Hot off the presses! Apr 01 Biomater

The Apr 01 issue of the Biomater is now up on Pubget (About Biomater): if you're at a subscribing institution, just click the link in the latest link at the home page. (Note you'll only be able to get all the PDFs in the issue if your institution subscribes to Pubget.)

Latest Articles Include:

• Editorial board
  - Biomater 32(10):IFC (2011)
  
• Silk fibroin in ocular tissue reconstruction
  - Biomater 32(10):2445-2458 (2011)
  The silk structural protein fibroin displays potential for use in tissue engineering. We present here our opinion of its value as a biomaterial for reconstructing tissues of clinical significance within the human eye. We review the strengths and weaknesses of using fibroin in those parts of the eye that we believe are most amenable to cellular reconstruction, namely the corneoscleral limbus, corneal stroma, corneal endothelium and outer blood-retinal barrier (Ruysch's complex). In these areas we find that by employing the range of manufacturing products afforded by fibroin, relevant structural assemblies can be made for cells expanded ex vivo. Significant questions now need to be answered concerning the effect of this biomaterial on the phenotype of key cell types and the biocompatibility of fibroin within the eye. We conclude that fibroin's strength, structural versatility and potential for modification, combined with the relative simplicity of associated manufact! uring processes, make fibroin a worthy candidate for further exploration.
• Cultivation and recovery of vascular endothelial cells in microchannels of a separable micro-chemical chip
  - Biomater 32(10):2459-2465 (2011)
  Various micro cell culture systems have recently been developed. However, it is extremely difficult to recover cultured cells from a microchannel because the upper and lower substrates of a microchip are permanently combined. Therefore, we developed a cell culture and recovery system that uses a separable microchip with reversible combining that allows separation between closed and open channels. To realize this system, two problems related to microfluidic control—prevention of leakage and non-invasive recovery of cultured cells from the substrate—must be overcome. In the present study, we used surface chemistry modification to solve both problems. First, octadecyltrimethoxysilane (ODTMS) was utilized to control the Laplace pressure at the liquid/vapor phase interface, such that it was directed toward the microchannels, which suppressed leakage from the slight gap between two substrates. Second, a thermoresponsive polymer poly(N-isopropyl acrylamide) (PNIPAAm) was ! used to coat the surface of the ODTMS-modified microchannel by UV-mediated photopolymerization. PNIPAAm substrates are well known for controlled cell adhesion/detachment by alteration of temperature. Finally, the ODTMS- and PNIPAAm-modified separable microchips were subjected to patterning, and human arterial endothelial cells (HAECs) were cultured in the resulting microchannels with no leakage. After 96 h of the culture, the HAECs were detached from the microchips by decreasing the temperature and were then recovered from the microchannels. This study is the first to demonstrate the recovery of living cells cultured in a microchannel, and may be useful as a fundamental technique for vascular tissue engineering.
• Controlling the adhesion and differentiation of mesenchymal stem cells using hyaluronic acid-based, doubly crosslinked networks
  - Biomater 32(10):2466-2478 (2011)
  We have created hyaluronic acid (HA)-based, cell-adhesive hydrogels that direct the initial attachment and the subsequent differentiation of human mesenchymal stem cells (MSCs) into pre-osteoblasts without osteogenic supplements. HA-based hydrogel particles (HGPs) with an average diameter of 5–6 μm containing an estimated 2.2 wt% gelatin (gHGPs) were synthesized by covalent immobilization of gelatin to HA HGPs prepared via an inverse emulsion polymerization technique. Separately, a photocrosslinkable HA macromer (HAGMA) was synthesized by chemical modification of HA with glycidyl methacrylate (GMA). Doubly crosslinked networks (DXNs) were engineered by embedding gHGPs in a secondary network established by HAGMA at a particle concentration of 2.5 wt%. The resultant composite gels, designated as HA-gHGP, have an average compressive modulus of 21 kPa, and are non-toxic to the cultured MSCs. MSCs readily attached to these gels, exhibiting an early stage of stress fiber ! assembly 3 h post seeding. By day 7, stellate-shaped cells with extended filopodia were found on HA-gHGP gels. Moreover, cells had migrated deep into the matrix, forming a three dimensional, branched and interconnected cell community. Conversely, MSCs on the control gels lacking gelatin moieties formed isolated spheroids with rounded cell morphology. After 28 days of culture on HA-gHGP, Type I collagen production and mineral deposition were detected in the absence of osteogenic supplements, suggesting induction of osteogenic differentiation. In contrast, cells on the control gels expressed markers for adipogenesis. Overall, the HA-gHGP composite matrix has great promise for directing the osteogenic differentiation of MSCs by providing an adaptable environment through the spatial presentation of cell-adhesive modules.
• Ruthenium-catalyzed photo cross-linking of fibrin-based engineered tissue
  - Biomater 32(10):2479-2488 (2011)
  Most cross-linking methods utilize chemistry or physical processes that are detrimental to cells and tissue development. Those that are not as harmful often do not provide a level of strength that ultimately meets the required application. The purpose of this work was to investigate the use of a ruthenium–sodium persulfate cross-linking system to form dityrosine in fibrin-based engineered tissue. By utilizing the tyrosine residues inherent to fibrin and cell-deposited proteins, at least 3-fold mechanical strength increases and 10-fold stiffness increases were achieved after cross-linking. This strengthening and stiffening effect was found to increase with culture duration prior to cross-linking such that physiologically relevant properties were obtained. Fibrin was not required for this effect as demonstrated by testing with collagen-based engineered tissue. Cross-linked tissues were implanted subcutaneously and shown to have minimal inflammation after 30 days, simil! ar to non-cross-linked controls. Overall, the method employed is rapid, non-toxic, minimally inflammatory, and is capable of increasing strength and stiffness of engineered tissues to physiological levels.
• Autologous extracellular matrix scaffolds for tissue engineering
  - Biomater 32(10):2489-2499 (2011)
  Development of autologous scaffolds has been highly desired for implantation without eliciting adverse inflammatory and immune responses. However, it has been difficult to obtain autologous scaffolds by tissue decellularization because of the restricted availability of autologous donor tissues from a patient. Here we report a method to prepare autologous extracellular matrix (aECM) scaffolds by combining culture of autologous cells in a three-dimensional template, decellularization, and template removal. The aECM scaffolds showed excellent biocompatibility when implanted. We anticipate that "Full Autologous Tissue Engineering" can be realized to minimize undesirable host tissue responses by culturing the patient's own cells in an aECM scaffold.
• Synthetic multicellular cell-to-cell communication in inkjet printed bacterial cell systems
  - Biomater 32(10):2500-2507 (2011)
  We utilized a commercially available materials printer to investigate synthetic multicellular cell-to-cell communication because inkjet printing technology makes it easy to print spatiotemporal patterns of soluble biomolecules and live cells. Since cells are genetically programmed to communicate with one another via synthetic biology, cell signaling molecules secreted by one cell microcolony can induce two neighboring cell microcolonies to respond by expressing or stopping the expression of fluorescent protein genes. In this work, we not only characterize the printing parameters such as the initial seeding numbers, spacing distances, microcolony sizes, printing timings, and printed patterns of cells but also demonstrate that the use of the proposed printing technology can provide a useful means for many synthetic biologists to simplify and speed up the investigation of cell-to-cell communication between synthetic bacterial cells.
• Stem-cell-capturing collagen scaffold promotes cardiac tissue regeneration
  - Biomater 32(10):2508-2515 (2011)
  Stem cell based therapy is coming of age. Besides stem cell transplantation, it has been a goal to use native autologous stem cells for tissue regeneration. However, the recruitment of native autologous stem cells at the targeting site has not been sufficient which limits the clinical application of autologous stem cells. Biomaterials have been increasingly used in tissue repair. They not only serve as scaffolds for cell proliferation, differentiation, and also provide guidance for 3-D reestablishment. In this study, we have attempted to enrich autologous stem cells at the wound site through a stem-cell-capturing collagen scaffold by conjugating with a stem cell specific antibody. Sca-1 is a common surface marker of hematopoietic, cardiac and skeletal muscle stem cells. Due to the interaction of antibody and antigen, Sca-1 positive cells could be enriched to the functional collagen scaffold both in vitro and in vivo. When the functional collagen scaffold is transplante! d into C57/BL6 mouse as a patch to repair a surgical heart defect, the regeneration of cardiomyocytes has been observed. Thus, the collagen scaffolds covalently conjugated with stem cell specific antibody could be an effective approach to promote tissue regeneration.
• The inhibition of platelet adhesion and activation on collagen during balloon angioplasty by collagen-binding peptidoglycans
  - Biomater 32(10):2516-2523 (2011)
  Collagen is a potent stimulator for platelet adhesion, activation, and thrombus formation, and provides a means for controlling blood loss due to injury, and recruiting inflammatory cells for fighting infection. Platelet activation is not desirable however, during balloon angioplasty/stent procedures in which balloon expansion inside an artery exposes collagen, initiating thrombosis, and inflammation. We have developed biomimetic polymers, termed peptidoglycans, composed of a dermatan sulfate backbone with covalently attached collagen-binding peptides. The peptidoglycan binds to collagen, effectively masking it from platelet activation. The lead peptidoglycan binds to collagen with high affinity (KD = 24 nm) and inhibits platelet binding and activation on collagen in both static studies and under flow, while promoting endothelial regrowth on collagen. Application for angioplasty is demonstrated in the Ossabaw miniature pig by fast delivery to the vessel wall through a ! therapeutic infusion catheter with a proprietary PTFE porous balloon. The peptidoglycan is an approach for locally preventing platelet deposition and activation on collagen. It can be used during angioplasty to prevent platelet deposition on target vessels and could be used in any vessel, including those not amenable to stent deployment.
• Hydrogel network design using multifunctional macromers to coordinate tissue maturation in ovarian follicle culture
  - Biomater 32(10):2524-2531 (2011)
  Synthetic hydrogels with tunable properties are appealing for regenerative medicine. A critical limitation in hydrogel design at low solids concentration is the formation of defects, which increase gelation times and swelling, and reduce elasticity. Here, we report that trifunctional cross-linking peptides applied to 4-arm poly-(ethylene glycol) (PEG) hydrogels decreased swelling and gelation time relative to bi-functional crosslinkers. In contrast to bi-functional peptides, the third cross-linking site on the peptide created a branch point if an intramolecular cross-link formed, which prevented non-functional "dangling-ends" in the hydrogel network and enhanced the number of elastically active cross-links. The improved network formation enabled mouse ovarian follicle encapsulation and maturation in vitro. Hydrogels with bi-functional crosslinkers resulted in cellular dehydration, likely due to osmosis during the prolonged gelation. For trifunctional crosslinkers, ! the hydrogels supported a 17-fold volumetric expansion of the tissue during culture, with expansion dependent on the ability of the follicle to rearrange its microenvironment, which is controlled through the sensitivity of the cross-linking peptide to the proteolytic activity of plasmin. The improved network design enabled ovarian follicle culture in a completely synthetic system, and can advance fertility preservation technology for women facing premature infertility from anticancer therapies.
• Intracranial microcapsule drug delivery device for the treatment of an experimental gliosarcoma model
  - Biomater 32(10):2532-2539 (2011)
  Controlled-release drug delivery systems are capable of treating debilitating diseases, including cancer. Brain cancer, in particular glioblastoma multiforme (GBM), is an extremely invasive cancer with a dismal prognosis. The use of drugs capable of crossing the blood–brain barrier has shown modest prolongation in patient survival, but not without unsatisfactory systemic, dose-limiting toxicity. Among the reasons for this improvement include a better understanding of the challenges of delivery of effective agents directly to the brain tumor site. The combination of carmustine delivered by biodegradable polyanhydride wafers (Gliadel®), with the systemic alkylating agent, temozolomide, allows much higher effective doses of the drug while minimizing the systemic toxicity. We have previously shown that locally delivering these two drugs leads to further improvement in survival in experimental models. We postulated that microcapsule devices capable of releasing temozolom! ide would increase the therapeutic capability of this approach. A biocompatible drug delivery microcapsule device for the intracranial delivery of temozolomide is described. Drug release profiles from these microcapsules can be modulated based on the physical chemistry of the drug and the dimensions of the release orifices in these devices. The drug released from the microcapsules in these experiments was the clinically utilized chemotherapeutic agent, temozolomide. In vitro studies were performed in order to test the function, reliability, and drug release kinetics of the devices. The efficacy of the temozolomide-filled microcapsules was tested in an intracranial experimental rodent gliosarcoma model. Immunohistochemical analysis of tissue for evidence of DNA strand breaks via terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay was performed. The experimental release curves showed mass flow rates of 36 μg/h for single-orifice devices and an 88 μg/h! mass flow rate for multiple-orifice devices loaded with temoz! olomide. In vivo efficacy results showed that localized intracranial delivery of temozolomide from microcapsule devices was capable of prolonging animal survival and may offer a novel form of treatment for brain tumors.
• Enhancement of cell recognition in vitro by dual-ligand cancer targeting gold nanoparticles
  - Biomater 32(10):2540-2545 (2011)
  A dual-ligand gold nanoparticle (DLGNP) was designed and synthesized to explore the therapeutic benefits of multivalent interactions between gold nanoparticles (GNPs) and cancer cells. DLGNP was tested on human epidermal cancer cells (KB), which had high expression of folate receptor. The cellular uptake of DLGNP was increased by 3.9 and 12.7 folds compared with GNP-folate or GNP-glucose. The enhanced cell recognition was due to multivalent interactions between both ligands on GNPs and cancer cells as shown by the ligand competition experiments. Furthermore, the multivalent interactions increased contrast between cells with high and low expression of folate receptors. The enhanced cell recognition enabled DLGNP to kill KB cells under X-ray irradiation at a dose that was safe to folate receptor low-expression (such as normal) cells. Thus DLGNP has the potential to be a cancer-specific nano-theranostic agent.
• An assessment of the risks of carcinogenicity associated with polyhydroxyalkanoates through an analysis of DNA aneuploid and telomerase activity
  - Biomater 32(10):2546-2555 (2011)
  Polyhydroxyalkanoates (PHA) are aliphatic polyesters synthesized by many bacteria. Because of their flexible mechanical strengths, superior elastic property, biodegradability and biocompatibility, PHA have been developed for applications as medical implants, drug delivery matrices, and devices to support cell growth. Lots of studies showed that PHA matrices improved cell proliferation and tissue regeneration. However, the possibility of whether rapid cell proliferation on PHA matrices will induce tumor formation is unclear. Here we confirmed that proliferating rat osteoblasts grown on films of various PHA including PHB, PHBV, P3HB4HB, PHBHHx and PHBVHHx did not lead to cancer induction at least for p8th. Cell proliferation was evaluated by the incorporation of 5-bromodeoxyuridine (BrdU), the transcript expression of cancer related genes Ki67, p53 and c-Fos was monitored by quantitative Real-time PCR, the results showed the cells proliferating on the PHA films were unde! r normal cell cycle regulation. Moreover, DNA aneuploid and telomerase activity were only detected in the positive control UMR-108 cells; compared with cells grown on films, UMR-108 cells had longer telomeres, further demonstrated the normal status of cells proliferating on the PHA films. It indicated that the above PHA family members could be used to support cell growth without indication of susceptibility to tumor induction. These results will be important for promoting the application of PHA as new members of biomaterials.
• Optical imaging of intracellular reactive oxygen species for the assessment of the cytotoxicity of nanoparticles
  - Biomater 32(10):2556-2565 (2011)
  The generation of intracellular reactive oxygen species (ROS) was optically monitored using ROS-sensitive gold nanoprobes in response to an exposure of nanoparticles (NPs). Fluorescent dye-labeled hyaluronic acid was grafted onto the surface of gold nanoparticles (HF-AuNPs) for imaging intracellular ROS. The ultrasensitive detection of intracellular ROS was utilized as a powerful analytical tool to assess early cellular toxicities of monodisperse polystyrene (PS) particles with different sizes and different functional groups on the surface. The effect of PEGylation on the surface of PS NPs was also investigated by evaluating intracellular ROS generation. For various PS NPs, the extent of intracellular ROS was well correlated with cellular uptake, apoptosis inducing activity, and cytotoxic effect of NPs. In addition to the nanoparticles, commonly used polymeric gene carriers such as linear and branched polyethylenimine (PEI) were tested to analyze their extent of intrac! ellular ROS generation related to cellular toxicity. This study demonstrated that sensitive and optical detection of intracellular ROS generation can provide a valuable toxicity index value for a wide range of NPs as an early indicator for cellular responses.
• Isolating single primary rat hippocampal neurons & astrocytes on ultra-thin patterned parylene-C/silicon dioxide substrates
  - Biomater 32(10):2566-2574 (2011)
  We report here the patterning of primary rat neurons and astrocytes from the postnatal hippocampus on ultra-thin parylene-C deposited on a silicon dioxide substrate, following observations of neuronal, astrocytic and nuclear coverage on strips of different lengths, widths and thicknesses. Neuronal and glial growth was characterized 'on', 'adjacent to' and 'away from' the parylene strips. In addition, the article reports how the same material combination can be used to isolate single cells along thin tracks of parylene-C. This is demonstrated with a series of high magnification images of the experimental observations for varying parylene strip widths and thicknesses. Thus, the findings demonstrate the possibility to culture cells on ultra-thin layers of parylene-C and localize single cells on thin strips. Such work is of interest and significance to the Neuroengineering and Multi-Electrode Array (MEA) communities, as it provides an alternative insulating mat! erial in the fabrication of embedded micro-electrodes, which can be used to facilitate single cell stimulation and recording in capacitive coupling mode.
• Multifunctional gadolinium-based dendritic macromolecules as liver targeting imaging probes
  - Biomater 32(10):2575-2585 (2011)
  The quest for highly efficient and safe contrast agents has become the key factor for successful application of magnetic resonance imaging (MRI). The gadolinium (Gd) based dendritic macromolecules, with precise and tunable nanoscopic sizes, are excellent candidates as multivalent MRI probes. In this paper, a novel series of Gd-based multifunctional peptide dendritic probes (generation 2, 3, and 4) possessing highly controlled structures and single molecular weight were designed and prepared as liver MRI probes. These macromolecular Gd-ligand agents exhibited up to 3-fold increase in T1relaxivity comparing to Gd-DTPA complexes. No obvious in vitro cytotoxicity was observed from the measured concentrations. These dendritic probes were further functionalized with multiple galactosyl moieties and led to much higher cell uptake in vitro as demonstrated in T1-weighted scans. During in vivo animal studies, the probes provided better signal intensity (SI) enhancement in mouse ! liver, especially at 60 min post-injection, with the most efficient enhancement from the galactosyl moiety decorated third generation dendrimer. The imaging results were verified with analysis of Gd content in liver tissues. The design strategy of multifunctional Gd-ligand peptide dendritic macromolecules in this study may be used for developing other sensitive MRI probes with targeting capability.
• Intracellularly monitoring/imaging the release of doxorubicin from pH-responsive nanoparticles using Förster resonance energy transfer
  - Biomater 32(10):2586-2592 (2011)
  Stimuli-responsive nanoparticles (NPs) have been receiving much attention as a drug-delivery vehicle for therapeutic applications; once internalized into cells, the intracellular fate of NPs and their drug release behavior in response to local stimuli must be understood for efficient delivery of therapeutics. In this study, we prepared pH-responsive doxorubicin (DOX)-loaded NPs, made of N-palmitoyl chitosan bearing a Cy5 moiety (Cy5–NPCS), as an anticancer delivery device. The results of our molecular dynamic simulations showed that the ability of Cy5–NPCS to self-associate offered the close proximity between the donor (DOX) and the acceptor (Cy5) required for Förster resonance energy transfer (FRET), while the pH-driven structure transition prescribed the on-to-off switch of the energy transfer. The caveolae-mediated pathway played a major role in the internalization of NPCS NPs. Using the concept of FRET, we found that the DOX fluorescence in the cytosol was fir! st seen when NPCS NPs were present in the slightly acidic early endosomes. Following NPCS NPs trafficking into a more acidic organelle (late endosomes/lysosomes), a more evident release of DOX into the cytosol was observed; the released DOX was then gradually accumulated in the cell nuclei, leading to a significant cytotoxicity. Understanding the fate of NPs with respect to their intracellular localization and drug release behavior is crucial for the rational design of drug carriers.
• Modulation of biological processes in the nucleus by delivery of DNA oligonucleotides conjugated with gold nanoparticles
  - Biomater 32(10):2593-2604 (2011)
  The development of a method that can efficiently deliver nucleic acids into the nucleus of living systems remains one of the key challenges for experimental and therapeutic use of nonbiological gene delivery agents. In the current study, we demonstrate a functionalized gold nanoparticle (AuNP) that can serve as a universal carrier for the delivery of DNA oligonucleotides (oligos) into the nucleus. We designed various types of DNA oligos to redirect alternative splicing of pre-mRNAs, such as MCL-1 and BCL-6, and to sequester transcriptional factors, including estrogen receptor α and p53. We successfully delivered the oligos into the nucleus, resulting in the targeted effects. In addition, injection of the antisense DNAs into a xenograft tumor in a mouse model system resulted in inhibited development of the tumor by redirecting the alternative splicing of the pre-mRNA. Our findings show that these nanoconjugates efficiently load and deliver antisense DNAs to redirect ge! ne splicing or double-stranded DNAs to decoy gene transcription by transcriptional factors into mammalian cells and in vivo animals. Therefore, our lego-like AuNP gene delivery system can be used universally to control different biological processes by modulating nuclear gene expression events in living systems.
• The effect of internalizing human single chain antibody fragment on liposome targeting to epithelioid and sarcomatoid mesothelioma
  - Biomater 32(10):2605-2613 (2011)
  Immunoliposomes (ILs) anchored with internalizing human antibodies capable of targeting all subtypes of mesothelioma can be useful for targeted imaging and therapy of this malignant disease. The objectives of this study were to evaluate both the in vitro and in vivo tumor targeted internalization of novel internalizing human single chain antibody (scFv) anchored ILs on both epithelioid (M28) and sarcomatoid (VAMT-1) subtypes of human mesothelioma. ILs were prepared by post-insertion of mesothelioma-targeting human scFv (M1) onto preformed liposomes and radiolabeled with 111In (111In-IL-M1), along with control non-targeted liposomes (111In-CL). Incubation of 111In-IL-M1 with M28, VAMT-1, and a control non-tumorigenic cell line (BPH-1) at 37 °C for 24 h revealed efficient binding and rapid internalization of ILs into both subtypes of tumor cells but not into the BPH-1 cells; internalization accounted for approximately 81–94% of total cell accumulation in mesothelioma ! cells compared to 37–55% in control cells. In tumor-bearing mice intravenous (i.v.) injection of 111In-IL-M1 led to remarkable tumor accumulation: 4% and 4.7% injected dose per gram (% ID/g) for M28 and VAMT-1 tumors, respectively, 48 h after injection. Furthermore, tumor uptake of 111In-IL-M1 in live xenograft animal models was verified by single photon emission computed tomography (SPECT/CT). In contrast, i.v. injection of 111In-CL in tumor-bearing mice revealed very low uptake in both subtypes of mesothelioma, 48 h after injection. In conclusion, M1 scFv-anchored ILs showed selective tumor targeting and rapid internalization into both epithelioid and sarcomatoid subtypes of human mesothelioma, demonstrating its potential as a promising vector for enhanced tumor drug targeting.
• Secreted Gaussia luciferase as a sensitive reporter gene for in vivo and ex vivo studies of airway gene transfer
  - Biomater 32(10):2614-2624 (2011)
  The cationic lipid GL67A is one of the more efficient non-viral gene transfer agents (GTAs) for the lungs, and is currently being evaluated in an extensive clinical trial programme for cystic fibrosis gene therapy. Despite conferring significant expression of vector-specific mRNA following transfection of differentiated human airway cells cultured on air liquid interfaces (ALI) cultures and nebulisation into sheep lung in vivo we were unable to detect robust levels of the standard reporter gene Firefly luciferase (FLuc). Recently a novel secreted luciferase isolated from Gaussia princeps (GLuc) has been described. Here, we show that (1) GLuc is a more sensitive reporter gene and offers significant advantages over the traditionally used FLuc in pre-clinical models for lung gene transfer that are difficult to transfect, (2) GL67A-mediated gene transfection leads to significant production of recombinant protein in these models, (3) promoter activity in ALI cultures mimics! published in vivo data and these cultures may, therefore, be suitable to characterise promoter activity in a human ex vivo airway model and (4) detection of GLuc in large animal broncho-alveolar lavage fluid and serum facilitates assessment of duration of gene expression after gene transfer to the lungs. In summary, we have shown here that GLuc is a sensitive reporter gene and is particularly useful for monitoring gene transfer in difficult to transfect models of the airway and lung. This has allowed us to validate that GL67A, which is currently in clinical use, can generate significant amounts of recombinant protein in fully differentiated human air liquid interface cultures and the ovine lung in vivo.
• Drug permeation across intestinal epithelial cells using porous silicon nanoparticles
  - Biomater 32(10):2625-2633 (2011)
  Mesoporous silicon particles hold great potential in improving the solubility of otherwise poorly soluble drugs. To effectively translate this feature into the clinic, especially via oral or parenteral administration, a thorough understanding of the interactions of the micro- and nanosized material with the physiological environment during the delivery process is required. In the present study, the behaviour of thermally oxidized porous silicon particles of different sizes interacting with Caco-2 cells (both non-differentiated and polarized monolayers) was investigated in order to establish their fate in a model of intestinal epithelial cell barrier. Particle interactions and TNF-α were measured in RAW 264.7 macrophages, while cell viabilities, reactive oxygen species and nitric oxide levels, together with transmission electron microscope images of the polarized monolayers, were assessed with both the Caco-2 cells and RAW 264.7 macrophages. The results showed a concen! tration and size dependent influence on cell viability and ROS-, NO- and TNF-α levels. There was no evidence of the porous nanoparticles crossing the Caco-2 cell monolayers, yet increased permeation of the loaded poorly soluble drug, griseofulvin, was shown.
• Controlled architectural and chemotactic studies of 3D cell migration
  - Biomater 32(10):2634-2641 (2011)
  Chemotaxis plays a critical role in tissue development and wound repair, and is widely studied using ex vivo model systems in applications such as immunotherapy. However, typical chemotactic models employ 2D systems that are less physiologically relevant or use end-point assays, that reveal little about the stepwise dynamics of the migration process. To overcome these limitations, we developed a new model system using microfabrication techniques, sustained drug delivery approaches, and theoretical modeling of chemotactic agent diffusion. This model system allows us to study the effects of 3D architecture and chemotactic agent gradient on immune cell migration in real time. We find that dendritic cell migration is characterized by a strong interplay between matrix architecture and chemotactic gradients, and migration is also influenced dramatically by the cell activation state. Our results indicate that Lipopolysaccharide-activated dendritic cells studied in a tradition! al transwell system actually exhibit anomalous migration behavior. Such a 3D ex vivo system lends itself for analyzing cell migratory behavior in response to single or multiple competitive cues and could prove useful in vaccine development.
• Lyophilized silk fibroin hydrogels for the sustained local delivery of therapeutic monoclonal antibodies
  - Biomater 32(10):2642-2650 (2011)
  The development of sustained delivery systems compatible with protein therapeutics continues to be a significant unmet need. A lyophilized silk fibroin hydrogel matrix (lyogel) for the sustained release of pharmaceutically relevant monoclonal antibodies is described. Sonication of silk fibroin prior to antibody incorporation avoids exposing the antibody to the sol–gel transition inducing shear stress. Fourier Transform Infrared (FTIR) analysis showed no change in silk structural composition between hydrogel and lyogel or with increasing silk fibroin concentration. Antibody release from hydrogels occurred rapidly over 10 days regardless of silk concentration. Upon lyophilization, sustained antibody release was observed over 38 days from lyogels containing 6.2% (w/w) silk fibroin and above. In 3.2% (w/w) silk lyogels, antibody release was comparable to hydrogels. Swelling properties of lyogels followed a similar threshold behavior. Lyogels at 3.2% (w/w) silk recovered ! approximately 90% of their fluid mass upon rehydration, while approximately 50% fluid recovery was observed at 6.2% (w/w) silk and above. Antibody release was primarily governed by hydrophobic/hydrophilic silk-antibody interactions and secondarily altered by the hydration resistance of the lyogel. Hydration resistance was controlled by altering β-sheet (crystalline) density of the matrix. The antibody released from lyogels maintained biological activity. Silk lyogels offer an advantage as a delivery matrix over other hydrogel materials for the slow release of the loaded protein, making lyogels suitable for long-term sustained release applications.
• Tuning the immune response of dendritic cells to surface-assembled poly(I:C) on microspheres through synergistic interactions between phagocytic and TLR3 signaling
  - Biomater 32(10):2651-2661 (2011)
  The artificial dsRNA polyriboinosinic acid-polyribocytidylic acid, poly(I:C), is a potent adjuvant candidate for vaccination, as it strongly drives cell-mediated immunity. However, because of its effects on non-immune bystander cells, poly(I:C) administration may bear danger for the development of autoimmune diseases. Thus poly(I:C) should be applied in the lowest dose possible. We investigated microspheres carrying surface-assembled poly(I:C) as a two-in-one adjuvant formulation to stimulate maturation of monocyte-derived dendritic cells (MoDCs). Negatively charged polystyrene microspheres were equipped with a poly(ethylene glycol) corona through electrostatically driven surface assembly of a library of polycationic poly(l-lysine)-graft-poly(ethylene glycol) copolymers, PLL-g-PEG. Stable surface assembly of poly(I:C) was achieved by incubation of polymer-coated microspheres in an aqueous poly(I:C) solution. Surface-assembled poly(I:C) exhibited a strongly enhanced eff! icacy to stimulate maturation of MoDCs by up to two orders of magnitude, as compared to free poly(I:C). Multiple phagocytosis events were the key factor to enhance the efficacy. The cytokine secretion pattern of MoDCs after exposure to surface-assembled poly(I:C) differed from that of free poly(I:C), while their ability to stimulate T cell proliferation was similar. Overall, phagocytic signaling plays an important role in defining the resulting immune response to such two-in-one adjuvant formulations.
• Tailoring nanostructured solid-lipid carriers for time-controlled intracellular siRNA kinetics to sustain RNAi-mediated chemosensitization
  - Biomater 32(10):2662-2672 (2011)
  Use of siRNA for silencing major oncogenic/chemoresistance targets such as survivin has strong potential for cancer therapy. However, a key clinical limitation is their short action, preventing them from sustaining their therapeutic RNA-interference activity for optimal chemosensitization. This issue is tackled from the perspective of intracellular siRNA kinetics using a novel lipid-based "nanostructured siRNA carrier" (NSC), which incorporates variable amount of oil phase into the solid-lipid matrix to modify its siRNA release behaviors. We demonstrate that by manipulating the degradation responses of NSC device to lysosomal enzyme, tailoring of intracellular siRNA kinetics is achievable. A tailored NSC design delivering survivin-siRNA can extend the survivin knockdown period to 9 days, translating into steady, effective in vitro and in vivo chemosensitization of prostate cancer to docetaxel for over a week. All in all, this new NSC design provides a convenient me! an to set up a clinically more appealing weekly or longer dosing cycle for siRNA therapy, which addresses a significant unmet need for prostate cancer treatment and is potentially useful for other chronic disease conditions as well.
• The glucose-lowering potential of exendin-4 orally delivered via a pH-sensitive nanoparticle vehicle and effects on subsequent insulin secretion in vivo
  - Biomater 32(10):2673-2682 (2011)
  Exendin-4 is a potent insulinotropic agent in diabetes patients; however, its therapeutic utility is limited due to the frequent injections required. In this study, an orally available exendin-4 formulation, using an enteric-coated capsule containing pH-responsive NPs, was developed. Following oral administration of 123I-labeled-exendin-4 loaded NPs in rats, the biodistribution of the administered drug was investigated using a dual isotope dynamic SPECT/CT scanner. The results showed that the radioactivity of 123I-exendin-4 propagated from the esophagus, stomach, and small intestine and then was absorbed into the systemic circulation; with time progressing, 123I-exendin-4 was metabolized and excreted into the urinary bladder. In the in vivo dissolution study, it was found that the enteric-coated capsule remained intact while in the stomach; the capsule was completely dissolved in the proximal segment of the small intestine and the loaded contents were then released. Or! al administration of the capsule containing exendin-4 loaded NPs showed a maximum plasma concentration at 5 h after treatment; the bioavailability, relative to its subcutaneous counterpart, was found to be 14.0 ± 1.8%. The absorbed exendin-4 could then stimulate the insulin secretion and provide a prolonged glucose-lowering effect. The aforementioned results suggest that the orally available exendin-4 formulation developed warrants further exploration as a potential therapy for diabetic patients.
• Click assembly of magnetic nanovectors for gene delivery
  - Biomater 32(10):2683-2688 (2011)
  Functionalization of iron oxide nanoparticles with quaternary ammonium ion-based aminooxy and oxime ether substrates provides a flexible route for generating magnetic gene delivery vectors. Using the MCF-7 breast cancer cell line, our findings show that pDNA magnetoplexes derived from the lipid-coated nanoparticle formulation dMLP transfect in the presence of 10% serum with or without magnetic assistance at significantly higher levels than a commonly used cationic liposome formulation, based on luciferase assay. The present ion-pairing, click chemistry approach furnishes Fe3O4 nanoparticles with lipid layers. The resultant magnetic nanovectors serve as transfection enhancers for otherwise transfection-inactive materials.