BIOREACTOR-BASED ENGINEERING OF OSTEOINDUCTIVE GRAFTS

Abstract

A major challenge to be faced in order to introduce cell-based therapies for bone repair into wide-spread surgical practice is to translate a research-scale production model into a manufacturing design that is reproducible, clinically effective, and economically viable. One possible means by which to achieve this goal is via a bioreactor system capable of controlling, automating, and streamlining all of the individual phases of the bone-tissue engineering process. In a first step to meeting this challenge, in this work we aimed at developing and validating a closed bioreactor system for

1. the efficient seeding of cells into 3-dimensional scaffolds and

2. the generation of osteoinductive constructs starting from human bone marrow-derived cells.

Our patented bioreactor technology essentially consists of scaffolds arranged in a circular plate, which is moved in alternating directions by a linear drive unit through a cell suspension/culture medium, thus resulting in the perfusion of the cell suspension/culture medium directly through the pores of the scaffolds in alternate directions. The cultivation chamber is fully isolated from the external environment, with liquid/gas exchange achieved through aseptic interfaces.

Human bone marrow nucleated cells from 3 donors were perfused through porous ceramic discs (8 mm diameter, 4 mm thick), resulting in adhesion of the osteoprogenitor cell fraction in the ceramic scaffolds. Efficiency of cell seeding was consistently greater than 80%. Cell seeded constructs were further cultivated under perfusion for a total of 20 days, resulting in the expansion of the osteoprogenitor cells directly within the scaffold pores and maintenance of greater than 90% cell viability. Ectopic implantation of the cultivated constructs yielded abundant and reproducible formation of bone tissue, distributed throughout the scaffold pores.

The developed bioreactor provides a simple and efficient approach

1. to establish and maintain 3D cultures of cells into scaffolds under perfusion, and

2. to generate osteoinductive grafts starting from minimally processed bone marrow aspirates and bypassing typical cell expansion in monolayers.

Incorporating the bioreactor unit into a system for automated medium change and monitoring/control of culture parameters is likely to lead to the development of a closed system for the standardized production of autologous cell-based bone substitutes.