Reentrant phase transition and network parameters of hydrophobically modified poly[2-(diethylamino)ethylmethacrylate-co-N-vinyl-2-pyrrolidone/octadecyl acrylate] hydrogels

Hydrophobically modified poly[2-(diethylamino)ethylmethacrylate-co-N-vinyl-2-pyrrolidone/octadecyl acrylate] [P(DEAEMA-NVP/OA)] hydrogels with different OA content were prepared by free-radical crosslinking copolymerization of corresponding monomers in tert-butanol. The swelling equilibrium of the hydrogels was investigated as a function of temperature and hydrophobic comonomer content in pure water. An interesting feature of the swelling behavior of the P(DEAEMA-NVP/OA) hydrogels was the reentrant phase transition where the hydrogels collapse once and reswell as temperature increased. The average molecular mass between crosslinks and polymer-solvent interaction parameter (χ) of the hydrogels were calculated from equilibrium swelling values. The enthalpy (ΔH) and entropy (ΔS) changes appearing in the χ parameter for the hydrogels were determined by using the Flory-Rehner theory. It was observed that the experimental swelling data of the hydrophobic hydrogels at different temperature agreed with the Flory-Rehner theory, that provided that the sensitive dependence of χ parameter on both temperature and polymer concentration is taken into account.     

Poly(N,N‐dimethylacrylamide)‐Based Microspheres Prepared by Heterogeneous Polymerizations

PDMAAm microspheres have been obtained by inverse suspension, inverse emulsion, and dispersion polymerization. Conventional inverse suspension polymerization in toluene/trichloroethene is modified by the use of ultrasound. The resulting hydrogel microspheres are examined by dynamic light scattering and scanning electron microscopy to afford the morphology, dispersity, and size of the microspheres. Inverse suspension polymerization yields 100‐µm particles, while those obtained by inverse emulsion polymerization are 0.13–1 µm in diameter. While the inverse techniques produce particles of broad size distribution, monodisperse microspheres are obtained by the Kraton G 1650‐stabilized dispersion polymerization of DMAAm in a toluene/heptane medium. The particle size and polydispersity could be controlled by the addition of water into the dispersed phase, and by varying the cellulose acetate butyrate or Kraton G 1650 concentration and the toluene/trichloroethene or toluene/heptane ratio.

     

RADIATION SYNTHESIS AND CHARACTERIZATION OF POLY(AA-co-NVP)/CLAY HYDROGELS

The pH-sensitive P(AA-co-NVP)/clay hydrogels were prepared with the monomers of acrylic acid(AA)and N-vinyl-2-pyrrolidone(NVP)based onγ-ray irradiation technique.The influence of pH values of buffer solutions and contents of clay and NVP on the equilibrium swelling ratio(SR)and compressive properties of the hydrogels was investigated in detail.The results of swelling property tests showed that,with the increase of clay content,the SR of hydrogels increases in the same buffer solution,and the SR of hydrog...     

Hybrid linear dendritic macromolecules: From synthesis to applications

Linear‐dendritic copolymers are intriguing macromolecules, which offer challenge and fascination as purely synthetic objects at the crossroad of organic and polymer chemistry and as promising materials for diverse advanced applications. This review traces their discovery and highlights the synthetic strategies used for their construction. The ambivalent character of the linear‐dendritic architecture opens numerous avenues towards emerging and potential applications. Specific solution properties enable the construction of nanometer‐sized nanoreactors for reactions in environmentally friendly media, and the creation of “nanosponges” for selective passive binding of fluorescent pH‐indicators for environmental or biomonitoring. Another structure–property relationship is used for noncovalent and site‐specific modification of glycoproteins, which leads to the formation of “semiartificial” enzymes with enhanced and broadened catalytic activity. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5295–5314, 2008     

Chitosan-Placental ECM Composite Thermos-Responsive Hydrogel as a Biomimetic Wound Dressing with Angiogenic Property

Attempts are being made to develop an ideal wound dressing with excellent biomechanical and biological properties. Here, a thermos-responsive hydrogel is fabricated using chitosan (CTS) with various concentrations (1%, 2.5%, and 5% w/v) of solubilized placental extracellular matrix (ECM) and 20% β-glycerophosphate to optimize a smart wound dressing hydrogel with improved biological behavior. The thermo-responsive CTS (TCTS) alone or loaded with ECMs (ECM-TCTS) demonstrate uniform morphology using SEM. TCTS and ECM1%-TCTS and ECM2.5%-TCTS show a gelation time of 5 min at 37 °C, while no gel formation is observed at 4 and 25 °C. ECM5%-TCTS forms gel at both 25 and 37 °C. The degradation and swelling ratios increase as the ECM content of the hydrogel increase. All the constructs show excellent biocompatibility in vitro and in vivo, however, the hydrogels with a higher concentration of ECM demonstrate better cell adhesion for fibroblast cells and induce expression of angiogenic factors (VEGF and VEGFR) from HUVEC. Only the ECM5%-TCTS has antibacterial activity against Acinetobacter baumannii ATCC 19606. The data obtained from the current study suggest the ECM2.5%-TCTS as an optimized smart biomimetic wound dressing with improved angiogenic properties now promises to proceed with pre-clinical and clinical investigations.     

Exosome-Hydrogel System in Bone Tissue Engineering: A Promising Therapeutic Strategy

Exosomes, as messengers of cell-to-cell communication, have many functional properties similar to those of their derived cells. Because they contain a large number of bioactive components that regulate recipient cell behavior, they are inanimate and do not require external maintenance or assistance. Various cell-derived exosomes are involved in many physiological processes of bone tissue repair. Hydrogels are widely used as scaffolding materials for bone tissue repair because their 3D network structure resembles the natural extracellular matrix. Moreover, their material properties and biological functions are adjustable. Exosomes can be delivered directly to the bone tissue damage site by hydrogel, and their duration of action in vivo can be prolonged by slow release. Therefore, the exosome-loaded hydrogel (Exo-Gel) system is a promising material for bone tissue engineering. In this study, the progress of the application of Exo-Gel in bone tissue repair and the improvement strategies, problems and research prospects of the current exosomes and hydrogels that have been applied to the Exo-Gel system for bone tissue repair are reviewed.     

Hydrogels as Scaffolds in Bone-Related Tissue Engineering and Regeneration

Several years have passed since the medical and scientific communities leaned toward tissue engineering as the most promising field to aid bone diseases and defects resulting from degenerative conditions or trauma. Owing to their histocompatibility and non-immunogenicity, bone grafts, precisely autografts, have long been the gold standard in bone tissue therapies. However, due to issues associated with grafting, especially the surgical risks and soaring prices of the procedures, alternatives are being extensively sought and researched. Fibrous and non-fibrous materials, synthetic substitutes, or cell-based products are just a few examples of research directions explored as potential solutions. A very promising subgroup of these replacements involves hydrogels. Biomaterials resembling the bone extracellular matrix and therefore acting as 3D scaffolds, providing the appropriate mechanical support and basis for cell growth and tissue regeneration. Additional possibility of using various stimuli in the form of growth factors, cells, etc., within the hydrogel structure, extends their use as bioactive agent delivery platforms and acts in favor of their further directed development. The aim of this review is to bring the reader closer to the fascinating subject of hydrogel scaffolds and present the potential of these materials, applied in bone and cartilage tissue engineering and regeneration.     

Effect of Composition of Lung Biomimetic Niche on the Mesenchymal Stem Cell Differentiation toward Alveolar Type II Pneumocytes

Pulmonary niche dynamically orchestrates the signals, such as proliferation or differentiation of mesenchymal stem cells (MSCs), which allows inducing tissue repair. Lung niche includes extracellular matrix (ECM), comprising hyaluronic acid (HA) and collagen (COLL), and several types of MSCs. Impaired ECM, in lung pathologies, makes the promising therapies based on MSCs ineffective, as it results in a reduced attachment and homing of MSCs, precluding their differentiation and viability. To overcome this problem, in this study a pulmonary biomimetic niche based on HA and COLL hydrogel is developed, with the specific aim to elucidate the role of COLL and HA/COLL semi-interpenetrating polymer networks (SIPNs) in directing the differentiation of MSCs into Alveolar Type II (ATII) cells. The effect of low (L), medium (M), and high (H) molecular weight (MW) HA is investigated, both like structural component of the SIPNs hydrogel and like trophic factor in cell culture media solution. HA in the culture media significantly improves surfactant protein (SP)-C expression (≈2 ng mL⁻¹), without showing difference in the MW tested, compared to control only (≈1 ng mL⁻¹). Furthermore, LMWHA/COLL hydrogel promotes the SPC expression (approximately two times) compared to COLL, MMWHA/COLL, and HMWHA/COLL hydrogels.     

The Synergistic Effect of Cationic Moieties and GRGDSF‐Peptides in Hydrogels on Neural Stem Cell Behavior

This article reports the behavior of embryonic neural stem cells on a hydrogel that combines cationic, non‐specific cell adhesion motifs with glycine‐arginine‐glycine‐aspartic acid‐serine‐phenylalanine (GRGDSF)‐peptides as specific cell adhesion moieties. Therefore, three hydrogels are prepared by free radical polymerization that contains either a GRGDSF‐peptide residue ( P1 ), amino ethylmethacrylate as a cationic residue ( P2 ), or a combination of both motifs ( P3 ). For each gel, cross linker concentrations of 8 mol% is used to have a comparable gel stiffness of 8–9 kPa. The cell experiments indicate a synergistic effect of the non‐specific, cationic residues, and the specific GRGDSF‐peptides on embryonic neural stem cell behavior that is especially pronounced in the cell adhesion experiments by more than doubling the number of cells after 72 h when comparing P3 with P2 and is less pronounced in the proliferation and differentiation experiments.