Operating activities
In 2020, cash used in operating activities was $4,933,015, attributable to a net loss of $6,914,992, and offset by a net change in our net operating assets and liabilities of $557,962 and non-cash charges of $1,424,015. Non-cash charges primarily consisted of $318,640 in stock-based compensation and $1,100,764 in depreciation and amortization. The change in our net operating assets and liabilities was primarily due to an increase in accounts payable, accrued expenses, and other liabilities totaling $931,170, offset by a decrease in lease liabilities of $445,733.
In 2019, cash used in operating activities was $11,005,996, attributable to a net loss of $11,271,948 and a net change in our net operating assets and liabilities of $1,080,339, partially offset by non-cash charges of $1,346,291. Non-cash charges primarily consisted of $358,841 in stock-based compensation, $1,094,624 in depreciation and amortization, partially offset by amortization of discount on investments of $110,497. The change in our net operating assets and liabilities was primarily due to a $469,364 decrease in accrued and other current liabilities, a $454,481 decrease in lease liabilities due to implementation of new accounting standards, and $111,106 increase in other assets.
Investing activities
In 2020, cash provided by investing activities was $968,319, attributable to maturities of short-term investments of $1,000,000 offset by the purchase of property and equipment of $8,352 and payments of patents and other intangible assets of $23,329.
In 2019, cash provided by investing activities was $12,317,506, attributable to maturities of short-term investments of $22,135,000, partially offset by the purchase of short-term investments of $9,120,995, the purchase of property and equipment of $593,358 and payments of patents and other intangible assets of $103,141.
Financing activities
In 2020, cash provided by financing activities was $871,648, consisting of the proceeds of the PPP note proceeds of $812,500, proceeds from the exercise of stock options of $153,200, and offset by deferred offering cost payments of $75,000 and payments under lease obligations of $19,052.
In 2019, cash used in financing activities was $127,782, primarily attributable to repayment of a note payable of $113,333 and payments under lease obligations of $17,075.
Comparison of the Three Months Ended March 31, 2021 and 2020 (unaudited)
The following table summarizes our cash flows for the three months ended March 31, 2021 and 2020:
Net cash used in operating activities | | | $(1,160,682) | | | $(1,803,116) |
Net cash provided by investing activities | | | — | | | 984,039 |
Net cash (used in) provided by financing activities | | | (144,991) | | | 48,376 |
Net change in cash and cash equivalents | | | $(1,305,673) | | | $(770,701) |
Operating activities
For the three months ending March 31, 2021, cash used in operating activities was $1,160,682, attributable to a net loss of $1,830,232, and offset by a net change in our net operating assets and liabilities of $345,351 and non-cash charges of $324,199. Non-cash charges consisted of $72,490 in stock-based compensation, $153,453 in depreciation and amortization, and $98,256 in right-of-use amortization. The change in our net operating assets and liabilities was primarily due to an increase in accounts payable, accrued expenses, and other liabilities for a total of $370,892, offset by a decrease in lease liabilities of $105,986.
For the three months ending March 31, 2020, cash used in operating activities was $1,803,116, attributable to a net loss of $2,201,727, and offset by a net change in our net operating assets and liabilities of $41,826 and non-cash charges of $356,785. Non-cash charges primarily consisted of $78,824 in stock-based compensation,