FACTORS INFLUENCING THE IN VIVO BIOMATERIAL INTERFACE: Cellular recruitment and differentiation in BONE

C. Rolfe Howlett, Nan Chen, David Lickorish, Ross Odell and Hong Zhou*

Dept of Pathology, University of New South Wales Sydney N.S.W. 2052, Australia
* Anzac Laboratory Concord Hospital, University of Sydney, N.S.W. 2006 Australia.

Following preparation of a site for the implantation of a biomaterial, the following tissue responses will take place regardless of whether the device or construct or material is present.

1. Traumatic inflammation with dominant phagocytosis of debris by macrophages.

2. Reparative ingrowth of tissue from adjoining viable sites (soft and hard tissue).

3. Differentiation of these reparative tissues.

4. Complete filling of the implant site by vascularized undifferentiated mesenchymal tissue followed by its centripetal osteogenic differentiation.

5. Young reparative osseous tissue is remodelled under the influence of many humoral and mechanical factors. The latter being important in the final equilibrium established between the adult (lamellar) reparative bone fusing to the pre-existent skeleton.

Placement of a construct of bioceramics, for instance, into the site adds further complexity to the expected healing response. In this circumstance major events that should be considered are:

A. Osteogenic cellular recruitment
B. Differentiation within a porous biomaterial.
C. Remodelling of the initially formed reparative osseous tissue together with the early - established interface between bone and bioceramic.

The chemistry of a biomaterial appears to influence the long termed interface formed and this appears to be independent of the amount bone enclosing the implant.

CELLULAR RECRUITMENT VERSUS DIFFERENTIATION

The understanding and separation of these 2 issues, as they are intimately intertwined, is demanding. It is proposed to discussed these issues in light of results obtained from a delayed healing calvarial defect and a non healing (critical sized) calvarial defect in the same species and age. Finally when designing a device and the materials to be used in its construction it is essential to characterize the mechanical forces that will be applied to the device as well as the underlying disease that necessitates reconstructive surgery and device implantation.

Biomaterials and Biocompatibility Challenges in Mechanical Circulatory Support Devices

John Woodard, Ventracor Limited, 126 Greville Street, Chatswood NSW 2067 Australia

Ventracor is an Australian based manufacturer of a Left Ventricular Assist System (LVAS), more commonly known as an “artificial heart”. The LVAS consists of an implantable blood pump and external control and power systems that supports the circulation of patients in severe heart failure. The company employs approximately 130 people, the majority of which are involved in research and development, manufacturing and quality assurance in Sydney.

Because the system is intended for permanent implant and is a life support system, excellent biocompatibility and extreme reliability are prerequisites. However, careful tradeoffs are required in materials choices, surface finishes and technology for commercial viability and to ensure a smooth regulatory approval process. Ventracor has chosen to concentrate on technologies that optimise both antithrombgenicity and minimise haemolysis using some novel approaches such as custom diamond-like carbon coatings on blood contacting surfaces.

Ventracor has conducted a number of research projects to evaluate the choice of biomaterials, surface finishes and engineering tolerances on the performance of the system. In addition to preclinical in vitro and in vivo testing, the effect of these choices has been recently evaluated in clinical trials in Australasia, Europe and USA with encouraging results.

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