A deletion in the gene encoding sphingomyelin phosphodiesterase 3 (Smpd3) results in osteogenesis and dentinogenesis imperfecta in the mouse.

The mouse mutation fragilitas ossium (fro) leads to a syndrome of severe osteogenesis and dentinogenesis imperfecta with no detectable collagen defect. Positional cloning of the locus identified a deletion in the gene encoding neutral sphingomyelin phosphodiesterase 3 (Smpd3) that led to complete loss of enzymatic activity. Our knowledge of SMPD3 function is consistent with the pathology observed in mutant mice and provides new insight into human pathologies.

Tissue engineering a complete vaginal replacement from a small biopsy of autologous tissue.

BACKGROUND: In women, a healthy, patent vagina is important for the maintenance of a good quality of life. Apart from congenital abnormalities, such as cloacal exstrophy, intersex disorders, and an absence of the posterior two thirds of the organ, individuals may also suffer from cancer, trauma, infection, inflammation, or iatrogenic injuries leading to tissue damage and loss -- all of which require vaginal repair or replacement. Of necessity, reconstruction is often performed with nonvaginal tissue substitutes, such as segments of large intestine or skin, which are not anatomically or functionally ideal (Hendren and Atala, J Urol 1994; 152: 752; Hendren and Atala, J Pediatr Surg 1995; 30: 91). Whenever such tissue is used additional complications often ensue, such as strictures, infection, hair growth, graft shrinkage, diverticuli, and even malignancy (Filipas et al., BJU Int 2000; 85: 715; Lai and Chang, Changgeng Yi Xue Za Zhi 1999; 22: 253; Parsons et al., J Pediatr Surg 2002; 37: 629; Seccia et al., Ann Plast Surg 2002; 49: 379; Filipas, Curr Opin Urol 2001; 11: 267). METHODS: Using a rabbit model, we report here the construction of a functional vagina using autologous cells expanded from a small vaginal biopsy. RESULTS.: Six months after total vaginal replacement, radiographic analysis of rabbits implanted with the neovagina demonstrated wide, patent vaginal calibers without strictures. Histologic analysis revealed well-organized epithelial and muscle cell layers. Physiologic studies showed normal-range responses to electrical stimulation or to an adrenergic agonist. CONCLUSIONS: These data indicate that a tissue engineering approach to clinical vaginal reconstruction in women is now a realistic possibility.

Bioprinting Cellularized Constructs Using a Tissue-specific Hydrogel Bioink.

Bioprinting has emerged as a versatile biofabrication approach for creating tissue engineered organ constructs. These constructs have potential use as organ replacements for implantation in patients, and also, when created on a smaller size scale as model "organoids" that can be used in in vitro systems for drug and toxicology screening. Despite development of a wide variety of bioprinting devices, application of bioprinting technology can be limited by the availability of materials that both expedite bioprinting procedures and support cell viability and function by providing tissue-specific cues. Here we describe a versatile hyaluronic acid (HA) and gelatin-based hydrogel system comprised of a multi-crosslinker, 2-stage crosslinking protocol, which can provide tissue specific biochemical signals and mimic the mechanical properties of in vivo tissues. Biochemical factors are provided by incorporating tissue-derived extracellular matrix materials, which include potent growth factors. Tissue mechanical properties are controlled combinations of PEG-based crosslinkers with varying molecular weights, geometries (linear or multi-arm), and functional groups to yield extrudable bioinks and final construct shear stiffness values over a wide range (100 Pa to 20 kPa). Using these parameters, hydrogel bioinks were used to bioprint primary liver spheroids in a liver-specific bioink to create in vitro liver constructs with high cell viability and measurable functional albumin and urea output. This methodology provides a general framework that can be adapted for future customization of hydrogels for biofabrication of a wide range of tissue construct types.

A hydrogel bioink toolkit for mimicking native tissue biochemical and mechanical properties in bioprinted tissue constructs.

Advancement of bioprinting technology is limited by the availability of materials that both facilitate bioprinting logistics as well as support cell viability and function by providing tissue-specific cues. Herein we describe a modular hyaluronic acid (HA) and gelatin-based hydrogel toolbox comprised of a 2-crosslinker, 2-stage polymerization technique, and the capability to provide tissue specific biochemically and mechanically accurate signals to cells within biofabricated tissue constructs. First, we prepared and characterized several tissue-derived decellularized extracellular matrix-based solutions, which contain complex combinations of growth factors, collagens, glycosaminoglycans, and elastin. These solutions can be incorporated into bioinks to provide the important biochemical cues of different tissue types. Second, we employed combinations of PEG-based crosslinkers with varying molecular weights, geometries (linear, 4-arm, and 8-arm), and functional groups to yield hydrogel bioinks that supported extrusion bioprinting and the capability to achieve final construct shear stiffness values ranging from approximately 100 Pa to 20 kPa. Lastly, we integrated these hydrogel bioinks with a 3-D bioprinting platform, and validated their use by bioprinting primary liver spheroids in a liver-specific bioink to create in vitro liver constructs with high cell viability and measurable functional albumin and urea output. This hydrogel bioink system has the potential to be a versatile tool for biofabrication of a wide range of tissue construct types. STATEMENT OF SIGNIFICANCE: Biochemical and mechanical factors both have important implications in guiding the behavior of cells in vivo, yet both realms are rarely considered together in the context of biofabrication in vitro tissue construct models. We describe a modular hydrogel system that (1) facilitates extrusion bioprinting of cell-laden hydrogels, (2) incorporates tissue-specific factors derived from decellularized tissue extracellular matrix, thus mimicking biochemical tissue profile, and (3) allows control over mechanical properties to mimic the tissue stiffness. We believe that employing this technology to attend to both the biochemical and mechanical profiles of tissues, will allow us to more accurately recapitulate the in vivo environment of tissues while creating functional 3-D in vitro tissue constructs that can be used as disease models, personalized medicine, and in vitro drug and toxicology screening systems.