People in both developing and developed worlds are increasingly facing musculoskeletal problems that require long-term clinical performance of orthopaedic implants including bone substitutes. Porous biomaterials could play an important role in improving the longevity and overall performance of orthopaedic implants and that is why they have been extensively studied recently. Highly porous biomaterials hold promise for such applications partly because their porous structures provide enough space for bone in-growth and vascularization. Controllability of mechanical properties is another favorable feature of such biomaterials that has led to their increased popularity for bone substitution. Nevertheless, the full potential of porous metallic biomaterials in general and porous titanium alloy structures in particular has not yet been fully exploited. In this thesis, some important aspects relevant for application of porous titanium alloy biomaterials as bone substitutes have been studied. In particular, we focus on the mechanical properties of porous titanium biomaterials, the modification of the surface properties of such biomaterials using chemical and electrochemical surface treatments, and on the effects of applied surface treatment on the mechanical properties of porous titanium biomaterials. To study the mechanical properties of porous titanium biomaterials, it is important to study the mechanical properties of bone that is replaced by the biomaterial. Given the fact that bone is a complex and heterogeneous material, a recently developed method called digital image correlation (DIC) was employed to study the full-field strain map and fracture behavior of the rat femur (chapter 2). It was found that bone fracture is strain-controlled and that the onset of fracture could be predicted using the equivalent strain criterion. On the other hand, segmental bone defect animal models are often used in pre-clinical studies of the bone regeneration performance of bone substitutes. In such animal models, it is very important to study how mechanical load is transferred after stabilization of the defect. In chapter 3, a specific animal model and fixation technique were considered. The load transferred through the femur and the distribution of the transferred load between the implant and fixation plate were studied for the considered animal model and fixation technique. It was found that there is a large variability in terms of the transmitted loads and that one needs to optimize the fixation technique in order to obtain a more consistent mechanical loading after surgery. Dynamic and static mechanical properties of selective laser melted porous titanium were studied in chapter 4 where the S-N curves of the porous structures were obtained for four different porosities. The S-N curves of the porous structures with different porosities were drastically different with more porous structures demonstrating a weaker fatigue behavior. When normalized with respect to the plateau stress, the S-N curves were mostly overlapping and very well conforming to a power law (R2=0.94). This power law might be useful for estimating the fatigue life of similar porous structures in the cases where actual fatigue tests could not be performed. In addition, it was found that the normalized endurance limit of porous structures is somewhat lower than that of the matrix material. Bio-functionalizing surface treatment are important for improving the surface properties of biomaterials. However, they might adversely affect the mechanical properties of the biomaterial. The effects of two different types of chemical surface treatments, namely alkali-acid-heat treatment and acid-alkali treatment, on the mechanical properties of porous titanium biomaterials were studied. It was found that while one of the surface treatments, namely alkali-acid-heat treatment, did not have any major adverse effect on the mechanical properties of the tested biomaterials, the other surface treatment resulted in significant mass loss and, thus, significant loss of mechanical properties. The nanotopographical features and crystal structure of an additional surface treatment technique, namely anodizing, were studied as well. The parameters of the surface treatment procedure were optimized to achieve a hierarchical structure on the surface of porous titanium biomaterials. In addition, it was found that the temperature and heat treatment duration need to be optimized, so as to ensure the nanotopographical features created using the surface treatment are not disrupted after heat treatment. All the three above-mentioned surface treatment techniques were subsequently evaluated in a longitudinal in-vivo and in-vitro study to assess the bone regeneration performance, apatite-forming ability, and cell response of the surface-treated porous titanium biomaterials. It was found that the applied surface treatments notably influenced both in-vitro and in-vivo performances of porous titanium alloy biomaterials. Acid-alkali treatment resulted in the best apatite forming ability and significantly larger volumes of regenerated bone as compared to anodizing. However, porous titanium biomaterials treated with anodizing exhibited significantly higher torsional strength. It was concluded that larger volumes of regenerated bone does not necessarily translate to better mechanical stability. Although this thesis tried to cover several aspects relevant for application of porous titanium biomaterials as bone substitutes, further research is needed to explore several other unexplored aspects of porous titanium biomaterials.