A Novel Technology and Stereotactic Accessory for Implanting Engineered Tissues,Cells,and Scaffold Materials into the Brain

Abstract

Disrupted circuitry in the adult mammalian central nervous system (CNS) is notoriously difficult to repair/reconstruct because of the inhibitory nature of the adult CNS. A novel strategy to bridge and/or re-establish damaged axonal connections is proposed here, where the complex environs of the adult CNS is circumvented via the implantation of neurons (and their projections) prematured from precursor cells in vitro. The concept (developed with laboratory rodents) involves the construction of a tubular scaffold that can both support the in vitro growth of neural tissue/cells, and be implanted, intact, in a way that bridges distal portions of the CNS. The important feature of this method is that it offers a unique technique for implanting neuronal tissues/cells into the CNS without altering the construct's spatial organization, or substantially disrupting the host tissue.

The method is comprised of three main component parts (Fig. 1).

FIG. 1.

Schematic diagram of the combined technology. Component I: (a) The scaffold is formed within the tip of the implantation needle, using the phase inversion method, from degradable and biostable polymers and then sterilized; (b) the needle is filled with culture medium and cells/tissues aspirated into the scaffold; (c) after culturing, the grown neuronal construct is ready for implantation. Component II: (d) before surgery, a supplementary tubular plunger is inserted into the needle filled with culture media; (e) the needle is fitted on the syringe of the implantation device; (f, f′) the supplementary plunger is then positioned exactly between the construct and the plunger of the syringe. Component III: (g) the implantation accessory is mounted onto the arm of the stereotaxic frame. Component IIIa depicts the construct deposition mechanism: (h) the needle is retracted while both the plunger and the construct are maintained in place; (i) the construct is laid out into the cavity formed by the retracting needle.

Component I—the technique for preparing scaffolds

The scaffold, made from suitable polymers, is a hollowed shell formed at the tip of an implantation glass needle. It is subsequently filled with cells/tissue (either primary or stem) suspended within a collagen-based gel, where the cells/tissues readily grow into three-dimensional structures.

Component II—the assembly to control the displacement of the grown construct from the capillary glass needle

To displace the neuronal construct from the needle, a tubular supplementary plunger is used to extend the action of the plunger from a standard Hamilton syringe (to which the needle is attached). This plunger is composed of glass capillary and has an external diameter matching exactly the internal diameter of the needle containing the construct.

Component III—an implantation accessory

The assembled syringe and needle (containing the matured neural construct) is subsequently affixed to an implantation accessory attached to a standard stereotaxic frame. For implantation, the tip of the needle is positioned at a desired point within the brain using stereotactic controls. The implantation accessory is then used to retract the needle to a distance equal to the length of the neural construct while the scaffold movements itself are blocked by the assembled plunger. Consequently, the scaffold remains in its position and is laid out into the space left by the retracting needle. Such low-force deposition of the construct and the encasement of the implanted material in the scaffold shell protect the spatial organization of the neuronal wires during the implantation procedure and limit damage to the host tissue.

The successful implanting of the grown neuronal constructs in our rat model (Fig. 2) indicates the novelty and feasibility of the technology. This set of techniques creates a methodology for the implantation of tissue-engineered constructs into a living CNS environment while keeping trauma to a minimum. The technology could be expanded for use in introducing other devices or implants containing various therapeutic agents into a range of mammalian species.

FIG. 2.

Histological image of a rat brain showing the implanted grown neuronal construct. The black arrow indicates the scaffold and the white arrow points the neuronal tissues.