Papers by Author: Peter Greil

Abstract: Knits made of cellulose are promising scaffolds for bone tissue engineering applications due to their multi-scale interconnected porosity, biocompatibility and adjustable biodegradability. The approach of this study combines the modification of cellulose with strontium to generate scaffolds capable of forming bone like apatite during exposure to physiological solutions and the release of strontium as an active agent, that might encourage the development of new bone tissue. The Sr-release kinetics during static exposure to simulated body fluid is dominated by an accelerated Sr-release in the initial state followed by a reduced release corresponding to a diffusion controlled rate. Microstructural analyses indicate that initially precipitated SrCO3 transforms to SrxCa1-xCO3 solid solutions that subsequently serve as a template for the precipitation of bone like carbonated hydroxyapatite.

Abstract: Hydroxy carbonated apatite (HCA) powders were prepared by precipitation from a modified SBF solution (5x M-SBF). The ionic concentrations were 5 times higher than in human blood plasma with the exception of Mg2+ and HCO3 - concentrations that were reduced in order to accelerate crystal growth. Spheroaggregates of HCA platelets with molar (Ca+Mg)/P ratios ranging from 1.44 to 1.56 were obtained after precipitation at 50 °C. The crystallite size in c-direction was approximately 20 nm and depending on the precipitation time a CO3 2- content of 1.8 to 5.2 wt.-% was determined. Using this low temperature precipitation method, HCA powders with a high specific surface area of 83 m2/g and a composition and crystallite size close to those of the mineral phase of human bone were obtained.

Abstract: Biomimetic apatite coatings are widely used in orthopaedic applications to provide bioinert material surfaces with bioactive behaviour by means of initiating bone growth at the implant surface. In this study we manufactured biomimetic calcium phosphate coatings consisting of a calcium deficient carbonated apatite by immersing activated titanium platelets into simulated body fluid (SBF). The development of the crystal phases was monitored by X-ray diffractometry (XRD) in addition to Fourier-transform infrared (FT-IR) spectroscopy. After annealing in air up to 600 °C luminescence of the biomimetically derived apatite was observed. The photo-induced emission spectra were recorded in the range from 400-750 nm at excitation wavelengths ranging 238 to 450 nm. A blue (437 nm) and a green (556 nm) emission were found between 200 to 600 °C visually appearing white. The results are discussed in terms of chemical and crystallographic changes in the biomimetic calcium phosphate layer during heat treatment.

Abstract: A composite material consisting of cellulose and HAp was prepared using coagulation of a native cellulose suspension. Composite tapes with a HAp content below 50 vol.% exhibit a gradient of filler particles across the cross-section of the sample due to gravity force that causes sedimentation of HAp, as long as the viscosity of the suspension is below a critical level during the coagulation process. According to gravimetric and solution analysis as well as SEM, the filler content influences the amount and uniformity of HCA precipitated in the surface of the tape. With increasing content of filler in the cellulose matrix, the apatite growth from SBF is promoted, due to a higher amount of HAp particles that serve as nucleation sites.

Abstract: Calcium phosphate bioceramics with an interconnective pore structure were produced by foaming of hydroxyapatite and methyl phenyl poly(silsequioxane) melts in the temperature range between 250 °C and 310 °C. The cellular structure of the resulting porous bodies were controlled by foaming parameters and filler load. A porosity of up to 92 % was achieved by decreasing the HAfiller amount and increasing the foaming temperature. Subsequent pyrolysis in air at temperatures of 900 °C and 1100 °C resulted in macroporous foams composed of HA and HA/b-TCP, respectively. The porous bodies with tailorable structure and composition are of interest for bone tissue engineering scaffolds and orthopedic implants.

Abstract: Fibrous cellulose templates are attractive candidates for the use as tissue engineering scaffolds due to their biocompatibility and the adjustable porosity. Nevertheless, a direct bond between cellulose and bone is not formed under physiological conditions. A simulated body fluid solution with a high degree of supersaturation (5*SBF) was used to accelerate the biomimetic formation of bonelike apatite on cellulose templates. After generating calcium phosphate nuclei on the cellulose fibers in 5*SBF with high Mg2+and HCO3 - concentrations the cellulose templates were immersed in a modified 5*M-SBF which was optimized in respect to crystal growth kinetics by reduced Mg2+and HCO3- concentrations. After 48 hours a hydroxy carbonated apatite (HCA) layer with a thickness of 20 µm was obtained.