Biomimetic mineralization of collagen fibrils is an essential process because the mineralized collagen fibers constitute the basic building block of natural bone. To overcome the limited availability and high cost of the noncollagenous proteins (NCPs) that regulate the mineralization process of collagen, commercially available analogues were developed to replicate sequestration and templating functions of NCPs. The use of branched polymers in intrafibrillar mineralization applications has never been explored. In this work, two novel carboxyl-rich brushlike polymers, a carboxylated polyethylene glycol terpolymer (PEG-COOH) and a polyethylene glycol/poly(acrylic acid) copolymer (PEG-PAA), were synthesized and modified to mimic the sequestration function of NCPs to induce intrafibrillar mineralization of collagen fibrils. It was found that these synthetic brushlike polymers are able to induce intrafibrillar mineralization by stabilizing the amorphous calcium phosphate (ACP) nanoprecursors and subsequently facilitating the infiltration of ACP into the gap zone of collagen microfibrils. Moreover, the weight ratios of mineral to collagen in the mineralized collagen fibrils in the presence of these brushlike polymers were 2.17 ± 0.07 for PEG-COOH and 2.23 ± 0.03 for PEG-PAA, while it is only 1.81 ± 0.21 for linear PAA. Plausible mineralization mechanisms using brushlike polymers are proposed that offer significant insight into the understanding of collagen mineralization induced by synthetic NCP analogues.
We report a detailed synthesis and characterization of novel polymeric supramolecular structures composed of semiconducting perylene diimide (PDI)−imidazole templates of varying methylene spacer length (n = 3, 4, and 6) hydrogenbonded to a conjugated polymer backbone of acid-functionalized polydiacetylene (PDA), 10,12 pentacosadiynoic acid. First, a combination of molecular and morphological characterization tools confirmed that the templated supramolecular structures are a result of the synergistic effect of intermolecular PDI π−π stacking coupled with noncovalent imidazole−acid interactions. Second, a simple and scalable solid-state polymerization of the drop-cast films by UV radiation delivers multichromic, multiresponsive films capable of unique phase/morphology-switching properties with a high degree of local ordering. Thermal studies by differential scanning calorimetry and morphological studies by wide-and small-angle X-ray scattering (WAXS/SAXS, respectively) show dramatic morphological effects and trends in crystallinity with methylene spacer group extension. Furthermore, UV−vis studies displayed an unusual PDA "purple phase" transition, which was additionally verified by SAXS as a coexistence of previously known red-and blue-phase PDA. Finally, the polymerized drop-cast films displayed reversible thermo-and solvatochromic responses after a second treatment of UV radiation and additional UV-thermal cycling revealed the extent of reversibility.
Nanostructures self-assembled from natural or biocompatible macromolecules attract increasing attention due to their potential in nanomedical and technological applications. Self-assembly and structural properties of flowerlike micelles formed by cholesterol end-capped polyethylene oxide (PEO) have been investigated by contrast-variation small-angle neutron scattering, small-angle X-ray scattering, dynamic light scattering, and molecular dynamics (MD) simulations. Three molecular weights (MWs) of the middle PEO block, (6, 10, and 20 kg/mole) have been synthesized and examined individually. As expected, the critical micelle concentration increases with PEO block length and for the two higher MW polymer samples, flower-like micelles coexist with unimers. A core− two-shell model was applied to analyze the small-angle neutron and X-ray scattering data, showing that in all cases, the cholesterol core of micelles is about 24 Å in radius and practically free of water, while the PEO corona contains a denser inner shell with about 50% of water and a well-hydrated outer shell (>88%). MD simulations with the same number of cholesterol units in the core based on the experimental outcome revealed a somewhat ellipsoidal cholesterol core with an average radius ∼24 Å, inner PEO shell, and well-hydrated outer shell, consistent with the experimental analysis. For all micelles studied, the PEO block was found to be slightly extended (∼30%) compared to the free coil configuration, while the cholesterol core and inner PEO shell were found to be very similar implying comparable aggregation numbers, nearly independent of the PEO length. The polymer concentration was below the overlap limit, and we observe well-defined stable non-clustering flower-like micelles, which have a nice potential for biomedical applications. This study provides a universal approach to unambiguously identify the morphology of flower-like micelles with detailed internal structural and compositional information.
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