Thin Gelatin Films Research Articles

Controlled Release of DSBP from Genipin-Crosslinked Gelatin Thin Films

Controlled release of a marker drug, 4,4′-bis(2-sulfostyryl) biphenyl (DSBP) from genipin crosslinked gelatin thin films, with application to drug delivery by transdermal patches is studied in this paper. A simple method for fabrication of nano-thin films, using basic lab equipment is introduced. This method consists of two steps: dipping of the substrate in a deposition solution, followed by centrifugation of the substrate. Also, swelling and drug release from thin films is modeled, using the Fick's second law of diffusion. The effect of genipin concentration on release of DSBP molecules from thin films is investigated, experimentally and numerically. The results show that controlled release of DSBP from the genipin-crosslinked gelatin thin films is achieved, using various concentrations of genipin in gelatin.

OPTICAL DATA STORAGE IN ACID RED DYES

High-density optical data storage is a current field gaining importance where research work is done in abundance to bring about holographic CDs to light. Dye-doped gelatin films are promising candidates as recording materials for holographic data storage because of the ease of preparation and low cost. In this report we suggest some acid red dyes as useful recording materials for optical data storage. Acid red dyes namely Acid Red 73 and Acid Red 114 that are completely water-soluble are used to sensitize gelatin thin films for data storage. These dyes have their absorption peak around 514 nm. Two coherent beams of Argon ion laser (514.5 nm) are used to form the grating in the dye-sensitized gelatin films. The grating formed is found to be permanent. The diffraction efficiency of each material as a function of different parameters like dye concentration, writing beam intensities and their ratios and spatial frequency has been studied and presented. An attempt to store data in the sample has been made.

Molecular mobility in water and glycerol plasticized cold- and hot-cast gelatin films

The molecular mechanisms that control functionality in gelatin films are poorly understood. We have used phosphorescence emission from erythrosin covalently attached to lysine residues to investigate the effect of plasticizer and physical cross-links on molecular mobility and oxygen diffusion in amorphous gelatin thin films. Phosphorescence emission energy and red-edge effects, which monitor the extent of matrix relaxation during the ∼0.5 ms probe lifetime, were modulated only slightly by either water or glycerol; the extent of matrix relaxation, however, was significantly greater in cold-cast films with, than in hot-cast films without physical cross-links. The phosphorescence intensity was well described using a stretched exponential in which the lifetime and the stretching factor, a measure of the lifetime heterogeneity, were the fit parameters. Lifetimes, which provide a measure of the rate of matrix collisional quenching, were essentially unaffected by hydration from 0 to 50% RH, slightly decreased from 50 to 84% RH, and greatly decreased at higher RH; rates of matrix collisional quenching were higher in cold-cast than in hot-cast films at all RH values. Glycerol, varied up to 50% by weight of gelatin, only slightly increased the rate of matrix collisional quenching. The rates of oxygen diffusion were higher in cold-cast than hot-cast films at 75 and 84% RH; there was no detectable oxygen diffusion at any glycerol content in dry films. Physical cross-links thus actually increased the molecular mobility of gelatin on the millisecond time scale and water and glycerol, despite their similarity as hydrogen-bonding molecules, had quantitatively different effects on the gelatin mobility.

One-Step Multilevel Microfabrication by Reaction−Diffusion

A new experimental technique is described that uses reaction--diffusion phenomena as a means of one-step microfabrication of complex, multilevel surface reliefs. Thin films of dry gelatin doped with potassium hexacyanoferrate are chemically micropatterned with a solution of silver nitrate delivered from an agarose stamp. Precipitation reaction between the two salts causes the surface to deform. The mechanism of surface deformation is shown to involve a sequence of reactions, diffusion, and gel swelling/contraction. This mechanism is established experimentally and provides a basis of a theoretical lattice-gas model that allows prediction surface topographies emerging from arbitrary geometries of the stamped features. The usefulness of the technique is demonstrated by using it to rapidly prepare two types of mold for passive microfluidic mixers.

Effect of fast neutrons on dielectric properties of pure and gelatin doped-poly (vinyl alcohol) films

Cast thin films of pure and gelatin doped poly(vinyl alcohol) (PVA) with concentrations of 2, 5, 7, 10, and 15 wt% were prepared and subjected to fast neutron fluences in the range of 105–108 n/cm2. The dielectric constant (e′), dielectric loss tangent (tanδ) and a.c. electrical conductivity (σa,c) were investigated as a function of field frequency and temperature for all samples before and after irradiation. A clear glass transition peak was observed in e′(T) and tanδ(T) curves. The irregular shift in the position of the glass transition temperature (Tg) in tanδ spectra with increasing neutron fluence can be attributed to either degradation or the predominance of the crosslinking process. The electric dipole moment and activation energy were calculated for pure and gelatin doped PVA samples before and after neutron irradiation.

Measuring the Elastic Properties of Thin Polymer Films with the Atomic Force Microscope

The elastic properties of thin gelatin films were investigated with the atomic force microscope (AFM). The degree of swelling and thus the softness of the gelatin can be tuned by immersing it in mixtures of propanol and water. Therefore, we have chosen gelatin films as a model system to characterize the measurement of elasticity of thin and soft samples. The major aim of this study was to investigate the influence of the film thickness on the apparent elastic (Young's) modulus. Thus, we prepared wedge-shaped samples with a well-defined thickness of up to 1 μm. The Young's modulus of our samples was between 1 MPa and 20 kPa depending on the degree of swelling. The elasticity was calculated by analyzing the recorded force curves with the help of the Hertz model. We show that the calculated Young's modulus is dependent on the local film thickness and the applied loading force of the AFM tip. Thus, the influence of the hard substrate on the calculated softness of the film can be characterized as a function of...

Quadratic electro-optic effects in bacteriorhodopsin: Measurement of γ(−ω;0,0,ω) in dried gelatin thin films

Quadratic electro-optic effects (dc or low frequency Kerr effect) of bacteriorhodopsin dispersed in dried gelatin thin films are examined in the near resonance region at three wavelengths: 633, 647, and 676 nm. The films show relatively large quadratic electro-optic effects compared to other molecular dispersed systems. The purple membrane is fixed within the polymerized gelatin matrix, and we show that the electronic contribution to γ dominates over possible orientational contributions. At 676 nm, the quadratic electro-optic coefficient s1133(−ω;0,0,ω) is 6.7×10−20 m2/V2 and the third order nonlinear susceptibility χ1133(3)(−ω;0,0,ω) is 7.0×10−13 cm4 statCoulomb−2, with both values obtained for a protein concentration of 6.9×1018 cm−3. The orientationally averaged second molecular hyperpolarizability 〈γ(−ω;0,0,ω)〉 determined from the quadratic electro-optic coefficients at 676 nm assuming an Onsager ellipsoidal local field factor is (10.8±5.1)×10−32 cm7 statCoulomb−2 [(1.34±0.63)×10−56 F3 m4 C−2]. The 〈γ(−ω;0,0,ω)〉 value increases roughly tenfold when the probe wavelength is decreased to 633 nm. The behavior of γ(−ω;0,0,ω), when fit to a two-state model, predicts that γ(−ω;0,0,ω) is strongly enhanced via type III processes. Thus, the magnitude of γ(−ω;0,0,ω) is dominated by a term (Δμ102×μ102)/(ω10−ω)3, where Δμ10 is the change in dipole moment, μ10 is the transition moment, and ω10 is the transition energy of the lowest-lying allowed 1Bu*+-like π,π* state. We calculate that Δμ10 is 12.8±1.2 D, in good agreement with previous Stark and two-photon experimental values. Time-dependent Hartree–Fock methods based on the MNDO Hamiltonian yield reasonable agreement with experiment, underestimating γ(−ω;0,0,ω) by factors of only 2–4, with the error increasing as the frequency approaches resonance.

Nanotribology on a polymer network film

Scanning force microscopy (SFM) of topography, frictional force, and stiffness on thin gelatin films reveals an entire spectrum of tribological behavior. Images display two distinct phases of gelatin whose characteristics relate to the degree of crystallinity. Dissimilar regimes of velocity- and load-dependent friction and wear on each phase indicate glassy, rubbery, or melt behavior. Of fundamental importance is the finding that energy transferred to the film in the vicinity of the sliding SFM microasperity modifies film response. Moderate frictional heating melts the highly crystalline phase, but reversibly induces rubbery behavior on the partially amorphous phase. More extreme frictional heating melts the latter and allows the liberated molecules to reassociate irreversibly into the highly crystalline phase. This relatively slow process (minutes) is imaged in real time on the submicron scale. Relaxation from rubbery to glassy behavior upon termination of perturbative scanning is extremely slow (hours) and also is characterized in frictional images. However, in this case the imaging process itself hastens the relaxation, apparently by providing energy to activate some relaxational processes.

Imaging soft samples with the atomic force microscope: gelatin in water and propanol

We have imaged mica coated with thin gelatin films in water, propanol, and mixtures of these two liquids by atomic force microscopy (AFM). The elastic modulus (Young's modulus) can be tuned from 20 kPa to more than 0.1 GPa depending on the ratio of propanol to water. The resolution is best in pure propanol, on the order of 20 nm, and becomes worse for the softer samples. The degradation in resolution can be understood by considering the elastic indentation of the gelatin caused by the AFM tip. This indentation becomes larger and thus the contact area becomes larger the softer the sample is. Therefore this study may be used to estimate the resolution to be expected with an AFM on other soft samples, such as cells. Nondestructive imaging was possible only by imaging at forces < 1 nN. This was difficult to achieve in contact mode because of drift in the zero load deflection of the cantilever, supposedly caused by temperature drift, but straightforward in tapping mode.

A distributed optical-fibre sensing system for multi-point humidity measurement

Abstract A novel multi-point distributed humidity-sensing system has been constructed based on the principle of using the absorption spectrum of a colorimetric reagent (cobalt chloride) immobilized on the surface of the core of a multimode optical fibre by employing a thin gelatin film. Two-wavelength detection is employed to provide intensity referencing. Light attenuation at the reference wavelength is only 0.2 dB. The basic design, construction and testing of an experimental sensor in the humidity region 20–80% RH and temperature range 25–50 °C is described. Resolution can be better than 2% RH and the time constant is about one second. Repeatability is at least as good as the resolution of measurement. A two-wavelength optical time-domain reflectometer (OTDR) has been developed and a four-sensor network has been built. The resolution of measurement on the network can be better than 4% RH, but because of noise in the OTDR the resolution value is dependent on the averaging time in the instrument.

Optical Limiting in Chromophore-Doped Gelatin Thin Films

AbstractTo develop optical power limiting thin films prepared from water-soluble materials, we have prepared chromophore-doped gelatin thin films. Thin films of gelatin were prepared by spin coating followed by annealing. We also prepared thin films doped with the water-soluble chromophore copper phthalocyanine sodium tetrasulfonate. The films were characterized by film profilometry and optical absorption spectroscopy. Optical power limiting measurements of these films, as well as comparisons with aqueous solution and gels were performed.

Probing Biopolymer Films with Scanning Force Methods

Scanning force microscopy of thin gelatin films on mica reveals two distinct film components with characteristic frictional, morphological and adsorptive signatures. A high-friction film 1–4 nm thick completely wets the mica surface, while a low-friction minority component is present primarily as porous islands on top of the high-friction layer. Additional domains of extremely high friction within the majority component are detected in frictional images obtained with a blunt, gelatin-covered tip; no corresponding topographic differences are imaged. A high-force scanning procedure remarkably transforms the majority component into the low-friction phase if a sufficient amount of water is present in or on the film. The nanostructure of both components is imaged using a nanometer-scale asperity of gelatin attached to the SFM tip. The anticipated network structure of gelatin is observed on the high-friction majority phase. The low-friction phase is interpreted as moieties of intramolecularly-folded gelatin, with thickness (1.5±0.2 nm) equal to the diameter of the collagen-fold triple helix, containing substantial structural water.

Crystalline Structure and Moisture Effects on Deformation Mechanisms of Gelatin Films Under Mode I Stress Field

AbstractCrazing and shear-deformation phenomena are found in thin gelatin films. The gelatin crystallinity and relative humidity affect these deformation mechanisms significantly. A deformation map of gelatin films at low strain rate is established.

生体組織とエキシマーレーザー

Laser-tissue interactions have been investigated through UV-Visible optical absorption, Fourier Transform Infrared Spectroscopy (FTIR) and Electron Micro Probe Analysis (EPMA). Gelatin thin films and cow thighbone were irradiated by KrF excimer and CO2 lasers and 3 excimer lasers (ArF, KrF and XeCl), respectively.In the case of gelatin, a broad absorption band was observed at around 280 nm by KrF excimer laser irradiation, although no absorption band was observed by CO2laser irradiation. From the result of FTIR measurements, it was clear that this band arised from cutting of C-N and C=0 bonds in polypeptide chain.The result of EPMA showed that P atoms were more spattered than Ca atoms from the surface of cow thighbone by only ArF laser irradiation.

Discrimination of two fibroblast progenitor populations in early explant cultures of hamster gingiva

Numerous metabolic studies have demonstrated heterogeneity of fibroblast populations in culture, yet little is known about the structure of fibroblast populations in adult tissues in vivo. To determine if populations of both cycling and non-cycling cells are present in gingiva, hamsters were labelled with [3H]-thymidine to label cycling cells in vivo, and explanted biopsies were subsequently incubated with bromodeoxyuridine to label cycling cells in vitro. Cycling cells were identified by combined immunohistochemistry and radioautography. Fibroblasts were recognized by the presence of vimentin and the absence of keratin as determined by immunofluorescence. The largest proportion of cells were double-labelled with [3H]-thymidine and bromodeoxyuridine (43.8%) indicating the presence of actively cycling populations that maintained their proliferative status upon explanation. Cultures also exhibited a second population of cells labelled only with bromodeoxyuridine (38.7%) that did not cycle in vivo, but retained the capacity for proliferation in vitro. However, limiting dilution analysis of single-cell suspensions revealed only a single class of progenitors capable of forming large colonies in vitro. Approximately 1 in 190 plated cells was capable of colony-formation, indicating that, upon explanation, a subset of the cycling cells in vitro exhibits extensive proliferative capacity. There was also a small population of cells unlabeled with either [3H]-thymidine or bromodeoxyuridine (9.4%) that appeared to be terminally differentiated. Different substrates, including glass and thin films of gelatin and collagen, did not significantly alter the fraction of cells labelled with [3H]-thymidine. These data demonstrate the existence of 2 separate progenitor-cell populations with different capacities for proliferation in vivo and in vitro.

Integration of holographic optical elements with polymer gelatin waveguides on GaAs, LiNbO_3, glass, and aluminum

We have observed waveguiding in thin films of polymer gelatin on GaAs, LiNbO(3), glass, and aluminum substrates. A graded-index profile can be induced in the gelatin layer and tuned by wet processing. This makes it possible to form waveguides on any smooth surface. Locally sensitizing the gelatin waveguide with ammonium dichromate allows us to integrate single and multiplexed gratings on the same substrate to perform various functions for optical interconnects and signal processing. A waveguide grating coupler that converts free-space TEM(00) laser light to a two-dimensional spherical guided wave with 50 degrees angle of divergence has also been demonstrated. An optical clock distribution network on wafer-scale integrated circuits is feasible with this new technology.

Methylene blue sensitized gelatin as a photosensitive medium for conventional and polarizing holography

The properties of thin gelatin films sensitized with a dye (methylene blue) when used as a holographic material are discussed. On illumination the excited dye molecule changes its structure giving a colorless molecule. The higher rate of bleaching and therefore the higher diffraction efficiency of the developed phase gratings are obtained in an oxygen-free atmosphere. Furthermore, the light absorption probability of the dye molecules depends on its position with respect to the electric vector of the light, with the result that the exposed part of the dye becomes dichroic when illuminated with linearly polarized light. This result allows the use of this material for polarizing holography.

Schistosoma mansoni: Histological localization of gelatinase in the preacetabular glands of cercariae

Proteolytic activity was demonstrated in secretions from the preacetabular glands of cercariae of Schistosoma mansoni. Thin gelatin film substrates were lysed by living cercariae stimulated to penetrate by application on the films of skin surface lipid. Lysis was directly related to number of cercariae, time, and temperature of incubation and pH of the medium. Gelatinase activity in unfixed frozen sections of cercariae incubated on the gelatin films was in the preacetabular glands which are the source of the secretion emptied into skin during penetration. Protease activity, therefore, appears to be related to penetration. The schistosome larvae which made the penetration attempt satisfied the accepted criteria for schistosomules, and therefore appeared to have transformed into schistosomules even though they did not successfully penetrate anything.

Laser with a waveguide-type traveling-wave ring resonator

Laser emission was obtained from rhodamine 6G in a traveling-wave ring resonator. The excitation was provided by the second-harmonic of Nd laser radiation. The ring resonator was in the form of a thin gelatin film on a glass rod. The concentration of rhodamine 6G in this film was 10–3–10–2 mole/liter.

Cytochemical demonstration of proteolytic activity of human and rat spermatozoa.

Summary. Proteolytic activity was demonstrated around the acrosomes of intact sperm cells with a simple cytochemical method using a gelatin substrate. The proteolytic activity was localized to the acrosomal region of both rat and human spermatozoa. Not all sperm cells showed the same digestive capacity in each sample studied. Rabbit sperm acrosomes have a denuding effect on the zona pellucida, as Srivastava, Adams & Hartree (1965a, b) have demonstrated. This finding suggested that penetration of a spermatozoon through the zona pellucida is mediated, at least in part, by the presence of hydrolytic enzymes. Recently, Stambaugh & Buckley (1969) found hyaluronidase and a 'trypsin-like' enzyme in acrosomal extracts of rabbit spermatozoa; apparently the proteolytic enzyme is mainly responsible for the ability to penetrate the zona pellucida in this species. The localization of proteolytic activity in intact sperm cells was accomplished by Gaddum & Blandau (1970), using an india-ink gelatin substrate method. The technique promised to be simple enough to allow further studies and even semiquantitative estimations of protease activity; however, in trying to repeat the method, we found that it gave inconstant results and obscured a great deal of the cytological details of the cells under study, nor was it possible to obtain clear-cut 'digestion halos' around the acrosomes, as illustrated in Gaddum & Blandau's original publication. We therefore attempted to develop a method that could clearly show proteolytic activity against gelatin, without significantly obscuring cytological detail. Human ejaculates and rat epididymal spermatozoa were used. The sperma¬ tozoa were washed twice in Hanks' solution with sodium bicarbonate 0-35 g/1 at a final pH of 7-4. The gelatin solution (5%) was prepared in a Veronalacetate buffer at a different pH ranging from 7-4 to 9. Washed spermatozoa were spread evenly on a glass slide; after 2 min at room temperature, smears were immersed once in the gelatin solution kept at about 28 to 30° C; the slides were set in a vertical position for a few minutes to obtain a thin gelatin film. After blotting the bottom edge, the slides were allowed to gel in a horizontal position in a humid chamber at room temperature from 12 to 48 hr. After incubation,