Using eddy currents for noninvasive in vivo pH monitoring for bone tissue engineering.

PURPOSE: The metabolic processes that regulate bone healing and bone induction in tissue engineering models are not fully understood. Eddy current excitation is widely used in technical approaches and in the food industry. The aim of this study was to establish eddy current excitation for monitoring metabolic processes during heterotopic osteoinduction in vivo. METHODS: Hydroxyapatite scaffolds were implanted into the musculus latissimus dorsi of six rats. Bone morphogenetic protein 2 (BMP-2) was applied 1 and 2 weeks after implantation. Weekly eddy current excitation measurements were performed. Additionally, invasive pH measurements were obtained from the scaffolds using fiber optic detection devices. Correlations between the eddy current measurements and the metabolic values were calculated. RESULTS: The eddy current measurements and pH values decreased significantly in the first 2 weeks of the study, followed by a steady increase and stabilization at higher levels towards the end of the study. The measurement curves and statistical evaluations indicated a significant correlation between the resonance frequency values of the eddy current excitation measurements and the observed pH levels (p = 0.0041). CONCLUSIONS: This innovative technique was capable of noninvasively monitoring metabolic processes in living tissues according to pH values, showing a direct correlation between eddy current excitation and pH in an in vivo tissue engineering model.

Endocultivation: metabolism during heterotopic osteoinduction in vivo--monitoring with fiber optic detection devices.

Reconstructions of facial bone defects are one of the most challenging aspects in surgical treatment of malignant diseases, large facial traumata, or congenital anomalies. High-level reconstruction techniques are often associated with an elevated morbidity by the harvest of autologous bone grafts from the patient. Tissue engineering techniques may help to solve this problem. The aim of this study was to monitor metabolic processes during cellular colonization of matrices in vivo in an established rat model for endocultivation. After implantation of computer-designed hydroxyapatite scaffolds into the latissimus dorsi muscle of six rats, 100 µg bone morphogenetic protein-2 (BMP-2) was injected twice, in week 1 and 2, directly into the center of the matrices. The development of pH value and oxygen (O2) saturation inside the matrix was followed by fiber optic detection technique over 8 weeks and analyzed by variance analyses. Bone density measurements were performed by computed tomography as well as histological evaluations. Two weeks after implantation, oxygen supply and pH value measurements had decreased significantly. In the following weeks both parameters increased and stabilized on higher levels. This is the first study reporting a reproducible method to follow metabolic processes during heterotopic osteoinduction in vivo. It was shown that in the beginning of the study pH value and O2 saturation decreased and it took several weeks to regain physiological levels. This is an important step to further understand the physiological process of bone induction.

Update on glycopeptide use in german university hospitals.

BACKGROUND: A previous study has shown considerable variation in glycopeptide use from 1992 through 1994 among four university hospitals in southern Germany. Active antimicrobial management in one of the hospitals was associated with the containment of glycopeptide consumption in the medical and surgical service at < 1.5 defined daily doses (DDD)/100 patient days in the subsequent period. In the present study, more recent data on comparative glycopeptide use in German university hospitals were analyzed. MATERIALS AND METHODS: Hospital pharmacy records from 1998 through 2000 were evaluated. The number of DDD (definition according to the World Health Organization [WHO]/Anatomic and Therapeutic Classification [ATC] index) per 100 patient days was calculated to compare glycopeptide use in different medical and surgical service areas between eight German university hospitals. RESULTS: The 3-year averages in recent glycopeptide use for the eight hospitals ranged between 1.3 and 8.8 DDD/100 patient days in the medical services, and between 0.7 and 1.8 DDD/100 patient days in the surgical services. Only one of the eight hospitals showed medical service glycopeptide use of < 1.5 DDD/100 patient days. In most hospitals, glycopeptide use was higher in the medical intensive care units (ICU) (median 8.6; range 4.3 to 12 DDD/100 patient days, data for the year 2000) than in the surgical ICUs (median 6.7; range 1.2 to 8.6 DDD/100 patient days, data for the year 2000). High use was also observed for hematology-oncology services (median 7.5; range 2.7 to 15.7 DDD/100 patient days, data for the year 2000). CONCLUSION: These recent data from a larger hospital sample confirm large variations in glycopeptide use, identify hematology-oncology services as a significant prescribing source along with ICUs, and indicate areas of probable overuse of glycopeptide antibiotics. The data may be useful as a benchmark for further focused drug use control interventions.