Dual-Lifetime Referencing (t-DLR) Optical Fiber Fluorescent pH Sensor for Microenvironments.

The pH behavior in the µm to cm thick diffusion boundary layer (DBL) surrounding many aquatic species is dependent on light-controlled metabolic activities. This DBL microenvironment exhibits different pH behavior to bulk seawater, which can reduce the exposure of calcifying species to ocean acidification conditions. A low-cost time-domain dual-lifetime referencing (t-DLR) interrogation system and an optical fiber fluorescent pH sensor were developed for pH measurements in the DBL interface. The pH sensor utilized dual-layer sol-gel coatings of pH-sensitive iminocoumarin and pH-insensitive Ru(dpp)3-PAN. The sensor has a dynamic range of 7.41 (±0.20) to 9.42 ± 0.23 pH units (95% CI, T = 20 °C, S = 35), a response time (t90) of 29 to 100 s, and minimal salinity dependency. The pH sensor has a precision of approximately 0.02 pHT units, which meets the Global Ocean Acidification Observing Network (GOA-ON) "weather" measurement quality guideline. The suitability of the t-DLR optical fiber pH sensor was demonstrated through real-time measurements in the DBL of green seaweed Ulva sp. This research highlights the practicability of optical fiber pH sensors by demonstrating real-time pH measurements of metabolic-induced pH changes.

Preparation, Properties and Cell Biocompatibility of Room Temperature LCST-Hydrogels Based on Thermoresponsive PEO Stars.

A series of star and linear polymers based on a poly(ethylene oxide) core and poly(diethylene glycol ethyl ether acrylate) outer arms were synthesised by atom-transfer radical polymerization. The polydispersity of the polymers were low, showing good control of initiation and growth. They all showed lower critical solution (LCST) behaviour, and at 30% concentration most gelled at or below room temperature. The behaviour depended on the number and length of the arms, with the polymers with longer arms gelling at a lower temperature and producing stiffer gels. The shear modulus of the gels varied between 1 and 48 kPa, with the gelling temperature varying between 16 and 23 °C. Attempted cell cultures with the polymers proved unsuccessful, which was determined to be due to the high concentration of polymers needed for gelling.

Self-referencing optical fiber pH sensor for marine microenvironments.

This study presents the development of an optical fiber pH sensor based on evanescent wave absorbance for continuous pH measurements in marine microenvironments. The sensing layer consists of an optimized sol-gel matrix of tetraethoxysilane and dimethyldiethoxysilane, which substantially improves the entrapment efficiency of the pH indicator meta-cresol purple, leading to a long useable lifetime. The optical fiber pH sensor conforms to the Global Ocean Acidification Observing Network "weather" measurement quality guideline with precision of approximately 0.02 pH units, has a dynamic pHT range of 7.4-9.7 in seawater, a response time of 2.5-6.5 min and a useable lifetime of 7 days. The optical fiber pH sensor has additional advantages of being self-referencing, without the need of an external sensor reference, having a simple fabrication method and basic spectrometer instrumentation. The suitability of the optical fiber pH sensor was demonstrated in real-time measurements of the ecologically significant green seaweed Ulva sp. The optical fiber pH sensor monitored pH variations due to metabolic activity over 7 days within the seaweed canopy and 4 days within the diffusion boundary layer interface, demonstrating the suitability for measurements in marine microenvironments.

Synthesis of fluorinated phosphorus-containing copolymers and their immobilization and properties on stainless steel.

A series of fluorinated-phosphonic acid methacrylates were synthesized by free radical polymerization using heptadecafluorodecyl methacrylate (HDFDMA) and (dimethoxyphosphoryl) methyl methacrylate (DMPMM) monomers for potential application as anti-corrosion coatings. The dimethyl protecting groups were then hydrolyzed, giving phosphonic acid groups that are able to stably bind onto metal oxide surfaces. The copolymers were then immobilized as a monolayer film to the surface of 316L stainless steel by treatment of dilute solutions in trifluoroacetic acid for 30 minutes followed by rinsing. The surfaces were analyzed using various techniques and contact angles as high as 128° were recorded for some copolymer functionalized surfaces. Results also demonstrated that the polymer films proved stable to hydrolysis over several weeks of immersion in water.

Formation of a robust, double-walled LiMOF from an L-shaped di-substituted N-heterocyclic adamantane-based ligand.

The properties of adamantane render it an attractive building block towards the synthesis of robust frameworks. This work describes the synthesis of the L-shaped 1,3-bis(3'-carboxypyridine)adamantane (L1) ligand and the corresponding Li(i), Zn(ii) and Cu(ii) frameworks. Three topologically analogous Li(i) frameworks LiMOF12, LiMOF30 and LiMOF50 are reported, with calculated solvent accessible void volumes of 46, 43 and 36%, respectively. The reaction between the carboxylate groups of L1 and the Li(i) cations resulted in the formation of Li-carboxylate rods. The Li-carboxylate rods contributed to the formation of a double-walled MOF with large, open one dimensional channels. The synergistic effect of the double wall, lithium-carboxylate rods and the adamantane core itself, resulted in the formation of a robust network stable up to temperatures of 300-350 °C and a minimum of three months stability in air. Furthermore, complexation of L1 with Cu(BF4)2·H2O and Zn(CF3SO3)2 provided a 2D → 3D interpenetrated network containing a classic dimeric copper paddle-wheel SBU, and an infinite 1D chain which extended into a 3D structure facilitated by hydrogen-bonding interactions, respectively.

Effect of chitosan infiltration on hydroxyapatite scaffolds derived from New Zealand bovine cancellous bones for bone regeneration.

Hydroxyapatite (HA) derived from bovine bones garnered wider interest as a bone substitute due to their abundant availability as meat wastes and similarities in morphology and mineral composition to human bone. In our previous work, we developed an easy and reproducible method to prepare xenograft HA scaffolds from NZ bovine cancellous bones (BHA). However, the processing methodology rendered the material mechanically weak. The present study investigated the infiltration of chitosan (CS) into the bovine HA scaffolds (CSHA) to improve the mechanical properties of BHA. The presence of characteristic functional groups of HA and CS as detected by infrared spectroscopy confirmed the infiltration of CS into the BHA scaffolds. X-ray Diffraction study confirmed the presence of the hydroxyapatite phase in both BHA and CSHA scaffolds. SEM and µCT analyses showed the CSHA scaffolds presented adequate porosity and an interconnected porous architecture required for cell migration and attachment. CSHA scaffolds presented good thermal, chemical and structural stability while demonstrating sustained biodegradability in simulated body fluid. CSHA scaffolds presented mechanical properties significantly higher than the BHA scaffolds. CSHA scaffolds were biocompatible with Saos-2 osteoblast cells and supported cell proliferation significantly better than the BHA scaffolds indicating their potential in bone tissue engineering.

Tough polymeric hydrogels using ion-pair comonomers.

Hydrogels with excellent mechanical properties were synthesized by radical photo-polymerization of three different types of ion-pair comonomers (IPC), without requiring any chemical cross-linking agent. Insoluble gels formed only at a specific solution concentration range, which was unique to the particular salt. The gels changed properties after one day soaking in water, becoming less stiff and more extendible, but remained stable after that. Strains of up to 4000% were measured for one salt pair and ultimate stresses of up to 2.53 MPa for another. Self-healing properties were noted along with some recovery of creep, due to the non-covalent nature of the gel. These properties arise through a combination of electrostatic and hydrophobic interactions of the polymer chains. Immersion of the gels in salt solution screened the electrostatic interactions, resulting in dissolution of the gel.

The structure and Hirshfeld surface analysis of the salt 3-methacryl-amido-N,N,N-tri-methyl-propan-1-aminium 2-acryl-amido-2-methyl-propane-1-sulfonate.

The title salt, C10H21N2O+·C7H12NO4S-, comprises a 3-methacryl-amido-N,N,N-tri-methyl-propan-1-aminium cation and a 2-acryl-amido-2-methyl-propane-1-sulfonate anion. The salt crystallizes with two unique cation-anion pairs in the asymmetric unit of the ortho-rhom-bic unit cell. The crystal studied was an inversion twin with a 0.52 (4):0.48 (4) domain ratio. In the crystal, the cations and anions stack along the b-axis direction and are linked by an extensive series of N-H⋯O and C-H⋯O hydrogen bonds, forming a three-dimensional network. Hirshfeld surface analysis was carried out on both the asymmetric unit and the two individual salts. The contribution of inter-atomic contacts to the surfaces of the individual cations and anions are also compared.

Structure and Hirshfeld surface analysis of the salt N,N,N-trimethyl-1-(4-vinyl-phen-yl)methanaminium 4-vinyl-benzene-sulfonate.

In the title compound, the asymmetric unit comprises an N,N,N-trimethyl-1-(4-vinyl-phen-yl)methanaminium cation and a 4-vinyl-benzene-sulfonate anion, C12H18N+·C8H7O3S-. The salt has a polymerizable vinyl group attached to both the cation and the anion. The methanaminium and vinyl substituents on the benzene ring of the cation subtend angles of 86.6 (3) and 10.5 (9)° to the ring plane, while the anion is planar excluding the sulfonate O atoms. The vinyl substituent on the benzene ring of the cation is disordered over two sites with a refined occupancy ratio of 0.542 (11):0.458 (11). In the crystal, C-H⋯O hydrogen bonds dominate the packing and combine with a C-H⋯π(ring) contact to stack the cations and anions along the a-axis direction. Hirshfeld surface analysis of the salt and of the individual cation and anion components is also reported.

Gel actuators based on polymeric radicals.

Low-voltage electrochemical actuation of radical polymer gels has been demonstrated in an organic electrolyte. Polymer gels were prepared by post-modification of active-ester precursor gels with an amine-functionalised radical. A combination of few-layer graphene and multiwall carbon nanotubes gave high conductivity and improved actuation in the gels, with 32% linear actuation. The actuator system showed good stability over at least 10 cycles, showing its promise. The cycle time was several hours due to mass-transport limited transport of ions and solvent into the device.

A Design Strategy for Single-Stranded Helicates using Pyridine-Hydrazone Ligands and PbII.

The reactions of py-hz ligands (L1-L5) with Pb(CF3 SO3 )2 ⋅H2 O resulted in some rare examples of discrete single-stranded helical PbII complexes. L1 and L2 formed non-helical mononuclear complexes [PbL1(CF3 SO3 )2 ]⋅CHCl3 and PbL2(CF3 SO3 )2 ][PbL2CF3 SO3 ]CF3 SO3 ⋅CH3 CN, which reflected the high coordination number and effective saturation of PbII by the ligands. The reaction of L3 with PbII resulted in a dinuclear meso-helicate [Pb2 L3(CF3 SO3 )2 Br]CF3 SO3 ⋅CH3 CN with a stereochemically-active lone pair on PbII . L4 directed single-stranded helicates with PbII , including [Pb2 L4(CF3 SO3 )3 ]CF3 SO3 ⋅CH3 CN and [Pb2 L4CF3 SO3 (CH3 OH)2 ](CF3 SO3 )3 ⋅2 CH3 OH⋅2 H2 O. The acryloyl-modified py-hz ligand L5 formed helical and non-helical complexes with PbII , including a trinuclear PbII complex [Pb3 L5(CF3 SO3 )5 ]CF3 SO3 ⋅3CH3 CN⋅Et2 O. The high denticity of the long-stranded py-hz ligands L4 and L5 was essential to the formation of single-stranded helicates with PbII .

A mechanically strengthened polyacrylamide gel matrix fully compatible with electrophoresis of proteins and nucleic acids.

Polyacrylamide gel electrophoresis is a universal tool in a biochemist's toolkit for protein and nucleic acid separation and subsequent visualisation and analysis. The standard formulation of polyacrylamide gels consists of acrylamide (ACM) monomer crosslinked with bisacrylamide (MBA) which creates a gel with excellent sieving properties but which is mechanically fragile and prone to tearing during post-electrophoresis manipulations involved in visualisation and analysis. By adding a poly(ethylene oxide) macro-crosslinker to the standard gel formulation, we have created a tough gel matrix that can be used to fractionate proteins and nucleic acids by polyacrylamide gel electrophoresis. The protein and nucleic acid resolving capabilities and performance during staining and electroblotting of the tough gel matrix rivals that of conventional acrylamide/bisacrylamide gels. The tough gel matrix is resistant to tear and remarkably elastic, capable of stretching to over four times its original length before breaking, and represents a significant improvement over standard polyacrylamide gel formulations.

Hydroxyapatite-polymer biocomposites for bone regeneration: A review of current trends.

Bone tissue engineering has emerged as one of the most indispensable approaches to address bone trauma in the past few decades. This approach offers an efficient and a risk-free alternative to autografts and allografts by employing a combination of biomaterials and cells to promote bone regeneration. Hydroxyapatite (HA) is a ceramic biomaterial that mimics the mineral composition of bones and teeth in vertebrates. HA, commonly produced via several synthetic routes over the years has been found to exhibit good bioactivity, biocompatibility, and osteoconductivity under both in vitro and in vivo conditions. However, the brittle nature of HA restricts its usage for load bearing applications. To address this problem, HA has been used in combination with several polymers in the form of biocomposite implants to primarily improve its mechanical properties and also enhance the implants' overall performance by simultaneously exploiting the positive effects of both HA and the polymer involved in making the biocomposite. This review article summarizes the past and recent developments in the evolution of HA-polymer biocomposite implants as an "ideal" biomaterial scaffold for bone regeneration. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2046-2057, 2018.

Hyperelastic Tough Gels through Macrocross-Linking.

The wet and soft nature of hydrogels makes them useful as a mimic for biological tissues, and in uses such as actuators and drug delivery vehicles. For many applications the mechanical performance of the gel is critical, but gels are notoriously weak and prone to fracture. Free radical polymerization is a very powerful technique allowing for fine spatial and temporal control of polymerization, but also allows for the use of a wide range of monomers and mixtures. In this work, it is demonstrated that extremely tough and extensible hydrogels can be readily produced through simple radical polymerization of acrylamide or acrylic acid with a poly(ethylene oxide) macrocross-linker. These gels, with a water content of 85%, are extremely elastic with an extension much more than 15 000% at 9 MPa true stress. They can be compressed over 98% at a stress of 17 MPa. They are notch-insensitive, and the usual trouser tear test does not work because the tear simply does not propagate. This highly extensible nature seems to be related to very long chain lengths between cross-links and efficient incorporation of chains into the network.

Crystal structures of the polymer precursors 3-(2,5-dimeth-oxy-3,4,6-tri-methyl-phen-yl)propyl methacrylate and 3-(2,4,5-trimethyl-3,6-dioxo-cyclo-hexa-1,4-dien-yl)propyl methacrylate.

The closely related title compounds, 3-(2,5-dimeth-oxy-3,4,6-tri-methyl-phen-yl)propyl methacrylate, C18H26O4 (I), and 3-(2,4,5-trimethyl-3,6-dioxo-cyclo-hexa-1,4-dien-yl)propyl methacrylate, C16H20O4 (II), are monomers suitable for the preparation of redox polymers. They consist of a propyl-methacrylate group and three methyl substituents on di-meth-oxy-benzene and quinone cores, respectively. Both crystal structures feature weak C-H⋯O hydrogen bonds and C-H⋯π(ring) contacts between methyl groups and the six-membered rings.

Cyclodextrin-polyhydrazine degradable gels for hydrophobic drug delivery.

An injectable and biocompatible hydrogel system was designed for hydrophobic drug delivery. This hydrogel consisted of degradable polymers with cyclodextrin (CD) moieties. CD groups were used to increase the solubility of a hydrophobic molecule (nicardipine) in an aqueous solution through the formation of the inclusion complex. Two sets of gels were prepared by mixing oxidized dextran (DA) and CD functionalized polyhydrazine (PH) at physiological conditions and different level of crosslinking via hydrazone bonds. Cytotoxicity studies on the gels and their components confirmed the biocompatibility of these materials. Gel-30 with higher crosslinking density showed a two week degradation period whereas this period was 10days for gel-10, with lower crosslinking density, to complete degradation. The results from swelling tests and rheological measurements were also found to be dependent on crosslinking density of the hydrogels. Release profile of the hydrogel displayed a sustained release of nicardipin up to 6days for gel-30 and a 4day release with initial burst release for gel-10.

Strong poly(ethylene oxide) based gel adhesives via oxime cross-linking.

There is a demand for materials to replace or augment the use of sutures and staples in surgical procedures. Currently available commercial surgical adhesives provide either high bond strength with biological toxicity or polymer and protein-based products that are biologically acceptable (though with potential sensitizing potential) but have much reduced bond strength. It is desirable to provide novel biocompatible and biodegradable surgical adhesives/sealants capable of high strength with minimal immune or inflammatory response. In this work, we report the end group derivatization of 8-arm star PEOs with aldehyde and amine end groups. Gels were prepared employing the Schiff-base chemistry between the aldehydes and the amines. Gel setting times, swelling behavior and rheological characterization were carried out for these gels. The mechanical-viscoelastic properties were found to be directly proportional to the crosslinking density of the gels, the 10K PEO gel was stiffer in comparison to the 20K PEO gel. The adhesive properties of these gels were tested using porcine skin and showed excellent adhesion properties. Cytotoxicity studies were carried out for the individual gel components using two different methods: (a) Crystal Violet Staining assay (CVS assay) and (b) impedance and cell index measurement by the xCELLigence system at concentrations >5%. Gels prepared by mixing 20% w/w solutions were also tested for cytotoxicity. The results revealed that the individual gel components as well as the prepared gels and their leachables were non-cytotoxic at these concentrations. STATEMENT OF SIGNIFICANCE: This work presents a new type of glue that is aimed at surgery applications using a water soluble star shaped polymer. It show excellent adhesion to skin and is tough and easy to use. We show that it is very biocompatible based on tests on live human cells, and could therefore in principle be used for internal surgery. Comparison with other reported and commercial glues shows that it is stronger than most, and does not swell in water to the same degree as many other water based bioadhesives.

Structures and packing of ferrocenylmethyl methacrylate and ferrocene-1,1'-diylbis(methylene) dimethacrylate.

Electroactive metallocene polymers are of interest due to the possibility that they offer a muscle-like response, and in gel systems very large volume changes are possible. The ferrocenyl moiety exhibits physical and electrochemical stability of the neutral and oxidized forms and could be a candidate for use as the redox-active group in these materials. The title compounds, [Fe(C5H5)(C10H11O2)], (I), and [Fe(C10H11O2)2], (II), comprise a typical ferrocene core with coplanar and approximately eclipsed cyclopentadienyl (Cp) rings. In (I), there is a single methyl methacrylate substituent, with the other Cp ring unsubstituted. In (II), a methyl methacrylate substituent on each Cp ring completes the structure. In both compounds, there is an s-trans geometry of the vinyl and carbonyl components of the methacrylate group. Inversion dimers formed through C-H...O contacts dominate the crystal packing of both molecules. Weak C-H...π(ring) contacts and, in the case of (I), an unusual C-H...π(alkene) contact further stabilize the structures.

Structure and packing of aminoxyl and piperidinyl acrylamide monomers.

The closely related title compounds, 4-acrylamido-2,2,6,6-tetramethylpiperidine-1-oxyl, C12H21N2O2, (I), and N-(2,2,6,6-tetramethylpiperidin-4-yl)acrylamide monohydrate, C12H22N2O·H2O, (II), are important monomers in the preparation of redox-active polymers. They comprise an acrylamide group of the usual s-cis configuration appended to a 2,2,6,6-tetramethyl-substituted piperidine-1-oxyl radical or a piperidinyl chair, respectively. The adjacent amide and piperidinyl H atoms are approximately trans across the C-N bond. The packing in (I) is dominated by N-H...O hydrogen bonds; these are supported by C-H...O contacts to form an R2(1)(6) ring repeat, a motif which has been observed in other acrylamide structures. In (II), hydrogen bonds are again key to the packing arrangements. In this case, the incorporated solvent water molecule acts as an acceptor through its O atom and as a donor through both H atoms, binding three adjacent piperidinylacrylamide molecules into layers. In both structures, weak C-H...O contacts involving the piperidinyl methyl H atoms and a proximal acrylamide carbonyl O atom extend the structure in the third dimension.

Reducing the Oxidation Level of Dextran Aldehyde in a Chitosan/Dextran-Based Surgical Hydrogel Increases Biocompatibility and Decreases Antimicrobial Efficacy.

A highly oxidized form of a chitosan/dextran-based hydrogel (CD-100) containing 80% oxidized dextran aldehyde (DA-100) was developed as a post-operative aid, and found to significantly prevent adhesion formation in endoscopic sinus surgery (ESS). However, the CD-100 hydrogel showed moderate in vitro cytotoxicity to mammalian cell lines, with the DA-100 found to be the cytotoxic component. In order to extend the use of the hydrogel to abdominal surgeries, reformulation using a lower oxidized DA (DA-25) was pursued. The aim of the present study was to compare the antimicrobial efficacy, in vitro biocompatibility and wound healing capacity of the highly oxidized CD-100 hydrogel with the CD-25 hydrogel. Antimicrobial studies were performed against a range of clinically relevant abdominal microorganisms using the micro-broth dilution method. Biocompatibility testing using human dermal fibroblasts was assessed via a tetrazolium reduction assay (MTT) and a wound healing model. In contrast to the original DA-100 formulation, DA-25 was found to be non-cytotoxic, and showed no overall impairment of cell migration, with wound closure occurring at 72 h. However, the lower oxidation level negatively affected the antimicrobial efficacy of the hydrogel (CD-25). Although the CD-25 hydrogel's antimicrobial efficacy and anti-fibroblast activity is decreased when compared to the original CD-100 hydrogel formulation, previous in vivo studies show that the CD-25 hydrogel remains an effective, biocompatible barrier agent in the prevention of postoperative adhesions.