editar_material.php

<!-- Modal composição -->
    <?php
    $select = "SELECT descricao FROM composicao";
    try{
        $query = $conecta->prepare($select);
        $query->execute();
        $resultado = $query->fetchAll(PDO::FETCH_ASSOC);
        }catch(PDOexception $error_insert){
            echo '[ERRO] ao selecionar descricao: '.$error_insert->getMessage();
    }
    ?>

    <!-- Modal -->
    <div id="percent-composicao" class="modal fade" role="dialog">
      <div class="modal-dialog">

        <!-- Modal content-->
        <div class="modal-content">
          <div class="modal-header">
            <button type="button" class="close" data-dismiss="modal">&times;</button>
            <h4 class="modal-title">Composição</h4>
          </div>
          <div class="modal-body">
            <form method="post" id="formComposicao" enctype="multipart/form-data">
                    <div class="row itemComposicao">
                        <div class="form-group" style="margin-bottom: 35px;">
                            <div class="col-xs-12 col-sm-6" id="item_composicao">
                                <select name="composicao" id="composicao" required="true" class="form-control composicao">
                                    <?php foreach($resultado as $res){ ?>
                                        <option value="<?php echo $res['descricao']; ?>"><?php echo $res['descricao']; ?></option>
                                    <?php } ?>
                                </select>
                            </div>
                            <div class="col-xs-12 col-sm-2" id="percent_comp">
                                <input class="form-control" name="percentComp" type="number"/>
                            </div>
                            <div class="col-xs-12 col-sm-2">
                                <button type="button" class="btn btn-danger" class="removeComp"><i class="fa fa-times" aria-hidden="true"></i>
</button>
                            </div>
                        </div>
                    </div>
            </form>
          </div>
          <div class="modal-footer">
            <button type="button" class="btn btn-primary" id="addComp">Adicionar</button>
            <button type="button" class="btn btn-success" data-dismiss="modal">Salvar</button>
          </div>
        </div>

      </div>
    </div><!--// Modal composição -->