Biological composition of adipose tissue
Adipose tissue has emerged as a clinically relevant reservoir of mesenchymal stromal/stem cells (MSCs) suitable for autologous regenerative applications. Human adipose tissue contains multipotent mesenchymal stromal cells similar to those present in bone marrow, as first described by Zuk and colleagues, who identified multilineage cells capable of supporting cell-based therapies. These adipose-derived stromal cells (ASCs) reside within the stromal vascular fraction (SVF) and represent a distinct component from mature adipocytes. The regenerative effect of adipose tissue grafts is attributed to the presence of adipose-derived stem cells (ADSCs), cytokines, growth factors, pre-adipocytes, and mature adipocytes, which together provide both structural and biological support to damaged tissues.
Within the SVF, several interrelated cell populations have been characterized, including ASC progenitors, pericytes, and endothelial progenitor cells. Additional analyses have further detailed the SVF as containing adipocyte progenitors, pericytes, endothelial progenitor cells, and transit-amplifying cells, underscoring the cellular heterogeneity of adipose tissue beyond its lipid-storing compartment. This complex cellular milieu is embedded in an extracellular matrix (ECM) that provides structural integrity and influences cell behavior. Enzymatic digestion techniques that disrupt the ECM and cell–cell binding are commonly used in research settings to isolate SVF cells, highlighting the importance of this matrix in maintaining tissue architecture.
ASCs are defined as plastic-adherent multipotent cells that can differentiate in vitro towards mesodermal lineages such as osteoblasts, adipocytes, and chondrocytes, and they express mesodermal markers CD73, CD90, and CD105 while lacking hematopoietic markers CD14, CD34, and CD45. Functionally, adipose-derived mesenchymal stem cells have demonstrated differentiation potential towards osteogenic, chondrogenic, myogenic, hepatogenic, and endothelial lineages in both in vitro and in vivo models. These properties support their use in regenerative strategies targeting bone, cartilage, muscle, and vascular structures.
Beyond differentiation, ASCs and related stromal cells secrete bioactive molecules that stimulate angiogenesis and revascularization of fat grafts and exhibit antifibrotic, anti-apoptotic, and immunomodulatory properties. These paracrine activities are considered central to the regenerative potential of adipose tissue in clinical applications, including improvement of skin trophism, acceleration of complex wound or ulcer closure, and enhancement of skin appearance after radiotherapy damage. The superficial adipose tissue (SAT), located adjacent to the dermis, has been shown to contain higher concentrations of mesenchymal and vascular stem cells, and is therefore a preferred target for harvesting in some autologous regenerative protocols.
Stromal vascular fraction (SVF): structure and function
The stromal vascular fraction represents the non-adipocyte cellular compartment of adipose tissue and is central to its role in autologous regenerative therapy. SVF is composed of multiple interrelated cell types, including ASC progenitors, pericytes, and endothelial progenitor cells, which together form a complex stromal network. Detailed characterization has further identified adipocyte progenitors, pericytes, endothelial progenitor cells, and transit-amplifying cells within SVF, confirming its heterogeneity and regenerative potential. These cells are embedded in ECM fragments and may be present as single cells or aggregates, depending on the harvesting and processing method.
ASCs within the SVF are abundant, comprising approximately 1% of adipose tissue, and are capable of adhering to plastic, proliferating, and differentiating into osteogenic, adipogenic, and chondrogenic lineages. Experimental work has demonstrated that ASCs isolated from adipose tissue harvested with different microcannulas retain the ability to form colony-forming unit fibroblasts (CFU-Fs) and to differentiate towards adipogenic, osteogenic, and chondrogenic lineages, confirming their stemness characteristics. These findings support the concept that SVF-derived cells can contribute to tissue repair both through direct differentiation and through paracrine mechanisms.
Functionally, SVF cells and ASCs secrete a wide variety of factors with antifibrotic, anti-apoptotic, immunomodulatory, and neo-vascularization properties. These secreted molecules are implicated in improved skin trophism, accelerated wound and ulcer closure, and enhanced skin quality after radiotherapy, as observed in clinical applications of adipose tissue grafting. In orthobiologic contexts, similar paracrine effects are considered relevant for cartilage repair and modulation of joint inflammation, although the precise mechanisms in each indication require further elucidation.
From a structural perspective, SVF can be obtained via enzymatic digestion, which disrupts the ECM and releases the cellular components, or via mechanical approaches that preserve more of the native tissue architecture. Enzymatic methods using collagenase are particularly effective for isolating SVF cells but are subject to regulatory constraints in some jurisdictions. Mechanical approaches, including micro-fragmentation during harvesting, yield adipose tissue naturally enriched in SVF cells and ADSCs without substantial manipulation, and have been shown to provide viable and proliferative cells suitable for regenerative use. In clinical autologous regenerative therapy, minimally manipulated SVF-containing micrografts are frequently preferred to align with regulatory frameworks while leveraging the biological functions of the SVF compartment.
Harvesting and processing techniques
Adipose tissue harvesting for autologous regenerative therapy has evolved towards techniques that maximize cell viability while minimizing manipulation. The SEFFI (Superficial Enhanced Fluid Fat Injection) and related guided systems are designed to harvest micro-fragmented adipose tissue from the superficial adipose tissue layer at a standardized depth of approximately 15 mm, adjacent to the dermis. The guided cannula and external guide ensure that tunneling is performed consistently within this superficial compartment, which has been shown to contain higher concentrations of mesenchymal and vascular stem cells. The harvesting cannulas used in these systems feature small side-port holes that mechanically dissociate adipose tissue into small clusters during aspiration, generating a highly fluid preparation without the need for subsequent processing steps.
Comparative studies have evaluated adipose tissue harvested with microcannulas having 0.8 mm and 1 mm side-port holes against tissue obtained with standard liposuction cannulas followed by enzymatic digestion. In one study, lipoaspirate derived from 0.8 mm and 1 mm cannulas yielded vital tissue with viable cells, and the average absorbance values, reflecting cell viability, were similar immediately after plating and after 72 hours for both cannula sizes. An increase in cell viability over 72 hours was observed in all conditions, including enzymatically digested samples, indicating that guided microcannula harvesting can provide a comparable amount of viable cells to enzymatic SVF isolation while avoiding enzymatic manipulation.
The SEFFI-based approach emphasizes minimal manipulation of adipose tissue. The rationale is that any additional mechanical processing may reduce stemness and cell viability, whereas harvesting with microcannulas that already select small cluster dimensions obviates the need for further fragmentation. Experimental data have shown that tissue harvested with this technique, without substantial manipulation, exhibits higher viability and growth rates compared with techniques involving additional mechanical manipulation. In parallel, analytical tools such as the Celector system have been used to characterize micro-SEFFI-derived tissue, demonstrating high fluidity and a defined composition in terms of red blood cell contamination, cell aggregates, and ECM fragments, and confirming the presence of ASCs with preserved proliferation and differentiation capacity.
Enzymatic digestion with collagenase remains a reference method for isolating SVF cells, as it effectively disrupts the ECM and releases adipocytes and stromal cells. However, regulatory issues related to enzymatic procedures, particularly in some regions, have stimulated the development of purely mechanical methods. Alternative mechanical techniques have demonstrated that viable SVF cells can be obtained without enzymes, supporting the use of micro-fragmented adipose tissue as a ready-to-use regenerative graft. In clinical practice, guided microcannula harvesting without chemical or substantial mechanical manipulation is considered a minimally invasive approach that yields adipose tissue rich in viable and proliferative cells, suitable for autologous regenerative applications in both aesthetic and orthopedic settings.
Advantages over other tissue sources
Adipose tissue has gained prominence as a source of autologous mesenchymal stromal cells due to its accessibility and cellular composition. Adult stem cells can be isolated from several tissues, including bone marrow, skin, heart, gut, and skeletal muscle, but adipose tissue has attracted substantial interest because it allows high recovery of tissue and is readily accessible with minimally invasive procedures. For the first time, Zuk and colleagues described human adipose tissue as a source of multipotent mesenchymal stromal/stem cells similar to those present in bone marrow, establishing adipose tissue as a practical alternative reservoir of MSCs.
Within adipose tissue, ASCs are relatively abundant, comprising approximately 1% of the tissue, and can be isolated from the SVF using established protocols. These cells demonstrate multipotent differentiation capacity towards osteogenic, chondrogenic, myogenic, hepatogenic, and endothelial lineages, supporting their use across a broad spectrum of regenerative indications. In addition to differentiation, ASCs secrete bioactive molecules that stimulate angiogenesis, support fat graft revascularization, and exert antifibrotic, anti-apoptotic, and immunomodulatory effects. This combination of abundance, multipotency, and paracrine activity underpins the appeal of adipose tissue as a regenerative resource.
From a procedural standpoint, harvesting adipose tissue with guided microcannulas is minimally invasive and can be standardized using devices such as SEFFI and micro-SEFFI systems. These systems allow targeted collection from superficial adipose tissue, which has been shown to contain higher densities of mesenchymal and vascular stem cells, while simultaneously micro-fragmenting the tissue into small clusters suitable for direct injection. The resulting micro-fragmented adipose tissue is naturally rich in SVF cells and ADSCs and can be used without enzymatic digestion, aligning with regulatory expectations for minimal manipulation and enabling single-session autologous procedures.
Clinical and experimental data indicate that neither the type of harvesting procedure nor the anatomical site of subcutaneous adipose tissue collection significantly affects the total number of viable cells obtainable from the SVF, suggesting a degree of flexibility in donor site selection. Furthermore, studies comparing guided microcannula harvesting with standard liposuction followed by enzymatic digestion have shown that microcannula-derived tissue yields a comparable amount of viable cells, reinforcing the practicality of adipose tissue as a regenerative source without complex processing. In the context of autologous regenerative therapy, these characteristics position adipose tissue as a versatile and efficient resource for delivering mesenchymal stromal cells and supportive stromal elements.
Applications in orthobiologics
Autologous adipose tissue and its SVF component have been increasingly applied in orthobiologic strategies, particularly for degenerative joint disease. Osteoarthritis (OA) is characterized by degeneration of articular cartilage, joint pain, and functional impairment, with current conservative treatments largely palliative and unable to reverse the degenerative process. Stem cell–based therapies have emerged as potential approaches for tissue repair and regeneration in orthopedics, where cell therapy has been used in conditions such as avascular bone necrosis, osteochondral defects, pseudoarthrosis, and traumatic cartilage defects. In this context, adipose-derived stem cells, particularly those residing in the SVF, are frequently used due to their intrinsic capacity to support regeneration of cartilage, tendons, and bone.
Autologous Regenerative Therapy (ART) utilizes the patient’s own mesenchymal stem cells in a single medical procedure to regenerate injured tissues or stimulate their repair, following principles of tissue engineering while maintaining procedural simplicity. In OA, the poor intrinsic healing capacity of joints, related to limited vascularization and restricted access to bone marrow progenitor cells, provides a rationale for introducing exogenous autologous MSCs from adipose tissue. ADSCs within the SVF can differentiate according to local signals and growth factors, making them suitable for addressing lesions involving multiple musculoskeletal tissues.
Intra-articular injection of micro-fragmented adipose tissue has been applied to hip and knee OA using guided SEFFI-based devices. The harvested adipose tissue, naturally containing SVF cells and ADSCs, is processed in a way that preserves cell viability and generates a fluid micrograft suitable for injection into the joint space. Clinical protocols typically involve harvesting from superficial adipose tissue, isolating SVF-rich micrografts, and injecting them intra-articularly within a single session lasting approximately 60–70 minutes. The injected material is autologous and has been reported to be well tolerated, with postoperative joint courses characterized mainly by transient swelling and low-grade pain.
Beyond OA, the biological properties of adipose-derived SVF and ASCs, including angiogenic, antifibrotic, and immunomodulatory effects, have been leveraged in other musculoskeletal and soft-tissue indications. Adipose tissue implantation has been used to improve skin trophism, accelerate closure of complex wounds or ulcers, and enhance skin appearance after radiotherapy, demonstrating the broader regenerative potential of adipose-derived cells. In aesthetic and reconstructive contexts, micro-fragmented adipose tissue grafts, naturally rich in SVF cells and ADSCs, are considered valuable for achieving both volumization and skin regeneration effects, and similar principles are being translated into orthobiologic applications where tissue quality and local biology are critical.
Evidence from preclinical and clinical studies
Preclinical studies have established the presence and functional capacity of adipose-derived mesenchymal stromal cells, supporting their use in regenerative medicine. Zuk and colleagues demonstrated that human adipose tissue contains multipotent stem cells capable of multilineage differentiation, with implications for cell-based therapies. Subsequent work confirmed that ASCs isolated from adipose tissue can differentiate towards osteogenic, chondrogenic, myogenic, hepatogenic, and endothelial lineages in vitro and in vivo, and that they exhibit antifibrotic, immunomodulatory, and pro-angiogenic properties. Experimental characterization of lipoaspirate samples harvested with SEFFI and micro-SEFFI cannulas has shown that ASCs isolated from these tissues maintain classical mesenchymal morphology, robust proliferation, CFU-F formation, and differentiation towards adipogenic, osteogenic, and chondrogenic lineages.
Analytical studies using technologies such as Celector have provided additional insights into the composition of micro-SEFFI-derived adipose tissue, documenting high fluidity, defined fractions of cell aggregates and ECM fragments, and the presence of viable stromal cells. These investigations confirmed that, despite smaller tissue cluster sizes and lower overall cellularity, micro-SEFFI samples still contain mesenchymal stromal cells with stemness characteristics that can be isolated and expanded. Complementary viability studies comparing adipose tissue harvested with 0.8 mm and 1 mm microcannulas to standard liposuction tissue processed by enzymatic digestion have shown that microcannula-harvested tissue contains viable and proliferative cells, with absorbance-based viability measures comparable to enzymatically derived SVF cells over 72 hours.
Clinical evidence for autologous micro-fragmented adipose tissue in orthobiologics includes observational data on patients with hip and knee OA treated by intra-articular injection of fat micrografts obtained with SEFFI-based devices. In a cohort of 250 patients with initial-stage degenerative OA of the hips and/or knees, intra-articular injection of autologous fat micrograft was performed after radiographic assessment and baseline clinical evaluation. Follow-up at 1, 3, 6, and 12 months included range of motion (ROM) measurements, stiffness assessment, Visual Analogue Scale (VAS) pain scores, and quality-of-life questionnaires. The donor site course was generally uneventful, with minimal discomfort, edema, and ecchymosis, and no major complications.
Clinically, an average increase of approximately 10 degrees in joint ROM was observed three months after treatment, accompanied by reduced stiffness as reported by patients. Pain reduction on the VAS scale began around three months, reaching a peak at six months for the knee and between six and twelve months for the hip. Improvement in pain and joint performance appeared more pronounced in younger patients with lower OA grades, although even patients with more severe OA experienced pain reduction and reported clinical satisfaction. At one year, 85% of patients reported satisfaction with the treatment and indicated they would undergo the procedure again, with a considerable improvement in pain and quality of life. Over a five-year follow-up, a minority of patients proceeded to joint replacement surgery, and the overall complication rate remained low, supporting the safety and feasibility of autologous adipose-derived SVF use in OA.
Sources (Bibliography)
- Trentani P, Meredi E, Zarantonello P, Gennai A. Role of Autologous Micro-Fragmented Adipose Tissue in Osteoarthritis Treatment. J Pers Med, 2024.
- Gennai A, Bovani B, Colli M, Melfa F, Piccolo D, Russo R, Roda B, Zattoni A, Reschiglian P, Zia S. Comparison of Harvesting and Processing Technique for Adipose Tissue Graft: Evaluation of Cell Viability. Int J Regen Med, 2021.
- Rossi M, et al. Characterization of Tissue and Stromal Cells for Facial Aging Treatment. Aesthetic Surgery Journal, 2020;40(6):679–690.
- Zuk PA, Zhu M, Mizuno H, et al. Multilineage Cells from Human Adipose Tissue: Implications for Cell-Based Therapies. Tissue Eng, 2001;7(2):211–228.
- Zuk PA, Zhu M, Ashjian P, et al. Human Adipose Tissue Is a Source of Multipotent Stem Cells. Mol Biol Cell, 2002;13:4279–4295.
- Zuk PA. The Adipose-Derived Stem Cell: Looking Back and Looking Ahead. Mol Biol Cell, 2010;21:1783–1787.
- Tallone T, Realini C, Böhmler A, et al. Adult Human Adipose Tissue Contains Several Types of Multipotent Cells. J Cardiovasc Transl Res, 2011;4(2):200–210.