Bacterial cellulose nanocomposites: An all-nano type of material.

Bacterial cellulose (BC) is a fascinating polymer with a three-dimensional structure formed by nanofibers of pure cellulose, synthesized by some bacteria and organized as a coherent network. Its biocompatibility and remarkable mechanical properties have promoted scientific interest for its use in a variety of applications including biomedical, electrical, among others. However, it is the possibility of incorporating nanosized materials into the coherent 3-D network structure displayed by BC what has propelled multiple investigations on the development of BC nanocomposites for different applications. Here we report the different methods and techniques used so far for the BC nanocomposites production. We have focused on the processing techniques that allow the incorporation of functional nanoreinforcements, nanofillers and additional phases without disturbing the original network structure, leading to the formation of nanomaterials. Processing methods, resulting structure-property relationships and potential applications of these novel nanocomposites are discussed and showcased as a fair example of integrated design and manufacture of materials.

Characterization of the mechanical properties of tough biopolymer fibres from the mussel byssus of Aulacomya ater.

Byssus fibres are tough biopolymer fibres produced by mussels to attach themselves to rocks. In this communication, we present the mechanical properties of the byssus from the South American mussel Aulacomya ater which have not been previously reported in the literature. The mechanical properties of the whole threads were assessed by uniaxial tensile tests of dry and hydrated specimens. Elastoplastic and elastomeric stress-strain curves were found for byssal threads from A. ater in the dry and hydrated state, respectively. The results obtained from mechanical tests were modelled using linear, power-law-type and Mooney-Rivlin relationships. These methods for dealing with tensile measurements of mussel byssus have the potential to be used with other stretchy biomaterials.

Molecular dynamics of carrageenan composites reinforced with Cloisite Na+ montmorillonite nanoclay.

Nanocomposites comprising biodegradable carrageenan and glycerol (KCg) as the host polymer, with different contents of natural montmorillonite (MMT) as filler, were prepared by a solution casting process. Different techniques have been used to determine the interaction/behavior among the different components of the samples such as Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Transmission electron microscope (TEM) and, mainly, Dielectric relaxation spectroscopy (DRS). FTIR indicates hydrogen interaction between carrageenan matrix and silicate that is confirmed by the XRD data indicating some kind of carrageenan intercalation between the MMT layers. A rather homogenous distribution of MMT into KCg matrix were observed using transmission electron microscopy. The MMT effect on the molecular mobility at the glass transition was studied by dielectric relaxation spectroscopy. The MMT addition resulted in a slower relaxation and a wider distribution of the relaxation times. The fragility index, m, increased upon MMT incorporation, which may be attributed to a reduction in mobility chains, due to the MMT confinement of the KCg network. In addition, the apparent activation energy associated with the relaxation dynamics of the chains at Tg increased with the MMT content. The modified films developed in this paper could be used to prepare biodegradable and edible packaging films and films for biomedical applications with improved mechanical and good dielectric response.

Monitoring molecular dynamics of bacterial cellulose composites reinforced with graphene oxide by carboxymethyl cellulose addition.

Broadband Dielectric Relaxation Spectroscopy was performed to study the molecular dynamics of dried Bacterial Cellulose/Carboxymethyl Cellulose-Graphene Oxide (BC/CMC-GO) composites as a function of the concentration of CMC in the culture media. At low temperature the dielectric spectra are dominated by a dipolar process labelled as a ß-relaxation, whereas electrode polarization and the contribution of dc-conductivity dominate the spectra at high temperatures and low frequency. The CMC concentration affects the morphological structure of cellulose and subsequently alters its physical properties. X-ray diffractometry measurements show that increasing the concentration of CMC promotes a decrease of the Iα/Iß ratio. This structural change in BC, that involves a variation in inter- and intramolecular interactions (hydrogen-bonding interactions), affects steeply their molecular dynamics. So, an increase of CMC concentration produces a significantly decrease of the ß-relaxation strength and an increase of the dc-conductivity.

Exploring the shock response of spider webs.

Spider orb-webs are designed to allow for quick energy absorption as well as the constraint of drastic oscillations occurring upon prey impact. Studies on spider silk illustrate its impressive mechanical properties and its capacity to be used as technical fibers in composite materials. Models have previously been used to study the mechanical properties of different silk fibers, but not the behavior of the spider web as a whole. Full spider webs have been impacted by a projectile and the transverse displacement was measured by means of a laser interferometer. The damping and stiffness of the entire webs were quantified considering the orb-web as a single-degree-of-freedom (SDOF) system. The amplitude, the period duration, and the energy dissipation of the oscillations have also been reported from the experiments. The analysis of the energy dissipation confirmed that the webs of orb-web spiders are optimized for the capture of a single or few large prey, rather than several small prey. The experiments also confirmed that the overall stiffness of the web displayed a non-linear behavior. Such non-linearity was also observed in the damping characteristics of the webs studied.

Impact and fracture analysis of fish scales from Arapaima gigas.

Fish scales from the Amazonian fish Arapaima gigas have been characterised to study their impact and fracture behaviour at three different environmental conditions. Scales were cut in two different directions to analyse the influence of the orientation of collagen layers. The energy absorbed during impact tests was measured for each sample and SEM images were taken after each test in order to analyse the failure mechanisms. The results showed that scales tested at cryogenic temperatures display fragile behaviour, while scales tested at room temperature did not fracture. Different failure mechanisms have been identified, analysed and compared with the failure modes that occur in bone. The impact energy obtained for fish scales was two to three times higher than the values reported for bone in the literature.

Immunological properties of Andean starch films are independent of their nanometric roughness and stiffness.

Starch is a natural material extracted from roots, seeds, stems and tubers of different plants. It can be processed as a thermoplastic to produce a variety promising products for biomedical applications, including foams, sheets and films. In the present work, we investigated the immunological properties of microfilms prepared with starches extracted from six different types of Andean potatoes and their relationship with the different film-surface features. We confirmed the biocompatibility of all the films using THP-1 human monocytes, noticing only slight decrease in cell viability in two of the tested starches. We also analyzed pro-inflammatory cytokine release and immune cell surface receptor modulation on THP-1 plated onto the films. Our data show differences in the immunological profile of the same cells cultured onto the different starch films. Furthermore, we examined whether the dissimilar stiffness or the nanometric roughness of the films might influence the immune stimulation of the THP-1 monocytes. Our results demonstrate no correlation between cultured THP-1 immune activation and surface film characteristics. We conclude that different Andean native potato starch films have specific ability to interact with cell membranes of immune cells, conceivably due to the different spatial localization of amylose and amylopectin in the diverse starches.

Correlation of antistaphylococcal antibody titers with severity of staphylococcal disease.

Counterimmunoelectrophoresis (CIE) was utilized to determine antistaphylococcal precipitin antibody titers in patients with various staphylococcal diseases and in control subjects. Patients with staphylococcal disease comprised five cases of endocarditis, 22 of deep tissue infection (including seven cases of osteomyelitis), six of bacteremia and six of skin infection. Control subjects consisted of 31 patients with nonstaphylococcal bacteremias, 29 hospitalized patients without infection and 30 healthy subjects. Antistaphylococcal antibodies were present in all patients with staphylococcal endocarditis and deep tissue staphylococcal infection, and all but three had titers greater than or equal to 1:4. No significant difference in titers was found between these two groups of patients. Antibodies, although present in some patients in the other categories, were detected less frequently; only two patients had titers greater than or equal to 1:4. Thus, an antistaphylococcal antibody titer by CIE of 1:4 or greater may be an additional diagnostic parameter helpful in distinguishing patients with staphylococcal endocarditis or deep tissue infection from those with other forms of staphylococcal infection and from noninfected subjects.

Application of counterimmunoelectrophoresis in rapid detection of cytomegalovirus antibodies.

Determination of cytomegalovirus antibodies by counterimmune-electrophoresis correlated well with results of complement-fixation antibody studies. The sensitivity and specificity of the counterimmunoelectrophoresis method (vs. complement fixation) was 88.9%. Fourfold antibody increases detected by complement fixation were also detected by counterimmunoelectrophoresis. In addition, no cross-reaction was observed in the counterimmunoelectrophoresis assay between other DNA viral antisera and cytomegalovirus antigen (Ad-169).

Comparison of counterimmunoelectrophoresis (CIE) with other serologic tests in the detection of antibodies to Trypanosoma cruzi.

Application of counterimmunoelectrophoresis (CIE) in detection of antibodies against Trypanosoma cruzi in sera of 180 subjects from an endemic area (Bolivia), and 50 subjects from a nonendemic area (U.S.A.) was carried out, and the results were compared to ones obtained with latex agglutination (LA) and indirect hemagglutination (IHA). The optimal conditions for CIE were determined to be as follows: barbitone buffer of pH 8.2 and ionic strength 0.05 M was used in the chambers and in preparing the 1% agarose plates. The wells in the plates were 5 mm in diameter and 3 mm apart. Electric current was applied at 500 volts and 25 mA for 60 minutes. T. cruzi antigen (Center for Disease Control) was used in a dilution of 1:2. The sera were studied undiluted. The study population comprised the following groups: LA+ IHA+ (group I); LA+ IHA- (group II); LA- IHA+ (group III); LA- IHA- (group IV); and the control group (group V). Each group was comprised of 50 sera, except for group II which was comprised of only 30 sera. Antibodies were detected by CIE in 94% of sera in group I, 40% in group II, 76% in group III and 6% in group IV. There were no positive reactions in group V. CIE was positive in 74% of sera from the combined LA+ serum groups (I and II), and in 85% of sera from the IHA+ groups (I and III). A good correlation between CIE and the other tests in the LA+ and IHA+ group (I), and the lack of false positive reactions in group V suggest that CIE is a good diagnostic method for detection of T. cruzi antibodies. However, this study showed that IHA is a more sensitive test in epidemiological surveys than CIE. The finding of 6% sera positive by CIE in group IV may indicate a lower specificity of the test.

Recurrent herpes simplex labialis: viral replication and clinical course.

The purpose of this study was to provide additional information on the clinical course and viral replication kinetics of herpes simplex virus (HSV) in recurrent herpes labialis. Data were obtained on 20 subjects who were followed for five days from the first day of the lesion. HSV was isolated in 17 subjects (85%); 75% were positive on day 1 of the lesion. Median HSV titer on day 1 was 1.7 x 10(3)/0.2ml. Isolation rates and titers dropped sharply and virus could no longer be detected by day 4. The clinical course both in terms of the frequency and the severity of the symptoms paralleled the kinetics of viral replication. Thermography delineated location of subsequent lesions in three early symptomatic patients who were studied at the time when no visible lesions were observed. These data are felt to provide useful background information for future studies on the efficacy of topical antiviral agents.

Reversible stress softening of collagen based networks from the jumbo squid mantle (Dosidicus gigas).

Dosidicus gigas is the largest and one of the most abundant jumbo squids in the eastern Pacific Ocean. In this paper we have studied the muscle of the mantle of D. gigas (DGM). Morphological, thermal and rheological properties were assessed by means of atomic force microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, differential scanning calorimetry, thermogravimetry and oscillatory rheometry. This study allowed us to assess the morphological and rheological properties of a collagen based network occurring in nature. The results showed that the DGM network displays a nonlinear effect called reversible stress softening (RSS) that has been previously described for other types of biological structures such as naturally occurring cellulose networks and actin networks. We propose that the RSS could play a key role on the way jumbo squids withstand hydrostatic pressure. The results presented here confirm that this phenomenon occurs in a wider number of materials than previously thought, all of them exhibiting different size scales as well as physical conformation.

Biodegradability and mechanical properties of starch films from Andean crops.

Different Andean crops were used to obtain starches not previously reported in literature as raw material for the production of biodegradable polymers. The twelve starches obtained were used to prepare biodegradable films by casting. Water and glycerol were used as plasticizers. The mechanical properties of the starch based films were assessed by means of tensile tests. Compost tests and FTIR tests were carried out to assess biodegradability of films. The results show that the mechanical properties (UTS, Young's modulus and elongation at break) of starch based films strongly depend on the starch source used for their production. We found that all the starch films prepared biodegrade following a three stage process and that the weight loss rate of all the starch based films tested was higher than the weight loss rate of the cellulose film used as control.

Supercontraction of dragline silk spun by lynx spiders (Oxyopidae).

Supercontraction is commonly considered as a functional adaptation of major ampullate gland (MA) silk to its role as the main structural material in orb-webs. However, the observation of supercontraction in the dragline silk of a lynx spider species, as it is shown in this work, offers a strong support to the hypothesis that the appearance of supercontraction preceded the advent of capture webs. Moreover, the absence of proline in the sequence of dragline silk spidroin in Oxyopidae and related spiders indicates that the presence of this amino acid may not be required for the existence of supercontraction. In this regard, the presence of particular subrepeats--in orb-web and non-orb-web building spiders--adds new clues for the understanding of supercontraction and associated effects.

Cherry pitter's thumb. Case report and review of the literature.

Perineural fibrosis and scarring of the digital nerves in the hand can result from chronic compression and repetitive trauma. The digital nerves in the thumb have been reported to undergo these changes as a result of such trauma from bowling and the use of fine instruments by a jeweler. This article describes a case of digital neuropathy of the thumb resulting from a cherry-pitting instrument. A protective neoprene thumb sleeve and avoidance of further trauma to the nerves relieved the patient's symptoms.

Counterimmunoelectrophoresis in the detection of antibodies against Coccidioides immitis.

In recent years counterimmunoelectrophoresis has been increasingly used in the diagnosis of microbial diseases, and our study was undertaken to evaluate its possible use in the rapid detection of antibodies against Coccidioides immitis. One hundred twelve specimens from 50 patients were studied. The study population comprised the following: Group I, 34 patients with an active coccidioidomycosis infection; Group II, five patients with a positive coccidioidin skin test; Group III, five patients with a negative coccidioidin skin test; and Group IV, six patients with other fungal infections. Counterimmunoelectrophoresis was positive in 93 of 96 specimens in Group I and negative in the other groups. The results obtained by counterimmunoelectrophoresis correlated well with complement fixation and double immunodiffusion and indicate that it is an excellent tool for the diagnosis of patients with coccidioidomycosis.