grant related work. During the nine months ended September 30, 2020, our research and development employees were either deployed to work-from-home status or reassigned to assist in activities related to increasing the production of CytoSorb.
Total revenues were approximately $32,383,000 for the nine months ended September 30, 2021, as compared to total revenues of approximately $29,049,000 for the nine months ended September 30, 2020, an increase of approximately $3,334,000 , or 11%.
Cost of Revenues:
For the nine months ended September 30, 2021 and 2020, cost of revenue was approximately $7,925,000 and $8,525,000, respectively, a decrease of approximately $600,000. Product cost of revenue was approximately $6,068,000 and $7,500,000, respectively, for the nine months ended September 30, 2021 and 2020, a decrease of approximately $1,432,000. This decrease was related to certain costs associated with the rapid ramp-up of production during the period ended September 30, 2020 that did not recur during the period ended September 30, 2021. These decreases were offset by the negative impact of non-recurring costs related to prior years tariffs as a result of an audit by the German Customs Authorities of approximately $732,000 and the offsetting non-recurring positive impact of the Employee Retention Tax Credit of approximately $388,000, both of which were recorded in the first quarter of 2021. Product gross margins were approximately 80% for the nine months ended September 30, 2021 compared to approximately 73% for the nine months ended September 30, 2020.
Research and Development Expenses:
For the nine months ended September 30, 2021, research and development expenses were approximately $10,244,000 as compared to research and development expenses of approximately $6,125,000 for the nine months ended September 30, 2020, an increase of approximately $4,119,000. This increase was due to an increase in costs associated with our clinical trial activities of approximately $2,035,000, an increase in salaries related to our clinical trial activities of approximately $1,304,000 due to the hiring of clinical expertise, an increase in rent expense of approximately $509,000 related to rent expense on our new facility and an increase in other research and development labor and other costs of approximately $271,000.
Legal, Financial and Other Consulting Expenses:
Legal, financial and other consulting expenses were approximately $2,090,000 for the nine months ended September 30, 2021, as compared to approximately $1,945,000 for the nine months ending September 30, 2020. The increase of approximately $145,000 was due to an increase an increase in consulting fees of approximately $244,000. These increases were offset by decreases in legal fees of approximately $76,000 and accounting fees of approximately $23,000.
Selling, General and Administrative Expenses:
Selling, general and administrative expenses were approximately $25,308,000 for the nine months ended September 30, 2021, as compared to $20,190,000 for the nine months ended September 30, 2020, an increase of $5,118,000. This increase is related to an increase in salaries, commissions and related costs of approximately $2,994,000, an increase in royalty expenses of approximately $201,000 due to the increase in product sales, and an increase in non-cash restricted stock expense of approximately $881,000 related to restricted stock units granted to the Company’s executive officers, an increase in non-cash stock option compensation expense of approximately $360,000, an increase in commercial insurance of approximately $209,000, an increase in sales and marketing costs, which include advertising and conference attendance and other general and administrative expenses of approximately $536,000 and an increase in other general and administrative costs of approximately $54,000. These increases were offset by a decrease in travel and entertainment costs of approximately $117,000 due primarily to travel restrictions related to the COVID-19 pandemic.
Interest Income/(Expense), net:
For the nine months ended September 30, 2021, interest income was approximately $16,000, as compared to interest expense of approximately $840,000 for the nine months ended September 30, 2020. This decrease in net interest expense of approximately $856,000 was the result of the payoff of our outstanding term loans with Bridge Bank in December of 2020.