OPBSMusculoskeletalBiomaterials
Must Know
- Musculoskeletal tissue fails either because cells stop maintaining the ECM or because the ECM itself fails mechanically.
- Cells used for repair are primary cells, multipotent mesenchymal progenitors and pluripotent stem cells.
- Cells occupy about 10 percent or less of adult musculoskeletal tissue volume.
- Carbon isotope studies show most soft tissue collagen present at skeletal maturity lasts for life.
- Primary cells expanded on rigid plastic become senescent, faster when taken from older donors.
- Expanded chondrocytes dedifferentiate within a few divisions to fibroblast-like cells, losing proteoglycan and type II collagen.
- ACI takes cartilage from a non-load-bearing area, expands chondrocytes and reimplants them into the defect.
- MACI seeds expanded chondrocytes onto a collagen carrier and is the first tissue engineered orthopaedic product.
- Coculture of chondrocytes with progenitor cells needs fewer cells and allows a single-stage procedure.
- A stem cell self-renews indefinitely and can differentiate. Limited fate makes a cell multipotent, best called a progenitor.
- Bone marrow MSCs can form bone, fat and cartilage. Lipoaspirate also holds similar progenitors.
- Chondrogenesis is favoured by high-density pellet or micromass culture and 3D settings that keep cells round.
- Pluripotent stem cells can form any cell type and can rebuild a whole organism via the germline.
- ESCs come from the inner cell mass of embryos.
- iPSCs are usually made from skin fibroblasts using the four Yamanaka transcription factors, resetting the epigenome.
- Cells more than minimally manipulated face stricter FDA review.
Cell Sources Compared
| Feature | Primary cells | MSCs | Pluripotent (ESC, iPSC) |
|---|---|---|---|
| Strength | Correct phenotype, autologous | Autologous from many sites, safety established | Any lineage, large expansion, iPSC autologous |
| Weakness | Few cells, phenotype loss, senescence | Incomplete or unstable differentiation, donor heterogeneity, senescence | Ethics and few lines (ESC), reprogramming vectors (iPSC), instability |
| Clinical use | ACI and MACI | Used, weak efficacy evidence, many trials | Little musculoskeletal use |
- Chondrogenic MSCs can drift to an osteogenic phenotype after implantation.
- MSC populations start from many clones of different potential, so they are heterogeneous by definition.
- Allogeneic MSC joint injection has shown safety in humans.
Materials Compared
| Feature | Natural | Synthetic |
|---|---|---|
| Examples | Collagen, fibrin, hyaluronic acid, SIS, agarose, alginate, chitosan | PEG, polylactic acid, polyglycolic acid and copolymers |
| Strength | Native binding sites and biochemistry | Defined, tunable mechanics and degradation |
| Weakness | Immunogenic if animal sourced, lose bioactivity with crosslinking, variable | No cell-binding motifs, foreign body response, regulatory burden |
- Agarose and alginate come from seaweed and algae. Chitosan comes from crustacean exoskeleton.
- PEG is inert and nondegradable with poor cell adhesion unless modified with peptides such as RGD or GFOGER.
- RGD is a fibronectin motif. GFOGER mimics collagen.
- Polylactic and polyglycolic acids degrade by hydrolysis, at a rate set by composition and molecular weight.
- Decellularisation removes cells and debris to give tissue-specific ECM materials.
Scaffold Forms
- Hydrogels. Water-swollen crosslinked networks that hold cells, release drugs by diffusion and trap new matrix.
- Collagen gel. Long used to deliver BMP in spinal fusion.
- Porous scaffolds. Solid polymer with voids, made by porogen leaching, fibre weaving or electrospinning.
- Electrospun fibres match native ECM scale and give topographic cues.
- Hyaluronic acid has been modified for light crosslinking, MMP-cleavable links, cell binding and viscoelasticity.
- 3D printing from MRI or micro CT allows patient-matched shape and controlled pore size.
More on examples heading to the clinic
- 3D woven degradable fibres can match the mechanical properties of articular cartilage.
- Printed meniscus scaffolds with sequential growth factor microspheres improved repair after partial meniscectomy in sheep.
- Woven femoral head scaffolds carrying gene vectors make invading cells release anti-inflammatory agents.
- Anatomic humeral head replacements have been made in rabbits.
- Porcine collagen membranes first covered ACI defects and are now MACI cell carriers.
Exam Traps
- Primary cells have the right phenotype but are few and dedifferentiate with expansion.
- MSCs are multipotent, not totipotent, and senesce with long culture.
- PEG alone gives poor cell adhesion. Natural materials carry native binding sites.
- Animal-derived natural materials carry immunogenic epitopes.
- iPSCs come from reprogrammed adult cells, not embryos.
Related pages. Platelet Rich Plasma, Bone Grafts and Substitutes
Source
Mauck RL. Cells and Materials for Soft-Tissue Repair and Regeneration. In. Aaron RK, editor. Orthopaedic Basic Science. Foundations of Clinical Practice. 5th ed. Philadelphia, Wolters Kluwer, 2021.
Practise Type X questions on this topic
Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 17 October 2026.