Artificial mucosa

Fig. 5.2. Numerical solutions of an analytical model for concentration for two compounds a and b at different positions, x, within the artificial mucosa. Carrier velocity inside the micro-channel is 15 cm s , mass distrihntion coefficients ka= i and fcj, = 2, and effective diffusion coefficients D a = 50 cm s and D = 10 cm s . Pnlse duration at inlet ( sniff time ), t = 5 s.

Differential sorption of compounds within the artificial mucosa gives rise to a temporal fingerprint in the chemosensor response which is sensitive to the concentrations and presence of different compounds. The important aspect here that is distinct from previous techniques exploiting the temporal dimension is that the delivery of the stimulus itself becomes specific to the compound(s) being delivered, which imposes... 

Chemical Sensor Behaviour within the Artificial Mucosa... 

In the coated case (the normal operational mode of the artificial mucosa -Figure 5.3b), the response of the outlet sensor after normalization shows very different temporal responses that are strongly stimulus specific. Here we see a clear additional latency in the onset of the response and also its duration is much longer, which is clearly due to spatio-temporal stimulus dynamics imposed by the coated mucosa when we compare to the uncoated case. This stimulus dependent difference in... 

For configurations with only one sensor, the ratio is always infinite since it is impossible to estimate the concentrations of the individual compounds from the average response of only one sensor, a task which on the other hand is possible to address when the temporal information is also considered. For small numbers of sensors the improvement of the performance of the system based on spatio-temporal information can be several orders of magnitude (Table 5.1), revealing that an artificial mucosa optimally designed for exploiting temporal features can increase largely the sensitivity as well as reduce the number of total sensors. 

More formally, a new information theory measure has been described which is capable of quantifying both spatial and temporal information in artificial mucosa based chemical sensor arrays. Importantly this analysis has demonstrated that the spatio-temporal case should outperform the purely spatial case emphasising the importance of time in these systems. 

Richter T, Keipert S (2004) In vitro permeation studies comparing bovine nasal mucosa, porcine cornea and artificial membrane androstenedione in microemulsions and their components. Eur J Pharm Biopharm 58 137-143. 

Artificial membranes soaked in animal mucin dispersions or animal model mucosae are used as biological substrates. Another apparatus proposed for in vitro measurements of bioadhesive properties of liquid formulations (polymer solutions or pessaries upon melting) consists of a thermostated inclined plane over which a mucosal membrane or a mucin film is layered. This test measures, as a function of time, the amount of formulation that after contact with the biological substrate, drops on a microbalance placed under the inclined plane [86] (Figure 22.3). 

The bioadhesive properties were first described by Lehr et al. (1992b) demonstrating that chitosan in the swollen state is an excellent mucoadhesive polymer in the porcine intestinal mucosa and is also suitable for repeated adhesion. The authors also reported that chitosan undergoes minimal swelling in artificial... 

By considering the role of timing of odorant delivery in biological olfaction (Rubin Cleland 2006), we have recently built a novel machine olfaction technology, termed an artificial olfactory mucosa , which demonstrates clearly a third principle of odour discrimination in artificial olfactory systems ... 

An Artificial Olfactory Mucosa for Enhanced Complex Odour Analysis... 

Fig. 5.3. Comparison of normalized chemosensor responses for an uncoated and coated artificial olfactory mucosa, a) Uncoated mucosa. Responses of sensor SI (PEVA sensor material composite) close to the inlet and S39 (PCL sensor material composite) close to the outlet of the microchannel. b) Responses from the same sensors in the coated mucosa. (Reprinted with permission by Royal Society, London).

In vitro experiments have shown that cyclotetraglucose dissolved in Bis-Tris buffer (50 mmol/l) is not degraded by human salivary or porcine pancreatic a-amylase or by artificial gastric juice (pH 2). Only 0.7% of cyclotetraglucose incurred ring opening during a 3-h incubation period with an acetone powder preparation of the rat intestinal mucosa to form a linear tetrasaccharide (Hashimoto et al., 2006). 

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