Here we report a modular strategy for preparing physically cross-linked and mechanically robust free-standing hydrogels comprising unique thermotropic liquid crystalline (LC) domains and magnetic nanoparticles both of which serve as the physical cross-linkers resulting in hydrogels that can be used as magnetically responsive soft actuators. A series of amphiphilic LC pentablock copolymers of poly(acrylic acid) (PAA), poly(5-cholesteryloxypentyl methacrylate) (PC5MA), and poly(ethylene oxide) (PEO) blocks in the sequence of PAA-PC5MA-PEO-PC5MA-PAA were prepared using reversible addition-fragmentation chain transfer polymerization. These pentablock copolymers served as macromolecular ligands to template Fe(3)O(4) magnetic nanoparticles (MNPs), which were directly anchored to the polymer chains through the coordination bonds with the carboxyl groups of PAA blocks. The resulting polymer/MNP nanocomposites comprised a complicated hierarchical structure in which polymer-coated MNP clusters were dispersed in a microsegregated pentablock copolymer matrix that further contained LC ordering. Upon swelling, the hierarchical structure was disrupted and converted to a network structure, in which MNP clusters were anchored to the polymer chains and LC domains stayed intact to connect solvated PEO and PAA blocks, leading to a free-standing LC magnetic hydrogel (LC ferrogel). By varying the PAA weight fraction (f(AA)) in the pentablock copolymers, the swelling degrees (Q) of the resulting LC ferrogels were tailored. Rheological experiments showed that these physically cross-linked free-standing LC ferrogels exhibit good mechanical strength with storage moduli G' of around 10(4)-10(5) Pa, similar to that of natural tissues. Furthermore, application of a magnetic field induced bending actuation of the LC ferrogels. Therefore, these physically cross-linked and mechanically robust LC ferrogels can be used as soft actuators and artificial muscles. Moreover, this design strategy is a versatile platform for incorporation of different types of nanoparticles (metallic, inorganic, biological, etc.) into multifunctional amphiphilic block copolymers, resulting in unique free-standing hybrid hydrogels of good mechanical strength and integrity with tailored properties and end applications.

A series of liquid crystalline–semicrystalline–liquid crystalline triblock copolymers, with poly(ethylene oxide) (PEO) as the semicrystalline central block and polymethacrylate bearing side-chain cholesteryl mesogens as the liquid crystalline (LC) end blocks, are prepared using reversible addition–fragmentation chain transfer (RAFT) polymerization. Starting with 20 kg/mol PEO, the weight fractions of the LC blocks in the triblock copolymers are varied from 21 to 86 wt %. The wide-angle and small-angle X-ray scattering (WAXS and SAXS) as well as transmission electron microscopy (TEM) studies show that with the increased LC content in the triblock copolymers different hierarchical structures including “LC lamellae in PEO lamellae” and “PEO cylinders in LC matrix” are observed sequentially. Differential scanning calorimetry (DSC) study shows that the triblock copolymers with “LC lamellae in PEO lamellae” crystallize at normal undercooling conditions (crystallization temperature T c observed at 31.0–36.4 °C, which is close to that of homopolymer PEO), while those with “PEO cylinders in LC matrix” crystallize at very large undercooling (T c drops to −23.5 to −27.8 °C). The large variation of the undercooling conditions required for PEO crystallization is attributed to the nanoconfinement effect from different hierarchical structures at varied LC contents. Avrami analysis has been performed to understand the PEO crystallization mechanism. In “LC lamellae in PEO lamellae”, the PEO crystallization is confined within 2D microdomains between LC lamellae and follows heterogeneous nucleation mechanism with subsequent long-range crystal growth. In “PEO cylinders in LC matrix”, the PEO crystallization is confined within 1D cylindrical microdomains and dominated by homogeneous nucleation, and long-range crystal growth is prohibited by the surrounding LC matrix. This study demonstrates that microsegregated LC domains can provide efficient confinement of the PEO crystallization, and by simply increasing the LC content, amorphous PEO can be obtained at room temperature. These LC–semicrystalline–LC triblock copolymers, with room temperature amorphous PEO confined in microsegregated nanodomains, may be used as scaffolds for lithium ion batteries and solid-state electrolytes.

In this paper, the thermal, optical and mesomorphic properties of side-chain liquid crystalline (SCLC) homopolymers (PNBCh-n), in which cholesteryl mesogens are linked to a polynorbornene backbone by different lengths of methylene spacer (n ¼ 4, 5, 9, 10 and 15), are investigated. By doing so, the impact of flexible spacer length on the formation of different types of LC mesophase is explained. Because of comb-shaped SCLC polymer architecture, smectic mesophases are primarily found in PNBCh-n. Interestingly, cholesteric mesophases are identified only in PNBCh-9 and 10, which are proved by (1) the selective light reflection in UV-Vis analysis, (2) the characteristic oily streak texture under polarized optical microscope (POM) and (3) a long range periodicity in the cross-sectioned films from transmission electron microscope (TEM) investigation. Moreover, temperature-controlled X-ray scattering measurements are performed to examine mesomorphic structure evolution. By comparing the mesomorphic structures in this series of SCLC homopolymers, both extent of mesogen interdigitation and motional decoupling between backbone and mesogenic side-chains are found to play a critical role in the development of cholesteric mesophase. This structure-property study of PNBCh-n will help elucidate the importance of molecular structure, particularly the length of spacers, on the formation of cholesteric mesophase and its importance in the design of thermochromic devices.

End-capping by covalently binding functional groups to the ends of polymer chains offers potential advantages for tissue engineering scaffolds, but the ability of such polymers to influence cell behavior has not been studied. As a demonstration, polylactide (PLA) was end-capped with lithium carboxylate ionic groups (hPLA13kLi) and evaluated. Thin films of the hPLA13kLi and PLA homopolymer were prepared with and without surface texturing. Murine osteoblast progenitor cells from collagen 1α1 transgenic reporter mice were used to assess cell attachment, proliferation, differentiation, and mineralization. Measurement of green fluorescent protein expressed by these cells and xylenol orange staining for mineral allowed quantitative analysis. The hPLA13kLi was biologically active, increasing initial cell attachment and enhancing differentiation, while reducing proliferation and strongly suppressing mineralization, relative to PLA. These effects of bound lithium ions (Li+) had not been previously reported, and were generally consistent with the literature on soluble additions of lithium. The surface texturing generated here did not influence cell behavior. These results demonstrate that end-capping could be a useful approach in scaffold design, where a wide range of biologically active groups could be employed, while likely retaining the desirable characteristics associated with the unaltered homopolymer backbone.