Bioactive glass disks from the MgO-CaO-P2O5-SiO2 system were placed in artificial saliva for time periods varying from 1 to 42 days. Surfaces were then analyzed using scanning electron microscopy (SEM) and x-ray diffraction to investigate surface morphologies and crystallinity. SEM examination exhibited dramatic surface changes as early as 2 d. X-ray results showed crystallinity in the form of apatite at 10 d, which became more developed though 42 d. The bioactive glass in water and non-bioactive glass in artificial saliva were used as controls; both exhibited no evidence of apatite formation on their surfaces through the 42 d time period. This study shows that bioactive glass reacts in artificial saliva to form apatite and that the apatite layer becomes better crystallized over an extended time period. These results give a better understanding of the surface changes and mineralization that occur over time and can be used to interpret results from in vitro and in vivo studies done on bioactive glass in the oral environment.

Recombinant retroviruses are a commonly used gene delivery tool in human gene therapy clinical trials as they permanently integrate the therapeutic DNA into the genome of the target cell. Despite their widespread use, however, retroviral gene transfer efficiencies remain disappointingly low. In the years since their initial development as vectors, it has become clear that the physicochemical properties of the recombinant retrovirus, as well as the properties of the target tissue, have a major impact on the success of gene transfer. In particular, the interaction between the native negative charge present on the vector and target cell membranes results in a significant electrostatic barrier which must be overcome in order for the transduction process to begin. Using a recently developed retrovirus adsorption assay, we have demonstrated that this electrostatic interaction is the dominant interaction during the initial steps of transduction. We have also established that cationic polymers enhance adsorption, and ostensibly transduction, by neutralizing this electrostatic barrier. Interestingly, we also found that this enhanced adsorption could be demonstrated even in the absence of a cellular receptor for the virus, suggesting that the first step of transduction does not involve binding of the virus to currently identified receptors, but is either a non-specific adsorption process or involves binding to an, as of yet, uncharacterized class of receptor. Based upon our finding that virus adsorption is non-gp70 mediated, we propose a new physical model of this initial step of transduction which is diffusion-limited, receptor and envelope independent, and modulable by positively charged compounds. Our findings may have significant implications for other gene and drug delivery systems which interact directly with target tissues at the level of the cell membrane.

Bioactive glass powder in the MgO-CaO-P2O5-SiO2 system was mixed with water to create a bioactive glass paste. The paste was then placed in 8 cavities in molars of Sinclair mini-pigs, isolated using a light-cure composite filling, and left in vivo for 4 weeks. Additionally, 4 controls were run where the bioactive glass was placed in an inert polymer substrate and then incubated at 37°C for 4 weeks. Specimens were cut longitudinally in two halves and prepared for chemical and x-ray analyses. Qualitative results showed that the paste in the molars stayed intact while there was little or no paste left in the polymer substrate after cutting. This observation suggested that the paste in the natural tissue had structural integrity which could be caused by chemical changes and/or mineralization encouraged by contact with dentinal tubule fluid. X-ray analysis did not reveal any crystallinity in the paste at 4 weeks, but chemical alterations were confirmed by electron microprobe analysis. The chemical inhomogeneity of the individual elemental maps revealed the formation of Ca-P-rich/Si-poor areas. These distinct chemical variations were not seen in chemical analyses run on the bioactive glass paste in its initial state.

A semipermeable and non-inflammatory membrane is a prerequisite for the development of an implantable biosensor for continuous pain free monitoring of glucose levels in vivo. Humic acids (HAs) have been reported to have therapeutically relevant characteristics such as antiviral and anti-inflammatory.[1] This encouraged us to investigate the in vivo compatibility of HAs based multilayered films as a potential membrane material for implantable glucose sensors. Electrostatic layer-by-layer self-assembly technique of HAs with oppositely charged ferric ions was utilized to grow these films. Quartz Crystal Microbalance (QCM) and ellipsometric studies have shown repeatable, stepwise increase in mass and in film thickness during self-assembly. The growth of these assemblies exhibited strong dependence on pH and ionic strength of HAs solution and was correlated with the degree of ionization of carboxyl groups and the neutralization induced surface spreading. HAs films used in the biocompatibility study were very well tolerated by the tissue and no difference with silastic tubing, used as control, could be observed. All types of samples, including the controls, induced similar long-term tissue reaction showing almost no inflammation and a light to moderate fibrosis with some blood vessels present.

Nanoparticles and polymeric vesicles for drug delivery and other industrial applications have been prepared by the probe sonication of poly-L-lysine graft copolymer amphiphiles in aqueous media. The amphiphiles, which have a poly-L-lysine backbone and varied levels of both hydrophilic methoxypolyethylene glycol (Mw ∼ 5,000) and hydrophobic palmitoyl pendant groups, were prepared from 2 different molecular weight poly-L-lysine hydrobromide samples (Mw ∼4,000 and ∼20,000 respectively). Poly-L-lysine based amphiphilic polymers (PLPs) were characterised using light scattering, 1H NMR and an assay for the level of free amino groups. Steric factors appear to limit the final level of lysine group modification that can be achieved and even an excess amount of grafting reactants still resulted in the production of polymers in which 22 – 26 mole% of the lysine terminal amino groups remain unsubstituted. Polymeric unilamellar vesicles (220 – 570nm in diameter) imaged by electron microscopy were produced by probe sonication of PLP, cholesterol. Vesicle formation was possible over a narrow spectrum of polymer architecture and was favoured by a low molecular weight and a low level of palmitoyl substitution. A vesicle formation index (F') has thus been derived for this PLP, cholesterol system = Where H = %molar level of unreacted L-lysine units, L = %molar level of substituted palmitoyl units and DP = square root of the degree of polymerisation of the polymer. Probe sonication of an aqueous dispersion of PLP samples resulted in the production of stable nanoparticles (80 -170nm in diameter) as imaged by electron microscopy. Nanoparticles were able to encapsulate the hydrophilic fluorophore fluorescein isothiocyanate (FITC)-dextran and encapsulation increased as the level of unreacted lysine terminal amino groups in PLP increased thus increasing as the level of hydrophilic domains increased. The size of both the nanoparticles and the vesicles was directly influenced by the molecular weight of PLP. PLPs of molecular weight 32,000 – 48,000 and 89,000 – 140,000 resulted in nanoparticles of 85 – 114 nm and 125 – 167 nm in diameter respectively and PLP of molecular weight 25,000 and 89,000 gave rise to polymeric vesicles of 252 nm and 570 nm in diameter respectively.

A key factor in designing a drug-in-adhesive transdermal drug delivery system is to understand the rate at which the drug and small-molecule excipients can diffuse in the adhesive matrix. The solubility of these components in the adhesive matrix is also of great importance. Results will be presented discussing the use of infrared-attenuated total reflectance (IR-ATR) spectroscopy as a method to measure both diffusion and solubility of small molecules in adhesives. In this method, the donor layer is either a doped adhesive or a free liquid that is placed in contact with a receptor layer which is an undoped adhesive in contact with an IR-ATR crystal. The IR-ATR crystal detects as a function of time any molecules that diffuse from the donor layer into and through the receptor layer.

Examples will be discussed of several different experiments that can be performed with this technique. Diffusion coefficients are presented here for testosterone and terpineol in an isooctyl acrylate based adhesive using a doped adhesive donor layer. Diffusion and solubility of liquids in several adhesives has been determined using the experiment where a free liquid is used as the donor. Solubility and diffusion coefficients determined using an oversaturated doped layer containing dispersed, as well as dissolved solute, are presented here for testosterone and for progesterone. Finally diffusion from a doped layer of one adhesive to an undoped layer of a different adhesive was performed as a partition measurement. The parameters that can be extracted from each of these experiments, as well as the limitations of each type of experiment will be discussed.

New hydrothermal technology for the preparation of hydroxyapatite designer particulates has been developed. Phase diagrams were constructed for the pH dependent equilibrium between monetite and HA from 50 to 200°C. Thermodynamic calculations were completed using temperature dependent functions for the relevant solution phase and solid-liquid equilibria and solute species activity coefficients. Model accuracy was evaluated through experiment at 50, 100, and 200°C and pHs between 2.2 and 8.9. The thermodynamic calculations and experimental results are in good agreement. Stoichiometric, crystalline HA has also been prepared by heterogeneous reaction of Ca(OH)2 powder and aqueous (NH4)2HPO4 at room temperature using mechanochemical-hydrothermal methods. This method appears to have very good reproducibility in terms of crystallinity and chemical composition.

new Ti-5Ag and Ti-5Ag-35Sn (wt.%) alloys were designed and synthesized by threedimensionalprinting (3DP). The identification of an appropriate binder, densificationtechnique, and densification parameters for fabricating cranio-maxillo-facial prostheses wasundertaken using microscopic observations, x-ray diffraction tests, microhardness testing, linearshrinkage and wettability measurements. Moreover, electrochemical tests and surface analysiswere used to evaluate the corrosion resistance and passivation behavior of the materials ofinterest. Silver nitrate was found to be an appropriate inorganic reactive binder for atomizedtitanium powder. The optimal temperature for densification of as-printed parts using sinteringwas determined for Ti-Ag alloys. In addition, the type of infiltrant material and use ofhomogenization in liquid-Sn infiltration was explored for Ti-Ag-Sn alloys. While the Ti-Agalloy exhibited superior corrosion and mechanical behavior to the Ti-Ag-Sn alloy, the lattershowed better dimensional stability.

We have developed a novel electrochemical system for field assisted, fluidic assembly of objects on a microfabricated silicon substrate by means of electrical addressing. The principle of our technique is based on the movement of charged species in solution to oppositely charged electrodes, as seen commonly in electrophoresis. Here, charged species such as beads and cells are moved electrokinetically through an aqueous solution towards a charged electrode. Micro patterning of the electrodes allows localization of charged species. We present a theoretical framework to predict the electric potential for assembly and disassembly of spherical objects. We correlate theoretical predictions with the motion of negatively charged polystyrene beads of 20 μm diameter on 100 μm feature micro patterned substrates. In addition, we extended these results to arraying of 20-30 μm diameter live mammalian cells by means of electrical addressing. This technique has applications in creation of ‘active’ cellular arrays for cell biology research, drug discovery and tissue engineering.

Vitamin E TPGS was found to be an effective structure-directing agent for the preparation of both hexagonal all silica DAM-1 and the alumina analog, Al-DAM-1. These free flowing powders offer many advantages in the handling and oral delivery of the sticky vitamin E TPGS. Upon exposure to simulated gastric fluid, the Al-DAM-1 host molecular sieve is dissolved releasing the vitamin E TPGS. As much as 0.6 grams of vitamin E TPGS can be immobilized into 1 gram of Al-DAM-1. Vitamin E TPGS also templates highly ordered mesoporous DAM-1 with tunable morphologies such as hexagons (various lengths), gyroids, rods, spheres and discoids depending upon the temperature and gel composition. Characterization of these composites as well as a preliminary evaluation of Al-DAM-1 as an oral drug delivery system under physiological conditions is presented.

The overall goal of this project is to develop an in-situ polymerizable, biodegradable material for use in cardiovascular applications that minimizes non-specific cell adhesion and contains functional moieties for the attachment of peptides to induce specific cell attachment. A novel block copolymer has been developed incorporating poly(propylene fumarate) (PPF) and poly(ethylene glycol) which satisfies these criteria. PPF is a new biodegradable polymer currently being investigated for orthopedic and cardiovascular applications while PEG is a hydrophilic polymer that has been extensively studied for biomedical applications. The copolymer is chemically crosslinked with PEG diacrylate using an ammonium persulfate-ascorbic acid redox initiator system to form the hydrogel. The PEG and PPF block lengths can be varied to modulate the properties of the hydrogel formed. In this study, the following three parameters were studied, (1) PPF block length, (2) PEG block length, and (3) initial water content, were varied to examine their effects on swelling, degradation and elastic modulus. A factorial experimental design was implemented to assess which of these three parameters had the greatest impact on swelling, degradation and elastic modulus. Swelling was found to be most affected by the initial water content followed by PEG block length and PPF block length. The swelling of the hydrogels ranged from 48% water uptake with low initial water content to up to 77% water uptake with the high initial water content. After three weeks, degradation of the hydrogels ranged from 4-13% mass fraction lost. Elastic modulus was determined by tensile testing of the various hydrogel formulations and ranged from 0.4 to 7.7 MPa.