Fabrication and characterization of porous calcium polyphosphate scaffolds
ABSTRACT Porous calcium polyphosphate (CPP) scaffolds with different polymerization degree and crystalline phases were prepared, and
then analyzed by scanning electron microscopy (SEM), Thermmogravimetry (TG) and X-ray diffraction (XRD). Number average polymerization
degree was calculated by analyzing the calcining process of raw material Ca(H2PO4)2, as a polycondensation reaction. Amorphous CPP were prepared by the quenching from the melt of Ca(H2PO4)2 after calcining, and CPP with different polymerization degree was prepared by controlling the calcining time. Meanwhile,
CPP with the same polymerization degree was prepared to amorphous or different crystalline phases CPP which was made from
crystallization of amorphous CPP. In vitro degradation studies using 0.1 M of tris-buffered solution were performed to assess the effect of polymerization degree or
crystalline phases on mechanical properties and weight loss of the samples. With the increase of polymerization degree, the
weight loss during the degradation decreased, contrarily the strength of CPP increased. The degradation velocity of amorphous
CPP, α-CPP, β-CPP and γ-CPP with the same polymerization degree decreased in turn at the same period. The full weight loss
period of CPP can be controlled between 17 days and more than 1 year. The results of this study suggest that CPP ceramics
have potential applications for bone tissue engineering.
- [show abstract] [hide abstract]
ABSTRACT: In this study we investigated not only osteoblastic cell proliferation and differentiation on the surface of calcium metaphosphate (CMP) matrices in vitro but also bone formation by ectopic implantation of these cell-matrix constructs in athymic mice in vivo. Interconnected porous CMP matrices with pores 200 microm in size were prepared to use as scaffolds for rat-marrow stromal-cell attachment. Cell-matrix constructs were cultured in vitro, and cell proliferation and ALPase activities were monitored for 56 days. In addition to their being cultured in vitro, cell-matrix constructs were implanted into subcutaneous sites of athymic mice. In vitro these porous CMP matrices supported the proliferation of osteoblastic cells as well as their differentiation, as indicated by high ALPase activity. In vivo the transplanted marrow cells gave rise to bone tissues in the pores of the CMP matrices. A small amount of woven bone formation was detected first at 4 weeks; osteogenesis progressed vigorously with time, and thick lamellar bones that had been remodeled were observed at 12 weeks. These findings demonstrate the potential for using a porous CMP matrix as a biodegradable scaffold ex vivo along with attached marrow-derived mesenchymal cells for transplantation into a site for bone regeneration in vivo.Journal of Biomedical Materials Research 03/2001; 54(2):216-23.
- [show abstract] [hide abstract]
ABSTRACT: Calcium phosphate glass ceramics with incorporation of small additions of two nucleating agents, MgO and K2O were prepared in the metaphosphate and pyrophosphate region, using an appropriate two-step heat treatment of controlled crystallization defined by differential thermal analysis results. Identification and quantification of crystalline phases precipitated from the calcium phosphate glass were performed using X-ray diffraction and Rietveld analysis. The β-Ca2P2O7 (β-DCP), KCa(PO3)3, β-Ca(PO3)2 and Ca4P6O19 phases were detected in the glass ceramics. In order to evaluate the degradation of the glass ceramics prepared, degradation studies were carried out during 42 days in Tris-HCl solution at 37 °C, pH 7.4, using granules in the range of 355–415 μm. The materials presented a weight loss ranging up to 12%. The ions leached during the immersion mainly originated from the KCa(PO3)3 phase, probably due to the presence of K+ ion in the calcium metaphosphate, and the residual glassy phase. The structural changes at the surface of materials during degradation have been analyzed by Fourier transform infrared spectroscopy and X-ray diffraction. Results showed that significant surface changes occurred with immersion time, with the decrease of KCa(PO3)3, β-Ca2P2O7 and β-Ca(PO3)2 phases occurring at different periods of immersion. This study has demonstrated an easy way to prepared calcium phosphate materials with specific calcium phosphate phases and crystallization, and therefore specific degradation rates.Journal of Non-Crystalline Solids. 01/2003;
- [show abstract] [hide abstract]
ABSTRACT: Solid freeform fabrication (SFF) involves the creation of a solid 3-D object of desired shape by successively adding raw materials in particles or layers. Its use in fabricating surgical implants is being explored. The objective of this study was to determine the feasibility of using SFF to build porous parts of calcium polyphosphate (CPP), a linear condensed phosphate that has been suggested as a material for forming bioresorbable skeletal replacement implants. CPP powders (<25 microm in particle size) were added to an UV curable monomer (SOMOS 6110) at a solids loading of 25 vol %, with the addition of a commercial dispersant to prevent particle agglomeration and settling. Viscosity and cure depth measurements were performed to insure that CPP suspension met the requirements deemed necessary for use in SFF. The CPP suspension was bulk cured and sintered in molds in order to assess binder removal and sintering parameters. Using a three-point bend test, the ultimate bending strength and energy-to-fracture of sintered CPP samples simulating parts to be formed by this strategy were characterized. In vitro degradation studies using 0.1M of tris-buffered solution were performed to assess the effect of aging on mechanical properties of the samples as a function of the processing route and resulting structures. The polymer binder successfully was removed from the cured ceramic suspension by developing a procedure that combined slow heating rates with low temperature dwells. Sintering CPP at 585 degrees C for 1 h produced amorphous material samples with average porosity of 27.7 +/- 2.0%. Sintering CPP at 600 degrees C for 1 h produced a crystalline material with samples having an average porosity of 22.9 +/- 1.3%. Crystalline CPP was found to exhibit superior bend strength and toughness compared with amorphous CPP. Both samples experienced a decline in mechanical properties during in vitro degradation; however, the effects were more pronounced with the amorphous CPP samples. Amorphous CPP was found to degrade four times faster than crystalline CPP, as shown by high levels of phosphate present in the degradation solution and a noticeable increase in the porosity of the samples. Crystalline CPP was more resistant to attack as dissolution was limited to surface features of the sintered particles.Journal of Biomedical Materials Research 10/2001; 56(4):504-15.