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To achieve the task of fabricating functional tissues, scaffold materials that can be sufficiently vascularized to mimic functionality and complexity of native tissues are yet to be developed. Here, we report development of synthetic, biomimetic hydrogels that allow the rapid formation of a stable and mature vascular network both in vitro and in vivo. Hydrogels were fabricated with integrin binding sites and protease-sensitive substrates to mimic the natural provisional extracellular matrices, and endothelial cells cultured in these hydrogels organized into stable, intricate networks of capillary-like structures. The resulting structures were further stabilized by recruitment of mesenchymal progenitor cells that differentiated into a smooth muscle cell lineage and deposited collagen IV and laminin in vitro. In addition, hydrogels transplanted into mouse corneas were infiltrated with host vasculature, resulting in extensive vascularization with functional blood vessels. These results indicate that these hydrogels may be useful for applications in basic biological research, tissue engineering, and regenerative medicine., (Copyright 2010 Elsevier Ltd. All rights reserved.)

The field of tissue engineering aims to recapitulate healthy human organs and 3-D tissue structures in vitro and then transplant these constructs in vivo where they can be effectively integrated within the recipient patient and become perfused by the host circulation. To improve the design of materials for artificial tissue scaffolds, it would be ideal to have a high-throughput imaging system that allows one to directly monitor transplanted tissue constructs in live animals over an extended period of time. By combining such an assay with transgenic, cell-specific fluorescent reporters, one could monitor such parameters as tissue construct perfusion, donor cell survival, and donor-host cell interaction/integration. Here, we describe a protocol for a modified version of the classical corneal micropocket angiogenesis assay, employing it as a live imaging "window" to monitor angiogenic poly(ethylene glycol) (PEG)-based hydrogel tissue constructs.

The development and optimization of near-infrared (NIR)-absorbing nanoparticles for use as photothermal cancer therapeutic agents has been ongoing. This work exploits the properties of gold/gold sulfide NIR-absorbing nanoparticles (approximately 35-55 nm) that provide higher absorption (98% absorption and 2% scattering for gold/gold sulfide versus 70% absorption and 30% scattering for gold/silica nanoshells) as well as potentially better tumor penetration. The ability to ablate tumor cells in vitro and efficacy for photothermal cancer therapy is demonstrated, and an in vivo model shows significantly increased long-term, tumor-free survival. Furthermore, enhanced circulation and biodistribution is observed in vivo. This class of NIR-absorbing nanoparticles has the potential to improve upon photothermal tumor ablation for cancer therapy.

The ability of cells to migrate in response to mechanical gradients (durotaxis) and differential cell behavior in adhesion, spreading, and proliferation in response to substrate rigidity are key factors both in tissue engineering, in which materials must be selected to provide the appropriate mechanical signals, and in studies of mechanisms of diseases such as cancer and atherosclerosis, in which changes in tissue stiffness may inform cell behavior. Using poly(ethylene glycol) diacrylate hydrogels with varying polymer chain length and photolithographic patterning techniques, we are able to provide substrates with spatially patterned, tunable mechanical properties in both gradients and distinct patterns. The hydrogels can be patterned to produce anisotropic structures and exhibit patterned strain under mechanical loading. These hydrogels may be used to study cell response to substrate rigidity in both two and three dimensions and can also be used as a scaffold in tissue-engineering applications., (2009 Wiley Periodicals, Inc.)

Cancer is a leading cause of death in the United States and contributes to yearly rising health care costs. Current methods of treating cancer involve surgical removal of easily accessible tumors, radiation therapy, and chemotherapy. These methods do not always result in full treatment of the cancer and can in many cases damage healthy cells both surrounding the tissue area and systemically. Nanoshells are optically tunable core/shell nanoparticles that can be fabricated to strongly absorb in the near-infrared (NIR) region where light transmits deeply into tissue. When injected systemically, these particles have been shown to accumulate in the tumor due to the enhanced permeability and retention (EPR) effect and induce photothermal ablation of the tumor when irradiated with an NIR laser. Tumor specificity can be increased via functionalizing the nanoshell surface with tumor-targeting moieties. Nanoshells can also be made to strongly scatter light and therefore can be used in various imaging modalities such as dark-field microscopy and optical coherence tomography (OCT).

While it has long been understood that cells can sense and respond to a variety of stimuli, including soluble and insoluble factors, light, and externally applied mechanical stresses, the extent to which cells can sense and respond to the mechanical properties of their environment has only recently begun to be studied. Cell response to substrate stiffness has been suggested to play an important role in processes ranging from developmental morphogenesis to the pathogenesis of disease states and may have profound implications for cell and tissue culture and tissue engineering. Given the importance of this phenomenon, there is a clear need for systems for cell study in which substrate mechanics can be carefully defined and varied independently of biochemical and other signals. This review will highlight past work in the field of cell response to substrate rigidity as well as areas for future study.

The strong cetyltrimethylammonium bromide (CTAB) surfactant responsible for the synthesis and stability of gold nanorod solutions complicates their biomedical applications. The critical parameter to maintain nanorod stability is the ratio of CTAB to nanorod concentration. The ratio is approximately 740,000 as determined by chloroform extraction of the CTAB from a nanorod solution. A comparison of nanorod stabilization by thiol-terminal PEG and by anionic polymers reveals that PEGylation results in higher yields and less aggregation upon removal of CTAB. A heterobifunctional PEG yields nanorods with exposed carboxyl groups for covalent conjugation to antibodies with the zero-length carbodiimide linker EDC. This conjugation strategy leads to approximately two functional antibodies per nanorod according to fluorimetry and ELISA assays. The nanorods specifically targeted cells in vitro and were visible with both two-photon and confocal reflectance microscopies. This covalent strategy should be generally applicable to other biomedical applications of gold nanorods as well as other gold nanoparticles synthesized with CTAB.

The highly vascularized mouse eye is an excellent model system in which to elucidate the molecular genetic basis of blood vessel development and disease. However, the analysis of ocular vessel defects has traditionally been derived from fixed tissue, which fails to account for dynamic events such as blood flow and cell migration. To overcome the limitations of static analysis, tremendous advances in imaging technology and fluorescent protein reporter mouse lines now enable the direct visualization of developing cells in vivo. Here, we demonstrate that the Flk1-myr::mCherry transgenic mouse is an extremely useful live reporter with broad applicability to retinal, hyaloid, and choroid vascular research., (2009 Wiley-Liss, Inc.)

Advances in nanotechnology are enabling many new diagnostic and therapeutic approaches in cancer. In this review, examples where nanoparticles are employed to induce localized heating within tumors are explored. Approaches to nanoparticle-mediated thermal therapy include absorption of infrared light, radio frequency ablation, and magnetically-induced heating. These approaches have demonstrated high efficacy in animal models, and two are already in human clinical trials.

Angiogenesis, which is morphogenesis undertaken by endothelial cells (ECs) during new blood vessel formation, has been traditionally studied on natural extracellular matrix proteins. In this work, we aimed to regulate and guide angiogenesis on synthetic, bioactive poly(ethylene glycol)-diacrylate (PEGDA) hydrogels. PEGDA hydrogel is intrinsically cell nonadhesive and highly resistant to protein adsorption, allowing a high degree of control over presentation of ligands for cell adhesion and signaling. Since these materials are photopolymerizable, a variety of photolithographic technologies may be applied to spatially control presentation of bioactive ligands. To manipulate EC adhesion, migration, and tubulogenesis, the surface of PEGDA hydrogels was micropatterned with a cell adhesive ligand, Arg-Gly-Asp-Ser (RGDS), in desired concentrations and geometries. ECs cultured on these RGDS patterns reorganized their cell bodies into cord-like structures on 50-microm-wide stripes, but not on wider stripes, suggesting that EC morphogenesis can be regulated by geometrical cues. The cords formed by ECs were reminiscent of capillaries with cells participating in the self-assembly and reorganization into multicellular structures. Further, endothelial cord formation was stimulated on intermediate concentration of RGDS at 20 microg/cm(2), whereas it was inhibited at higher concentrations. This work has shown that angiogenic responses can be tightly regulated and guided by micropatterning of bioactive ligands and also demonstrated great potentials of micropatterned PEGDA hydrogels for various applications in tissue engineering, where vascularization prior to implantation is critical.

The development and use of functional tissue-engineered products is currently limited by the challenge of incorporating microvasculature. To this end, we have investigated strategies to facilitate vascularization in scaffold materials, in this case poly(ethylene glycol) (PEG) hydrogels. These hydrogels are hydrophilic and resist protein adsorption and subsequent non-specific cell adhesion, but can be modified to contain cell-adhesive ligands and growth factors to support cell and tissue function. Additionally, the hydrogel matrix can include proteolytically degradable peptide sequences in the backbone of the structure to allow cells to control scaffold biodegradation, allowing three-dimensional migration. Vascular endothelial growth factor (VEGF), a potent angiogenic signal, and the cell-adhesive peptide RGDS were each covalently attached to PEG monoacrylate linkers. PEGylated RGDS and VEGF were then covalently immobilized in PEG-diacrylate (PEGDA) hydrogels in 2D and 3D. Immobilized VEGF increased endothelial cell tubulogenesis on the surface of non-degradable PEGDA hydrogels 4-fold compared to controls without the growth factor. Endothelial cell behavior in 3D collagenase-degradable hydrogels modified with RGDS and VEGF was observed using time-lapse confocal microscopy. Bulk immobilization of VEGF in 3D collagenase-degradable RGDS-modified hydrogels increased endothelial cell motility 14-fold and cell-cell connections 3-fold. Covalent incorporation of PEGylated VEGF in PEG hydrogels can be a useful tool to promote endothelial cell migration, cell-cell contact formation and tubulogenesis in an effort to produce vascularized tissue-engineered constructs.

Controlled drug delivery systems represent advanced systems that can be tightly modulated by stimuli in order to treat diseases in which sustained drug release is undesirable. Among the many different stimuli-sensitive delivery systems, temperature-sensitive drug delivery systems offer great potential over their counterparts due to their versatility in design, tunability of phase transition temperatures, passive targeting ability and in situ phase transitions. Thus, thermosensitive drug delivery systems can overcome many of the hurdles of conventional drug delivery systems in order to increase drug efficacies, drug targeting and decrease drug toxicities. In an effort to further control existing temperature-responsive systems, current innovative applications have combined temperature with other stimuli such as pH and light. The result has been the development of highly sophisticated systems, which demonstrate exquisite control over drug release and represent huge advances in biomedical research.

Background: Biologic matrices offer a new approach to the management of abdominal wall defects when the use of other foreign material is not ideal. A member of our team (GEA) developed a biological decellularized matrix generated from harvested blood vessels of swine blood vessel matrix (BVMx). The aim of our study was to investigate whether this novel collagen-based biological matrix is safe and effective for the repair of abdominal wall hernia defects in a rat model., Methods: Full thickness abdominal wall defects were created in rats and repaired with our BVMx. After implantation as an underlay for 30 and 90 days, animals were sacrificed and the implanted material evaluated for herniation, adhesions, breaking strength, inflammation, and revascularization., Results: No evidence of herniation was noted at 30 (n = 7) or 90 (n = 7) days after repair. Adhesions, if present, were filmy and easily separated. The mean area of visceral adhesions to the BVMx was 18.9 +/- 11.0% at 30 days and 7.1 +/- 3.1% at 90 days post implantation (P = 0.33). The breaking strength of the BVMx-fascial interface was 4.5 +/- 0.8 N at 30 days and 4.5 +/- 2.4 N at 90 days post implantation (P = 0.98). Histologic analysis demonstrated that the BVMx elicited a mild transient inflammatory response and supported fibroblast migration, deposition of newly formed collagen, and neovascularization., Conclusions: These data confirm that this BVMx supports vascular ingrowth and provides adequate strength for the repair of abdominal wall defects. Future studies in a large animal model are required to assess its validity for human application.

Micropatterning techniques that control three-dimensional (3D) arrangement of biomolecules and cells at the microscale will allow development of clinically relevant tissues composed of multiple cell types in complex architecture. Although there have been significant developments to regulate spatial and temporal distribution of biomolecules in various materials, most micropatterning techniques are applicable only to two-dimensional patterning. We report here the use of two-photon laser scanning (TPLS) photolithographic technique to micropattern cell adhesive ligand (RGDS) in hydrogels to guide cell migration along pre-defined 3D pathways. The TPLS photolithographic technique regulates photo-reactive processes in microscale focal volumes to generate complex, free from microscale patterns with control over spatial presentation and concentration of biomolecules within hydrogel scaffolds. The TPLS photolithographic technique was used to dictate the precise location of RGDS in collagenase-sensitive poly(ethylene glycol-co-peptide) diacrylate hydrogels, and the amount of immobilized RGDS was evaluated using fluorescein-tagged RGDS. When human dermal fibroblasts cultured in fibrin clusters were encapsulated within the micropatterned collagenase-sensitive hydrogels, the cells underwent guided 3D migration only into the RGDS-patterned regions of the hydrogels. These results demonstrate the prospect of guiding tissue regeneration at the microscale in 3D scaffolds by providing appropriate bioactive cues in highly defined geometries.

Gold-coated silica nanoshells are a class of nanoparticles that can be designed to possess strong absorption of light in the near infrared (NIR) wavelength region. When injected intravenously, these nanoshells have been shown to accumulate in tumors and subsequently mediate photothermal treatment, leading to tumor regression. In this work, we sought to improve their specificity by targeting them to prostate tumor cells. We report selective targeting of PC-3 cells with nanoshells conjugated to ephrinA I, a ligand for EphA2 receptor that is overexpressed on PC-3 cells. We demonstrate selective photo-thermal destruction of these cells upon application of the NIR laser.

Although there have been extensive research efforts to create functional tissues and organs, most successes in tissue engineering have been limited to avascular or thin tissues. The major hurdle in development of more complex tissues lies in the formation of vascular networks capable of delivering oxygen and nutrients throughout the engineered constructs. Sufficient neovascularization in scaffold materials can be achieved through coordinated application of angiogenic factors with proper cell types in biomaterials. This review present the current research developments in the design of biomaterials and their biochemical and biochemical modifications to produce vascularized tissue constructs.

We are developing a novel approach to specifically target malignant brain tumor cells for photothermal ablation using antibody-tagged, near infrared-absorbing gold-silica nanoshells, referred to as immunonanoshells. Once localized to tumor cells, these nanoshells are extremely efficient at absorbing near-infrared light and can generate sufficient heat to kill cancer cells upon exposure to laser light. In this study, we evaluated the efficacy of immunonanoshells in vitro against both medulloblastoma and high-grade glioma cell lines. We used an antibody against HER2 to target gold-silica nanoshells to medulloblastoma cells, since HER2 is frequently overexpressed in medulloblastoma. We show that treatment with HER2-targeted nanoshells, but not non-targeted nanoshells, followed by exposure to laser light, can induce cell death in the HER2-overexpressing medulloblastoma cell line Daoy.2, as well as the parental Daoy cell line, which expresses HER2 at a moderate level, but not in dermal fibroblasts that do not express HER2. In an analogous set of experiments, we conjugated gold-silica nanoshells to an antibody against interleukin-13 receptor-alpha 2 (IL13Ralpha2), an antigen that is frequently overexpressed in gliomas. We demonstrate that these immunonanoshells are capable of inducing cell death in two high-grade glioma cell lines that express IL13Ralpha2, U373 and U87, but not in A431 epidermoid carcinoma cells that do not express significant levels of IL13Ralpha2. We believe that the use of antibody-tagged gold-silica nanoshells to selectively target cancer cells presents a promising new strategy for the treatment of central nervous system tumors that will minimize the damage and resulting toxicity to the surrounding normal brain.

Thrombosis and intimal hyperplasia are the principal causes of small-diameter vascular graft failure. To improve the long-term patency of polyurethane vascular grafts, we have incorporated both poly(ethylene glycol) and a diazeniumdiolate nitric oxide (NO) donor into the backbone of polyurethane to improve thromboresistance. Additionally, we have incorporated the laminin-derived cell adhesive peptide sequence YIGSR to encourage endothelial cell adhesion and migration, while NO release encourages endothelial cell proliferation. NO production by polyurethane films under physiological conditions demonstrated biphasic release, in which an initial burst of 70% of the incorporated NO was released within 2 days, followed by sustained release over 2 months. Endothelial cell proliferation in the presence of the NO-releasing material was increased as compared to control polyurethane, and platelet adhesion to polyethylene glycol-containing polyurethane was decreased significantly with the addition of the NO donor.

Silica-gold (SiO(2)-Au) nanoshells are a new class of nanoparticles that consist of a silica dielectric core that is surrounded by a gold shell. These nanoshells are unique because their peak extinctions are very easily tunable over a wide range of wavelengths particularly in the near infrared (IR) region of the spectrum. Light in this region is transmitted through tissue with relatively little attenuation due to absorption. In addition, irradiation of SiO(2)-Au nanoshells at their peak extinction coefficient results in the conversion of light to heat energy that produces a local rise in temperature. Thus, to develop a photothermal modulated drug delivery system, we have fabricated nanoshell-composite hydrogels in which SiO(2)-Au nanoshells of varying concentrations have been embedded within temperature-sensitive hydrogels, for the purpose of initiating a temperature change with light. N-isopropylacrylamide-co-acrylamide (NIPAAm-co-AAm) hydrogels are temperature-sensitive hydrogels that were fabricated to exhibit a lower critical solution temperature (LCST) slightly above body temperature. The resulting composite hydrogels had the extinction spectrum of the SiO(2)-Au nanoshells in which the hydrogels collapsed reversibly in response to temperature (50 degrees C) and laser irradiation. The degree of collapse of the hydrogels was controlled by the laser fluence as well as the concentration of SiO(2)-Au nanoshells. Modulated drug delivery profiles for methylene blue, insulin, and lysozyme were achieved by irradiation of the drug-loaded nanoshell-composite hydrogels, which showed that drug release was dependent upon the molecular weight of the therapeutic molecule.

Mesenchymal stem cells (MSCs) are used extensively in cartilage tissue engineering. We have developed a photopolymerizable poly(ethylene glycol diacrylate) (PEGDA) and poly(ethylene glycol) (PEG) semi-interpenetrating network that facilitates the in vitro chondrogenesis of human MSCs (hMSCs). Network parameters were altered and tested for their effects on subsequent matrix elaboration. The mesh size, calculated for each network based on equilibrium swelling ratios, was larger with lower PEGDA:PEG ratios and with higher PEGDA molecular weight. Changes in xi correlated with changes in extracellular matrix content and deposition in hMSC-seeded networks cultured in vitro for 6 weeks in defined chondrogenic medium. Networks constructed with PEGDA (6 kDa) and PEG (88 kDa) at 1:2 displayed intercellular deposition of proteoglycan. Furthermore, their proteoglycan contents were significantly higher than with PEGDA (6 kDa) hydrogels constructed without the PEG component and those constructed at a PEGDA:PEG ratio of 2:1, which both exhibited pericellular proteoglycan deposition. However, networks constructed with PEGDA (12 and 20 kDa) and PEG (88 kDa) exhibited intercellular deposition of proteoglycan regardless of the ratio employed. Collagen content was lower in networks constructed with PEGDA (12 and 20 kDa) and PEG (88 kDa) at a ratio of 1:2 than in those fabricated at the same PEGDA molecular weights at a ratio of 2:1. This study demonstrated that semi-interpenetrating network parameters influence not only extracellular matrix content, but also the deposition of the matrix molecules by hMSCs undergoing chondrogenesis. It is important that these parameters be considered carefully when creating scaffolds for tissue-engineered cartilage.

Metal nanoshells are core/shell nanoparticles that can be designed to either strongly absorb or scatter within the near-infrared (NIR) wavelength region ( approximately 650-950 nm). Nanoshells were designed that possess both absorption and scattering properties in the NIR to provide optical contrast for improved diagnostic imaging and, at higher light intensity, rapid heating for photothermal therapy. Using these in a mouse model, we have demonstrated dramatic contrast enhancement for optical coherence tomography (OCT) and effective photothermal ablation of tumors.

We have developed collagenase-sensitive hydrogels by incorporating a collagenase-sensitive fluorogenic substrate (CS-FS) within the backbone of a polyethylene glycol (PEG) copolymer to visualize collagenase activity during three-dimensional cell migration. CS-FS was synthesized by conjugating Bodipy dyes to a peptide with collagenase-sensitive sequence, Leu-Gly-Pro-Ala (LGPA), and the products were grafted into the collagenase-sensitive PEG hydrogels. CS-FS both in solution and hydrogels had an increase in the fluorescence intensity after proteolytic degradation by collagenase, but not by non-targeted proteases nor in the absence of an enzyme. Fibroblasts inside the hydrogels conjugated with CS-FS spread and extended lamellipodia in three dimensions over several days, and their pericellular collagenase-mediated proteolysis of the hydrogel was visualized via confocal microscopy. A matrix metalloproteinase inhibitor, served as a negative control, significantly reduced the degradation rate of CS-FS by collagenase and prevented cell migration and cell-mediated collagenase activity inside these hydrogels. In summary, we have fabricated collagenase-sensitive hydrogels incorporated with CS-FS and successfully visualized the collagenase activity during three-dimensional cell migration.

The success of ex vivo viral gene therapy systems for promoting bone formation could be improved through the development of systems to spatially localize gene expression. Towards this goal, we have encapsulated adenovirus-transduced human diploid fetal lung fibroblasts (MRC-5) expressing bone morphogenetic protein-type 2 (BMP-2) within non-degradable poly(ethylene glycol)-diacrylate (PEG-DA) hydrogels and implanted these intramuscularly to promote endochondral bone formation. To optimize BMP-2 secretion, the molecular weight of the polymers and cell densities were varied. Polymers with molecular weights of 6, 10, and 20 kDa were used to prepare hydrogels containing 1, 5, or 10 million transduced cells. The results showed that 10 million transduced fibroblasts that was the maximum number of cells feasible for encapsulation within PEG-DA 10 and 20 kDa hydrogels produced the highest amount of secreted BMP-2 protein. Encapsulation of MRC-5 and transduced fibroblasts resulted in 71 and 58% cell viability, respectively. The bioactivity of secreted BMP-2 protein from the hydrogels was confirmed with an alkaline phosphatase assay. Micro-CT of the lower limb muscles of NOD/SCID mice following implantation with hydrogels showed 39.5 +/- 25.0 mm3 mineralized tissue and 31.8 +/- 7.8 mm3 for the cell-injected mice, and the bone was localized to the hydrogel surfaces. Histology revealed bone as well as cartilage for both hydrogel implanted and cell-injected animals.

Transendothelial migration of neutrophils induces phenotypic changes that influence the interactions of neutrophils with extravascular tissue components. To assess the influence of transmigration on neutrophil chemokinetic motility, we used polyethylene glycol hydrogels covalently modified with specific peptide sequences relevant to extracellular matrix proteins. We evaluated fMLP-stimulated human neutrophil motility on peptides Arg-Gly-Asp-Ser (RGDS) and TMKIIPFNRTLIGG (P2), alone and in combination. RGDS is a bioactive sequence found in a number of proteins, and P2 is a membrane-activated complex-1 (Mac-1) ligand located in the gamma-chain of the fibrinogen protein. We evaluated, via video microscopy, cell motility by measuring cell displacement from origin and total accumulated distance traveled and then calculated average velocity. Results indicate that although adhesion and shape change were supported by hydrogels containing RGD alone, motility was not. Mac-1-dependent motility was supported on hydrogels containing P2 alone. Motility was enhanced through combined presentation of RGD and P2, engaging Mac-1, alpha(V)beta(3), and beta(1) integrins. Naïve neutrophil motility on combined peptide substrates was dependent on Mac-1, and alpha(4)beta(1) while alpha(6)beta(1) contributed to speed and linear movement. Transmigrated neutrophil motility was dependent on alpha(v)beta(3) and alpha(5)beta(1), and alpha(4)beta(1), alpha(6)beta(1), and Mac-1 contributed to speed and linear motion. Together, the data demonstrate that efficient neutrophil migration, dependent on multi-integrin interaction, is enhanced after transendothelial migration.

We have fabricated a hepatic tissue construct using a multilayer photopatterning platform for embedding cells in hydrogels of complex architecture. We first explored the potential of established hepatocyte culture models to stabilize isolated hepatocytes for photoencapsulation (e.g., double gel, Matrigel, cocultivation with nonparenchymal cells). Using photopolymerizable PEG hydrogels, we then tailored both the chemistry and architecture of the hydrogels to further support hepatocyte survival and liver-specific function. Specifically, we incorporated adhesive peptides to ligate key integrins on these adhesion-dependent cells. To identify the appropriate peptides for incorporation, the integrin expression of cultured hepatocytes was monitored by flow cytometry and their functional role in cell adhesion was assessed on full-length extracellular matrix (ECM) molecules and their adhesive peptide domains. In addition, we modified the hydrogel architecture to minimize barriers to nutrient transport for these highly metabolic cells. Viability of encapsulated cells was improved in photopatterned hydrogels with structural features of 500 microm in width over unpatterned, bulk hydrogels. Based on these findings, we fabricated a multilayer photopatterned PEG hydrogel structure containing the adhesive RGD peptide sequence to ligate the alpha5beta1 integrin of cocultured hepatocytes. Three-dimensional photopatterned constructs were visualized by digital volumetric imaging and cultured in a continuous flow bioreactor for 12 d where they performed favorably in comparison to unpatterned, unperfused constructs. These studies will have impact in the field of liver biology as well as provide enabling tools for tissue engineering of other organs.

Mechanical conditioning represents a potential means to enhance the biochemical and biomechanical properties of tissue engineered vascular grafts (TEVGs). A pulsatile flow bioreactor was developed to allow shear and pulsatile stimulation of TEVGs. Physiological 120 mmHg/80 mmHg peak-to-trough pressure waveforms can be produced at both fetal and adult heart rates. Flow rates of 2 mL/sec, representative of flow through small diameter blood vessels, can be generated, resulting in a mean wall shear stress of approximately 6 dynes/cm(2) within the 3 mm ID constructs. When combined with non-thrombogenic poly(ethylene glycol) (PEG)-based hydrogels, which have tunable mechanical properties and tailorable biofunctionality, the bioreactor represents a flexible platform for exploring the impact of controlled biochemical and biomechanical stimuli on vascular graft cells. In the present study, the utility of this combined approach for improving TEVG outcome was investigated by encapsulating 10T-1/2 mouse smooth muscle progenitor cells within PEG-based hydrogels containing an adhesive ligand (RGDS) and a collagenase degradable sequence (LGPA). Constructs subjected to 7 weeks of biomechanical conditioning had significantly higher collagen levels and improved moduli relative to those grown under static conditions.

Eph receptors and ephrin ligands are essential for vascular development and angiogenic remodeling. In this work, we developed biomimetic poly(ethylene glycol)-diacrylate hydrogels incorporated with ephrin-A1 and examined their angiogenic properties. Ephrin-A1 was covalently immobilized on the surface of hydrogels by chemical modification and photopolymerization. Ephrin-A1 immobilized on hydrogels was found to retain its capacity to stimulate endothelial cell adhesion in a dose-dependent manner as similar findings were observed on polystyrene culture wells pre-adsorbed with ephrin-A1. Cell adhesion stimulated by ephrin-A1 was abolished by treatment with soluble RGDS and anti-alpha(v)beta3 integrin but not anti-alpha(v)beta5 integrin antibodies, suggesting that ephrin-A1 activates cell adhesion through alpha(v)beta3 integrins. Also, surface immobilized ephrin-A1 was found to induce endothelial tubule formation with luminal diameters ranging 5-30 microm on hydrogels. The results of these studies demonstrate that pro-angiogenic properties of ephrin-A1 are preserved in hydrogels and suggest potential applications of this hydrogel system in regenerative medicine and tissue engineering.

The binding of activated integrins on the surface of leukocytes facilitates the adhesion of leukocytes to vascular endothelium during inflammation. Interactions between selectins and their ligands mediate rolling, and are believed to play an important role in leukocyte adhesion, though the minimal recognition motif required for physiologic interactions is not known. We have developed a novel system using poly(ethylene glycol) (PEG) hydrogels modified with either integrin-binding peptide sequences or the selectin ligand sialyl Lewis X (SLe(X)) within a parallel plate flow chamber to examine the dynamics of leukocyte adhesion to specific ligands. The adhesive peptide sequences arginine-glycine-aspartic acid-serine (RGDS) and leucine-aspartic acid-valine (LDV) as well as sialyl Lewis X were bound to the surface of photopolymerized PEG diacrylate hydrogels. Leukocytes perfused over these gels in a parallel plate flow chamber at physiological shear rates demonstrate both rolling and firm adhesion, depending on the identity and concentration of ligand bound to the hydrogel substrate. This new system provides a unique polymer-based model for the study of interactions between leukocytes and endothelium as well as a platform to develop improved scaffolds for cardiovascular tissue engineering.

We investigated the physical properties of low concentration ferroelectric nematic colloids, using calorimetry, optical methods, infrared spectroscopy, and capacitance studies. The resulting homogeneous colloids possess a significantly amplified nematic orientational coupling. We find that the nematic orientation coupling increases by approximately 10% for particle concentrations of 0.2%. A manifestation of the increased orientational order is that the clearing temperature of a nematic colloid increases by up to 40 degrees C compared to the pure liquid crystal host. A theoretical model is proposed in which the ferroelectric particles induce local dipoles whose effective interaction is proportional to the square of the orientational order parameter.

In this study, we aimed to increase crosslinking in collagen and elastin in the extracellular matrix through overexpression of lysyl oxidase (LO) in order to improve mechanical strength in dermal wounds during healing. We had used a gene activated matrix (GAM) approach to locally deliver plasmid DNA (pDNA) complexed with polyethylenimine (PEI) in collagen gels at the wound site for localized and sustained transfection of cells involved in the healing process. We first demonstrated in vitro that PEI-pDNA complexes in collagen gels could be taken up and expressed by cultured fibroblasts for at least 20 days. In vitro studies showed that fibroblast-seeded GAMs with the LO transgene exhibited over a 3-fold increase in mechanical strength as compared with a green fluorescent protein (GFP)-transgene control. Addition of an inhibitor of LO abolished this increase. We applied this system in a rat dermal wound healing model and showed that treatment with LO-producing GAMs led to significantly enhanced mechanical strength of the wound site.

Nanocrystalline titanium dioxide (nano-TiO(2)) is an important material used in commerce today. When designed appropriately it can generate reactive species (RS) quite efficiently, particularly under ultraviolet (UV) illumination; this feature is exploited in applications ranging from self-cleaning glass to low-cost solar cells. In this study, we characterize the toxicity of this important class of nanomaterials under ambient (e.g., no significant light illumination) conditions in cell culture. Only at relatively high concentrations (100 microg/ml) of nanoscale titania did we observe cytotoxicity and inflammation; these cellular responses exhibited classic dose-response behavior, and the effects increased with time of exposure. The extent to which nanoscale titania affected cellular behavior was not dependent on sample surface area in this study; smaller nanoparticlulate materials had effects comparable to larger nanoparticle materials. What did correlate strongly to cytotoxicity, however, was the phase composition of the nanoscale titania. Anatase TiO(2), for example, was 100 times more toxic than an equivalent sample of rutile TiO(2). The most cytotoxic nanoparticle samples were also the most effective at generating reactive oxygen species; ex vivo RS species generation under UV illumination correlated well with the observed biological response. These data suggest that nano-TiO(2) samples optimized for RS production in photocatalysis are also more likely to generate damaging RS species in cell culture. The result highlights the important role that ex vivo measures of RS production can play in developing screens for cytotoxicity.

When captured by a flat nematic-isotropic interface, colloidal particles can be dragged by it. As a result spatially periodic structures may appear, with the period depending on particle mass, size, and interface velocity (J.L. West, A. Glushchenko, G.X. Liao, Y. Reznikov, D. Andrienko, M.P. Allen, Phys. Rev. E 66, 012702 (2002)). If liquid crystal is sandwiched between two substrates, the interface takes a wedge-like shape, accommodating the interface-substrate contact angle and minimizing the director distortions on its nematic side. Correspondingly, particles move along complex trajectories: they are first captured by the interface and then "glide" towards its vertex point. Our experiments quantify this scenario, and numerical minimization of the Landau-de Gennes free energy allows for a qualitative description of the interfacial structure and the drag force.

We report the development of laser-scanning lithography (LSL), which employs a laser-scanning confocal microscope to pattern photoresists that can be utilized, for example, in the fabrication of masters for use in soft lithography. This convenient technique provides even exposure across the entire view field and facilitates accurate alignment of successive photoresist exposures. Features on the scale of 3 microm have been achieved to date with a 10x objective (NA 0.45). Virtual masks, instructions for laser irradiation, were drawn using the Region of Interest (ROI) function of a Zeiss LSM 510 microscope. These regions were then exposed to a 458 nm argon laser for 32 micros (0.9 mW/microm(2)). Differential interference contrast (DIC) imaging was utilized with a non-destructive 514 nm argon laser as an immediate quality check of each exposure, to align successive exposures, and to reduce chromatic aberration between imaging and exposure. Developed masters were replica-molded with poly(dimethylsiloxane) (PDMS); these masters were then utilized for microcontact printing of cell-adhesive self-assembled monolayers (SAMs) to demonstrate the utility of this process. Initial studies confirmed that human dermal fibroblast adhesion and spreading were limited to cell-adhesive SAM areas. LSL is a rapid, flexible, and readily available technique that will accelerate master design and preparation; moreover, it can be applied to additional forms of photolithography and photopolymerization for studies in cell biology, biomaterials design and evaluation, materials science, and surface chemistry.

A simple, inexpensive photolithographic method for surface patterning deformable, solvated substrates is demonstrated using photoactive poly(ethylene glycol) (PEG)-diacrylate hydrogels as model substrates. Photolithographic masks were prepared by printing the desired patterns onto transparencies using a laser jet printer. Precursor solutions containing monoacryloyl-PEG-peptide and photoinitiator were layered onto hydrogel surfaces. The acrylated moieties in the precursor solution were then conjugated in monolayers to specific hydrogel regions by exposure to UV light through the transparency mask. The effects of UV irradiation time and precursor solution concentration on the levels of immobilized peptide were characterized, demonstrating that bound peptide concentration can be controlled by tuning these parameters. Multiple peptides can be immobilized to a single hydrogel surface in distinct patterns by sequential application of this technique, opening up its potential use in co-cultures. In addition, 3D structures can be generated by incorporating PEG-diacrylate into the precursor solution. To evaluate the feasibility of using these patterned surfaces for guiding cell behavior, human dermal fibroblast adhesion on hydrogel surfaces patterned with acryloyl-PEG-RGDS was investigated. This patterning method may find use in tissue engineering, the elucidation of fundamental structure-function relationships, and the formation of immobilized cell and protein arrays for biotechnology.

Basic fibroblast growth factor (bFGF), stored bound to heparan sulfate proteoglycans in the extracellular matrix (ECM) of the arterial media, may initiate smooth muscle cell (SMC) proliferation after coronary intervention, thus contributing to restenosis. bFGF mobilization from ECM stores after injury may be induced by platelet degranulation products such as heparanase. Therapies aimed at the inhibition of bFGF release and activation may assist in prevention of restenosis. To test this theory, we first examined the mobilization and activation of bFGF in the arterial media by platelet-derived heparanase. Heparanase, locally delivered to the rat carotid artery, was found to release bFGF and induce substantial SMC proliferation in the absence of actual vascular injury. An antibody that neutralizes heparanase was then developed and evaluated in a rat carotid balloon injury model. Local delivery of anti-heparanase IgG was found to inhibit bFGF release by approximately 60% ( p < 0.001) at 4 d; this correlated with the significant reduction in neointima formation observed at 14 d (intimal area/medial area: control 1.3 +/- 0.3, anti-heparanase 0.35 +/- 0.12, p < 0.0001). Platelet-derived heparanase is therefore likely to be important in initiating events leading to restenosis via bFGF mobilization. Furthermore, heparanase neutralization may assist in the prevention of restenosis following vascular injury.

The cytotoxic response of cells in culture is dependant on the degree of functionalization of the single-walled carbon nanotube (SWNT). After characterizing a set of water-dispersible SWNTs, we performed in vitro cytotoxicity screens on cultured human dermal fibroblasts (HDF). The SWNT samples used in this exposure include SWNT-phenyl-SO(3)H and SWNT-phenyl-SO(3)Na (six samples with carbon/-phenyl-SO(3)X ratios of 18, 41, and 80), SWNT-phenyl-(COOH)(2) (one sample with carbon/-phenyl-(COOH)(2) ratio of 23), and underivatized SWNT stabilized in 1% Pluronic F108. We have found that as the degree of sidewall functionalization increases, the SWNT sample becomes less cytotoxic. Further, sidewall functionalized SWNT samples are substantially less cytotoxic than surfactant stabilized SWNTs. Even though cell death did not exceed 50% for cells dosed with sidewall functionalized SWNTs, optical and atomic force microscopies show direct contact between cellular membranes and water-dispersible SWNTs; i.e. the SWNTs in aqueous suspension precipitate out and selectively deposit on the membrane.

A number of strategies have been investigated to improve therapeutic vascularization of ischemic and bioengineered tissues. In these studies, we genetically modified vascular smooth muscle cells (VSMC) to promote endothelial cell proliferation, migration, and formation of microvascular networks. VSMCs were virally transduced to produce vascular endothelial growth factor (VEGF), which acts as a chemoattractant and mitogen of endothelial cells (EC). VSMCs transduced with VEGF(165) cDNA produced significant levels of the protein (2-4 ng/10(5) cell/day). The proliferation of ECs increased after exposure to VEGF-transfected SMCs or their conditioned media. The chemotactic response of ECs to the VEGF-producing cells was explored in two in vitro systems, the modified Boyden chamber assay and a 2-D fence-style migration assay, and both demonstrated increased migration of ECs in response to VEGF-transfected cells. Furthermore, endothelial cells seeded on top of the VEGF-transfected SMCs formed capillary-like structures. These results suggest that VSMCs genetically modified to produce VEGF could be a potential delivery mechanism to enhance endothelial cell migration and subsequent capillary formation, which in turn could improve vascularization of ischemic or regenerating tissue. Furthermore, this system could potentially be used as an in vitro test bed for evaluation of novel angiogenic and anti-angiogenic compounds.

Metal nanoshells are a new class of nanoparticles with highly tunable optical properties. Metal nanoshells consist of a dielectric core nanoparticle such as silica surrounded by an ultrathin metal shell, often composed of gold for biomedical applications. Depending on the size and composition of each layer of the nanoshell, particles can be designed to either absorb or scatter light over much of the visible and infrared regions of the electromagnetic spectrum, including the near infrared region where penetration of light through tissue is maximal. These particles are also effective substrates for surface-enhanced Raman scattering (SERS) and are easily conjugated to antibodies and other biomolecules. One can envision a myriad of potential applications of such tunable particles. Several potential biomedical applications are under development, including immunoassays, modulated drug delivery, photothermal cancer therapy, and imaging contrast agents.

Consisting of a silica core surrounded by a thin gold shell, nanoshells possess an optical tunability that spans the visible to the near infrared (NIR) region, a region where light penetrates tissues deeply. Conjugated with tumor-specific antibodies, NIR-absorbing immunonanoshells can preferentially bind to tumor cells. NIR light then heats the bound nanoshells, thus destroying the targeted cells. Antibodies can be consistently bound to the nanoshells via a bifunctional polyethylene glycol (PEG) linker at a density of approximately 150 antibodies per nanoshell. In vitro studies have confirmed the ability to selectively induce cell death with the photothermal interaction of immunonanoshells and NIR light. Prior to incubation with anti-human epidermal growth factor receptor (HER2) immunonanoshells, HER2-expressing SK-BR-3 breast carcinoma cells were seeded alone or adjacent to human dermal fibroblasts (HDFs). Anti-HER2 immunonanoshells bound to HER2-expressing cells resulted in the death of SK-BR-3 cells after NIR exposure only within the irradiated area, while HDFs remained viable after similar treatment since the immunonanoshells did not bind to these cells at high levels. Control nanoshells, conjugated with nonspecific anti-IgG or PEG, did not bind to either cell type, and cells continued to be viable after treatment with these control nanoshells and NIR irradiation.

A liquid-crystal optical phased-array technology that uses stressed liquid crystals provides a new type of tip-tilt wavefront corrector. It demonstrates a very fast time response (10 kHz) and high beam-steering efficiency (approximately 91%). The new technology presented here will allow for a nonmechanical, high-speed correction with simple device construction.

This study extends the capability for directing cell behavior using PEG-based hydrogels in tissue-engineering applications to include control over the spatial distribution of the adhesive peptide, RGDS. A continuous linear gradient was formed by simultaneously using a gradient maker to combine precursor solutions and using photopolymerization to lock the RGDS gradient in place. Hydrogels containing entrapped gradients of bovine serum albumin (BSA) were characterized using Coomassie brilliant blue stain, which indicated that BSA concentration increases along the hydrogel's length and that the steepness of the gradient's slope can be varied by changing the relative BSA concentrations in the precursor solutions. Human dermal fibroblasts responded to covalently immobilized RGDS gradients by changing their morphology to align in the direction of increasing RGDS concentration. After 24 h, approximately 46% of fibroblasts were aligned with the RGDS-gradient axis. This proportion of cells further increased to approximately 53% (p < 0.05) and approximately 58% after 48 and 96 h, respectively. Also, fibroblasts migrated differentially depending on the concentration of RGDS. Fibroblasts migrated approximately 48% further going up the concentration gradient (0 to 6 micromol/ml PEG-RGDS) than going down the concentration gradient. Migration up the concentration gradient was also approximately 33% greater than migration on control surfaces with a constant concentration of RGDS (2 micromol/ml), while migration down the gradient was reduced approximately 12% relative to the control surface. In addition, directed migration was further enhanced by increasing the RGDS gradient's slope. This hydrogel system is expected to be useful for directing cell migration to enhance the formation of engineered tissues.

This study examines the biological effects of water-soluble fullerene aggregates in an effort to evaluate the fundamental mechanisms that contribute to the cytotoxicity of a classic engineered nanomaterial. For this work we used a water-soluble fullerene species, nano-C60, a fullerene aggregate that readily forms when pristine C60 is added to water. Nano-C60 was cytotoxic to human dermal fibroblasts, human liver carcinoma cells (HepG2), and neuronal human astrocytes at doses>or= 50 ppb (LC50=2-50 ppb, depending on cell type) after 48 h exposure. This water-soluble nano-C60 colloidal suspension disrupts normal cellular function through lipid peroxidation; reactive oxygen species are responsible for the membrane damage. Cellular viability was determined through live/dead staining and LDH release. DNA concentration and mitochondrial activity were not affected by the nano-C60 inoculations to cells in culture. The integrity of cellular membrane was examined by monitoring the peroxy-radicals on the lipid bilayer. Subsequently, glutathione production was measured to assess the cell's reaction to membrane oxidation. The damage to cell membranes was observed both with chemical assays, and confirmed physically by visualizing membrane permeability with high molecular weight dyes. With the addition of an antioxidant, L-ascorbic acid, the oxidative damage and resultant toxicity of nano-C60 was completely prevented.

Many optical diagnostic approaches rely on changes in scattering and absorption properties to generate optical contrast between normal and diseased tissue. Recently, there has been increasing interest in using exogenous agents to enhance this intrinsic contrast with particular emphasis on the development for targeting specific molecular features of disease. Gold nanoshells are a class of core-shell nanoparticles with an extremely tunable peak optical resonance ranging from the near-UV to the mid-IR wavelengths. Using current chemistries, nanoshells of a wide variety of core and shell sizes can easily be fabricated to scatter and/or absorb light with optical cross sections often several times larger than the geometric cross section. Using gold nanoshells of different size and optical parameters, we employ Monte Carlo models to predict the effect of varying concentrations of nanoshells on tissue reflectance. The models demonstrate the importance of absorption from the nanoshells on remitted signals even when the optical extinction is dominated by scattering. Furthermore, because of the strong optical response of nanoshells, a considerable change in reflectance is observed with only a very small concentration of nanoshells. Characterizing the optical behavior of gold nanoshells in tissue will aid in developing nanoshells as contrast agents for optical diagnostics.

Using novel nitric oxide (NO)-generating polymeric hydrogels that can be rapidly photopolymerized in situ, we can deliver NO locally at the site of vascular injury. Depending on material design, these poly(ethylene glycol) (PEG)-based hydrogels can generate NO for up to 50 d. This study demonstrates the ability of nitric oxide-generating hydrogels (PEG-Cys-NO) to influence key components of the restenosis cascade both in vitro and in vivo. PEG-Cys-NO hydrogels inhibited smooth muscle cell proliferation, increased endothelial cell proliferation, and inhibited platelet adhesion in vitro. Moreover, in vivo, PEG-Cys-NO hydrogels inhibited intimal thickening in a rat carotid balloon injury model. The perivascular application of NO-generating polymers post-injury reduced neointima formation at 14 d by approximately 80% compared to controls (intimal area/medial area (I/M): PEG-Cys-NO=0.20+/-0.17, control=0.84+/-0.19, p<0.00002; intimal thickness: PEG-Cys-NO=12+/-10 microm, control=60+/-18 microm, p<0.00002). Treatment with the PEG-Cys-NO hydrogels caused a significant decrease in the per cent of proliferating cell nuclear antigen positive medial cells (29+/-5%) at 4 d as compared to treatment with the control hydrogels (51+/-1%, p<0.02). Additionally, vessel re-endothelialization at 14 d was slightly enhanced in the presence of the NO-generating hydrogels. These data indicate that localized delivery of NO from these hydrogels can significantly inhibit neointima formation in a rat carotid balloon injury model and suggest that these materials may be useful in preventing restenosis.

We have developed proteolytically degradable hydrogels with covalently immobilized fluorogenic protease substrates to visualize extracellular proteolytic activity and cell migration in three dimensions. Dye quenched-bovine serum albumin (DQ-BSA), a quenched, proteolytically activated fluorogenic substrate, was conjugated to poly(ethylene glycol) (PEG)-monoacrylate, and the product (DQ-BSA-PEG) was then covalently incorporated into proteolytically degradable and cell adhesive PEG hydrogels via photopolymerization. The DQ-BSA-PEG substrate in solution and incorporated into hydrogels exhibited significantly enhanced fluorescence after exposure to enzymes. Fibroblasts seeded within this hydrogel spread in three dimensions and extended lamellipodia. Cell migration and proteolytic activity were visualized using confocal microscopy. Proteolytic activity was concentrated near cell surfaces and remained present in the tracks where cell migration had occurred.

We have developed a novel nanoparticulate luminescent probe with inherent signal amplification upon interaction with a targeted proteolytic enzyme. This construct may be useful for imaging in cancer detection and diagnosis. In this system, quantum dots (QDs) are bound to gold nanoparticles (AuNPs) via a proteolytically degradable peptide sequence to non-radiatively suppress luminescence. A 71% reduction in luminescence was achieved with conjugation of AuNPs to QDs. Release of AuNPs by peptide cleavage restores radiative QD photoluminescence. Initial studies observed a 52% rise in luminescence over 47 h of exposure to 0.2 mg/mL collagenase. These probes can be customized for targeted degradation simply by changing the sequence of the peptide linker.

The ultimate goal of this research is to develop an injectable cell-scaffold system capable of permitting adipogenesis to abrogate soft tissue deficiencies resulting from trauma, tumor resection, and congenital abnormalities. The present work compares the efficacy of photopolymerizable poly(ethylene glycol) and specific derivatives as a scaffold for preadipocyte (adipocyte precursor cell) viability, adhesion, and proliferation. Four variations of a poly(ethylene glycol) scaffold are prepared and examined. The first scaffold consists of poly(ethylene glycol) diacrylate, which is not susceptible to hydrolysis or enzymatic degradation. Preadipocyte death is observed over 1 week in this hydrogel configuration. Adhesion sites, specifically the laminin-binding peptide sequence YIGSR, were incorporated into the second scaffold to promote cellular adhesion as a prerequisite for preadipocyte proliferation. Preadipocytes remain viable in this scaffold system, but do not proliferate in this nondegradable hydrogel. The third scaffold system studied consists of poly(ethylene glycol) modified with the peptide sequence LGPA to permit polymer degradation by cell-secreted collagenase. No adhesion peptide is incorporated into this scaffold system. Cellular proliferation is initially observed, followed by cell death. The previous three scaffold configurations do not permit preadipocyte adhesion and proliferation. In contrast, the fourth system studied, poly(ethylene glycol) modified to incorporate both LGPA and YIGSR, permits preadipocyte adherence and proliferation subsequent to polymer degradation. Our results indicate that a scaffold system containing specific degradation sites and cell adhesion ligands permits cells to adhere and proliferate, thus providing a potential cell-scaffold system for adipogenesis.

Background and Objective: Gold nanoshells are a new class of nanoparticles that can be designed to strongly absorb light in the near infrared (NIR). These particles provide much larger absorption cross-sections and efficiency than can be achieved with currently used chemical chromophores without photobleaching. In these studies, we have investigated the use of gold nanoshells as exogenous NIR absorbers to facilitate NIR laser-tissue welding., Study Design/materials and Methods: Gold nanoshells with peak extinction matching the NIR wavelength of the laser being used were manufactured and suspended in an albumin solder. Optimization work was performed on ex vivo muscle samples and then translated into testing in an in vivo rat skin wound-healing model. Mechanical testing of the muscle samples was immediately performed and compared to intact tissue mechanical properties. In the in vivo study, full thickness incisions in the dorsal skin of rats were welded, and samples of skin were excised at 0, 5, 10, 21, and 32 days for analysis of strength and wound healing response., Results: Mechanical testing of nanoshell-solder welds in muscle revealed successful fusion of tissues with tensile strengths of the weld site equal to the uncut tissue. No welding was accomplished with this light source when using solder formulations without nanoshells. Mechanical testing of the skin wounds showed sufficient strength for closure and strength increased over time. Histological examination showed good wound-healing response in the soldered skin., Conclusions: The use of nanoshells as an exogenous absorber allows the usage of light sources that are minimally absorbed by tissue components, thereby, minimizing damage to surrounding tissue and allowing welding of thicker tissues., ((c) 2005 Wiley-Liss, Inc.)

Bioactive polyurethaneurea modified with polyethylene glycol (PEG) and the endothelial cell-adhesive peptide YIGSR was synthesized and fabricated into microporous scaffolds. This material has shown appropriate mechanical properties for vascular graft applications, resists platelet adhesion, and promotes endothelialization. In the current study, microporous scaffolds were formed by a gasfoaming and salt-leaching method. The scaffolds showed highly interconnected open pores throughout the matrices, with porosity of approximately 78% and pore sizes of 20-200 microm. The peptide modified scaffolds showed superior mechanical properties over peptide-free scaffolds (tensile strength, 1.4 +/- 0.03 versus 0.19 +/- 0.01 MPa; p < 0.01). Bovine aortic endothelial cells were seeded on the scaffolds, and cell attachment, proliferation, extracellular matrix production, and migration were investigated. Histological and scanning electron microscopy analysis showed that few cells adhered on peptide-free scaffolds, whereas confluent endothelial cell monolayers formed along the pores in peptide-modified scaffolds. DNA content, hydroxyproline production, and cell migration were also significantly greater in peptide-modified scaffolds.

Independent optical control of microfluidic valves formed from optomechanically responsive nanocomposite hydrogels is achieved using strongly absorbing Au nanoparticles or nanoshells embedded within a thermally responsive polymer. Valves formed from composites with different nanoparticles could be independently controlled by changing the illumination wavelength., (Copyright © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)