Regulation of the thermal sensitivity of hydroxypropyl cellulose by poly(N-isopropylacryamide) side chains

Synthesis and characterization of temperature-sensitive microspheres based on acrylamide grafted hydroxypropyl cellulose and chitosan for the controlled release of amoxicillin trihydrate

This study deals with the preparation of temperature-sensitive chitosan/hydroxypropyl cellulose-graft-polyacrylamide (CS/HPC-g-PAAm) blend microspheres as a controlled drug release system. For this purpose, HPC-g-PAAm copolymers of hydroxypropyl cellulose (HPC) with acrylamide (AAm) were synthesized using cerium (IV) ammonium nitrate as initiator. The HPC-g-PAAm copolymers were characterized by using Fourier transform infrared spectroscopy (FTIR), elemental analysis, and differential scanning calorimetry (DSC). Lower critical solution temperatures (LCST) of the synthesized copolymers were determined. Temperature-sensitive blend microspheres of HPC-g-PAAm and chitosan were prepared by emulsion cross-linking method using glutaraldehyde (GA) as a cross-linker in the hydrochloric acid catalyst (HCl) and they were used to achieve controlled release of amoxicillin trihydrate (AMX), an antibiotic drug. The microspheres were characterized by DSC, X-ray diffraction (X-RD), and FTIR spectroscopy. In addition, surfaces of empty and drug-loaded microspheres were examined by scanning electron microscopy (SEM). The effects of variables such as CS/HPC-g-PAAm ratio, drug/polymer ratio, amount of cross-linker, and reaction time of grafting on AMX release were investigated at three different pH environments (1.2, 6.8, 7.4) at 25 °C, 37 °C, and 50 °C. The release results showed that the microspheres had temperature sensitivity and the AMX release was slightly more controlled by especially increasing graft yield (%).

A facile method to control the phase behavior of hydroxypropyl cellulose

We report a facile chemical method to convert the hydroxyl groups of hydroxypropyl cellulose (HPC) into carbamates. It was achieved by the reaction of HPC with N-methyl carbamoylimidazole, which is a safe and easy to handle replacement for the particularly hazardous reagent methyl isocyanate. Using a series of HPC with a range of molar substitution of hydroxypropyl groups, we synthesized HPC methylcarbamates showing lower critical solution temperature (LCST) in the range between 94 and 15 °C. A linear dependence of LCST versus methylcarbamate degree of substitution is observed. The lower the initial hydroxypropyl content of HPC, the greater the effect of methylcarbamate on the LCST. Surface tension study showed that methylcarbamate modification has an insignificant effect on the hydrophilic-hydrophobic balance of the macromolecules below LCST unless the molecular substitution of hydroxypropyl groups is so low (0.8) that the native cellulose OH groups can react with N-methyl carbamoylimidazole.

Thermoresponsive 2-hydroxy-3-isopropoxypropyl hydroxyethyl cellulose with tunable LCST for drug delivery

Thermoresponsive polymer 2-hydroxy-3-isopropoxypropyl hydroxyethyl celluloses (HIPECs) were successfully synthesized, characterized, and applied for thermoresponsive drug delivery. The lower critical solution temperature (LCST) of HIPEC could be easily tuned from 21.1 to 56.1 °C as the molar substitution (MS) increased from 1.21 to 2.88. Dynamic light scattering and transmission electron microscopy experiments revealed that HIPEC can self-assemble into nano-sized aggregates, and their size could be changed by variation in temperature. Additionally, the critical aggregation concentration (CAC) ranged from 0.101 to 0.805 g L⁻¹ by changing MS of HIPEC. In vitro drug delivery studies indicated that the amphotericin B (AmpB) release rate was much faster at temperatures above LCST; approximately 95% of the drug was released from aggregates in 40 h. MTT assays were conducted to evaluate the cytotoxicity of HIPEC, and the observation of the Hoechst 33342 living cell stain using confocal laser scanning microscopy confirmed the high cell viability as HIPECs were used.

Thermoresponsive polymer 2-hydroxy-3-isopropoxypropyl hydroxyethyl celluloses (HIPECs) were successfully synthesized, characterized, and applied for thermoresponsive drug delivery.

Recent Developments in the Synthesis of Biomacromolecules and their Conjugates by Single Electron Transfer-Living Radical Polymerization

Single electron transfer-living radical polymerization (SET-LRP) represents a robust and versatile tool for the synthesis of vinyl polymers with well-defined topology and chain end functionality. The crucial step in SET-LRP is the disproportionation of the Cu(I)X generated by activation with Cu(0) wire, powder, or nascent Cu(0) generated in situ into nascent, extremely reactive Cu(0) atoms and nanoparticles and Cu(II)X₂. Nascent Cu(0) activates the initiator and dormant chains via a homogeneous or heterogeneous outer-sphere single-electron transfer mechanism (SET-LRP). SET-LRP provides an ultrafast polymerization of a plethora of monomers (e.g., (meth)-acrylates, (meth)-acrylamides, styrene, and vinyl chloride) including hydrophobic and water insoluble to hydrophilic and water soluble. Some advantageous features of SET-LRP are (i) the use of Cu(0) wire or powder as readily available catalysts under mild reaction conditions, (ii) their excellent control over molecular weight evolution and distribution as well as polymer chain ends, (iii) their high functional group tolerance allowing the polymerization of commercial-grade monomers, and (iv) the limited purification required for the resulting polymers. In this Perspective, we highlight the recent advancements of SET-LRP in the synthesis of biomacromolecules and of their conjugates.

Temperature-Responsive Nanofibrillar Hydrogels for Cell Encapsulation

Natural extracellular matrices often have a filamentous nature, however, only a limited number of artificial extracellular matrices have been designed from nanofibrillar building blocks. Here we report the preparation of temperature-responsive nanofibrillar hydrogels from rod-shaped cellulose nanocrystals (CNCs) functionalized with a copolymer of N-isopropylacrylamide and N,N'-dimethylaminoethyl methacrylate. The composition of the copolymer was tuned to achieve gelation of the suspension of copolymer-functionalized CNCs at 37 °C in cell culture medium and gel dissociation upon cooling it to room temperature. The mechanical properties and the structure of the hydrogel were controlled by changing copolymer composition and the CNC-to-copolymer mass ratio. The thermoreversible gels were used for the encapsulation and culture of fibroblasts and T cells and showed low cytotoxicity. Following cell culture, the cells were released from the gel by reducing the temperature, thus, enabling further cell characterization. These results pave the way for the generation of injectable temperature-responsive nanofibrillar hydrogels. The release of cells following their culture in the hydrogels would enable enhanced cell characterization and potential transfer in a different cell culture medium.

Cu(0)-mediated living radical polymerization: recent highlights and applications; a perspective

Cu(0)-mediated living radical polymerization or single electron transfer living radical polymerization (Cu(0)-mediated LRP or SET-LRP) is a versatile polymerization technique that has attracted considerable interest during the past few years for the facile preparation of advanced materials.