self.physicsBody = [SKPhysicsBody bodyWithEdgeLoopFromRect:self.frame];
    self.physicsBody.categoryBitMask = SceneEdgeCategory;

hero.physicsBody.collisionBitMask = SceneEdgeCategory;

//make sure that you define the topLeftPoint, bottomLeftPoint, topRightPoint and bottomLeftPoint variables

self.leftPhysicsBody = [SKPhysicsBody bodyWithEdgeFromPoint:topLeftPoint toPoint:bottomLeftPoint];
self.leftPhysicsBody.categoryBitMask = SceneEdgeCategory;

self.rightPhysicsBody = [SKPhysicsBody bodyWithEdgeFromPoint:topRightPoint toPoint:bottomRightPoint];
self.rightPhysicsBody.categoryBitMask = SceneEdgeCategory;

CGPoint topRightPoint = CGPointMake(self.frame.size.width, self.frame.size.height);