Surface Wettability of Cellulose Sponges on Effective Oil Uptake

Designing absorbents having specific wettability toward both oil and water is the key for selective and effective oil absorption and removal. For this purpose, establishing explicit correlations between surface tension of oils and surface wettability of absorbent is crucial. In this study, we modified common low-cost cellulose sponges with various organosilanes to achieve a range of hydrophobicity/oleophilicity and then assessed their oil uptake selectivity and capability. Oil uptake was followed as mass uptake versus time and analyzed based on the spreading coefficient (S) of a liquid over a solid surface. The results showed that sponges needed to be hydrophobic, not necessarily superhydrophobic, to selectively absorb oil from an oil/water mixture. To achieve a fast uptake and a high uptake capacity, an S ≥ 0 was necessary, that is, when the sponges were completely wet by the oil. Increasing the porosity of cellulose sponge led to a slight increase in oil uptake capacity, and a greater increase resulted when bacterial cellulose sponges that consisted of smaller and more uniform voids/pores were used. S ≥ 0 could be used as a criterion for evaluating effective and rapid oil uptake for porous absorbents, especially for those containing heterogeneous pore structures, such as common cellulose sponges.

Thermoresponsive Poly(vinyl methyl ether) (PVME) Retained by 3-Aminopropyltriethoxysilane (APTES) Network

Thermoresponsive polymers (TRP)s have been widely used for various applications from controlling membrane fouling in separation to cell/cell sheet harvesting in regenerative medicine. While poly(N-isopropylacrylamide) (pNIPAAm) is the most commonly used TRP, less expensive and easily processed poly(vinyl methyl ether) (PVME) also shows a hydrophilic to hydrophobic transition at 32-35 °C, near physiological conditions. In this study, we investigated the processing conditions for retaining a stable layer of PVME thin film on silica surfaces via entrapment in a 3-aminopropyltriethoxysilane (APTES) network. In addition, the thermoresponsive behaviors (TRB) of the retained PVME films were evaluated. Blend thin films of PVME/APTES with 90:10 and 50:50 mass ratios were spin-coated from their solutions in ethanol under ambient conditions and then annealed in a vacuum oven at 40, 60, 80, or 120 °C for 1, 2, or 3 days. The annealed films were then thoroughly rinsed with room temperature water and then soaked in water for 3 days. Our results showed that annealing at a temperature of ≥40 °C was necessary for retaining a PVME film on the surface. The higher annealing temperature led to greater film retention, probably due to the formation of a tighter APTES network. Regardless of processing conditions, all retained PVME films showed TRB, determined by water contact angles below and above the transition temperature of PVME. Additionally, particle attachment and protein adsorption on retained PVME films showed lower attachment or adsorption at room temperature as compared to that at 37 °C, and a greater difference was observed for the 90:10 blend where more PVME was consisted. Furthermore, human mesenchymal stem cells attached and proliferated on the retained PVME surfaces at 37 °C and rapidly detached at room temperature. These results illustrated the potential applications of PVME surfaces as thermoresponsive supports for low-fouling applications and noninvasive cell harvesting.

Alignment of inducible vascular progenitor cells on a micro-bundle scaffold improves cardiac repair following myocardial infarction

Ischemic heart disease is still the leading cause of death even with the advancement of pharmaceutical therapies and surgical procedures. Early vascularization in the ischemic heart is critical for a better outcome. Although stem cell therapy has great potential for cardiovascular regeneration, the ideal cell type and delivery method of cells have not been resolved. We tested a new approach of stem cell therapy by delivery of induced vascular progenitor cells (iVPCs) grown on polymer micro-bundle scaffolds in a rat model of myocardial infarction. iVPCs partially reprogrammed from vascular endothelial cells (ECs) had potent angiogenic potential and were able to simultaneously differentiate into vascular smooth muscle cells (SMCs) and ECs in 2D culture. Under hypoxic conditions, iVPCs also secreted angiogenic cytokines such as vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) as measured by enzyme-linked immunosorbent assay (ELISA). A longitudinal micro-scaffold made from poly(lactic-co-glycolic acid) was sufficient for the growth and delivery of iVPCs. Co-cultured ECs and SMCs aligned well on the micro-bundle scaffold similarly as in the vessels. 3D cell/polymer micro-bundles formed by iVPCs and micro-scaffolds were transplanted into the ischemic myocardium in a rat model of myocardial infarction (MI) with ligation of the left anterior descending artery. Our in vivo data showed that iVPCs on the micro-bundle scaffold had higher survival, and better retention and engraftment in the myocardium than free iVPCs. iVPCs on the micro-bundles promoted better cardiomyocyte survival than free iVPCs. Moreover, iVPCs and iVPC/polymer micro-bundles treatment improved cardiac function (ejection fraction and fractional shortening, endocardial systolic volume) measured by echocardiography, increased vessel density, and decreased infarction size [endocardial and epicardial infarct (scar) length] better than untreated controls at 8 weeks after MI. We conclude that iVPCs grown on a polymer micro-bundle scaffold are new promising approach for cell-based therapy designed for cardiovascular regeneration in ischemic heart disease.

Amino Acid-Based Zwitterionic Polymer Surfaces Highly Resist Long-Term Bacterial Adhesion

The surfaces or coatings that can effectively suppress bacterial adhesion in the long term are of critical importance for biomedical applications. Herein, a group of amino acid-based zwitterionic polymers (pAAZ) were investigated for their long-term resistance to bacterial adhesion. The polymers were derived from natural amino acids including serine, ornithine, lysine, aspartic acid, and glutamic acid. The pAAZ brushes were grafted on gold via the surface-initiated photoiniferter-mediated polymerization (SI-PIMP). Results show that the pAAZ coatings highly suppressed adsorption from the undiluted human serum and plasma. Long-term bacterial adhesion on these surfaces was investigated, using two kinds of representative bacteria [Gram-positive Staphylococcus epidermidis and Gram-negative Pseudomonas aeruginosa] as the model species. Results demonstrate that the pAAZ surfaces were highly resistant to bacterial adhesion after culturing for 1, 5, 9, or even 14 days, representing at least 95% reduction at all time points compared to the control unmodified surfaces. The bacterial accumulation on the pAAZ surfaces after 9 or 14 days was even lower than on the surfaces grafted with poly[poly(ethyl glycol) methyl ether methacrylate] (pPEGMA), one of the most common antifouling materials known to date. The pAAZ brushes also exhibited excellent structural stability in phosphate-buffered saline after incubation for 4 weeks. The bacterial resistance and stability of pAAZ polymers suggest they have good potential to be used for those applications where long-term suppression to bacterial attachment is desired.

Applicability of the extended Derjaguin-Landau-Verwey-Overbeek theory on the adsorption of bovine serum albumin on solid surfaces

Protein adsorption is the prerequisite for bacterial attachment and cellular adhesion, which are critical for many biomedical applications. To understand protein adsorption onto substrates, predictive models are generally informative prior to experimental studies. In this study, the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory was employed to determine whether or not it could interpret the protein adsorption behaviors. The experimental results of fluorescein isothiocyanate labeled bovine serum albumin (BSA) adsorbed on six different surfaces: glass, octadecyltrichlorosilane modified glass, 2-[methoxypoly(ethyleneoxy)propyl]trimethoxy-silane (PEG)-modified glass, polystyrene, poly(dimethylsiloxane), and poly(methyl methacrylate) were utilized. The XDLVO interaction energy curves, especially from the contribution of acid-base interactions, obtained using the surface properties of substrates and BSA molecules qualitatively predict/interpret the protein adsorption behaviors on these surfaces. Some derivation of the experimental results from the prediction was noticed for the glass and the PEG-modified glass. When including a hydration layer to the PEG-modified glass surface, the nonfouling result of such surface by proteins was also elucidated by the XDLVO theory.

Effects of rhamnolipids and shear on initial attachment of Pseudomonas aeruginosa PAO1 in glass flow chambers

BACKGROUND, AIM, AND SCOPE

Solid surfaces in contact with water have been found to be biofouled due to the attachment of various organisms. For better understanding of the biofilm formation, the important initial stage of bacterial attachment was investigated with Pseudomonas aeruginosa PAO1 as a model microorganism. Effects of the biosurfactant rhamnolipids and the shear conditions were particularly examined.

MATERIALS AND METHODS

A highly reproducible procedure was employed. The procedure involved monitoring and counting the number of attached cells on glass walls of the flow chambers, through which a PAO1 suspension was circulated and, subsequently, a saline solution was passed for washing. The experiments were made under different circulation rates (exerting different shear on the bacteria) and rhamnolipid concentrations.

RESULTS AND DISCUSSIONS

Reproducibility of the procedure was confirmed. The velocity profiles near the flow chamber wall were determined. Rhamnolipids, even at a very low concentration of 13 mg/l, were found to deter the bacterial attachment substantially. Prewashing the cells with a 100 mg/l rhamnolipid solution, however, did not affect the attachment significantly. As for the effect of shear, the PAO1 attachment showed an increasing-then-decreasing trend in the range investigated, i.e., 1.0 to 26 mN/m(2) shear stresses at the chamber wall. The diffusion-limited transport of cells to the chamber wall might have contributed to, but could not fully explain, the increasing attachment observed in the very low shear range (up to 3.5-5.0 mN/m(2)).

CONCLUSIONS

As compared to static systems, the flow chamber systems significantly improved the reproducibility of initial attachment results. Flow chamber systems were more suitable for experimental investigations of bacterial attachment to surfaces. Rhamnolipids were found to be potent antifoulants for PAO1 attachment on glass. The initial cell attachment increased with increasing shear at the very low shear range (up to 3.5-5.0 mN/m(2)), but the attachment could be minimized with further increase of the shear.

Self-Assembling of Polymer-Enzyme Conjugates at Oil/Water Interfaces

Interface-binding enzymes are desirable for biphasic reactions in that they offer simultaneous access to substrates dissolved in both phases across the interface. It has been shown that conjugating water-soluble enzymes with hydrophobic polymers facilitated the assembling of enzymes at oil/water interfaces. In this work, the interfacial assembling of alpha-chymotrypsin conjugated with polystyrene, poly(methyl methacrylate), and poly(l-lactic acid) was examined using the pendant drop method. The interface-assembling process of the conjugates from the organic phase followed a similar pattern of that of native alpha-chymotrypsin from the aqueous buffer phase, i.e., the interfacial tension decreased gradually with time. However, when the conjugates were dispersed in the form of particulates in the aqueous phase, in which the conjugate was insoluble, the assembling occurred faster and the interfacial tension quickly approached zero. It was suspected that the assembling in this case involved two steps, i.e., the adsorption of the particulates and the subsequent rearrangement, dissociation, and redispersion of the conjugates at the interface. The effect of other factors, including the polarity of organic solvent and pH and ionic strength of the aqueous phase, was evaluated. It was found that the polar solvent slightly facilitated the assembling, whereas pH and ionic strength showed minimal effects.

Assessment of antifouling effectiveness of two natural product antifoulants by attachment study with freshwater bacteria

GOAL, SCOPE, BACKGROUND: The traditional solution for keeping unwanted organisms from attaching to submerged surfaces is to apply anti-fouling coatings. The most common antifoulant was tributyltin (TBT). TBT systems were highly effective but were also toxic to non-target organisms. The use of the TBT based coatings will be completely banned by January 1, 2008. Therefore, there is an urgent need to seek out suitable non-toxic alternatives.

METHODS

The aim of this work was to evaluate the effectiveness of capsaicin and zosteric acid as natural product antifoulants (NPAs) in deterring bacterial attachment. Two fresh water bacteria systems Pseudomonas putida (Pp) and bacteria isolated from Lake Erie (LE) were used to assess the attachment when the NPAs dispersed in the water. Effectiveness was ascertained based on the decrease in microbial attachment, limited toxicity, and minimum alteration of the coatings properties.

RESULTS AND DISCUSSION

A significant inhibition of bacteria attachment was achieved when aqueous capsaicin concentration was increased from 0 to 40 mg/L. For instance, after 14 days the LE system depicted 93.5% and 98.5% less biofilm coverage for 20 mg/L and 40 mg/L capsaicin, respectively when pared to systems without NPA. Biofilm coverage was reduced by 92.5% and 98.2%, respectively with 50 mg/L and 500 mg/L zosteric acid.

CONCLUSIONS

Both capsaicin and zosteric acid was effective at preventing bacteria attachment. As the NPA aqueous concentration increased, biofilm formation decreased. Evaluating changes in aqueous pH, conductivity, dissolved oxygen, aqueous microbial population and biofilm formation suggested that the primary antifoulant mechanism of these two NPAs was to block the bacteria's active sites versus posing a lethal level.

RECOMMENDATION AND PERSPECTIVE

From the attachment study, zosteric acid appeared to be more effective in preventing bacterial attachment when the NPAs were dispersed in the aqueous environment. For practical applications, the antifoulant needs to be incorporated into a coating and have a slow release rate. Thus the ability to successfully incorporate zosteric acid into a coating, without deterring bacterial attachment, needs to be investigated.

Effectiveness of sodium benzoate as a freshwater low toxicity antifoulant when dispersed in solution and entrapped in silicone coatings

The traditional solution for preventing organisms from attaching to submerged surfaces is to apply antifouling coatings or biocides. Based on the varied defence mechanisms exhibited by biofilms, the antifoulant needs to prevent bacterial attachment during the early stages of biofilm formation. The potential of benzoic acid and sodium benzoate (NaB) as antifoulants for deterring freshwater bacterial attachment was evaluated with the antifoulants dispersed in solution or entrapped in silicone coatings. Effectiveness was based on the decrease in microbial attachment, limited toxicity, and minimum alteration of the properties of the coatings. The optimal NaB concentration when dispersed in solution, 700 mg l-1, resulted in a biofilm surface coverage of only 3.34% after four weeks. The model silicone, Sylgard 184, demonstrated a better overall performance than the commercial coating, RTV11. Sylgard 184 containing sodium benzoate had 41-52% less biofilm in comparison to the control Sylgard 184, whereas both the control and NaB-entrapped RTV11 coatings had significant biofilm coverage.