Tailoring the mechanical properties of 3D-designed poly(glycerol sebacate) scaffolds for cartilage applications

Matching tissue engineering scaffold modulus to that of native tissue is highly desirable. Effective scaffold modulus can be altered through changes in base material modulus and/or scaffold pore architecture. Because the latter may be restricted by tissue in-growth requirements, it is advantageous to be able to alter the base material modulus of a chosen scaffold material. Here, we show that the bulk modulus of poly(glycerol sebacate) (PGS) can be changed by varying molar ratios during prepolymer synthesis and by varying curing time. We go on to show that PGS can be used to create 3D designed scaffolds via solid freeform fabrication methods with modulus values that fall within the ranges of native articular cartilage equilibrium modulus. Furthermore, using base material modulus inputs, homogenization finite element analysis can effectively predict the tangent modulus of PGS scaffold designs, which provides a significant advantage for designing new cartilage regeneration scaffolds. Lastly, we demonstrate that this relatively new biomedical material supports cartilaginous matrix production by chondrocytes in vitro . © 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75767/1/32653_ftp.pd

Mechanically Stable Solid Freeform Fabricated Scaffolds with Permeability Optimized for Cartilage Tissue Engineering.

Clinical treatment options for articular cartilage repair are progressing with the incorporation of synthetic matrices alongside current autologous chondrocyte implantation techniques. This work explores mechanical and mass transport design of potential matrices. Solid freeform fabrication (SFF) is used to create highly reproducible scaffolds with precise structural features in order to explore the mechanical potential of 3D designed poly(ε-caprolactone) (PCL) and poly(glycerol sebacate) (PGS) scaffolds, and to examine the effects of a designed physical property, permeability, for cartilage regeneration. Our first aim explores the potential of PCL and PGS scaffolds to provide temporary mechanical function within a tissue defect. We find that PCL mimics the viscoelastic nature of cartilage; however its stiffness properties cannot be changed through alterations in molecular weight or melting temperature. Fabricated into the architectures explored, it has aggregate modulus (HA) values within the correct magnitude, but higher than native cartilage. Furthermore, we demonstrate the importance of mechanically testing PCL scaffolds at physiological temperatures and we quantify their contraction in polar environments. Poly(glycerol sebacate) has never been used for cartilage tissue engineering. We characterize how variations in the molar ratios of glycerol to sebacic acid (during pre-polymer synthesis) or variations in curing time can be used to change the stiffness of PGS, enabling fabrication of scaffolds with a wide range of architectures (designed for optimal tissue regeneration) that all support in vivo loads. Chondrocytes seeded onto PGS produce cartilaginous matrix and express cartilage specific genes similar to or better than cells cultured on PCL, showing the biocompatibility of PGS for cartilage applications for the first time. Our second aim looks at enhancing cartilage regeneration by optimizing scaffold permeability. We show that chondrocytes prefer a lower permeable scaffold that mimics the natural environment of native tissue, producing significantly more matrix and increased expression of cartilage specific markers. Bone marrow stromal cells (BMSCs) display the opposite trend, favoring a higher permeable environment for chondrogenic differentiation, as displayed through collagen 2 to collagen 1 expression, suggesting that increased access to chondrogenic induction factors in media is more important to these cells than mimicking the low permeable environment of native tissue.Ph.D.Biomedical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/61582/1/jessmw_1.pd

Effect of Polycaprolactone Scaffold Permeability on Bone Regeneration In Vivo

Successful bone tissue engineering depends on the scaffold's ability to allow nutrient diffusion to and waste removal from the regeneration site, as well as provide an appropriate mechanical environment. Since bone is highly vascularized, scaffolds that provide greater mass transport may support increased bone regeneration. Permeability encompasses the salient features of three-dimensional porous scaffold architecture effects on scaffold mass transport. We hypothesized that higher permeability scaffolds will enhance bone regeneration for a given cell seeding density. We manufactured poly---caprolactone scaffolds, designed to have the same internal pore design and either a low permeability (0.688-10-7m4/N-s) or a high permeability (3.991-10-7m4/N-s), respectively. Scaffolds were seeded with bone morphogenic protein-7-transduced human gingival fibroblasts and implanted subcutaneously in immune-compromised mice for 4 and 8 weeks. Micro-CT evaluation showed better bone penetration into high permeability scaffolds, with blood vessel infiltration visible at 4 weeks. Compression testing showed that scaffold design had more influence on elastic modulus than time point did and that bone tissue infiltration increased the mechanical properties of the high permeability scaffolds at 8 weeks. These results suggest that for polycaprolactone, a more permeable scaffold with regular architecture is best for in vivo bone regeneration. This finding is an important step toward the end goal of optimizing a scaffold for bone tissue engineering.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90462/1/ten-2Etea-2E2010-2E0560.pd

The pore size of polycaprolactone scaffolds has limited influence on bone regeneration in an in vivo model

Bone tissue engineering scaffolds should be designed to optimize mass transport, cell migration, and mechanical integrity to facilitate and enhance new bone growth. Although many scaffold parameters could be modified to fulfill these requirements, pore size is an important scaffold characteristic that can be rigorously controlled with indirect solid freeform fabrication. We explored the effect of pore size on bone regeneration and scaffold mechanical properties using polycaprolactone (PCL) scaffolds designed with interconnected, cylindrical orthogonal pores. Three scaffold designs with unique microarchitectures were fabricated, having pore sizes of 350, 550, or 800 Μm. Bone morphogenetic protein-7 transduced human gingival fibroblasts were suspended in fibrin gel, seeded into scaffolds, and implanted subcutaneously in immuno-compromised mice for 4 or 8 weeks. We found that (1) modulus and peak stress of the scaffold/bone constructs depended on pore size and porosity at 4 weeks but not at 8 weeks, (2) bone growth inside pores depended on pore size at 4 weeks but not at 8 weeks, and (3) the length of implantation time had a limited effect on scaffold/bone construct properties. In conclusion, pore sizes between 350 and 800 Μm play a limited role in bone regeneration in this tissue engineering model. Therefore, it may be advantageous to explore the effects of other scaffold structural properties, such as pore shape, pore interconnectivity, or scaffold permeability, on bone regeneration when designing PCL scaffolds for bone tissue engineering. © 2009 Wiley Periodicals, Inc. J Biomed Mater Res, 2010Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/64538/1/32381_ftp.pd

SPEN haploinsufficiency causes a neurodevelopmental disorder overlapping proximal 1p36 deletion syndrome with an episignature of X chromosomes in females

Deletion 1p36 (del1p36) syndrome is the most common human disorder resulting from a terminal autosomal deletion. This condition is molecularly and clinically heterogeneous. Deletions involving two non-overlapping regions, known as the distal (telomeric) and proximal (centromeric) critical regions, are sufficient to cause the majority of the recurrent clinical features, although with different facial features and dysmorphisms. SPEN encodes a transcriptional repressor commonly deleted in proximal del1p36 syndrome and is located centromeric to the proximal 1p36 critical region. Here, we used clinical data from 34 individuals with truncating variants in SPEN to define a neurodevelopmental disorder presenting with features that overlap considerably with those of proximal del1p36 syndrome. The clinical profile of this disease includes developmental delay/intellectual disability, autism spectrum disorder, anxiety, aggressive behavior, attention deficit disorder, hypotonia, brain and spine anomalies, congenital heart defects, high/narrow palate, facial dysmorphisms, and obesity/increased BMI, especially in females. SPEN also emerges as a relevant gene for del1p36 syndrome by co-expression analyses. Finally, we show that haploinsufficiency of SPEN is associated with a distinctive DNA methylation episignature of the X chromosome in affected females, providing further evidence of a specific contribution of the protein to the epigenetic control of this chromosome, and a paradigm of an X chromosome-specific episignature that classifies syndromic traits. We conclude that SPEN is required for multiple developmental processes and SPEN haploinsufficiency is a major contributor to a disorder associated with deletions centromeric to the previously established 1p36 critical regions

SPEN haploinsufficiency causes a neurodevelopmental disorder overlapping proximal 1p36 deletion syndrome with an episignature of X chromosomes in females

Deletion 1p36 (del1p36) syndrome is the most common human disorder resulting from a terminal autosomal deletion. This condition is molecularly and clinically heterogeneous. Deletions involving two non-overlapping regions, known as the distal (telomeric) and proximal (centromeric) critical regions, are sufficient to cause the majority of the recurrent clinical features, although with different facial features and dysmorphisms. SPEN encodes a transcriptional repressor commonly deleted in proximal del1p36 syndrome and is located centromeric to the proximal 1p36 critical region. Here, we used clinical data from 34 individuals with truncating variants in SPEN to define a neurodevelopmental disorder presenting with features that overlap considerably with those of proximal del1p36 syndrome. The clinical profile of this disease includes developmental delay/intellectual disability, autism spectrum disorder, anxiety, aggressive behavior, attention deficit disorder, hypotonia, brain and spine anomalies, congenital heart defects, high/narrow palate, facial dysmorphisms, and obesity/increased BMI, especially in females. SPEN also emerges as a relevant gene for del1p36 syndrome by co-expression analyses. Finally, we show that haploinsufficiency of SPEN is associated with a distinctive DNA methylation episignature of the X chromosome in affected females, providing further evidence of a specific contribution of the protein to the epigenetic control of this chromosome, and a paradigm of an X chromosome-specific episignature that classifies syndromic traits. We conclude that SPEN is required for multiple developmental processes and SPEN haploinsufficiency is a major contributor to a disorder associated with deletions centromeric to the previously established 1p36 critical regions.The article is available via Open Access. Click on the 'Additional link' above to access the full-text.Published version, accepted version (6 month embargo), submitted versio