Resorption rate assessment of adipose tissue-engineered constructs by intravital magnetic resonance imaging.

Engineering of adipose tissue by implantation of preadipocytes within biodegradable materials has already been extensively reported. However, a method that allows to accurately determine the resorption rate of adipose tissue constructs has not been described to date. The purpose of this study was to determine whether the non-invasive and non-destructive technique of magnetic resonance imaging (MRI) could be used to assess the resorption rate of adipose tissue substitutes after injection of human preadipocytes within fibrin into athymic nude mice. Different concentrations of undifferentiated preadipocytes were injected within fibrin into athymic nude mice. Two days, 3 months and 6 months post-implantation, the mice were anaesthetised and an MRI was performed using a 9.4 Tesla device in order to determine both volume and resorption rate of the implants. Subsequently, the specimens were explanted and qualitative analysis of adipose tissue formation was performed by histological examination. After implantation, a progressive resorption of all constructs was macroscopically observed. Implants could be easily visualised and delimited from the surrounding tissues by MRI. Magnetic resonance analysis demonstrated a resorption rate of the implants of 99-100% at 6 months, which was also confirmed by histological analysis. In the remaining implants, formation of human adipose tissue could be immunohistologically confirmed. Here, we show that MRI provides an efficient and non-invasive method for the assessment of implant resorption in adipose tissue engineering.

Comparison of pre-adipocyte yield, growth and differentiation characteristics from excised versus aspirated adipose tissue.

Adipose tissue precursor cells (pre-adipocytes) are part of a stromal vascular fraction that can be easily isolated from fat tissue. Adipose tissue can be harvested by 2 methods: aspiration and excision. We analyzed whether the pre-adipocyte yield, growth characteristics and ability to differentiate into mature adipose tissue are influenced by the type of harvesting procedure. Adipose tissue was simultaneously harvested from the abdomen by surgical excision or aspiration according to the Coleman procedure in 10 individuals. This permitted inter- and intra-individual comparisons. Cell viability and yield were determined directly after isolation of pre-adipocytes. The growth kinetics were investigated in culture. Furthermore, pre-adipocytes were cultured under adipogenic conditions to compare their differentiation potential. The number of viable pre-adipocytes was significantly higher after excision of adipose tissue compared to aspiration. The proliferation kinetic was not influenced by the type of harvesting. No differences were observed in the differentiation potential of the pre-adipocytes between both groups. Compared to excision, aspiration of adipose tissue negatively affects the yield of pre-adipocytes. However, growth characteristics and differentiation potential of viable cultured cells are not influenced by the type of surgical harvesting. Due to its reduced donor site morbidity, we conclude that aspiration of adipose tissue is a valid harvesting method for isolation of pre-adipocytes.

Evoked EEG patterns during burst suppression with propofol.

BACKGROUND: During EEG suppression with isoflurane or sevoflurane anaesthesia, median nerve stimulation causes cortical responses of two kinds: an N20 wave with a latency of 20 ms and an EEG burst with a latency of 200 ms. We tested the possibility that median nerve stimulation during EEG suppression with propofol would cause an EEG response that was consistent enough to be of use for neuromonitoring. METHODS: Eight patients were anaesthetized with propofol to allow burst suppression. Electrical stimulation of the median nerve was applied during general anaesthesia and the EEG was measured. RESULTS: The EEG response to a painful stimulus had four successive components: (i) N20 and P22 potentials, reflecting activation of fast somatosensory pathways; (ii) a high-amplitude negative wave, possibly reflecting activation of the somatosensory cortex SII bilaterally; (iii) a burst (i.e. a negative slow wave with superimposed 10 Hz activity, probably reflecting an arousal mechanism); and (iv) a 13-15 Hz spindle, probably originating from the thalamus, similar to sleep spindles. These could be seen separately and in different combinations. Bursts and spindles during burst suppression were also seen without stimulation. In deepening propofol anaesthesia, spindles were seen in the continuous EEG before burst suppression was achieved. In deep anaesthesia, spindles were seen when bursts had ceased, and painful stimuli evoked sharp waves without subsequent bursts. CONCLUSION: In addition to SSEP (somatosensory evoked potentials), three different evoked responses are noted that could be useful for clinical monitoring.

Tibial nerve somatosensory evoked potentials during EEG suppression in sevoflurane anaesthesia.

OBJECTIVES AND METHODS: Cortical tibial nerve somatosensory evoked potentials (TSEPs) were recorded from 10 subjects in sevoflurane anaesthesia in order to study TSEP during EEG suppression. RESULTS: With a stimulation frequency less than one per second the major component was a positive wave which had maximal amplitude parietally ipsilaterally to stimulus and mean latency of 46.1 ms. It probably corresponds to the P40 wave. It was preceded by a widespread smaller positive wave, which corresponds to the subcortical P30 wave. In two patients a high amplitude negative wave, a couple of milliseconds before the positive wave, and maximal parietally contralateral to stimulus, was seen. All later waves were absent. CONCLUSION: The results are in agreement with our previous results from median nerve SEPs showing that the first cortical response from primary somatosensory cortex is enhanced, and later waves are suppressed. Hence, recording TSEPs during EEG suppression provides a way to record the activity of the primary somatosensory cortex accurately and rapidly due to the very good signal to noise ratio, so that even single responses to stimuli can be seen without averaging. Our results suggest that new cortical generators, which are not recordable awake, may be discovered in some patients.