Table 2.

Predicted optimal levels of hierarchy versus experimental observations for various load-bearing biological materials.

	Φ (%)a	optimal N		Nb observed in nature
		Θp = 35%	Θp = 100%
bone	45	4	6	7
mineralized tendon	15	4	6	4–6
shell	95	1	4	2–3

^aJackson et al. [6], Jager & Fraatzl [7], Menig et al. [21] and Landis [34].

^bRho et al. [16], Weier & Wagner [17], Puxkandl et al. [18], Kastelic et al. [19] and Menig et al. [21].