increase in direct sales of approximately $1,492,000 resulting from sales to both new customers and repeat orders from existing customers and an increase in distributor sales of approximately $353,000. Sales to hospitals in the United States under the EUA granted by the FDA amounted to approximately $362,000 for the three months ended June 30, 2021. Though difficult to quantitate, we estimate that approximately $1.7 million of total product sales in the second quarter of 2021 was due to the demand for CytoSorb to treat COVID-19 patients. In addition, as a result of the increase in the average exchange rate of the Euro to the U.S. dollar, 2021 product sales were positively impacted by approximately $819,000. For the three months ended June 30, 2021, the average exchange rate of the Euro to the U.S. dollar was $1.21 as compared to an average exchange rate of $1.10 for the three months ended June 30, 2020.
Grant income was approximately $659,000 for the three months ended June 30, 2021 as compared to approximately $275,000 for the three months ended June 30, 2020, an increase of approximately $384,000, or 140%. This increase was a result of the easing of the COVID-19 pandemic during the three months ended June 30, 2021 and a corresponding increase in grant related work. During the three months ended June 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 $12,024,000 for the three months ended June 30, 2021, as compared to total revenues of approximately $9,795,000 for the three months ended June 30, 2020, an increase of approximately $2,229,000, or 23%.
Cost of Revenues:
For the three months ended June 30, 2021 and 2020, cost of revenue was approximately $2,710,000 and $3,250,000, respectively, a decrease of approximately $540,000. Product cost of revenue was approximately $2,094,000 and $2,901,000, respectively, for the three months ended June 30, 2021 and 2020, a decrease of approximately $807,000. This decrease was due to certain costs associated with the rapid ramp-up of production during the three months ended June 30, 2020 that did not recur during the three months ended June 30, 2021. Product gross margins were approximately 82% for the three months ended June 30, 2021 as compared to approximately 70% for the three months ended June 30, 2020. The increase in the gross margin percentage in 2021 was due manufacturing efficiencies achieved during the three months ended June 30, 2021 and the impact of the ramp-up costs incurred during the three months ended June 30, 2020 that did not recur in 2021.
Research and Development Expenses:
For the three months ended June 30, 2021, research and development expenses were approximately $3,699,000, as compared to research and development expenses of approximately $2,406,000 for the three months ended June 30, 2020, an increase of approximately $1,293,000. This increase was due to an increase in our clinical trial activities of approximately $452,000 due to pre-enrollment activities related to our STAR-T trial in the United States, an increase in salaries related to our clinical trial activities of approximately $506,000 due to the hiring of clinical expertise, an increase in rent expense of approximately $181,000 related to rent expense on our new facility and an increase in non-grant related research and development labor and other costs of approximately $154,000.
Legal, Financial and Other Consulting Expenses:
Legal, financial and other consulting expenses were approximately $718,000 for the three months ended June 30, 2021, as compared to approximately $846,000 for the three months ended June 30, 2020. The decrease of approximately $128,000 was due to a decrease in legal fees of approximately $98,000, a decrease in employment agency fees of approximately $46,000, and a decrease in accounting and auditing fees of approximately $23,000. The decreases were offset by an increase in consulting fees of approximately $39,000.
Selling, General and Administrative Expenses:
Selling, general and administrative expenses were approximately $9,821,000 for the three months ended June 30, 2021, as compared to approximately $6,591,000 for the three months ending June 30, 2020, an increase of $3,231,000. Approximately $1,396,000, or 43%, of this increase was associated with non-cash related expenses including restricted stock expense of approximately $884,000 related to restricted stock units granted to the Company’s executive officers and an increase in stock compensation expense of approximately $512,000. The remaining increases in selling, general and administrative expense are related to an increase in salaries, commissions and related costs of approximately $1,127,000, an increase in royalty expenses of approximately $156,000 due to the increase in product sales, an increase in commercial insurance of approximately $194,000 and an increase in sales and marketing costs, which include