laden with a mixture of octenidine dihydrochloride and 2-phenoxyethanol (Octenisept®, OCT) possess accurate printability and shape fidelity. This study also provides the protocol of ink's use for the 3D printing of hydrogel scaffolds. The hydrogel's physicochemical properties and drug release profiles from the hydrogel specimens to the external solution have been determined at two temperatures (20 and 37 °C). The release test showed a sustained OCT delivery into ultrapure water and the PBS solution. The temperature-responsive hydrogel exhibited antimicrobial activity against Staphylococcus aureus, Candida albicans, and Pseudomonas aeruginosa and demonstrated non-cytotoxicity towards fibroblasts. The thermoresponsive behavior along with biocompatibility, antimicrobial activity, and controlled drug release make this hydrogel a promising class of materials for wound dressing applications.

Nanogel: A Versatile Nano-Delivery System for Biomedical Applications

Nanogel-based nanoplatforms have become a tremendously promising system of drug delivery. Nanogels constructed by chemical crosslinking or physical self-assembly exhibit the ability to encapsulate hydrophilic or hydrophobic therapeutics, including but not limited to small-molecule compounds and proteins, DNA/RNA sequences, and even ultrasmall nanoparticles, within their 3D polymer network. The nanosized nature of the carriers endows them with a specific surface area and inner space, increasing the stability of loaded drugs and prolonging their circulation time. Reactions or the cleavage of chemical bonds in the structure of drug-loaded nanogels have been shown to trigger the controlled or sustained drug release. Through the design of specific chemical structures and different methods of production, nanogels can realize diverse responsiveness (temperature-sensitive, pH-sensitive and redox-sensitive), and enable the stimuli-responsive release of drugs in the microenvironments of various diseases. To improve therapeutic outcomes and increase the precision of therapy, nanogels can be modified by specific ligands to achieve active targeting and enhance the drug accumulation in disease sites. Moreover, the biomembrane-camouflaged nanogels exhibit additional intelligent targeted delivery features. Consequently, the targeted delivery of therapeutic agents, as well as the combinational therapy strategy, result in the improved efficacy of disease treatments, though the introduction of a multifunctional nanogel-based drug delivery system.

Synthesis, micellar structures and emission mechanisms of an AIE and DDED-featured fluorescent pH- and thermo-meter

A new nanoprobe, the luminescent diblock copolymer PNIPAM(MAh-4)-b-P4VP (PN4P), with pH- and thermo-responsive deprotonation-driven emission decay (DDED) and aggregation-induced emission (AIE) features was designed and synthesized. The nanoprobe PN4P can form micellar structures in water with reversible dual-responsive fluorescence (FL) behavior within a wide pH range of 2–11. The critical solution temperature was found at about 32, 30 and 27 °C as the pH switched from 2, 7 to 11. The critical pH value of the probe was about 4.0, and the micelles showed a core–shell inversion in response to pH and thermal stimuli, accompanied by a desirable emission tunability. P4VP as the micellar shell at pH = 2 was more easily dehydrated with the increase in temperature as compared to PNIPAM as the micellar shell at pH > 4. The strongest dehydration of the P4VP shell would make PN4P the most strongly aggregated and the most AIE-active, which supports the 2.10-fold most distinguished thermal-responsive emission enhancement at pH = 2. Moreover, a dramatic acidochromic redshift of the emission band from 450 (pH > 4) to 490 nm (pH = 2) was observed, and the maximum emission at pH = 2 was enhanced by about 2.07-fold as compared with that at pH = 7. Therefore, the probe displays the desired dual responses and good reversibility. AIE and DDED are the two major mechanisms responsible for the dual-responsive emission change, with AIE playing a more important role than DDED. This work offers a promising approach to interpreting temperature (range from 28 to 40 °C) and pH changes (range from 2 to 7) in water.

A nanoprobe in water features pH- and thermal-responsive micellar/clustering structures, deprotonation-driven emission decay (DDED) and aggregation-induced emission (AIE).

Degradable, thermo-, pH- and redox-sensitive hydrogel microcapsules for burst and sustained release of drugs

Polymer microcapsules offer a possibility of storing increased amounts of drugs. Appropriate design and composition of the microcapsules allow tuning of the drug-release process. In this paper, we report on synthesis of hydrogel microcapsules sensitive to temperature and pH and degradable by glutathione and hydrogen peroxide. Microcapsules were based on thermo-responsive poly(N-isopropylacrylamide) and degradable cystine crosslinker, and were synthesized by applying precipitation polymerization. Such way of polymerization was appropriately modified to limit the crosslinking in the microcapsule center. This led to a possibility of washing out the pNIPA core at room temperature and the formation of a capsule. Microcapsules revealed rather high drug-loading capacity of ca. 17%. The degradation of the microcapsules by the reducing agent (GSH) and the oxidizing agent (H₂O₂) was confirmed by using the DLS, UV-Vis, SEM and TEM techniques. Depending on pH and concentration of the reducing/oxidizing agents a fast or slow degradation of the microcapsules and a burst or long-term release of doxorubicin (DOX) were observed. The DOX loaded microcapsules appeared to be cytotoxic against A2780 cancer cells similarly to DOX alone, while unloaded microcapsules did not inhibit proliferation of the cells.

Light, temperature, and pH control of aqueous azopyridine-terminated poly(N-isopropylacrylamide) solutions

Azopyridines (AzPy) act as light-sensitive groups that undergo reversible cis–trans isomerization upon UV irradiation, as hydrogen-bond acceptors, and as ionizable moieties.

Aggregation-Induced Expansion of Poly-(N-isopropyl acrylamide) Solutions Observed Directly by the Transient Grating Imaging Technique

The anomalous volume expansion of poly-(N-isopropyl acrylamide) (PNIPAM) solutions was observed during the thermally induced polymer phase transition of aqueous solutions having concentrations in the 3-7 wt % range. The process occurred on a millisecond time scale, and a laser temperature-jump time-resolved technique was used to bring about the process. After heating a solution with a pulse laser exploiting light absorption by dyes added to the solution itself, a phase transition was observed to take place, and the temporal changes associated with it were visualized through the transient grating imaging technique, whereby the solution was heated with a stripe pattern. We found several processes occurring on a millisecond time scale, all of which clearly took place after each PNIPAM molecule had collapsed structurally from a coiled to a globular conformation. During the so-called demixing process, the globular polymers aggregated with each other within 10 ms, and suddenly the polymer phase expanded as aggregation progressed further. After this process, the individual globular polymers reverted to their coiled conformation via hydration during the remixing process. We proposed that solution expansion was caused by the mutual entangling of multiple globular PNIPAM molecules, instead each globule polymer was separated.

A Near-Infrared and Temperature-Responsive Pesticide Release Platform through Core-Shell Polydopamine@PNIPAm Nanocomposites

Controlled stimuli-responsive release systems are a feasible and effective way to increase the efficiency of pesticides and help improve environmental pollution issues. However, near-infrared (NIR)-responsive systems for encapsulation of pesticides for controlling release have not been reported because of high cost and load ability of conventional NIR absorbers as well as complicated preparation process. Herein, we proposed polydopamine (PDA) microspheres as a photothermal agent owing to their abundant active sites, satisfactory photothermal efficiency, low cost, and easy fabrication, followed by capping with a PNIPAm thermosensitive polymer shell. In this core-shell PDA@PNIPAm hybrid system, the PDA core provided excellent temperature and NIR-light sensitivity as well as high loading capacity, while the PNIPAm applied as both a thermosensitive gatekeeper and a pesticide reservoir. The structure of the PDA@PNIPAm nanocomposites was characterized by transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, dynamic light scattering, and thermogravimetric analysis; the results showed that the nanocomposites had a well-defined core-shell configuration for efficient loading of small pesticide molecules. Moreover, the core-shell PDA@PNIPAm nanocomposites exhibited high loading capacity and temperature- or NIR-controlled release performance. Overall, this system has significant potential in controlled drug release and agriculture-related fields as a delivery system for pesticides with photothermal responsive behavior.

Responsive copolymer–graphene oxide hybrid microspheres with enhanced drug release properties

Graphene oxide deposited on thermoresponsive copolymer microspheres enhances their barrier diffusion properties and drug release performance.

Nanomedicine approaches in acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is the malignancy with the highest incidence amongst children (26% of all cancer cases), being surpassed only by the cancers of the brain and of the nervous system. The most recent research on ALL is focusing on new molecular therapies, like targeting specific biological structures in key points in the cell cycle, or using selective inhibitors for transmembranary proteins involved in cell signalling, and even aiming cell surface receptors with specifically designed antibodies for active targeting. Nanomedicine approaches, especially by the use of nanoparticle-based compounds for the delivery of drugs, cancer diagnosis or therapeutics may represent new and modern ways in the near future anti-cancer therapies. This review offers an overview on the recent role of nanomedicine in the detection and treatment of acute lymphoblastic leukemia as resulting from a thorough literature survey. A short introduction on the basics of ALL is presented followed by the description of the conventional methods used in the ALL detection and treatment. We follow our discussion by introducing some of the general nano-strategies used for cancer detection and treatment. The detailed role of organic and inorganic nanoparticles in ALL applications is further presented, with a special focus on gold nanoparticle-based nanocarriers of antileukemic drugs.

Hollow Casein-Based Polymeric Nanospheres for Opaque Coatings

Casein-based hollow polymeric sphere were fabricated through emulsifier-free polymerization coupled with alkali swelling approach. Hollow structure and nanoscale size of casein-based polymeric spheres were verified by TEM, AFM, SEM, and UV-vis spectra. The as-obtained hollow spheres were proved exhibiting superior opaque characteristic. Through adjusting the structural parameters, for example, MAA usages and MAA content in seed to core, sphere film showed tunable visible-light transmittance and antiultraviolet property. The formation mechanism of casein-based hollow sphere has been discussed in depth. Worth mentioning, the resultant hollow polymeric sphere can easily form films itself at room temperature, which would open a new possibility of designing opaque coatings in several fields, such as leather, packaging, paper making, biomedical, and special indoor coating applications.

Dermal Patch with Integrated Flexible Heater for on Demand Drug Delivery

Topical administration of drugs and growth factors in a controlled fashion can improve the healing process during skin disorders and chronic wounds. To achieve this goal, a dermal patch is engineered that utilizes thermoresponsive drug microcarriers encapsulated within a hydrogel layer attached to a flexible heater with integrated electronic heater control circuitry. The engineered patch conformally covers the wound area and enables controlled drug delivery by electronically adjusting the temperature of the hydrogel layer. The drugs are encapsulated inside microparticles in order to control their release rates. These monodisperse thermoresponsive microparticles containing active molecules are fabricated using a microfluidic device. The system is used to release two different active molecules with molecular weights similar to drugs and growth factors and their release profiles are characterized. This platform is a key step towards engineering smart and closed loop systems for topical applications.

Inkjet printing based assembly of thermoresponsive core–shell polymer microcapsules for controlled drug release

A thermoresponsive polymer microcapsule with a hollow core–porous shell structure was fabricated based on inkjet printing, which can be used to control drug release by changing the temperature at around 38 °C.

Fabrication of PVCL-co-PMMA nanofibers with tunable volume phase transition temperatures and maintainable shape for anti-cancer drug release

Thermo responsive PVCL-co-PMMA nanofibers for controlled release of anticancer drugs were fabricated. The thermo response temperatures of the nanofibers could be easily tuned, and the fibrous shapes could be maintained after heating–cooling cycles.

Thermoresponsive copolymer/SiO2 nanoparticles with dual functions of thermally controlled drug release and simultaneous carrier decomposition

The preparation of thermoresponsive drug carriers with a self-destruction property is presented. These drug carriers were fabricated by incorporation of drug molecules and thermoresponsive copolymer, poly(N-isopropylacrylamide-co-acrylamide), into silica nanoparticles in a one-pot preparation process. The enhanced drug release was primarily attributed to faster molecule diffusion resulting from the particle decomposition triggered by phase transformation of the copolymer upon the temperature change. The decomposition of the drug carriers into small fragments should benefit their fast excretion from the body. In addition, the resulting drug-loaded nanoparticles showed faster drug release in an acidic environment (pH 5) than in a neutral one. The controlled drug release of methylene blue and doxorubicin hydrochloride and the self-decomposition of the drug carriers were successfully characterized by using TEM, UV/Vis spectroscopy, and confocal microscopy. Together with the nontoxicity and excellent biocompatibility of the copolymer/SiO2 composite, the features of controlled drug release and simultaneous carrier self-destruction provided a promising opportunity for designing various novel drug-delivery systems.

Binding affinity of thermoresponsive polyelectrolyte hydrogels for charged amphiphilic ligands. A DSC approach

Controlled drug binding and release stand among top requirements postulated for targeted drug delivery systems of the new generations. "Smart" polymers and gels are highly suitable for the controlled delivery due to their structural sensitivity to minor environmental variations. The aim of this work was to study thermoresponsive polyanionic and polycationic hydrogels of N-isopropylacrylamide copolymers with acrylic acid and N-aminopropylmethacrylamide in terms of their interaction with two widely used drugs, propranolol and ibuprofen. Binding energetics of these drugs by the gels in swollen and collapsed state was estimated by means of high-sensitivity differential scanning calorimetry. Thermodynamic parameters of the gel collapse (transition temperature, enthalpy, heat capacity increment, and width) were determined as a dependence of the drug concentrations. From these data the excess free energy of collapse was calculated as a function of drug concentration. Deconvolution of this function resulted in the evaluation of binding parameters and contributions from interactions of various types to the free energy of binding. The binding mechanism of both drugs to the swollen and collapsed gels was elucidated. Its main features are the cooperative character of the drug binding by the collapsed gel and the predominant role of the hydrophobicity of drugs in their affinity for the swollen gel.

Tunable thermosensitive behavior of multiple responsive chitin

Chitin can be dissolved and homogeneously functionalized in NaOH/urea aqueous solvent. Previously, we reported that chitin modified with acrylamide (AMC) possesses high water solubility and can undergo a sol-gel transition responding to pH and cationic ions. In this report, we further explored the thermosensitive behavior of this multiple responsive chitin. We showed that the sol-gel transition temperature of AMC can be facilely adjusted by the degree of substitution (DS), pH, polymer concentration and the presence of anions or cations. Importantly, AMC can form a hydrogel at 37 °C and return to solution at 4 °C by adjusting experimental parameters. We anticipate this multiple responsive chitin may have potential applications in injectable materials and smart drug delivery.

Preparation and adsorption behavior of new hollow-like spherical sludge chars for methylene blue

Hollow-like spherical sludge char (HSC) was prepared to decrease low pressure and increase high surface area to 1008 m² g⁻¹.