Fibers and 3D mesh scaffolds from biodegradable starch-based blends: production and characterization

The aim of this work is the production of fibers from biodegradable polymers to obtain 3D scaffolds for tissue engineering of hard tissues. The scaffolds required for this highly demanding application need to have, as well as the biological and mechanical characteristics, a high degree of porosity with suitable dimensions for cell seeding and proliferation. Furthermore, the open cell porosity should have adequate interconnectivity for a continuous flow of nutrients and outflow of cell metabolic residues as well as to allow cell growth into confluent layers. Blends of corn starch, a natural biodegradable polymer, with other synthetic polymers (poly(ethylene vinyl alcohol), poly(epsilon-caprolactone), poly(lactic acid)) were selected for this work because of their good balance of properties, namely biocompatibility, processability and mechanical properties. Melt spinning was used to produce fibers from all the blends and 3D meshes from one of the starch-poly(lactic acid) blends. The experimental characterization included the evaluation of the tensile mechanical properties and thermal properties of the fibers and the compression stiffness, porosity and degradation behavior of the 3D meshes. Light microscopy picture of 3D meshes.     

Thermally produced biodegradable scaffolds for cartilage tissue engineering

A novel process was developed to fabricate biodegradable polymer scaffolds for tissue engineering applications, without using organic solvents. Solvent residues in scaffolds fabricated by processes involving organic solvents may damage cells transplanted onto the scaffolds or tissue near the transplantation site. Poly(L-lactic acid) (PLLA) powder and NaCl particles in a mold were compressed and subsequently heated at 180 degrees C (near the PLLA melting temperature) for 3 min. The heat treatment caused the polymer particles to fuse and form a continuous matrix containing entrapped NaCl particles. After dissolving the NaCl salts, which served as a porogen, porous biodegradable PLLA scaffolds were formed. The scaffold porosity and pore size were controlled by adjusting the NaCl/PLLA weight ratio and the NaCl particle size. The characteristics of the scaffolds were compared to those of scaffolds fabricated using a conventional solvent casting/particulate leaching (SC/PL) process, in terms of pore structure, pore-size distribution, and mechanical properties. A scanning electron microscopic examination showed highly interconnected and open pore structures in the scaffolds fabricated using the thermal process, whereas the SC/PL process yielded scaffolds with less interconnected and closed pore structures. Mercury intrusion porosimetry revealed that the thermally produced scaffolds had a much more uniform distribution of pore sizes than the SC/PL process. The utility of the thermally produced scaffolds was demonstrated by engineering cartilaginous tissues in vivo. In summary, the thermal process developed in this study yields tissue-engineering scaffolds with more favorable characteristics, with respect to, freedom from organic solvents, pore structure, and size distribution than the SC/PL process. Moreover, the thermal process could also be used to fabricate scaffolds from polymers that are insoluble in organic solvents, such as poly(glycolic acid). Cartilage tissue regenerated from thermally produced PLLA scaffold.     

Based on MFe2O4 (M=Co,Cu, and Ni): Magnetically recoverable nanocatalysts in synthesis of heterocyclic structural scaffolds

Abstract

Catalysis research under magnetically recoverable nanocatalysts is a well-known topic in organic synthesis. In recent times, catalysis research has clearly experienced a renaissance in the area of utility of ferrite nanoparticles based on their ability to recovery and reusability. In this review, the focus is on the fabrication, characterization and of application the MFe₂O₄ (M=Co, Cu, and Ni) nanocatalysts in synthesis of heterocyclic structural scaffolds.     

Molecular reactors and machines: applications, potential, and limitations

Molecular reactors are miniature vessels for the assembly of reactants at the molecular level, in order to change the nature of chemical transformations. It seems probable that those that will find most immediate applications are those that change product ratios or give products which would not readily form in the absence of the reactors, and thereby afford easy access to materials that are otherwise difficult to obtain. Molecular machines consist of interrelated parts with separate functions and perform some kind of work, at the molecular level. Practical examples are likely to be relatively uncomplicated and not based on individual functions of single-molecule devices. Instead they will probably rely on extensive redundancy of the molecular components and their interactions and reactions, as well as of the machines themselves.     

Palladium-catalyzed intramolecular CH acylation of indoles with thioester

A palladium-catalyzed intramolecular CH acylation of indole with thioester is described, providing a direct and effective approach for the synthesis of the biologically active indole-indolone scaffolds. The method obviates the need for the prefunctionalized starting materials including organometallic reagents, alkyl halides, and NHP esters in previous metal-catalyzed cross-coupling reaction with thioester. Substrates bearing sensitive halo groups are compatible in the reaction, leaving a functional handle for further structural elaborations.     

Surface Modification of GTA Crosslinked Collagen‐based Composite Scaffolds with Low Temperature Plasma Technology

In this study for preparing the better performance scaffold materials for peripheral nerve repairing, the collagen‐based composite scaffolds are crosslinked with glutaraldehyde and their structure and performance are investigated. The results of FTIR indicated that the collagen and chitosan are certainly crosslinked through GTA without any significant change in the chemical property. It was observed under a scanning electron microscope (SEM) that the crosslinked collagen‐based composite scaffolds had a porous three‐dimensional cross‐linked structure. The experiments showed that the biostability of the scaffold is greatly enhanced, but the GTA crosslinking induces the potential cytotoxicity and poor hydrophilic nature. To overcome these disadvantages, the low temperature plasma technology is utilized to modify the surface of the cross‐linked collagen‐based composite scaffolds in this study. Measurements of water contact angle showed that hydrophilic nature of surface of the scaffolds was improved after low temperature plasma technology modification. The cell proliferation experiments revealed that the modified collagen‐based composite scaffolds still kept their bioactivity and benefited the proliferation.     

Scaffold Effects on Osteogenic Differentiation of Equine Mesenchymal Stem Cells: An In Vitro Comparative Study

The in vitro viability, osteogenic differentiation, and mineralization of four different equine mesenchymal stem cells (MSCs) from bone marrow, periosteum, muscle, and adipose tissue are compared, when they are cultured with different collagen‐based scaffolds or with fibrin glue. The results indicate that bone marrow cells are the best source of MSCs for osteogenic differentiation, and that an electrochemically aggregated collagen gives the highest cell viability and best osteogenic differentiation among the four kinds of scaffolds studied.

     

Synthesis of Privileged Scaffolds by Using Diversity‐Oriented Synthesis

An elegant reagent‐controlled strategy has been developed for the generation of a diverse range of biologically active scaffolds from a chiral bicyclic lactam. Reduction of the chiral lactam with LAH or alkylation with LHMDS to trigger different cyclization reactions have been shown to generate privileged scaffolds, such as pyrrolidines, indolines, and cyclotryptamines. Their amenability to substitution allows us to create various compound libraries by using these scaffolds. In silico studies were used to estimate the drug‐like properties of these compounds. Selected compounds were subjected to anticancer screening by using three different cell lines. In addition, all these compounds were subjected to antibacterial screening to gauge the spectrum of biological activity that was conferred by our DOS methodology. Gratifyingly, with no additional iterative cycles, our method directly generated anticancer compounds with potency at low nanomolar concentrations, as represented by spiroindoline 14 .     

Divergent synthetic routes to biologically relevant types of compounds: chiral polyfunctional γ-lactams and amino acids

Divergent and versatile synthetic routes leading to the title compounds are described. They start from a common chiral precursor derived from (−)-(S)-verbenone and afford polyfunctional γ-lactams and γ- and ε-amino acids. The cyclobutane moiety in these molecules acts as a chiral and polyfunctional platform providing stereogenic centres with unambiguous absolute configuration that control the chirality of the newly produced asymmetric carbons. Furthermore, it affords functional groups and carbon chains suitable not only to create the basic skeleton of the desired products but additional functional groups. These features confer on these derivatives a great versatility for further uses in the development of new drugs and as synthetic building blocks.