How to print a string into a array - php

Question

I tried to print a string into a array.
The form will be submitted trough a array. The amount of forms is unknow because user is allowed to add extra inputs if needed (Order system).
To run my validation of the form it needs to be like this:
$toxValidate = new toxValidate();
$toxValidation = $toxValidate->check('$_POST', array(
'part1' => array('required' => TRUE),
'part2' => array('required' => TRUE),
'part3' => array('required' => TRUE),
'part4' => array('required' => TRUE),
'part5' => array('required' => TRUE)
));
But because we dont know how many inputs it will be, there needs for every input one line of: 'part1' => array('required' => TRUE),.
This is what i tried:
for($i=0; $i<count($part); $i++){
$parts .= "part".$i." => array('required' => true)";
$t0x = $t0x + 1;
if($t0x < count($part)){
$parts .= ', ';
}
}
This would be the var_dump output of $parts when submitting 3 forms
''part0' => array('required' => true), 'part1' => array('required' => true), 'part2' => array('required' => true)'
That looks exactly what needs to be printed in:
$toxValidation = $toxValidate->check($_POST, array(
#HERE#
));
i tried with print and echo which i allready tought wouldt work.
How can i print $parts into the array.
Update
HTML Form:
<div id="form">
<p class="order">
<label style="margin-left:20px;">Partnumber:</label><br />
<input type="text" style="margin-left:20px;" class="text medium" id="part" name="part[]" placeholder="SP partnumber" />
</p>
<p class="order" >
<label style="margin-left:20px">Qty</label><br>
<input type="text" id="qty" name="qty[]" style="margin-left:20px;" class="text small" placeholder="Qty" />
<p class="order">
<label style="margin-left:20px">Price</label><br>
<input type="text" style="margin-left:20px;" class="text small" id="price" placeholder="Price" tabindex="-1" readonly /><br>
</p>
</div><p>
jQuery to add a other line of inputs:
$('#addpart').click(function(){
var loop = $('#loop').val();
var html;
html = '<p>';
html += '<input type="text" name="part[]" style="margin-left:20px;" class="text medium" id="part" placeholder="SP partnumber" />';
html += '<input type="text" name="qty[]" style="margin-left:20px;" class="text small" placeholder="Qty" />';
html += '<input type="text" style="margin-left:20px;" class="text small" id="price" placeholder="Price" tabindex="-1" readonly />';
html += '</p>';
for (i = 0; i < loop; i++) {
$("#form").append(html);
}
});
Update 2
But there also needs to be other 'inputs' to be check. Like Purchase order, backorder, date. See below:
$toxValidation = $toxValidate->check('$_POST', array(
'po' => array('required' => TRUE),
'date' => array('required' => TRUE),
'bo' => array('required' => TRUE),
'remarks' => array('required' => TRUE),
#PARTS HERE#
));