Experimental and clinical methods used for fat volume maintenance after autologous fat grafting.

REVIEW PAPER

Experimental and Clinical Methods Used for Fat Volume Maintenance After Autologous Fat Grafting Wojciech Konczalik, BMBS, MRCS and Maria Siemionow, MD, PhD, DSc Abstract: Management of soft tissue deficits resulting from congenital abnormalities, trauma, systemic disease, and tumors is a particularly challenging field of plastic and reconstructive surgery. Fat grafting, a technique traditionally used in the correction of facial asymmetry, is commonly seen in aesthetic procedures which use the grafted fat for soft tissue augmentation and recontouring. Despite its widespread use in reconstruction and aesthetic surgery, therapeutic modalities applied in fat grafting are crude and the results of this intervention are unpredictable. The aim of this review was to present the most recent evidence regarding experimental studies and designs which confirmed or disproved fat volume expansion or fat maintenance after autologous fat grafting. Key Words: fat volume maintenance, autologous fat grafting, experimental methods, clinical methods (Ann Plast Surg 2014;72: 475Y483)

A

utologous fat transplantation by means of pedicle or transposition f laps has been performed for thousands of years, with Indian surgeons presumably treating nose defects in this manner since 1000 BC. The first documented case of fat autotransplantation for soft tissue augmentation dates back to 1893.1 The injection of fat for soft tissue augmentation is also a well-documented method, which has shown favorable results particularly in the management of facial lipoatrophy in patients with human immunodeficiency virus,2,3 the treatment of mild velopharyngeal incompetence,4 facial recontouring,5 and breast reconstruction.6 Fat grafting may also slow the progression of fibrosis in chronic radiodermatitis, as demonstrated by Rigotti et al.7 However, due to the small sample size and no further human studies since this study, the true value of fat grafting in radiotherapy-induced tissue damage is yet to be established. A significant drawback of autologous fat transplantation is the unpredictable resorption of the transplanted adipose tissue, which may be partly related to the insufficient vascularity of the transplant.8 In its natural state, endogenous fat is highly vascular and exhibits angiogenic properties9; however, a limitation of the graft survival is the presence of the vasculature in the vicinity of the transplant.10 Without adequate vascularization, integration with the host tissue, and adipogenesis, the transplant fails to maintain the intended shape and dimensions, resulting in poor long-term clinical outcome.11Y14 Although inadequate adipose tissue stores for harvest are exceedingly rare in the developed world, the use of autologous fat transplantation in certain conditions may encounter potential issues. It may be limited by both graft availability as well as increased risk of donor-site morbidity in Received June 14, 2013, and accepted for publication, after revision, December 8, 2013. From the Department of Plastic and Reconstructive Surgery, Cleveland Clinic, Cleveland, OH. Conflicts of interest and sources of funding: none declared. Reprints: Maria Siemionow, MD, PhD, DSc, Department of Plastic and Reconstructive Surgery, Cleveland Clinic, 9500 Euclid Ave, Desk A-60, Cleveland, OH 44195. E-mail: [email protected]. Copyright * 2014 by Lippincott Williams & Wilkins ISSN: 0148-7043/14/7204-0475 DOI: 10.1097/SAP.0000000000000117

Annals of Plastic Surgery

& Volume 72, Number 4, April 2014

patients with systemic lipodystrophy associated with chronic systemic illness and malabsorptive disorders. Limitations of allogenic fat tissue grafts and biosynthetic materials lie in their potential to induce a host immune response, leading to adverse allergic reactions or rejection.15Y17 Eremia and Newman18 performed a retrospective study of 116 patients with fat transplanted into the nasolabial and melolabial folds and found that, at 3 and 4 months after the procedure, all patients were satisfied with the results; however, after 5 to 8 months, this figure decreased to 25%. A true long-term correction, lasting for more than 14 months, was only noted in 3% to 4% of the patients. A similar outcome was observed by Duskova and Kristen19 with the use of fat grafts for the management of scar depressions secondary to cleft palate surgery. The initial cosmetically pleasing effect was temporary; and to improve the outcome, repeated application every 7 months was recommended. Despite the limited success of the longterm efficacy of fat autotransplantation, studies evaluating treatment success based on patient-reported outcomes are emerging and continue to produce positive data. Their results, however, are largely based on subjective evaluations such as photographic evidence before and after the surgery and are not supported by quantifiable evidence of fat graft viability.5,8,20Y22 In 1950, Peer et al23 established that approximately 45% of the volume of the original graft remains at 1 year after implantation. In the 1990s, novel fat graft volume assessment methods demonstrated that up to 70% of the initial volume of the fat graft is reabsorbed.24,25 The process that leads to graft volume shrinkage over time is mainly due to the adipocytes low tolerance to ischemia. Slow revascularization rates of the fat tissue result in early apoptosis and necrosis of mature transplanted adipocytes, and this process persists even after revascularization of the graft.26,27 To increase the maintenance of fat graft volume and allow for fat graft expansion, clinicians look for novel, more effective approaches. Thus far, the primary focus has been on the standardization of the fat grafting procedure and improving methods of fat cell processing.28,29

Surgical Factors Impacting on Fat Graft Volume Maintenance The purpose of lipoharvesting is the collection of adipose tissue without disturbing adipocyte viability or traumatizing the donor site.30 In order for the lipoharvesting procedure to effectively achieve those goals, each step of the process needs to be evaluated on an individual basis: harvesting, processing, storage, and delivery of the tissue to the recipient site. Sites most commonly selected for fat graft harvesting include the abdominal wall, trochanteric area, medial knee, dorsocervical fat pad, and the extremities. The association between site selection for lipoharvesting and postoperative fat graft viability has not yet been adequately assessed and no conclusive data regarding a superior donor site exist.31 Adipose tissue can be obtained by vacuum extraction, syringe aspiration, and surgical excision. Conventional liposuction techniques using high negative pressures for vacuum extraction are not optimal as they can result in the rupture of up to 90% of adipocytes.8 It is also uncertain if the method of syringe aspiration or surgical excision is a favorable one; comparison of those methods was impossible in both animal models and human subjects because the size www.annalsplasticsurgery.com

Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.

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TABLE 1. Advantages and Disadvantages of the Surgical Methods Implemented for Fat Volume Maintenance Investigator Year Neuber G

1

Nordstrom REA58

Ullmann Y59 Har-Shai Y22

Yuksel E42

Rohrich RJ36

Kaufman MR39

Technique

1893 Surgically excised fat transplant for soft tissue augmentation

Advantages

Disadvantages 56

Abundant source of material; rich in ADSCs Only successful for small (‘‘almond which promote adipogenesis, angiogenesis size’’) transplants; unpredictable and play a vital role in immunomodulation45,50,57 resorption; inadequate integration with the host tissue; increased risk of donor-site morbidity and may be limited by graft availability; a true long-term correction lasting for more than 12 mo has been observed in only a limited number of patients15,19,23Y27,44 Maximizes the surface area of grafted adipose Damage to the surrounding tissue; the tissue exposed to adjacent vascular structures grafted sites have to be immobilized for a week with a compression dressing46Y48,58

1997 ‘‘Fanning-out’’ technique with distribution of small parcels of adipose tissue within multiple tissue planes 1998 Supplementation of aspirated fat Addition of MCDB 153 into the harvested aspirate with enriched serum-free cell proved superior with regard to fat weight culture mediumVMCDB 153* maintenance when compared to saline 1999 Suspension of centrifuged fat aspirate Technique demonstrated prolongation of adipocyte in an enriched cell culture medium, survival ex vivo; good cosmetic result at 6 and and injection of the cell suspension 24 mo follow-up into preformed subdermal tunnels 2000 Local delivery of insulin and IGF-1 Supplementation of excised fat with insulin and in excised fat using a IGF-1 was found to increase fat-graft survival PLGA-polyethylene glycol rates and cellular/stromal ratio when compared to microsphere delivery system untreated controls in animal models. Insulin60,61 and IGF62 promote adipocyte differentiation 2004 Gentle centrifugation of lipoaspirate Preferred method as it allows for the disposal of obtained by low-pressure cell debris, free triglycerides and bloodVfactors syringe aspiration which can induce an inflammatory response, thus increasing the risk of graft degradation39 2007 Syringe aspiration of adipose tissue SimplicityVthe most common method of fat and fat injection techniques harvesting applied in clinical practice28

Cervelli V63 2009 Addition of PRP to lipoaspirate

Perez-Cano R66

2012 Augmentation of lipoaspirate with ADSCs

Liu B71

2013 Addition of PRF to lipoaspirate

PRP promotes proliferation of ADSCs ex vivo; safe and abundant source of endogenous biologically active substances essential in tissue regeneration64,65 ADSC have been shown to enhance angiogenesis ex vivo.67 Associated with increased skin elasticity, reduced scar tethering, and improved skin flap viability.

PRF promotes release endogenous growth factors, but also exhibit good manageability, negligible immunogenicity and is cost effective.72Y74 Reduced resorption rates observed at 24 wk when compared with traditional methods

Fat weight maintenance did not differ significantly at 15 wk when compared with traditional methods of fat aspiration Small cohort of patients; lack of quantitative evidence supporting improved adipocyte survival in vivo Requires microsphere delivery system; lack of studies demonstrating efficacy in human models

Lack of evidence supporting increased adipocyte viability postcentrifugation

Lidocaine is commonly used as anesthetic despite the fact that this substance has been shown to impede human adipocyte growth in cell culture33; adipocytes placed further than 2 mm from an arterial supply undergo necrosis and are replaced by fibrous tissue.43 Fat injection with high positive pressures could be potentially destructive to the adipocytes’ cellular membranes and ultimately reduce graft survival20,23,44,58 Little published clinical evidence that proves the efficacy of PRP in humans

Human studies limited to breast reconstruction/augmentation. Exact mechanism of action remains unknown.68 Similar results being obtained when using traditional grafts.69 Scientific evidence regarding the safety of the ADSC technique is limited, and the correlation between stem cell concentration and fat graft volume maintenance remains unproven70 No studies demonstrating efficacy in humans; need for improved protocols for optimization of growth factor release from PRF

*MCDB 153Vmedium with trace elements, L-glutamine, and 28-mM HEPES, without sodium bicarbonate. Originally developed for clonal and long-term growth of human epidermal keratinocytes under serum-free conditions.

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Fat Maintenance After Autologous Fat Grafting

of the fat graft as well as the methods of aspiration largely differed between the studies.32Y35 Despite the lack of conclusive evidence, syringe aspiration of adipose tissue remains the most common method of fat harvesting applied in clinical practice. 36 An important factor inf luencing adipocyte survival is the concomitant use of medication. Injection of the donor site with local anesthetic like lidocaine is a common practice despite the fact that this substance has been shown to impede human adipocyte growth in cell culture for as long as the cells were exposed to the agent. The effect was reversible and adipocytes regained their normal function after washing from lidocaine.37 Currently available techniques of processing harvested fat include centrifugation, decantation, filtration, and straining.38 Centrifugation is the preferred method as it allows for the disposal of fat cell debris, ruptured membranes, free triglycerides, and bloodVall of which have the potential to induce an inf lammatory response and subsequently result in graft degradation.39,40 The rationale behind harvested fat centrifugation has been challenged by Rohrich et al who found no quantitative difference in the viability of centrifuged and noncentrifuged fat tissue.41 There are studies indicating that exposure to room air, which occurs during centrifugation, may result in permanent cellular damage.42 A pneumatic tourniquet may be used to create a bloodless field, eliminating the need for further processing altogether.21 The washing of harvested grafts with solution containing nutrients (vitamins and amino acids) and anabolic hormones [thyroxine, growth hormone, insulin, insulin-like growth factor (IGF)-1, and basic fibroblast growth factor] is believed to improve clinical outcome.43 However, no conclusive evidence regarding the efficacy of this practice in promoting fat graft survival is currently available as the studies significantly vary in their methodology, thus making it difficult to establish clinical applicability.21,43,44 As of today, there are no human studies evaluating the impact of hyperbaric oxygen on the recovery of the fat graft after autologous transplantation.43 Storage of harvested fat for future autotransplantation is not recommended, despite the fact that freezing for 12 months was associated with minimal damage to adipose tissue architecture,45Y48 as the process of cryopreservation has been shown to reduce the activity of adipocyte-specific enzymes which may adversely affect fat graft survival after autotransplantation.49 Fat injection techniques are all based on the principle that fat survival is dependent on the proximity of oxygenated blood. It is has been demonstrated that adipocytes placed further than 2 mm from an arterial supply undergo necrosis and are replaced by fibrous tissue.50 To maximize the surface area of the graft exposed to adjacent vascularized tissue, multiple authors advocate the use of the ‘‘fanning-out’’ technique which involves the creation of a large number of small tunnels with a cannula and depositing fat particles in multiple, distinct parcels.18,21,51Y55 Table 1 summarizes the advantages and disadvantages of the surgical techniques currently used in autologous fat graft volume maintenance.

response,84 modulation of apoptosis,83 and extracellular matrix (ECM) remodeling.85 Studies have established that ADSC can prevent graftversus-host disease and sepsis.86,87 Adipose-derived stem cells are found in the nonbuoyant cellular fraction obtained by enzymatic digestion of fat tissue and are believed to improve graft survival by facilitating vascularization.80,88 Adipose-derived stem cells positively inf luence fat graft viability by secreting multiple angiogenesis-related cytokines such as hepatocyte growth factor, vascular endothelial growth factor (VEGF), transforming growth factor A (TGF-A), angiopoietin 1, stromal cellYderived factor 1, and fibroblast growth factor 2 (FGF-2).83,88,89 These angiogenesis-related factors are thought to play a vital role in the modulation of the immune response, apoptosis, and recruitment of endogenous stem cell populations. Vascular endothelial growth factor and hepatocyte growth factor enhance cell growth and the release of VEGF in response to TNF and other cytokines, thereby counteracting tissue ischemia and reducing inf lammation.67,80,84,89 Stromal cellYderived factor 1, a member of the CXC chemokine family secreted by ADSC regulates multiple physiological processes including organ homeostasis and neovascularization by interacting with the CXCR4 receptor.90,91 One of the main advantages of ADSC is their availability.92 Adipose-derived stem cells are obtained from the processing of liposuctioned or surgically excised adipose tissue. Fat contains up to 1000 times more multipotent cells per cubic centimeter than bone marrow and it is possible to harvest up to 200 106 ADSCs from 500 mL of lipoaspirate.72,80 An even greater yield can be achieved with surgical excision,56 which is largely due to the fact that most of ADSCs are located in the vicinity of large blood vessels, which remain intact during liposuction.93 Furthermore, a number of ADSCs are discarded with the supernatant portion of the lipoaspirate. These findings indicate that harvesting and preparation of ADSC may enrich traditional fat grafts, leading to a more sustained clinical outcome. An assortment of laboratory techniques and devices used in ADSC harvesting is currently available; however, they all use collagenases for lysis of the covalent bonds, attaching the cells to vascular structures found in the stromal vascular fraction (SVF).93 None of these devices are currently approved by the US Food and Drug Administration (FDA). Due to the variability in cell counts and viability, which is dependent not only on the processing of the cells but also on host factors, harvesting technique, and method of delivery, it is imperative that thorough research is performed to compare the efficacy of the various devices and laboratory techniques and to establish factors inf luencing treatment outcome. Two classes of cells make up the majority of adipose tissue: mature adipocytes and stromal cells collectively termed the SVF. Although the obtaining of ADSCs is a relatively straightforward process, their culture is both time-consuming and expensive.94 The SVF contains a heterogeneous pool of cells such as endothelial cells, pericytes, smooth muscle cells, mast cells, leukocytes, and ADSCs. It is possible to obtain a sufficient number of ADSC from the SVF to meet the clinical demand, thus eliminating the need for cell culture.56,95,96 Uncultured SVF, therefore, offers an alternative source of cells and has been shown to regenerate new adipose tissue in vitro when seeded onto a porous collagen sponge.97 Importantly, SVF is able to maintain its adipogenic properties after cryopreservation in a serum-free freezing medium, enabling the storage of cells for future clinical application.75 Recent studies in the field of breast reconstruction suggest that ADSC-enriched fat grafts have improved volume maintenance and were associated with a lower incidence of calcification and radiological abnormalities and also displayed a healthier histological appearance than traditional fat grafts.6,98Y101 A recently published RESTORE-2 trial evaluated the safety and efficacy of stem cellYenriched fat grafts in soft tissue augmentation.66 An improved clinical outcome


The Role of Adipose-Derived Stem Cells in Improving Fat Graft Volume Retention The regenerative potential of mesenchymal stem cells obtained from bone marrow is well documented in medical literature.75 In recent years, interest in the developmental plasticity and therapeutic potential of stromal cells isolated from human adipose tissue has rapidly grown,45,50,57 reinvigorating the field of fat grafting. Adipose-derived stem cells (ADSCs) have the potential of differentiating into tissue of mesenchymal origin, namely bone, fat, cartilage, muscle, and neural progenitors,45,76Y78 but they are not capable of generating hematopoietic stem cells like bone marrow stem cells.79 Tissue-engineering techniques can influence ADSC differentiation,80 allowing for the creation of tissue structures individually tailored for specific pathologies.73,81,82 In addition to their proliferative capabilities, the ADSCs have been shown to secrete a host of compounds important for angiogenesis,83 immune * 2014 Lippincott Williams & Wilkins



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and sustained results at 1 year, which were superior to traditional fat grafts, were reported. Furthermore, data from this trial led to the conclusion that volume augmentation using ADSC-enriched grafts is permanent at 6 months and is associated with increased skin elasticity and reduced scar tethering. Human in vivo studies have shown improved skin flap viability and improved tissue repair after ADSC application.67,102 Ever since the discovery of ADSCs in adult human fat in 2001,57 the inconsistencies in fat graft survival have been attributed to the function of stromal cells found in adipose tissue.50,76,98,100,103 This fact, however, remains inconclusive. The exact mechanism of action of ADSC in autologous transplantation has not been established and their role in improving fat graft viability needs further evaluation.68 The American Society of Plastic Surgeons and the American Society for Aesthetic Plastic Surgery recently published a joint statement regarding stem cells,69,70 which highlighted the lack of sufficient evidence to justify the addition of ADSC to fat grafts, with similar results being obtained when using traditional grafts. Scientific evidence regarding the safety of the ADSC technique is limited, and the correlation between stem cell concentration and fat graft volume maintenance remains unproven.104 Preliminary results from ongoing clinical trials are promising in showing a tendency for increased fat survival with higher ADSC concentrations, long-term data, however, are not yet available.105 The role of cell-enriched fat transfer in facial fat grafting remains unclear, and the data are limited to only a few studies. A prospective study by Sterodimas et al105 provided important evidence that cell-enriched fat transfer grafts required fewer reoperations than traditional grafts. As with new technological advancement in medicine, the use of stem cell therapy has been met with both enthusiasm and criticism from the public and the medical community, prompting further

research to establish the true advantages and applications of the technique.98,106Y108

The Role of Bioengineered Scaffold Constructs in Fat Grafting Tissue engineering uses biological scaffolds to provide a 3dimensional environment that facilitates the growth and differentiation of seeded cells. Biomaterials replicate the biological and mechanical properties of the native ECM and act as a vehicle for the delivery of bioactive compounds (eg, cell adhesion peptides, and growth factors) to desired sites in the body.109 The ideal fat graft scaffold needs to be readily manufactured in large quantities, provide an optimal environment for adipogenesis, exhibit biocompatibility with host tissue, and biodegrade into nontoxic organic metabolites. To date, no consensus as to the best biomaterials has been achieved. The main difficulty encountered with tissue engineering of fat is satisfying the vascular demands of the growing tissue. Recent investigations have indicated that expanding adipose tissue is one of the few examples of active angiogenesis in adults.84 De novo adipogenesis is achieved by proliferation of the patients’ adipose precursor cells in culture and seeding them onto a scaffold which is then implanted, allowing for cell differentiation to occur in vivo.54,55 The capacity for differentiation of the preadipocytes is patient-dependent and decreases with age.52,53 To ensure effective adipogenesis, a thorough understanding of the cellular and molecular mechanisms underlying adipose tissue differentiation and growth is necessary. Figure 1 illustrates the lineages of adipose tissue development including key regulators involved in adipocyte differentiation. A number of transcription factors play a vital role in the regulation of adipogenesis including the CCAAT/enhancer binding protein gene family and peroxisome proliferatorYactivated receptor-g.110 Insulin60,61 and IGF62 promote adipocyte differentiation. Similar

FIGURE 1. Adipose tissue lineages with key regulators involved in adipocyte differentiation. 478






findings were reported with the addition of agents such as dexamethasone and isobutylmethylxanthine into the culture medium.61 Sex hormones may also play a role in ensuring fat graft viability; in vitro studies show that administration of estrogen accelerated preadipocyte proliferation.111 Growth hormone, retinoic acid, vitamin D, and other compounds are also likely to have an impact on adipogenesis; however, the clinical significance of hormonal manipulation of fat grafts has not yet been fully evaluated. The key challenge in improving the clinical potential of scaffolds is ensuring adequate vascularization, which strongly correlates with long-term survival of implanted tissue constructs.112Y114 Prevascularization is a concept whereby a microvascular network is generated within the scaffold before its implantation, which in theory should hasten reperfusion as the preformed network simply has to inosculate with the host microvasculature.115,116 Scaffolds are infused with a cocktail of endothelial cells, mural cells, and ADSC, all of which are capable of microvessel production after several days of culture.117,118 Matrix metalloproteases released by endothelial cells regulate cell proliferation and migration and stimulate ECM remodelling.119,120 When seeded with microvascular fragments, porous nanosized hydroxyapatite particles/poly(ester-urethane) composite scaffolds exhibited excellent biocompatibility and lower immunogenicity than nonY prevascularized scaffolds.112,121 The application of dynamic positive and negative pressures to the cell-containing scaffold allowed for homogenous distribution of microvascular fragments, impacting positively on the quality and density of mature microvessels. Inosculation may be either internal or external. The former indicates that host vasculature invades the scaffold and forms interconnections with preformed microvessels within the implant. The latter, which has been shown to be the primary method of inosculation in a study by Laschke et al,112 implies that the preformed vessels expand outward into the neighboring host tissue. The same study also found no evidence of perfusion in the central part of the implant until day 6. This phenomenon was explained by the fact that the formation of vascular interconnections between the prevascularized scaffold and host microvasculature is a time-consuming process, which is proving to be a major obstacle to widespread use of this technology. Three classes of biomaterials are currently used in tissue engineering: naturally derived materials (ie, collagen and alginate), acellular tissue matrices (ie, bladder submucosa and small-intestinal submucosa), and synthetic polymers [ie, polyglycolic acid (PGA), polylactic acid (PLA), and polylactic-coglycolic acid (PLGA)].122,123 Scaffolds can be made of either fibrous or injectible materials, such as hydrogels containing a mixture of cells and trophic factors involved in adipogenesis and angiogenesis.25 The addition of angiogenic growth factors (FGF-2, VEGF, platelet-derived growth factor) was found to increase cell infiltration and promote early angiogenesis.124 These promising initial reports are encouraging further research to establish the optimal concentrations of bioactive compounds that best recreate physiological conditions, as well as to establish methods of their sustained delivery of the following implantation.125,126 A variety of biomaterials have been incorporated into scaffold designs to improve the vascularity of the transplanted tissue and promote cell differentiation. Currently used materials include hyaluronic acid (HA) derivatives, collagen sponges, PGA fiber meshes, and gelatin microspheres.17,127Y130 The use of natural materials and acellular tissue matrices carries the advantage of biologic recognition; however, unlike synthetic polymers, they cannot be manufactured on a large scale in a reproducible manner. Acellular tissue matrices are structures rich in collagen and are prepared by removing cellular tissue components. They degrade after implantation and are replaced and remodeled by ECM proteins synthesized by neighboring cells.131,132 Polymers such as PGA, PLA, and PLGA are polyesters of naturally occurring >hydroxy acids and are widely used in regenerative medicine. Degradation products of these polymers are nontoxic and are eliminated from

the body in the form of water and carbon dioxide.123 Hyaluronic acid is an essential component of the ECM and plays a vital role in a variety of biological processes. Inherent biocompatibility, biodegradability, and lack of immunogenicity all make HA an attractive material for constructing hydrogels with desired morphology, stiffness, and biological activity.133 Hyaluronic acid hydrogels ensure that cells are provided with a microenvironment that fosters cell proliferation, migration, and ECM production, ultimately leading to tissue expansion. Although intact HA maintains the tissue in a hydrated state, degraded HA stimulates cell proliferation and angiogenesis, minimizing scarring of the wound site.133 A new concept termed endogenous regenerative medicine is currently being explored for therapeutic purposes. It circumvents the challenges of biomaterial development and adipogenic factor delivery by obtaining growth factors and fibrin scaffolds from the patient’s own blood.64,74,134Y136 There is a growing interest in the exploitation of platelet-rich plasma (PRP) for biomedical purposes, as it is a safe and easily attainable source of multiple endogenous biologically active substances essential for wound healing and tissue regeneration.63Y65 Substances involved in tissue repair, such as platelet-derived growth factor, TGF-A, and epidermal growth factor are contained in platelet > granules. The regenerative potential of PRP is therefore dependent on the level of secretory proteins released as a result of platelet activation.137 Autologous PRP used as an adjuvant in fat grafting has enhanced clinical outcomes in plastic surgery.63 A new generation of platelet concentrates called platelet-rich fibrin (PRF) has been shown to be advantageous to traditional PRP. Platelet-rich fibrin contains high levels of growth factors including PDGF-BB, VEGF, FGF-2, epithelial growth factor (EGF), IGF-I, and TGF-A.11 Liu et al demonstrated that the addition of PRF and the SVF augmented autologous adipose tissue transplantation, with in vivo adipose tissue formation noted at 4 weeks post-implantation and reduced resorption rates observed at 24 weeks when compared with traditional methods.71 Autologous PRF scaffolds hold great promise for fat grafting as not only do they release endogenous growth factors, but also exhibit good manageability, negligible immunogenicity, and are cost effective.55,74,94,135 A more effective mechanism of growth factor extraction from PRF will further enhance clinical outcomes. Studies investigating the use of adjuvants such as heparinconjugated biomaterials in PRF constructs are underway.71 These biomaterials bind to growth factors such as VEGF, PDGF, and FGF-2 and release them in a sustained manner producing a desired durable effect on tissue regeneration. This is in-keeping with evidence suggesting that moderation of growth factor release is essential for effective adipogenesis.138,139 The efficacy of the various biomaterials used in scaffolds is not yet adequately evaluated, and the optimized scaffolds have not been identified.14,140 Despite laboratory studies revealing potential benefits of adipose tissue engineering, the safety and efficacy of bioengineered fat grafts in clinical practice remain to be defined.17 Table 2 summarizes the advantages and disadvantages of bioengineered scaffold constructs currently under investigation for their potential benefit in fat volume maintenance.



CONCLUSIONS Although autologous fat transfer can be effective in the management of soft tissue deficits, currently available techniques lack reproducibility and durable results. Despite this concern, surgical outcomes are associated with high degrees of patient satisfaction. The most effective methods of autologous fat transfer are yet to be established. Preliminary evaluation of ADSCs in fat grafting reveals advantages of stem cellYenriched tissue injections over traditional autologous fat transplantation. Adipose-derived stem cells counteract ischemia by increasing angiogenesis, decreasing the inf lammatory www.annalsplasticsurgery.com


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TABLE 2. Advantages and Disadvantages of Currently Available Bioengineered Scaffolds Investigator

Year

Scaffold Design

Nature of Biomaterial

Kulkarni RK141 1966

PLA polymers

Friedman SL142

1989

Collagen polymers

Freed LE123

1994

Synthetic

Dahms SE132

1998

Poly(ethylene glycol) polymers Acellular tissue matrix polymers

Patrick CW143

1999

PLGA polymers

Synthetic

Kimura Y128 Cen L122

2002 2008

Matrigel polymers PGA polymers

Natural Synthetic

Hedeń P144

2011

Natural

Atala A109

2012

Hyaluronan polymers Adipose-derived ECM polymers

Liu B71

2013

Fibrin polymers

Natural

Synthetic

Natural

Natural

Natural

Advantages Supports adipogenesis in vitro and in vivo; approved by the FDA on August 3, 2004, for the treatment of facial fat loss (Sculptra) Prevalent in native adipose ECM; well characterized; improves adipose tissue outcomes Supports adipogenesis; maintains shape after culture in vivo Cannot be manufactured on a large-scale in a reproducible manner Supports adipogenesis; induces vascularization in vivo Supports adipogenesis Supports adipogenesis both in vitro and in vivo Favorable mechanical properties; supports adipogenesis Native ECM promotes microenvironment for adipogenesis Biocompatible; supports adipogenesis in vivo

Disadvantages Degrades in vivo after 12 wk132

Fast degradation rate in vivo123,131

Degradation rate in vivo not well characterized Degrades post-implantation and is replaced/remodeled by ECM proteins synthesized by neighboring cells Lack of studies demonstrating long-term efficacy in vitro or in vivo Cannot be used for human in vivo applications Degrades in vivo after 4 wk Three-dimensional porous scaffolds not associated with improved adipose outcomes130 Has not been formulated as a 3-dimensional porous scaffold Has not been formulated as a 3-dimensional porous scaffold

10. Verseijden F, Posthumus-Van Sluijs SJ, van Neck JW, et al. Vascularization of prevascularized and non-prevascularized fibrin-based human adipose tissue constructs after implantation in nude mice. J Tissue Eng Regen Med. 2012;6:169Y178.

response, and modulating apoptosis. The clinical applicability of bioengineered scaffolds in fat transplantation remains uncertain. However, more research is needed to characterize the optimal method of autologous fat graft transplantation for use in routine clinical practice, with consistently reproducible results and predictable fat volume augmentation and maintenance.

11. Blanton MW, Hadad I, Johnstone BH, et al. Adipose stromal cells and platelet-rich plasma therapies synergistically increase revascularization during wound healing. Plast Reconstr Surg. 2009;123:56Y64.

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483

[Autologous fat grafting and rhinoplasty].

Experimental In-Vivo Models Used in Fat Grafting Research for Volume Augmentation in Soft Tissue Reconstruction.

Autologous fat grafting for whole breast reconstruction.

Autologous fat grafting for painful finger scars.

Fat Ful'fill'ment: A Review of Autologous Fat Grafting.

Autologous fat grafting in facial volumetric restoration.

Autologous Fat Grafting Improves Facial Nerve Function.

Autologous fat grafting for breast augmentation in underweight women.

Characterization of adipose tissue for autologous fat grafting.

The effect of pressure and shear on autologous fat grafting.

Autologous Fat Grafting as a Novel Approach to Parastomal Soft-tissue Volume Deficiencies.

Procedure, applications, and outcomes of autologous fat grafting.

Alleviation of neuropathic scar pain using autologous fat grafting.

Autologous fat grafting alleviates burn-induced neuropathic pain in rats.

Autologous fat grafting: in search of the optimal technique.

Correction of deep gluteal depression by autologous fat grafting.

Magnetic resonance imaging and ultrasound evaluation after breast autologous fat grafting combined with platelet-rich plasma.

Autologous facial fat transplantation: improved graft maintenance by microbead bioactivation.

Contrast-enhanced ultrasonography evaluation after autologous fat grafting in scar revision.

Oncological safety of autologous fat grafting after breast conservative treatment: a prospective evaluation.

Recurrence of invasive ductal breast carcinoma 10 months after autologous fat grafting.

Subconjunctival fat infiltration complicating autologous fat injection for facial augmentation.

Comparative analysis of processing methods in fat grafting.

Use of autologous fat grafting for reconstruction postmastectomy and breast conserving surgery: a systematic review protocol.