Research and Development
Research and development costs were $21.7 million for the three months September 30, 2021, compared to $5.4 million for the three months ended September 30, 2020. The $16.3 million increase mainly reflected a $9.8 million increase in personnel-related costs and recruiting expenses for personnel in research and development departments, a $1.3 million increase in stock compensation expense, a $1.7 million increase in research and development materials expense, a $1.6 million increase in Technology licensed and software subscription licenses related expenses, a $0.7 million increase in depreciation and amortization expense with the remainder due to changes in freight and other research and development related expenses.
Research and development costs were $44.2 million for the nine months September 30, 2021, compared to $21.0 million for the nine months ended September 30, 2020. The $23.2 million increase mainly reflected a $12.4 million increase in personnel-related costs and recruiting expenses for personnel in research and development departments, a $4.4 million increase in stock compensation expense, a $2.4 million increase in research and development materials expense, a $1.8 million increase in Technology licensed and software subscription licenses related expenses and a $1.0 million increase in depreciation and amortization expense with the remainder due to changes in freight and other research and development expenses.
Sales and Marketing
Sales and Marketing expenses were $1.1 million for the three months ended September 30, 2021. There were no sales and marketing expenses in the three months ended September 30, 2020 as the Company was primarily focused on research and development activities.
Sales and Marketing expenses were $2.2 million for the nine months ended September 30, 2021. There were no sales and marketing expenses in the nine months ended September 30, 2020 as the Company was primarily focused on research and development activities. The sales and marketing expenses primarily consists of personnel-related costs and consulting charges.
General and Administrative
General and administrative expenses were $19.7 million for the three months ended September 30, 2021, compared to $2.4 million for the three months ended September 30, 2020. The $17.4 million increase was primarily due to a $5.7 million increase in employee-related costs, a $1.3 million increase in stock-based compensation expense, a $3.1 million increase from transaction costs incurred and expensed by the Company in relation to the Apollo Merger, a $1.5 million increase in third-party consulting and recruitment costs, a $2.1 million increase in accounting and legal related expenses, a $1.7 million increase in insurance related expenses with the remainder due to changes in facilities costs, software subscription fees and other general and administrative related expenses.
General and administrative expenses were $50.7 million for the nine months ended September 30, 2021, compared to $9.3 million for the nine months ended September 30, 2020. The $41.4 million increase was primarily due to a $15.4 million increase in stock-based compensation expense, a $6.2 million increase from transaction costs incurred and expensed by the Company in relation to the business combination and Apollo Merger, a $7.9 million increase in employee costs, a $4.2 million increase in third-party consulting and recruitment costs, a $3.1 million increase in accounting, audit and legal related fees, a $1.8 million increase in insurance related expenses and a $1.5 million increase in facility and rent, with the remainder due to changes in facilities costs, IT equipment fees, and software subscription fees.
Interest (Expense) Income, Net
There was no interest expense for the three months ended September 30, 2021, compared to $1.3 million for the three months ended September 30, 2020. The $1.3 million decrease in interest expense was primarily due to the settlement of convertible notes on January 28, 2021, therefore we incurred no interest expense related to convertible notes for three months ended September 30, 2021 while we incurred $1.3 million interest expense related to convertible notes for three months ended September 30, 2020.
Interest expense, net was $1.2 million for the nine months ended September 30, 2021, compared to $3.6 million for the nine months ended September 30, 2020. The $2.3 million decrease in interest expense was primarily due to the settlement of convertible notes on January 28, 2021, therefore we incurred $0.5 million and $3.5 million interest expense related to convertible notes for nine months ended September 30, 2021 and 2020, respectively, offset by an increase of $0.6 million in interest expense related to Bridge Loan and SVB loan for nine months ended September 30, 2021.
Other Income, Net
Other income, net was $25.9 million for the three months ended September 30, 2021, compared to $3.9 million for the three months ended September 30, 2020. The $22.0 million increase in other income was primarily due to a $20.4 million in income from change in fair value of warrant liability, a $4.9 million in income from a gain on forgiveness of PPP Note and a $0.6 million in income from government research and development contracts for the three months ended September 30, 2021 offset by a $2.6 million in income from a gain on the mark to market derivative liability related to convertible notes and a $1.2 million in income from government research and development contracts for the three months ended September 30, 2020. The remaining $0.1 million was due to other nonrecurring income for three months ended September 30, 2021.
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