Rapid Mix Preparation of Bioinspired Nanoscale Hydroxyapatite for Biomedical Applications

Hydroxyapatite (HA) has been widely used as a medical ceramic due to its good biocompatibility and osteoconductivity. Recently there has been interest regarding the use of bioinspired nanoscale hydroxyapatite (nHA). However, biological apatite is known to be calcium-deficient and carbonate-substituted with a nanoscale platelet-like morphology. Bioinspired nHA has the potential to stimulate optimal bone tissue regeneration due to its similarity to bone and tooth enamel mineral. Many of the methods currently used to fabricate nHA both in the laboratory and commercially, involve lengthy processes and complex equipment. Therefore, the aim of this study was to develop a rapid and reliable method to prepare high quality bioinspired nHA. The rapid mixing method developed was based upon an acid-base reaction involving calcium hydroxide and phosphoric acid. Briefly, a phosphoric acid solution was poured into a calcium hydroxide solution followed by stirring, washing and drying stages. Part of the batch was sintered at 1,000 °C for 2 h in order to investigate the products' high temperature stability. X-ray diffraction analysis showed the successful formation of HA, which showed thermal decomposition to β-tricalcium phosphate after high temperature processing, which is typical for calcium-deficient HA. Fourier transform infrared spectroscopy showed the presence of carbonate groups in the precipitated product. The nHA particles had a low aspect ratio with approximate dimensions of 50 x 30 nm, close to the dimensions of biological apatite. The material was also calcium deficient with a Ca:P molar ratio of 1.63, which like biological apatite is lower than the stoichiometric HA ratio of 1.67. This new method is therefore a reliable and far more convenient process for the manufacture of bioinspired nHA, overcoming the need for lengthy titrations and complex equipment. The resulting bioinspired HA product is suitable for use in a wide variety of medical and consumer health applications

The relationship between particle morphology and rheological properties in injectable nano-hydroxyapatite bone graft substitutes

Biomaterials composed of hydroxyapatite (HA) are currently used for the treatment of bone defects resulting from trauma or surgery. However, hydroxyapatite supplied in the form of a paste is considered a very convenient medical device compared to the materials where HA powder and liquid need to be mixed immediately prior to the bone treatment during surgery. In this study we have tested a series of hydroxyapatite (HA) pastes with varying microstructure and different rheological behaviour to evaluate their injectability and biocompatibility. The particle morphology and chemical composition were evaluated using HRTEM, XRD and FTIR. Two paste-types were compared, with the HA particles of both types being rod shaped with a range of sizes between 20 and 80 nm while differing in the particle aspect ratio and the degree of roundness or sharpness. The pastes were composed of pure HA phase with low crystallinity. The rheological properties were evaluated and it was determined that the pastes behaved as shear-thinning, non-Newtonian liquids. The difference in viscosity and yield stress between the two pastes was investigated. Surprisingly, mixing of these pastes at different ratios did not alter viscosity in a linear manner, providing an opportunity to produce a specific viscosity by mixing the two materials with different characteristics. Biocompatibility studies suggested that there was no difference in vitro cell response to either paste for primary osteoblasts, bone marrow mesenchymal stromal cells, osteoblast-like cells, and fibroblast-like cells. This class of nanostructured biomaterial has significant potential for use as an injectable bone graft substitute where the properties may be tailored for different clinical indications

Nanoscale strontium-substituted hydroxyapatite pastes and gels for bone tissue regeneration

Injectable nanoscale hydroxyapatite (nHA) systems are highly promising biomaterials to address clinical needs in bone tissue regeneration, due to their excellent biocompatibility, bioinspired nature, and ability to be delivered in a minimally invasive manner. Bulk strontium-substituted hydroxyapatite (SrHA) is reported to encourage bone tissue growth by stimulating bone deposition and reducing bone resorption, but there are no detailed reports describing the preparation of a systematic substitution up to 100% at the nanoscale. The aim of this work was therefore to fabricate systematic series (0–100 atomic% Sr) of SrHA pastes and gels using two different rapid-mixing methodological approaches, wet precipitation and sol-gel. The full range of nanoscale SrHA materials were successfully prepared using both methods, with a measured substitution very close to the calculated amounts. As anticipated, the SrHA samples showed increased radiopacity, a beneficial property to aid in vivo or clinical monitoring of the material in situ over time. For indirect methods, the greatest cell viabilities were observed for the 100% substituted SrHA paste and gel, while direct viability results were most likely influenced by material disaggregation in the tissue culture media. It was concluded that nanoscale SrHAs were superior biomaterials for applications in bone surgery, due to increased radiopacity and improved biocompatibility

Generalized parton distributions and double distributions for q q-bar pions

We consider two simple covariant models for pions (one with scalar and the other with spin-1/2 constituents). Pion generalized parton distributions are derived by integration over the light-cone energy. The model distributions are consistent with all known properties of generalized parton distributions, including positivity. We also construct the corresponding double distributions by appealing to Lorentz invariance. These ostensibly constructed double distributions lead to different generalized parton distributions that need not respect the positivity constraints. This inconsistency arises from the ambiguity inherent in defining double distributions in a one-component formalism (even in the absence of the Polyakov-Weiss term). We demonstrate that the correct model double distributions can be calculated from non-diagonal matrix elements of twist-two operators.Comment: 10 pages, 7 figures, RevTex4, reference added, typos correcte

Agenda-Setting With Local and National Issues

Three factors lead to the hypothesis that agenda-setting should be weaker at the local political level compared to the national level: (1) the more directly observable nature of local political problems, (2) the nature and strength of local interpersonal political communication networks, and (3) the relatively heavier media coverage of national political issues. This hypothesis was supported with data from respondents assigned at random to either local or national issue conditions and from a content analysis of television and newspaper coverage in Toledo, Ohio, of local and national issues. Contrary to the findings of certain previous studies, network television was found to exercise a stronger agenda-setting influence than newspapers at the national level. Newspapers, on the other hand, were the dominant agenda-setter at the local level. The relative agenda-setting influences of television versus newspapers are consistent with other data from this study concerning the relative strengths of the various media as sources of issue information.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67066/2/10.1177_009365027700400404.pd

The rare cancer network: ongoing studies and future strategy.

The Rare Cancer Network (RCN) was formed in the early 1990's to create a global network that could pool knowledge and resources in the studies of rare malignancies whose infrequency prevented both their study with prospective clinical trials. To date, the RCN has initiated 74 studies resulting in 46 peer reviewed publications. The First International Symposium of the Rare Cancer Network took place in Nice in March of 2014. Status updates and proposals for new studies were heard for fifteen topics. Ongoing studies continue for cardiac sarcomas, thyroid cancers, glomus tumors, and adult medulloblastomas. New proposals were presented at the symposium for primary hepatic lymphoma, solitary fibrous tumors, Rosai-Dorfman disease, tumors of the ampulla of Vater, salivary gland tumors, anorectal melanoma, midline nuclear protein in testes carcinoma, pulmonary lymphoepithelioma-like carcinoma, adenoid cystic carcinoma of the trachea, osteosarcomas of the mandible, and extra-cranial hemangiopericytoma. This manuscript presents the abstracts of those proposals and updates on ongoing studies, as well a brief summary of the vision and future of the RCN

Asymptotic Expansions for Stationary Distributions of Perturbed Semi-Markov Processes

New algorithms for computing of asymptotic expansions for stationary distributions of nonlinearly perturbed semi-Markov processes are presented. The algorithms are based on special techniques of sequential phase space reduction, which can be applied to processes with asymptotically coupled and uncoupled finite phase spaces.Comment: 83 page

Status of an Investigation of the 3-He Wave Function by Quasi-Free Scattering

This research was sponsored by the National Science Foundation Grant NSF PHY-931478

Status of an Investigation of the 3-He Wave Function by Quasi-Free Scattering

This research was sponsored by the National Science Fooundation Grant NSF PHY-931478

Status of an Investigation of the 3-He Wave Function by Quasi-Free Scattering

This research was sponsored by the National Science Foundation Grant NSF PHY-931478