Tissue engineering - Orthopaedic Biomaterials in Research and Practice - page 239

Standards
Tissue engineering is still relatively nascent in terms of its development.
The testing and evaluation of tissue-engineered products are extremely
varied owing to the numerous classes of products, indications, and
approaches to design and production. The standards process for tissue-
engineered medical products first began in 1997, when categories of
importance were developed. Since then, several standards have been
developed by the American Society for Testing and Materials (ASTM).
For example, the ASTM has provided guidance on writing materials
specification for raw or starting biomaterials, which are intended for use
in tissue-engineering scaffolds for growth, support, or delivery of cells
or biomolecules (ASTM F2027: Standard guide for characterization and
testing of raw or starting biomaterials for tissue-engineered medical
products). This standard takes advantage of existing test methods and
standards for contemporary biomaterials and covers the specifications
and characterizations of these biomaterials. However, because the focus
of this standard is on the raw or starting materials, this standard does not
provide safety and biocompatibility requirements for evaluations that are
typically performed on the final form of the product. Guidance for the
characterization and testing of biomaterials after they have been formed
into 3D scaffolds is provided by ASTM F2150 (Standard guide for charac-
terization and testing of biomaterial scaffolds used in tissue-engineered
medical products). This will be discussed in Chapter 10, along with other
relevant standards ASTM F2212 (Standard guide for characterization of
Type I collagen as starting material for surgical implants and substrates
for tissue engineered medical products [TEMPS]) and ASTM F2347
(Standard guide for characterization and testing of hyaluronan as start-
ing materials intended for use in biomedical and tissue engineered medi-
cal product applications).
The physicochemical attributes of the raw or starting biomaterial
used in tissue-engineered scaffolds carry significant potential to affect
product performance through affecting cell behavior or the release of
bioactive molecules or drugs. Thus, ASTM F2027 seeks to recom-
mend specifications or characterizations of raw or starting biomateri-
als to ensure reproducibility prior to their fabrication into implantable
tissue-engineered scaffolds or controlled release matrices. The speci-
fied chemical requirements for the biomaterials depend on the class of
material (ceramics, metals, polymers, composites) (Table 9.1). Natural
materials made of proteins, nucleic acids, or polysaccharides are clas-
sified as polymers, while anorganic bone and other naturally occurring
inorganic substances are classified as ceramics. All classes of materials
require information about the chemical formula or composition. In addi-
tion, for ceramics, chemical specifications include, but are not limited
to, phase content, purity, major/minor elemental constituents, processing
aids, and the allowable amount of foreign material contaminants. For
metals, typically specified chemical requirements include phase content,
purity, major/minor elemental constituents, corrosion susceptibility, and