In-vitro viability of bone scaffolds fabricated using the adaptive foam reticulation technique.

The adaptive foam reticulation technique combines the foam reticulation and freeze casting methodologies of fabricating bone reparative scaffolds to offer a potential alternative to autografts. For the first time this paper studies the effect of processing on the mechanical properties and in-vitro cell growth of controllably generating a hierarchical structure of macro- (94 ± 6 to 514 ± 36 µm) and microporosity (2-30 µm) by the inclusion of camphene as a porogen during processing. Scaffolds were produced with porogen additions of 0-25 wt%. Porosity values of the structures of 85-96% were determined using the Archimedes technique and verified using X-ray Computed Tomography. The strength of the hydroxyapatite scaffolds, 5.70 ± 1.0 to 159 ± 61 kPa, correlated to theoretically determined values, 3.71 ± 0.8 to 134 ± 12 kPa, calculated by the novel incorporation of a shape factor into a standard equation. Fibroblast (3T3) and pre-osteoblast (MC3T3) cell growth was found to be significantly (P < 0.005) improved using 25 wt% porogen. This was supported by increased levels of alkaline phosphatase and was thought to result from greater dissolution as quantified by increased calcium levels in incubating media. The combination of these properties renders adaptive foam reticulation-fabricated scaffolds suitable for non-structural bone regenerative applications in non-load bearing bone defects.

3D printing of porous hydroxyapatite scaffolds intended for use in bone tissue engineering applications.

A systematic characterisation of bone tissue scaffolds fabricated via 3D printing from hydroxyapatite (HA) and poly(vinyl)alcohol (PVOH) composite powders is presented. Flowability of HA:PVOH precursor materials was observed to affect mechanical stability, microstructure and porosity of 3D printed scaffolds. Anisotropic behaviour of constructs and part failure at the boundaries of interlayer bonds was highlighted by compressive strength testing. A trade-off between the ability to facilitate removal of PVOH thermal degradation products during sintering and the compressive strength of green parts was revealed. The ultimate compressive strength of 55% porous green scaffolds printed along the Y-axis and dried in a vacuum oven for 6h was 0.88 ± 0.02 MPa. Critically, the pores of 3D printed constructs could be user designed, ensuring bulk interconnectivity, and the imperfect packing of powder particles created an inherent surface roughness and non-designed porosity within the scaffold. These features are considered promising since they are known to facilitate osteoconduction and osteointegration in-vivo. Characterisation techniques utilised in this study include two funnel flow tests, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), compressive strength testing and computed tomography (CT).

Preparation and characterisation of nanophase Sr, Mg, and Zn substituted hydroxyapatite by aqueous precipitation.

Hydroxyapatite (HA) substituted with 2 mol% Sr, 10 mol% Mg, and 2 mol% Zn were precipitated under identical alkaline conditions (pH 11) at 20°C from an aqueous solution. As-synthesised materials were confirmed to be phase pure by XRD and samples prepared in air contained surface adsorbed CO2 as observed by FTIR. SEM studies revealed a globular morphology and agglomeration behaviour, typical of precipitated nHA. EDS spectra confirmed nominal compositions and substitution of Sr, Mg and Zn. At the levels investigated cationic doping was not found to radically influence particle morphology. An indication of the potential in-vivo bioactivity of samples was achieved by analysing samples immersed in SBF for up to 28 days by interferometry and complementary SEM micrographs. Furthermore, a live/dead assay was used and confirmed the viability of seeded MC3T3 osteoblast precursor cells on HA and substituted HA substrates up to 7 days of culture.

Low temperature aqueous precipitation of needle-like nanophase hydroxyapatite.

The use of tissue engineered biodegradable porous scaffolds has become an important focus of the biomedical research field. The precursor materials used to form these structures play a vital role in their overall performance thus making the study and synthesis of these selected materials imperative. The authors present a comparison and characterisation of hydroxyapatite (HA), a popular calcium phosphate (CaP) biomaterial, synthesised by an aqueous precipitation (AP) method. The influence of various reaction conditions on the phase, crystallinity, particle size as well as morphology, molecular structure, potential in-vivo bioactivity and cell viability were assessed by XRD, SEM and TEM, FTIR, a simulated body fluid (SBF) test and a live/dead assay using MC3T3 osteoblast precursor cells, respectively. Naturally carbonated nanoparticles of HA with typically needle-like morphology were synthesised by the reported AP method. Initial pH was found to influence the crystallisation process and determine the CaP phase formed as well as the resultant particle and crystallite sizes. A marked change in particle morphology was also observed above pH 9. The use of toluene as a replacement solvent for water up to 60% was found to reduce the crystallinity of as-synthesised HA. This has marked influence on the effect of ethanolamine (5 wt%), which was found to improve HA crystallinity. SEM and EDS were used to confirm the growth of carbonated apatite on the surface of HA pellets immersed in SBF for up to 28 days. Cell culture results revealed viable cells on all samples where pH was controlled and maintained at 10-11 during precipitation, including those that used ethanolamine and toluene in preparation. When the initial alkali pH was not maintained non-viable cells were observed on HA substrates.

Biomaterial scaffolds for tissue engineering.

Reconstruction and regeneration of new tissues are challenges facing scientists, technologists and clinicians. This review describes strategies of selection and design of biomaterials having significant impact on various possible synthesis routes for scaffold fabrication. The criteria for three-dimensional (3D) scaffold architectures are explored in tandem with biomaterial properties such as porosity, interconnectivity and mechanical integrity. The cell-surface biointerface is outlined in terms of biomaterial composition, target tissues and biological evaluation with emphasis on bone tissue engineering. Comparative merits and demerits of conventional and rapid prototyping (RP) approaches of fabrication are discussed. The conventional methods are often simple to design, inexpensive and flexible to optimise or modulate physicochemical properties. Despite being expensive and suffering from certain drawbacks of choice of materials and capital costs many generic RP techniques are extremely attractive in their ability to mimic new tissue structures and possibility of incorporating pharmaceutical agents. The future directions include scaffold development using nanobiomaterial based biosystems /biointerfaces where cell biology including genetically modified tissue engineering approaches can play a cross-disciplinary role for the success of tissue augmentation.

Three-dimensional porous bioscaffolds for bone tissue regeneration: fabrication via adaptive foam reticulation and freeze casting techniques, characterization, and cell study.

Highly interconnected and 3D porous bioactive hydroxyapatite (HAP) and Bioglass scaffolds have been fabricated by an adaptive version of camphene based foam reticulation (ARM) and camphene freeze casting (CFC) methods. Controlled sublimation of camphene during freeze casting at -78°C produced process optimized bioscaffolds with open, uniform, and interconnected porous structures. HAP and Bioglass scaffolds with desired porosity, pore size, and microtopography were successfully fabricated using polyurethane foam templates of appropriate structures. Macropores of 50-1100 µm with microporosity of 1-10 µm, known to facilitate cell adhesion and proliferation, were obtained. Compressive yield strength of 0.8 MPa close to the upper range of cancellous bone was achieved. The mean compressive strength of HAP scaffolds compared favorably with the theoretical model of porosity variation with strength and was higher than reported values. The nature of pore development, morphology, porosity, crystal structure, chemical composition, and thermal behavior were characterized using scanning electron and optical microscopy, X-ray diffraction, thermal analysis, and mercury porosimetry. These scaffolds are suited for nonstructural graft and were not cytotoxic in vitro when osteoblast-like MG63 cells were cultured with the HAP constructs. The cells attached indicated by cell metabolic activity by resazurin assay and spread well when cultured on the surface of the materials.