how can i put checkbox in place of textbox in custom grid view given below

Dim strb As New StringBuilder()
        strb.Append("<table id=""tableID"" class=""tableClass""  style=""width=700px; border: solid 1px #336699;""  >")
        strb.Append("<tr>")
        ' strb.Append("<td colspan='" & tb_rowCols & "'></td>")
        Dim header As DataTable = tb_header_col()
        strb.Append("<td style=""display:none""></td>")
        For i As Integer = 1 To header.Rows.Count - 1
            strb.Append("<td style=""background-color:gray;border-style: none; height:25px; color:white; text-align: right;"">" + header.Rows(i)("col_name") & "</td>")
        Next
        strb.Append("</tr>")
        strb.Append("<th style=""display:none""></th>")
        For i As Integer = 1 To header.Rows.Count - 1
            strb.Append("<th style=""text-align: right; color:green;"" class=""tot""></th>")
        Next
        Dim row_value As DataTable = maindt
        For j As Integer = 0 To row_value.Rows.Count - 1
            strb.Append("<tr>")
            strb.Append("<td style=""display:none"" >")
            strb.Append(row_value.Rows(j)("studentid"))
            strb.Append("</td>")
            strb.Append("<td >")
            strb.Append(row_value.Rows(j)("student"))
            strb.Append("</td>")
            For x As Integer = 2 To maindt.Columns.Count - 1
                If IsDBNull(row_value(j)(x)) Then
                    row_value(j)(x) = 0
                End If

                strb.Append("<td width=""60px"">")
                strb.Append("<input id=""Text1"" style=""width: 80px; text-align: right;"" class=""txt"" type=""text"" name='value_" & (x + 1) & "_" & (j + 1) & "_txb' value='" & IIf(row_value(j)(x) = 0, "", row_value(j)(x)) & "' />")
                strb.Append("</td>")
            Next
            strb.Append("</tr>")
        Next
        strb.Append("</table>")
        tableValue = strb.ToString(