SUMMARYThe embryonic head mesoderm gives rise to cranial muscle and contributes to the skull and heart. Prior to differentiation, the tissue is regionalised by the means of molecular markers. We show that this pattern is established in three discrete phases, all depending on extrinsic cues. Assaying for direct and first-wave indirect responses, we found that the process is controlled by dynamic combinatorial as well as antagonistic action of retinoic acid (RA), Bmp and Fgf signalling. In phase 1, the initial anteroposterior (a-p) subdivision of the head mesoderm is laid down in response to falling RA levels and activation of Fgf signalling. In phase 2, Bmp and Fgf signalling reinforce the a-p boundary and refine anterior marker gene expression. In phase 3, spreading Fgf signalling drives the a-p expansion of MyoR and Tbx1 expression along the pharynx, with RA limiting the expansion of MyoR. This establishes the mature head mesoderm pattern with markers distinguishing between the prospective extra-ocular and jaw skeletal muscles, the branchiomeric muscles and the cells for the outflow tract of the heart.

The optimum incubation period was 10 h using collagenase at a 0.2% (w/v) solution. An average of 1-1.5 × 10(6) cells could be harvested per gram of cartilage using this method.

Despite extensive research into cartilage tissue engineering (CTE), there is still no scaffold ideal for clinical applications. Various synthetic and natural polymers have been investigated in vitro and in vivo, but none have reached widespread clinical use. The authors investigate the potential of POSS-PCU, a synthetic nanocomposite polymer, for use in CTE. POSS-PCU is modified with silsesquioxane nanostructures that improve its biological and physical properties. The ability of POSS-PCU to support the growth of ovine nasoseptal chondrocytes was evaluated against a polymer widely used in CTE, polycaprolactone (PCL). Scaffolds with varied concentrations of the POSS molecule were also synthesized to investigate their effect on chondrocyte growth. Chondrocytes were seeded onto scaffold disks (PCU negative control; POSS-PCU 2%, 4%, 6%, 8%; PCL). Cytocompatibilty was evaluated using cell viability, total DNA, collagen and GAG assays. Chondrocytes cultured on POSS-PCU (2% POSS) scaffolds had significantly higher viability than PCL scaffolds (p < 0.001). Total DNA, collagen and sGAG protein were also greater on POSS-PCU scaffolds compared with PCL (p > 0.05). POSS-PCU (6% and 8% POSS) had improved viability and proliferation over an 18 day culture period compared with 2% and 4% POSS-PCU (p < 0.0001). Increasing the percentage of POSS in the scaffolds increased the size of the pores found in the scaffolds (p < 0.05). POSS-PCU has excellent potential for use in CTE. It supports the growth of chondrocytes in vitro and the POSS modification significantly enhances the growth and proliferation of nasoseptal chondrocytes compared with traditional scaffolds such as PCL.

Cartilage tissue engineering is a rapidly progressing area of regenerative medicine with advances in cell biology and scaffold engineering constantly being investigated. Many groups are now capable of making neocartilage constructs with some level of morphological, biochemical, and histological likeness to native human cartilage tissues. The application of this useful technology in articular cartilage repair is well described in the literature; however, few studies have evaluated its application in head and neck reconstruction. Although there are many studies on auricular cartilage tissue engineering, there are few studies regarding cartilage tissue engineering for complex nasal reconstruction. This study therefore highlighted the challenges involved with nasal reconstruction, with special focus on nasal cartilage tissue, and examined how advancements made in cartilage tissue engineering research could be applied to improve the clinical outcomes of total nasal reconstructive surgery.

Currently, the gold standard for reconstruction after rhinectomy or severe trauma to the nose, includes transposition of autologous mucosal flaps plus autologous cartilage grating and coverage using a skin flap. Difficulties with this approach arise where; cartilage and mucosa harvested from autologous donor sites is insufficient to achieve a passable aesthetic and functional reconstruction. Skin flaps are often bulky, poor color matches with hair follicles that reduce the aesthetic quality of the reconstruction. We suggest that tissue engineering could be a source of functional replacement tissues for nasal reconstructive surgery. However, the advancement of such an approach is dependent on the dissemination of scientific information into the clinical community, regarding the engineering of tissues such as mucosa, skin, and cartilage. This paper therefore reviews how the tissue engineering strategies available for producing clinically viable tissues could help resolve issues around reconstructing the human nose.

Autologous hydrogel manufacture is an exciting technique within the field of regenerative medicine. Fibrin is a protein with many biocompatible and regenerative features. The ability to generate fibrin scaffolds with the necessary matrix topography for cell integration, from a patient's autologous tissue, could improve the translation of many tissue engineering efforts from bench to clinical application. Here we describe the rapid extraction and production of fibrin hydrogels for development of organs, using a simple low-cost series of centrifugations and ethanol precipitation, which produces hydrogels of a more predictable amount and morphology.

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