Synthesis of a Novel Biodegradable Polyurethane with Phosphatidylcholines

A novel polyurethane was successfully synthesized by chain-extension of biodegradable poly (l-lactide) functionalized phosphatidylcholine (PC) with hexamethylene diisocyanate (HDI) as chain extender (PUR-PC). The molecular weights, glass transition temperature (Tg) increased significantly after the chain-extension. The hydrophilicity of PUR-PC was better than the one without PC, according to a water absorption test. Moreover, the number of adhesive platelets and anamorphic platelets on PUR-PC film were both less than those on PUR film. These preliminary results suggest that this novel polyurethane might be a better scaffold than traditional biodegradable polyurethanes for tissue engineering due to its better blood compatibility. Besides, this study also provides a new method to prepare PC-modified biodegradable polyurethanes

Polymerization of Affinity Ligands on a Surface for Enhanced Ligand Display and Cell Binding

Surfaces functionalized with affinity ligands have been widely studied for applications such as biological separations and cell regulation. While individual ligands can be directly conjugated onto a surface, it is often important to conjugate polyvalent ligands onto the surface to enhance ligand display. This study was aimed at exploring a method for surface functionalization via polymerization of affinity ligands, which was achieved through ligand hybridization with DNA polymers protruding from the surface. The surface with polyvalent ligands was evaluated via aptamer-mediated cell binding. The results show that this surface bound target cells more effectively than a surface directly functionalized with individual ligands in situations with either equal amounts of ligand display or equal amounts of surface reaction sites. Therefore, this study has demonstrated a new strategy for surface functionalization to enhance ligand display and cell binding. This strategy may find broad applications in settings where surface area is limited or the surface of a material does not possess sufficient reaction sites

Programmable Hydrogels for Controlled Cell Catch and Release Using Hybridized Aptamers and Complementary Sequences

The ability to regulate cell–material interactions is important in various applications such as regenerative medicine and cell separation. This study successfully demonstrates that the binding states of cells on a hydrogel surface can be programmed by using hybridized aptamers and triggering complementary sequences (CSs). In the absence of the triggering CSs, the aptamers exhibit a stable, hybridized state in the hydrogel for cell-type-specific catch. In the presence of the triggering CSs, the aptamers are transformed into a new hybridized state that leads to the rapid dissociation of the aptamers from the hydrogel. As a result, the cells are released from the hydrogel. The entire procedure of cell catch and release during the transformation of the aptamers is biocompatible and does not involve any factor destructive to either the cells or the hydrogel. Thus, the programmable hydrogel is regenerable and can be applied to a new round of cell catch and release when needed

Aptamer-Based Polyvalent Ligands for Regulated Cell Attachment on the Hydrogel Surface

Natural biomolecules are often used to functionalize materials to achieve desired cell-material interactions. However, their applications can be limited owing to denaturation during the material functionalization process. Therefore, efforts have been made to develop synthetic ligands with polyvalence as alternatives to natural affinity biomolecules for the synthesis of functional materials and the control of cell-material interactions. This work was aimed at investigating the capability of a hydrogel functionalized with a novel polyvalent aptamer in inducing cell attachment in dynamic flow and releasing the attached cells in physiological conditions through a hybridization reaction. The results show that the polyvalent aptamer could induce cell attachment on the hydrogel in dynamic flow. Moreover, cell attachment on the hydrogel surface was significantly influenced by the value of shear stress. The cell density on the hydrogel was increased from 40 cells/mm² to nearly 700 cells/mm² when the shear stress was decreased from 0.05 to 0.005 Pa. After the attachment onto the hydrogel surface, approximately 95% of the cells could be triggered to detach within 20 min by using an oligonucleotide complementary sequence that displaced polyvalent aptamer strands from the hydrogel surface. While it was found that the cell activity was reduced, the live/dead staining results show that ≥98% of the detached cells were viable. Therefore, this work has suggested that the polyvalent aptamer is a promising synthetic ligand for the functionalization of materials for regulated cell attachment

Chimeric Aptamer–Gelatin Hydrogels as an Extracellular Matrix Mimic for Loading Cells and Growth Factors

It is important to synthesize materials to recapitulate critical functions of biological systems for a variety of applications such as tissue engineering and regenerative medicine. The purpose of this study was to synthesize a chimeric hydrogel as a promising extracellular matrix (ECM) mimic using gelatin, a nucleic acid aptamer, and polyethylene glycol. This hydrogel had a macroporous structure that was highly permeable for fast molecular transport. Despite its high permeability, it could strongly sequester and sustainably release growth factors with high bioactivity. Notably, growth factors retained in the hydrogel could maintain ∼50% bioactivity during a 14-day release test. It also provided cells with effective binding sites, which led to high efficiency of cell loading into the macroporous hydrogel matrix. When cells and growth factors were coloaded into the chimeric hydrogel, living cells could still be observed by day 14 in a static serum-reduced culture condition. Thus, this chimeric aptamer–gelatin hydrogel constitutes a promising biomolecular ECM mimic for loading cells and growth factors