Promoting chondrocyte cell clustering through tuning of a poly(ethylene glycol)-poly(peptide) thermosensitive hydrogel with distinctive microarchitecture

Thermo-induced physically crosslinked polypeptide-based block copolymer hydrogels for biomedical applications

Stimuli-responsive synthetic polypeptide-containing block copolymers have received considerable attention in recent years. Especially, unique thermo-induced sol-gel phase transitions were observed for elaborately-designed amphiphilic diblock copolypeptides and a range of poly(ethylene glycol) (PEG)-polypeptide block copolymers. The thermo-induced gelation mechanisms involve the evolution of secondary conformation, enhanced intramolecular interactions, as well as reduced hydration and increased chain entanglement of PEG blocks. The physical parameters, including polymer concentrations, sol-gel transition temperatures and storage moduli, were investigated. The polypeptide hydrogels exhibited good biocompatibility in vitro and in vivo, and displayed biodegradation periods ranging from 1 to 5 weeks. The unique thermo-induced sol-gel phase transitions offer the feasibility of minimal-invasive injection of the precursor aqueous solutions into body, followed by in situ hydrogel formation driven by physiological temperature. These advantages make polypeptide hydrogels interesting candidates for diverse biomedical applications, especially as injectable scaffolds for 3D cell culture and tissue regeneration as well as depots for local drug delivery. This review focuses on recent advances in the design and preparation of injectable, thermo-induced physically crosslinked polypeptide hydrogels. The influence of composition, secondary structure and chirality of polypeptide segments on the physical properties and biodegradation of the hydrogels are emphasized. Moreover, the studies on biomedical applications of the hydrogels are intensively discussed. Finally, the major challenges in the further development of polypeptide hydrogels for practical applications are proposed.

The Role of Polymeric Biomaterials in the Treatment of Articular Osteoarthritis

Osteoarthritis is a high-prevalence joint disease characterized by the degradation of cartilage, subchondral bone thickening, and synovitis. Due to the inability of cartilage to self-repair, regenerative medicine strategies have become highly relevant in the management of osteoarthritis. Despite the great advances in medical and pharmaceutical sciences, current therapies stay unfulfilled, due to the inability of cartilage to repair itself. Additionally, the multifactorial etiology of the disease, including endogenous genetic dysfunctions and exogenous factors in many cases, also limits the formation of new cartilage extracellular matrix or impairs the regular recruiting of chondroprogenitor cells. Hence, current strategies for osteoarthritis management involve not only analgesics, anti-inflammatory drugs, and/or viscosupplementation but also polymeric biomaterials that are able to drive native cells to heal and repair the damaged cartilage. This review updates the most relevant research on osteoarthritis management that employs polymeric biomaterials capable of restoring the viscoelastic properties of cartilage, reducing the symptomatology, and favoring adequate cartilage regeneration properties.

Growth factor-loaded microspheres in mPEG-polypeptide hydrogel system for articular cartilage repair

We developed an injectable hydrogel system with a sustained release of TGF-β3 through growth factor-loaded microsphere to mimic the cartilage-like microenvironment. Poly(lactic-co-glycolic acid) (PLGA) microspheres incorporated in three dimensional (3D) scaffolds were chosen because of its regulatory approval, good biodegradability, and acting as carriers with sustained release behavior. We evaluated sustained release of TGF-β3 by PLGA microspheres encapsulated in methoxy poly(ethylene glycol)-poly(alanine) (mPA) hydrogels and the resulting enhanced chondrogenic effects. We reported here the effect of the proposed system for sustained release of growth factors on chondrogenesis in cartilage regeneration. PLGA microspheres were used in our thermosensitive mPA hydrogel system with bovine serum albumin as a stabilizing and protecting agent for the emulsion and TGF-β3 enabling sustained release. Gelation, structural properties, and in-vitro release of this composite, that is, microspheres in hydrogel, system were investigated. Using PLGA microspheres to carry growth factors could complement the mPA hydrogel's ability to provide an excellent 3D microenvironment for the promotion of chondrogenic phenotype as compared the systems using mPA hydrogel or microspheres alone. Our study demonstrated that this synthesized composite hydrogel system is capable of modulating the biosynthetic and differentiation activities of chondrocytes. The sustained release of TGF-β3 in this novel hydrogel system could improve biomedical applicability of mPEG-polypeptide scaffolds. The distinctive local growth factor delivery system successfully combined the use of both polymers to be a suitable candidate for prolonged articular cartilage regeneration.

Noninvasive Tracking of mPEG-poly(Ala) Hydrogel-Embedded MIN6 Cells after Subcutaneous Transplantation in Mice

Recently, we demonstrated the feasibility of subcutaneous transplantation of MIN6 cells embedded in a scaffold with poly(ethylene glycol) methyl ether (mPEG)-poly(Ala) hydrogels. In this study, we further tracked these grafts using magnetic resonance (MR) and bioluminescence imaging. After being incubated overnight with chitosan-coated superparamagnetic iron oxide (CSPIO) nanoparticles and then mixed with mPEG-poly(Ala) hydrogels, MIN6 cells appeared as dark spots on MR scans. For in vivo experiments, we transfected MIN6 cells with luciferase and/or incubated them overnight with CSPIO overnight; 5 × 10⁶ MIN6 cells embedded in mPEG-poly(Ala) hydrogels were transplanted into the subcutaneous space of each nude mouse. The graft of CSPIO-labeled MIN6 cells was visualized as a distinct hypointense area on MR images located at the implantation site before day 21. However, this area became hyperintense on MR scans for up to 64 days. In addition, positive bioluminescence images were also observed for up to 64 days after transplantation. The histology of removed grafts showed positive insulin and iron staining. These results indicate mPEG-poly(Ala) is a suitable scaffold for β-cell encapsulation and transplantation. Moreover, MR and bioluminescence imaging are useful noninvasive tools for detecting and monitoring mPEG-poly(Ala) hydrogel-embedded MIN6 cells at a subcutaneous site.

Ring opening polymerization of α-amino acids: advances in synthesis, architecture and applications of polypeptides and their hybrids

This review provides a comprehensive overview of the latest advances in the synthesis, architectural design and biomedical applications of polypeptides and their hybrids.

Injectable polypeptide hydrogel/inorganic nanoparticle composites for bone tissue engineering

The general concept of tissue engineering is to restore biological function by replacing defective tissues with implantable, biocompatible, and easily handleable cell-laden scaffolds. In this study, osteoinductive and osteoconductive super paramagnetic Fe₃O₄ nanoparticles (MNP) and hydroxyapatite (HAP) nanoparticles were incorporated into a di-block copolymer based thermo-responsive hydrogel, methoxy(polyethylene glycol)-polyalanine (mPA), at various concentrations to afford composite, injectable hydrogels. Incorporating nanoparticles into the thermo-responsive hydrogel increased the complex viscosity and decreased the gelation temperature of the starting hydrogel. Functionally, the integration of inorganic nanoparticles modulated bio-markers of bone differentiation and enhanced bone mineralization. Moreover, this study adopted the emerging method of using either a supplementary static magnetic field (SMF) or a moving magnetic field to elicit biological response. These results demonstrate that combining external (magnet) and internal (scaffold) magnetisms is a promising approach for bone regeneration.

Advances and Biomedical Applications of Polypeptide Hydrogels Derived from α-Amino Acid N-Carboxyanhydride (NCA) Polymerizations

Polypeptide hydrogels, having the ability to mimic certain properties of natural, native extracellular matrix components, are being actively designed and described for various applications in the construction of tissue engineering scaffolds, living cell encapsulation, and drug delivery systems. Compared to conventional hydrogels, polypeptide hydrogels possess biocompatibility, biodegradability, bioactivity, functional diversity, and structural advantage based on the unique secondary structures (α-helix and β-sheet). Furthermore, the progresses in functional N-carboxyanhydride polymerization combined with advanced orthogonal conjugation techniques significantly promote the development of the polypeptide materials. This progress report focuses on the recent advances in designing and engineering polypeptide hydrogels obtained from ring opening polymerization, highlighting the precise manipulation of their properties for biomedical applications.

Structure and Properties of Hydrophobic Aggregation Hydrogel with Chemical Sensitive Switch

Hydrogels with chemical sensitive switch have control release properties in special environments. A series of polyacrylamide-octadecyl methacrylate hydrogels crosslinked by N,N′-bis (acryloyl) cystamine were synthesized as potential chemical sensitive system. When this hydrogel encounters dithiothreitol it can change its quality. The properties of the hydrogels were characterized by infrared spectroscopy, contact angle, and scanning electron microscopy. The water absorption of the hydrogel has the maximum value of 475%, when the content of octadecyl methacrylate is 5 wt%. The amount of weight loss was changed from 34.6% to 17.2%, as the content of octadecyl methacrylate increased from 3 wt% to 9.4 wt%. At the same time, the stress of the hydrogel decreased from 67.01% to 47.61%; the strength of the hydrogel reaches to the maximum 0.367 Mpa at 7 wt% octadecyl methacrylate. The increasing content of octadecyl methacrylate from 3 wt% to 9.4 wt% can enhance the hydrophobicity of the hydrogel; the contact angle of water to hydrogel changed from 14.10° to 19.62°. This hydrogel has the porous structure which permits loading of oils into the gel matrix. The functionalities of the hydrogel make it have more widely potential applications in chemical sensitive response materials.