How to Programatically create Multiple textboxes in an aspx page and save to database?

I am trying to populate textboxes (txtFirstName, txtSecondName) programatically by allowing the users to type in (say, 4) in a textbox and press the button to populate these into a panel. So if they put 2 in then they will get 2 rows of textboxes for first and last name. My problem is when I save I cannot get the text from these textboxes that were created on the fly. Any suggestions?

//button         
protected void Button1_Click(object sender, EventArgs e)
{
    int number = int.Parse(TextBox1.Text);

    for (int i = 0; i < number; i++)
    {
        //Horizontal line
        LiteralControl hrline = new LiteralControl();
        hrline.Text = "<hr />";

        //Textboxes
        TextBox txtFirstName = new TextBox();
        TextBox txtSecondName = new TextBox();

        //FirstName
        txtFirstName.ID = "txtFirstName" + i;
        txtFirstName.Text = "First Name " + i;

        //Second name
        txtSecondName.ID = "txtSecondName" + i;
        txtSecondName.Text = "Last Name " + i;

        buttonPanel.Controls.Add(hrline);
        pnlteacherExp.Controls.Add(txtFirstName);
        pnlteacherExp.Controls.Add(txtSecondName);
        pnlteacherExp.Controls.Add(hrline);
    }
}

Save button to save to database:

protected void btnSave_Click(object sender, EventArgs e)
{
    int number = int.Parse(TextBox1.Text);

    for (int i = 0; i < number; i++)
    {
        string connectionString = WebConfigurationManager.ConnectionStrings["crud_connection"].ConnectionString;
        SqlConnection sqlConnection1 = new SqlConnection(connectionString);
        SqlCommand cmd = new SqlCommand();

        cmd.CommandText = "Store_proc";
        cmd.CommandType = CommandType.StoredProcedure;
        cmd.Connection = sqlConnection1;
        sqlConnection1.Open();

        cmd.Parameters.AddWithValue("@staffPayroll", "payroll_num");
        cmd.Parameters.AddWithValue("@FirstName", ??);
        cmd.Parameters.AddWithValue("@Surname", ??);

        cmd.ExecuteNonQuery();
        sqlConnection1.Close();
    }                
}