Net Cash Used In Operating Activities
For the three months ended March 31, 2022, the $367 thousand of cash used in operating activities was attributable to net income of $142 thousand, adjusted for non-cash charges of $64 thousand, unrealized gains on marketable securities of $156 thousand, and cash used in changes in operating assets and liabilities of $417 thousand.
For the three months ended March 31, 2021, the $1 thousand of cash used in operating activities was attributable to net loss of $43 thousand, adjusted for non-cash charges of $71 thousand, non-cash gain on forgiveness of PPP loan of $186 thousand, and cash provided by changes in operating assets and liabilities of $157 thousand.
Accounts receivable increased from $1.080 million at December 31, 2021 to $1.300 million at March 31, 2022 due to higher shipments during the first quarter of 2022 compared to the fourth quarter of 2021. Many of our customers pay promptly and accounts receivable is generally related to the most recent shipments. Inventories decreased slightly from $814 thousand at December 31, 2021 to $799 thousand at March 31, 2022. Inventory balances fluctuate depending on the timing of materials purchases and product shipments. Prepaid expenses and other current assets were relatively unchanged at $388 thousand at March 31, 2022 compared to $391 thousand at December 31, 2021. Accounts payable and accrued liabilities decreased from $845 thousand at December 31, 2021 to $584 thousand at March 31, 2022, primarily due to the timing of payment for purchases of materials, compensation accruals, and other outside services.
Net Cash Used in Investing Activities
Net cash used in investing activities of $2.185 million for the three months ended March 31, 2022 consisted of purchases of $2.179 million of marketable securities and $6 thousand of property, plant, and equipment. Net cash used in investing activities of $12 thousand for the three months ended March 31, 2021 consisted of purchases of property, plant, and equipment.
Net Used In Financing Activities
Net cash used in financing activities of $100 thousand for the three months ended March 31, 2022 consisted of payment of dividends on our Series A Convertible Preferred Stock. There was no cash provided by or used in financing activities during the three months ended March 31, 2021.
Off-Balance Sheet Arrangements
We do not have any off-balance sheet arrangements.
Item 3. Quantitative and Qualitative Disclosures About Market Risk
Not Applicable.
Item 4. Controls and Procedures
Evaluation of Disclosure Controls and Procedures
The phrase “disclosure controls and procedures” refers to controls and procedures designed to ensure that information required to be disclosed in our reports filed or submitted under the Securities Exchange Act of 1934, as amended, or the Exchange Act, such as this Quarterly Report on Form 10-Q, is recorded, processed, summarized and reported within the time periods specified in the rules and forms of the U.S. Securities and Exchange Commission, or SEC. Disclosure controls and procedures are also designed to ensure that such information is accumulated and communicated to our management, including our chief executive officer, or CEO, and chief financial officer, or CFO, as appropriate to allow timely decision regarding required disclosure.
Our management, with the participation of our CEO and CFO, has evaluated the effectiveness of our disclosure controls and procedures (as defined in Rules 13a-15(e) and 15d-15(e) under the Exchange Act), as of March 31, 2022, the end of the period covered by this Quarterly Report on Form 10-Q. Based on such evaluation, our CEO and CFO had concluded that as of March 31, 2022, our disclosure controls and procedures were designed at a reasonable assurance level and were effective to provide reasonable assurance that information we are required to disclose in reports that we file or submit under the Exchange Act is recorded, processed,