Drug‐Loaded Elastin‐Like Polypeptide–Collagen Hydrogels with High Modulus for Bone Tissue Engineering

Emphasizing the role of hydrogel stiffness and cellular differentiation, this study develops collagen and elastin‐like polypeptide (ELP)–based bone regenerative hydrogels loaded with recombinant human bone morphogenetic protein‐2 (rhBMP‐2) and doxycycline with mechanical properties suitable for osteogenesis. The drug‐incorporated collagen–ELP hydrogels has significantly higher modulus of 35 ± 5 kPa compared to collagen‐only hydrogels. Doxycycline shows a bi‐phasic release with an initial burst release followed by a gradual release, while rhBMP‐2 exhibits a nearly linear release profile for all hydrogels. The released doxycycline shows anti‐microbial activity against Pseudomonas aeruginosa, Streptococcus sanguinis, and Escherichia coli. Microscopic observation of the hydrogels reveals their interconnected, macroporous, 3D open architecture with pore diameters between 160 and 400 µm. This architecture supports human adipose–derived stem cell attachment and proliferation from initial days of cell seeding, forming a thick cellular sheath by day 21. Interestingly, in collagen and collagen–ELP hydrogels, cell morphology is elongated with stretched slender lamellipodial formation, while cells assemble as spheroidal aggregates in crosslinked as well as drug‐loaded hydrogels. Osteogenic markers, alkaline phosphatase and osteocalcin, are expressed maximally for drug‐loaded hydrogels compared to those without drugs. The drug‐loaded collagen–ELP hydrogels are thus promising for combating bacterial infection and promoting guided bone regeneration.     

Refractive index‐modulated grating in two‐mode planar polymeric waveguide produced by two‐photon polymerization

A polymeric waveguide film was manufactured by spinning the materials on quartz substrate. Two‐photon‐initiated photopolymerization was carried out by tight‐focusing femtosecond laser pulses in the two‐mode planar waveguide. A typical index‐modulated grating of 2.5 × 2 mm areas without morphology was fabricated. The results show that peak‐to‐peak modulation depth of the surface profile of grating region was only about 7 nm. The diffraction efficiency (DE) of the grating with a spacing period 2 µm was 0.17% and the corresponding index modulation reached 5.7 × 10^?3. Copyright © 2007 John Wiley & Sons, Ltd.     

Three‐dimensional microfabrication of protein hydrogels via two‐photon‐excited thiol‐vinyl ester photopolymerization

Engineering three‐dimensional (3D) hydrogels with well‐defined architectures has become increasingly important for tissue engineering and basic research in biomaterials science. To fabricate 3D hydrogels with (sub)cellular‐scale features, two‐photon polymerization (2PP) shows great promise although the technique is limited by the selection of appropriate hydrogel precursors. In this study, we report the synthesis of gelatin hydrolysate vinyl esters (GH‐VE) and its copolymerization with reduced derivatives of bovine serum albumin (acting as macrothiols). Photorheology of the thiol‐ene copolymerization shows a much more rapid onset of polymerization and a higher end modulus in reference to neat GH‐VE. This allowed 2PP to provide well‐defined and stable hydrogel microstructures. Efficiency of the radical‐mediated thiol‐vinyl ester photopolymerization allows high 2PP writing speed (as high as 50 mm s^?1) with low laser power (as low as 20 mW). MTT assays indicate negligible cytotoxicities of the GH‐VE macromers and of the thiol‐ene hydrogel pellets. Osteosarcoma cells seeded onto GH‐VE/BSA hydrogels with different macromer relative ratios showed a preference for hydrogels with higher percentage of GH‐VE. This can be attributed both to a favorable modulus and preferable protein environment since gelatin favors cell adhesion and albumin incurs nonspecific binding. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4799–4810     

A study on the micro‐injection molding of multi‐cavity ultra‐thin parts

In this study, we report the micro‐injection molding of ultra‐thin parts (100, 250, and 500 µm). The results show that the flow resistance increases as the cavity becomes thinner. The melt front is not symmetric when filling a four‐cavity ultra‐thin part and filling the eight‐cavity mold under a low temperature. If we increase the mold temperature or cavity thickness, the melt front becomes symmetric. Finally, we construct the operation windows of molding for three kinds of plastics (PS, PMMA, PC) and provide a molding range based on mold temperature and injections speed. Meanwhile, the relationship between the thickness and the operation windows are also investigated. The thinner the cavity is, the smaller the operation window is. We need to increase the injection speed significantly for molding the ultra‐thin parts with micro‐features on both surfaces which are 60 µm in thickness. Furthermore, we succeed in molding 30 µm ultra‐thin parts in this experiment. Copyright © 2009 John Wiley & Sons, Ltd.     

Surface‐Initiated Ring‐Opening Polymerization of ϵ‐Caprolactone from a Patterned Poly(hydroxymethyl‐ p‐xylylene)

A new strategy toward patterned polymer brushes combining the spatially controlled deposition of poly[(hydroxymethyl‐p‐xylylene)‐co‐(p‐xylylene)] ( 1 ) by chemical vapor deposition (CVD) polymerization of 4‐(hydroxymethyl)[2.2]paracyclophane and surface‐initiated ring‐opening polymerization was developed. Patterns of polymer brushes with thicknesses between 53 and 538 Å were created. The approach does not require photolithographic tools and has potential applicability to a wide range of different substrates, such as glasses, polymers, metals or composites.     

Tailored thioxanthone‐based photoinitiators for two‐photon‐controllable polymerization and nanolithographic printing

Printing of high‐resolution three‐dimensional nanostructures utilizing two‐photon polymerization has gained significant attention recently. In particular, isopropyl thioxanthone (ITX) has been implemented as a photoinitiator due to its capability of initiating and depleting polymerization on demand, but new photoinitiating materials are still needed in order to reduce the power requirements for the high‐throughput creation of 3D structures. To address this point, a suite of new thioxanthone‐based photoinitiators were synthesized and characterized. Then two‐photon polymerization was performed using the most promising photoinitiating molecule. Importantly, one of the initiators, 2,7‐bis[(4‐(dimethylamino)phenyl ethynyl)‐9H‐thioxanthen‐9‐one] (BDAPT), showed a fivefold improvement in the writing threshold over the commonly used ITX molecule. To elucidate the fundamental mechanism, the excitation and inhibition behavior of the BDAPT molecule were evaluated using density functional theory (DFT) calculations, low‐temperature phosphorescence spectroscopy, ultra‐fast transient absorption spectroscopy, and the two‐photon Z‐scan spectroscopic technique. The improved polymerization threshold of this new photoinitiator presents a clear pathway for the modification of photoinitiators in 3D nanoprinting. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1462–1475     

3D Microfibrous Scaffolds Selectively Promotes Proliferation and Glial Differentiation of Adult Neural Stem Cells: A Platform to Tune Cellular Behavior in Neural Tissue Engineering

Biomaterials are essential for the development of innovative biomedical and therapeutic applications. Biomaterials‐based scaffolds can influence directed cell differentiation to improve cell‐based strategies. Using a novel microfluidics approach, poly (ε‐caprolactone) (PCL), is used to fabricate microfibers with varying diameters (3–40 µm) and topographies (straight and wavy). Multipotent adult rat hippocampal stem/progenitor cells (AHPCs) are cultured on 3D aligned PCL microfibrous scaffolds to investigate their ability to differentiate into neurons, astrocytes, and oligodendrocytes. The results indicate that the PCL microfibers significantly enhance proliferation of the AHPCs compared to control, 2D planar substrates. While the AHPCs maintained their multipotent differentiation capacity when cultured on the PCL scaffolds, there is a significant and dramatic increase in immunolabeling for astrocyte and oligodendrocyte differentiation when compared with growth on planar surfaces. Our results show a 3.5‐fold increase in proliferation and 23.4‐fold increase in astrocyte differentiation for cells on microfibers. Transplantation of neural stem/progenitor cells within a PCL microfiber scaffold may provide important biological and topographic cues that facilitate the survival, selective differentiation, and integration of transplanted cells to improve therapeutic strategies.     

Fabrication of poly(2‐oxy‐6‐naphthoyl) particles by direct polycondensation of 2‐hydroxy‐6‐naphthoic acid

Morphology control of poly(2‐oxy‐6‐naphthoyl) (PON) was examined by using reaction‐induced crystallization of oligomers during direct polycondensation of 2‐hydroxy‐6‐naphthoic acid with p‐toluenesulfonyl chloride and N,N‐dimethylformamide in pyridine. PON particles were obtained of which the diameter was in the range of 8.0–8.3 µm. The particles were comprised of many lamellae and exhibited spherulitic morphology. They possessed high crystallinity evaluated from wide‐angle X‐ray scattering (WAXS). Formation mechanism of the particles was clarified from the results of morphology observation, yield, density and WAXS. When the number average degree of polymerization of the oligomers exceeded a critical value of ca. 4–5, they were precipitated to form lamellae. The lamellae grew to spherulites through screw dislocation with continuous precipitation of the oligomer from the solution. Finally, further polymerization occurred gradually in the precipitates. Copyright © 2005 John Wiley & Sons, Ltd.     

Antibacterial and Antifungal Activities of 2‐(substituted ether)‐5‐(1‐phenyl‐5‐(trifluoromethyl)‐1H‐pyrazol‐4‐yl)‐1,3,4‐oxadiazole Derivatives

By replacing the amide bond into 1,3,4‐oxadiazole moiety, a series of 1‐phenyl‐5‐(trifluoromethyl)‐1H‐pyrazole derivatives bearing 1,3,4‐oxadiazole were synthesized and evaluated their antibacterial and antifungal activity. The bioassay results revealed that compounds 7a and 7b showed the strongest antibacterial activity toward pathogen Xanthomonas oryzae pv. oryzae with the EC50 values of 15.0 and 6.4 µg/mL, respectively; compound 6a exhibited comprehensive antifungal activity toward six kinds of fungi; compound 6f could selectively inhibit the growth of Sclertinia sclerotiorum and Rhizoctonia solani with the inhibition rates of 82.5 and 80.3% at the concentrate of 100 µg/mL, respectively; compound 7b exerted good antifungal activity toward Fusarium oxysporum, Cytospora mandshurica, and Rhizoctonia solani with the inhibition rates of 70.8, 69.5, and 71.5%, respectively. The results suggested that this kind of compounds could be further studied as promising antimicrobial agents.     

Electron field emission of iron and cobalt‐doped DLC films fabricated by electrochemical deposition

Using a simple electrochemical depositing process, iron and cobalt‐doped diamond‐like carbon (DLC) films were deposited on Si (100) substrates. The results showed that metallic elements were inhomogeneously doped into highly cross‐linking amorphous carbon matrix, forming the typical nanocrystalline/amorphous nanocomposite structure, and simultaneously the microsturcture of amorphous carbon was changed by the doping of metals. Field emission performance showed that the incorporation of iron and cobalt effectively decreases the threshold field from 13.5 V/µm to 8.0 V/µm and 6.5 V/µm, respectively, and a highest current density of the Co‐DLC film was about 1.2 mA/cm² at the electric field of 23.5 V/µm. Copyright © 2012 John Wiley & Sons, Ltd.     

Two‐photon microfabrication of poly(ethylene glycol) diacrylate and a novel biodegradable photopolymer—comparison of processability for biomedical applications

Two‐photon polymerization (2PP) is a versatile microfabrication tool for biomedical applications as it provides unparalleled resolution for accurate three‐dimensional (3D) replication of biological microstructures. To widen the selection of biomaterials suitable for 2PP, this paper presents the processing of a methacrylated poly(ε‐caprolactone)‐based oligomer (PCL‐o) and a poly(ethylene glycol) diacrylate (PEGda) hydrogel into microstructures. PCL‐o is a novel biodegradable photopolymer that has not been previously processed with 2PP, and the fabrication of both polymers with an Nd:YAG laser is reported here for the first time. The overall 2PP processability and achievable resolution were studied by polymerizing arbitrary microstructures on glass substrates. The samples were characterized with scanning electron microscopy. Additionally, the effect of photoinitiator concentration on the resolution was investigated. Also, a preliminary cell attachment test was performed with UV cured films in order to investigate the impact of the used material–initiator combination on cell viability and migration. As a result, laser‐induced polymerization of both PCL‐o and PEGda was successfully demonstrated, and the Nd:YAG laser was proven adequate for the 2PP processing of the novel biodegradable photoresist. Resolution in the order of 1 µm was achieved with PCL‐o. With the easy processing of both PEGda and PCL‐o, these materials have great potential for different biomedical applications. Copyright © 2011 John Wiley & Sons, Ltd.     

Characterization of size‐segregated aerosols using ToF‐SIMS imaging and depth profiling

Size‐segregated particles were collected with a ten‐stage micro‐orifice uniform deposit impactor from a busy walkway in a downtown area of Hong Kong. The surface chemical compositions of aerosol samples from each stage were analyzed using time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) operated in the static mode. The ToF‐SIMS spectra of particles from stage 2 (5.6–10 µm), stage 6 (0.56–1 µm), and stage 10 (0.056–0.1 µm) were compared, and the positive ion spectra from stage 2 to stage 10 were analyzed with principal component analysis (PCA). Both spectral analysis and PCA results show that the coarse‐mode particles were associated with inorganic ions, while the fine particles were associated with organic ions. PCA results further show that the particle surface compositions were size dependent. Particles from the same mode exhibited more similar surface features. Particles from stage 2 (5.6–10 µm), stage 6 (0.56–1 µm), and stage 10 (0.056–0.1 µm) were further selected as representatives of the three modes, and the chemical compositions of these modes of particles were examined using ToF‐SIMS imaging and depth profiling. The results reveal a non‐uniform chemical distribution from the outer to the inner layer of the particles. The coarse‐mode particles were shown to contain inorganic salts beneath the organics surface. The accumulation‐mode particles contained sulfate, nitrate, ammonium salts, and silicate in the regions below a thick surface layer of organic species. The nucleation‐mode particles consisted mainly of soot particles with a surface coated with sulfate, hydrocarbons, and, possibly, fullerenic carbon. The study demonstrated the capability of ToF‐SIMS depth profiling and imaging in characterizing both the surface and the region beneath the surface of aerosol particles. It also revealed the complex heterogeneity of chemical composition in size and depth distributions of atmospheric particles. Copyright © 2014 John Wiley & Sons, Ltd.     

On‐line sample preconcentration by polarity switching in floating electrode‐integrated microchannel

In this study, we found that the polarity switching was effective to enrich and separate fluorescent analytes which have weakly‐dissociated groups in a floating platinum electrode (width, 50 µm; thickness, 2.5 µm)‐integrated straight‐channel in microchip electrophoresis (MCE). In the straight channel filled with an Alexa Flour 488 (AF488) solution, a sharp peak was observed after the polarity inversion with a 530‐fold enhancement of the sensitivity relative to the conventional MCE analysis. By using a fluorescent pH indicator, we verified that a sharp high‐pH zone was generated nearby the floating electrode and moved toward the anode with maintaining the high pH, which induced the sample enrichment like a dynamic pH junction mechanism. In the floating electrode‐embedded channel, the mixture of AF488‐labeled proteins was also well concentrated and separated within 100 s.     

Monte‐Carlo simulation of spatial distribution of characteristic x‐rays in multi‐film targets: source size of Al Kα x‐rays in W/Al film targets

A Monte‐Carlo simulation approach has been applied to describe the spatial distribution of characteristic x‐rays in W/Al film targets of different combinations of film thicknesses for the optimal design of a small‐sized x‐ray source having a high x‐ray intensity. The result has led to optimal combinations of W and Al film targets for 100 kV electrons, e.g. W(1 µm)/Al(20 µm), W(3 µm)/Al(15 µm) and W(5 µm)/Al(8 µm). These Al/W targets could be used as x‐ray sources for a medical instrument currently under development. Copyright © 2004 John Wiley & Sons, Ltd.     

Alternating copolymers of 2,6‐bis(p‐dihexylaminostyryl)anthracene‐9,10‐diyl and N‐octylcarbazole with large two‐photon cross sections

We report the synthesis, thermal, one‐ and two‐photon properties of poly(2,6‐bis(p‐dihexylaminostyryl)anthracene‐9,10‐diyl‐alt‐N‐octylcarbazole‐3,6‐/2,7‐diyl) ( P1/P2 ). The as‐synthesized polymers exhibit number‐average molecular weights of 1.7 × 10⁴ for P1 and 2.1 × 10⁴ g/mol for P2 . They emit strong one‐ and two‐photon excitation fluorescence with the peak around 502 nm, and the fluorescence quantum yields around 0.76 in chloroform. In film state, P1 and P2 show different red‐shift emission with the peaks at 512 nm and 523 nm, respectively. The DSC measurement reveals that as‐synthesized polymers are all amorphous aggregates with the glass transition temperatures of 131 °C for P1 and 152 °C for P2 . The solution two‐photon absorption (TPA) properties of P1 and P2 in chloroform are measured by the two‐photon‐induced fluorescence method using femtosecond laser pulses (120 fs). The TPA cross sections (δ) are measured over the range of 700–900 nm. The maximal δ of P1 and P2 all appear at ～800 nm and are 1010 GM and 940 GM per repeating unit, respectively. This suggests that no notable interactions among structure units that impair their fluorescence and TPA properties, and the polymers with large δ can be obtained by using the high TPA‐active units as building blocks. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

High‐resolution resist for screen printing: application to direct fabrication of Ag circuit

High‐resolution screen printing was devised. New resist formulation contains a base polymer, which consists of acid‐labile tetrahydropyranyl‐protected carboxylic acid, hydroxyl, and methacrylic functions. As crosslinkers, multifunctional acrylates were employed. Photoacid generators were used for pattern formation. A 10‐µm feature size of resist on a screen plate was obtained on irradiation at 365 nm and followed by development on a stainless steel screen. Post‐exposure curing improved the mechanical characteristics of the resist patterns. A 13‐µm feature size silver circuit was successfully printed on poly(ethylene terephthalate) film without defect. Copyright © 2011 John Wiley & Sons, Ltd.     

Catalytic Polymerization of Liquid Propylene: Effect of Low‐Yield Hexene Prepolymerization on Kinetics and Morphology

Summary: A Ziegler‐Natta‐catalyst was used in ultra low‐yield slurry prepolymerization followed by liquid propylene (main) polymerizations. Complete catalyst disintegration down to 1.5–2 µm particle size is observed at prepolymerization yields of 10 g per g cat. The initial (main) polymerization rate increased up to 55% and the final average particle diameter can be controlled between 50 and 1 500 µm at main polymerization yields of 20 kg PP per g cat · hr⁻¹. Tension generation within the particle and the absence of a polymer layer explains these results.

Surface SEM. Top: Catalyst surface covered with polyhexene. Bottom: Cracks on catalyst surface after washing with hexane.     

Voltammetric Determination of 4‐Nitrophenol and 5‐Nitrobenzimidazole Using Different Types of Silver Solid Amalgam Electrodes – A Comparative Study

The voltammetric behavior of two genotoxic nitro compounds (4‐nitrophenol and 5‐nitrobenzimidazole) has been investigated using direct current voltammetry (DCV) and differential pulse voltammetry (DPV) at a polished silver solid amalgam electrode (p‐AgSAE), a mercury meniscus modified silver solid amalgam electrode (m‐AgSAE), and a mercury film modified silver solid amalgam electrode (MF‐AgSAE). The optimum conditions have been evaluated for their determination in Britton‐Robinson buffer solutions. The limit of quantification (L_Q) for 5‐nitrobenzimidazole at p‐AgSAE was 0.77 µmol L^?1 (DCV) and 0.47 µmol L^?1 (DPV), at m‐AgSAE it was 0.32 µmol L^?1 (DCV) and 0.16 µmol L^?1 (DPV), and at MF‐AgSAE it was 0.97 µmol L^?1 (DCV) and 0.70 µmol L^?1 (DPV). For 4‐nitrophenol at p‐AgSAE, L_Q was 0.37 µmol L^?1 (DCV) and 0.32 µmol L^?1 (DPV), at m‐AgSAE it was 0.14 µmol L^?1 (DCV) and 0.1 µmol L^?1 (DPV), and at MF‐AgSAE, it was 0.87 µmol L^?1 (DCV) and 0.37 µmol L^?1 (DPV). Thorough comparative studies have shown that m‐AgSAE is the best sensor for voltammetric determination of the two model genotoxic compounds because it gives the lowest L_Q, is easier to prepare, and its surface can be easily renewed both chemically (by new amalgamation) and/or electrochemically (by imposition of cleaning pulses). The practical applicability of the newly developed methods was verified on model samples of drinking water.     

Evaluation of 3D Printed Gelatin‐Based Scaffolds with Varying Pore Size for MSC‐Based Adipose Tissue Engineering

Adipose tissue engineering aims to provide solutions to patients who require tissue reconstruction following mastectomies or other soft tissue trauma. Mesenchymal stromal cells (MSCs) robustly differentiate into the adipogenic lineage and are attractive candidates for adipose tissue engineering. This work investigates whether pore size modulates adipogenic differentiation of MSCs toward identifying optimal scaffold pore size and whether pore size modulates spatial infiltration of adipogenically differentiated cells. To assess this, extrusion‐based 3D printing is used to fabricate photo‐crosslinkable gelatin‐based scaffolds with pore sizes in the range of 200–600 µm. The adipogenic differentiation of MSCs seeded onto these scaffolds is evaluated and robust lipid droplet formation is observed across all scaffold groups as early as after day 6 of culture. Expression of adipogenic genes on scaffolds increases significantly over time, compared to TCP controls. Furthermore, it is found that the spatial distribution of cells is dependent on the scaffold pore size, with larger pores leading to a more uniform spatial distribution of adipogenically differentiated cells. Overall, these data provide first insights into the role of scaffold pore size on MSC‐based adipogenic differentiation and contribute toward the rational design of biomaterials for adipose tissue engineering in 3D volumetric spaces.     

Two‐Photon‐Responsive Supramolecular Hydrogel for Controlling Materials Motion in Micrometer Space

Spatiotemporal control of fluidity inside a soft matrix by external stimuli allows real‐time manipulation of nano/micromaterials. In this study, we report a two‐photon‐responsive peptide‐based supramolecular hydrogel, the fluidity of which was dramatically controlled with high spatial resolution (10 μm×10 μm×10 μm). The off–on switching of the Brownian motion of nanobeads and chemotaxis of bacteria by two‐photon excitation was successfully demonstrated.