Nisin F-loaded brushite bone cement prevented the growth of Staphylococcus aureus in vivo

Aims: To determine if nisin F‐loaded self‐setting brushite cement could control the growth of Staphylococcus aureus in vivo. Methods and Results: Brushite cement was prepared by mixing equimolar concentrations of β‐tricalcium phosphate and monocalcium phosphate monohydrate. Nisin F was added at 5·0, 2·5 and 1·0% (w/w) and the cement moulded into cylinders. In vitro antibacterial activity was determined using a delayed agar diffusion assay. Release of nisin F from the cement was determined using BCA protein assays. Based on scanning electron microscopy and X‐ray diffraction analysis, nisin F did not cause significant changes in cement structure or chemistry. Cement containing 5·0% (w/w) nisin F yielded the most promising in vitro results. Nisin F‐loaded cement was implanted into a subcutaneous pocket on the back of mice and then infected with S. aureus Xen 36. Infection was monitored for 7 days, using an in vivo imaging system. Nisin F prevented S. aureus infection for 7 days and no viable cells were isolated from the implants. Conclusions: Nisin F‐loaded brushite cement successfully prevented in vivo growth of S. aureus. Significance and Impact of the Study: Nisin F incorporated into bone cement may be used to control S. aureus infection in vivo.     

Phosphate Solubility and the Cyanate-Mediated Synthesis of Pyrophosphate

The justification for a less alkaline primordial ocean (than present) is briefly reviewed, along with constraints on aqueous phosphate under such conditions. Based on the assumption that CaHPO₄ dihydrate determined the availability of phosphorus species, we have carried out laboratory simulations to determine equilibrium concentrations as a function of pH (in PIPES buffer) with added NaCl and CaCl₂. Consistent with expectations, solubility declines with higher pH and [CaCl₂], but increases only slightly with [NaCl]. Significantly, PIPES shows no specific effect on the dissolution beyond its influence on pH and ionic strength. Data are also presented on the synthesis of pyrophosphate from the NaOCN/CaHPO₄·2H₂O system, which could have provided a source of this phosphate anhydride on the early Earth.     

Brushite cement additives inhibit attachment to cell culture beads

Brushite‐forming calcium phosphate cements are of great interest as bone replacement materials because they are resorbable in physiological conditions. Cell‐attached culture beads formed from this material could be of great use for cell therapy. Despite a significant amount of work on optimizing the physicochemical properties of these materials, there are very few studies that have evaluated the capacity of the materials to facilitate cell adhesion. In this study, we have formed resorbable calcium phosphate (brushite) culture beads and for the first time we showed that cell attachment to the surface of the brushite cement (BC) could be inhibited by the presence of an intermediate dicalcium phosphate–citrate complex, formed in the cement as a result of using citric acid, a retardant and viscosity modifier used in many cement formulations. The BC beads formed from the mixture of β‐TCP/orthophosphoric acid using citric acid did not allow cell attachment without further treatment. Ageing of BC beads in serum‐free Dulbecco's Modified Eagle's Medium (DMEM) solution at 37°C for 1 week greatly enhanced the cell adhesion capacity of the material. Scanning electron microscopy, X‐ray diffraction (XRD), and confocal Raman microspectrometry indicated the increased capacity for cell adhesion was due to the changes in phase composition of BC. XRD patterns collected before and after ageing in aqueous solution and a high initial mass loss, suggest the formation of a dicalcium phosphate–citrate complex within the matrix. Since compacts formed from brushite powder supported cell attachment, it was hypothesized that the dicalcium phosphate–citrate complex prevented attachment to the cement surface. Biotechnol. Bioeng. 2013; 110: 1487–1494. © 2012 Wiley Periodicals, Inc.