Surface Modification of Polycaprolactone Scaffold With Improved Biocompatibility and Controlled Growth Factor Release for Enhanced Stem Cell Differentiation

Polycaprolactone (PCL) has been widely used as a scaffold material for tissue engineering. Reliable applications of the PCL scaffolds require overcoming their native hydrophobicity and obtaining the sustained release of signaling factors to modulate cell growth and differentiation. Here, we report a surface modification strategy for electrospun PCL nanofibers using an azide-terminated amphiphilic graft polymer. With multiple alkylation and pegylation on the side chains of poly-L-lysine, stable coating of the graft polymer on the PCL nanofibers was achieved in one step. Using the azide-alkyne “click chemistry”, we functionalized the azide-pegylated PCL nanofibers with dibenzocyclooctyne-modified nanocapsules containing growth factor, which rendered the nanofiber scaffold with satisfied cell adhesion and growth property. Moreover, by specific immobilization of pH-responsive nanocapsules containing bone morphogenetic protein 2 (BMP-2), controlled release of active BMP-2 from the PCL nanofibers was achieved within 21 days. When bone mesenchyme stem cells were cultured on this nanofiber scaffold, enhanced ossification was observed in correlation with the time-dependent release of BMP-2. The established surface modification can be extended as a generic approach to hydrophobic nanomaterials for longtime sustainable release of multiplex signaling proteins for tissue engineering.

Heat Managing Organic Materials: Phase Change Materials with High Thermal Conductivity and Shape Stability

An advanced heat managing graft polymer (AHG) was fabricated by introducing a mesogen-based molecular building block that facilitates photon transfer. The fabricated AHGs exhibit excellent thermal conductivity as well as...

Mechanism of Post-Radiation-Chemical Graft Polymerization of Styrene in Polyethylene

Structural and morphological features of graft polystyrene (PS) and polyethylene (PE) copolymers produced by post-radiation chemical polymerization have been investigated by methods of X-ray microanalysis, electron microscopy, DSC and wetting angles measurement. The studied samples differed in the degree of graft, iron(II) sulphate content, sizes of PE films and distribution of graft polymer over the polyolefin cross section. It is shown that in all cases sample surfaces are enriched with PS. As the content of graft PS increases, its concentration increases both in the volume and on the surface of the samples. The distinctive feature of the post-radiation graft polymerization is the stepped curves of graft polymer distribution along the matrix cross section. A probable reason for such evolution of the distribution profiles is related to both the distribution of peroxide groups throughout the sample thickness and to the change in the monomer and iron(II) salt diffusion coefficients in the graft polyolefin layer. According to the results of electron microscope investigations and copolymer wettability during graft polymerization, a heterogeneous system is formed both in the sample volume and in the surface layer. It is shown that the melting point, glass transition temperature and degree of crystallinity of the copolymer decreases with the increasing proportion of graft PS. It is suggested that during graft polymerization a process of PE crystallite decomposition (melting) and enrichment of the amorphous phase of graft polymer by fragments of PE macromolecules occurs spontaneously. The driving force of this process is the osmotic pressure exerted by the phase network of crystallites on the growing phase of the graft PS.

Synthesis of Graphene Oxide-Polystyrene Graft Polymer Based on Reversible Addition Fragmentation Chain Transfer and Its Effect on Properties, Crystallization, and Rheological Behavior of Poly (Lactic Acid)

Graphene oxide-polystyrene graft polymer (SGO-PS) was prepared by reversible addition-fragmentation chain transfer radical polymerization method. Orthogonal experiments indicated that the optimum synthesis reaction conditions for SGO-PS were as follows: the millimole ratio of chain transfer agent to initiator was 0.15 : 0.3, and the amount of styrene was 8 mL at 80°C for 12 hours. The products were characterized by Fourier transform infrared spectroscopy and thermal weightlessness analysis, and the highest grafting rate of SGO-PS was 62.46%. Then, PLA/SGO-PS nanocomposites were prepared using SGO-PS as fillers by melt intercalation method, and its crystallinity, mechanical properties, and thermal stability were significantly improved. Compared with pure PLA, the crystallinity of PLA/SGO-PS (0.3 wt%) nanocomposites was increased by 5 times. Multiple melting behavior tests showed that the introduction of SGO-PS caused the PLA molecular chain to be discharged into the unit cell in time, and the melting temperature shifted to a higher temperature, which ultimately made the grain structure of PLA composites more complete and stable than pure PLA. The rheological performance test showed that the uniform dispersion of SGO-PS in the PLA matrix inhibited the free movement of the PLA molecular chain and caused higher flow resistance, resulting in an increase in the complex viscosity, storage modulus, and loss modulus of PLA/SGO-PS.