“Tissue Engineering Grade” Reagents and Materials: Grade Meaning, Critical Quality Attributes, and Selection Methods
“Tissue Engineering Grade” Reagents and Materials: Grade Meaning, Critical Quality Attributes, and Selection Methods
In tissue engineering research, materials are used not only as reaction raw materials but may also come into direct contact with cells, encapsulate cells, form three-dimensional scaffolds, or participate in the construction of bioinks and injectable hydrogels. Therefore, the evaluation of these products cannot be based solely on chemical purity. Residues, microbial and endotoxin control, material functionality, cytocompatibility, and batch-to-batch consistency must also be considered.
“Tissue engineering grade” is commonly used to indicate that a product has quality specifications or application validation tailored to tissue engineering research. It is more appropriately regarded as a product specification designation based on intended use rather than a general statutory grade defined by a uniform purity value.
1 What Does “Tissue Engineering Grade” Mean?
1.1 Basic Meaning
“Tissue engineering grade” generally means that a product has been subject to targeted control of its chemical composition, impurities, material properties, or cell-related applications according to the requirements of tissue engineering research.
These products are commonly used in:
① Cell encapsulation and three-dimensional culture;
② Preparation of hydrogels or porous scaffolds;
③ Three-dimensional bioprinting;
④ Cell–material interaction studies;
⑤ Construction of drug- or cell-delivery matrices;
⑥ Material degradation and tissue regeneration models.
Compared with general-purpose synthetic raw materials, tissue engineering-grade products may include additional controls or information regarding:
① Impurities and residues that may affect cell status;
② Inhibitors, degree of functionalization, and residual monomers that may affect crosslinking reactions;
③ Molecular weight, viscosity, gelation time, and rheological properties;
④ Endotoxins, microorganisms, or material sources;
⑤ Cell-related testing under specified conditions;
⑥ Consistency of critical parameters between batches.
1.2 “Tissue Engineering Grade” Is Not a Uniform Statutory Reagent Grade
Existing publicly available standards have established requirements for tissue-engineered medical products, raw-material characterization, hydrogels, scaffolds, and biological evaluation. However, no uniform set of limits for “tissue engineering-grade reagents” applicable to all chemicals and biomaterials has been established.
YY/T 1445—2016 specifies terminology for tissue-engineered medical device products. ISO/TS 21560:2020, issued by the International Organization for Standardization (ISO), specifies general requirements for tissue-engineered medical products in terms of materials, manufacturing, quality control, and unintended biological effects. ASTM F2027—25 provides guidance for developing specifications for raw or starting materials used in tissue-engineered scaffolds. None of these documents provides a uniform set of purity, endotoxin, sterility, or mechanical-performance limits under a grade called “tissue engineering grade.” [1–3]
This means that even when different products are all labeled “tissue engineering grade,” their test items and acceptance criteria may still differ. For example, a crosslinkable polymer may focus on the degree of functionalization and inhibitor content; a natural polysaccharide may focus on molecular weight, residual proteins, and endotoxin; and a bioink may additionally require evaluation of rheological properties and printability.
1.3 Who Determines the Specific Meaning of “Tissue Engineering Grade”?
The practical meaning of “tissue engineering grade” is generally shaped jointly by standard requirements, supplier specifications, and user requirements.
Entity | Primary Role | Influence on Product Selection |
Standards-setting organizations | Provide terminology, principles, and characterization methods for tissue-engineered products, raw materials, hydrogels, scaffolds, and biological evaluation | Indicate which attributes require attention but generally do not directly define commercial grades |
Product suppliers | Establish product specifications, test methods, acceptance criteria, and batch-release test items | Determine the actual technical meaning of “tissue engineering grade” for a specific product |
Product users | Establish acceptance requirements according to cell type, mode of contact, material application, and stage of research | Determine whether the specifications provided by the supplier meet the requirements of a specific experiment |
A practical conclusion can therefore be drawn:
Standards provide the basis for evaluation, suppliers provide product data, and users determine suitability according to the intended experimental application.
1.4 How Does YY/T 1445—2016 Help in Understanding “Tissue Engineering Grade”?
YY/T 1445—2016, Tissue-Engineered Medical Device Products—Terminology, defines terms including tissue engineering, tissue-engineered medical products, tissue-engineered medical device products, scaffolds, biomaterials, biocompatibility, hydrogels, porosity, permeability, processing, and adventitious agents.
The standard also defines “processing materials” as materials that come into contact with cells, tissues, or organs during processing but do not form part of the tissue-engineered medical device product. Its relational schematic connects tissue components, biomaterials, biomolecules, technological principles, manufacturing processes, tissue-engineered products, and intended repair functions. [1]
These definitions help distinguish between:
① The scaffold body and ancillary processing materials;
② Raw materials and final tissue-engineered products;
③ Chemical composition and biological applications;
④ The intrinsic properties of a material and its properties after processing.
2 What Can the “Tissue Engineering Grade” Label Indicate?
2.1 Potential Quality-Control Elements
Tissue engineering-grade specifications for different products may contain the following five categories of information.
Quality Dimension | Potential Indicators | Influence on Experimental Results |
Chemical identity and composition | Chemical structure, main-component content, molecular weight, composition ratio, degree of substitution, and degree of functionalization | Determine material identity, reactivity, and network structure |
Impurities and residues | Residual monomers, solvents, catalysts, crosslinking agents, inhibitors, preservatives, and metal impurities | May affect cell status, crosslinking efficiency, and material stability |
Biological and microbiological items | Endotoxin, sterility, microbial limits, mycoplasma, adventitious agents, and animal-origin information | Affect cell culture, animal experiments, and source-related risk assessment |
Material functionality | Solubility, viscosity, gelation time, rheological properties, mechanical properties, swelling, degradation, and mass transport | Determine whether a hydrogel, scaffold, or bioink can form the intended structure |
Consistency and documentation | Batch specifications, test methods, certificates of analysis, raw-material sources, stability, and change information | Affect experimental reproducibility and the continuity of long-term projects |
Not every tissue engineering-grade product needs to be tested for all the items listed in the table. The test items should correspond to the material type, mode of contact, and intended use.
For example, an ordinary buffer salt may not require rheological or mechanical testing, whereas a photocrosslinkable polymer used for cell encapsulation may require simultaneous evaluation of the degree of functionalization, photoinitiation conditions, gelation time, residues, and cell status.
2.2 Properties That Cannot Be Inferred Directly from the Grade Name
“Tissue engineering grade” itself cannot replace the following specific declarations or test results.
Property That Should Not Be Directly Inferred | Information Requiring Further Verification |
The product is already sterile | Whether sterilization has been performed, which process was used, and whether sterility testing has been completed |
The product is a low-endotoxin product | Endotoxin limit, unit, test method, and batch-specific result |
The product contains no animal-derived components | Source information for the primary raw materials, auxiliary materials, culture media, and manufacturing process |
The product is manufactured under Good Manufacturing Practice conditions | Manufacturing site, quality system, documentation, and change-management status |
The product is suitable for animal implantation | Sterilization, endotoxin, degradation products, final material, and evaluation of the animal-study protocol |
The product can be used for human or clinical manufacturing | Registered intended use, regulatory status, manufacturing quality system, and submission documentation |
Biocompatibility of the raw material means that the formulation is also biocompatible | Overall evaluation of crosslinking agents, initiators, processing, washing, sterilization, and final material form |
Biocompatibility is not a fixed property independent of intended use and test conditions. ISO 10993-1:2025 incorporates the biological safety evaluation of medical devices into the risk-management process. ASTM F2027—25 also states that compliance of a raw material with a material specification does not automatically demonstrate its suitability for a specific application, and that the final material may still require application-specific evaluation. [3,5]
2.3 How Commercial Products Reflect Different Specification Elements
Polyethylene glycol dimethacrylate (PEGDMA), Product No. 946192, is labeled “Tissue Engineering grade” in the product name. The supplier information lists the absence of added inhibitor, a degree of functionalization of not less than 90%, and low-cytotoxicity research testing under the recommended formulation and curing conditions as its principal features. [8]
Gelatin methacryloyl (GelMA), Product No. 938408, is specified primarily by a gel strength of 300 Bloom, a degree of substitution of 80%, and relatively low batch-to-batch variation, with its applications directed toward tissue engineering and three-dimensional bioprinting. [9]
These two examples demonstrate that:
① Synthetic photocrosslinkable polymers may emphasize terminal-group functionalization and inhibitor content;
② Modified natural materials may emphasize raw-material characteristics, degree of substitution, and batch-to-batch consistency;
③ “Suitable for tissue engineering” and “tissue engineering grade” are not identical product descriptions;
④ The technical meaning of a product grade must be assessed on the basis of its specific specifications and test documentation.
2.4 How Is “Tissue Engineering Grade” Translated into Specific Product Specifications?
Using Aladdin tissue engineering-grade chitosan products as examples, chitosan hydrochloride uses the degree of deacetylation as an important structural parameter, carboxylated chitosan uses the degree of carboxylation to characterize the extent of modification, and carboxymethyl chitosan improves the material’s aqueous-processability through carboxymethylation. These parameters affect material solubility, charge state, intermolecular interactions, crosslinking behavior, and subsequent functionalization.
Representative Aladdin Tissue Engineering-Grade Chitosan Products and Their Research Applications
Classification | CAS No. | Aladdin Catalog No. | Name | Specification or Purity | Product Features and Applications |
Water-soluble chitosan salt | 70694-72-3 | Chitosan hydrochloride | Tissue engineering grade, degree of deacetylation ≥90% | The hydrochloride form facilitates the dissolution and preparation of chitosan in aqueous systems. The degree of deacetylation characterizes the proportion of deacetylated units and amino groups. It may be used in water-soluble chitosan systems, polyelectrolyte complexes, hydrogels, scaffold materials, and cell–material interaction studies. | |
Carboxylated chitosan derivative | 9012-76-4 | Carboxylated chitosan | Degree of carboxylation ≥80%, tissue engineering grade | Carboxylation introduces carboxyl functional sites and improves adaptability to aqueous processing. It may be used in chitosan-based hydrogels, composite scaffolds, material-surface functionalization, and biomolecule-conjugation studies. The degree of carboxylation is an important parameter affecting material charge state, crosslinking reactions, and composite performance. | |
Carboxymethyl chitosan derivative | 83512-85-0 | Carboxymethyl chitosan | Tissue engineering grade | Carboxymethylation introduces carboxyl groups and improves the water solubility of chitosan. It may be used in hydrogels, composite scaffolds, material coatings, delivery carriers, and material-degradation studies. Practical applications must also be evaluated in conjunction with the degree of substitution, molecular weight, viscosity, and formulation conditions. |
The applications listed in the table are research directions summarized on the basis of material structure and common tissue engineering applications. They do not indicate that the products have been validated in all formulations, cell models, or animal models. For use in cell encapsulation, three-dimensional culture, or animal studies, information such as molecular weight, viscosity, sterility, endotoxin, microbial control, material source, and batch-specific certificates of analysis must still be verified.
3 Which Tissue Engineering Indicators Should Be Considered for Different Materials?
3.1 Different Materials Cannot Be Evaluated Using the Same Set of Indicators
Tissue engineering materials include synthetic polymers, natural polymers, proteins, polysaccharides, inorganic ceramics, and composite materials. Different materials perform different functions and therefore have different sources of risk and critical parameters.
ASTM F2027—25 states that raw-material specifications should be selected according to the safety, performance requirements, and risks of the specific product. The typical attributes listed in the document may not all be applicable and may not be sufficient to demonstrate that a material is suitable for a particular use. YY/T 1435—2016 separately lists biological properties, formation kinetics, physicochemical properties, stability, and mass transport as categories for hydrogel characterization. [3,4]
3.2 Key Indicators for Different Materials
Material Type | Key Indicators | Primary Reason |
Photocrosslinkable synthetic polymers | Molecular weight and distribution, degree of terminal-group functionalization, inhibitors, residual monomers, solvents, gelation time, and crosslinking conversion | Determine polymerization rate, network formation, and the amount of unreacted components |
Collagen and gelatin | Species and tissue source, collagen type, molecular integrity, gel strength, protein impurities, residual nucleic acids, endotoxin, and adventitious agents | Natural sources and processing may introduce biological impurities and batch-to-batch variation |
Modified proteins such as GelMA | Raw-material source, gel strength, degree of substitution, residual modification reagents, photoinitiation conditions, degradation, and mechanical properties | The degree of substitution and crosslinking density alter gel structure and the cellular environment |
Hyaluronic acid, alginate, and chitosan | Molecular weight, molecular-weight distribution, viscosity, degree of deacetylation or substitution, proteins, nucleic acids, metals, endotoxin, and gelation properties | Structural parameters affect solution behavior, crosslinking rate, and degradation |
Hydrogels and bioinks | Solid content, composition, gelation time, storage modulus, viscosity, shear response, printability, swelling, degradation, and cell-encapsulation performance | Must simultaneously meet the requirements of processing, structural formation, and cell culture |
Ceramic powders, particles, and composite-material raw materials | Crystal phase, chemical composition, particle size and distribution, specific surface area, trace elements, and dissolution or degradation behavior; after scaffold formation, porosity, pore size and distribution, pore interconnectivity, and mechanical properties should be evaluated separately | Determine the structural stability and material-release behavior of bone-related scaffolds |
Culture media, cytokines, enzymes, and antibodies | Biological activity, sterility, endotoxin, mycoplasma, source, batch-to-batch consistency, and process residues | Primarily used as cell-processing materials and do not necessarily serve a structural scaffold function |
Materials bearing the same name also cannot be replaced solely on an equal-mass basis. For example, two hyaluronic acid products may have different molecular weights and viscosities; two GelMA products may have different degrees of substitution; and two PEGDMA products may differ in terminal-group conversion or inhibitor status. After replacement, the formulation must be recalculated and the material performance reevaluated.
3.3 Scaffold Materials and Ancillary Processing Materials Must Be Evaluated Separately
Scaffold materials are generally intentionally retained in tissue-engineered constructs to support cells, form spatial structures, or regulate mass transport. Culture media, enzymes, cytokines, antibodies, and certain buffers are generally used during processing and removed in subsequent steps.
YY/T 1445—2016 defines processing materials as materials that come into contact with cells, tissues, or organs but do not form part of the tissue-engineered medical device product. [1]
ISO 20399:2022 applies to ancillary materials that contact active substances during cell processing but are not intentionally incorporated into cellular or gene-therapy products, and it explicitly excludes scaffolds from its scope. United States Pharmacopeia (USP) General Chapter 〈1043〉 similarly focuses on the selection, supplier evaluation, suitability, and residual control of ancillary materials used in the manufacture of cell, gene, and tissue-engineered products. [6,7]
Therefore, the quality requirements for culture media or cytokines cannot directly replace the evaluation of gelation, mechanical properties, and degradation of scaffold materials. Likewise, tissue engineering application data for scaffold materials cannot replace the evaluation of the activity, sterility, and residual control of ancillary materials.
4 Which Research and Experimental Applications May Use Tissue Engineering-Grade Products?
Experimental Scenario | Primary Reason for Selecting Tissue Engineering-Grade Products | Key Items Requiring Verification |
Three-dimensional cell culture | Materials remain in prolonged contact with cells and affect cell adhesion, migration, and morphology | Residues, endotoxin, gel properties, and cell-related testing |
Cell encapsulation | Cells are directly exposed to polymers, crosslinking agents, initiators, and the crosslinking process | Degree of functionalization, crosslinking conditions, unreacted components, and cell viability |
Hydrogel and scaffold preparation | Raw-material properties determine scaffold structure, mechanical properties, and degradation behavior | Molecular weight, viscosity, gelation time, swelling, and mechanical properties |
Three-dimensional bioprinting | Materials must simultaneously satisfy requirements for flow, extrusion, shape retention, and cell culture | Rheological properties, printability, crosslinking rate, and cell status |
Cell–material interaction studies | Material impurities, surface properties, and batch-to-batch differences may affect experimental conclusions | Surface properties, residues, batch-to-batch consistency, and material blank controls |
Degradation and tissue-regeneration studies | Materials and their degradation products remain in contact with cells or tissues | Degradation rate, degradation products, local pH, and biological responses |
Animal implantation and preclinical studies | The test system enters a complex biological environment, increasing requirements for source and contamination control | Sterility, endotoxin, source traceability, sterilization, and final-material evaluation |
For basic synthesis, structural characterization, reaction-condition screening, and early-stage material preparation that do not involve cell contact, synthetic grade, analytical reagent grade, or other suitable specifications may be selected according to the experimental stage. The value of tissue engineering-grade products lies primarily in whether their additional specifications correspond to the risks of the experiment.
5 Differences Between “Tissue Engineering Grade” and Related Product Grades
Grade or Product Designation | Primary Focus | Relationship to Tissue Engineering Applications |
Synthetic grade or general research grade | Chemical identity, content, and basic impurities | May be used for material synthesis and process exploration but generally lacks cell-related and material-function data |
Analytical reagent grade | Content and conventional impurities controlled according to applicable reagent specifications or supplier standards | Suitable for routine analysis and solution preparation but does not indicate suitability for direct cell contact |
Molecular biology grade | Nucleases, proteases, or substances that interfere with molecular biology reactions | Suitable for nucleic-acid and protein experiments but does not necessarily include endotoxin or gelation-performance specifications |
Cell culture grade or tissue culture grade | Suitability for cell culture and product-related items such as sterility, endotoxin, pH, or osmolality | Suitable for cell operations but generally does not evaluate scaffold crosslinking, mechanical properties, or degradation |
Tissue engineering grade | A combination of cell-related quality attributes and material-function indicators | Suitable for scaffolds, hydrogels, bioinks, and cell-encapsulation systems; specific items are determined by the product specification |
Pharmacopoeial grade | Compliance with the identification, assay, and impurity requirements of the stated pharmacopoeia and corresponding monograph | Provides a standardized basis for chemical quality but does not necessarily include tissue engineering functional evaluation |
Manufactured under Good Manufacturing Practice conditions | Good Manufacturing Practice (GMP)-related manufacturing, documentation, traceability, and change control | Reflects the manufacturing-management status but does not directly indicate that a material has specific gelation or cellular functions |
Medical grade or biomedical grade | Supplier specifications intended for medical or biomedical applications | The underlying standards, registered intended use, and technical documentation must be verified |
Sterile, low-endotoxin, or animal-origin-free | A specific individual quality attribute | A single-attribute declaration that cannot replace a complete evaluation of suitability for the intended use |
These designations do not form a single hierarchy arranged from lower to higher grades.
For example, a pharmacopoeial-grade material may have clearly defined assay and impurity limits but no data on gelation time or cell encapsulation. A cell culture-grade solution may have sterility and endotoxin information but lack the crosslinking and mechanical parameters required to form a scaffold. A tissue engineering-grade material may have functional data but may not necessarily be manufactured under GMP conditions.
6 How to Determine Whether Tissue Engineering-Grade Products Are Suitable for an Experiment
6.1 First Determine the Role of the Material in the Experiment
Before product selection, the following questions may be considered in sequence:
① Does the material come into direct contact with living cells?
② Is the contact short-term or long-term?
③ Is the material intentionally retained in the hydrogel, scaffold, or construct?
④ Does the material need to undergo crosslinking, sterilization, or degradation?
⑤ Is the experiment at the stage of material screening, cellular validation, animal research, or translational development?
In general, the more direct and prolonged the contact between the material and cells, or the longer the material remains within the construct, the greater the requirements for impurity control, biological contamination control, functional consistency, and source documentation.
6.2 Determine Critical Quality Attributes According to the Experiment
Experimental Requirement | Indicators to Verify as a Priority |
Photocrosslinkable hydrogel | Degree of functionalization, inhibitors, residual monomers, initiators, gelation time, and crosslinking conversion |
Natural-polymer scaffold | Source, molecular weight, viscosity, residual proteins and nucleic acids, and endotoxin |
Cell encapsulation | Sterility status, endotoxin, pH, osmolality, crosslinking process, and cell status |
Three-dimensional bioprinting | Rheological properties, extrudability, shape retention, crosslinking rate, and batch-to-batch stability |
Animal studies | Source traceability, sterility, endotoxin, sterilization method, degradation products, and final material |
Long-term repeated experiments | Batch-release criteria, continuity of supply, change notifications, and batch-comparison data |
When reviewing endotoxin information, the unit and sample form must also be confirmed. For example, EU/mg, EU/mL, and EU/item represent different bases of evaluation and cannot be compared directly on a numerical basis.
6.3 Review Product Quality Documentation
6.3.1 Technical Data Sheet
A Technical Data Sheet (TDS) generally describes the product’s properties, applications, typical performance, and recommended operating conditions.
Key information to review includes:
① Whether the product specifies a particular tissue engineering application;
② Whether molecular weight, degree of substitution, viscosity, or gel parameters are provided;
③ Which formulation and test conditions were used for the cell-related data;
④ Which dissolution, crosslinking, and storage methods are recommended.
6.3.2 Certificate of Analysis
A Certificate of Analysis (COA) records the test items and results for a specific batch.
For critical experimental indicators such as degree of substitution, molecular weight, endotoxin, or viscosity, actual batch-specific results generally provide a more useful basis for evaluation than general product descriptions.
6.3.3 Safety Data Sheet
A Safety Data Sheet (SDS) is primarily used to describe hazards, storage and transportation, spill handling, and personal protection.
An SDS cannot replace a TDS or COA, nor can it be used to demonstrate that a product is sterile, low in endotoxin, or suitable for tissue engineering experiments.
6.3.4 Source and Traceability Documentation
For naturally extracted, animal-derived, or recombinant materials, the following information should also be reviewed:
① Species and tissue source;
② Production host or expression system;
③ Sources of raw materials and auxiliary materials;
④ Control of adventitious agents;
⑤ Batch-traceability information;
⑥ Management of changes to manufacturing processes or raw materials.
6.4 Conduct Small-Scale Validation in the Actual System
Even after the raw-material specifications meet expectations, validation should still be performed under the actual formulation and process conditions.
This may include solubility and reconstitution time; pH and osmolality; reproducibility of gel formation and crosslinking; cell viability, morphology, or function; material blanks and reagent blanks; effects of extracts or degradation products; comparison of results between batches; and comparison of material parameters before and after sterilization.
Application data provided by the raw-material supplier cannot completely replace validation under the laboratory’s own conditions.
6.5 Rapid Product-Selection Checklist
Checklist Question | Reasonable Basis for Evaluation |
Is only the designation “tissue engineering grade” provided? | Specific specifications, test items, or application conditions should also be available |
Are numerical values and units listed? | Focus on the acceptance range rather than descriptions such as “high purity” or “low endotoxin” alone |
Does the COA cover the critical indicators? | Distinguish among batch-specific test values, statements of conformity, and typical data |
Are sterility and endotoxin described separately? | They are different quality attributes |
Is the material source specified? | This is particularly important for natural, animal-derived, and recombinant materials |
Are functional parameters provided? | For scaffolds and hydrogels, attention should be paid to gelation, rheological, mechanical, or degradation data |
Are the application data relevant to the current experiment? | Compare the cells, concentration, crosslinking method, culture duration, and test method |
Has performance after sterilization been evaluated? | Applicable to materials requiring sterilization or intended for animal studies |
Are batch and change information provided? | Applicable to long-term projects and reproducibility studies |
7 Precautions for the Use of Tissue Engineering-Grade Products
7.1 Sterility and Low Endotoxin Must Be Confirmed Separately
Sterility and low endotoxin are different quality attributes.
Sterility and low endotoxin are different quality attributes. Sterilization primarily targets viable microorganisms and cannot be used to infer that endotoxin requirements have been met. FDA information indicates that endotoxin may still be present in sterile products and that methods such as filtration, irradiation, and ethylene oxide treatment have limited effectiveness in reducing endotoxin that is already present. Therefore, when immune cells, stem cells, primary cells, or animal studies are involved, the sterility status, endotoxin limit, test method, and batch-specific results must be verified separately. [11]
7.2 Sterilization and Microbial-Removal Treatments May Alter Material Properties
Autoclaving, irradiation, ultraviolet treatment, filtration, and chemical sterilization affect materials differently and may alter:
① Polymer-chain length or crosslinking state;
② Molecular weight and viscosity;
③ Functional groups and degree of substitution;
④ Gelation time;
⑤ Mechanical and degradation properties;
⑥ Color, solubility, and residues.
ASTM F2027—25 regards processing and sterilization as factors that may affect the safety and performance of the final material. Raw-material specifications therefore cannot replace evaluation of the material after processing. [3]
Materials requiring sterilization should be treated using the same method intended for the formal experiment, and the critical parameters before and after treatment should be compared.
7.3 The Crosslinking System Must Be Evaluated as a Whole
The experimental performance of a crosslinkable material is determined not only by the polymer raw material but also by the following factors:
① Type of initiator or chemical crosslinking agent;
② Concentration of the initiator and crosslinking agent;
③ Light wavelength, intensity, and exposure time;
④ Material thickness and oxygen inhibition;
⑤ Unreacted monomers and post-crosslinking washing;
⑥ Gel porosity and mass transport.
The availability of tissue engineering application data for a raw material does not mean that the same results can be obtained with any formulation, concentration, or crosslinking condition.
7.4 Store and Reconstitute Products According to Product Requirements
Modified polymers and natural materials may be affected by temperature, light, oxygen, moisture, and repeated freeze–thaw cycles.
The following precautions should be observed during use:
① Store at the specified temperature and under light-protected conditions;
② Control the duration of exposure to room temperature;
③ Minimize repeated freeze–thaw cycles;
④ Use the specified solvent and reconstitution temperature;
⑤ Record the times of opening, reconstitution, and solution preparation;
⑥ Strengthen protection from light and storage control for inhibitor-free or photosensitive materials.
“Inhibitor-free” indicates that no corresponding stabilizer has been intentionally added to the product. This may help reduce inhibition and interference from residual stabilizers, but it may also increase the risk of spontaneous polymerization during storage and handling.
7.5 Revalidate After Changing the Batch or Supplier
Natural polymers, protein materials, and modified polymers may exhibit batch-to-batch differences because of variations in raw-material source, molecular weight, degree of substitution, moisture content, and purification process.
Even when two products are both labeled “tissue engineering grade,” they should not be directly substituted on an equal-mass basis. When changing products, the amount used should be recalculated according to the solid content, moisture content, molecular weight, degree of functionalization, and actual amount of active component.
7.6 Source Evaluation Should Be Strengthened for Animal- and Human-Derived Materials
Animal- and human-derived materials may involve issues related to identity, adventitious agents, batch-to-batch variation, donor screening, and source traceability.
A 2024 draft guidance issued by the U.S. Food and Drug Administration (FDA) states that when human- or animal-derived materials are used in the manufacture of cell, gene-therapy, and tissue-engineered medical products, attention should be paid to material identity, batch-to-batch consistency, the risk of transmission of adventitious agents, and material qualification. [10]
For research product selection, the following information may be verified as a priority:
① Animal species and tissue source;
② Recombinant expression host;
③ Donor or raw-material screening;
④ Control of viruses, mycoplasma, and other adventitious agents;
⑤ Traceability of raw-material batches and manufacturing batches.
7.7 Research Use and Clinical Use Must Be Distinguished
“Tissue engineering grade” is generally intended for research, material development, method establishment, and prototype validation. The designation itself does not indicate that the product has been authorized for human use, clinical use, or medical-device manufacturing.
When proceeding to animal implantation, preclinical development, or regulatory submission, the following must also be considered:
① Intended use and site of contact;
② Quality systems for raw materials and suppliers;
③ Manufacturing processes and change control;
④ Sterilization and packaging validation;
⑤ Evaluation of degradation products and extractables;
⑥ Biological safety evaluation of the final product;
⑦ Traceability and regulatory-submission documentation.
ISO/TS 21560:2020 addresses the materials, manufacturing, quality control, and unintended biological effects of tissue-engineered medical products, whereas ISO 10993-1:2025 requires the biological safety of medical devices to be evaluated within a risk-management process. These requirements extend beyond what can be demonstrated by a single commercial grade designation. [2,5]
References
[1] YY/T 1445—2016. Tissue-Engineered Medical Device Products—Terminology.
[2] International Organization for Standardization. ISO/TS 21560:2020, General Requirements of Tissue-Engineered Medical Products.
[3] ASTM International. ASTM F2027—25, Standard Guide for Characterization and Testing of Raw or Starting Materials for Tissue-Engineered Medical Products.
[4] YY/T 1435—2016. Tissue-Engineered Medical Device Products—Guidelines for Hydrogel Characterization.
[5] International Organization for Standardization. ISO 10993-1:2025, Biological Evaluation of Medical Devices—Part 1: Requirements and General Principles for the Evaluation of Biological Safety Within a Risk Management Process.
[6] United States Pharmacopeia. General Chapter 〈1043〉, Ancillary Materials for Cell, Gene, and Tissue-Engineered Products. USP–NF, 2019.
[7] International Organization for Standardization. ISO 20399:2022, Biotechnology—Ancillary Materials Present During the Production of Cellular Therapeutic Products and Gene Therapy Products.
[8] Sigma-Aldrich. Poly(ethylene glycol) dimethacrylate, Mₙ 10,000, Tissue Engineering grade, Product No. 946192. Product information page.
[9] Sigma-Aldrich. TissueFab® Discrete GelMA, 300 Bloom, 80% degree of substitution, Product No. 938408. Product information page.
[10] U.S. Food and Drug Administration. Considerations for the Use of Human- and Animal-Derived Materials in the Manufacture of Cell and Gene Therapy and Tissue-Engineered Medical Products: Draft Guidance for Industry. April 2024.
[11] U.S. Food and Drug Administration. Bacterial Endotoxins/Pyrogens. Inspection Technical Guide No. 40.
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