print with php [closed]

I have this code:

foreach($this->table_descriptor->getColumns() as $column){
  $buf .= "\t\t$this->$".$column['Field']." = NULL,\n";
}

what should print:

$this->Columna = NULL,

but I get the following error:

syntax error, unexpected T_CHARACTER, expecting T_STRING in 

Any suggestions? Thank you!