PHP - guardar datos de una base de datos en checkbox

<label for="material-1">

	<input id="material-1" type="checkbox" name="materiales[]" value="material-1"> Material 1

</label>

<label for="material-2">

	<input id="material-2" type="checkbox" name="materiales[]" value="material-2"> Material 2

</label>

$materiales = $_POST['materiales'];

foreach ($materiales as $material) {

	//aquí añades cada material ($material) a la bbdd

}

<div class="col-sm-3">

    <select name="idmaterial" class="form-control">

    <option>Material </option>

    <?php if(!is_null($material)) :

while ($fila = mysqli_fetch_array($material)) : ?>

    <option value="<?php echo $fila['id_material']; ?>" > <?php echo utf8_encode($fila['material']); ?> </option>

        <?php endwhile;

            endif; ?>

        </select>

</div>

<div class="col-sm-3">

      <?php if(!is_null($material)) :

        while ($fila = mysqli_fetch_array($material)) : ?>

    <label>

    <input type="checkbox"> <?php echo utf8_encode($fila['material']); ?> </label>

       <?php endwhile;

    endif; ?>

</div>