Filtration-Free vs. Filter-Based BMAC Preparation: What Is the Difference?
- Mustafa Üneş
- Aug 10
- 7 min read
What Is BMAC?
Bone Marrow Aspirate Concentrate, commonly known as BMAC, is a point-of-care biologic preparation produced from autologous bone marrow aspirate.
Bone marrow contains a heterogeneous mixture that may include:
hematopoietic cells,
mesenchymal stromal/progenitor cells,
platelets,
mononuclear cells,
cytokines,
growth factors,
plasma,
red blood cells,
and other marrow components.
Importantly, mesenchymal stromal/progenitor cells represent only a small fraction of the nucleated cell population in native bone marrow. For this reason, both harvesting technique and subsequent processing can substantially influence the characteristics of the final concentrate.
BMAC should therefore not be evaluated simply by the volume of bone marrow collected.
The quality and composition of the final concentrate are more relevant parameters.
Why Does BMAC Processing Matter?
BMAC is not a universally standardized biological product.
Different commercial preparation systems use different combinations of:
aspiration volumes,
anticoagulants,
centrifugation protocols,
processing chambers,
filters,
separation mechanisms,
final concentrate volumes,
and collection techniques.
A laboratory comparison of three commercially available BMAC systems demonstrated meaningful differences in the recovery and concentration of CFU-F, CD34+ cells, white blood cells and platelets between systems.
This means:
Two products both called “BMAC” may not necessarily have the same cellular composition.
This is one of the most important concepts when comparing BMAC technologies.
What Is a Filter-Based BMAC Preparation System?
Some BMAC preparation workflows incorporate a filtration step.
Depending on the particular system, filtration may be used to help remove:
bone fragments,
particulate material,
tissue debris,
clots,
or other unwanted larger components.
A published technical protocol, for example, describes passing bone marrow aspirate through a 200-μm mesh filter before subsequent centrifugation and cellular processing.
The exact purpose, pore size and position of a filter within the workflow vary between devices.
Therefore, the term “filter-based BMAC system” does not describe a single standardized technology.
What Is a Filtration-Free BMAC Preparation System?
A filtration-free BMAC system is designed to process bone marrow aspirate without requiring an external filtration membrane as a primary separation step.
Instead, the system may rely on controlled physical principles such as:
density differences,
sedimentation,
centrifugation,
chamber geometry,
and selective collection of cellular layers.
During centrifugation, components of bone marrow separate according to their physical properties and density.
This enables the operator or device to isolate a selected cellular fraction while reducing unwanted components in the final concentrate.
Filtration-Free vs. Filter-Based BMAC: Key Differences
Parameter | Filter-Based Processing | Filtration-Free Processing |
External filter | Typically present | Not required |
Particulate management | Mechanical filtration | Separation/sedimentation |
Centrifugation | May be used | Commonly used |
Closed processing | Device dependent | Device dependent |
Processing steps | Device dependent | Potentially simplified depending on system |
Final cell composition | System dependent | System dependent |
Cell recovery | Must be measured | Must be measured |
Clinical superiority | Not established | Not established |
This last point is particularly important.
Current scientific evidence does not support a universal conclusion that filtration-based or filtration-free BMAC processing is clinically superior.
A review comparing commercially available point-of-care bone marrow concentration systems concluded that the available data were insufficient to recommend one device over another because technical characteristics and reporting methods varied substantially between systems.
The More Important Question: What Is Recovered?
Instead of asking only:
“Does this BMAC kit use a filter?”
a more scientifically relevant set of questions would be:
What cellular populations are recovered, at what concentration, with what consistency and in what final volume?
Relevant parameters may include:
Total Nucleated Cell Count — TNC
TNC provides information about the overall nucleated cellular population within the preparation.
CFU-F
Colony-forming unit-fibroblast assays are commonly used as an indirect measure of mesenchymal progenitor activity.
CD34+ Cells
CD34+ populations represent hematopoietic and other progenitor populations and are frequently reported in BMAC characterization studies.
Platelets
Bone marrow concentrate may also contain platelets and platelet-derived signaling molecules.
Red Blood Cell Content
Residual RBC concentration can vary substantially depending on processing methodology.
Final Concentrate Volume
Concentration alone does not describe the complete biological product. Final volume and total cellular dose should also be considered.
Cell Recovery May Be More Important Than Concentration Alone
This distinction is particularly important.
Imagine that:
System A
starts with 100 units of a target cellular population and recovers 80.
System B
starts with 100 units and recovers 40, but produces a smaller final volume.
System B might report a high concentration, despite recovering fewer total target cells.
Therefore:
Concentration and recovery are not the same measurement.
Research comparing commercial BMAC systems demonstrates this clearly.
In one study, CFU-F recovery among evaluated systems varied considerably, while CD34+, WBC and platelet recovery also differed between devices.
For future BMAC standardization, reporting both concentration and total cell recovery/yield is therefore important.
Why Bone Marrow Aspiration Technique Also Matters
The BMAC kit is only one part of the process.
Before the sample even enters the processing device, aspiration technique can influence its composition.
Variables include:
aspiration site,
aspiration volume,
syringe size,
needle positioning,
anticoagulant,
number of aspiration locations,
and peripheral blood dilution.
A review of BMAC processing variables emphasizes that harvesting and processing parameters can materially affect the final MSC/progenitor yield.
A recent systematic review also found substantial variability in progenitor-cell concentrations across BMAC samples.
Therefore:
BMAC quality begins at aspiration—not at centrifugation.
Why Standardization Is One of the Biggest Challenges in BMAC
One of the major limitations in the BMAC literature is inconsistent reporting.
Different studies may describe:
different aspiration protocols,
different centrifugation systems,
different final volumes,
different cell-counting methods,
and different biological endpoints.
A systematic review of clinical orthopaedic literature identified substantial variability in BMAC preparation and inadequate characterization of both starting bone marrow aspirate and final BMAC products.
This makes direct comparisons between devices and clinical studies difficult.
For this reason, future BMAC research should increasingly focus on standardized reporting of:
Input → Processing → Recovery → Final Composition → Cellular Dose → Clinical Outcome
rather than simply reporting that “BMAC was used.”
STEMMEX® BMAC: A Filtration-Free Approach
STR Biotechnologies developed the STEMMEX® BMAC Kit as a closed, sterile bone marrow processing system based on controlled centrifugation and separation.
The system is designed to prepare bone marrow concentrate without requiring an external filtration membrane as the primary separation mechanism.
The STEMMEX approach focuses on:
closed-system processing,
sterile workflow,
controlled centrifugation,
cellular layer separation,
simplified point-of-care preparation,
and filtration-free processing.
This design philosophy distinguishes STEMMEX from BMAC preparation workflows that incorporate separate mechanical filtration stages.
However, the absence of a filtration membrane should not itself be interpreted as evidence of clinical superiority.
The performance of any BMAC preparation technology should ultimately be assessed through validated parameters such as cellular recovery, final composition, reproducibility, sterility and appropriately designed clinical studies.
How Should a BMAC Preparation System Be Evaluated?
Healthcare professionals evaluating a BMAC preparation system should consider the entire processing workflow rather than one isolated design characteristic.
Important questions include:
Is the system closed?
Is the processing pathway sterile?
What initial bone marrow volume is required?
What final BMAC volume is obtained?
How is particulate material managed?
Is external filtration required?
What centrifugation protocol is used?
What is the TNC recovery?
What are the reported CFU-F and progenitor-cell yields?
How reproducible is the final preparation?
Is biological characterization available?
Is there scientific or clinical evidence supporting the methodology?
This approach provides a much more meaningful comparison than focusing only on centrifugation speed or the presence of a filter.
Conclusion
Filtration-free and filter-based BMAC systems represent different engineering approaches to bone marrow processing.
Filter-based workflows use mechanical filtration as part of the preparation process, whereas filtration-free systems can use controlled centrifugation, density separation and system geometry to manage different marrow components.
Neither approach should automatically be considered superior.
Published evidence demonstrates that commercially available BMAC systems can produce substantially different cellular compositions and recovery profiles. Therefore, the most meaningful evaluation should focus on cell recovery, cellular composition, reproducibility, sterility, processing efficiency and clinical evidence.
As orthobiologic technologies continue to evolve, improved standardization of BMAC preparation and reporting will be essential for comparing technologies and interpreting clinical outcomes.
Related STR Products
STEMMEX® BMAC Kit
Closed, sterile and filtration-free bone marrow concentrate preparation system developed for point-of-care BMAC processing.
LABFUGE® Centrifuge
Centrifugation platform developed for regenerative medicine preparation protocols.
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What Is BMAC?
BMAC vs PRP: What Is the Difference?
How to Choose a BMAC Preparation Kit
Cell Recovery in BMAC Preparation
Bone Marrow Aspiration: Why Harvest Technique Matters
BMAC in Knee Osteoarthritis: Scientific Evidence
Scientific References
Schäfer R, et al. A Review of Commercially Available Point-of-Care Devices to Concentrate Bone Marrow for the Treatment of Osteoarthritis and Focal Cartilage Lesions. Cartilage. 2019.
Gaul F, et al. Evaluation of the Consistency and Composition of Commercially Available Bone Marrow Aspirate Concentrate Systems. Orthopaedic Journal of Sports Medicine. 2020.
Piuzzi NS, et al. Variability in the Preparation, Reporting, and Use of Bone Marrow Aspirate Concentrate in Musculoskeletal Disorders. JBJS. 2018.
Gianakos AL, et al. Bone Marrow Aspirate Concentrate Harvesting and Processing Technique. Arthroscopy Techniques. 2017.
Dave U, et al. Bone marrow aspirate concentrate harvested in the axial and appendicular skeleton does not differ in progenitor cell count: A systematic review and meta-analysis. 2025.
Review of process variables affecting mesenchymal stromal-cell yield from bone marrow aspirate concentrate.
Commercial BMAC device review · Commercial BMAC system comparison study · BMAC preparation variability review · 2025 BMAC systematic review and meta-analysis
Frequently Asked Questions
What is the difference between filtration-free and filter-based BMAC preparation?
Filter-based systems incorporate a mechanical filtration step to help manage particulate material, while filtration-free systems may rely on centrifugation, sedimentation, density differences and device geometry for separation. The exact workflow varies by device.
Is filtration-free BMAC better than filtered BMAC?
Current scientific evidence does not establish universal clinical superiority of either approach. Final cellular composition, recovery, sterility, reproducibility and clinical evidence are more meaningful criteria.
Does filtering bone marrow remove stem cells?
This cannot be generalized across all filters or systems. Cell retention depends on filter characteristics, processing method and the biological populations being measured. Device-specific validation is required.
What determines BMAC quality?
Important factors include aspiration technique, peripheral blood dilution, processing method, total nucleated-cell recovery, progenitor-cell content, final volume, RBC content, sterility and reproducibility.
Is BMAC the same as stem cell therapy?
No. BMAC is a heterogeneous autologous bone marrow concentrate containing multiple cellular populations and soluble biological factors. It should not simply be described as a purified mesenchymal “stem cell” product.
What is STEMMEX® BMAC Kit?
STEMMEX® is STR Biotechnologies' closed and sterile BMAC preparation system designed around controlled centrifugation and filtration-free separation.
