There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

http://nathan.instras.com/ResearchProposalDB/doc-109.pdf

A review on polymer nanofibers by electrospinning and their applications in nanocomposites

New generations of synthetic biomaterials are being developed at a rapid pace for use as three-dimensional extracellular microenvironments to mimic the regulatory characteristics of natural extracellular matrices (ECMs) and ECM-bound growth factors, both for therapeutic applications and basic biological studies. Recent advances include nanofibrillar networks formed by self-assembly of small building blocks, artificial ECM networks from protein polymers or peptide-conjugated synthetic polymers that present bioactive ligands and respond to cell-secreted signals to enable proteolytic remodeling. These materials have already found application in differentiating stem cells into neurons, repairing bone and inducing angiogenesis. Although modern synthetic biomaterials represent oversimplified mimics of natural ECMs lacking the essential natural temporal and spatial complexity, a growing symbiosis of materials engineering and cell biology may ultimately result in synthetic materials that contain the necessary signals to recapitulate developmental processes in tissue- and organ-specific differentiation and morphogenesis.

https://sisu.ut.ee/sites/default/files/quantum/files/synthetic_biomaterials_as_instructive_extracellular_microenvironments_for_morphogenesis_in_tissue_engineering_lutolf_m.p_hubbell_j.a_2005_0.pdf

Synthetic biomaterials as instructive extracellular microenvironments for morphogenesis in tissue engineering

Electrospinning: a fascinating fiber fabrication technique.

Electrospinning is a highly versatile method to process solutions or melts, mainly of polymers, into continuous fibers with diameters ranging from a few micrometers to a few nanometers. This technique is applicable to virtually every soluble or fusible polymer. The polymers can be chemically modified and can also be tailored with additives ranging from simple carbon-black particles to complex species such as enzymes, viruses, and bacteria. Electrospinning appears to be straightforward, but is a rather intricate process that depends on a multitude of molecular, process, and technical parameters. The method provides access to entirely new materials, which may have complex chemical structures. Electrospinning is not only a focus of intense academic investigation; the technique is already being applied in many technological areas.

Electrospinning: A Fascinating Method for the Preparation of Ultrathin Fibers

A biopolymer film and other materials that exhibit nonlinear optical (NLO) properties and a method for making this film. Alignment of biopolymer molecules, which is required for NLO phenomena, is achieved by application of an electric field parallel to the surface of a biopolymer solution as the film is formed. In one embodiment, a solution of poly(γ-benzyl-L-glutamate), PBLG, in methylene chloride is employed. Upon application of an electric field, laminar structures perpendicular to both the field direction and to the film surface are formed. These ordered structures are captured in the film upon evaporation of the biopolymer solvent.

Method of making biopolymer-based nonlinear optical materials

Diblock copolymers of acetylene and styrene were prepared by treating Ti(OBu)4 with polystyryl lithium followed by reaction with acetylene. Reliable evidence for the formation of block copolymers was derived from dual radiotagging experiments.

Towards the synthesis of electroactive block copolymers via anionic-to-Ziegler-Natta transformation reactions

Composites of trans‐polyacetylene (t‐(CH)x) and low density polyethylene (LDPE) have been studied by Electron Nuclear Double Resonance (ENDOR), Electron Nuclear Nuclear Triple Resonance (TRIPLE), and Electron Spin Echo (ESE) spectroscopies. The results are compared with analogous studies conducted on pure t‐(CH)x films and on samples containing mixtures of cis/trans isomers. ENDOR measurements indicate that the paramagnetic electron in all materials studied resides in a pure π molecular orbital. The measured spin densities at carbon of ‖0.06 and ‖0.02‖ for two inequivalent 13C nuclei along the polyene backbone imply that the defect spin density is spread over a polyene segment length on the order of 70 A. The absolute magnitude of the spin densities, +0.06 and −0.02, obtained by TRIPLE indicate the existence of electron Coulomb correlation effects. Detailed analysis of ENDOR spectra places strict limits on the allowable soliton diffusion coefficient. ENDOR, ESE phase memory (TM), and ESE spin‐lattice (T1e...

Study of polyacetylene and composites of polyacetylene/polyethylene by electron nuclear double resonance, electron nuclear nuclear triple resonance, and electron spin echo spectroscopies

Ion implantation causes an increase by ~14 orders of magnitude in the electricalconductivity of normally insulating polymers such as polyacrylonitrile (PAN), poly(2,6 dimethyl phenylene-oxide) (PPO), and poly (pphenylene sulfide) (PPS), after ion implantation with Br at fluences of 3 × 10 15 ions/cm 2 . The temperature dependence of the dc conductivity was measured in the range 23 〈 T 〈 293 K and results show an exponential law σ ~ exp(−T o /T) a ) for PAN, PPO and PPS with α =1/2, suggesting a one-dimensional hopping mechanism. The temperature dependence of the thermoelectric power (TEP) identifies the sign of the dominant carrier type. The TEP exhibits linear metallic behavior, with small magnitudes (~3μV/K), and shows Br implantation to yield p-type material in PPS and n-type material in PAN with extremely low values of mobility (〈 10 −3 cm 2 /V sec) and correspondingly very high values of the carrier concentration estimated to be 5 × 10 22 cm -3 . Results are also reported for the frequency dependence of the AC conductivity and of similarly implanted PPS and PAN samples.

Implantation-induced conductivity of polymers.

Bacterial and fungal pathogens have caused serious problems to the human health. This is particularly true for untreatable infectious diseases and clinical situations where there is no reliable treatment for infected patients. To increase the antimicrobial activity of materials, we introduce silver nanoparticle (NP) patches in which the NPs are incorporated to the surface of smooth and uniform poly(acrylic acid) (PAA) nanofibers. The PAA nanofibers were thermally crosslinked with ethylene glycol via heat treatment through a mild method. The characterization of the resulting PAA-silver NP patches was done using scanning electron microscopy (SEM), UV spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). To demonstrate the antimicrobial activity of PAA, we incorporated the patches containing the silver NPs into strains of fungi such as Candida albicans (C. albican) and bacteria such as Methicillin-resistant Staphylococcus aureus (MRSA). The PAA-silver fibers achieved zones of inhibition against C. albicans and MRSA indicating their antimicrobial activity against both fungi and bacteria. We conclude that silver NP patches exhibited multiple inhibitory actions for the interruption and blockage of activity fungal and bacterial strains, which has the potential as an antimicrobial agent in infectious diseases. Moreover, the proposed material has the potential to be used in antimicrobial textile fabrics, food packaging films, and wound dressings.

Gary E. Wnek

Papers

Method of making biopolymer-based nonlinear optical materials

Towards the synthesis of electroactive block copolymers via anionic-to-Ziegler-Natta transformation reactions

Study of polyacetylene and composites of polyacetylene/polyethylene by electron nuclear double resonance, electron nuclear nuclear triple resonance, and electron spin echo spectroscopies

Implantation-induced conductivity of polymers.

Antimicrobial Activity of Silver Containing Crosslinked Poly(Acrylic Acid) Fibers