Inserting array using Laravel Eloquent

I have an array which I combined using array_combine. I am trying to store each array KEY AND VALUE into a child table. However, I can't figure out to do this. Please help!

HERE'S AN EXAMPLE OF A RETURNED ARRAY array:2 [▼ "Design" => "Pattern" "Brand" => "Sony" ]

PRODUCT MODEL

  public function productAttributes()
    {
        return $this->hasMany('App\ProductAttribute');
 }

PRODUCT ATTRIBUTE MODEL

protected $fillable = [
    'attribute_name', 'attribute_value', 'used_as_filter'
];

public function product()
{
    return $this->belongsTo('App\Product');
}

PRODUCT CONTROLLER

$product = new Product();
    $product->category_id = $request->category_list;
    $product->name = $request->name;
    $product->price = $request->price;

    $product->save();

    /**Optional Data**/
    if ($request->has('attribute_name')){
        $attributes = array_combine($request->input('attribute_name'), $request->input('attribute_value'));

        $product->productAttributes()->create($attributes);
    }

When I run this, I get one row inserted into the product table, and one row inserted into the product_attribute table. However, the columns attribute_name and attribute_value is blank.

via Chebli Mohamed