Current bone tissue engineering strategies aim to grow a tissue similar to native bone by combining cells and biologically active molecules with a scaffold material. In this study, a macroporous scaffold made from the seaweed-derived polymer alginate was synthesized and mineralized for cell-based bone tissue engineering applications. Nucleation of a bone-like hydroxyapatite mineral was achieved by incubating the scaffold in modified simulated body fluids (mSBF) for four weeks. Analysis using scanning electron microscopy and energy dispersive x-ray analysis indicated growth of a continuous layer of mineral primarily composed of calcium and phosphorous. X-ray diffraction analysis showed peaks associated with hydroxyapatite, the major inorganic constituent of human bone tissue. In addition to the mineral characterization, the ability to control nucleation on the surface, into the bulk of the material, or on the inner pore surfaces of scaffolds was demonstrated. Finally, human MSCs attached and proliferated on the mineralized scaffolds and cell attachment improved when seeding cells on mineral coated alginate scaffolds. This novel alginate- HAP composite material could be used in bone tissue engineering as a scaffold material to deliver cells, and perhaps also biologically active molecules.

In this study, we have developed mineral coatings on polycaprolactone scaffolds to serve as templates for growth factor binding and release. Mineral coatings were formed using a biomimetic approach that consisted in the incubation of scaffolds in modified simulated body fluids (mSBF). To modulate the properties of the mineral coating, which we hypothesized would dictate growth factor release, we used carbonate (HCO3) concentration in mSBF of 4.2 mM, 25mM, and 100mM. Analysis of the mineral coatings formed using scanning electron microscopy indicated growth of a continuous layer of mineral with different morphologies. X-ray diffraction analysis showed peaks associated with hydroxyapatite, the major inorganic constituent of human bone tissue in coatings formed in all HCO3 concentrations. Mineral coatings with increased HCO3 substitution showed more rapid dissolution kinetics in an environment deficient in calcium and phosphate but showed re-precipitation in an environment with the aforementioned ions. The mineral coating provided an effective mechanism for growth factor binding and release. Peptide versions of vascular endothelial growth factor (VEGF) and bone morphogenetic protein 2 (BMP2) were bound with efficiencies up to 90% to mineral mineral-coated PCL scaffolds. We also demonstrated sustained release of all growth factors with release kinetics that were strongly dependent in the solubility of the mineral coating.

Mineral coatings are presented as a temporally controllable protein release system on a common orthopedic device material, β‐tricalcium phosphate (β‐TCP). Proteins are bound to coatings via electrostatic interactions and release of one or more proteins is temporally controlled in a predictable manner by modulating the physicochemical properties of mineral coatings, including morphology and dissolution rate.

It is known that angiogenesis plays an important role in bone regeneration and that release of angiogenic and osteogenic growth factors can enhance bone formation. Multiple growth factors play key roles in processes that lead to tissue formation/regeneration during natural tissue development and repair. Therefore, treatments aiming to mimic tissue regeneration can benefit from multiple growth factor release, and there remains a need for simple clinically relevant approaches for dual growth factor release. We hypothesized that mineral coatings could be used as a platform for controlled incorporation and release of multiple growth factors. Specifically, mineral-coated scaffolds were ''dip coated'' in multiple growth factor solutions, and growth factor binding and release were dictated by the growth factor-mineral binding affinity. Beta tricalcium phosphate (b-TCP) scaffolds were fabricated using indirect solid-free form fabrication techniques and coated with a thin conformal mineral layer. Mineral-coated b-TCP scaffolds were sequentially dipped in recombinant human vascular endothelial growth factor (rhVEGF) and a modular bone morphogenetic peptide, a mineral-binding version of bone morphogenetic protein 2 (BMP2), solutions to allow for the incorporation of each growth factor. The dual release profile showed sustained release of both growth factors for over more than 60 days. Scaffolds releasing either rhVEGF alone or the combination of growth factors showed an increase in blood vessel ingrowth in a dosedependent manner in a sheep intramuscular implantation model. This approach demonstrates a ''modular design'' approach, in which a controllable biologics carrier is integrated into a structural scaffold as a thin surface coating.

β-Tricalcium phosphate (β-TCP) is an attractive ceramic for bone tissue repair because of its similar composition to bone mineral and its osteoconductivity. However, compared with other ceramics β-TCP has a rapid and uncontrolled rate of degradation. In the current study β-TCP granules were mineral coated with the aim of influencing the dissolution rate of β-TCP, and also to use the coating as a carrier for controlled release of the growth factors recombinant human vascular endothelial growth factor (rhVEGF), modular VEGF peptide (mVEGF), and modular bone morphogenetic protein 2 peptide (mBMP2). The biomineral coatings were formed by heterogeneous nucleation in aqueous solution using simulated body fluid solutions with varying concentrations of bicarbonate (HCO3). Our results demonstrate that we could coat β-TCP granules with mineral layers possessing different dissolution properties. The presence of a biomineral coating delays the dissolution rate of the β-TCP granules. As the carbonate (CO32−) content in the coating was increased the dissolution rate of the coated β-TCP also increased, but remained slower than the dissolution of uncoated β-TCP. In addition, we showed sustained release of multiple growth factors, with release kinetics that were controllable by varying the identity of the growth factor or the CO32− con-tent in the mineral coating. Released rhVEGF induced human umbilical vein endothelial cell (HUVEC) proliferation, and mVEGF enhanced migration of mouse embryonic endothelial cells in a scratch wound healing assay, indicating that each released growth factor was biologically active.