Bioinspired materials for regenerative medicine: going beyond the human archetypes

Living organisms are skilful innovators and fabricators of materials, driven by the forces of evolution. We describe the translation process between natural material innovations and human tissue engineering.

Trace elemental imaging of coralline hydroxyapatite by laser-ablation inductively coupled plasma-mass spectroscopy

The determination of trace element concentrations, as well as their distribution in different biomaterials aimed for clinical applications, is a challenging task in both the areas of biological and materials research. In this research, LA-ICP-MS was employed for image mapping of the trace element distribution in a hydrothermally converted coralline hydroxyapatite material aimed for tissue-scaffolding applications. Quantification using synthetic matrix-matched standards was successfully applied for the determination and distribution of elements of interest, Sr and Mg, that influences the mechanical and biological properties of hydroxyapatite-based bone graft materials. The results showed that the instrument can successfully analyse trace elements and a relatively good image can be produced that identifies their distribution. The LA-ICP-MS method can provide an easy and effective tool, in the field of biomaterials with respect to distribution of trace elements, to better understand tissue-implant interactions, and will open up a new window for in vitro and in vivo analysis and imaging of different tissues and structures.

Strontium- and magnesium-enriched biomimetic β-TCP macrospheres with potential for bone tissue morphogenesis

During the last two decades, biogenic mineral ions have become important additives in treatments for bone regeneration and repair. Prominent among these is strontium, which is a potent suppressor of osteoclast bone resorption. Another is magnesium, which has a key influence in mineralization processes. The shells of benthic foraminiferans, hydrothermally converted into β-TCP, have been shown to effectively release a number of bone-promoting drugs at clinically relevant levels. In this study we characterized the effects of converted foraminiferan calcium dissolution and the concomitant release profile of intrinsic strontium and magnesium. We tested the effects of strontium- and magnesium-enriched macrospheres on human osteoblast (SaOS-2) and monocytoid (U937) cell lines, which can be induced to express equivalent phagocytic activities to osteoclasts. On dissolution in a biomimetic physiological solution, the macrospheres released biologically significant quantities of calcium and phosphate ions in the first 18 days. At 3 days, during which biogenic mineral ions are released, the number of U937 osteoclast-like monocyte cells decreased, while 4 days later the osteoblast cell number increased. These results show that strontium and magnesium naturally enriched macrospheres are capable of altering the metabolic activities of the cells regulating bone homeostasis. These unique macrospheres are natural origin bone void filler particles that resorb, and release physiologically significant levels of incorporated strontium, magnesium and calcium, which together make a uniquely multifunctional in situ remedy for bone regeneration and repair and the treatment of bone-wasting diseases.

In vivo patency of endothelial cell-lined expanded polytetrafluoroethylene prostheses in an ovine model

The performance of small-diameter vascular prostheses may be improved by implantation of grafts lined with endothelial cells. Expanded polytetrafluoroethylene (ePTFE) prostheses (4 mm x 40 mm) were coated with fibronectin (20 micrograms/ml), seeded with endothelial cells, and cultured for 48 h to produce a confluent, autologous endothelial cell lining. They were implanted as carotid interposition grafts in sheep. Seeded ePTFE grafts were compared with nonseeded ePTFE grafts and autologous carotid artery grafts. No anticoagulant or antiplatelet therapy was administered, making this a stringent test model for the thromboresistance of a small-diameter prosthesis. After 13 weeks the patencies of seeded, nonseeded, and autologous artery grafts were 16% (1/6), 0% (0/6), and 100% (6/6), respectively. The one seeded graft that was patent was fully lined with endothelial cells and showed no stenosis. The remaining five seeded grafts were occluded by fibrous tissue and displayed substantial spindle cell hyperplasia. There was no apparent difference between the autologous artery grafts and normal arterial tissue, and the anastomoses showed no stenosis. The ovine model provides a conservative test of prosthesis survival and may be useful for study of graft failure.

Induction of endothelial cell migration by proline analogs and its relevance to angiogenesis

The proline analogs cis-4-hydroxy-L-proline, 3,4-dehydro-L-proline, and 2-azetidinecarboxylic acid induced increases in the migration rate of retinal capillary endothelial cells, aortal endothelial cells, corneal endothelial cells, aortal smooth muscle cells, and retinal pericytes. cis-4-hydroxy-D-proline did not. The optimal concentration for migration induction by any of the active agents was approximately 10(-5) M. At higher concentrations (5 x 10(-4) M) migration was not induced or was inhibited. When tested by subcutaneous implant assays in rabbits, cis-4-hydroxy-L-proline and 2-azetidinecarboxylic acid consistently elicited a marked angiogenic response. Whereas these compounds are known to modulate collagen synthesis and secretion, the concentrations at which they are effective inducers of migration suggest that they may have a more specific target than general collagen synthesis.