Fabrication and characterization of poly(lactic-co-glycolic acid) microsphere/amorphous calcium phosphate scaffolds.

Although hydroxyapatite (HAP) and ß-tricalcium phosphate have been used extensively as osteoconductive minerals in biomaterial scaffolds for bone regeneration, they lack the capacity to stimulate osteoblastic differentiation of progenitor cells. In contrast, amorphous calcium phosphates (ACPs), which convert to HAP under aqueous conditions, have the potential to facilitate osteoblastic differentiation through the transient local release of calcium and phosphate ions. Therefore, in this study ACPs were synthesized using zinc and zirconia divalent cations as stabilizers (denoted ZnACP and ZrACP, respectively) and compared to HAP. Analysis of ion release into serum-containing cell culture medium revealed transiently elevated levels of calcium and phosphorous, consistent with the enhanced solubility of ZrACP and ZnACP relative to HAP. In addition, X-ray diffraction analysis revealed partial conversion of ZrACP to HAP but no conversion of ZnACP after 96 h. Next, scaffolds were fabricated by sintering mixtures of 300-500 µm poly(D,L-lactic-co-glycolic acid) (PLGA) microspheres and 0.5 wt% calcium phosphate mineral (HAP, ZrACP or ZnACP) at 70 °C for 24 h. Scanning electron microscopy revealed a porous microsphere matrix with calcium phosphate particulates clinging to the microsphere surfaces both prior to and after 14 days in culture medium. Finally, the incorporation of calcium phosphate resulted in a lower compressive modulus in the range 127 to 74-89 MPa. Taken together, these results indicate that ZrACP, ZnACP and HAP minerals exhibit very different properties, and therefore may elicit different osteoblastic responses in vitro.

In vitro evaluation of osteoblastic differentiation on amorphous calcium phosphate-decorated poly(lactic-co-glycolic acid) scaffolds.

Calcium phosphate-decorated polyester matrices are promising scaffolds for bone tissue engineering that combine the tunable degradation of synthetic polymers and the osteoconductivity of calcium phosphate minerals. In this study, scaffolds decorated with stabilized amorphous calcium phosphate (ACP) minerals-which exhibit sustained dissolution and release of calcium and phosphate ions-were tested for their ability to support osteoblast proliferation and stimulate differentiation. The two ACPs tested were zirconia-hybridized ACP (ZrACP), which releases ions over a few days and converts in aqueous solution to hydroxyapatite (HAP), and zinc-hybridized ACP (ZnACP), which has a longer period of sustained ion release. MC3T3-E1 pre-osteoblasts were cultured in these scaffolds for up to 21 days, and cell number, alkaline phosphatase (ALP) activity and expression of osteogenic and bone-specific proteins were measured. Cell number, prostaglandin E(2) (PGE(2) ) synthesis and osteopontin (OPN) mRNA expression were elevated on calcium phosphate-decorated scaffolds relative to PLGA controls, while mRNA expression of osteocalcin (OCN), bone sialoprotein and bone morphogenetic protein (BMP)-4 were suppressed. Although MC3T3-E1 responses to the two ACPs were not statistically different, ZrACP-which converts more quickly to HAP-gave rise to slightly higher levels of mRNA expression for BMP-4, osterix, vascular endothelial growth factor (VEGF)-A, OCN and OPN, but slightly lower levels of PGE(2) synthesis, ALP activity and cell number. These results indicate that sintered PLGA microsphere scaffolds decorated with 0.5 wt% ZnACP or ZrACP support cell attachment and elicit a series of biological responses, but these responses do not appear to accelerate osteoblast differentiation.

Self-folding micropatterned polymeric containers.

We demonstrate self-folding of precisely patterned, optically transparent, all-polymeric containers and describe their utility in mammalian cell and microorganism encapsulation and culture. The polyhedral containers, with SU-8 faces and biodegradable polycaprolactone (PCL) hinges, spontaneously assembled on heating. Self-folding was driven by a minimization of surface area of the liquefying PCL hinges within lithographically patterned two-dimensional (2D) templates. The strategy allowed for the fabrication of containers with variable polyhedral shapes, sizes and precisely defined porosities in all three dimensions. We provide proof-of-concept for the use of these polymeric containers as encapsulants for beads, chemicals, mammalian cells and bacteria. We also compare accelerated hinge degradation rates in alkaline solutions of varying pH. These optically transparent containers resemble three-dimensional (3D) micro-Petri dishes and can be utilized to sustain, monitor and deliver living biological components.