Introduction to artificial cells: concept, history, design, current status and future - Artificial Cells, Cell Engineering and Therapy - page 10

Table 1.3 Selection considerations of biomaterials and methods used for cell
encapsulation

Material characteristics/chemistry
· Availability of clinical grade materials with reproducible characteristics
· Potential impurities and leachable residues, e.g. endotoxin, solvent, additive,
initiator, cross-linker, pore-forming agent, precipitating agent
· Biocompatibility, non-cytotoxicity to both host and encapsulated cells
· Non-thrombogenity if contacted with blood, non-tumorigenity
· Must not trigger host immune response
· No interference with cell functions in vitro and in vivo
· Sterilization options for materials
· Cost

Formulation and processing
· Ease of processing
· Reproducibility of critical desired features
· Complete encapsulation
· Lackof harshchemicals, temperaturesor pHneeded for synthesis andcrosslinking
· Maintenance of cell survival and function during processing and storage (for pre-
formed device)
· Sterilization during processing and after manufacture
· Ease of sealing

Artificial cell properties
· Geometry, surface morphology and charge, dimensions scaled between species
and implant sites
· Adequatemechanical integrity towithstand handling, application and retrieval (if
needed), minimize defects
· Provide suitable extracellular microenvironment for cell growth and proliferation
· Highly selective permeability (high diffusion in the low MW nutrient range and
low diffusion in the high MW immunoglobulin range)
· Adequate stability of critical properties (e.g. membrane transport and resistance
to biodegradation) in the host environment for the implant lifetime
· Appropriate biodegradability if desired
· Alternation of the host physiology of the biological fluids/tissue environment
(material itself and potential degraded substance)

1.3 (opposite) Photomicrographs of (A) HepG2mammalian cells encapsulated
in alginate±chitosan±polyethylene glycol (PEG) ± poly- L -lysine±alginate
(ACPPA) microcapsules in minimum essential medium (MEM) 5 days after
coating, empty ACPPA microcapsules in physiological solution. Capsule size:
45030m. (Magnification: 6.5).

53

(B) Alginate-poly- L -lysine±alginate
(APA) membrane system for encapsulation and oral delivery of empty
microcapsules and microcapsules containing E. coli DH5 cells.

37,57

(C) APA
microcapsules for oral delivery of thalidomide and photomicrograph of
alginate±chitosan microcapsule (right) under 250 magnification.

55

(D)
Encapsulated HepG2 cells in alginate±poly- L -lysine±PEG±alginate (APPA)
microcapsules 1 day after encapsulating; magnification: 10, size: 450 m
and alginate±chitosan±PEG (ACP) microcapsules 1 week after encapsulating;
magnification: 10, size: 450 m.

51

(E) CLSM (confocal laser scanning
microscopy) images of genipin crosslinked microcapsules under normal and
fluorescent light. Bars represent 200 m. 111