Comparison of fibrillar collagen response to inhaled versus bolus aspiration of MWCNTs. Although the total lung burden of these two routes differs by a factor of approximately 3, the time course and magnitude of response to bolus aspiration and inhalation exposure of MWCNT to the lungs are remarkable similar. Therefore, the fibrogenic potency of inhaled MWCNTs is approximately 3-fold greater than aspirated MWCNT (bolus exposure) on an equivalent lung burden basis. Fibrillar collagen response data following bolus aspiration exposure to MWCNTs from Mercer et al. , Figure 6 (Mean ± S.E., N = 6).