3. INTANGIBLE ASSETS

Intangible assets consist of patents, patent applications, and licenses. Capitalized patent application costs are included with patents. Intangible assets are amortized on a straight-line basis over their estimated useful lives or terms of their agreement, whichever is shorter. There were no abandonments or impairment adjustments to intangible assets during the years ended December 31, 2017 and 2016.

Intangible assets at December 31, 2017 and 2016 consist of the following:


	December 31, 2017				December 31, 2016
	Gross Carrying		Accumulated		Gross Carrying		Accumulated
	Amount		Amortization		Amount		Amortization

Amortized intangible assets:
Patents	$	476,177	$	(126,032)	$	437,199	$	(103,238)
License		50,000		(48,959)		50,000		(45,834)
	$	526,177	$	(174,991)	$	487,199	$	(149,072)


	2017		2016
Aggregate amortization expense:
For the years ended December 31	$	25,919	$	25,115

Estimated amortization expense for the years ending December 31:


2018	$	24,000
2019		23,000
2020		22,000
2021		22,000
2022		22,000

In connection with the license agreement, the Company has agreed to pay royalties ranging from 3% to 5% on the sales of products subject to the agreements. The Company incurred $11,000 and $12,000 of expense under these agreements during 2017 and 2016, respectively, which are included in selling, general and administrative expenses in the Statements of Operations.