| (12) | Prepaid expenses and other current assets |
| | | December 31, | | |||||||
| | | 2017 | | 2016 | | 2015 | | |||
| Advances to suppliers of inventories | | $ | 234,458 | | | 929,815 | | | 1,224,454 | |
| Prepaid expenses of services | | | 235,652 | | | 217,244 | | | 130,086 | |
| Prepaid expenses of insurance and bonds | | | 88,533 | | | 185,678 | | | 82,238 | |
| Other current assets | | | 80,028 | | | 171,208 | | | 151,030 | |
| Total | | $ | 638,671 | | | 1,503,945 | | | 1,587,808 | |