In general, this invention relates to compositions and methods useful in enhancing articular cartilage repair by providing for the sustained release of growth factors to articular cartilage cells to induce cell proliferation and extracellular matrix synthesis. In one aspect, a method includes determining that a user has submitted a question to be viewed by trusted participants of an online conversation, wherein the trusted participants include the user, one or more advertisers and one or more social network friends of the user, obtaining a reply to the question from one of the trusted participants, and providing the reply to the trusted participants. The elastic extending portion elastically expands in the diametrical direction together with the tip side portion when the cylindrical body is inserted into the insertion hole, thereby the elastic extending portion elastically contacts the outer circumferential surface of the cylindrical body while maintaining elastic restoring force in the contracting direction.