The production of complex inorganic forms, based on naturally occurring scaffolds offers an exciting avenue for the construction of a new generation of ceramic-based bone substitute scaffolds. The following study reports an investigation into the architecture (porosity, pore size distribution, pore interconnectivity and permeability), mechanical properties and cytotoxic response of hydroxyapatite bone substitutes produced using synthetic polymer foam and natural marine sponge performs. Infiltration of polyurethane foam (60 pores/in2) using a high solid content (80wt %), low viscosity (0.126Pas) hydroxyapatite slurry yielded 84-91% porous replica scaffolds with pore sizes ranging from 50?m - 1000?m (average pore size 577?m), 99.99% pore interconnectivity and a permeability value of 46.4 x10-10m2. Infiltration of the natural marine sponge, Spongia agaricina , yielded scaffolds with 56- 61% porosity, with 40% of pores between 0-50?m, 60% of pores between 50-500?m (average pore size 349 ?m), 99.9% pore interconnectivity and a permeability value of 16.8 x10-10m2. The average compressive strengths and compressive moduli of the natural polymer foam and marine sponge replicas were 2.46±1.43MPa/0.099±0.014GPa and 8.4±0.83MPa /0.16±0.016GPa respectively. Cytotoxic response proved encouraging for the HA Spongia agaricina scaffolds; after 7 days in culture medium the scaffolds exhibited endothelial cells (HUVEC and HDMEC) and osteoblast (MG63) attachment, proliferation on the scaffold surface and penetration into the pores. It is proposed that the use of Spongia agaricina as a precursor material allows for the reliable and repeatable production of ceramic-based 3-D tissue engineered scaffolds exhibiting the desired architectural and mechanical characteristics for use as a bone 3 scaffold material. Moreover, the Spongia agaricina scaffolds produced exhibit no adverse cytotoxic response.

Macroporosity(>100?m) in bone void fillers is a known prerequisite for tissue regeneration, but recent literature has highlighted the added benefit of microporosity(0.5 - 10?m). The aim of this study was to compare the in vitro performances of a novel interconnective microporous hydroxyapatite (HA) derived from red algae to four clinically available macroporous calcium phosphate (CaP) bone void fillers. The use of algae as a starting material for this novel void filler overcomes the issue of sustainability, which overshadows continued use of scleractinian coral in the production of some commercially available materials, namely Pro-Osteon TM and Bio-Coral ® . This study investigated the physicochemical properties of each bone voidfiller material using x-ray diffraction, fourier transform infrared spectroscopy, inductive coupled plasma, and nitrogen gas absorption and mercury porosimetry. Biochemical analysis, XTT, picogreen and alkaline phosphatase assays were used to evaluate the biological performances of the five materials. Results showed that algal HA is non-toxic to human foetal osteoblast (hFOB) cells and supports cell proliferation and differentiation. The preliminary in vitro testing of microporous algal-HA suggests that it is comparable to the four clinically approved macroporous bone void fillers tested. The results demonstrate that microporous algal HA has good potential for use in vivo and in new tissue engineered strategies for hard tissue repair.

Critical-sized bone defects, whether caused by congenital malformation, tumor resection, trauma, or implant loosening, remain a major challenge for orthopaedic management. In this study we describe a bone tissue engineering approach in mice for the co-delivery of recombinant human Bone Morphogenetic Protein-2 (rhBMP-2) and the IKK inhibitor PS-1145.

Scaffold implants were manufactured from poly(lactide-co-glycolide)(PLGA) by Thermally-Induced Phase Separation (TIPS), with rhBMP-2 (10 μg) and the IKK inhibitor PS-1145 (0 μg, 40 μg or 80 μg) incorporated into the polymer. These scaffolds were then surgically implanted into the hind limb muscle of C57BL6/J mice. One group of mice also received systemic 50 mg/kg PS-1145 (days 11-20). Specimens were harvested at week 3 for X-ray and microCT analyses and descriptive histology.

Local and systemic delivery PS-1145 both significantly increased the net rhBMP-2 induced bone at 3 weeks. A maximal response was seen with the 40 μg PS-1145 group, although there was no significant difference between the 40 μg and 80 μg PS-1145 regimens. No local cytotoxicity was seen with either dose of PS-1145. In summary, local co-delivery of rhBMP-2 and PS-1145 via a porous PLGA scaffold represents a new tissue engineering approach for maintaining new bone in an unloaded environment.

Dynamic and cellular histomorphometry of trabeculae is the most biologically relevant way of assessing steady state bone health. Traditional measurement involves manual visual feature identification by a trained and qualified professional. Inherent with this methodology is the time and cost expenditure, as well as the subjectivity that naturally arises under human visual inspection. In this work, we propose a rapidly deployable, automated, and objective method for dynamic histomorphometry. We demonstrate that our method is highly effective in assessing cellular activities in distal femur and vertebra of mice which are injected with calcein and alizarin complexone 7 and 2 days prior to sacrifice. The mineralized bone tissues of mice are cryosectioned using a tape transfer protocol. A sequential workflow is implemented in which endogenous fluorescent signals (bone mineral, green and red mineralization
lines), tartrate resistant acid phosphatase identified by ELF97 and alkaline phosphatase identified by Fast Red are captured as individual tiled images of the section for each fluorescent color. All the images are then submitted to an image analysis pipeline that automates identification of the mineralized regions of bone and selection of a region of interest. The TRAP and AP stained images are aligned to the mineralized image using strategically placed fluorescent registration beads. Fluorescent signals are identified and are related to the trabecular surface within the ROI. Subsequently, the pipelined method computes static measurements, dynamic measurements, and cellular activities of osteoclast and osteoblast related to the trabecular surface. Our method has been applied to the distal femurs and vertebrae of 8 and 16 week old male and female C57Bl/6 mice. The histomorphometric results reveal a significantly greater bone turnover rate in female in contrast to male irrespective of age, validating similar outcomes reported by other studies.

Tissue engineering has emerged as a potential alternative or complementary solution to organ failure or damage. Adult stem cell based approaches can provide a powerful platform for regeneration, given these cells capacity to differentiate into multiple tissues, given the appropriate signals. However, a barrier in the development of tissue in 3D constructs is the transport limitations of nutrients and by products to the core, producing low volumes of regenerated tissue. The microenvironment in the immediate vicinity of the cells, the number of cells that adhere to the substrate and their localization may play an important role in differentiation and tissue regeneration. In this study, we aim to overcome compromised development of hard tissue using 3D cell-based tissue engineering strategies. Specifically, we quantified the effect of a biomimetic template and cell seeding techniques in Gap Junction Intercellular Communication (GJIC), differentiation (Osteocalcin and Alkaline Phosphatase mRNA) In-vitro and bone volume fraction (In-vivo) of adult stem cells (Bone Marrow Stromal Cells) seeded in 3D rigid scaffolds. Significant increases in amount and distribution of bone were achieved when altering both the template and initial seeding conditions. Our findings indicate that creating a biomimetic environment and altering initial seeding conditions that enhance cell adhesion and cell-cell communication in rigid scaffolds are powerful strategies to overcome the incomplete regeneration of cell-based engineered tissue.