Error: Trying to get property of non-object

When you performed the print_r , the data type gives you as a result that it is a Array , and since it is an array type, it is obviously not an object, therefore, the error

  

Trying to get property of non-object

To traverse the array using foreach is as follows:

foreach ($data as $value) {
    print_r($value["mat_id"]);

  }

You're going through it badly. When you do the foreach $ value it assumes the values directly so there is no object.

Try this way

foreach ($data as $clave => $valor) {
    print_r($valor);
}