Animal models that are reliably reproducible, appropriate analogues to the clinical condition they are used to investigate, and that offer minimal morbidity and periprocedural mortality to the subject are the keystone to the preclinical development of translational technologies. For bone tissue engineering, a number of small animal models exist. Here we describe the protocol for one such model, the rat calvarial defect. This versatile model allows for evaluation of biomaterials and bone tissue engineering approaches within a reproducible, nonload-bearing orthotopic site. Critical steps to ensure appropriate experimental control and troubleshooting tips learned through extensive experience with this model are provided. The surgical procedure itself takes approximately 30 minutes to complete with approximately 2 hours of perioperative care, and tissue harvest is generally performed 4 to 12 weeks postoperatively. Several analytical techniques are presented, which evaluate the cellular and extracellular matrix components, functionality and mineralization, including histological, mechanical and radiographic methods.

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Background: Bone marrow-derived mesenchymal stem cells (BMSCs) are a widely researched adult stem cell population capable of differentiation into various lineages. Because many promising applications of tissue engineering require cell expansion following harvest and involve the treatment of diseases and conditions found in an aging population, the effect of donor age and ex vivo handling must be understood in order to develop clinical techniques and therapeutics based on these cells. Furthermore, there currently exists little understanding as to how these two factors may be influenced by one another.

Engineering complex tissues requires a precisely formulated combination of cells, spatiotemporally released bioactive factors, and a specialized scaffold support system. Injectable materials, particularly those delivered in aqueous solution, are considered ideal delivery vehicles for cells and bioactive factors and can also be delivered through minimally invasive methods and fill complex 3D shapes. In this review, we examine injectable materials that form scaffolds or networks capable of both replacing tissue function early after delivery and supporting tissue regeneration over a time period of weeks to months. The use of these materials for tissue engineering within the craniofacial complex is challenging but ideal as many highly specialized and functional tissues reside within a small volume in the craniofacial structures and the need for minimally invasive interventions is desirable due to aesthetic considerations. Current biomaterials and strategies used to treat craniofacial defects are examined, followed by a review of craniofacial tissue engineering, and finally an examination of current technologies used for injectable scaffold development and drug and cell delivery using these materials.