A flexible approach to the preparation of polymer scaffolds for tissue engineering

Biodegradable polyester unimolecular systems as emerging materials for therapeutic applications

Unimolecular micelles, as a class of single-molecular micelles, are structurally stable regardless of their concentrations or alterations of the outer environment such as pH, temperature, ion strength etc. in comparison with conventional polymeric micelles. Polyester unimolecular micelles are extensively applied in bio-medical fields because of their stability, biocompatibility, biodegradability, structural-controllabilty etc. In this review, the most recent developments in polyester unimolecular micelle designs in terms of Boltorn polymer H40 core, cyclodextrin, dendrimer or dendrimer-like polymer, or polyhedral oligomeric silsesquioxane (POSS) based polyester unimolecular micelles are presented. The significance and application in biomedical fields including drug delivery, bio-imaging and theranostics are also classified in this review. Finally, the remaining challenges and future perspectives for further development of unimolecular micelles as therapeutic materials are also discussed.

A review on core-shell structured unimolecular nanoparticles for biomedical applications

Polymeric unimolecular nanoparticles (NPs) exhibiting a core-shell structure and formed by a single multi-arm molecule containing only covalent bonds have attracted increasing attention for numerous biomedical applications. This unique single-molecular architecture provides the unimolecular NP with superior stability both in vitro and in vivo, a high drug loading capacity, as well as versatile surface chemistry, thereby making it a desirable nanoplatform for therapeutic and diagnostic applications. In this review, we surveyed the architecture of various types of polymeric unimolecular NPs, including water-dispersible unimolecular micelles and water-soluble unimolecular NPs used for the delivery of hydrophobic and hydrophilic agents, respectively, as well as their diverse biomedical applications. Future opportunities and challenges of unimolecular NPs were also briefly discussed.

Responsive hydrogels produced via organic sol-gel chemistry for cell culture applications

In this study, we report the synthesis of novel environmentally responsive polyurea hydrogel networks prepared via organic sol-gel chemistry and demonstrate that the networks can stabilize pH while releasing glucose both in simple aqueous media and in mammalian cell culture settings. Hydrogel formulations have been developed based on the combination of an aliphatic triisocyanate with pH-insensitive amine functional polyether and pH-sensitive poly(ethyleneimine) segments in a minimally toxic solvent suitable for the sol-gel reaction. The polyether component of the polyurea network is sufficiently hydrophilic to give rise to some level of swelling independent of environmental pH, while the poly(ethyleneimine) component contains tertiary amine groups providing pH sensitivity to the network in the form of enhanced swelling and release under acidic conditions. The reaction of these materials to form a network is rapid and requires no catalyst. The resultant material exhibits the desired pH-responsive swelling behavior and demonstrates its ability to simultaneously neutralize lactic acid and release glucose in both cell-free culture media and mammalian cell culture, with no detectable evidence of cytotoxicity or changes in cell behavior, in the case of either SA-13 human hybridomas or mouse embryonic stem cells. Furthermore, pH is observed to have a clear effect on the rate at which glucose is released from the hydrogel network. Such characteristics promise to maintain a favorable cell culture environment in the absence of human intervention.

In situ photopolymerization of biomaterials by thiol-yne click chemistry

The thiol-yne click chemistry reaction has been used for the in situ photocrosslinking of an aliphatic hyperbranched polyester. The biocompatibility of the resulting networks has been studied and marked cytotoxicity was not found for HeLa (human cervical carcinoma) tumoral cells and COS7 fibroblasts. The photoinduced thiol-yne process allows the generation of patterned structures with different geometries in films by DLW and these materials can be used as substrates for cell adhesion. The influence of the substrate geometry on cell adhesion has been studied by culturing cells onto these substrates and a preference for the photopatterned polymeric material can be seen in some of the structures by contrast phase microscopy. Actin and vinculin fluorescent staining revealed different adhesion behavior for HeLa cells and COS7 fibroblasts and this could be assigned to the different motility of cells. The thiol-yne photoreaction has proven to be an attractive approach for the preparation of micropatterned biomaterials.

Design and applications of biodegradable polyester tissue scaffolds based on endogenous monomers found in human metabolism

Synthetic polyesters have deeply impacted various biomedical and engineering fields, such as tissue scaffolding and therapeutic delivery. Currently, many applications involving polyesters are being explored with polymers derived from monomers that are endogenous to the human metabolism. Examples of these monomers include glycerol, xylitol, sorbitol, and lactic, sebacic, citric, succinic, alpha-ketoglutaric, and fumaric acids. In terms of mechanical versatility, crystallinity, hydrophobicity, and biocompatibility, polyesters synthesized partially or completely from these monomers can display a wide range of properties. The flexibility in these macromolecular properties allows for materials to be tailored according to the needs of a particular application. Along with the presence of natural monomers that allows for a high probability of biocompatibility, there is also an added benefit that this class of polyesters is more environmentally friendly than many other materials used in biomedical engineering. While the selection of monomers may be limited by nature, these polymers have produced or have the potential to produce an enormous number of successes in vitro and in vivo.