The morphology of ADMET-synthesized polyethylene with n-butyl branches precisely spaced on every 39th carbon (EH39) was studied in comparison with an ethylene/1-hexene addition copolymer possessing the same branching probability, the goal being to elucidate the effect of the intramolecular sequence length heterogeneity on the lamella crystal thickness and its distribution. EH39 was found to have an orthorhombic crystalline polymorphism, which is normal for commercialized polyethylenes and different from that of the other ADMET polyethylenes with shorter CH 2 spacing (C15, C21). EH39 exhibits a narrow lamella thickness distribution; the average thickness (l c,av. ) corresponds exactly to the space length between two consecutive branches, suggesting the complete exclusion of n-butyl branches from the crystal stem. The average thickness, l c,av. mentioned above is also coincident with that obtained from WAXS and SAXS. On the other hand, the 1-hexene copolymer forms much thicker lamellae and a broader thickness distribution than ADMET polyethylene. Here, the average thickness l c,av. determined by TEM observation of the copolymer is 1.5 times larger than that calculated from the most probable ethylene sequence length obtained from 13 C NMR, or for a theoretical ethylene sequence length distribution, indicating that the lamellae are composed predominantly of the sparsely branched longer ethylene sequences that are statistically included. The intramolecular sequence distribution is considered significant to determine the lamella thickness and thickness distribution for short chain-branched polyethylenes with a narrow intermolecular chemical composition distribution.

Several biomaterials, including natural polymers, are used to increase cellular interactions as an effective way to treat bone injuries. Chitosan (CS) is one of the most studied biocompatible natural polymers. Graphene oxide (GO) is a carbon-based nanomaterial capable of imparting desired properties to the scaffolds. In the present study, CS and GO were used for scaffold preparation. CS was extracted from the mycelium of the fungus Aspergillus niger. On the other hand, GO was synthesized using an improved Hummers-Offemann method and was characterized by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, atomic force microscopy (AFM), X-ray diffraction (XRD), and dynamic light scattering (DLS). Subsequently, three formulations (GO 0%, 0.5%, and 1%) were used to prepare the scaffolds by the freeze-drying technique. The scaffolds were characterized by FTIR, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM), to determine their thermal stability and pore size, demonstrating that their stability increased with the increase of GO amount. Finally, the scaffolds were implanted, recollected 30 days later, and studied with an optical microscope, which evidenced the recovery of the tissue architecture and excellent biocompatibility. Hence, these results strongly suggested the inherent nature of chitosan/graphene oxide (CS/GO) scaffolds for their application in bone tissue regeneration.

Today, tissue regeneration is one of the greatest challenges in the field of medicine, since it represents hope after accidents or illnesses. Tissue engineering is the science based on improving or restoring tissues and organs. In this work, five formulations of chitosan/poly(vinyl alcohol)/graphene oxide (CS/PVA/GO) nanocomposites were studied for the development of biodegradable films with potential biomedical applications. The characterization of the films consisted of Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The antibacterial activity was evaluated in vitro against Gram-positive bacteria Bacillus cereus and Staphylococcus aureus and Gram-negative Salmonella spp. and Escherichia coli, by contact of the film above inoculum bacterial in Müeller–Hinton agar. On the other hand, in vivo tests in which the material implanted in the subcutaneous tissue of Wistar rats demonstrated that the formulation CS/PVA/GO (14.25:85:0.75) was the best antibacterial film with adequate degradation in vivo. All together, these results indicate the potential of the films using nanocomposites of CS/PVA/GO in tissue engineering and cell regeneration.

Summary: Latent reactivity has been employed to create processable elastomers constructed of carbosilane and either carbosiloxane or polyether segments. Two types of latent modes have been introduced: “chain‐internal” and “chain‐end” sites through the use of labile silicon methoxy and trifunctional olefinic functionalities. These latent reactive sites remain inert during formation of the linear copolymer; subsequent exposure to moisture triggers hydrolysis of the methoxy group and formation of a chemically crosslinked thermoset. These “chain‐end” sites limit the formation of dangling chains improving the overall mechanical properties of the material. The thermoset's mechanical response can be potentially varied from plastic to elastic behavior, depending on the ratio of hard and soft monomers employed. The concentration of “chain‐internal” and “chain‐end” crosslink sites enhances strength; modification to the run length and structure of the soft phase enhances elasticity, generating samples having moduli of 6 MPa, tensile strengths of 0.6 MPa and elongations of 400%.“Latent reactive” silicon elastomer.magnified image“Latent reactive” silicon elastomer.

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