Polypyrrole thin films formed by admicellar polymerization support the osteogenic differentiation of mesenchymal stem cells

The objective of this study was to evaluate the attachment, proliferation, and differentiation of rat mesenchymal stem cells (MSC) toward the osteoblastic phenotype seeded on polypyrrole (PPy) thin films made by admicellar polymerization. Three different concentrations of pyrrole (Py) monomer (20, 35, and 50 x 10(-3) M) were used with the PPy films deposited on tissue culture polystyrene dishes (TCP). Regular TCP dishes and PPy polymerized on TCP by chemical polymerization without surfactant using 5 x 10(-3) M Py, were used as controls. Rat MSC were seeded on these surfaces and cultured for up to 20 d in osteogenic media. Surface topography was characterized by atomic force microscopy, X-ray photoelectron spectroscopy, and static contact angle. Cell attachment, proliferation, alkaline phosphatase (ALP) activity, and calcium content were measured to evaluate the ability of MSC to adhere and differentiate on PPy-coated TCP. Increased monomer concentrations resulted in PPy films of increased thickness and surface roughness. PPy films generated by different monomer concentrations induced drastically different cellular events. A wide spectrum of cell attachment characteristics (from excellent cell attachment to the complete inability to adhere) were obtained by varying the monomer concentration from 20 m to 50 x 10(-3) M. In particular the 20 x 10(-3) M PPy thin films demonstrated superior induction of MSC osteogenicity, which was comparable to standard TCP dishes, unlike PPy films of similar thickness prepared by chemical polymerization without surfactant. Adhesion of mesenchymal stem cells on tissue culture plates (TCP) coated with polypyrrole thin films made by admicellar polymerization.     

Magnetically Responsive Polymeric Microparticles for the Triggered Delivery of a Complex Mixture of Human Placental Proteins

Bone loss through traumatic injury is a significant clinical issue. Researchers have created many scaffold types to mimic an extracellular matrix to provide structural support for the formation of new bone, however functional regeneration of larger scaffolds has not been fully achieved. Newer scaffolds aim to deliver bioactive molecules to improve tissue regeneration. To achieve a more comprehensive regenerative response, a magnetically triggerable polymeric microparticle platform is developed for the on‐demand release of a complex mixture of isolated human placental proteins. This system is composed of polycaprolactone (PCL) microparticles, encapsulating magnetic nanoparticles (MNPs), and placental proteins. When subjected to an alternating magnetic field (AMF), the MNPs heat and melt the PCL, enhancing the diffusion of proteins from microparticles. When the field is off, the PCL re‐solidifies. This potentially allows for cyclic drug delivery. Here the design, synthesis, and proof‐of‐concept experiments for this system are reported. In addition, it is shown that the proteins retain function after being magnetically released. The ability to trigger the release of complex protein mixtures on‐demand may provide a significant advantage with wounds where stagnation of healing processes can occur (e.g., large segmented bone defects).     

Modification of single walled carbon nanotube surface chemistry to improve aqueous solubility and enhance cellular interactions

Single walled carbon nanotubes (SWNTs) continue to demonstrate the potential of nanoscaled materials in a wide range of applications. The ability to modulate the mechanical or electrical properties of a material by varying the SWNT component may result in diverse "application tunable" materials. Similarly, biomaterials used in tissue engineering applications may benefit from these characteristics by varying electrical and mechanical properties to enhance or direct tissue specific regeneration. The interactions between SWNTs and cellular systems need to be optimized to integrate these highly hydrophobic nanoparticles within an aqueous environment while maintaining their unique properties. We assessed solubility, conductance, and cellular interactions between four different SWNT preparations (unrefined, refined, and SWNT with either albumin or human plasma adsorbed). Initial interactions between cells and SWNTs were assessed within a 3D environment using a red blood cell lysis model, with longer-term interactions assessing the effects on PC12 and 3T3 fibroblast function when cultured on SWNT-collagen composite hydrogels. After SWNT purification, the lytic effect on red blood cells (RBCs) is significantly reduced from 11% to 0.7%, indicating manufacturing contaminants play a significant role in undesirable cell interactions. Nanotubes with either human plasma or albumin physisorbed onto the nanotube surface were significantly more hydrophilic than either unrefined or refined preparations and displayed improved RBC interactions. Despite improved dispersion, purification, and adsorption of either plasma or albumin, SWNTs caused a significant reduction in conductance. Although the molecular interactions occurring at the cell membrane remain unclear, these investigations have identified two main factors contributing to membrane failure: manufacturing impurities and to a lesser extend the material's innate hydrophobicity. Although purification is a critical step to remove toxic manufacturing contaminants, care must be taken to ensure improved aqueous dispersion does not compromise desirable mechanical and electrical attributes.