Synthesis of Chiral Oligomer-Grafted Biodegradable Polyurethanes and Their Chiral-Dependent Influence on Bone Marrow Stem Cell Behaviors.

Chirality is one of the most fascinating and ubiquitous features in nature, especially in biological systems. The effects of chiral surfaces, especially in combination with degradable materials of good biocompatibility, on stem cell behaviors has not yet been tackled. In this communication, the chiral monomers N-acryloyl-l(d)-valine (l(d)-AV) are synthesized and are polymerized to obtain chiral (l(d)-PAV-SH) oligomers, which are covalently immobilized onto electron-deficient poly(propylene fumarate) polyurethane (PPFU) via Michael addition. The PPFU-l-PAV can interact more strongly and actively with bone marrow stem cells (BMSCs) than PPFU-d-PAV, leading to a larger cell spreading area, faster migration velocity, and stronger osteodifferentiation tendency.

Grafting of CAG peptides and (polyethylene glycol) on unsaturated polyurethane films to promote selective adhesion and migration of urethral epithelial cells.

Selective adhesion and migration of urethral epithelial cells (HUCs) over fibroblasts (FIBs) are very important in the reconstruction of the urethral epithelial layer and prevention of ureteral scarring and stenosis. In this study, unsaturated polyurethane (PPFU-CO-SS) films were co-grafted with a cell-resisting poly(ethylene glycol) (PEG) layer and HUC-selective Cys-Ala-Gly (CAG) peptides, whose physicochemical changes were confirmed by X-ray photon spectroscopy, fluorescence spectroscopy and water contact angle measurements. The adhesion and activation of platelets on the PEG/CAG grafted surface were significantly reduced compared to those on the PPFU-CO-SS, resulting in a similar status as that on a PEG-grafted surface. The HUC-selective material could obviously promote the adhesion and migration of HUCs. The ratio of the urethral epithelial cells to fibroblasts on the PEG/CAG grafted surface was nearly 3-fold that on the unmodified PPFU-CO-SS in a co-culture competitive environment. The urethral epithelial cells cultured on the PEG/CAG grafted surface also had the highest migration rate, which was 2.24-fold compared to that on the PPFU-CO-SS control.

Adsorption of serum proteins on titania nanotubes and its role on regulating adhesion and migration of mesenchymal stem cells.

Migration and differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) is an important biological process in tissue regeneration. Nanostructured titanium materials are believed to play a fundamental role in dental and orthopedic applications. However, the protein adsorption on nanostructured titanium materials and its correlation with the subsequent cell behaviors have not been studied. In this work, the titania nanotube arrays with different tubular diameters ranging from 27.3 to 88.2 nm were fabricated by using an electrochemical etching method. The adsorbed amounts and types of cell adhesion-related proteins (such as fibronectin, vitronectin, and laminin) from serum were investigated, revealing that these proteins were preferred to bind onto the surface with nanotubes of a smaller diameter. Adhesion and migration of BMSCs were studied as a function of different nanotube diameters in the presence or absence of serum proteins. Compared with the nanotube surface with a larger tubular diameter (88.2 nm), the surface with a smaller one could better support BMSCs in terms of adhesion and spreading. The pre-adsorbed serum proteins significantly enhanced adhesion and migration abilities of BMSCs. However, the adequate interactions between cells and serum proteins on the nanotubes surface with smallest nanotubes in diameter weakened cell mobility. Arrangement of cytoskeleton and expressions of key genes and proteins were studied, revealing that the nanostructured surfaces and pre-adsorbed proteins jointly mediated the adhesion and migration of BMSCs.

Methylcobalamin-Loaded PLCL Conduits Facilitate the Peripheral Nerve Regeneration.

The feasible fabrication of nerve guidance conduits (NGCs) with good biological performance is important for translation in clinics. In this study, poly(d,l-lactide-co-caprolactone) (PLCL) films loaded with various amounts (wt; 5%, 15%, 25%) of methylcobalamin (MeCbl) are prepared, and are further rolled and sutured to obtain MeCbl-loaded NGCs. The MeCbl can be released in a sustainable manner up to 21 days. The proliferation and elongation of Schwann cells, and the proliferation of Neuro2a cells are enhanced on these MeCbl-loaded films. The MeCbl-loaded NGCs are implanted into rats to induce the regeneration of 10 mm amputated sciatic nerve defects, showing the ability to facilitate the recovery of motor and sensory function, and to promote myelination in peripheral nerve regeneration. In particular, the 15% MeCbl-loaded PLCL conduit exhibits the most satisfactory recovery of sciatic nerves in rats with the largest diameter and thickest myelinated fibers.

Unsaturated polyurethane films grafted with enantiomeric polylysine promotes macrophage polarization to a M2 phenotype through PI3K/Akt1/mTOR axis.

The immune system responds immediately to tissue trauma and to biomaterial implants under the participation of M1/M2 macrophages polarization. The surface properties of biomaterials can significantly influence the tissue repair progress through modulating the macrophage functions. In this study, the surface of poly(propylene fumarate) polyurethane films (PPFU) is grafted with a same density of enantiomeric poly-l-lysine (PPFU-g-PLL) and poly-d-lysine (PPFU-g-PDL), leading to a similar level of enhanced surface wettability for the PPFU-g-PLL and PPFU-g-PDL. The polylysine-grafted PPFU can restrict the M1 polarization, whereas promote M2 polarization of macrophages in vitro, judging from the secretion of cytokines and expression of key M1 and M2 related genes. Comparatively, the PPFU-g-PDL has a stronger effect in inducing M2 polarization in vivo, resulting in a thinner fibrous capsule surrounding the implant biomaterials. The CD44 and integrins of macrophages participate in the polarization process probably by activating focal adhesion kinase (FAK) and Rho-associated protein kinase (ROCK), and downstream PI3K/Akt1/mTOR signal axis to up regulate M2 related gene expression. This study confirms for the first time that polylysine coating is an effective method to regulate the immune response of biomaterials, and the polylysine-modified thermoplastic PPFU with the advantage to promote M2 polarization may be applied widely in regenerative medicine.

Biodegradable Anisotropic Microparticles for Stepwise Cell Adhesion and Preparation of Janus Cell Microparticles.

The biomimetic anisotropic particles have different physicochemical properties on the opposite two sides, enabling diverse applications in emulsion, photonic display, and diagnosis. However, the traditional anisotropic particles have a very small size, ranging from submicrons to a few microns. The design and fabrication of anisotropic macron-sized particles with new structures and properties is still challenging. In this study, anisotropic polycaprolactone (PCL) microparticles well separated with each other were prepared by crystallization from the dilute PCL solution in a porous 3D gelatin template. They had fuzzy and smooth surfaces on each side, and a size as large as 70 µm. The fuzzy surface of the particle adsorbed significantly larger amount of proteins, and was more cell-attractive regardless of the cell types. The particles showed stronger affinity toward fibroblasts over hepatocytes, which paved a new way for cell isolation merely based on the surface morphology. After a successive seeding process, Janus cell microparticles with fibroblasts and endothelial cells (ECs) on each side were designed and obtained by making use of the anisotropic surface morphology, which showed significant difference in EC functions in terms of prostacyclin (PGl2) secretion, demonstrating the unique and appealing functions of this type of anisotropic microspheres.

Fabrication of polyurethane microcapsules with different shapes and their influence on cellular internalization.

The shape of particles is recognized as an important parameter to influence their interactions with cells. In this study, spherical and discal polyurethane microcapsules were prepared via an adsorption and crosslinking method on the templates with corresponding shapes in organic solvent. Both types of capsules could be well dispersed in aqueous medium and maintain their original shapes. The internalization behaviors of the microcapsules were investigated by co-incubation with RAW 264.7 and HepG2 cells. Compared with the spherical capsules, the discal microcapsules could be internalized with faster rate and higher amount by both types of cells. Both types of capsules did not show significant cytotoxicity even after co-incubation for 72h at a high ratio of capsule to cell.

Aligned PLLA nanofibrous scaffolds coated with graphene oxide for promoting neural cell growth.

UNLABELLED: The graphene oxide (GO) has attracted tremendous attention in biomedical fields. In order to combine the unique physicochemical properties of GO nanosheets with topological structure of aligned nanofibrous scaffolds for nerve regeneration, the GO nanosheets were coated onto aligned and aminolyzed poly-l-lactide (PLLA) nanofibrous scaffolds. Scanning electronic microscopy (SEM) and atomic force microscopy (AFM) revealed that the surface of aligned PLLA nanofibers after being coated with GO became rougher than those of the aligned PLLA and aminolyzed PLLA nanofibrous scaffolds. The GO nanosheets did not destroy the alignment of nanofibers. The characterizations of X-ray photoelectron spectroscopy (XPS) and water contact angle displayed that the aligned PLLA nanofibrous scaffolds were introduced with hydrophilic groups such as NH2, COOH, and OH after aminolysis and GO nanosheets coating, showing better hydrophilicity. The GO-coated and aligned PLLA nanofibrous scaffolds significantly promoted Schwann cells (SCs) proliferation with directed cytoskeleton along the nanofibers compared with the aligned PLLA and aminolyzed PLLA nanofibrous scaffolds. These scaffolds also greatly improved the proliferation of rat pheochromocytoma 12 (PC12) cells, and significantly promoted their differentiation and neurite growth along the nanofibrous alignment in the presence of nerve growth factor (NGF). This type of scaffolds with nanofibrous surface topography and GO nanosheets is expected to show better performance in nerve regeneration. STATEMENT OF SIGNIFICANCE: Recovery of damaged nerve functions remains a principal clinical challenge in spite of surgical intervention and entubulation. The use of aligned fibrous scaffolds provides suitable microenvironment for nerve cell attachment, proliferation and migration, enhancing the regeneration outcome of nerve tissue. Surface modification is generally required for the synthetic polymeric fibers by laminin, fibronectin and YIGSR peptides to stimulate specific cell functions and neurite outgrowth. Yet these proteins or peptides present the poor processibility, limited availability, and high cost, influencing their application in clinic. In this work, we combined GO nanosheets and topological structure of aligned nanofibrous scaffolds to direct cell migration, proliferation, and differentiation, and to induce neurite outgrowth for nerve regeneration. The GO coating improved several biomedical properties of the aligned PLLA nanofibrous scaffolds including surface roughness, hydrophilicity and promotion of cells/material interactions, which significantly promoted SCs growth and regulated cell orientation, and induced PC12 cells differentiation and neurite growth. The design of this type of structure is of both scientific and technical importance, and possesses broad interest in the fields of biomaterials, tissue engineering and regenerative medicine.