Tissue engineering, often referred to as regenerative medicine and reparative medicine, is an interdisciplinary field that necessitates the combined effort of cell biologists, engineers, material scientists, mathematicians, geneticists, and clinicians toward the development of biological substitutes that restore, maintain, or improve tissue function. It has emerged as a rapidly expanding approach to address the organ shortage problem and comprises tissue regeneration and organ substitution. Cells placed on/or within constructs is the most common strategy in tissue engineering. Successful cell seeding depends on fast attachment of cell to scaffolds, high cell survival and uniform cell distribution. The seeding time is strongly dependent on the scaffold material and architecture. Scaffolds provide an initial biochemical substrate for the novel tissue until cells can produce their own extra-cellular matrix (ECM). Thus scaffolds not only define the 3D space for the formation of new tissues, but also serve to provide tissues with appropriate functions. These scaffolds are often critical, both in vivo (within the body) or in vitro (outside the body) mimicking in vivo conditions. Additive fabrication processes represent a new group of non-conventional fabrication techniques recently introduced in the biomedical engineering field. In tissue engineering, additive fabrication processes have been used to produce scaffolds with customised external shape and predefined internal morphology, allowing good control of pore size and pore distribution. This article provides a comprehensive state-of-the-art review of the application of biomanufacturing additive processes in the field of tissue engineering. New and moving trends in biomanufacturing technologies and the concept of direct cell-printing technologies are also discussed.

Study Design.: An experimental laboratory-based biomechanical study. Objective.: To investigate the correlation between cage size and subsidence and to quantify the resistance to subsidence that a larger cage can provide. Summary of Background Data.: The assumption that a bigger interbody cage confers less subsidence has not been proven. There was no previous study that has shown the superiority of lateral cages to bullet cages in terms of subsidence and none that has quantified the correlation between cage size and subsidence. Methods.: A cage was compressed between two standardized polyurethane foam blocks at a constant speed. Four sizes of bullet cages used for transforaminal lumbar interbody fusion (TLIF) and six sizes of lateral cages used for lateral lumbar interbody fusion (LLIF) were tested. The force required for a 5 mm subsidence, axial area of cages, and stiffness were analyzed. Results.: A larger cage required a significantly higher force for a 5 mm subsidence. Longer bullet cages required marginal force increments of only 6.2% to 14.6% compared to the smallest bullet cage. Lateral cages, however, required substantially higher increments of force, ranging from 136.4% to 235.7%. The average force of lateral cages was three times that of bullet cages (6426.5 vs. 2115.9 N), and the average stiffness of the LLIF constructs was 3.6 times that of the TLIF constructs (635.5 vs. 2284.2 N/mm). There was a strong correlation between the axial area of cages and the force for a 5 mm subsidence. Every 1 mm² increment of axial area corresponded to approximately 8 N increment of force. Conclusion.: Cage size correlated strongly with the force required for a 5 mm subsidence. The LLIF constructs required higher force and were stiffer than the TLIF constructs. Among bullet cages, longer cages only required marginal increments of force. Lateral cages, however, required substantially higher force. Level of Evidence: N/A