Effect of coating techniques on the creation of a calcified zone for implant-tendon entheses

An attachment or insertion site of tendon, ligament or joint capsule to bone, so called entheses, is either fibrous or fibrocartilaginous. A well characterized fibrocartilaginous entheses is comprised of four zones- pure dense fibrous connective tissue, uncalcified and calcified fibrocartilage,and bone. Increase in hardness from fibrous tissue to bone appears to be a natural way of dealing with mechanical stresses in the entheses region. Calcified zone, which is made up of mineralized extracellular matrix (ECM), acts as a transitional zone between the hard and soft regions of the entheses. Thus, success of long term orthopedic implants depends upon the creation of a bio-mimicked calcified zone on their surface. As tendon/ligament entheses are basically composed collagen based ECM, in this in vitro investigation, we made use of collagen based bioscaffolds; specifically, gelatin B and porcine small intestinal submucosa (SIS) were used in the creation of a calcified zone on a model orthopedic biomaterial-titanium sheet, by mixing them with saturated levels of hydroxyapatite (HA). In order to enhance attachment on an implant, we gelatinized these bioscaffolds by heat denaturation in water followed by spin coating or coating by pipette on a titanium (Ti) sheet by taking advantage of the self-assembling properties of collagen. Our scanning electron microscope (SEM) results suggest that the calcification as well as the area covered by their coating on Ti is better during a pipette technique as compared to spin coating. Further, gelatin B and SIS behaved differently in terms of coating uniformity, except in the pipette coating where the proportion of surface area covered by gelatin B is similar to SIS. In this manner, a coating technique and method has been developed which is promising for entheses biomaterials.