Supramolecular semicrystalline hydrogels are soft functional materials consisting of water-swollen hydrophilic polymer chains interconnected by hydrophobic segments forming lamellar crystals. Although such hydrogels with high crystallinity are mechanically strong, with elastic moduli and tensile strength of 80−300 MPa and 4−7 MPa, respectively, they are brittle and rupture at a stretch of less than 20% without yielding. Here, we report that the incorporation of a small amount of a weak hydrophobe into semicrystalline hydrogels significantly increases their toughness and stretchability without losing their high modulus and high strength. We design a highly entangled physical network based on poly(N,N-dimethylacrylamide) (PDMA) chains containing n-octadecyl acrylate (C18A) and lauryl methacrylate (C12M) segments with side chain lengths of 18 and 12 carbons, respectively. By including 0.1−0.4 mol % C12M into the PDMA backbone containing 30 mol % C18A segments, we were able to create more ordered and thinner lamellar crystals with a layered structure. Simultaneously, a brittle-to-ductile transition was observed due to the appearance of necking behavior leading to 10-fold increase of toughness. The significant toughness improvement upon incorporation of C12M into the semicrystalline hydrogels could be explained with the appearance of active tie molecules under external force interconnecting the lamellar clusters. The hydrogels also exhibit reversible tensile deformation induced by heating above the melting temperature of crystalline domains.

Natural extracellular matrix (ECM) consists of complex signals interacting with each other to organize cellular behavior and responses. This sophisticated microenvironment can be mimicked by advanced materials presenting essential biochemical and physical properties in a synergistic manner. In this work, we developed a facile fabrication method for a novel nanofibrous self-assembled peptide amphiphile (PA) and poly(ethylene glycol) (PEG) composite hydrogel system with independently tunable biochemical, mechanical, and physical cues without any chemical modification of polymer backbone or additional polymer processing techniques to create synthetic ECM analogues. This approach allows noninteracting modification of multiple niche properties (e.g., bioactive ligands, stiffness, porosity), since no covalent conjugation method was used to modify PEG monomers for incorporation of bioactivity and porosity. Combining the self-assembled PA nanofibers with a chemically cross-linked polymer network simply by facile mixing followed by photopolymerization resulted in the formation of porous bioactive hydrogel systems. The resulting porous network can be functionalized with desired bioactive signaling epitopes by simply altering the amino acid sequence of the self-assembling PA molecule. In addition, the mechanical properties of the composite system can be precisely controlled by changing the PEG concentration. Therefore, nanofibrous self-assembled PA/ PEG composite hydrogels reported in this work can provide new opportunities as versatile synthetic mimics of ECM with independently tunable biological and mechanical properties for tissue engineering and regenerative medicine applications. In addition, such systems could provide useful tools for investigation of how complex niche cues influence cellular behavior and tissue formation both in two-dimensional and three-dimensional platforms.

Glycosaminoglycans (GAGs) and glycoproteins are vital components of the extracellular matrix, directing cell proliferation, differentiation, and migration and tissue homeostasis. Here, we demonstrate supramolecular GAG-like glycopeptide nanofibers mimicking bioactive functions of natural hyaluronic acid molecules. Self-assembly of the glycopeptide amphiphile molecules enable organization of glucose residues in close proximity on a nanoscale structure forming a supramolecular GAG-like system. Our in vitro culture results indicated that the glycopeptide nanofibers are recognized through CD44 receptors, and promote chondrogenic differentiation of mesenchymal stem cells. We analyzed the bioactivity of GAG-like glycopeptide nanofibers in chondrogenic differentiation and injury models because hyaluronic acid is a major component of articular cartilage. Capacity of glycopeptide nanofibers on in vivo cartilage regeneration was demonstrated in microfracture treated osteochondral defect healing. The glycopeptide nanofibers act as a cell-instructive synthetic counterpart of hyaluronic acid, and they can be used in stem cell-based cartilage regeneration therapies.

PURPOSEThe aim of the study was to evaluate the effect of annealing on the nanostructure and hardness of Co-Cr metal ceramic samples that were fabricated with a direct metal laser sintering (DMLS) technique.MATERIALS AND METHODSFive groups of Co-Cr dental alloy samples were manufactured in a rectangular form measuring 4 × 2 × 2 mm. Samples fabricated by a conventional casting technique (Group I) and prefabricated milling blanks (Group II) were examined as conventional technique groups. The DMLS samples were randomly divided into three groups as not annealed (Group III), annealed in argon atmosphere (Group IV), or annealed in oxygen atmosphere (Group V). The nanostructure was examined with the small-angle X-ray scattering method. The Rockwell hardness test was used to measure the hardness changes in each group, and the means and standard deviations were statistically analyzed by one-way ANOVA for comparison of continuous variables and Tukey's HSD test was used for post hoc analysis. P values of <.05 were accepted as statistically significant.RESULTSThe general nanostructures of the samples were composed of small spherical entities stacked atop one another in dendritic form. All groups also displayed different hardness values depending on the manufacturing technique. The annealing procedure and environment directly affected both the nanostructure and hardness of the Co-Cr alloy. Group III exhibited a non-homogeneous structure and increased hardness (48.16 ± 3.02 HRC) because the annealing process was incomplete and the inner stress was not relieved. Annealing in argon atmosphere of Group IV not only relieved the inner stresses but also decreased the hardness (27.40 ± 3.98 HRC). The results of fitting function presented that Group IV was the most homogeneous product as the minimum bilayer thickness was measured (7.11 Å).CONCLUSIONAfter the manufacturing with DMLS technique, annealing in argon atmosphere is an essential process for Co-Cr metal ceramic substructures. The dentists should be familiar with the materials that are used in clinic for prosthodontics treatments.

One of the most fascinating challenges in recent years has been to produce mechanically robust and tough polymers with smart functions such as self-healing and shape-memory behavior. Here, we report a simple and versatile strategy for the preparation of a highly tough and highly stretchable interconnected interpenetrating polymer network (c-IPN) based on butyl rubber (IIR) and poly(n-octadecyl acrylate) (PC18A) with thermally induced healing and shape-memory functions. Solventfree UV polymerization of n-octadecyl acrylate (C18A) at 30 ± 2 °C in the presence of IIR leads to IIR/PC18A c-IPNs with seaisland or co-continuous morphologies depending on their IIR contents. The lamellar crystals with a melting temperature T m of 51−52 °C formed by side-by-side packed octadecyl (C18) side chains are responsible for more than 99% of effective cross-links in c-IPNs, the rest being hydrophobic associations and chemical cross-links. The c-IPNs exhibit varying stiffness (9−34 MPa), stretchability (72−740%), and a significantly higher toughness (1.9− 12 MJ•m −3 ) than their components, which can be tuned by changing the IIR/PC18A weight ratio. The properties of c-IPNs could also be tuned by incorporating a second, noncrystallizable hydrophobic monomer, namely, lauryl methacrylate (C12M), in the melt mixture. We show that the lamellar clusters acting as sacrificial bonds break at the yield point by dissipation of energy, while the ductile amorphous continuous phase keeps the structure together, leading to the toughness improvement of c-IPNs. They exhibit a two-step healing process with >90% healing efficiency with respect to the modulus and a complete shape-recovery ratio induced by heating above T m of alkyl crystals. The temperature-induced healing occurs via a quick step where C18 bridges form between the damaged surfaces followed by a slow step controlled by the interdiffusion of C18A segments in the bulk. We also show that the strategy developed here is suitable for a variety of rubbers and n-alkyl (meth)acrylates of various side-chain lengths.

No abstract

No abstract

Synthetic vaccines utilize viral signatures to trigger immune responses. Although the immune responses raised against the biochemical signatures of viruses are well characterized, the mechanism of how they affect immune response in the context of physical signatures is not well studied. In this work, we investigated the ability of zero- and one-dimensional self-assembled peptide nanostructures carrying unmethylated CpG motifs (signature of viral DNA) for tuning immune response. These nanostructures represent the two most common viral shapes, spheres and rods. The nanofibrous structures were found to direct immune response towards Th1 phenotype, which is responsible for acting against intracellular pathogens such as viruses, to a greater extent than nanospheres and CpG ODN alone. In addition, nanofibers exhibited enhanced uptake into dendritic cells compared to nanospheres or the ODN itself. The chemical stability of the ODN against nuclease-mediated degradation was also observed to be enhanced when complexed with the peptide nanostructures. In vivo studies showed that nanofibers promoted antigen-specific IgG production over 10-fold better than CpG ODN alone. To the best of our knowledge, this is the first report showing the modulation of the nature of an immune response through the shape of the carrier system.