Craniofacial tissue engineering by stem cells

Abstract

Craniofacial tissue engineering promises the regeneration or de novo formation of dental, oral, and craniofacial structures lost to congenital anomalies, trauma, and diseases. Virtually all craniofacial structures are derivatives of mesenchymal cells. Mesenchymal stem cells are the offspring of mesenchymal cells following asymmetrical division, and reside in various craniofacial structures in the adult. Cells with characteristics of adult stem cells have been isolated from the dental pulp, the deciduous tooth, and the periodontium. Several craniofacial structures--such as the mandibular condyle, calvarial bone, cranial suture, and subcutaneous adipose tissue--have been engineered from mesenchymal stem cells, growth factor, and/or gene therapy approaches. As a departure from the reliance of current clinical practice on durable materials such as amalgam, composites, and metallic alloys, biological therapies utilize mesenchymal stem cells, delivered or internally recruited, to generate craniofacial structures in temporary scaffolding biomaterials. Craniofacial tissue engineering is likely to be realized in the foreseeable future, and represents an opportunity that dentistry cannot afford to miss.

Figure 1

Engineered neogenesis of human-shaped mandibular condyle from mesenchymal stem cells. (A) Harvested osteochondral construct retained the shape and dimension of the cadaver human mandibular condyle after in vivo implantation. Scale bar: 5 mm. (B) Von Kossa-stained section showing the interface between stratified chondral and osseous layers. Multiple mineralization nodules are present in the osseous layer (lower half of the photomicrograph), but absent in the chondral layer. (C) Positive safranin O staining of the chondrogenic layer indicates the synthesis of abundant glycosaminoglycans. (D) H&E-stained section of the osteogenic layer showing a representative osseous island-like structure consisting of MSC-differentiated osteoblast-like cells on the surface and in the center. Reproduced with permission from Biomedical Engineering Society.

Figure 2

Histologic and immunohistochemical characterization of a human-shaped mandibular condyle engineered from mesenchymal stem cells after in vivo implantation. (A) Representative photomicrograph showing positive safranin O staining of the upper cartilage layer, indicating the presence of abundant glycosaminoglycans. In contrast, the osseous portion shows negative safranin O staining. (B) Positive immunohistochemical localization of type II collagen in the cartilage portion. The osseous portion was negative to type II collagen immunolocalization. (C) Positive immunolocalization of osteopontin within the osseous portion. By contrast, the cartilage portion lacks osteopontin expression. (D) Representative micrograph of hydrogel control cell-free construct showing host fibrous-tissue capsule surrounding the construct, but a lack of host cell invasion. Reproduced with permission from Mary Ann Liebert.

Figure 3

Design and engineering of minipig mandibular condyle. (A) Original Computed Tomography (CT) scan of minipig mandible. (B) Image-based design of condyle scaffold. (C) PCL (polycaprolactone) degradable polymer scaffold fabricated with SLS (Selective Laser Sintering) attached to the ramus. (D) Regrowth of condyle following 3 months’ implantation (new condyle shown in red circle). (E) Comparison with normal condyle from contralateral side in Yucatan minipig.

Figure 4

Delivery approaches for periodontal bioengineering. Ex vivo gene therapy involves the harvesting of tissue biopsies, expansion of cell populations, genetic manipulations of cells, and subsequent transplantation to periodontal osseous defects (A), while the in vivo gene transfer approach involves the direct delivery of growth factor transgenes to the periodontal osseous defects (B).

Figure 5

Bone metabolic activity of animals implanted with control (no cells) or adipose-derived adult stromal (ADS) cell-seeded scaffolds, as determined by radiolabeled methylene diphosphonate incorporation overlaid with micro-CT images. For each time-point, the top row displays the micro-CT scan, the middle row displays the metabolic activity, and the lower row displays the overlaid composite of metabolic activity and micro-CT scan. For all columns at each time-point, the left column is the x axis, the middle column is the y axis, and the right column is the z axis. For orientation, we have marked the defect with a yellow arrow for the three views of the micro-CT image. The location of the defect does not change between 2 and 12 weeks. Bone scan intensity is indicated in color on the left axis of the image, with white and red indicating the highest value and black and blue indicating lowest value. This Fig. originally appeared in Cowan et al. (2004) and is reproduced here with permission from the Nature Publishing Group (http://www.nature.com/).