Encapsulation of adipogenic factors to promote differentiation of adipose-derived stem cells

Hedgehog Activation for Enhanced Rotator Cuff Tendon-to-Bone Healing

BACKGROUND

Rotator cuff repair is a common orthopaedic procedure, yet the rate of failure to heal after surgery is high. Repair site rupture is due to poor tendon-to-bone healing and lack of regeneration of the native fibrocartilaginous enthesis. During development, the enthesis is formed and mineralized by a pool of progenitors activated by hedgehog signaling. Furthermore, hedgehog signaling drives regenerative enthesis healing in young animals, in contrast to older animals, in which enthesis injuries heal via fibrovascular scar and without participation of hedgehog signaling.

HYPOTHESIS

Hedgehog activation improves tendon-to-bone healing in an animal model of rotator cuff repair.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 78 adult Sprague-Dawley rats were used. Supraspinatus tendon injury and repair were completed bilaterally, with microsphere-encapsulated hedgehog agonist administered to right shoulders and control microspheres administered to left shoulders. Animals were sacrificed after 3, 14, 28, or 56 days. Gene expression and histological, biomechanical, and bone morphometric analyses were conducted.

RESULTS

At 3 days, hedgehog signaling pathway genes Gli1 (1.70; P = .029) and Smo (2.06; P = .0173), as well as Runx2 (1.69; P = .0386), a transcription factor of osteogenesis, were upregulated in treated relative to control repairs. At 14 days, transcription factors of tenogenesis, Scx (4.00; P = .041), and chondrogenesis, Sox9 (2.95; P = .010), and mineralized fibrocartilage genes Col2 (3.18; P = .031) and Colx (1.85; P = .006), were upregulated in treated relative to control repairs. Treatment promoted fibrocartilage formation at the healing interface by 28 days, with improvements in tendon-bone maturity, organization, and continuity. Treatment led to improved biomechanical properties. The material property strength (2.43 vs 1.89 N/m2; P = .046) and the structural property work to failure (29.01 vs 18.09 mJ; P = .030) were increased in treated relative to control repairs at 28 days and 56 days, respectively. Treatment had a marginal effect on bone morphometry underlying the repair. Trabecular thickness (0.08 vs 0.07 mm; P = .035) was increased at 28 days.

CONCLUSION

Hedgehog agonist treatment activated hedgehog signaling at the tendon-to-bone repair site and prompted increased mineralized fibrocartilage production. This extracellular matrix production and mineralization resulted in improved biomechanical properties, demonstrating the therapeutic potential of hedgehog agonism for improving tendon-to-bone healing after rotator cuff repair.

CLINICAL RELEVANCE

This study demonstrates the therapeutic potential of hedgehog agonist treatment for improving tendon-to-bone healing after rotator cuff injury and repair.

Injectable anti-cancer drug loaded silk-based hydrogel for the prevention of cancer recurrence and post-lumpectomy tissue regeneration aiding triple-negative breast cancer therapy

A single system capable of delivering anticancer drugs and growth factors by a minimally invasive approach is in demand for effective treatment of triple-negative breast cancer (TNBC) after lumpectomy. Here, we showcase one such holistic system for TNBC therapy and its assessment via 3D in vitro lumpectomy model, a first of its kind. Firstly, Bombyx mori silk fibroin (BMSF) and Antheraea assamensis silk fibroin (AASF) blended hydrogels were prepared and biophysically characterized. Secondly, a 3D in vitro lumpectomy model was developed using MDA-MB-231 cell line to assess the efficacy of localized delivery of doxorubicin (dox) using injectable hydrogel system in terminating remaining breast cancer after lumpectomy. Additionally, we have also evaluated the adipose tissue regeneration in the lumpectomy region by delivering dexamethasone (dex) using injectable hydrogels. Rheological studies showed that the BMSF/AASF blended hydrogels exhibit viscoelasticity and injectability conducive for minimally invasive application. The developed hydrogels by virtue of its slow and sustained release of dox exerted cytotoxicity towards MDA-MB-231 cells assessed through in vitro studies. Further, dex loaded hydrogel supported adipogenic differentiation of adipose tissue derived stem cells (ADSCs), while the secreted factors were found to aid in vascularization and macrophage polarization. This was confirmed through in vitro angiogenic tube formation assay and macrophage polarization study respectively. The corroborated results vouch for potential application of this injectable hydrogels for localized anticancer drug delivery and aiding in breast reconstruction, post lumpectomy.

New perspectives in regenerative medicine and surgery: the bioactive composite therapies (BACTs)

Regenerative medicine and surgery is a rapidly expanding branch of translational research in tissue engineering, cellular and molecular biology. To date, the methods to improve cell intake, survival, and isolation need to comply with a complex and still unclear regulatory frame, becoming everyday more restrictive and often limiting the effectiveness and outcome of the therapeutic choices. Thus, the authors developed a novel 360° regenerative strategy based on the synergic action of several new components called the bioactive composite therapies (BACTs) to improve grafted cells intake, and survival in total compliance with the legal and ethical limits of the current regulatory frame. The rationale at the origin of this new technology is based on the evidence that cells need supportive substrate to survive in vitro and this observation, applying the concept of translational medicine, is true also in vivo. Bioactive composite mixtures (BACMs) are tailor-made bioactive mixtures containing several bioactive components that support cells' survival and induce a regenerative response in vivo by stimulating the recipient site to act as an in situ real bioreactor. Many different tissues have been used in the past for the isolation of cells, molecules, and growth factors, but the adipose tissue and its stromal vascular fraction (SVF) remains the most valuable, abundant, safe, and reliable source of regenerative components and particularly of adipose-derived stems cells (ADSCs). The role of plastic surgeons as the historical experts in all the most advanced techniques for harvesting, manipulating, and grafting adipose tissue is fundamental in this constant process of expansion of regenerative procedures. In this article, we analyze the main causes of cell death and the strategies for preventing it, and we present all the technical steps for preparing the main components of BACMs and the different mixing modalities to obtain the most efficient regenerative action on different clinical and pathological conditions. The second section of this work is dedicated to the logical and sequential evolution from simple bioactive composite grafts (BACGs) that distinguished our initial approach to regenerative medicine, to BACTs where many other fundamental technical steps are analyzed and integrated for supporting and enhancing the most efficient regenerative activity. Level of Evidence: Not gradable.

Encapsulation of troglitazone and AVE0991 by gelation microspheres promotes epithelial transformation of adipose-derived stem cells

Deformities in human soft tissue caused by trauma or burn present a difficult problem in plastic surgery. In this study, we encapsulated troglitazone and angiotensin 1-7 mimetic AVE0991 in gelation microspheres with the goal of inducing epithelial transformation for potential applications in tissue reconstruction. After troglitazone or AVE0991 were encapsulated to gelation microspheres, their release kinetics and bioactivity were examined. Surface morphology and diameter of the gelation microspheres were evaluated using light microscopy. The release of the drugs was assessed in the presence of human adipose-derived stem cells (ADSCs). Treatment with troglitazone microspheres increased cell viability and activated the β-catenin in ADSCs. Moreover, the AVE0991 microspheres also increased cell viability and C-myc expression of ADSCs. These results showed that troglitazone and AVE0991 microspheres promoted the activity of ADSCs. Furthermore, ADSCs were co-treated with troglitazone and AVE0991 microspheres. Western blot and immunofluorescent staining showed that co-treatment with troglitazone and AVE0991 microspheres elevated the expression of epithelialization associated protein CK14 in ADSCs. In conclusion, our findings indicate that microspheres with troglitazone and AVE0991 can significantly improve the viability and epithelialization of ADSCs, which provides a new approach for the construction of tissue-engineered skin.

Sustained low-dose dexamethasone delivery via a PLGA microsphere-embedded agarose implant for enhanced osteochondral repair

Articular cartilage defects are a common source of joint pain and dysfunction. We hypothesized that sustained low-dose dexamethasone (DEX) delivery via an acellular osteochondral implant would have a dual pro-anabolic and anti-catabolic effect, both supporting the functional integrity of adjacent graft and host tissue while also attenuating inflammation caused by iatrogenic injury. An acellular agarose hydrogel carrier with embedded DEX-loaded poly(lactic-co-glycolic) acid (PLGA) microspheres (DLMS) was developed to provide sustained release for at least 99 days. The DLMS implant was first evaluated in an in vitro pro-inflammatory model of cartilage degradation. The implant was chondroprotective, as indicated by maintenance of Young's modulus (EY) (p = 0.92) and GAG content (p = 1.0) in the presence of interleukin-1β insult. In a subsequent preliminary in vivo experiment, an osteochondral autograft transfer was performed using a pre-clinical canine model. DLMS implants were press-fit into the autograft donor site and compared to intra-articular DEX injection (INJ) or no DEX (CTL). Functional scores for DLMS animals returned to baseline (p = 0.39), whereas CTL and INJ remained significantly worse at 6 months (p < 0.05). DLMS knees were significantly more likely to have improved OARSI scores for proteoglycan, chondrocyte, and collagen pathology (p < 0.05). However, no significant improvements in synovial fluid cytokine content were observed. In conclusion, utilizing a targeted DLMS implant, we observed in vitro chondroprotection in the presence of IL-1-induced degradation and improved in vivo functional outcomes. These improved outcomes were correlated with superior histological scores but not necessarily a dampened inflammatory response, suggesting a primarily pro-anabolic effect. STATEMENT OF SIGNIFICANCE: Articular cartilage defects are a common source of joint pain and dysfunction. Effective treatment of these injuries may prevent the progression of osteoarthritis and reduce the need for total joint replacement. Dexamethasone, a potent glucocorticoid with concomitant anti-catabolic and pro-anabolic effects on cartilage, may serve as an adjuvant for a variety of repair strategies. Utilizing a dexamethasone-loaded osteochondral implant with controlled release characteristics, we demonstrated in vitro chondroprotection in the presence of IL-1-induced degradation and improved in vivo functional outcomes following osteochondral repair. These improved outcomes were correlated with superior histological cartilage scores and minimal-to-no comorbidity, which is a risk with high dose dexamethasone injections. Using this model of cartilage restoration, we have for the first time shown the application of targeted, low-dose dexamethasone for improved healing in a preclinical model of focal defect repair.

Current Therapeutic Strategies for Adipose Tissue Defects/Repair Using Engineered Biomaterials and Biomolecule Formulations

Tissue engineered scaffolds for adipose restoration/repair has significantly evolved in recent years. Patients requiring soft tissue reconstruction, caused by defects or pathology, require biomaterials that will restore void volume with new functional tissue. The gold standard of autologous fat grafting (AFG) is not a reliable option. This review focuses on the latest therapeutic strategies for the treatment of adipose tissue defects using biomolecule formulations and delivery, and specifically engineered biomaterials. Additionally, the clinical need for reliable off-the-shelf therapies, animal models, and challenges facing current technologies are discussed.

Biodegradable silk catheters for the delivery of therapeutics across anatomical repair sites

Biodegradable silk catheters for the delivery of therapeutics are designed with a focus on creating porous gradients that can direct the release of molecules away from the implantation site. Though suitable for a range of applications, these catheters are designed for drug delivery to transplanted adipose tissue in patients having undergone a fat grafting procedure. A common complication for fat grafts is the rapid reabsorption of large volume adipose transplants. In order to prolong volume retention, biodegradable catheters can be embedded into transplanted tissue to deliver nutrients, growth factors or therapeutics to improve adipocyte viability, proliferation, and ultimately extend volume retention. Two fabrication methods are developed: a silk gel-spinning technique, which uses a novel flash-freezing step to induce high porosity throughout the bulk of the tube, and a dip-coating process using silk protein solutions doped with a water soluble porogen. Increased porosity aids in the diffusion of drug through the silk tube in a controllable way. Additionally, we interface the porous tubes with ALZET osmotic pumps for implantation into a subcutaneous nude mouse model. The work described herein will discuss the processing parameters as well as the interfacing between pump and cargo therapeutic and the resulting release profiles. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2018. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 501-510, 2019.

Dynamical release nanospheres containing cell growth factor from biopolymer hydrogel via reversible covalent conjugation

For practical adipose regeneration, the challenge is to dynamically deliver the key adipogenic insulin-like growth factors in hydrogels to induce adipogenesis. In order to achieve dynamic release, smart hydrogels to sense the change in the blood glucose concentration is required when glucose concentration increases. In this study, a heparin-based hydrogel has been developed for use in dynamic delivery of heparin nanospheres containing insulin-like growth factor. The gel scaffold was facilely prepared in physiological conditions by the formation of boronate-maltose ester cross-links between boronate and maltose groups of heparin derivatives. Due to its intrinsic glucose-sensitivity, the exposure of gel scaffold to glucose induces maltose functionalized nanospheres dissociation off hydrogel network and thereby could dynamically move into the microenvironment. The potential of the hydrogel as a cell scaffold was demonstrated by encapsulation of human adipose-derived stem cells (ASCs) within the gel matrix in vitro. Cell culture showed that this dynamic hydrogel could support survival and proliferation of ASCs. This biocompatible coupling chemistry has the advantage that it introduces no potentially cytotoxic groups into injectable gel scaffolds formed and can create a more biomimetic microenvironment for drug and cell delivery, rendering them more suitable for potential in vivo biomedical applications. All these results indicate that this biocompatible gel scaffold can render the formulation of a therapeutically effective platform for diabetes treatment and adipose regeneration.

Hydrogel Encapsulation Facilitates Rapid-Cooling Cryopreservation of Stem Cell-Laden Core-Shell Microcapsules as Cell-Biomaterial Constructs

Core-shell structured stem cell microencapsulation in hydrogel has wide applications in tissue engineering, regenerative medicine, and cell-based therapies because it offers an ideal immunoisolative microenvironment for cell delivery and 3D culture. Long-term storage of such microcapsules as cell-biomaterial constructs by cryopreservation is an enabling technology for their wide distribution and ready availability for clinical transplantation. However, most of the existing studies focus on cryopreservation of single cells or cells in microcapsules without a core-shell structure (i.e., hydrogel beads). The goal of this study is to achieve cryopreservation of stem cells encapsulated in core-shell microcapsules as cell-biomaterial constructs or biocomposites. To this end, a capillary microfluidics-based core-shell alginate hydrogel encapsulation technology is developed to produce porcine adipose-derived stem cell-laden microcapsules for vitreous cryopreservation with very low concentration (2 mol L-1 ) of cell membrane penetrating cryoprotective agents (CPAs) by suppressing ice formation. This may provide a low-CPA and cost-effective approach for vitreous cryopreservation of "ready-to-use" stem cell-biomaterial constructs, facilitating their off-the-shelf availability and widespread applications.

Adipose derived delivery vehicle for encapsulated adipogenic factors

Hydrogels derived from adipose tissue extracellular matrix (AdECM) have shown potential in the ability to generate new adipose tissue in vivo. To further enhance adipogenesis, a composite adipose derived delivery system (CADDS) containing single- and double-walled dexamethasone encapsulated microspheres (SW and DW Dex MS) has been developed. Previously, our laboratory has published the use of Dex MS as an additive to enhance adipogenesis and angiogenesis in adipose tissue grafts. In the current work, AdECM and CADDS are extensively characterized, in addition to conducting in vitro cell culture analysis. Study results indicate the AdECM used for the CADDS has minimal cellular and lipid content allowing for gelation of its collagen structure under physiological conditions. Adipose-derived stem cell (ASC) culture studies confirmed biocompatibility with the CADDS, and adipogenesis was increased in experimental groups containing the hydrogel scaffold. In vitro studies of AdECM hydrogel containing microspheres demonstrated a controlled release of dexamethasone from SW and DW formulations. The delivery of Dex MS via an injectable hydrogel scaffold combines two biologically responsive components to develop a minimally, invasive, off-the-shelf biomaterial for adipose tissue engineering.

STATEMENT OF SIGNIFICANCE

Scientists and doctors have yet to develop an off-the-shelf product for patients with soft tissue defects. Recently, the use of adipose derived extracellular matrix (adECM) to generate new adipose tissue in vivo has shown great promise but individually, adECM still has limitations in terms of volume and consistency. The current work introduces a novel composite off-the-shelf construct comprised of an adECM-based hydrogel and dexamethasone encapsulated microspheres (Dex MS). The hydrogel construct serves not only as an injectable protein-rich scaffold but also a delivery system for the Dex MS for non-invasive application to the defect site. The methods and results presented are a progressive step forward in the field of adipose tissue engineering.

Controlled dexamethasone delivery via double-walled microspheres to enhance long-term adipose tissue retention

Current materials used for adipose tissue reconstruction have critical shortcomings such as suboptimal volume retention, donor-site morbidity, and poor biocompatibility. The aim of this study was to examine a controlled delivery system of dexamethasone to generate stable adipose tissue when mixed with disaggregated human fat in an athymic mouse model for 6 months. The hypothesis that the continued release of dexamethasone from polymeric microspheres would enhance both adipogenesis and angiogenesis more significantly when compared to the single-walled microsphere model, resulting in long-term adipose volume retention, was tested. Dexamethasone was encapsulated within single-walled poly(lactic-co-glycolic acid) microspheres (Dex SW MS) and compared to dexamethasone encapsulated in a poly(lactic-co-glycolic acid) core surrounded by a shell of poly-l-lactide. The double-walled polymer microsphere system in the second model was developed to create a more sustainable drug delivery process. Dexamethasone-loaded poly(lactic-co-glycolic acid) microspheres (Dex SW MS) and dexamethasone-loaded poly(lactic-co-glycolic acid)/poly-l-lactide double-walled microspheres (Dex DW MS) were prepared using single and double emulsion/solvent techniques. In vitro release kinetics were determined. Two doses of each type of microsphere were examined; 50 and 27 mg of Dex MS and Dex DW MS were mixed with 0.3 mL of human lipoaspirate. Additionally, 50 mg of empty MS and lipoaspirate-only controls were examined. Samples were analyzed grossly and histologically after 6 months in vivo. Mass and volume were measured; dexamethasone microsphere-containing samples demonstrated greater adipose tissue retention compared to the control group. Histological analysis, including hematoxylin and eosin and CD31 staining, indicated increased vascularization (p < 0.05) within the Dex MS-containing samples. Controlled delivery of adipogenic factors, such as dexamethasone via polymer microspheres, significantly affects adipose tissue retention by maintaining healthy tissue formation and vascularization. Dex DW MS provide an improved model to former Dex SW MS, resulting in notably longer release time and, consequently, larger volumes of adipose retained in vivo. The use of microspheres, specifically double-walled, as vehicles for controlled drug delivery of adipogenic factors therefore present a clinically relevant model of adipose retention that has the potential to greatly improve soft tissue repair.

Adipose regeneration and implications for breast reconstruction: update and the future

The evolution of breast reconstruction and management of breast cancer has evolved significantly since the earliest descriptions in the Edwin Smith Papyrus (3,000 BC). The development of surgical and scientific expertise has changed the way that women are managed, and plastic surgeons are now able to offer a wide range of reconstructive options to suit individual needs. Beyond the gold standard autologous flap based reconstructions, regenerative therapies promise the elimination of donor site morbidity whilst providing equivalent aesthetic and functional outcomes. Future research aims to address questions regarding ideal cell source, optimisation of scaffold composition and interaction of de novo adipose tissue in the microenvironment of breast cancer.

Dexamethasone Release from Within Engineered Cartilage as a Chondroprotective Strategy Against Interleukin-1α

While significant progress has been made toward engineering functional cartilage constructs with mechanical properties suitable for in vivo loading, the impact on these grafts of inflammatory cytokines, chemical factors that are elevated with trauma or osteoarthritis, is poorly understood. Previous work has shown dexamethasone to be a critical compound for cultivating cartilage with functional properties, while also providing chondroprotection from proinflammatory cytokines. This study tested the hypothesis that the incorporation of poly(lactic-co-glycolic acid) (PLGA) (75:25) microspheres that release dexamethasone from within chondrocyte-seeded agarose hydrogel constructs would promote development of constructs with functional properties and protect constructs from the deleterious effects of interleukin-1α (IL-1α). After 28 days of growth culture, experimental groups were treated with IL-1α (10 ng/mL) for 7 days. Reaching native equilibrium moduli and proteoglycan levels, dexamethasone-loaded microsphere constructs exhibited tissue properties similar to microsphere-free control constructs cultured in dexamethasone-supplemented culture media and were insensitive to IL-1α exposure. These findings are in stark contrast to constructs containing dexamethasone-free microspheres or no microspheres, cultured without dexamethasone, where IL-1α exposure led to significant tissue degradation. These results support the use of dexamethasone delivery from within engineered cartilage, through biodegradable microspheres, as a strategy to produce mechanically functional tissues that can also combat the deleterious effects of local proinflammatory cytokine exposure.

Magnetic hyaluronic acid nanospheres via aqueous Diels-Alder chemistry to deliver dexamethasone for adipose tissue engineering

Biopolymer-based nanospheres have great potential in the field of drug delivery and tissue regenerative medicine. In this work, we present a flexible way to conjugate a magnetic hyaluronic acid (HA) nanosphere system that are capable of vectoring delivery of adipogenic factor, e.g. dexamethasone, for adipose tissue engineering. Conjugation of nanospheres was established by aqueous Diels-Alder chemistry between furan and maleimide of HA derivatives. Simultaneously, a furan functionalized dexamethasone peptide, GQPGK, was synthesized and covalently immobilized into the nanospheres. The magnetic HA nanospheres were fabricated by encapsulating super-paramagnetic iron oxide nanoparticles, which exhibited quick magnetic sensitivity. The aqueous Diels-Alder chemistry made nanospheres high binding efficiency of dexamethasone, and the vectoring delivery of dexamethasone could be easily controlled by a external magnetic field. The potential application of the magnetic HA nanospheres on vectoring delivery of adipogenic factor was confirmed by co-culture of human adipose-derived stem cells (ASCs). In vitro cytotoxicity tests demonstrated that incorporation of dexamethasone into magnetic HA nanospheres showed high efficiency to promote ASCs viabilities, in particular under a magnetic field, which suggested a promising future for adipose regeneration applications.

Biodegradable hyaluronic acid hydrogels to control release of dexamethasone through aqueous Diels-Alder chemistry for adipose tissue engineering

A robust synthetic strategy of biopolymer-based hydrogels has been developed where hyaluronic acid derivatives reacted through aqueous Diels-Alder chemistry without the involvement of chemical catalysts, allowing for control and sustain release of dexamethasone. To conjugate the hydrogel, furan and maleimide functionalized hyaluronic acid were synthesized, respectively, as well as furan functionalized dexamethasone, for the covalent immobilization. Chemical structure, gelation time, morphologies, swelling kinetics, weight loss, compressive modulus and dexamethasone release of the hydrogel system in PBS at 37°C were studied. The results demonstrated that the aqueous Diels-Alder chemistry provides an extremely selective reaction and proceeds with high efficiency for hydrogel conjugation and covalent immobilization of dexamethasone. Cell culture results showed that the dexamethasone immobilized hydrogel was noncytotoxic and preserved proliferation of entrapped human adipose-derived stem cells. This synthetic approach uniquely allows for the direct fabrication of biologically functionalized gel scaffolds with ideal structures for adipose tissue engineering, which provides a competitive alternative to conventional conjugation techniques such as copper mediated click chemistry.

Autologous Stem Cell Therapy: How Aging and Chronic Diseases Affect Stem and Progenitor Cells

During recent years different types of adult stem/progenitor cells have been successfully applied for the treatment of many pathologies, including cardiovascular diseases. The regenerative potential of these cells is considered to be due to their high proliferation and differentiation capacities, paracrine activity, and immunologic privilege. However, therapeutic efficacy of the autologous stem/progenitor cells for most clinical applications remains modest, possibly because of the attenuation of their regenerative potential in aged patients with chronic diseases such as cardiovascular diseases and metabolic disorders. In this review we will discuss the risk factors affecting the therapeutic potential of adult stem/progenitor cells as well as the main approaches to mitigating them using the methods of regenerative medicine.

Adipogenic factor-loaded microspheres increase retention of transplanted adipose tissue

The aim of this study was to develop and test a controlled delivery system of two adipogenic factors (insulin and dexamethasone [Dex]), to generate stable adipose tissue when mixed with disaggregated human fat. Both drugs were encapsulated in poly(lactic-co-glycolic acid), (PLGA) microspheres (MS) and mixed with human lipoaspirate to induce adipogenesis in vivo. It was hypothesized that the slow release of insulin and Dex would enhance both adipogenesis and angiogenesis, thus retaining the fat graft volume in a nude mouse model. Insulin/Dex-loaded PLGA MS (Insulin/Dex MS) were prepared using both single and double emulsion/solvent extraction techniques. The bioactivity of the drugs was assessed by mixing the MS with human lipoaspirate and injecting subcutaneously into the dorsal aspect of an athymic mouse. Five doses of the drugs were examined and samples were analyzed grossly and histologically after 5 weeks in vivo. Mass and volume of the grafts were measured with the microsphere-containing samples, demonstrating increased mass and volume with increasing drug doses. Histological analysis, including H&E and CD31, indicated increased vascularization within the insulin/Dex MS-containing samples compared with the lipoaspirate-only samples. This study demonstrates that the controlled delivery of adipogenic factors such as insulin and Dex through polymer MS can significantly enhance tissue formation and vascularization, therefore presenting a potentially clinically relevant model of adipose retention.

Adipose-derived stem cells: Implications in tissue regeneration

Adipose-derived stem cells (ASCs) are mesenchymal stem cells (MSCs) that are obtained from abundant adipose tissue, adherent on plastic culture flasks, can be expanded in vitro, and have the capacity to differentiate into multiple cell lineages. Unlike bone marrow-derived MSCs, ASCs can be obtained from abundant adipose tissue by a minimally invasive procedure, which results in a high number of cells. Therefore, ASCs are promising for regenerating tissues and organs damaged by injury and diseases. This article reviews the implications of ASCs in tissue regeneration.

Sustained volume retention in vivo with adipocyte and lipoaspirate seeded silk scaffolds

Current approaches to soft tissue regeneration include the use of fat grafts, natural or synthetic biomaterials as filler materials. Fat grafts and natural biomaterials resorb too quickly to maintain tissue regeneration, while synthetic materials do not degrade or regenerate tissue. Here, we present a simple approach to volume stable filling of soft tissue defects. In this study, we combined lipoaspirate with a silk protein matrix in a subcutaneous rat model. Silk biomaterials can be tailored to fit a variety of needs, and here were processed silk biomaterials into a porous sponge format to allow for tissue ingrowth while remaining mechanically robust. Over an 18 month period, the lipoaspirate seeded silk protein matrix regenerated subcutaneous adipose tissue while maintaining the original implanted volume. A silk protein matrix alone was not sufficient to regenerate adipose tissue, but yielded a fibrous tissue, although implanted volume was maintained. This work presents a significant improvement to the standard approaches to filling soft tissue defects by matching biomaterial degradation and tissue regeneration profiles.

Injectable nanohybrid scaffold for biopharmaceuticals delivery and soft tissue engineering

An injectable nanofibrous hydrogel scaffold integrated with growth factors (GFs) loaded polysaccharide nanoparticles was developed that specifically allows for targeted adipose-derived stem cells (ASCs) encapsulation and soft tissue engineering. The nanofibrous hydrogel was produced via biological conjugation of biotin-terminated star-shaped poly(ethylene glycol) (PEG-Biotin) and streptavidin-functionalized hyaluronic acid (HA-Streptavidin). The polysaccharide nanoparticles were noncovalently assembled via electrostatic interactions between low-molecular-weight heparin (LMWH) and N,N,N-trimethylchitosan chloride (TMC). Vascular endothelial growth factor (VEGF) was entrapped in the LMWH/TMC nanoparticles by affinity interactions with LMWH.