Synthesis and Characterization of Collagen Grafted Poly(hydroxybutyrate–valerate) (PHBV) Scaffold for Loading of Bovine Serum Albumin Capped Silver (Ag/BSA) Nanoparticles in the Potential Use of Tissue Engineering Application

The objective of this study is to synthesize and characterize collagen grafted poly­(3-hydroxylbutyrate-<i>co</i>-3-hydroxylvalerate) (PHBV) film for loading of BSA capped silver (Ag/BSA) nanoparticles. Thermal radical copolymerization and aminolysis methods were used to functionalize macroporous PHBV, followed by collagen grafting so as to formulate collagen-<i>g</i>-poly­(hydroxyethylmethyl acrylate)-<i>g</i>-poly­(3-hydroxylbutyrate-<i>co</i>-3-hydroxylvalerate) [collagen-<i>g</i>-PHEMA-<i>g</i>-PHBV] and collagen-<i>g</i>-aminated-poly­(3-hydroxylbutyrate-<i>co</i>-3-hydroxylvalerate) [collagen-<i>g</i>-NH₂-PHBV] films, respectively. Spectroscopic (FTIR, XPS), physical (SEM), and thermal (TGA) techniques were used to characterize the functionalized PHBV films. The amount of collagen present on grafted PHBV film was quantified by the Bradford method. The Ag/BSA nanoparticles were then loaded on collagen grafted and untreated PHBV films, and the nanoparticles loading were determined by atomic absorption spectrometry. The amount of nanoparticles loaded on collagen grafted PHBV film was found to be significantly greater than that on the untreated PHBV film. The nanoparticles loaded PHBV film can potentially serve as a scaffold to promote the growth of bone cells while inhibiting the bacterial growth

Adsorption–Desorption Study of BSA Conjugated Silver Nanoparticles (Ag/BSA NPs) on Collagen Immobilized Substrates

There has been a growing interest in the use of protein conjugated nanoparticles for applications in biomedical, sensing, and advanced imaging. The objective of this study was to understand the interaction of protein conjugated silver nanoparticles (Ag/BSA NPs) with biological substrate (collagen layer). The adsorption behavior of synthesized Ag/BSA NPs on collagen immobilized silanized surface was followed by UV–vis spectroscopy by initially studying the formation of collagen layer and subsequent adsorption of Ag/BSA NPs to the immobilized layer. Surface plasmon resonance (SPR) data provided the real time profile of adsorption of Ag/BSA NPs from solution onto collagen immobilized and control substrates as well as desorption of nanoparticles from the substrates. The retention of NPs to substrate is sensitive to chemistry of the underlying substrate and on the external environment. UV–vis and atomic absorption spectrometric analysis of Ag/BSA NPs desorption performed under different pH conditions showed more NPs retained at physiological pH than the acidic and basic conditions. Nanoparticles retention on collagen immobilized substrate at physiological pH could influence properties of biological interest such as circulation lifetime and biodistribution of nanoparticles in the body

Polymer-Grafted Nanoparticles with Variable Grafting Densities for High Energy Density Polymeric Nanocomposite Dielectric Capacitors

Designing high energy density dielectric capacitors for advanced energy storage systems needs nanocomposite-based dielectric materials, which can utilize the properties of both inorganic and polymeric materials. Polymer-grafted nanoparticle (PGNP)-based nanocomposites alleviate the problems of poor nanocomposite properties by providing synergistic control over nanoparticle and polymer properties. Here, we synthesize “core–shell” barium titanate–poly(methyl methacrylate) (BaTiO3–PMMA) grafted PGNPs using surface-initiated atom transfer polymerization (SI-ATRP) with variable grafting densities of (0.303 to 0.929) chains/nm2 and high molecular masses (97700 g/mL to 130000 g/mol) and observe that low grafted density and high molecular mass based PGNP show high permittivity, high dielectric strength, and hence higher energy densities (≈ 5.2 J/cm3) as compared to the higher grafted density PGNPs, presumably due to their “star-polymer”-like conformations with higher chain-end densities that are known to enhance breakdown. Nonetheless, these energy densities are an order of magnitude higher than their nanocomposite blend counterparts. We expect that these PGNPs can be readily used as commercial dielectric capacitors, and these findings can serve as guiding principles for developing tunable high energy density energy storage devices using PGNP systems

Pattern-Directed Phase Separation of Polymer-Grafted Nanoparticles in a Homopolymer Matrix

The controlled organization of nanoparticle (NP) constituents into superstructures of well-defined shape, composition, and connectivity represents a continuing challenge in the development of novel hybrid materials for many technological applications. We show that the phase separation of polymer-tethered nanoparticles immersed in a matrix of a chemically different polymer provides an effective and scalable method for fabricating well-defined submicron-sized amorphous NP domains in melt polymer thin films. We investigate this phenomenon with a view toward a better understanding and control of the phase separation process in these novel “blends”. In particular, we consider isothermally annealed thin films of polystyrene-grafted gold nanoparticles (AuPS) dispersed in a poly­(methyl methacrylate) (PMMA) matrix. A morphology transition from discrete AuPS domains to bicontinuous to inverse domain structure is observed with increasing nanoparticle loading, consistent with composition dependence of classic binary polymer blends phase separation. However, the phase separation kinetics of the NP–polymer blends exhibit unique features compared to the parent PS/PMMA homopolymer blends. We further illustrate how to manipulate the AuPS nanoparticle domain shape, size, and location through the imposition of an external symmetry-breaking perturbation. Specifically, topographically patterned elastomer confinement is introduced to direct the nanoparticles into long-range ordered submicron-sized domains having a dense and well-dispersed distribution of noncrystallizing nanoparticles. The simplicity, versatility, and roll-to-roll adaptability of this novel method for controlled nanoparticle assembly should make it useful in creating desirable patterned nanoparticle domains for a variety of functional materials and applications

Directed Self-Assembly of Block Copolymers for High Breakdown Strength Polymer Film Capacitors

Emerging needs for fast charge/discharge yet high-power, lightweight, and flexible electronics requires the use of polymer-film-based solid-state capacitors with high energy densities. Fast charge/discharge rates of film capacitors on the order of microseconds are not achievable with slower charging conventional batteries, supercapacitors and related hybrid technologies. However, the current energy densities of polymer film capacitors fall short of rising demand, and could be significantly enhanced by increasing the breakdown strength (<i>E</i>_BD) and dielectric permittivity (ε_r) of the polymer films. Co-extruded two-homopolymer component multilayered films have demonstrated much promise in this regard showing higher <i>E</i>_BD over that of component polymers. Multilayered films can also help incorporate functional features besides energy storage, such as enhanced optical, mechanical, thermal and barrier properties. In this work, we report accomplishing multilayer, multicomponent block copolymer dielectric films (BCDF) with soft-shear driven highly oriented self-assembled lamellar diblock copolymers (BCP) as a novel application of this important class of self-assembling materials. Results of a model PS-<i>b</i>-PMMA system show ∼50% enhancement in <i>E</i>_BD of self-assembled multilayer lamellar BCP films compared to unordered as-cast films, indicating that the breakdown is highly sensitive to the nanostructure of the BCP. The enhancement in <i>E</i>_BD is attributed to the “barrier effect”, where the multiple interfaces between the lamellae block components act as barriers to the dielectric breakdown through the film. The increase in <i>E</i>_BD corresponds to more than doubling the energy storage capacity using a straightforward directed self-assembly strategy. This approach opens a new nanomaterial paradigm for designing high energy density dielectric materials