Biomaterials (v.28, #12)

Polymers for pro- and anti-angiogenic therapy by Claudia Fischbach; David J. Mooney (2069-2076).
Dysregulated growth factor signaling is traditionally targeted via bolus injections of therapeutic molecules, but this approach may not recreate necessary qualitative and quantitative aspects of biologic growth factor delivery systems. Polymeric delivery systems may, instead, mimic certain sequestration and binding characteristics of the extracellular matrix and lead to the provision of therapeutic molecules at therapeutically efficient local concentrations [V], in the form of spatial gradients (d[V]/dx) and temporal gradients (d[V]/dt), and in combination with other morphogenetic cues. Both physicochemical and biological attributes dictate their design, and they may be fabricated from synthetic and natural polymers. General concepts for manipulating growth factor signaling with these systems are discussed in the context of angiogenesis with vascular endothelial growth factor (VEGF), and these strategies may be broadly adapted to a multitude of other morphogens and growth factors.
Keywords: Growth factors; Drug delivery; Hydrogel; Angiogenesis;

Hydrogel effects on bone marrow stromal cell response to chondrogenic growth factors by Rhima M. Coleman; Natasha D. Case; Robert E. Guldberg (2077-2086).
The aim of this study was to investigate the effects of alginate and agarose on the response of bone marrow stromal cells (BMSCs) to chondrogenic stimuli. Rat BMSCs were expanded in monolayer culture with or without FGF-2 supplementation. Cells were then seeded in 2% alginate and agarose gels and cultured in media with or without TGF-β1 or dexamethasone (Dex). Sulfated glycosaminoglycans (sGAGs), collagen type II, and aggrecan were expressed in all groups that received TGF-β1 treatment during hydrogel culture. Expansion of rat BMSCs in the presence of FGF-2 increased production of sGAG in TGF-β1-treated groups over those cultures that were treated with TGF-β1 alone in alginate cultures. However, in agarose, cells exposed to FGF-2 during expansion produced less sGAG within TGF-β1-supplemented groups over those cultures treated with TGF-β1 alone. Dex was required for optimal matrix synthesis in both hydrogels, but was found to decrease cell viability in agarose constructs. These results indicate that the response of BMSCs to a chondrogenic growth factor regimen is scaffold dependent.
Keywords: Hydrogel; Progenitor cell; Cartilage tissue engineering; Cell culture; Growth factors;

The enhancement of osteogenesis by nano-fibrous scaffolds incorporating rhBMP-7 nanospheres by Guobao Wei; Qiming Jin; William V. Giannobile; Peter X. Ma (2087-2096).
It is advantageous to incorporate controlled growth factor delivery into tissue engineering strategies. The objective of this study was to develop a three-dimensional (3D) porous tissue engineering scaffold with the capability of controlled releasing recombinant human bone morphogenetic protein-7 (rhBMP-7) for enhancement of bone regeneration. RhBMP-7 was first encapsulated into poly(lactic-co-glycolic acid) (PLGA) nanospheres (NS) with an average diameter of 300 nm. Poly(l-lactic acid) (PLLA) scaffolds with interconnected macroporous and nano-fibrous architectures were prepared using a combined sugar sphere template leaching and phase separation technique. A post-seeding technique was then utilized to immobilize rhBMP-7 containing PLGA nanospheres onto prefabricated nano-fibrous PLLA scaffolds with well-maintained 3D structures. In vitro release kinetics indicated that nanosphere immobilized scaffold (NS-scaffold) could release rhBMP-7 in a temporally controlled manner, depending on the chemical and degradation properties of the NS which were immobilized onto the scaffold. In vivo, rhBMP-7 delivered from NS-scaffolds induced significant ectopic bone formation throughout the scaffold while passive adsorption of rhBMP-7 into the scaffold resulted in failure of bone induction due to either the loss of rhBMP-7 biological function or insufficient duration within the scaffold. We conclude that the interconnected macroporous architecture and the sustained, prolonged delivery of bioactive rhBMP-7 from NS immobilized nano-fibrous scaffolds actively induced new bone formation throughout the scaffold. The approach offers a new delivery method of BMPs and a novel scaffold design for bone regeneration.
Keywords: BMP; Controlled delivery; Nano fiber; Scaffold; Tissue engineering; Nanospheres;

Enhanced neurite growth from mammalian neurons in three-dimensional salmon fibrin gels by Yo-El Ju; Paul A. Janmey; Margaret E. McCormick; Evelyn S. Sawyer; Lisa A. Flanagan (2097-2108).
Three-dimensional fibrin matrices have been used as cellular substrates in vitro and as bridging materials for central nervous system repair. Cells can be embedded within fibrin gels since the polymerization process is non-toxic, making fibrin an attractive scaffold for transplanted cells. Most studies have utilized fibrin prepared from human or bovine blood proteins. However, fish fibrin may be well suited for neuronal growth since fish undergo remarkable central nervous system regeneration and molecules implicated in this process are present in fibrin. We assessed the growth of mammalian central nervous system neurons in bovine, human, and salmon fibrin and found that salmon fibrin gels encouraged the greatest degree of neurite (dendrite and axon) growth and were the most resistant to degradation by cellular proteases. The neurite growth-promoting effect was not due to the thrombin used to polymerize the gels nor to any copurifying plasminogen. Copurified fibronectin partially accounted for the effect on neurites, and blockade of fibrinogen/fibrin-binding integrins markedly decreased neurite growth. Anion exchange chromatography revealed different elution profiles for salmon and mammalian fibrinogens. These data demonstrate that salmon fibrin encourages the growth of neurites from mammalian neurons and suggest that salmon fibrin may be a beneficial scaffold for neuronal regrowth after CNS injury.
Keywords: Matrix; Integrin; Scaffold; Nerve regeneration; Cortical; Spinal cord;

In this study, we present a novel composite scaffold fabricated using a thermally induced phase separation (TIPS) process from poly(lactic-co-glycolic) (PLGA) and biomedical polyurethane (PU). This processing method has been tuned to allow intimate (molecular) mixing of these two very different polymers, giving rise to a unique morphology that can be manipulated by controlling the phase separation behaviour of an initially homogenous polymer solution. Pure PLGA scaffolds possessed a smooth, directional fibrous sheet-like structure with pore sizes of 0.1–200 μm, a porous Young's modulus of 93.5 kPa and were relatively brittle to touch. Pure PU scaffolds had an isotropic emulsion-like structure, a porous Young's modulus of 15.7 kPa and were much more elastic than the PLGA scaffolds. The composite PLGA/PU scaffold exhibits advantageous morphological, mechanical and cell adhesion and growth supporting properties, when compared with scaffolds fabricated from PLGA or PU alone. This novel method provides a mechanism for the formation of tailored bioactive scaffolds from nominally incompatible polymers, representing a significant step forward in scaffold processing for tissue-engineering applications.
Keywords: Composite; Scaffold; Polyurethane; Polylactic acid; Mechanical properties; Cell spreading;

Prevention of pin tract infection in external stainless steel fixator frames using electric current in a goat model by Arnout J. van der Borden; Patrick G.M. Maathuis; Eefje Engels; Gerhard Rakhorst; Henny C. van der Mei; Henk J. Busscher; Prashant Kumar Sharma (2122-2126).
Pin tract infections of external fixators used in orthopaedic reconstructive bone surgery are serious complications that can eventually lead to periostitis and osteomyelitis. In vitro experiments have demonstrated that bacteria adhering to stainless steel in a biofilm mode of growth detach under the influence of small electric currents, while remaining bacteria become less viable upon current application. Therefore, we have investigated whether a 100 μA electric current can prevent signs of clinical infection around percutaneous pins, implanted in the tibia of goats. Three pins were inserted into the lateral right tibia of nine goats, of which one served for additional frame support. Two pins were infected with a Staphylococcus epidermidis strain of which one pin was subjected to electric current, while the other pin was used as control. Pin sites were examined daily. The wound electrical resistance decreased with worsening of the infection from a dry condition to a purulent stage. After 21 days, animals were sacrificed and the pins taken out. Infection developed in 89% of the control pin sites, whereas only 11% of the pin sites in the current group showed infection. These results show that infection of percutaneous pin sites of external fixators in reconstructive bone surgery can be prevented by the application of a small DC electric current.
Keywords: Bacterial adhesion; Infection; Electric current; Bacterial detachment; Reconstructive bone surgery; Stainless steel;

In vitro biocompatibility and bioactivity of microencapsulated heparan sulfate by Emma Luong-Van; Lisbeth Grøndahl; Victor Nurcombe; Simon Cool (2127-2136).
The glycosaminoglycan sugar heparan sulfate (HS) is an attractive agent for the repair of bone defects due to its ability to regulate endogenous growth factors. The sustained delivery of HS to the localized wound site over the period of healing which can last for over 1 month may prove advantageous for its therapeutic use. In this study we investigated the encapsulation of HS by the water-in oil-in water (W1/O/W2) technique in polycaprolactone (PCL) microcapsules as a prolonged delivery device. Encapsulation efficiencies of 70% could be achieved by using a 1:1 mixture of dichloromethane (DCM) and acetone as the solvent in the organic phase, while DCM alone gave poor encapsulation. Although addition of polyvinyl alcohol (PVA) to the drug phase did not affect the size or drug loading of the microcapsules, it did however produce a large change in the morphology and drug distribution, which resulted in different release rates. Release from capsules made with PVA in the drug phase reached 60% after 40 days, while those made with water in the drug phase completed release after 20 days. In vitro biocompatibility studies were performed and detected no increase in cell death in human mesenchymal stem cells (hMSC) or induction of an inflammatory response in macrophages after exposure to release products from HS-loaded microcapsules. The released HS retained its ability to increase the proliferation of hMSC after the encapsulation process. These results indicate that encapsulation of HS by the W1/O/W2 method creates a promising device for the repair of bone tissue.
Keywords: Microencapsulation; Drug delivery; Bone repair; Polycaprolactone; Heparan sulfate;

In an effort to develop an alternative formulation of paclitaxel suitable for parenteral administration, paclitaxel-loaded sterically stabilized solid lipid nanoparticles (SLNs) were prepared, characterized and examined for in vitro cytotoxicity. The SLNs, comprising trimyristin (TM) as a solid lipid core and egg phosphatidylcholine and pegylated phospholipid as stabilizers, were prepared using a hot homogenization method. Regardless of paclitaxel loading, the particle sizes and zeta potentials of the prepared SLNs were around 200 nm and −38 mV, respectively, suggesting that they would be suitable as a parenteral formulation. Cryo-scanning electron microscopy showed that the SLNs were homogeneous and spherical in shape, while differential scanning calorimetry measurement of the melting peak revealed that the TM exists as a solid in our formulation. Paclitaxel was loaded to the solid cores at a w/w ratio of 6%. Gel column chromatography showed that paclitaxel co-eluted with the phospholipids, indicating that paclitaxel was incorporated in the SLNs. An in vitro drug release study showed that paclitaxel was released from the SLNs in a slow but time-dependent manner. Furthermore, treatment of the OVCAR-3 human ovarian cancer cell line and the MCF-7 breast cancer cell line with paclitaxel-loaded SLNs yielded cytotoxicities comparable to those of a commercially available Cremophor EL-based paclitaxel formulation. These results collectively suggest that our optimized SLN formulation may have a potential as alternative delivery system for parenteral administration of paclitaxel.
Keywords: Paclitaxel; Solid lipid nanoparticles; Cancer; Drug delivery;

The ideal immobilization methods that are suitable for binding immuno-active materials with high efficiency onto the sensing surface are the key target to pursue in the current biosensor design. In this paper, a new hybrid material formed by assembling gold nanoparticles (GNP) onto nano-sized hydroxyapatite (HA) has been employed for the interface design of piezoelectric immunosensor, on which the antibodies were bound. The detection performances of the resulting immunosensor were investigated by use of the antibody–antigen model system of α-Fetoprotein (AFP), an important indicator in the diagnosis of clinical cancers. The hybrid material was characterized by the UV–vis spectroscopy, the SEM and TEM measurements. The frequency and electrochemical impedance responses characteristics for the processes of immobilization and immunoreaction of anchored anti-AFP antibodies were studied in detail. The immunoresponse of the proposed immunosensor was compared with those antibodies immobilized by using HA or GNP alone. It was found that the developed sensing interface has some advantages such as the activation-free immobilization and the high antigen-binding activities of antibodies. The as-prepared immunosensor can allow for the determination of AFP in the concentration range of 15.3–600.0 ng ml−1. Such an interface design with the nano-sized hybrid materials should be tailored as a new alternative used for biosensor design.
Keywords: Gold nanoparticles; Hydroxyapatite; Immunosensor; AFP;

The in vitro osteoclastic degradation of nacre by D. Duplat; A. Chabadel; M. Gallet; S. Berland; L. Bédouet; M. Rousseau; S. Kamel; C. Milet; P. Jurdic; M. Brazier; E. Lopez (2155-2162).
Osteoclast activity was studied on nacre, the mother of pearl (MOP) in order to assess the plasticity of bone resorbing cells and their capacity to adapt to a biomineralized material with a different organic and mineral composition from that of its natural substrate, bone. Pure MOP, a natural biomineralized CaCO3 material, was obtained from Pinctada oyster shell. When implanted in the living system, nacre has proven to be a sustainable bone grafting material although a limited surface degradation process. Osteoclast stem cells and mature osteoclasts were cultured on MOP substrate and osteoclast precursor cells were shown to differentiate into osteoclasts capable of resorbing nacre substrate. However, analysis of the organization of the cytoskeleton showed that both a sealing zone and a podosome structure were observed on the nacre substrate. Moreover, MOP resorption efficiency was consistently found to be lower than that of bone and appeared to be a limited process.
Keywords: Nacre; Bone graft; Osteoclast; Adhesion; Biodegradation;