在不剪切标记的情况下拆分HTML

我一直在尝试将PHP字符串拆分为每次拆分任意数量的字符。然而，我正在寻找一种不破坏HTML标记的方法。这里有一个例子：

$string = 'Section 1: 
<table width = "528" border="0" cellpadding="0" cellspacing="0">
<tr>    <td width="20"> </td>   <td width="15" valign="top"> &bull; </td>   <td valign="top"> Element 1 </td></tr>
<tr>    <td width="20"> </td>   <td width="15" valign="top"> &bull; </td>   <td valign="top"> Element 2 </td></tr>
<tr>    <td width="20"> </td>   <td width="15" valign="top"> &bull; </td>   <td valign="top"> Element 3 </td></tr>
<tr>    <td width="20"> </td>   <td width="15" valign="top">&bull; </td>    <td valign="top"> Element 4 </td></tr>
<tr>    <td width="20"> </td>   <td width="15" valign="top"> &bull; </td>   <td valign="top"> Element 5 </td></tr>
<tr>    <td width="20"> </td>   <td width="15" valign="top"> &bull; </td>   <td valign="top"> Element 6 </td></tr>
</table>
Section 2:
<table width = "528" border="0" cellpadding="0" cellspacing="0">
<tr>    <td width="20"> </td>   <td width="15" valign="top"> &bull; </td>   <td valign="top"> Element 7 </td></tr>
<tr>    <td width="20"> </td>   <td width="15" valign="top"> &bull; </td>   <td valign="top"> Element 8 </td></tr>
<tr>    <td width="20"> </td>   <td width="15" valign="top"> &bull; </td>   <td valign="top"> Element 9 </td></tr>
<tr>    <td width="20"> </td>   <td width="15" valign="top"> &bull; </td>   <td valign="top"> Element 10 </td></tr>
<tr>    <td width="20"> </td>   <td width="15" valign="top"> &bull; </td>   <td valign="top"> Element 11 </td></tr>
<tr>    <td width="20"> </td>   <td width="15" valign="top"> &bull; </td>   <td valign="top"> Element 12 </td></tr>
<tr>    <td width="20"> </td>   <td width="15" valign="top"> &bull; </td>   <td valign="top"> Element 13 </td></tr>
</table>';
$charAmount = 450;
$textSplit = array();
while ($string){
    array_push($textSplit, substr($string, 0, $charAmount));
    $string = substr($string, $charAmount);
}
var_dump($textSplit);

在这种情况下，有两个标签损坏。我希望在拆分结束时剪切的任何标签都能跳到下一个拆分，但我不知道如何做到这一点。