Titanium (Ti) is broadly used for clinical purposes in various medical fields related to bone repair because of its favorable mechanical properties and its ability to osseointegrate in host bone tissue. Nowadays, Ti surfaces can be functionalized in order to provide potentially beneficial additional properties. In this review, we summarize different surface modifications of Ti implants, focusing on biological relevance and the biological issues targeted by each specific approach. We first define the historical relevance of Ti as an implantable material, the osseointegration process, and the main complications related to it before describing the biological rationale which motivates Ti surface modification in implantable devices. Then, we explore a variety of physical and chemical modifications feasible on Ti surfaces. Thereafter, we focus on inorganic and organic coatings being developed for implantable Ti devices that are currently under investigation. Finally, we summarize the surface-modification approaches clinically available or undergoing clinical trials.

Porous ceramic scaffolds are widely studied in the tissue engineering field due to their potential in medical applications as bone substitutes or as bone-filling materials. Solid free form (SFF) fabrication methods allow fabrication of ceramic scaffolds with fully controlled pore architecture, which opens new perspectives in bone tissue regeneration materials. However, little experimentation has been performed about real biological properties and possible applications of SFF designed 3D ceramic scaffolds. Thus, here the biological properties of a specific SFF scaffold are evaluated first, both in vitro and in vivo, and later scaffolds are also implanted in pig maxillary defect, which is a model for a possible application in maxillofacial surgery. In vitro results show good biocompatibility of the scaffolds, promoting cell ingrowth. In vivo results indicate that material on its own conducts surrounding tissue and allow cell ingrowth, thanks to the designed pore size. Additional osteoinductive properties were obtained with BMP-2, which was loaded on scaffolds, and optimal bone formation was observed in pig implantation model. Collectively, data show that SFF scaffolds have real application possibilities for bone tissue engineering purposes, with the main advantage of being fully customizable 3D structures.

A variety of biomaterials have been introduced as potential substrates for cartilage repair. One such candidate is chitosan, which shares some characteristics with glycosaminoglycan and hyaluronic acid present in articular cartilage. Depending on chitosan source and preparation procedure, variations into its properties can be attained. Thus, the aim of this article is to study and select the most adequate chitosan properties for in vivo osteochondral tissue regeneration. In this work, chitosan molecular weight, deacetylation degree, and calcium content are tested as material variable properties. According to these properties, porous scaffolds were prepared, implanted in rabbit knee osteochondral defects, and evaluated 3 months after surgery. Results show in vitro a considerable influence of the material molecular weight on the scaffold structure. In vivo, different tissue responses were observed depending on the implanted chitosan properties. Some samples showed no material degradation, multiple adverse tissue responses, and no bone/cartilage tissue formation. Other samples showed no adverse responses and bone and cartilage tissue regeneration. The chitosan with intact mineral content (17.9 wt %), lowest molecular weight (11.49 KDa), and lowest deacetylation degree (83%) shows a well structured subchondral bone and noticeable cartilaginous tissue regeneration, being it the best one of those tested for osteochondral defect regeneration.

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