In tissue engineering, the hydrophilicity of porous scaffolds is essential and influences protein and cell adhesion as well as nutrient diffusion into the scaffold. The relative low hydrophilicity of degradable polyesters, which limits diffusion of nutrients, is a major drawback in large porous scaffolds of these materials when used for bone tissue engineering and repair of critical size defects. Designing porous biodegradable polymer scaffolds with improved hydrophilicity, while maintaining their mechanical, thermal, and degradation properties is therefore of clinical interest. Here, surfactants were used to tune the hydrophilicity and material properties. A total of 3-20% (w/w) of surfactant, polysorbate 80 (Tween 80), was used as an additive in poly(L-lactide-co-1,5-diozepan-2-one) [poly(LLA-co-DXO)] and poly(L-lactide)-co-(epsilon-caprolactone) [poly(LLA-co-CL)] scaffolds. A significantly decreased water contact angle was recorded for all the blends and the crystallinity, glass transition temperature and crystallization temperature were reduced with increased amounts of surfactant. Copolymers with the addition of 3% Tween 80 had comparable mechanical properties as the pristine copolymers. However, the E-modulus and tensile stress of copolymers decreased significantly with the addition of 10 and 20% Tween 80. Initial cell response of the material was evaluated by seeding human osteoblast-like cells (HOB) on the scaffolds. The addition of 3% Tween 80 did not significantly influence cell attachment or proliferation, while 20% Tween 80 significantly inhibited osteoblast proliferation. RT-PCR results showed that 3% Tween 80 stimulated mRNA expression of alkaline phosphatase (ALP), osteoprotegerin (OPG), and bone morphogenetic protein-2 (BMP-2).

Significant evidence has indicated that poly(L-lactide)-co-(epsilon-caprolactone) [(poly(LLA-co-CL)] scaffolds could be one of the suitable candidates for bone tissue engineering. Oxygen-terminated nanodiamond particles (n-DP) were combined with poly(LLA-co-CL) and revealed to be positive for cell growth. In this study, we evaluated the influence of poly(LLA-co-CL) scaffolds modified by n-DP on attachment, proliferation, differentiation of bone marrow stromal cells (BMSCs) in vitro, and on bone formation using a sheep calvarial defect model. BMSCs were seeded on either poly(LLA-co-CL)-or n-DP-coated scaffolds and incubated for 1 h. Scanning electron microscopy (SEM) and fluorescence microscopy were used in addition to protein and DNA measurements to evaluate cellular attachment on the scaffolds. To determine the effect of n-DP on proliferation of BMSCs, cell/scaffold constructs were harvested after 3 days and evaluated by Bicinchoninic Acid (BCA) protein assay and SEM. In addition, the osteogenic differentiation of cells grown for 2 weeks on the various scaffolds and in a dynamic culture condition was evaluated by real-time RT-PCR. Unmodified and modified scaffolds were implanted into the calvaria of six-year-old sheep. The expression of collagen type I (COL I) and bone morphogenetic protein-2 (BMP-2) after 4 weeks as well as the formation of new bone after 12 and 24 weeks were analyzed by immunohistochemistry and histology. Scaffolds modified with n-DP supported increased cell attachment and the mRNA expression of osteopontin (OPN), bone sialoprotein (BSP), and BMP-2 were significantly increased after 2 weeks of culture. The BMSCs had spread well on the various scaffolds investigated after 3 days in the study with no significant difference in cell proliferation. Furthermore, the in vivo data revealed more positive staining of COLI and BMP-2 in relation to the n-DP-coated scaffolds after 4 weeks and presented more bone formation after 12 and 24 weeks. n-DP modification significantly increased cell attachment and differentiation of BMSCs on poly(LLA-co-CL) scaffolds in vitro and enhanced bone formation in vivo.

Polylactide-modified nanodiamond particles (n-DP-g-PLA) are prepared by sodium-hydride-activated nanodiamond-initated anionic ring-opening polymerization. Activated nanodiamond particles repel each other, preventing agglomeration during the polymerization. This universal modification provides a platform for the functionalization of all types of nanoparticles containing hydroxyl groups.

Severe phase separation was observed in blending nanodiamond particle (n-DP) in poly (L-lactide-co-e-caprolactone) (poly(LLA-co-CL)) scaffold. In this study we optimized the scaffold by the addition of 1-50% (w/w) polylactide modified n-DP (n-DP-PLA) or benzoquinone-modified n-DP (n-DP-BQ). Composed by 10% n-DP-PLA, composite had 6 times higher E-modulus in tensile test, whereas the maximum reinforcement can be higher than 15 times. However, n-DP-BQ composites conserved the mechanical properties, and thermal properties of the polymer substrate. The attachment, spreading and growth of UE7T13 cells on modified n-DP composites were similar to poly(LLA-co-CL), and independent to n-DP concentrations. In summary, a proper modified n-DP is the key to reinforce poly(LLA-co-CL) for tissue engineering.

The mechanical properties of amorphous, degradable, and highly porous poly(lactide-co-caprolactone) structures have been improved by using a 3D fiber deposition (3DF) method. Two designs of 3DF scaffolds, with 45 degrees and 90 degrees layer rotation, were printed and compared with scaffolds produced by a salt-leaching method. The scaffolds had a porosity range from 64% to 82% and a high interconnectivity, measured by micro-computer tomography. The 3DF scaffolds had 89 times higher compressive stiffness and 35 times higher tensile stiffness than the salt-leached scaffolds. There was a distinct decrease in the molecular weight during printing as a consequence of the high temperature. The chain microstructure was, however, not affected; the glass transition temperature and the decomposition temperature were constant. Human OsteoBlast-like cells were cultured in vitro and the cell morphology and distribution were observed by scanning electron microscopy and fluorescence microscopy. The cell distribution on the 3DF scaffolds was more homogeneous than the salt-leached scaffolds, suggesting that 3DF scaffolds are more suitable as porous biomaterials for tissue engineering. These results show that it is possible to design and optimize the properties of amorphous polymer scaffolds. The 3DF method produce amorphous degradable poly(lactide-co-caprolactone) that are strong and particularly suitable for cell proliferation.