Macroporous Constructs Research Articles

Impactability and time‐dependent mechanical properties of porous titanium particles for application in impaction grafting

Impaction grafting with bone particles is a successful technique to restore bone stock loss during hip revision surgery. Allograft shortage is expected within the near future. This study investigates the feasibility of porous titanium particles (TiP) to replace bone particles (BoP) and to compare mechanical properties of TiP and a commercially available porous ceramic bone graft extender (CeP). Impactability and time-dependent mechanical properties (stability and stiffness during physiologic loading (0.1-2.5 MPa)) were assessed by standardized impaction and a confined compression test. Loaded samples were used for particle release analysis. TiP were more impactable than BoP and created a stable, highly entangled macroporous construct. CeP were crushed during impaction, resulting in non-cohesive specimens of small ceramic particles. TiP showed very little deformation at the end of physiological loading. Impacted TiP were stiffer than BoP but more elastic than CeP. TiP generated a low volume of microparticles (0.2% of original TiP weight) with a bimodal size distribution (diameter range, 7-2000 microm). TiP are impactable and create a stable, elastic and highly entangled, macroporous layer. Further in-vitro testing and biological studies are warranted to verify whether the promising results are maintained with THA reconstructions.

Synergistic induction of bone formation by hOP-1, hTGF-β3 and inhibition by zoledronate in macroporous coral-derived hydroxyapatites

Thirty coral-derived calcium carbonate-based macroporous constructs with limited hydrothermal conversion to hydroxyapatite (7% HA/CC) were implanted in the rectus abdominis of three adult non-human primate Papio ursinus to investigate the intrinsic induction of bone formation. Macroporous constructs with 125μg human recombinant osteogenic protein-1 (hOP-1) or 125μg human recombinant transforming growth factor-β3 (hTGF-β3) were also implanted. The potential synergistic interaction between morphogens was tested by implanting binary applications of hOP-1 and hTGF-β3 5:1 by weight, respectively. To evaluate the role of osteoclastic activity on the implanted macroporous surfaces, coral-derived constructs were pre-loaded with 0.24mg of bisphosphonate zoledronate (Zometa®). To correlate the morphology of tissue induction with osteogenic gene expression and activation, harvested specimens on day 90 were analyzed for changes in OP-1 and TGF-β3 mRNA synthesis by quantitative real-time polymerase chain reaction (qRT-PCR). The induction of bone formation in 7% HA/CC solo correlated with OP-1 expression. Massive bone induction formed by binary applications of the recombinant morphogens. Single applications of hOP-1 and hTGF-β3 also resulted in substantial bone formation, not comparable however to synergistic binary applications. Zoledronate-treated macroporous constructs showed limited bone formation and in two specimens bone formation was altogether absent; qRT-PCR showed a prominent reduction of OP-1 gene expression whilst TGF-β3 expression was far greater than OP-1. The lack of bone formation by zoledronate-treated specimens indicates that osteoclastic activity on the implanted coral-derived constructs is critical for the spontaneous induction of bone formation. Indirectly, zoledronate-treated samples showing lack of OP-1gene expression and absent or very limited bone formation by induction confirm that the spontaneous induction of bone formation by coral-derived macroporous constructs is initiated by secreted BMPs/OPs, in context the OP-1 isoform.

Fabrication of ice-templated macroporous TiO2–chitosan scaffolds for photocatalytic applications

Higher-ordered 3D macroporous TiO2-functionalized chitosan scaffolds were prepared by ice segregation induced self-assembly (ISISA), in which homogenous dispersions of 6, 27 or 200 nm sized TiO2nanoparticles and chitosan cross-linked with glycidoxypropyltrimethoxysilane were unidirectionally frozen at −196 °C. Scanning electron microscopy showed that under established optimum conditions the monoliths comprised well-aligned 30–50 µm sized micro-channels running parallel to the direction of ice growth. The surface morphology of the internal wall structure was influenced by the size of the titania nanoparticles. Scaffolds prepared in the presence of 6 nm sized anatase particles showed featureless walls with concealed/embedded nanoparticles, whereas larger TiO2 particles remained exposed at the surface of the channel walls. Mechanical properties of the composite scaffolds were studied under compressive loads and stress–strain measurements obtained, and the effect of particle size on the elastic properties of the macroporous constructs determined. The hybrid scaffolds were shown to be reusable substrates for the photocatalytic degradation of methylene blue and Orange II dye molecules.