We have studied the size and orientation of mineral crystals in cortical bone of oim/oim mice, which are known to produce only ␣ 1(I) collagen homotrimers and which may serve as a model for human osteogenesis imperfecta. Long bones (femur and tibia) from young (5 wk old) oim/oim mice and from unaffected heterozygous counterparts were investigated by small-angle x-ray scattering (SAXS), which is sensitive to structures smaller than 50 nm. Mineral crystals were compared in terms of their thickness and their alignment with respect to the long bone axis. While electron microscopic tomography has recently shown the existence of large mineral blocks (with all dimensions typically exceeding 50 nm) in mineralized tendons of oim/oim mice, SAXS revealed a family of thin, possibly needle-like, crystals in cortical bone. These crystals were similar in shape to those observed previously in normal mice, but they were thinner and less well aligned in oim/oim mice relative to heterozygotes. Moreover, the crystal thickness and their alignment with the bone axis were more variable in oim/oim bone, with a close correlation ( r ϭ 0.94, P Ͻ 0.001) between the two parameters. The presence of smaller crystals with more variable alignment in corticalis of oim/oim mice may contribute to the brittleness of their bone, similar to that of human osteogenesis imperfecta. ( J. Clin. Invest. 1996. 97:396-402.)

Osteogenesis imperfecta (OI) is a disease attributable to any of a large number of possible mutations of type I collagen. The disease is clinically characterized in part by highly brittle bone, the cause of this feature being unknown. Recently a mouse model of OI, designated as osteogenesis imperfecta murine (oim), and having a well defined genetic mutation, has been studied and found to contain mineral crystals different in their alignment with respect to collagen and in their size. These observations are consistent with those reported in human OI and the unusual crystal alignment and size undoubtedly contribute to the reduced mechanical properties of OI bone. While the mineral has been investigated, no information is available on the tensile properties of oim collagen. In this study, the mechanical properties of tendon collagen under tension have been examined for homozygous (oim/oim), heterozygous ( ϩ /oim), and control ( ϩ / ϩ ) mice under native wet conditions. The ultimate stress and strain found for oim/oim collagen were only about half the values for control mice. Assuming that prestrained collagen molecules carry most of the tensile load in normal bone while the mineral confers rigidity and compression stability, the reported results suggest that the brittleness of OI bone in the mouse model may be related to a dramatic reduction of the ultimate tensile strain of the collagen. ( J. Clin. Invest. 1997. 100:40-45.) Key words: collagen • osteogenesis imperfecta • mechanical properties • stress/strain • x-ray scattering

Osteogenesis imperfecta (OI) is a heritable disease characterized by skeletal deformities and brittle bones. In the current study, the nature of the mineral in long bones of a mouse model of OI (oim/oim, a mutant which produces an alpha 1(I) collagen homotrimer) was examined by Fourier transform infrared microscopy. The mineral:matrix ratio of oim/oim cortical bone was greater than that of the heterozygous oim/+ and of the normal +/+ bones, probably as a result of reduced collagen content. The molecular environments of the apatitic phosphates differed among the oim/oim and the oim/+ and the +/+ bones. This was attributable to several factors, including dissimilar mineral-matrix interactions and differences in the chemical composition of the mineral. It was concluded from these data that the defective collagen matrix leads to abnormal mineral formation at the molecular level and thus results in tissues with reduced mechanical properties.

Results give insight into construct processes of tissue regeneration and development and suggest more complete tissue-engineered cartilage, bone, and tendon models. These should have significant future scientific and clinical applications in medicine, including their use in plastic surgery, orthopaedics, craniofacial reconstruction, and teratology.

Methods for tissue engineering have led to many advances in the growth and development of a variety of cell types on biodegradable scaffolds. Resulting cell-polymer constructs hold great promise ultimately as vehicles for generating new tissue in the human body. As an example in this context, models of human phalanges have been fabricated by suturing three different cell-polymer constructs to produce a distal phalanx, a middle phalanx, and a distal interphalangeal joint [1]. Bovine periosteum, cartilage, and tendon were obtained as a source of osteoblasts, chondrocytes, and tenocytes, respectively. Periosteal sheets were wrapped about a biodegradable co-polymer of polyglycolic acid (PGA) and poly-L-lactic acid (PLLA), and isolated chondrocytes and tenocytes were separately seeded on PGA scaffolds [1]. The three phalanx constructs were cultured for one week and then implanted in athymic (nude) mice for up to 60 weeks. On retrieval of constructs after 20 and 40 weeks of implantation, histology [1] or in situ hybridization [2] showed that bone, cartilage and tendon had developed with intact interfaces between the cell types; models maintained original shapes of human phalanges; a putative cartilaginous growth plate appeared in phalanx models; the initial bovine phenotype of models persisted over time; and the bone of models was vascularized in rudimentary fashion by the host nude mice. The latter observation was investigated more completely by transmission electron microscopy to gain insight into possible means by which phalanx models were supported in their nutrition and growth.

A principal purpose of tissue engineering is the augmentation, repair or replacement of diseased or injured human tissue. This study was undertaken to determine whether human biopsies as a cell source could be utilized for successful engineering of human phalanges consisting of both bone and cartilage. This paper reports the use of cadaveric human chondrocytes and periosteum as a model for the development of phalanx constructs. Two factors, osteogenic protein-1 [OP-1/bone morphogenetic protein-7 (BMP7)], alone or combined with insulin-like growth factor (IGF-1), were examined for their potential enhancement of chondrocytes and their secreted extracellular matrices. Design of the study included culture of chondrocytes and periosteum on biodegradable polyglycolic acid (PGA) and poly-l-lactic acid (PLLA)-poly-ε-caprolactone (PCL) scaffolds and subsequent implantation in athymic nu/nu (nude) mice for 5, 20, 40 and 60 weeks. Engineered constructs retrieved from mice were characterized with regard to genotype and phenotype as a function of developmental (implantation) time. Assessments included gross observation, X-ray radiography or microcomputed tomography, histology and gene expression. The resulting data showed that human cell-scaffold constructs could be successfully developed over 60 weeks, despite variability in donor age. Cartilage formation of the distal phalanx models enhanced with both OP-1 and IGF-1 yielded more cells and extracellular matrix (collagen and proteoglycans) than control chondrocytes without added factors. Summary data demonstrated that human distal phalanx models utilizing cadaveric chondrocytes and periosteum were successfully fabricated and OP-1 and OP-1/IGF-1 accelerated construct development and mineralization. The results suggest that similar engineering and transplantation of human autologous tissues in patients are clinically feasible. Copyright © 2016 John Wiley & Sons, Ltd.

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Treatment of human congenital malformations and for loss of tissue or organ function is a serious clinical concern, frequently supported by harvesting autogenous tissue for reconstructive surgery. This paper summarizes an alternate approach through novel tissue engineering methods and describes cell-polymer composites that could be fundamental in developing advances for digit and joint replacement. The work utilizes cells from different sources transplanted on biodegradable polymer matrices to form structures with defined shape, morphological features and composition resembling those of human phalanges and intact joints.Polyglycolic acids (PGA) fibers (Albany International, Mansfield, MA) 15 μm in diameter were used as a mesh support for cell attachment and matrix formation. For cartilage and tendon cells, PGA alone served as a flat surface without specific shape. For bone cells, PGA was copolymerized with poly-L-lactic acid (PLLA) (Polysciences, Warrington, PA) and shaped after a human phalanx molded from cadaveric distal and middle phalangeal bones. Polymers were sterilized with ethylene oxide before use.