Preparation and Characterization of Temperature-Sensitive Poly(N-isopropylacrylamide)-b-poly(d,l-lactide) Microspheres for Protein Delivery

Thermoresponsiveness Across the Physiologically Accessible Range: Effect of Surfactant, Cross-Linker, and Initiator Content on Size, Structure, and Transition Temperature of Poly(N-isopropylmethacrylamide) Microgels

The influence of surfactant, cross-linker, and initiator on the final structure and thermoresponse of poly(N-isopropylmethacrylamide) (pNIPMAM) microgels was evaluated. The goals were to control particle size (into the nanorange) and transition temperature (across the physiologically accessible range). The concentration of the reactants used in the synthesis was varied, except for the monomer, which was kept constant. The thermoresponsive suspensions formed were characterized by dynamic light scattering, small-angle X-ray scattering, atomic force microscopy, and rheology. Increasing surfactant, sodium dodecyl sulfate content, produced smaller microgels, as expected, into the nanorange and with greater internal entanglement, but with no change in phase transition temperature (LCST), which is contrary to previous reports. Increasing cross-linker, N,N-methylenebis acrylamide, content had no impact on particle size but reduced particle deformability and, again contrary to previous reports of decreases, progressively increased the LCST from 39 to 46 °C. The unusual LCST trends were confirmed using different rheological techniques. Initiator, potassium persulfate, content was found to weakly influence the outcomes. An optimized content was identified that provides functional nanogels in the 100 nm (swollen) size range with controlled LCST, just above physiological temperature. The study contributes chemistry-derived design rules for thermally responsive colloidal particles with physiologically accessible LCST for a variety of biomedical and soft robotics applications.

Evaluation of a temperature-responsive magnetotocosome as a magnetic targeting drug delivery system for sorafenib tosylate anticancer drug

In this investigation, a polymeric fusion of chitosan (CS) and thermosensitive poly (N-isopropyl acrylamide) - PNIPAAm - encapsulated a magnetotocosome, biocompatible nanocarrier. This encapsulation strategy demonstrated improved drug entrapment efficiency, achieving up to 98.8 %. Additionally, it exhibited extended stability, optimal particle dimensions, and the potential for industrial scaling, thus facilitating controlled drug delivery of sorafenib tosylate to cancerous tissue. Reversible Addition-Fragmentation Chain Transfer (RAFT) techniques were employed to synthesize PNIPAAm. The effects of polymer molecular weight and polydispersity index on the lower critical solution temperature (LCST) were evaluated. The resulting polymeric amalgamation, involving the thermosensitive PNIPAAm synthesized using RAFT techniques and CS that coated the magnetotocosome (CS-Raft PNIPAAm-magnetotocosome) with an LCST approximately at 45 °C, holds the potential to enhance drug bioavailability and enable applications in hyperthermia treatment, controlled release, and targeted drug delivery.

Extreme Extensibility in Physically Cross-Linked Nanocomposite Hydrogels Leveraging Dynamic Polymer-Nanoparticle Interactions

Designing yield stress fluids to exhibit desired functional properties is an integral challenge in many applications such as 3D printing, drilling, food formulation, fiber spinning, adhesives, and injectable biomaterials. Extensibility in particular has been found to be a highly beneficial characteristic for materials in these applications; however, few highly extensible, high water content materials have been reported to date. Herein we engineer a class of high water content nanocomposite hydrogel materials leveraging multivalent, noncovalent, polymer-nanoparticle (PNP) interactions between modified cellulose polymers and biodegradable nanoparticles. We show that modulation of the chemical composition of the PNP hydrogels controls the dynamic cross-linking interactions within the polymer network and directly impacts yielding and viscoelastic responses. These materials can be engineered to stretch up to 2000% strain and occupy an unprecedented property regime for extensible yield stress fluids. Moreover, a dimensional analysis of the relationships between extensibility and the relaxation and recovery time scales of these nanocomposite hydrogels uncovers generalizable design criteria that will be critical for future development of extensible materials.

Investigation of temperature-responsive tocosomal nanocarriers as the efficient and robust drug delivery system for Sunitinib malate anti-cancer drug: Effects of MW and chain length of PNIPAAm on LCST and dissolution rate

In this study, for the first time, the coated tocosome by blend of chitosan, CS, and poly(N-isopropylacrylamide), PNIPAAm, was developed as the efficient and robust drug delivery system with improved drug encapsulation efficiency, extended stability, proper particle size and industrial upscaling for Sunitinib malate anti-cancer drug. Tocosome was synthesized by using Mozafari method as a scalable and robust method and without the need for organic solvents. The effects of tocosome composition and drug concentration on the stability, particle size of tocosome, zeta potential, encapsulation efficacy and loading of drug into it were investigated by Taguchi method, and optimum composition was selected for combining with the polymeric blend. Homopolymer of PNIPAAm was synthesized by two different polymerization methods, including free radical and reversible addition-fragmentation chain transfer (RAFT). Effects of molecular weight (MW) and chain length of the polymers on lower critical solution temperature (LCST) were examined. The developed nanocarrier in this research, CS-Raft-PNIPAAm-tocosome, indicated LCST value beyond 37°C (about 45°C) and this is suitable for hyperthermia and spatio-temporal release of drug particles.

Hypoxia and temperature dual-stimuli-responsive random copolymers: facile synthesis, self-assembly and controlled release of drug

The micelles self-assembled from P(NIPAM-co-AA-co-NIA) copolymers presented hypoxia and temperature dual-stimuli-responsive properties and a controlled release of drug was achieved using them.

Triggering the Mechanical Release of Mineralized Pickering Emulsion-Based Capsules

Taking advantage of the benefit of Pickering-based emulsions and sol-gel chemistry, we synthesized mineralized Pickering emulsion-based capsules constituted of a dodecane core and a siliceous shell. To trigger the oily core mechanical release, we first made use of the one-step polycondensation synthesis path, reaching limited shell thickness from 43 to 115 nm with a resistance against the application of an external pressure from 0.5 to 6 MPa. When addressing a sequential mineralization route, we were able to reach both better shell homogeneity and higher values of shell thickness from 85 to 135 nm associated with a shell breaking pressure varying from 1.2 to 10 MPa. In this last configuration, the shell homogeneity and thickness are acting cooperatively toward enhancing the shell mechanical toughness and the associated effective breaking pressure of the dodecane@SiO2 core-shell particles.

Synthesis, micellization, and thermally-induced macroscopic micelle aggregation of poly(vinyl chloride)-g-poly(N-isopropylacrylamide) amphiphilic copolymer

PVC-g-PNIPAM amphiphilic copolymers with controlled graft lengths and densities are synthesized, which form unique macroscopic aggregates with well-defined 3D shapes in dilute aqueous solution above the LCST.

P(NIPAAM-co-HEMA) thermoresponsive hydrogels: an alternative approach for muscle cell sheet engineering

Loss of skeletal muscle tissue caused by traumatic injury or damage due to myopathies produces a deficit of muscle function for which there is still no clinical treatment. Transplantation of myogenic cells, themselves or combined with materials, has been proposed to increase the regenerative capacity of skeletal muscle but it is hampered by many limitations, such as low cell survival and engraftment or immunological reaction and low biocompatibility of the exogenous materials. Recently, myoblast sheet engineering, obtained with thermoresponsive culture dishes, has attracted attention as a new technique for muscle damage treatment. For this purpose, a series of thermoresponsive hydrogels, constituted by poly(N-isopropylacrylamide-co-2-hydroxyethylmethacrylate) [p(NIPAAM-co-HEMA)] were synthesized by a simple and inexpensive free-radical polymerization of the two co-monomers with a redox initiator. Different ratios of N-isopropylacrylamide (NIPAAm) and 2-hydroxyethylmethacrylate (HEMA) have been examined to evaluate the effects on physicochemical, mechanical and optical hydrogel properties. The murine muscle cell line C₂ C₁₂ has been exploited to test the cytotoxicity of the thermoresponsive hydrogels, depending on different synthesis conditions. In this study, we have identified a thermoresponsive hydrogel that allows cell adhesion and viability, together with the detachment of viable sheet of muscle cells, giving the chance to develop further applications for muscle damage and disease. Copyright © 2014 John Wiley & Sons, Ltd.

Tunable thermo-responsive P(NIPAAm-co-DMAAm)-b-PLLA-b-P(NIPAAm-co-DMAAm) triblock copolymer micelles as drug carriers

Thermo-responsive P(NIPAAm-co-DMAAm)-b-PLLA-b-P(NIPAAm-co-DMAAm) triblock copolymers are synthesized via combination of ring-opening polymerization and atom transfer radical polymerization.

Microcarriers designed for cell culture and tissue engineering of bone

Microspherical particulates have been an attractive form of biomaterials that find usefulness in cell delivery and tissue engineering. A variety of compositions, including bioactive ceramics, degradable polymers, and their composites, have been developed into a microsphere form and have demonstrated the potential to fill defective bone and to populate tissue cells on curved matrices. To enhance the capacity of cell delivery, the conventional solid form of spheres is engineered to have either a porous structure to hold cells or a thin shell to in-situ encapsulate cells within the structure. Microcarriers can also be a potential reservoir system of bioactive molecules that have therapeutic effects in regulating cell behaviors. Due to their specific form, advanced technologies to culture cell-loaded microcarriers are required, such as simple agitation or shaking, spinner flask, and rotating chamber system. Here, we review systematically, from material design to culture technology, the microspherical carriers used for the delivery of cells and tissue engineering, particularly of bone.

Antitumor activity of peptide amphiphile nanofiber-encapsulated camptothecin

Self-assembling peptide amphiphile (PA) nanofibers were used to encapsulate camptothecin (CPT), a naturally occurring hydrophobic chemotherapy agent, using a solvent evaporation technique. Encapsulation by PA nanofibers was found to improve the aqueous solubility of the CPT molecule by more than 50-fold. PAs self-assembled into nanofibers in the presence of CPT as demonstrated by transmission electron microscopy. Small-angle X-ray scattering results suggest a slight increase in diameter of the nanofiber to accommodate the hydrophobic cargo. In vitro studies using human breast cancer cells show an enhancement in antitumor activity of the CPT when encapsulated by the PA nanofibers. In addition, using a mouse orthotopic model of human breast cancer, treatment with PA nanofiber-encapsulated CPT inhibited tumor growth. These results highlight the potential of this model PA system to be adapted for delivery of hydrophobic therapies to treat a variety of diseases including cancer.

Thermostimulable wax@SiO2 core-shell particles

We propose a new synthesis pathway without any sacrificial template to prepare original monodisperse thermoresponsive capsules made of a wax core surrounded by a silica shell. Under heating, the inner wax expands and the shell breaks, leading to the liquid oil release. Such capsules that allow triggered deliverance provoked by an external stimulus belong to the class of smart materials. The process is based on the elaboration of size-controlled emulsions stabilized by particles (Pickering emulsions) exploiting the limited coalescence phenomenon. Then the emulsions are cooled down and the obtained suspensions are mineralized by the hydrolysis and condensation of a monomer at the wax-water interface, leading to the formation of capsules. The shell break and the liquid oil release are provoked by heating above the wax melting temperature. We characterize the obtained materials and examine the effect of processing parameters and heating history. By an appropriate choice of the wax, the temperature of release can easily be tuned.

Smart core/shell nanocomposites: intelligent polymers modified gold nanoparticles

Recently, the polymer modified gold nanoparticles have showed much potential in advanced materials. In this paper, the smart core/shell nanocomposites of intelligent polymers and gold nanoparticles were reviewed from the preparation, properties to potential applications. The main preparative methods were detailed including the direct-synthesis method, "graft-to" strategy, "graft-from" strategy and physical adsorption method, in which the surface-initiated radical polymerization such as atom-transfer radical polymerization and reversible-addition fragmentation chain-transfer radical polymerization displayed several advantages for well-defined nanostructures. The stimuli-responsive property and potential uses of such-fabricated nanocomposites were sorted to thermosensitive, pH responsive and other responsive catalogues to describe more clarified. In application, the combination of gold nanoparticles and intelligent polymers provides a facile path for intelligent materials and might be encouraged to hold enormous chances in biotechnology and nanotechnology.

PEG-grafted chitosan nanoparticles as an injectable carrier for sustained protein release

The development of injectable nanoparticulate "stealth" carriers for protein delivery is a major challenge. The objective of this work was to investigate the possibility of achieving the controlled release of a model protein, insulin, from PEG-grafted chitosan (PEG-g-chitosan) nanoparticles (mean diameter 150-300 nm) prepared by the ion gelation method. Insulin was efficiently incorporated into the nanoparticles, and reached as high as 38%. In vitro release showed that it could control the insulin release by choosing the composition, loading and release temperature. We observed that the composition of the nanoparticle surface (C/O ratio) increased from 2.40 to 3.23, with an increase in the incubation time. Therefore, we concluded that during this time, insulin release from PEG-g-chitosan nanoparticles followed a diffusion mechanism in which erosion was negligible. The experiments also demonstrated that PEG-g-chitosan helped to maintain the natural structure of the protein entrapped in the nanoparticles.

Preparation and Characterization of Stimuli-Responsive Magnetic Nanoparticles

In this work, the main attention was focused on the synthesis of stimuli-responsive magnetic nanoparticles (SR-MNPs) and the influence of glutathione concentration on its cleavage efficiency. Magnetic nanoparticles (MNPs) were first modified with activated pyridyldithio. Then, MNPs modified with activated pyridyldithio (MNPs-PDT) were conjugated with 2, 4-diamino-6-mercaptopyrimidine (DMP) to form SR-MNPs via stimuli-responsive disulfide linkage. Fourier transform infrared spectra (FTIR), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) were used to characterize MNPs-PDT. The disulfide linkage can be cleaved by reduced glutathione (GHS). The concentration of glutathione plays an important role in controlling the cleaved efficiency. The optimum concentration of GHS to release DMP is in the millimolar range. These results had provided an important insight into the design of new MNPs for biomedicine applications, such as drug delivery and bio-separation.

Biodegradable microspheres containing poly(epsilon-caprolactone)-Pluronic block copolymers for temperature-responsive release of proteins

Temperature-responsive microspheres were fabricated for the purpose of releasing protein in responsive to surrounding temperature changes. Temperature-responsive polymer, Pluronic was synthesized into block copolymers of poly(epsilon-caprolactone)-Pluronic with two different chain lengths of poly(epsilon-caprolactone). Microspheres loaded with proteins were prepared by a W/O/W emulsion method. The surface morphology was examined by scanning electron microscopy, showing that microspheres with diblock copolymers had porous structures due to hydrophilicity of Pluronic blocks. After incubating the microsphere at 37 degrees C for 7 days, temperature-responsive protein release was monitored with alternating temperature changes between 20 and 37 degrees C. The protein release was attenuated when the microsphere was incubated at 20 degrees C but the release rate was recovered at 37 degrees C, confirming variable release rate according to the temperature changes. The variable release rate of protein was dependent on the length of poly(epsilon-caprolactone) blocks attached to Pluronic.

Thermosensitive Copolymer Networks Modify Gold Nanoparticles for Nanocomposite Entrapment

The core-shell gold nanoparticles and copolymer of N-isopropylacrylamide (NIPAM) and N,N'-methylenebisacrylamide (MBAA) hybrids (Au@copolymer) were fabricated through surface-initiated atom-transfer radical polymerization (ATRP) on the surface of gold nanoparticles in 2-propanol/water mixed solvents. The surface of citrate-stabilized gold nanoparticles was first modified by a disulfide initiator for ATRP. The slight cross-linking polymerization between NIPAM and MBAA occurred on the gold surface and resulted in the formation of core-shell Au@copolymer nanostructures that were characterized by TEM, and FTIR and UV-visible spectroscopy. Such synthesized Au@copolymer hybrids possess clearly thermosensitive properties and exhibit "inspire" and "expire" water behavior in response to temperature changes in aqueous solution. Because of this property, we enable to trap and encapsulate smaller nanoparticles by using the free space of the copolymer-network scaffold anchored at the gold surface.

Hydrogels in controlled release formulations: network design and mathematical modeling

Over the past few decades, advances in hydrogel technologies have spurred development in many biomedical applications including controlled drug delivery. Many novel hydrogel-based delivery matrices have been designed and fabricated to fulfill the ever-increasing needs of the pharmaceutical and medical fields. Mathematical modeling plays an important role in facilitating hydrogel network design by identifying key parameters and molecule release mechanisms. The objective of this article is to review the fundamentals and recent advances in hydrogel network design as well as mathematical modeling approaches related to controlled molecule release from hydrogels. In the first section, the niche roles of hydrogels in controlled release, molecule release mechanisms, and hydrogel design criteria for controlled release applications are discussed. Novel hydrogel systems for drug delivery including biodegradable, smart, and biomimetic hydrogels are reviewed in the second section. Several mechanisms have been elucidated to describe molecule release from polymer hydrogel systems including diffusion, swelling, and chemically-controlled release. The focus of the final part of this article is discussion of emerging hydrogel delivery systems and challenges associated with modeling the performance of these devices.