Rationalizing the design of polymeric biomaterials

Multi-scale modelling of rubber-like materials and soft tissues: an appraisal

We survey, in a partial way, multi-scale approaches for the modelling of rubber-like and soft tissues and compare them with classical macroscopic phenomenological models. Our aim is to show how it is possible to obtain practical mathematical models for the mechanical behaviour of these materials incorporating mesoscopic (network scale) information. Multi-scale approaches are crucial for the theoretical comprehension and prediction of the complex mechanical response of these materials. Moreover, such models are fundamental in the perspective of the design, through manipulation at the micro- and nano-scales, of new polymeric and bioinspired materials with exceptional macroscopic properties.

Developing a Suitable Model for Water Uptake for Biodegradable Polymers Using Small Training Sets

Prediction of the dynamic properties of water uptake across polymer libraries can accelerate polymer selection for a specific application. We first built semiempirical models using Artificial Neural Networks and all water uptake data, as individual input. These models give very good correlations (R² > 0.78 for test set) but very low accuracy on cross-validation sets (less than 19% of experimental points within experimental error). Instead, using consolidated parameters like equilibrium water uptake a good model is obtained (R² = 0.78 for test set), with accurate predictions for 50% of tested polymers. The semiempirical model was applied to the 56-polymer library of L-tyrosine-derived polyarylates, identifying groups of polymers that are likely to satisfy design criteria for water uptake. This research demonstrates that a surrogate modeling effort can reduce the number of polymers that must be synthesized and characterized to identify an appropriate polymer that meets certain performance criteria.

Engineered Polymeric Hydrogels for 3D Tissue Models

Polymeric biomaterials are widely used in a wide range of biomedical applications due to their unique properties, such as biocompatibility, multi-tunability and easy fabrication. Specifically, polymeric hydrogel materials are extensively utilized as therapeutic implants and therapeutic vehicles for tissue regeneration and drug delivery systems. Recently, hydrogels have been developed as artificial cellular microenvironments because of the structural and physiological similarity to native extracellular matrices. With recent advances in hydrogel materials, many researchers are creating three-dimensional tissue models using engineered hydrogels and various cell sources, which is a promising platform for tissue regeneration, drug discovery, alternatives to animal models and the study of basic cell biology. In this review, we discuss how polymeric hydrogels are used to create engineered tissue constructs. Specifically, we focus on emerging technologies to generate advanced tissue models that precisely recapitulate complex native tissues in vivo.

A Co-blended Locust Bean Gum and Polymethacrylate-NaCMC Matrix to Achieve Zero-Order Release via Hydro-Erosive Modulation

Locust bean gum (LBG) was blended with a cellulose/methacrylate-based interpolyelectrolyte complex (IPEC) to assess the hydro-erosive influence of addition of a polysaccharide on the disposition and drug delivery properties inherent to IPEC matrix. The addition of LBG modulated the drug (levodopa) release characteristics of the IPEC by reducing excessive swelling and preventing bulk erosion. After 8 h in pH 4.5 dissolution medium, gravimetric analysis established that IPEC tablet matrix eroded by 30% of the initial weight due to bulk erosion while LBG-blended IPEC (LBG-b-IPEC) demonstrated surface erosion accounting to 62% of initial weight (596→226.8 mg). Mathematical modeling of the drug release data depicted a transformation from non-Fickian mechanism (IPEC matrices) to zero-order drug release pattern (LBG-b-IPEC matrices) with the linearity of release profile being close to 1 (R (2) = 0.99). Physicochemical characterizations employing Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) explicated that LBG interacted with IPEC by its hydrophilic groups associating with the existing water-holding bodies of IPEC to produce compact matrices. The lattice atomistic modeling elucidated that LBG acted as a linker with the formation of intra- and intermolecular hydrogen bonds generating a highly stabilized polysaccharide-polyelectrolytic structure which influenced the improved properties observed.

Microbial production of scleroglucan and downstream processing

Synthetic petroleum-based polymers and natural plant polymers have the disadvantage of restricted sources, in addition to the non-biodegradability of the former ones. In contrast, eco-sustainable microbial polysaccharides, of low-cost and standardized production, represent an alternative to address this situation. With a strong global market, they attracted worldwide attention because of their novel and unique physico-chemical properties as well as varied industrial applications, and many of them are promptly becoming economically competitive. Scleroglucan, a β-1,3-β-1,6-glucan secreted by Sclerotium fungi, exhibits high potential for commercialization and may show different branching frequency, side-chain length, and/or molecular weight depending on the producing strain or culture conditions. Water-solubility, viscosifying ability and wide stability over temperature, pH and salinity make scleroglucan useful for different biotechnological (enhanced oil recovery, food additives, drug delivery, cosmetic and pharmaceutical products, biocompatible materials, etc.), and biomedical (immunoceutical, antitumor, etc.) applications. It can be copiously produced at bioreactor scale under standardized conditions, where a high exopolysaccharide concentration normally governs the process optimization. Operative and nutritional conditions, as well as the incidence of scleroglucan downstream processing will be discussed in this chapter. The relevance of using standardized inocula from selected strains and experiences concerning the intricate scleroglucan scaling-up will be also herein outlined.

Design of Thiol- and Light-sensitive Degradable Hydrogels using Michael-type Addition Reactions

Injectable depots that respond to exogenous and endogenous stimuli present an attractive strategy for tunable, patient-specific drug delivery. Here, the design of injectable and multimodal degradable hydrogels that respond to externally applied light and physiological stimuli, specifically aqueous and reducing microenvironments, is reported. Rapid hydrogel formation was achieved using a thiol-maleimide click reaction between multifunctional poly(ethylene glycol) macromers. Hydrogel degradation kinetics in response to externally applied cytocompatible light, reducing conditions, and hydrolysis were characterized, and degradation of the gel was controlled over multiple time scales from seconds to days. Further, tailored release of an encapsulated model cargo, fluorescent nanobeads, was demonstrated.

Supramolecular polycationic hydrogels with high swelling capacity prepared by partial methacrylation of polyethyleneimine

Partial methacrylation of polyethyleneimine leads to novel highly hydrophilic supramolecular hydrogels that absorb and retain up to 95% of water.

Current strategies in multiphasic scaffold design for osteochondral tissue engineering: A review

The repair of osteochondral defects requires a tissue engineering approach that aims at mimicking the physiological properties and structure of two different tissues (cartilage and bone) using specifically designed scaffold-cell constructs. Biphasic and triphasic approaches utilize two or three different architectures, materials, or composites to produce a multilayered construct. This article gives an overview of some of the current strategies in multiphasic/gradient-based scaffold architectures and compositions for tissue engineering of osteochondral defects. In addition, the application of finite element analysis (FEA) in scaffold design and simulation of in vitro and in vivo cell growth outcomes has been briefly covered. FEA-based approaches can potentially be coupled with computer-assisted fabrication systems for controlled deposition and additive manufacturing of the simulated patterns. Finally, a summary of the existing challenges associated with the repair of osteochondral defects as well as some recommendations for future directions have been brought up in the concluding section of this article.

Effect of gamma irradiation on structural and biological properties of a PLGA-PEG-hydroxyapatite composite

Gamma irradiation is able to affect various structural and biological properties of biomaterials In this study, a composite of Hap/PLGA-PEG and their ingredients were submitted to gamma irradiation doses of 25 and 50 KGy. Various properties such as molecular weight (GPC), thermal behavior (DSC), wettability (contact angle), cell viability (MTT assay), and alkaline phosphatase activity were studied for the composites and each of their ingredients. The results showed a decrease in molecular weight of copolymer with no change in the glass transition and melting temperatures after gamma irradiation. In general gamma irradiation can increase the activation energy ΔH of the composites and their ingredients. While gamma irradiation had no effect on the wettability of copolymer samples, there was a significant decrease in contact angle of hydroxyapatite and composites with increase in gamma irradiation dose. This study showed an increase in biocompatibility of hydroxyapatite with gamma irradiation with no significant effect on cell viability in copolymer and composite samples. In spite of the fact that no change occurred in alkaline phosphatase activity of composite samples, results indicated a decrease in alkaline phosphatase activity in irradiated hydroxyapatites. These effects on the properties of PLGA-PEG-hydroxyapatite can enhance the composite application as a biomaterial.

Biodegradable and biocompatible poly(ethylene glycol)-based hydrogel films for the regeneration of corneal endothelium

Corneal endothelial cells (CECs) are responsible for maintaining the transparency of the human cornea. Loss of CECs results in blindness, requiring corneal transplantation. In this study, fabrication of biocompatible and biodegradable poly(ethylene glycol) (PEG)-based hydrogel films (PHFs) for the regeneration and transplantation of CECs is described. The 50-μm thin hydrogel films have similar or greater tensile strengths to human corneal tissue. Light transmission studies reveal that the films are >98% optically transparent, while in vitro degradation studies demonstrate their biodegradation characteristics. Cell culture studies demonstrate the regeneration of sheep corneal endothelium on the PHFs. Although sheep CECs do not regenerate in vivo, these cells proliferate on the films with natural morphology and become 100% confluent within 7 d. Implantation of the PHFs into live sheep corneas demonstrates the robustness of the films for surgical purposes. Regular slit lamp examinations and histology of the cornea after 28 d following surgery reveal minimal inflammatory responses and no toxicity, indicating that the films are benign. The results of this study suggest that PHFs are excellent candidates as platforms for the regeneration and transplantation of CECs as a result of their favorable biocompatibility, degradability, mechanical, and optical properties.

Drug-releasing implants: current progress, challenges and perspectives

This review presents the different types and concepts of drug-releasing implants using new nanomaterials and nanotechnology-based devices.

Image-based analysis of droplets in microfluidics

In order to design a microfluidic device that can produce monodispersed encapsulated enzymes as droplets, it is essential to be able to evaluate the system during its development. An automated method to determine the size of the droplets as well as a method to tag and track droplets as they move in the system is desirable for system evaluation. We apply the Hough transform for circles to determine droplet size. Most of the droplets in the images are detected, and the best results are obtained at 20x magnification. We also test the ability of the ImageJ 'particle tracker' plugin to determine the behaviour of the droplets as they move in microfluidic systems. It is effective in tracking droplets that travel less than 50 pixels between frames.

Tuning the density profile of surface-grafted hyaluronan and the effect of counter-ions

The present paper investigates the structure and composition of grafted sodium hyaluronan at a solid-liquid interface using neutron reflection. The solvated polymer at the surface could be described with a density profile that decays exponentially towards the bulk solution. The density profile of the polymer varied depending on the deposition protocol. A single-stage deposition resulted in denser polymer layers, while layers created with a two-stage deposition process were more diffuse and had an overall lower density. Despite the diffuse density profile, two-stage deposition leads to a higher surface excess. Addition of calcium ions causes a strong collapse of the sodium hyaluronan chains, increasing the polymer density near the surface. This effect is more pronounced on the sample prepared by two-stage deposition due to the initial less dense profile. This study provides an understanding at a molecular level of how surface functionalization alters the structure and how surface layers respond to changes in calcium ions in the solvent.

Is Montgomery tracheal Safe-T-Tube clinical failure induced by biofilm?

OBJECTIVES

Montgomery Safe-T-Tube deterioration and early biofilm colonization may explain the discomfort claimed by many patients and clinical failures. The aim of the study was to analyze the deterioration of Montgomery Safe-T-Tube morphological and mechanical properties in vivo in 16 patients by using microbiological methods, optical and electron microscopy, and engineering tests.

STUDY DESIGN

Prospective controlled study at a single medical center.

SETTING

University hospital.

SUBJECTS AND METHODS

The study, conducted from April 2007 to February 2012 at the "Sapienza" University of Rome, was designed to collect 2 Montgomery Safe-T-Tubes from each patient. The first was removed 3 to 15 days after insertion (group A) and the second at least 90 days after (group B). Specimens underwent microbiologic assays, electron microscopic analysis, immunocytologic analysis, and mechanical tests.

RESULTS

Microorganisms were not isolated in 2 group A cases (12%), whereas they were in all group B cases. Biofilm was identified in 11 of 16 (69%) group A samples and in 16 of 16 (100%) group B samples (P = .0149) using scanning electron microscopy. Immunohistochemistry showed monocyte-granulocyte line cells producing interleukin-1β on the external surfaces of Montgomery Safe-T-Tubes. The tensile test showed that the wear related to the longer period of use makes Montgomery Safe-T-Tubes more rigid than newer ones.

CONCLUSION

Early biofilm colonization takes place in Montgomery Safe-T-Tubes in most cases. The mechanical decay could be justified in part by the destructive biofilm activity and by the release of inflammatory effectors and enzymes.

Surface treatments for microfluidic biocompatibility

Microfluidic systems allow small volumes of liquids to be manipulated, either by being passed through channels or moved around as liquid droplets. Such systems have been developed to separate, purify, analyze, and deliver molecules to reaction zones. Although volumes are small, reaction rates, catalysis, mixing, and heat transfer can be high, enabling the accurate sensing of tiny quantities of agents and the synthesis of novel products. The incorporation of multiple components, such as pumps, valves, mixers, and heaters, onto a single microfluidic platform has brought about the field of lab-on-a-chip devices or micro total analysis systems (μTAS). Although used in the research laboratory for numerous years, few of these devices have made it into the commercial market, due to their complexity of fabrication and limited choice of material. As the dimensions of these systems become smaller, interfacial interactions begin to dominate in terms of device performance. Appropriate selection of bulk materials, or the application of surface coatings, can allow control over surface properties, such as the adsorption of (bio)molecules. Here we review current microfluidic technology in terms of biocompatibility issues, examining the use of modification strategies to improve device longevity and performance.

Biocompatibility of bacterial cellulose based biomaterials

Some bacteria can synthesize cellulose when they are cultivated under adequate conditions. These bacteria produce a mat of cellulose on the top of the culture medium, which is formed by a three-dimensional coherent network of pure cellulose nanofibers. Bacterial cellulose (BC) has been widely used in different fields, such as the paper industry, electronics and tissue engineering due to its remarkable mechanical properties, conformability and porosity. Nanocomposites based on BC have received much attention, because of the possibility of combining the good properties of BC with other materials for specific applications. BC nanocomposites can be processed either in a static or an agitated medium. The fabrication of BC nanocomposites in static media can be carried out while keeping the original mat structure obtained after the synthesis to form the final nanocomposite or by altering the culture media with other components. The present article reviews the issue of biocompatibility of BC and BC nanocomposites. Biomedical aspects, such as surface modification for improving cell adhesion, in vitro and in vivo studies are given along with details concerning the physics of network formation and the changes that occur in the cellulose networks due to the presence of a second phase. The relevance of biocompatibility studies for the development of BC-based materials in bone, skin and cardiovascular tissue engineering is also discussed.

Biodegradable microparticulate drug delivery system of diltiazem HCl

The efficacy of a drug in a specific application requires the maintenance of appropriate drug blood level concentration during a prolonged period of time. Controlled release delivery is available for many routes of administration and offers many advantages (as microparticles and nanoparticles) over immediate release delivery. These advantages include reduced dosing frequency, better therapeutic control, fewer side effects, and, consequently, these dosage forms are well accepted by patients. Advances in polymer material science, particle engineering design, manufacture, and nanotechnology have led the way to the introduction of several marketed controlled release products and several more are in pre-clinical and clinical development. The objective of this work is to prepare and evaluate diltiazem HCl loaded albumin microparticles using a factorial design. Albumin (natural polymer) microparticles were prepared by emulsion heat-stabilization method. Selected formulations were characterized for their entrapment efficiency, particle size, surface morphology, and release behavior. Analysis of variance for entrapment efficiency indicates that entrapment efficiency is best fitted to a response surface linear model. Surface morphology was studied by scanning electron microscopy. Scanning electron microscopy of the microparticles revealed a spherical, nonporous and uniform appearance, with a smooth surface. The geometric mean diameter of the microparticles was found to be 2-9 µm, which more than 75% were below 3.5 µm and drug incorporation efficiency of 59.74 to 72.48% (w/w). In vitro release profile for formulations containing diltiazem HCl loaded BSA microparticles with heat stabilization technique shows slow controlled the release of the drug up to 24 hours. The release pattern was biphasic, characterized by an initial burst effect followed by a slow release. All selected microparticles exhibited a prolonged release for almost 24 hours. On comparing regression-coefficient (r²) values for Hixson Crowel, Higuchi and Peppas kinetic models, different batches of microparticles showed Fickian, non-Fickian, and diffusion kinetics. The release mechanism was regulated by D:P ratio. From the statistical analysis it was observed that as the drug:polymer (D:P) ratio increased, there was a significant increase in the encapsulation efficiency. Based on the particle size, entrapment efficiency and physical appearance, DTM-3 formulations were selected for in vivo release study and stability study. The in vivo result of drug loaded microparticles showed preferential drug targeting to liver followed by lungs, kidneys and spleen. Stability studies showed that maximum drug content and closest in vitro release to initial data were found in the formulation stored at 4 ºC. In present study, diltiazem HCl loaded BSA microparticles were prepared and targeted to various organs to satisfactory level and were found to be stable at 4 ºC.

Development and characterization of local anti-inflammatory implantation for the controlled release of the hexane extract of the flower-heads of Euryops pectinatus L. (Cass.)

A hexane extract of the flower-heads of Euryops pectinatus L. (Cass.) was formulated into local anti-inflammatory implantation patches with controlled release. Cross-linked sodium hyaluronate patches (F1-F3) and chitosan patches (F4-F6) were prepared by a casting/solvent evaporation technique. Morphological and mechanical characterizations including the components ratio, surfactant and the loaded amount of the hexane extract (50, 100, and 200 mg/kg b.wt.) were investigated. Release studies were performed during 24 h using a diffusion cell. Films with optimum in vitro release rate have been investigated for testing the anti-inflammatory activity and the sustaining effect of the formulations. The sustained anti-inflammatory effect of the hexane extract of E. pectinatus flower-heads from the selected films was studied by inducing paw edema in rats with 1% (w/v) carrageenan solution. The results indicated the compatibility of hexane extract with both sodium hyaluronate and chitosan patches forming yellowish transparent films. Based on variations in drug release profiles throughout the 24-h among the formulations (F1-F6) studies, F3 and F6 were selected for further investigation. When the films were applied 1 h before the subplantar injection of carrageenan in the hind paw of male Albino rats, formulation (F3) provided its maximum inhibition of paw edema in rats (91.3%) 4 h after edema induction whereas, formulation (F6) showed less inhibition after 4 h (70.6%). The previous two formulations (F3 and F6) produced potent results (95.3 and 89.5%, respectively) after 24 h when compared with a local market preparation containing 25% β-sitosterol used as positive control. Histophathological investigation was conducted for 1, 4, and 12 weeks to study the tissue response for the two formulations (F3 and F6) at the implantation site. Chemical investigation of the hexane extract was achieved for both unsaponifiable matter (USM) and fatty acid methyl esters (FAME) using gas liquid chromatography (GLC). The USM was dominated by n-pentacosane (14.40%), phytosterols (Cholesterol, Campesterol, Stigmasterol, β-sitosterol, α-amyrin) reached 33.44% and the FAME was dominated by Linoleinic (49.97%). Quality control of the local implantation was evaluated by GLC using cholesterol as an analytical marker and phytosterols as an active marker compared to the plain extract.

Ag@AgI, core@shell structure in agarose matrix as hybrid: synthesis, characterization, and antimicrobial activity

A novel in situ core@shell structure consisting of nanoparticles of Ag (Ag Nps) and AgI in agarose matrix (Ag@AgI/agarose) has been synthesized as a hybrid, in order to have an efficient antibacterial agent for repetitive usage with no toxicity. The synthesized core@shell structure is very well characterized by XRD, UV-visible, photoluminescence, and TEM. A detailed antibacterial studies including repetitive cycles are carried out on Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) bacteria in saline water, both in dark and on exposure to visible light. The hybrid could be recycled for the antibacterial activity and is nontoxic toward human cervical cancer cells (HeLa cells). The water insoluble Ag@AgI in agarose matrix forms a good coating on quartz, having good mechanical strength. EPR and TEM studies are carried out on the Ag@AgI/agarose and the bacteria, respectively, to elucidate a possible mechanism for killing of the bacteria.

NSGA-II-RJG applied to multi-objective optimization of polymeric nanoparticles synthesis with silicone surfactants

Polydimethylsiloxane nanoparticles were obtained by nanoprecipitation, using a siloxane surfactant as stabilizer. Two neural networks and a genetic algorithm were used to optimize this process, by minimizing the particle diameter and the polydispersity, finding in this way the optimum values for surfactant and polymer concentrations, and storage temperature. In order to improve the performance of the non-dominated sorting genetic algorithm, NSGA-II, a genetic operator was introduced in this study — the transposition operator — “real jumping genes”, resulting NSGA-II-RJG. It was implemented in original software and was applied to the multi-objective optimization of the polymeric nanoparticles synthesis with silicone surfactants. The multi-objective function of the algorithm included two fitness functions. One fitness function was calculated with a neural network modelling the variation of the particle diameter on the surfactant concentration, polymer concentration, and storage temperature, and the other was computed by a neural network modelling the dependence of polydispersity index on surfactant and polymer concentrations. The performance of the software program that implemented NSGA-II-RJG was highlighted by comparing it with the software implementation of NSGA-II. The results obtained from simulations showed that NSGA-II-RJG is able to find non-dominated solutions with a greater diversity and a faster convergence time than NSGA-II.

Evaluation of peritoneal adhesions formation and tissue response to polypropylene - poli (2-hydroxyethyl methacrylate)-(polyHEMA) implant on rats' abdominal wall

PURPOSE

To verify if the composit poli (2-hydroxyethyl methacrylate)-PolyHEMA/polypropylene mesh implanted in the female rat's abdominal wall could be suitable for the prevention of peritoneal adhesions, and for the evaluation of the tecidual response produced by this biomaterial.

METHODS

Polypropylene meshes (Group PP, n=20) and polypropylene meshes coated with a layer of poli (2-hydroxyethyl methacrylate)-PolyHEMA (Group PH, n=20) were implanted on the abdominal wall of Wistar female rats. Ten animals from each group were submitted to euthanasia at 15 and 30 days of the postoperative period.

RESULTS

The animals from the group PP presented visceral adhesions on the mesh surface, which was not observed in the ones from group PH. At the histopathological examination foreign body response was observed in both groups, whilst there was a greater intensity of inflammatory response in group PH on both moments.

CONCLUSION

The poli (2-hydroxyethyl methacrylate) polyHEMA hydrogel associated to polypropylene mesh reduces visceral adhesion formation in rats, although it may be associated to greater inflammatory reaction.

Study of Antibacterial Efficacy of Hybrid Chitosan-Silver Nanoparticles for Prevention of Specific Biofilm and Water Purification

Antibacterial efficacy of silver nanoparticles (Ag NPs) deposited alternatively layer by layer (LBL) on chitosan polymer in the form of a thin film over a quartz plate and stainless steel strip has been studied. An eight-bilayer chitosan/silver (Cs/Ag)8 hybrid was prepared having a known concentration of silver. Techniques such as UV-visible spectroscopy, inductively coupled plasma optical emission spectroscopy (ICP-OES), and atomic force microscopy (AFM) were carried out to understand and elucidate the physical nature of the film. Gram-negative bacteria, Escherichia coli (E. coli), were used as a test sample in saline solution for antibacterial studies. The growth inhibition at different intervals of contact time and, more importantly, the antibacterial properties of the hybrid film on repeated cycling in saline solution have been demonstrated. AFM studies are carried out for the first time on the microbe to know the morphological changes affected by the hybrid film. The hybrid films on aging (3 months) are found to be as bioactive as before. Cytotoxicity experiments indicated good biocompatibility. The hybrid can be a promising bioactive material for the prevention of biofilms specific to E. coli and in purification of water for safe drinking.

Tuning the mechanical properties of bioreducible multilayer films for improved cell adhesion and transfection activity

A simple approach to the mechanical modulation of layer-by-layer (LbL) films is through manipulation of the film assembly. Here, we report results based on altering the salt concentration during film assembly and its effect on film rigidity. Based on changes in film rigidity, cell adhesion characteristics and transfection activity were investigated in vitro. LbL films consisting of reducible hyperbranched poly(amide amine) (RHB) have been implemented along with DNA for investigating fibroblast adhesion on [RHB/DNA](n/2) films with varying rigidities. The rigidity was varied by changing the ionic concentration of the deposition solution between 0.01 m NaCl and 1.0 m NaCl. Molecular force probe (MFP) measurements were performed to measure the apparent Young's modulus, E(APP), of the films in situ. Cell adhesion and stress-fiber characteristics were investigated using total internal reflectance microscopy (TIRF-M). The average cell peripheral area, fiber density and average fiber length during 5 days of cell growth on films with either low (below 2.0 MPa) or high (above 2.0 MPa) film elastic modulus were investigated. Transfection studies were performed using gfpDNA and SEAP-DNA to investigate if changes in cell adhesion affect transfection activity. Furthermore, cell proliferation and cytotoxicity studies were used to investigate cellular viability over a week. The results have shown that surface modification of bioreducible LbL films of controlled thickness and roughness promotes cellular adhesion, stress-fiber growth and increased transfection activity without the need for an additional adhesive protein pre-coating of the surface or chemical cross-linking of the film.

Sum frequency generation and solid-state NMR study of the structure, orientation, and dynamics of polystyrene-adsorbed peptides

The power of combining sum frequency generation (SFG) vibrational spectroscopy and solid-state nuclear magnetic resonance (ssNMR) spectroscopy to quantify, with site specificity and atomic resolution, the orientation and dynamics of side chains in synthetic model peptides adsorbed onto polystyrene (PS) surfaces is demonstrated in this study. Although isotopic labeling has long been used in ssNMR studies to site-specifically probe the structure and dynamics of biomolecules, the potential of SFG to probe side chain orientation in isotopically labeled surface-adsorbed peptides and proteins remains largely unexplored. The 14 amino acid leucine-lysine peptide studied in this work is known to form an alpha-helical secondary structure at liquid-solid interfaces. Selective, individual deuteration of the isopropyl group in each leucine residue was used to probe the orientation and dynamics of each individual leucine side chain of LKalpha14 adsorbed onto PS. The selective isotopic labeling methods allowed SFG analysis to determine the orientations of individual side chains in adsorbed peptides. Side chain dynamics were obtained by fitting the deuterium ssNMR line shape to specific motional models. Through the combined use of SFG and ssNMR, the dynamic trends observed for individual side chains by ssNMR have been correlated with side chain orientation relative to the PS surface as determined by SFG. This combination provides a more complete and quantitative picture of the structure, orientation, and dynamics of these surface-adsorbed peptides than could be obtained if either technique were used separately.

Development of a Novel Cell Encapsulation System Based on Natural Origin Polymers for Tissue Engineering Applications

Cells microencapsulated in biocompatible semi-permeable polymeric membranes are effective as cell delivery systems while protecting the host against immune responses. In this study, cell encapsulation membranes were prepared based on carrageenan and alginate, two natural cationic polymers. Different formulations/conditions were explored to optimize the microcapsules which were characterized with respect to their morphology, mechanical stability, and cytotoxicity. Spherical-shaped microcapsules were obtained from all the polymeric systems. The iota-carrageenan/sodium alginate microcapsules exhibited the best stability and permeability, and therefore, these were selected for the cell encapsulation. These capsules provided an environment that supported cell proliferation and have the potential for tissue engineering as well as other cell-based therapy applications.

Synthesis, biocompatibility and cell labeling of L-arginine-functional beta-cyclodextrin-modified quantum dot probes

A series of quantum dots (QDs), CdSe, CdSe/CdS and CdSe/ZnSe, coated with L-arginine-modified beta-cyclodextrin (beta-CD-L-Arg) were prepared in a solution of H2O and hexane by ultrasonic method and characterized using PL, UV-vis, TEM, EDX and FTIR techniques. We observed that beta-CD-L-Arg-coated QDs are water-soluble and stable with high colloidal properties in water. Their photophysical properties are similar to those of trioctylphosphine oxide (TOPO)-coated nanocrystals. The quantum yield (QY) of beta-CD-L-Arg/CdSe/ZnSe QDs in water is 68%, which is much higher than those of beta-CD-L-Arg/CdSe/CdS (26%) and beta-CD-L-Arg/CdSe (13%). The in vitro cytotoxicity of these QDs was evaluated in ECV-304, SH-SY5Y and Hela cells and low cytotoxicity was observed. In particular, the beta-CD-L-Arg/CdSe/ZnSe QDs presented lower cytotoxicity to these cells (CC(50) value is 173 microg/mL in ECV-304 cells for 48h). This may be due to the presence of the ZnSe and beta-CD-L-Arg outlayer, which may improve the biocompatibility of QDs. The QDs were further investigated for biological labeling in ECV-304 cells using confocal laser scanning fluorescence microscopy. We found that these QDs were capable of localing to the cytoplasm of cells. These results demonstrate that the beta-CD-L-Arg-coated QDs could be used as a potential photoluminescent nanocrystal probing agent with good biocompatibility.

A solid-state deuterium NMR and sum-frequency generation study of the side-chain dynamics of peptides adsorbed onto surfaces

The artificial amphiphilic peptide LKalpha14 adopts a helical structure at interfaces, with opposite orientation of its leucine (L, hydrophobic) and lysine (K, hydrophilic) side chains. When peptides are adsorbed onto surfaces, different residue side chains necessarily have different proximities to the surface, depending on both their position in the helix and the composition of the surface itself. Deuterating the individual leucine residues (isopropyl-d(7)) permits the use of solid-state deuterium NMR spectroscopy as a site-specific probe of side-chain dynamics. In conjunction with sum-frequency generation as a probe of the peptide-binding face, we demonstrate that the mobility of specific leucine side chains at the interface is quantifiable in terms of their surface proximity.