Experimental 70% hydrofluoric acid burns: histological observations in an established human skin explants ex vivo model

Figures & data

Figure 1.  Chemical reactions between fluoride ions and calcium/magnesium.

Table 1.  Mean thickness of the human skin explants layers.

Thickness (µm)
Total skin	3972
Epidermis	72	Stratum corneum + granulosum + spinosum	57
		Basal layer	15
Dermis	3900	Papillary dermis	248
		Reticular dermis	3652

Note: Standard deviations (SDs) or standard errors of the mean (SEMs) were not calculated.

Figure 2.  Normal aspect of skin optical microscopy with 40× objective.

Figure 3.  Skin histological aspect after a 20-sec exposure to 30 µL of 70% hydrofluoric acid (HF). No deterioration of the epidermal or dermal structures.

Figure 4.  Skin histological aspect at 1 min after a 20-sec exposure to 30 µL of 70% hydrofluoric acid (HF). The epidermis showed four to five cellular layers with a slightly modified morphology. The cells showed gray cytoplasm in the upper layer and the nuclei became pyknotic. The cellular structures of the basal epidermis and throughout the dermis showed normal morphologies.

Figure 5.  Skin histological aspect at 2 min after a 20-sec exposure to 30 µL of 70% hydrofluoric acid (HF). The skin showed four to five cellular layers with definitely abnormal morphology: cells with nuclei becoming pyknotic, especially in the higher epidermal layers, and the cytoplasm becoming acidophilic as reflected by orange keratinocyte pigmentation. The cellular structures in the dermis showed normal morphology.

Figure 6.  Skin histological aspect at 3 min after a 20-sec exposure to 30 µL of 70% hydrofluoric acid (HF). Lesions of four to five epidermis cellular layers were characterized by numerous cells with moderately pyknotic nuclei and edema surrounding the nuclei. At the base of the stratum corneum and in the basal epidermis layer, cells showed characteristic cytoplasmic alterations. In the papillary dermis, the cellular structures were slightly pyknotic. The reticular dermis remained normal.

Figure 7.  Skin histological aspect at 4 min after a 20-sec exposure to 30 µL of 70% hydrofluoric acid (HF). The same deteriorations in the epidermis were observed compared with those described at 3 min. In the papillary dermis, cells more clearly showed pyknotic nuclei, but the reticular dermis remained normal.

Figure 8.  Skin histological aspect at 5 min after a 20-sec exposure to 30 µL of 70% hydrofluoric acid (HF). The same lesions as those detected after 4 min were observed in the epidermis and papillary dermis. However, as the HF had penetrated into the reticular dermis, slightly pyknotic nuclei were observed in cells in this deepest layer.

Table 2.  Comparison between known values of skin thickness.

Authors	Epidermis (µm)	Dermis (µm)	Total thickness (µm)
Cowdry [26]	20–100
Maximow and Bloom [27]	70–140	1000–3000	Calculated*: 1070–3140
Southwood [28]	20–140	400–2500	Calculated*: 420–3900
Artz et al. [30]	39–64	956–1911	Calculated*: 995–1975
Lee and Hwang [29]	31–637	469–1942	Measured*: 521–1277
Our explants	72	3900	Measured*: 3972

*Measured histologically. There are differences between the calculated values (sum of the minimal and the maximal data) and the measured one because the thinnest epidermis was not necessarily associated with the thinnest dermis and vice versa. Values given are means. Neither SDs nor SEMs were calculated. There data are only intended to show the relative similarity of the human skin explants utilized in this study to published values for normal skin thickness.

Table 3.  Comparison of thickness of abdomen skin between races.

Abdomen thickness (µm)*	Epidermis	Dermis	% E (E+D)
European	41–40	1640–1492	2.4–2.6
Asian	69	1248	6.0
Our experiment	72	3900 (papillary dermis: 248, reticular dermis: 3652)	1.8

*European values taken from Southwood [28] and Artz et al. [30] versus Asian from Lee and Hwang [29]. Last line: our experimental data.

Table 4.  Dynamics of appearance of lesions after skin exposure to 70% hydrofluoric acid (HF).

Duration of exposure	Microscopic morphology
1 min	Beginning of the attack in the higher part of the epidermis
2 min	Attack of the basal layer of the epidermis
3 min	Epidermis completely damagedFirst lesions of the papillary dermis (superficial part of the dermis)
4 min	Epidermis completely damagedClear attack of the papillary dermis
5 min	Epidermis completely damagedBeginning of attack of the reticular dermis (deeper layer of the dermis)

Table 5.  Details of histological cell alterations during a 5-min skin exposure to 70% hydrofluoric acid (HF).

20 sec	Epidermis	GM*(Good morphology)
	Papillary dermis
	Reticular dermis
1 min	Epidermis	SlightlyPN + AC (Pyknotic nucleus and acidophilic cytoplasm)
	Papillary dermis	GM
	Reticular dermis
2 min	Epidermis	PN + AC
	Papillary dermis	GM
	Reticular dermis
3 min	Epidermis	PN + AC
	Papillary dermis	Slightly PN + AC
	Reticular dermis	GM
4 min	Epidermis	PN + AC
	Papillary dermis
	Reticular dermis	GM
5 min	Epidermis	PN + AC
	Papillary dermis
	Reticular dermis	Slightly PN + AC

*Cell alterations: good morphology (GM), pyknotic nucleus (PN), and acidophilic cytoplasm (AC).

Figure 9.  Kinetics of 70% hydrofluoric acid (HF) through human ex vivo skin explants.

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