Hot off the presses! Nov 01 Biomaterials

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Latest Articles Include:

• Editorial board
  - Biomaterials 32(31):IFC (2011)
  
• Porous scaffold design using the distance field and triply periodic minimal surface models
  - Biomaterials 32(31):7741-7754 (2011)
  An effective method for the 3D porous scaffold design of human tissue is presented based on a hybrid method of distance field and triply periodic minimal surface (TPMS). By the creative application of traditional distance field algorithm into the Boolean operations of the anatomical model and TPMS-based unit cell library, an almost defects free porous scaffolds having the complicated micro-structure and high quality external surface faithful to a specific anatomic model can be easily obtained without the difficult and time-consuming trimming and re-meshing processes. After generating the distance fields for the given tissue model and required internal micro-structure, a series of simple modifications in distance fields enable us to obtain a complex porous scaffold. Experimental results show that the proposed scaffold design method has the potential to combine the perfectly interconnected pore networks based on the TPMS unit cell libraries and the given external geometr! y in a consistent framework irrespective of the complexity of the models.
• Multiobjective design optimisation of coronary stents
  - Biomaterials 32(31):7755-7773 (2011)
  We present here a multi-objective and multi-disciplinary coronary stent design optimization paradigm. Coronary stents are tubular, often mesh-like, structures which are deployed in diseased (stenosed) artery segments to provide a scaffolding feature that compresses atheromatus plaque, hence restoring luminal area and maintaining vessel patency. A three variable geometry parameterisation of a CYPHER (Cordis Corporation, Johnson & Johnson co.) type stent is proposed to explore the functionality of a sequence of circumferential rings connected by 'n' shaped links. The performance of each design is measured by six figures of merit (objectives/metrics) representing (i) acute recoil, (ii) tissue stresses, (iii) haemodynamic disturbance, (iv) drug delivery, (v) uniformity of drug distribution, and (vi) flexibility. These metrics are obtained from computational simulations of (i) structural deformation through balloon inflated expansion of a stent into contact with a steno! sed vessel, (ii) pulsatile flow over the deformed stent embedded in the vessel wall, (iii) steady-state drug distribution into the tissue, and (iv) flexibility of a stent in response to an applied moment. Design improvement is obtained by a multi-objective surrogate modelling approach using a non-dominated sorting genetic algorithm (NSGA-II) to search for an optimal family of designs. A number of trade-offs between the different objectives are identified. In particular a conflict between pairs of the following objectives are shown -- (a) volume average stress vs. recoil, (b) volume average drug vs. volume average stress, (c) flexibility vs. volume average stress, (d) flexibility vs. haemodynamic disturbance, (e) volume average drug vs. haemodynamic disturbance, and (f) uniformity of drug vs. volume average stress. Different paradigms to choose the optimal designs from the obtained Pareto fronts are presented and under each such paradigm, the optimal designs and there relati! ve positions with respect to a representative CYPHER stent are! shown. The methodology and the results of this work could potentially be useful in further optimisation studies and development of a family of stents with increased resistance to in-stent restenosis and thrombosis.
• Carboxyl-ebselen-based layer-by-layer films as potential antithrombotic and antimicrobial coatings
  - Biomaterials 32(31):7774-7784 (2011)
  A carboxyl-ebselen-based layer-by-layer (LbL) film was fabricated by alternatively assembling carboxyl-ebselen immobilized polyethylenimine (e-PEI) and alginate (Alg) onto substrates followed by salt annealing and cross-linking. The annealed films exhibiting significantly improved stability are capable of generating nitric oxide (NO) from endogeneous S-nitrosothiols (RSNOs) in the presence of a reducing agent. The NO generation behaviors of different organoselenium species in solution phase are compared and the annealing mechanism to create stable LbL films is studied in detail. An LbL film coated polyurethane catheter is capable of generating physiological levels of NO from RSNOs even after blood soaking for 24 h, indicating potential antithrombotic applications of the coating. Further, the LbL film is also demonstrated to be capable of reducing living bacterial surface attachment and killing a broad spectrum of bacteria, likely through generation of superoxide (O2−! ) from oxygen. This type of film is expected to have potential application as an antithrombotic and antimicrobial coating for different biomedical device surfaces.
• Minimally invasive, longitudinal monitoring of biomaterial-associated inflammation by fluorescence imaging
  - Biomaterials 32(31):7785-7792 (2011)
  Implant-associated inflammation is a major cause for the reduced performance/lifetime and failure of numerous medical devices. Therefore, the ability to non-invasively and quantitatively monitor implant-associated inflammation is critically important. Here we show that implant-associated inflammation can be imaged via fluorescence imaging using near-infrared hydrocyanine dyes delivered either locally or intravenously in living mice. This imaging strategy allowed quantitative longitudinal monitoring of inflammation by detecting reactive oxygen species (ROS) released by inflammatory cells in response to implanted poly(ethylene terephthalate) (PET) disks or injected poly (lactic-co-glycolic acid) (PLGA) microparticles, and exhibited a strong correlation to conventional analysis of inflammation. Furthermore, modulation of inflammatory responses via controlled release of the anti-inflammatory agent dexamethasone was detected using this sensitive imaging approach. Thus, hydr! ocyanine-based fluorescence imaging of ROS could serve as a surrogate measure for monitoring implant-associated inflammation as well as evaluating the efficacy of therapeutic approaches to modulate host responses to implanted medical devices.
• Directing human embryonic stem cell differentiation by non-viral delivery of siRNA in 3D culture
  - Biomaterials 32(31):7793-7800 (2011)
  Human embryonic stem cells (hESCs) hold great potential as a resource for regenerative medicine. Before achieving therapeutic relevancy, methods must be developed to control stem cell differentiation. It is clear that stem cells can respond to genetic signals, such as those imparted by nucleic acids, to promote lineage-specific differentiation. Here we have developed an efficient system for delivering siRNA to hESCs in a 3D culture matrix using lipid-like materials. We show that non-viral siRNA delivery in a 3D scaffolds can efficiently knockdown 90% of GFP expression in GFP-hESCs. We further show that this system can be used as a platform for directing hESC differentiation. Through siRNA silencing of the KDR receptor gene, we achieve concurrent downregulation (60–90%) in genes representative of the endoderm germ layer and significant upregulation of genes representative of the mesoderm germ layer (27–90 fold). This demonstrates that siRNA can direct stem cell diff! erentiation by blocking genes representative of one germ layer and also provides a particularly powerful means to isolate the endoderm germ layer from the mesoderm and ectoderm. This ability to inhibit endoderm germ layer differentiation could allow for improved control over hESC differentiation to desired cell types.
• An epidermal stem cells niche microenvironment created by engineered human amniotic membrane
  - Biomaterials 32(31):7801-7811 (2011)
  How to amplify epidermal stem cells (ESCs) rapidly is a challenging crux in skin tissue engineering research. The present study describes the preparation of 3D micronized (300–600 μm) amniotic membrane (mAM) by means of repeated freeze-thawing cycles to deplete cell components and homogenized with a macrohomogenizer in liquid nitrogen. This newly prepared mAM not only possessed the characteristics of a microcarrier but completely retained the basement membrane structure and abundant active substances such as NGF, HGF, KGF, bFGF, TGF-β1 and EGF in the AM matrix. The result showed that mAM combined with rotary cell culture system (RCCS) was able to amplify ESCs quickly. The relative cell viability at day 7 and 14 was significantly higher than that of the conventional 2D plate culture (326 ± 28% and 535 ± 47% versus 232 ± 21% and 307 ± 32%, P < 0.05). In addition, the new method was able to prevent cell differentiation effectively and retain the characteristics of! stem cells. When mAM loaded with ESCs (ESC-mAM) was further transplanted to full-thickness skin defects in nude mice, ESCs survived well and formed a new epidermis. Four weeks after transplantation, papilla-like structures were observed, and collagen fibers were well and regularly arranged in the newly formed dermal layer. In conclusion, the mAM as a novel natural microcarrier possesses an intact basement membrane structure and bioactivities. It not only provides the microenvironment similar to the stem cell niche within the human body favorable for ex vivo culture and amplification of ESCs but can be used as the dermal scaffold in constructing a skin substitute containing ESCs for the repair of full-thickness skin defects.
• Using acellular porcine limbal stroma for rabbit limbal stem cell microenvironment reconstruction
  - Biomaterials 32(31):7812-7821 (2011)
  To investigate the feasibility of using acellular porcine limbal stroma for limbal stem cell microenvironment reconstruction. Limbal reconstruction was performed in rabbit partial limbal defect models. Rabbits were randomly divided into four groups: acellular porcine limbal stroma, de-epithelized rabbit limbal autograft stroma, de-epithelized porcine limbal stroma and acellular porcine corneal stroma transplantation groups. In both the acellular porcine limbal stroma and de-epithelized rabbit limbal autograft stroma groups, cornea transparency and epithelium integrity were sustained and graft rejection was not observed. The basal epithelial cells of the grafts showed the K3+/P63+/Ki67+ phenotype at postoperative month 1, but it returned to K3−/P63+/Ki67+(phenotype characteristic of limbal epithelium) by postoperative months 3 and 6. In the de-epithelized porcine limbal stroma group, acute and serious immune rejection occurred by postoperative days 8–10. The basal e! pithelial cells of the grafts showed the K3+/P63+/Ki67+ phenotype at postoperative month 1. In the acellular porcine corneal stroma group, there were some new vessel invasion into the peripheral cornea and mild corneal opacity. The basal epithelial cells of the grafts showed the K3+/P63+/Ki67+ phenotype at postoperative months 1, 3, and 6. In conclusion, acellular porcine limbal stroma possessed very low immunogenicity, retained a good original limbal ECM microenvironment, and thus the reconstructed rabbit limbal microenvironment maintained limbal epithelial stem cell stemness and proliferation.
• The effect of scaffold architecture on odontogenic differentiation of human dental pulp stem cells
  - Biomaterials 32(31):7822-7830 (2011)
  Previous studies have shown the superiority of nanofibrous (NF) poly(l-lactic acid) (PLLA) scaffolds in supporting the osteogenic differentiation of a few cell types and bone regeneration. The aim of the current study was to investigate whether NF-PLLA scaffolds are advantageous for the odontogenic differentiation and mineralization of human dental pulp stem cells (DPSCs) over solid-walled (SW) PLLA scaffolds. The in vitro studies demonstrated that, compared with SW scaffolds, NF scaffolds enhanced attachment and proliferation as well as odontogenic differentiation of human DPSCs. The alkaline phosphatase (ALP) activity and the expression of odontogenic genes of human DPSCs were increased on NF scaffolds compared with that on SW scaffolds. In addition, more mineral deposition was observed on the NF scaffolds, as demonstrated by von Kossa staining, calcium content measurement and scanning electron microscopy. Consistent with the in vitro studies, NF scaffolds promoted o! dontogenic differentiation and hard tissue formation compared with SW scaffolds after 8 weeks of ectopic transplantation in nude mice, as confirmed by von Kossa staining, Masson's trichrome staining and immunohistochemical staining for dentin sialoprotein. In conclusion, NF-PLLA scaffolds enhanced the odontogenic differentiation of human DPSCs and mineralization both in vitro and in vivo, and are promising scaffolds for dentin regeneration.
• The role of moderate static magnetic fields on biomineralization of osteoblasts on sulfonated polystyrene films
  - Biomaterials 32(31):7831-7838 (2011)
  We have investigated the effects of moderate static magnetic fields (SMFs) on murine MC3T3-E1 osteoblasts, and found that they enhance proliferations and promote differentiation. The increase in proliferation rates in response to SMFs was greater in cultures grown on partially sulfonated polytstyrene (SPS, degree of sulfonation: 33%) than in cultures grown on tissue culture plastic. We have previously shown that when the degree of sulfonation exceeded a critical value (12%) [1], spontaneous fibrillogenesis occured which allowed for direct observation of the ECM fibrillar organization under the influence of external fields. We found that the ECM produced in cultures grown on the SPS in the presence of the SMFs assembled into a lattice with larger dimensions than the ECM of the cultures grown in the absence of SMFs. During the early stages of the biomineralization process (day 7), the SMF exposed cultures also templated mineral deposition more rapidly than the control cu! ltures. The rapid response is attributed to orientation of diamagnetic ECM proteins already present in the serum, which could then initiate further cellular signaling. SMFs also influenced late stage osteoblast differentiation as measured by the increased rate of osteocalcin secretion and gene expression beginning 15 days after SFM exposure. This correlated with a large increase in mineral deposition, and in cell modulus. GIXD and EDXS analysis confirmed early deposition of crystalline hydroxyapatite. Previous studies on the effects of moderate SMF had focused on cellular gene and protein expression, but did not consider the organization of the ECM fibers. Our ability to form these fibers has allowed us explore this additional effect and highlight its significance in the initiation of the biomineralization process.
• Nanostructuring PEG-fibrinogen hydrogels to control cellular morphogenesis
  - Biomaterials 32(31):7839-7846 (2011)
  The nanostructuring of hydrogel scaffolds used in tissue engineering aims to provide an ability to control cellular morphogenesis through defined cell–matrix interactions. Toward this objective, we developed a method that alters the molecular network structure of biosynthetic hydrogel scaffolds made from crosslinked poly(ethylene glycol)-fibrinogen conjugates (PEG-fibrinogen, PF). The modifications were based on Pluronic® F127 micelles that were formed in the hydrogel precursor solution and that altered the hydrogel network assembly during photopolymerization crosslinking. Two variations of the cell-encapsulating hydrogels (high and low crosslinking density) were prepared with three concentrations of Pluronic® F127 (3%, 7%, 10% w/v). Quantitative morphometrics were used to characterize fibroblast shape parameters (both transient and stable) in all hydrogels, and rheological characterizations were used to measure the elastic (storage) component of the complex shear ! modulus of these hydrogels. The morphometric data was then correlated to both the nanostructure and modulus of the hydrogels for day 1 and day 4 in culture. These correlations revealed that structural features imparted by the Pluronic® F127 micelles were able to reverse the normally strong correlations found between indicators of cell spreading and the hydrogel's mechanical properties. Therefore, the data supports the conclusion that nanostructural features in the encapsulating hydrogel culture environment can facilitate better cell spreading in a dense hydrogel milieu, simply by introducing imperfections into the network structure. This research also provides further prospective regarding biocompatible approaches toward making structural modifications to hydrogel scaffolds for the purpose of 3-D cell culture and tissue engineering.
• The assembly of cell-encapsulating microscale hydrogels using acoustic waves
  - Biomaterials 32(31):7847-7855 (2011)
  Microscale hydrogels find widespread applications in medicine and biology, e.g., as building blocks for tissue engineering and regenerative medicine. In these applications, these microgels are assembled to fabricate large complex 3D constructs. The success of this approach requires non-destructive and high throughput assembly of the microgels. Although various assembly methods have been developed based on modifying interfaces, and using microfluidics, so far, none of the available assembly technologies have shown the ability to assemble microgels using non-invasive fields rapidly within seconds in an efficient way. Acoustics has been widely used in biomedical arena to manipulate droplets, cells and biomolecules. In this study, we developed a simple, non-invasive acoustic assembler for cell-encapsulating microgels with maintained cell viability (>93%). We assessed the assembler for both microbeads (with diameter of 50 μm and 100 μm) and microgels of different sizes an! d shapes (e.g., cubes, lock-and-key shapes, tetris, saw) in microdroplets (with volume of 10 μL, 20 μL, 40 μL, 80 μL). The microgels were assembled in seconds in a non-invasive manner. These results indicate that the developed acoustic approach could become an enabling biotechnology tool for tissue engineering, regenerative medicine, pharmacology studies and high throughput screening applications.
• Engineering vessel-like networks within multicellular fibrin-based constructs
  - Biomaterials 32(31):7856-7869 (2011)
  Sufficient vascularization in engineered tissues can be achieved through coordinated application of improved biomaterial systems with proper cell types. In this study, we employed 3D fibrin gels alone or in combination with the synthetic poly(l-lactic acid) (PLLA)/polylactic-glycolic acid (PLGA) sponges to support in-vitro construct vascularization and to enhance neovascularization upon implantation. Two multicellular assays were embedded in these constructs: (a) co-culture of endothelial (EC) and fibroblast cells, and (b) a tri-culture combination of ECs, fibroblasts and tissue specific skeletal myoblast cells. In-vitro vessel network formation was examined under advanced confocal microscopy in various time points from cell seeding. Vessel network maturity levels and morphology were found to be highly regulated by fibrinogen concentrations in-vitro. Combination of PLLA/PLGA sponges with fibrin matrices provided added mechanical strength and featured highly mature vess! els-like networks. Implantation studies revealed that the implanted ECs developed into 3D interconnected vessel-like networks in-vivo. The PLLA/PLGA scaffold proved to be a key stimulator of neovascularization and perfusion of implanted grafts. Our findings demonstrate that complex biomaterial platform involving fibrin and PLLA/PLGA synthetic scaffold provide a way to enhancing vascularization in-vitro and in-vivo.
• The pro-myogenic environment provided by whole organ scale acellular scaffolds from skeletal muscle
  - Biomaterials 32(31):7870-7882 (2011)
  In the pursuit of a transplantable construct for the replacement of large skeletal muscle defects arising from traumatic or pathological conditions, several attempts have been made to obtain a highly oriented, vascularized and functional skeletal muscle. Acellular scaffolds derived from organ decellularization are promising, widely used biomaterials for tissue engineering. However, the acellular skeletal muscle extra cellular matrix (ECM) has been poorly characterized in terms of production, storage and host–donor interactions. We have produced acellular scaffolds at the whole organ scale from various skeletal muscles explanted from mice. The acellular scaffolds conserve chemical and architectural features of the tissue of origin, including the vascular bed. Scaffolds can be sterilely stored for weeks at +4 °C or +37 °C in tissue culture grade conditions. When transplanted in wt mice, the grafts are stable for several weeks, whilst being colonized by inflammatory a! nd stem cells. We demonstrate that the acellular scaffold per se represents a pro-myogenic environment supporting de novo formation of muscle fibers, likely derived from host cells with myogenic potential. Myogenesis within the implant is enhanced by immunosuppressive treatment. Our work highlights the fundamental role of this niche in tissue engineering application and unveils the clinical potential of allografts based on decellularized tissue for regenerative medicine.
• The use of de-differentiated chondrocytes delivered by a heparin-based hydrogel to regenerate cartilage in partial-thickness defects
  - Biomaterials 32(31):7883-7896 (2011)
  Partial-thickness cartilage defects, with no subchondral bone injury, do not repair spontaneously, thus there is no clinically effective treatment for these lesions. Although the autologous chondrocyte transplantation (ACT) is one of the promising approaches for cartilage repair, it requires in vitro cell expansion to get sufficient cells, but chondrocytes lose their chondrogenic phenotype during expansion by monolayer culture, leading to de-differentiation. In this study, a heparin-based hydrogel was evaluated and optimized to induce cartilage regeneration with de-differentiated chondrocytes. First, re-differentiation of de-differentiated chondrocytes encapsulated in heparin-based hydrogels was characterized in vitro with various polymer concentrations (from 3 to 20 wt.%). Even under a normal cell culture condition (no growth factors or chondrogenic components), efficient re-differentiation of cells was observed with the optimum at 10 wt.% hydrogel, showing the comple! te re-differentiation within a week. Efficient re-differentiation and cartilage formation of de-differentiated cell/hydrogel construct were also confirmed in vivo by subcutaneous implantation on the back of nude mice. Finally, excellent cartilage regeneration and good integration with surrounding, similar to natural cartilage, was also observed by delivering de-differentiated chondrocytes using the heparin-based hydrogel in partial-thickness defects of rabbit knees whereas no healing was observed for the control defects. These results demonstrate that the heparin-based hydrogel is very efficient for re-differentiation of expanded chondrocytes and cartilage regeneration without using any exogenous inducing factors, thus it could serve as an injectable cell-carrier and scaffold for cartilage repair. Excellent chondrogenic nature of the heparin-based hydrogel might be associated with the hydrogel characteristic that can secure endogenous growth factors secreted from chondrocyt! es, which then can promote the chondrogenesis, as suggested by! the detection of TGF-β1 in both in vitro and in vivo cell/hydrogel constructs.
• Injectable in situ crosslinkable RGD-modified alginate matrix for endothelial cells delivery
  - Biomaterials 32(31):7897-7904 (2011)
  Cell-based therapies offer an attractive approach for revascularization and regeneration of tissues. However, and despite the pressing clinical needs for effective revascularization strategies, the successful immobilization of viable vascular cells within 3D matrices has been difficult to achieve. In this paper the in vitro potential of a natural, injectable RGD-alginate hydrogel as an in situ forming matrix to deliver endothelial cells was evaluated. Several techniques were employed to investigate how these microenvironments could influence the behavior of vascular cells, namely their ability to promote the outward migration of viable, proliferative cells, retaining the ability to form a 3D arrangement. Cells within RGD-grafted alginate hydrogel were able to proliferate and maintained 80% of viability for at least 48 h post-immobilization. Additionally, entrapped cells created a 3D organization into cellular networks and, when put in contact with matrigel, cells migra! ted out of the RGD-matrix. Overall, the obtained results support the idea that the RGD peptides conjugated to alginate provide a 3D environment for endothelial cells adhesion, survival, migration and organization.
• 3D in vitro bioengineered tumors based on collagen I hydrogels
  - Biomaterials 32(31):7905-7912 (2011)
  Cells cultured within a three-dimensional (3D) in vitro environment have the ability to acquire phenotypes and respond to stimuli analogous to in vivo biological systems. This approach has been utilized in tissue engineering and can also be applied to the development of a physiologically relevant in vitro tumor model. In this study, collagen I hydrogels cultured with MDA-MB-231 human breast cancer cells were bioengineered as a platform for in vitro solid tumor development. The cell–cell and cell-matrix interactions present during in vivo tissue progression were encouraged within the 3D hydrogel architecture, and the biocompatibility of collagen I supported unconfined cellular proliferation. The development of necrosis beyond a depth of 150–200 μm and the expression of hypoxia-inducible factor (HIF)-1α were demonstrated in the in vitro bioengineered tumors. Oxygen and nutrient diffusion limitations through the collagen I matrix as well as competition for available! nutrients resulted in growing levels of intra-cellular hypoxia, quantified by a statistically significant (p < 0.01) upregulation of HIF-1α gene expression. The bioengineered tumors also demonstrated promising angiogenic potential with a statistically significant (p < 0.001) upregulation of vascular endothelial growth factor (VEGF)-A gene expression. In addition, comparable gene expression analysis demonstrated a statistically significant increase of HIF-1α (p < 0.05) and VEGF-A (p < 0.001) by MDA-MB-231 cells cultured in the 3D collagen I hydrogels compared to cells cultured in a monolayer on two-dimensional tissue culture polystyrene. The results presented in this study demonstrate the capacity of collagen I hydrogels to facilitate the development of 3D in vitro bioengineered tumors that are representative of the pre-vascularized stages of in vivo solid tumor progression.
• Elucidating the mechanobiology of malignant brain tumors using a brain matrix-mimetic hyaluronic acid hydrogel platform
  - Biomaterials 32(31):7913-7923 (2011)
  Glioblastoma multiforme (GBM) is a malignant brain tumor characterized by diffuse infiltration of single cells into the brain parenchyma, which is a process that relies in part on aberrant biochemical and biophysical interactions between tumor cells and the brain extracellular matrix (ECM). A major obstacle to understanding ECM regulation of GBM invasion is the absence of model matrix systems that recapitulate the distinct composition and physical structure of brain ECM while allowing independent control of adhesive ligand density, mechanics, and microstructure. To address this need, we synthesized brain-mimetic ECMs based on hyaluronic acid (HA) with a range of stiffnesses that encompasses normal and tumorigenic brain tissue and functionalized these materials with short Arg-Gly-Asp (RGD) peptides to facilitate cell adhesion. Scanning electron micrographs of the hydrogels revealed a dense, sheet-like microstructure with apparent nanoscale porosity similar to brain extr! acellular space. On flat hydrogel substrates, glioma cell spreading area and actin stress fiber assembly increased strongly with increasing density of RGD peptide. Increasing HA stiffness under constant RGD density produced similar trends and increased the speed of random motility. In a three-dimensional (3D) spheroid paradigm, glioma cells invaded HA hydrogels with morphological patterns distinct from those observed on flat surfaces or in 3D collagen-based ECMs but highly reminiscent of those seen in brain slices. This material system represents a brain-mimetic model ECM with tunable ligand density and stiffness amenable to investigations of the mechanobiological regulation of brain tumor progression.
• Multi-core vesicle nanoparticles based on vesicle fusion for delivery of chemotherapic drugs
  - Biomaterials 32(31):7924-7931 (2011)
  The Pluronic nanoparticles (NPs) composed of Pluronic (F-68) and liquid polyethylene glycol (PEG, molecular wt: 400) containing docetaxel (DTX) were stabilized with the vesicle fusion. When DTX-loaded Pluronic NPs were mixed with vesicles in the aqueous medium, DTX-loaded Pluronic NPs were incorporated into vesicles to form multi-core vesicle NPs. The morphology and size distribution of multi-core vesicle NPs were observed using FE-SEM, cryo-TEM and a particle size analyzer. To apply multi-core vesicle NPs as a delivery system for DTX, a model anti-cancer drug, the release pattern of DTX was observed and the tumor growth was monitored by injecting the DTX-loaded multi-core vesicle NPs into the tail veins of tumor-bearing mice. We also evaluated the time-dependent excretion profile, in vivo biodistribution, circulation time, and tumor targeting capability of multi-core vesicle NPs using a non-invasive live animal imaging technology.
• Influence of chondroitin sulfate and hyaluronic acid on structure, mechanical properties, and glioma invasion of collagen I gels
  - Biomaterials 32(31):7932-7940 (2011)
  To mimic the extracellular matrix surrounding high grade gliomas, composite matrices composed of either acid-solubilized (AS) or pepsin-treated (PT) collagen and the glycosaminoglycans chondroitin sulfate (CS) and hyaluronic acid (HA) are prepared and characterized. The structure and mechanical properties of collagen/CS and collagen/HA gels are studied via confocal reflectance microscopy (CRM) and rheology. CRM reveals that CS induces fibril bundling and increased mesh size in AS collagen but not PT collagen networks. The presence of CS also induces more substantial changes in the storage and loss moduli of AS gels than of PT gels, in accordance with expectation based on network structural parameters. The presence of HA significantly reduces mesh size in AS collagen but has a smaller effect on PT collagen networks. However, both AS and PT collagen network viscoelasticity is strongly affected by the presence of HA. The effects of CS and HA on glioma invasion is then stu! died in collagen/GAG matrices with network structure both similar to (PT collagen-based gels) and disparate from (AS collagen-based gels) those of the corresponding pure collagen matrices. It is shown that CS inhibits and HA has no significant effect on glioma invasion in 1.0 mg/ml collagen matrices over 3 days. The inhibitory effect of CS on glioma invasion is more apparent in AS than in PT collagen gels, suggesting invasive behavior in these environments is affected by both biochemical and network morphological changes induced by GAGs. This study is among the few efforts to differentiate structural, mechanical and biochemical effects of changes to matrix composition on cell motility in 3D.
• Hyaluronan-modified magnetic nanoclusters for detection of CD44-overexpressing breast cancer by MR imaging
  - Biomaterials 32(31):7941-7950 (2011)
  We fabricated hyaluronan-modified magnetic nanoclusters (HA-MNCs) for detection of CD44-overexpressing breast cancer using magnetic resonance (MR) imaging. CD44 is closely associated with cancer growth, including proliferation, metastasis, invasion, and angiogenesis. Hence, pyrenyl hyaluronan (Py–HA) conjugates were synthesized as CD44-targetable surfactants with hyaluronan (HA) and 1-pyrenylbutyric acid (Py) to modify hyaluronan on hydrophobic magnetic nanocrystals. Subsequently, HA-MNCs were fabricated using the nano-emulsion method; magnetic nanocrystals were simultaneously self-assembled with Py–HA conjugates, and their physical and magnetic properties depended on the degree of substitution (DS) of Py in Py–HA conjugates. HA-MNCs exhibited superior targeting efficiency with MR sensitivity as well as excellent biocompatibility through in vitro/in vivo studies. This suggests that HA-MNCs can be a potent cancer specific molecular imaging agent via targeted detec! tion of CD44 with MR imaging.
• Gadolinium-labeled peptide dendrimers with controlled structures as potential magnetic resonance imaging contrast agents
  - Biomaterials 32(31):7951-7960 (2011)
  Gadolinium (Gd3+) based dendrimers with precise and tunable nanoscopic sizes are excellent candidates as magnetic resonance imaging (MRI) contrast agents. Control of agents' sensitivity, biosafety and functionality is key to the successful applications. We report the synthesis of Gd(III)-based peptide dendrimers possessing highly controlled and precise structures, and their potential applications as MRI contrast agents. These agents have no obvious cytotoxicity as verified by in vitro studies. One of the dendrimer formulations with mPEG modification showed a 9-fold increase in T1 relaxivity to 39.2 Gd(III) mM−1 s−1 comparing to Gd-DTPA. In vivo studies have shown that the mPEGylated Gd(III)-based dendrimer provided much higher signal intensity enhancement (SI) in mouse kidney, especially at 60 min post-injection, with 54.8% relatively enhanced SI. The accumulations of mPEGylated dendrimer in mouse liver and kidney were confirmed through measurement of gadolinium ! by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Meanwhile, mPEGylated dendrimer showed much higher Gd(III) concentration in blood with 38 μg Gd(III)/g blood at 1 h post-injection comparing to other dendrimer formulations. These findings provide an attractive alternative strategy to the design of multifunctional gadolinium-based dendrimers with controlled structures, and open up possibilities of using the Gd(III)-based peptide dendrimers as MRI probes.
• Surface camouflage of pancreatic islets using 6-arm-PEG-catechol in combined therapy with tacrolimus and anti-CD154 monoclonal antibody for xenotransplantation
  - Biomaterials 32(31):7961-7970 (2011)
  This study proposes a new combination method of using 6-arm-PEG-catechol to enhance the PEG effect on one hand and another combination of using low doses of Tacrolimus (FK506) and anti-CD154 mAb (MR1) with PEGylation for effective immunoprotection on the other in a xenogenic islet transplantation model. The surface coverage of PEG, viability and functionality of islets were evaluated in vitro, and the effect of surface camouflage on immunoprotection for transplanted islets was evaluated. In addition, the synergistic effects of surface camouflaged islets with low doses of immunosuppressant drugs, such as FK506 and MR1, were evaluated in the xenotransplantation model. The median survival time (MST) of 6-arm-PEG-catechol grafted islets (12.0 ± 1.1 days) was not significantly increased, compared to that of unmodified islets (10.5 ± 1.3 days). However, when 0.2 mg/kg of FK506 was daily administered, the MST of 6-arm-PEG-catechol grafted islet (21.0 ± 1.9 days) was increa! sed twice, compared to that of unmodified islets treated with 0.2 mg/kg of FK506 (10.0 ± 0.9 days). Interestingly, when the recipients of 6-arm-PEG-catechol grafted islets were treated with 0.2 mg/kg of FK506 and 0.1 mg/mouse of MR1, normoglycemia was maintained up to 50 days of transplantation without any fluctuation of glucose level. Therefore, a newly developed protocol using 6-arm-PEG-catechol with FK506 and MR1 would certainly be an effective combination therapy for the treatment of type 1 diabetes.
• Immobilization of anticoagulant-loaded liposomes on cell surfaces by DNA hybridization
  - Biomaterials 32(31):7971-7977 (2011)
  An unresolved obstacle in transplantation of islets of Langerhans is the early graft loss caused by thrombotic reactions on the surface of islets after intraportal transplantation. We investigated a versatile method for modifying the surface of islets with liposomes carrying the anticoagulant argatroban using an amphiphilic poly(ethylene glycol)-phospholipid conjugate derivative (PEG-lipid) and DNA hybridization. Argatroban was gradually released from the liposomes on the islets, and antithrombic activity was detected in culture medium. Modified islets retained the ability to control insulin release in response to glucose concentration changes. Although we mainly examined surface modification of islets, this technique may be useful for immobilizing various types of small molecules on cells and tissues and thus may have many applications in cell therapy and regenerative medicine.
• Multifunctional quantum-dot-based siRNA delivery for HPV18 E6 gene silence and intracellular imaging
  - Biomaterials 32(31):7978-7987 (2011)
  The functional quantum dots (QDs) were specifically designed to overcome barriers in siRNA delivery such as siRNA protection, cellular penetration, endosomal release, carrier unpacking, intracellular transport and gene silencing. In this paper, two l-arginine-functional-modified CdSe/ZnSe QDs were synthesized as siRNA carriers to silence HPV18 E6 gene in HeLa cells. Using such constructs, these QDs showed significantly low cellular cytotoxicity and good siRNA protection. Flow cytometric and confocal microscopic analyses confirmed that the QDs delivered siRNA into HeLa cells efficiently. Importantly, superior gene silencing efficiency was achieved as evaluated by Reverse Transcription-PCR (RT-PCR) and Western blotting and HeLa cells growth was inhibited in xCELLigence installation analysis and MTT assay when treated with QD-siRNA complexes. Interestingly, the QDs coated with β-CD-l-Arg showed optimized property compared with those coated with l-Arg. Furthermore, these! QDs complexes could also be used as nanocrystal probing agents, allowing real-time tracking and localization of QDs during delivery and transfection. The properties and capabilities of these QDs showed that amino acid-modified QDs could be used as useful siRNA carriers to effectively silence a target gene as well as fluorescence probes to analyze intracellular imaging in vivo.
• The use of a gold nanoparticle-based adjuvant to improve the therapeutic efficacy of hNgR-Fc protein immunization in spinal cord-injured rats
  - Biomaterials 32(31):7988-7998 (2011)
  As a common receptor for three myelin associated inhibitors, Nogo-66 receptor (NgR) mediates their inhibitory activities on neurite outgrowth in the adult mammalian central nervous system (CNS). Therapeutic vaccination protocol targeting NgR emulsified with Freund's adjuvant (FA) has been used in spinal cord injury (SCI) models. However, the vaccine emulsified with FA may induce some side effects, which are not suitable for further clinical application. As an adjuvant, gold nanoparticles (GNPs) could stimulate a stronger immune response without producing detectable toxicity and physiological damage than FA. There is, however, uncertainty regarding the efficacy of axon regeneration and neuroprotection in vaccines with GNPs as an adjuvant. In this investigation, a recombinant protein vaccine targeting NgR, human NgR-Fc (hNgR-Fc) fusion protein conjugated with 15 nm GNPs was prepared and its effects on axonal regeneration and functional recovery in spinal cord-injured r! ats were investigated. The results showed that adult rats immunized with the protein vaccine produced higher titers of anti-NgR antibody than that with FA, and the antisera promoted neurite outgrowth in presence of MAG in vitro. In a spinal cord dorsal hemisection model, vaccine immunized with GNPs promoted axonal regeneration more effectively than FA, resulted in significant protection from neuronal loss, and improved functional recovery. Thus, as an adjuvant, 15 nm GNPs can effectively boost the immunogenicity of hNgR-Fc protein vaccine, and promote the repair of spinal cord-injured rats. The utilization of GNPs, for clinical considerations, may be a more beneficial supplement than FA to the promising therapeutic vaccination strategy for promoting SCI repair.
• A starch-based microparticulate system dedicated to diagnostic and therapeutic nuclear medicine applications
  - Biomaterials 32(31):7999-8009 (2011)
  The aim of this work was to develop a new microparticulate system able to form a complex with radionuclides with a high yield of purity for diagnostic or therapeutic applications. Owing to its properties potato starch was chosen as starting material and modified by oxidization and coupling of a ligand (polyamine) enabling modified starch to chelate radionuclides. The choice of suitable experiments was based on a combination of a Rechtschaffner experimental design and a surface response design to determine the influence of experimental parameters and to optimize the final product. Starch-based microparticle formulations from the experimental plans were compared and characterized through particle size analysis, scanning electron microscopy, elemental analysis and, for the most promising formulations, by in vitro labeling stability studies and determination of free polyamine content or in vivo imaging studies. The mechanism of starch-based microparticle degradation was id! entified by means of size measurements. The results of the Rechtschaffner design showed the positive qualitative effect of the temperature and the duration of coupling reaction whereas surface response analysis clearly showed that, by increasing the oxidization level and starch concentration, the nitrogen content in the final product is increased. In vitro and in vivo characterization led to identification of the best formulation. With a size around 30 μm, high radiochemical purity (over 95%) and a high signal-to-noise ratio (over 600), the new starch-based microparticulate system could be prepared as ready-to-use kits and sterilized without modification of its characteristics, and thus meet the requirement for in vivo diagnostic and therapeutic applications.
• Aptamer-functionalized PEG–PLGA nanoparticles for enhanced anti-glioma drug delivery
  - Biomaterials 32(31):8010-8020 (2011)
  Targeted delivery of therapeutic nanoparticles in a disease-specific manner represents a potentially powerful technology especially when treating infiltrative brain tumors such as gliomas. We developed a nanoparticulate drug delivery system decorated with AS1411 (Ap), a DNA aptamer specifically binding to nucleolin which was highly expressed in the plasma membrane of both cancer cells and endothelial cells in angiogenic blood vessels, as the targeting ligand to facilitate anti-glioma delivery of paclitaxel (PTX). Ap was conjugated to the surface of PEG–PLGA nanoparticles (NP) via an EDC/NHS technique. With the conjugation confirmed by Urea PAGE and XPS, the resulting Ap-PTX-NP was uniformly round with particle size at 156.0 ± 54.8 nm and zeta potential at −32.93 ± 3.1 mV. Ap-nucleolin interaction significantly enhanced cellular association of nanoparticles in C6 glioma cells, and increased the cytotoxicity of its payload. Prolonged circulation and enhanced PTX ac! cumulation at the tumor site was achieved for Ap-PTX-NP, which eventually obtained significantly higher tumor inhibition on mice bearing C6 glioma xenografts and prolonged animal survival on rats bearing intracranial C6 gliomas when compared with PTX-NP and Taxol®. The results of this contribution demonstrated the potential utility of AS1411-functionalized nanoparticles for a therapeutic application in the treatment of gliomas.
• The ROS scavenging and renal protective effects of pH-responsive nitroxide radical-containing nanoparticles
  - Biomaterials 32(31):8021-8028 (2011)
  The ultimate objective of nanoparticle-based therapy is to functionalize nanomedicines in a micro-disease environment without any side effects. Here, we reveal that our pH-responsive nitroxide radical-containing nanoparticles (RNPpH) disintegrate within the renal acidic lesion and act as scavengers of reactive oxygen species (ROS), leading to a relief of acute kidney injury (AKI). RNPpH was prepared using amphiphilic block copolymers possessing 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) moieties via amine linkage as a side chain of the hydrophobic segment. The self-assembled RNPpH disintegrated at pH below 7.0 because of a protonation of the amino groups in the hydrophobic core of the nanoparticles, thereby resulting in an improvement in ROS scavenging activity. Using a renal ischemia-reperfusion AKI model in mice, the therapeutic effect of RNPpH on ROS damage was evaluated. Unlike the RNP without pH-triggered disintegration (RNPNon−pH), the RNPpH showed extremely ! high ROS scavenging activity and renal protective effects. It is interesting to note that the side effect of nitroxide radicals was markedly suppressed due to the compartmentalization of nitroxide radicals in the core of RNPpH in untargeted area. The morphology changes in RNPpH were confirmed by analyzing electron spin resonance spectra, and these findings provide the evidence of the real therapeutic effect of the environment-sensitive specific disintegration of nanoparticles in vivo.
• Accelerated healing of cutaneous leishmaniasis in non-healing BALB/c mice using water soluble amphotericin B-polymethacrylic acid
  - Biomaterials 32(31):8029-8039 (2011)
  Cutaneous leishmaniasis (CL) is a neglected tropical disease that causes prominent skin scaring. No water soluble, non-toxic, short course and low cost treatment exists. We developed a new water soluble amphotericin B-polymethacrylic acid (AmB-PMA) using established and scalable chemistries. AmB-PMA was stable for 9 months during storage. In vitro, it was effective against Leishmania spp. promastigotes and amastigote infected macrophages. It was also less toxic and more effective than deoxycholate-AmB, and similar to liposomal AmB. Its in vivo activity was determined in both early and established CL lesion models of Leishmania major infection in genetically susceptible non-healing BALB/c mice. Intradermal AmB-PMA at a total dose of 18 mg of AmB/kg body weight led to rapid parasite killing and lesion healing. No toxicity was seen. No parasite relapse occurred after 80 days follow-up. Histological studies confirmed rapid parasite clearance from macrophages followed by ac! celerated fibroblast mediated tissue repair, regeneration and cure of the infection. Quantitative mRNA studies of the CL lesions showed that accelerated healing was associated with increased Tumour Necrosis Factor-α and Interferon-γ, and reduced Interleukin-10. These results suggest that a cost-effective AmB-PMA could be used to pharmacologically treat and immuno-therapeutically accelerate the healing of CL lesions.