Reactive Imprint Lithography: Combined Topographical Patterning and Chemical Surface Functionalization of Polystyrene‐block‐poly(tert‐butyl acrylate) Films

Here, reactive imprint lithography (RIL) is introduced as a new, one‐step lithographic tool for the fabrication of large‐area topographically patterned, chemically activated polymer platforms. Films of polystyrene‐block‐poly(tert‐butyl acrylate) (PS‐b‐PtBA) are imprinted with PDMS master stamps at temperatures above the corresponding glass transition and chemical deprotection temperatures to yield structured films with exposed carboxylic acid and anhydride groups. Faithful pattern transfer is confirmed by AFM analyses. Transmission‐mode FTIR spectra shows a conversion of over 95% of the tert‐butyl ester groups after RIL at 230 °C for 5 minutes and a significantly reduced conversion to anhydride compared to thermolysis of neat films with free surfaces in air or nitrogen. An enrichment of the surface layer in PS is detected by angle‐resolved X‐ray photoelectron spectroscopy (XPS). In order to demonstrate application potentials of the activated platforms, a 7 nm ± 1 nm thick NH₂‐terminated PEG layer (grafting density of 0.9 chains nm^?2) is covalently grafted to RIL‐activated substrates. This layer reduces the non‐specific adsorption (NSA) of bovine serum albumin by 95% to a residual mass coverage of 9.1 ± 2.9 ng cm^?2. As shown by these examples, RIL comprises an attractive complementary approach to produce bio‐reactive polymer surfaces with topographic patterns in a one‐step process.     

Direct Writing of Three‐Dimensional Polymer Scaffolds Using Colloidal Gels

Polymer scaffolds intended to provide a substrate for cell attachment and proliferation benefit if the geometric architecture, mechanical properties, and surface chemistry are controllable within the range applicable for the target tissue. Such scaffolds may be made bioinductive through the inclusion of surface proteins and release of growth factors. Furthermore, the polymer support may be formed of biodegradable polymers for use as tissue‐engineering scaffolds. In this study, a new scaffold‐fabrication technique based on the direct writing of polymer colloidal‐gel‐based inks is described. The colloidal approach allows for the modular design of inks where the structure and composition of the colloidal particles, surface adsorbed molecules, and dissolved species may be easily controlled. Polyacrylate latex particles are formulated into colloidal gels by using a thermoreversible gel‐forming poly(ethylene oxide)–poly(propylene oxide) block‐copolymer adsorbed layer. The resulting colloidal gels are laced with the model protein bovine serum albumin (BSA) either dissolved in the solvent phase of the ink or dispersed in chitosan nanoparticles as a second colloid. Ink development and rheological characterization are presented along with demonstration of assembly of mesoporous scaffolds. After assembly and drying of the scaffold structure, the drug‐release kinetics are measured upon re‐exposure to an aqueous environment. Protein activity appears to be unaffected by the processing route of these scaffolds. Finally, the assembly of heterogeneous scaffolds is demonstrated to illustrate the possibilities for staged or heterogeneous drug release. This approach to scaffold fabrication offers a new route for scaffold assembly from water‐insoluble polymers while allowing the inclusion of sensitive biomolecules without risk of denaturation.     

Carbon Nanotube Coatings on Bioglass‐Based Tissue Engineering Scaffolds

The coating of highly porous Bioglass^® based 3D scaffolds with multi‐walled carbon nanotubes (CNT) was investigated. Foam like Bioglass^® scaffolds were fabricated by the replica technique and electrophoretic deposition was used to deposit homogeneous layers of CNT throughout the scaffold pore structure. The optimal experimental conditions were determined to be: applied voltage 15 V and deposition time 20 minutes, utilizing a concentrated aqueous suspension of CNT with addition of a surfactant and iodine. The scaffold pore structure remained invariant after the CNT coating, as assessed by SEM. The incorporation of CNTs induced a nanostructured internal surface of the pores which is thought to be beneficial for osteoblast cell attachment and proliferation. Bioactivity of the scaffolds was assessed by immersion studies in simulated body fluid (SBF) for periods of up to 2 weeks and the subsequent determination of hydroxyapatite (HA) formation. The presence of CNTs can enhance the bioactive behaviour of the scaffolds since CNTs can serve as template for the ordered formation of a nanostructured HA layers, which does not occur on uncoated Bioglass^® surfaces.     

Supercritical CO2: A Clean and Low Temperature Approach to Blending PDLLA and PEG

The unique combination of the gas like viscosity and liquid like density of supercritical CO₂ (scCO₂) is exploited to blend poly(D,L‐lactic acid) (P_DLLA) and poly(ethylene glycol) (PEG) at near ambient temperatures. This novel process lowers the polymer blend viscosity and also permits incorporation of thermally and solvent labile protein based drugs. A series of blends are prepared with agitation in scCO₂. Differential scanning calorimetry (DSC) data shows that miscible blends can be produced at moderate temperatures. A surprising region of miscibility is revealed between 8 and 25%w/w PEG. The properties of this miscible region are probed with high pressure parallel plate rheological studies, showing that the viscosity in scCO₂ is directly related to the miscibility. Using the particles from gas saturated solutions (PGSS) method, microparticles of these P_DLLA/PEG blends are produced using scCO₂ and it is determined that the yields obtained are proportional to the miscibility of the polymers. Thus scCO₂ provides a unique route to low temperature, solvent free processing that accesses a window of miscibility that has not previously been observed. Finally, DSC analyses of these sprayed microparticles confirm the presence of the same high miscibility region observed in the bulk samples prepared under supercritical conditions.     

Stimuli‐Responsive Scaffold for Breast Cancer Treatment Combining Accurate Photothermal Therapy and Adipose Tissue Regeneration

Development of new therapeutic scaffolds to selectively destruct tumors under gentle conditions meanwhile promoting adipose tissue formation would be a promising strategy for clinical treatment of breast cancer. Herein, a stimuli‐responsive scaffold composed of polyacrylic acid‐g‐polylactic acid (PAA‐g‐PLLA) modified graphene oxide (GO) with a cleavable bond in between (GO‐PAA‐g‐PLLA), gambogic acid (GA), and polycaprolactone (PCL) is fabricated and then preseeded on adipose‐derived stem cells (ADSCs) for breast cancer treatment. This GO–GA‐polymer scaffold is able to simultaneously perform pH‐triggered low temperature (45 °C) photothermal therapy to selectively induce the apoptosis of tumor cells and significantly improve ADSCs growth without any photothermal damage. The low‐temperature photothermal therapy of the scaffolds can induce more than 95% of cell death for human breast cancer (MCF‐7) in vitro, which further completely inhibits tumor growth and finally eliminates tumor tissue in mice. Meanwhile, the prepared GO–GA‐polymer scaffold possesses the improved capability to stimulate the differentiation of ADSCs into adipocytes by upregulating adipo‐related gene expression, and significantly promotes new adipose tissue formation whether with or without NIR irradiation. These results successfully demonstrate that the prepared GO–GA‐polymer scaffolds with bifunctional properties will be a promising candidate for clinical cases involving both tumor treatment and tissue engineering.     

White Electroluminescence from a Single‐Polymer System with Simultaneous Two‐Color Emission: Polyfluorene Blue Host and Side‐Chain‐Located Orange Dopant

Four single polymers with two kinds of attachment of orange chromophore to blue polymer host for white electroluminescence (EL) were designed. The effect of the side‐chain attachment and main‐chain attachment on the EL efficiencies of the resulting polymers was compared. The side‐chain‐type single polymers are found to exhibit more efficient white EL than that of the main‐chain‐type single polymers. Based on the side‐chain‐type white single polymer with 4‐(4‐alkyloxy‐phenyl)‐7‐(4‐diphenylamino‐phenyl)‐2,1,3‐benzothiadiazoles as the orange‐dopant unit and polyfluorene as the blue polymer host, white EL with simultaneous orange (λ_max = 545 nm) and blue emission (λ_max = 432 nm/460 nm) is realised. A single‐layer device (indium tin oxide/poly(3,4‐ethylenedioxythiophene)/polymer/Ca/Al) made of these polymers emits white light with the Commission Internationale de l'Éclairage coordinates of (0.30,0.40), possesses a turn‐on voltage of 3.5 V, luminous efficiency of 10.66 cd A^–1, power efficiency of 6.68 lm W^–1, and a maximum brightness of 21 240 cd m^–2.     

Imaging Surface Immobilization Chemistry: Correlation with Cell Patterning on Non‐Adhesive Hydrogel Thin Films

High‐fidelity surface functional group (e.g., N‐hydroxysuccinimide (NHS) reactive ester) patterning is readily and reliably achieved on commercial poly(ethylene glycol) (PEG)‐based polymer films already known to exhibit high performance non‐fouling properties in full serum and in cell culture conditions. NHS coupling chemistry co‐patterned with methoxy‐capped PEG using photolithographic methods is directly spatially imaged using imaging time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) and principal components statistical analysis. Patterned NHS surface reactive zones are clearly resolved at high sensitivity despite the complexity of the polymer matrix chemistry. ToF‐SIMS imaging also reveals the presence of photo‐resist residue remaining from typical photolithography processing methods. High cross‐correlation between various ion‐derived ToF‐SIMS images is observed, providing sensitive chemical corroboration of pattern chemistry and biological reactivity in complex milieu. Surface‐specific protein coupling is observed first by site‐selective reaction of streptavidin with NHS patterns, followed by identical patterns of biotinylated Alexa‐labeled albumin coupling. This suggests that streptavidin immobilized on the patterns remains bioactive. Fluorescently labeled full serum is shown to react selectively with NHS‐reactive regions, with minimal signal from methoxy‐capped regions. Insufficient serum is adsorbed under any conditions to these surfaces to support cell attachment in serum‐containing media. This reflects the high intrinsic non‐adsorptive nature of this chemistry. Fibroblasts attach and proliferate in serum culture only when a cell adhesion peptide (RGD) is first grafted to NHS regions on the PEG‐based surfaces. Longer‐term serum‐based cell culture retains high cell‐pattern fidelity that correlates with chemical imaging of both the NHS and RGD patterns and also lack of cell adhesion to methoxy‐capped regions. Cell staining shows orientation of adherent cells within the narrow patterned areas. Cell patterns are consistently retained beyond 15 days in serum media.     

Programmed Shape‐Morphing Scaffolds Enabling Facile 3D Endothelialization

Rapid formation of a confluent endothelial monolayer is the key to the success of small‐diameter vascular grafts, which is significantly important for treating dangerous and even sometimes deadly vascular disorders. However, the difficulty to homogenously locate endothelial cells onto the lumen of small‐diameter tubular scaffolds makes 3D endothelialization greatly challenging. Here, novel shape‐morphing scaffolds enabling programmed deformation from planar shapes to small‐diameter tubular shapes are designed and developed by combining biocompatible shape memory polymer and electrospun nanofibrous membrane. Endothelial cells can be conveniently seeded and attached on the 2D surface of the scaffolds and subsequently self‐rolled into 3D organization at physiological temperature. Endothelial cell responses and functions are varied on the shape‐morphing scaffolds with different nanofibrous electrospun membranes as the inner layer, arisen from the inducement of scaffolds with different morphological, physical, and biochemical characteristics. Owing to excellent properties of the nanofibrous membrane fabricated by the coelectrospinning of poly‐ε‐caprolactone (PCL) and gelatin methacrylate (GelMA), the shape‐morphing scaffolds with a nanofibrous PCL/GelMA inner layer support desirable homogeneous endothelial cell attachment as well as the rapid formation of biomimetic cell–scaffold interaction and cell–cell interaction under the 3D cell culture condition, therefore offering a visible approach for facile 3D endothelialization.     

Solid Free‐Form Fabrication of Tissue‐Engineering Scaffolds with a Poly(lactic‐co‐glycolic acid) Grafted Hyaluronic Acid Conjugate Encapsulating an Intact Bone Morphogenetic Protein–2/Poly(ethylene glycol) Complex

Despite wide applications of bone morphogenetic protein–2 (BMP‐2), there are few methods to incorporate BPM‐2 within polymeric scaffolds while maintaining biological activity. Solid free‐form fabrication (SFF) of tissue‐engineering scaffold is successfully carried out with poly(lactic‐co‐glycolic acid) grafted hyaluronic acid (HA‐PLGA) encapsulating intact BMP‐2/poly(ethylene glycol) (PEG) complex. HA‐PLGA conjugate is synthesized in dimethyl sulfoxide (DMSO) by the conjugation reaction of adipic acid dihydrazide modified HA (HA‐ADH) and PLGA activated with N,N′‐dicyclohexylcarbodiimide (DCC) and N‐hydroxysuccinimide (NHS). BMP‐2 is complexed with PEG, which is encapsulated within the PLGA domain of the HA‐PLGA conjugate by SFF to prepare tissue‐engineering scaffolds. In vitro release tests confirm the sustained release of intact BMP‐2 from the scaffolds for up to a month. After confirmation of the enhanced osteoblast cell growth, and high gene‐expression levels of alkaline phosphatase (ALP), osteocalcin (OC), and osterix (OSX) in the cells, the HA‐PLGA/PEG/BMP‐2 scaffolds are implanted into calvarial bone defects of Sprague Dawley (SD) rats. Microcomputed tomography (μCT) and histological analyses with Masson's trichrome, and hematoxylin and eosin (H&E) staining reveal effective bone regeneration on the scaffolds of HA‐PLGA/PEG/BMP‐2 blends.     

The Implications of Polymer Selection in Regenerative Medicine: A Comparison of Amorphous and Semi‐Crystalline Polymer for Tissue Regeneration

Biodegradable polymeric scaffolds are being investigated as scaffolding materials for use in regenerative medicine. While the in vivo evaluation of various three‐dimensional (3D), porous, biodegradable polymeric scaffolds has been reported, most studies are ≤3 months in duration, which is typically prior to bulk polymer degradation, a critical event that may initiate an inflammatory response and inhibit tissue formation. Here, a 6 month in vitro degradation and corresponding in vivo studies that characterized scaffold changes during complete degradation of an amorphous, 3D poly(lactide‐co‐glycolide)(3D‐PLAGA) scaffold and near‐complete degradation of a semi‐crystalline3D‐PLAGA scaffold are reported. Using sintered microsphere matrix technology, constructs were fabricated in a tubular shape, with the longitudinal axis void and a median pore size that mimicked the architecture of native bone. Long‐term quantitative measurements of molecular weight, mechanical properties, and porosity provided a basis for theorization of the scaffold degradation process. Following implantation in a critical size ulnar defect model, histological analysis and quantitative microCT indicated early solubilization of the semi‐crystalline polymer created an acidic microenvironment that inhibited mineralized tissue formation. Thus, the use of amorphous over semi‐crystalline PLAGA materials is advocated for applications in regenerative medicine.     

Mosaic,Single‐Crystal CaCO3 Thin Films Fabricated on Modified Polymer Templates

Mosaic, single‐crystal CaCO₃ thin films have been prepared on modified poly(ethylene terephthalate) (PET) templates. Surface modification of PET through the introduction of carboxylic acid groups (COOH‐PET), and the subsequent physical and chemical adsorption of poly(allylamine hydrochloride) (PAH) at pH 8 (PAH8‐PET) and pH 11 (PAH11‐PET), afford template surfaces that influenced the phase transition of an amorphous CaCO₃ (ACC) films during crystallization in air. Macroscopic ACC thin films are prepared on modified PET films in the presence of poly(acrylic acid). Polycrystalline, spherulitic vaterite (CaCO₃) films are observed to form on native PET and PAH11‐PET, while mosaic, single‐crystal calcitic (CaCO₃) films form on COOH‐PET and PAH8‐PET templates. These results confirm that single‐crystal CaCO₃ growth patterns are dependent on the surface characteristics of the PET template. We infer therefore, that the nucleation and growth of ceramic films on polymeric templates can be controlled by chemical modification of the polymeric template surface, and by the subsequent attachment of ionic polyelectrolytes.     

Electronic Transport Properties of Ensembles of Perylene‐Substituted Poly‐isocyanopeptide Arrays

The electronic transport properties of stacks of perylene‐bis(dicarboximide) (PDI) chromophores, covalently fixed to the side arms of rigid, helical polyisocyanopeptides, are studied using thin‐film transistors. In device architectures where the transistor channel lengths are somewhat greater than the average polymer chain length, carrier mobilities of order 10^?3 cm² V^?1 s^?1 at 350 K are found, which are limited by inter‐chain transport processes. The influence of π–π interactions on the material properties is studied by using PDIs with and without bulky substituents in the bay area. In order to attain a deeper understanding of both the electronic and the electronic‐transport properties of these systems, studies of self‐assembly on surfaces are combined with electronic characterization using Kelvin probe force microscopy, and also a theoretical study of electronic coupling. The use of a rigid polymer backbone as a scaffold to achieve a full control over the position and orientation of functional groups is of general applicability and interest in the design of building blocks for technologically important functional materials, as well as in more fundamental studies of chromophoric interactions.     

3D Superelastic Scaffolds Constructed from Flexible Inorganic Nanofibers with Self‐Fitting Capability and Tailorable Gradient for Bone Regeneration

Repair of bone defects with irregular shapes or at soft tissue insertion sites faces a huge challenge. Scaffolds capable of adapting to bone cavities, generating stiffness gradients, and inducing osteogenesis are necessary. Herein, a superelastic 3D ceramic fibrous scaffold is developed by assembly of intrinsically rigid, structurally flexible electrospun SiO₂ nanofibers with chitosan as bonding sites (SiO₂ NF‐CS) via a lyophilization technique. SiO₂ NF‐CS scaffolds exhibit excellent elasticity (full recovery from 80% compression), fast recovery rate (>500 mm min^?1), and good fatigue resistance (>10 000 cycles of compression) in an aqueous medium. SiO₂ NF‐CS scaffolds induce human mesenchymal stem cell (hMSC) elongation and differentiation into osteoblasts. In vivo self‐fitting capability is demonstrated by implanting compressed SiO₂ NF‐CS scaffolds into different shaped mandibular defects in rabbits, with a spontaneous recovery and full filling of defects. Rat calvarial defect repair validates enhanced bone formation and vascularization by cell (hMSC) histomorphology analysis. Further, subchondral bone scaffolds with gradations in SiO₂ nanofibers are developed, leading to a stiffness gradient and spatially chondrogenic and osteogenic differentiation of hMSCs. This work presents a type of 3D ceramic fibrous scaffold, which can closely match bone defects with irregular shapes or at different implant sites, and is promising for clinical translation.     

Porous Silicon Nanoparticles Embedded in Poly(lactic‐co‐glycolic acid) Nanofiber Scaffolds Deliver Neurotrophic Payloads to Enhance Neuronal Growth

Scaffolds made from biocompatible polymers provide physical cues to direct the extension of neurites and to encourage repair of damaged nerves. The inclusion of neurotrophic payloads in these scaffolds can substantially enhance regrowth and repair processes. However, many promising neurotrophic candidates are excluded from this approach due to incompatibilities with the polymer or with the polymer processing conditions. This work provides one solution to this problem by incorporating porous silicon nanoparticles (pSiNPs) that are preloaded with the therapeutic into a polymer scaffold during fabrication. The nanoparticle‐drug‐polymer hybrids are prepared in the form of oriented poly(lactic‐co‐glycolic acid) nanofiber scaffolds. Three different therapeutic payloads are tested: bpV(HOpic), a small molecule inhibitor of phosphatase and tensin homolog (PTEN); an RNA aptamer specific to tropomyosin‐related kinase receptor type B (TrkB); and the protein nerve growth factor (NGF). Each therapeutic is loaded using a loading chemistry that is optimized to slow the rate of release of these water‐soluble payloads. The drug‐loaded pSiNP‐nanofiber hybrids release approximately half of their TrkB aptamer, bpV(HOpic), or NGF payload in 2, 10, and >40 days, respectively. The nanofiber hybrids increase neurite extension relative to drug‐free control nanofibers in a dorsal root ganglion explant assay.     

Modular and Versatile Spatial Functionalization of Tissue Engineering Scaffolds through Fiber‐Initiated Controlled Radical Polymerization

Native tissues are typically heterogeneous and hierarchically organized, and generating scaffolds that can mimic these properties is critical for tissue engineering applications. By uniquely combining controlled radical polymerization (CRP), end‐functionalization of polymers, and advanced electrospinning techniques, a modular and versatile approach is introduced to generate scaffolds with spatially organized functionality. Poly‐ε‐caprolactone is end functionalized with either a polymerization‐initiating group or a cell‐binding peptide motif cyclic Arg‐Gly‐Asp‐Ser (cRGDS), and are each sequentially electrospun to produce zonally discrete bilayers within a continuous fiber scaffold. The polymerization‐initiating group is then used to graft an antifouling polymer bottlebrush based on poly(ethylene glycol) from the fiber surface using CRP exclusively within one bilayer of the scaffold. The ability to include additional multifunctionality during CRP is showcased by integrating a biotinylated monomer unit into the polymerization step allowing postmodification of the scaffold with streptavidin‐coupled moieties. These combined processing techniques result in an effective bilayered and dual‐functionality scaffold with a cell‐adhesive surface and an opposing antifouling non‐cell‐adhesive surface in zonally specific regions across the thickness of the scaffold, demonstrated through fluorescent labelling and cell adhesion studies. This modular and versatile approach combines strategies to produce scaffolds with tailorable properties for many applications in tissue engineering and regenerative medicine.     

Protein Adsorption Modes Determine Reversible Cell Attachment on Poly(N‐isopropyl acrylamide) Brushes

Protein adsorption and reversible cell attachment are investigated as a function of the grafting density of poly(N‐isopropyl acrylamide) (PNIPAM) brushes. Prior studies demonstrated that the thermally driven collapse of grafted PNIPAM above the lower critical solution temperature of 32 °C is not required for protein adsorption. Here, the dependence of reversible, protein‐mediated cell adhesion on the polymer chain density, above and below the lower critical solution temperature, is reported. Above 32 °C, protein adsorption on PNIPAM brushes grafted from a non‐adsorbing, oligo(ethylene oxide)‐coated surface exhibits a maximum with respect to the grafting density. Few cells attach to either dilute or densely grafted PNIPAM chains, independent of whether the polymer brush collapses above 32 °C. However, both cells and proteins adsorb reversibly at intermediate chain densities. This supports a model in which the proteins, which support reversible cell attachment, adsorb by penetrating the brushes at intermediate grafting densities, under poor solvent conditions. In this scenario, reversible protein adsorption to PNIPAM brushes is determined by the thermal modulation of relative protein‐segment attraction and osmotic repulsion.     

Adopting the Principles of Collagen Biomineralization for Intrafibrillar Infiltration of Yttria‐Stabilized Zirconia into Three‐Dimensional Collagen Scaffolds

In this paper, a process for generating collagen‐yttria‐stabilized amorphous zirconia hybrid scaffolds by introducing acetylacetone‐inhibited zirconia precursor nanodroplets into a poly(allylamine)‐coated collagen matrix is reported. This polyelectrolyte coating triggers intrafibrillar condensation of the precursors into amorphous zirconia, which is subsequently transformed into yttria‐stabilized zirconia after calcination. These findings represent a new paradigm in the synthesis of non‐naturally occurring collagen‐based hybrid scaffolds under alcoholic mineralizing conditions.     

Iron Oxide‐Labeled Collagen Scaffolds for Non‐Invasive MR Imaging in Tissue Engineering

Non‐invasive imaging holds significant potential for implementation in tissue engineering. It can be used to monitor the localization and function of tissue‐engineered implants, as well as their resorption and remodelling. Thus far, however, the vast majority of effort in this area of research have focused on the use of ultrasmall super‐paramagnetic iron oxide (USPIO) nanoparticle‐labeled cells, colonizing the scaffolds, to indirectly image the implant material. Reasoning that directly labeling scaffold materials might be more beneficial (enabling imaging also in the case of non‐cellularized implants), more informative (enabling the non‐invasive visualization and quantification of scaffold degradation), and easier to translate into the clinic (cell‐free materials are less complex from a regulatory point‐of‐view), three different types of USPIO nanoparticles are prepared and incorporated both passively and actively (via chemical conjugation; during collagen crosslinking) into collagen‐based scaffold materials. The amount of USPIO incorporated into the scaffolds is optimized, and correlated with MR signal intensity, showing that the labeled scaffolds are highly biocompatible, and that scaffold degradation can be visualized using MRI. This provides an initial proof‐of‐principle for the in vivo visualization of the scaffolds. Consequently, USPIO‐labeled scaffold materials seem to be highly suitable for image‐guided tissue engineering applications.     

Poly(ϵ‐caprolactone)‐Functionalized Carbon Nanotubes and Their Biodegradation Properties

Biodegradable poly(?‐caprolactone) (PCL) has been covalently grafted onto the surfaces of multiwalled carbon nanotubes (MWNTs) by the “grafting from” approach based on in‐situ ring‐opening polymerization of ?‐caprolactone. The grafted PCL content can be controlled easily by adjusting the feed ratio of monomer to MWNT‐supported macroinitiators (MWNT‐OH). The resulting products have been characterized with Fourier‐transform IR (FTIR), NMR, and Raman spectroscopies, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). After PCL was coated onto MWNT surfaces, core/shell structures with nanotubes as the “hard” core and the hairy polymer layer as the “soft” shell are formed, especially for MWNTs coated with a high density of polymer chains. Such a polymer shell promises good solubility/dispersibility of the MWNT–PCL nanohybrids in low‐boiling‐point organic solvents such as chloroform and tetrahydrofuran. Biodegradation experiments have shown that the PCL grafted onto MWNTs can be completely enzymatically degraded within 4 days in a phosphate buffer solution in the presence of pseudomonas (PS) lipase, and the carbon nanotubes retain their tubelike morphologies, as observed by SEM and TEM. The results present possible applications for these biocompatible PCL‐functionalized CNTs in bionanomaterials, biomedicine, and artificial bones.     

Temperature‐Induced Hydrogels Through Self‐Assembly of Cholesterol‐Substituted Star PEG‐b‐PLLA Copolymers: An Injectable Scaffold for Tissue Engineering

Partially cholesterol‐substituted 8‐arm poly(ethylene glycol)‐block‐poly(L ‐lactide) (8‐arm PEG‐b‐PLLA‐cholesterol) has been prepared as a novel star‐shaped, biodegradable copolymer derivative. The amphiphilic 8‐arm PEG‐b‐PLLA‐cholesterol aqueous solution (polymer concentration, above 3 wt%) exhibits instantaneous temperature‐induced gelation at 34 °C, but the virgin 8‐arm PEG‐b‐PLLA does not, irrespective of concentration. Moreover, an extracellular matrix (ECM)‐like micrometer‐scale network structure has been created with favorable porosity for three‐dimensional proliferation of cells inside the hydrogel. This network structure is mainly attributed to specific self‐assembly between cholesterol groups. The 10 and 20 wt% hydrogels are eroded gradually in phosphate buffered saline at 37 °C over the course of a month, and after that the gel becomes completely dissociated. Moreover, L929 cells encapsulated into the hydrogel are viable and proliferate three‐dimensionally inside the hydrogels. Thus, in‐vitro cell culture studies demonstrate that 8‐arm PEG‐b‐PLLA‐cholesterol is a promising candidate as a novel injectable cellular scaffold.