Growth Factor Delivery System Research Articles

Osteogenic Differentiation of Human Adipose-Derived Stem Cells Seeded on a Biomimetic Spongiosa-like Scaffold: Bone Morphogenetic Protein-2 Delivery by Overexpressing Fascia.

Human adipose-derived stem cells (hADSCs) have the capacity for osteogenic differentiation and, in combination with suitable biomaterials and growth factors, the regeneration of bone defects. In order to differentiate hADSCs into the osteogenic lineage, bone morphogenetic proteins (BMPs) have been proven to be highly effective, especially when expressed locally by route of gene transfer, providing a constant stimulus over an extended period of time. However, the creation of genetically modified hADSCs is laborious and time-consuming, which hinders clinical translation of the approach. Instead, expedited single-surgery gene therapy strategies must be developed. Therefore, in an in vitro experiment, we evaluated a novel growth factor delivery system, comprising adenoviral BMP-2 transduced fascia tissue in terms of BMP-2 release kinetics and osteogenic effects, on hADSCs seeded on an innovative biomimetic spongiosa-like scaffold. As compared to direct BMP-2 transduction of hADSCs or addition of recombinant BMP-2, overexpressing fascia provided a more uniform, constant level of BMP-2 over 30 days. Despite considerably higher BMP-2 peak levels in the comparison groups, delivery by overexpressing fascia led to a strong osteogenic response of hADSCs. The use of BMP-2 transduced fascia in combination with hADSCs may evolve into an expedited single-surgery gene transfer approach to bone repair.

Composite Bioinks With Mesoporous Bioactive Glasses-A Critical Evaluation of Results Obtained by In Vitro Experiments.

Besides osteoconductivity and a high degradation rate, mesoporous bioactive glasses (MBGs) are specific for their highly ordered channel structure and high specific surface area, making them suitable as drug and/or growth factor delivery systems. On the other hand, the mesoporous channel structure and MBG composition can have an effect on common cell evaluation assays, leading to inconclusive results. This effect is especially important when MBG is mixed in composite bioinks, together with cells. Additionally, the hydrogel component of the ink can influence the degradation of MBG, leading to different ion releases, which can additionally affect the analyses. Hence, our aim here was to show how the MBG structure and composition influence common cell viability and differentiation assays when calcium (Ca)- or magnesium (Mg)-containing glass is part of an alginate-based composite bioink. We suggested pre-labeling of cells with DiI prior to bioprinting and staining with calcein-AM to allow identification of metabolically active cells expressing signals in both green and red channels, allowing the use of fluorescence imaging for cell viability evaluations in the presence of high amounts (7 wt %) of MBGs. The release and uptake of ions during degradation of CaMBG and MgMBG were significantly changed by alginate in the composite bioinks, as confirmed by higher release and uptake from bulk glasses. Additionally, we detected a burst release of Mg2+ from composites only after 24 h of incubation. Furthermore, we demonstrated that released ions and the mesoporous channel structure affect the measurement of lactate dehydrogenase (LDH) and alkaline phosphatase activity (ALP) in bioprinted composite scaffolds. Measured LDH activity was significantly decreased in the presence of CaMBG. On the other hand, the presence of MgMBG induced increased signal measured for the ALP. Taken together, our findings show how composite bioinks containing MBGs can interfere with common analyses, obtaining misleading results.

Comparison of bone formation mediated by bone morphogenetic protein delivered by nanoclay gels with clinical techniques (autograft and InductOs®) in an ovine bone model

Development of a growth factor delivery vehicle providing appropriate temporal-spatial release together with an appropriate preclinical large animal model to evaluate bone formation is critical in the development of delivery strategies for bone tissue regeneration. Smectite nanoclays such as LAPONITE™ possess unique thixotropic and protein retention properties offering promise for use in growth factor delivery in bone repair and regeneration. This study has examined bone formation mediated by a clinically approved growth factor delivery system (InductOs®) in combination with Laponite gel in an aged female ovine femoral condyle defect preclinical model (10 weeks). Two different designs, one containing a low volume of Laponite gel (LLG) in combination with the InductOs® absorbable collagen sponge (ACS), the other in which Laponite gel formed the implant (HLG), were compared against InductOs® alone and an autograft positive control. Thus, five groups: (i) empty defect, (ii) autograft, (iii) BMP2 + ACS, (iv) BMP2 + ACS + LLG and (v) BMP2 + HLG + ACS were examined in 9 mm × 12 mm defects performed bilaterally in the medial femoral condyles of 24 aged (>5 years) sheep. Bone formation within the defect was assessed using micro-computed tomography (micro-CT), digital volume correlation (DVC) for biomechanical characterisation as well as histology. The autograft and InductOs® mediated enhanced bone formation (p < 0001) compared to blank controls, while no significant differences were observed between the Laponite/Collagen/BMP delivery vehicles. However, the current study illustrated the excellent biocompatibility of Laponite and its ability to deliver localised active BMP-2, with the opportunity for improved efficacy with further optimisation. Interestingly, DVC-computed strain distributions indicated that the regenerated bone structure is mechanically adapted to bear external loads from the early remodelling stages of the bone reparation cascade. The current studies of selected nanoclay delivery platforms for BMP, assessed in a clinically relevant large animal model auger well for the development of bone fracture therapeutics for an ageing population.

Gelatin-Alginate Coacervates Optimized by DOE to Improve Delivery of bFGF for Wound Healing.

Metabolic disorders in diabetic patients are associated with altered protein and lipid metabolism and defects in granulation tissue formation, resulting in non-healing wounds such as diabetic foot ulcers (DFU). Growth factors have essential roles in tissue re-epithelization and angiogenesis during wound healing. In this study, a complex coacervate was evaluated as an enhanced delivery system for fibroblast growth factor (bFGF) to control its release rate and protect it from proteases. Coacervates composed of gelatin Type A (GA) and sodium alginate (SA) were optimized by the Design of Experiments (DOE), with the polymer ratio and the medium’s pH as the independent variables, and turbidity, particle size, polydispersity index, and encapsulation efficiency (EE, %) as the responses. The optimized coacervate protected bFGF from trypsin digestion and showed controlled release compared with bFGF in solution or a physical mixture of GA and SA. It enhanced the viability, migration, and procollagen I C-terminal propeptide synthesis of human dermal fibroblasts in hyperglycemic conditions. In summary, the DOE approach was successfully applied to optimize bFGF GA-SA coacervates as a potential novel therapeutic modality to treat DFU.

Spatiotemporal regulation of angiogenesis/osteogenesis emulating natural bone healing cascade for vascularized bone formation

Engineering approaches for growth factor delivery have been considerably advanced for tissue regeneration, yet most of them fail to provide a complex combination of signals emulating a natural healing cascade, which substantially limits their clinical successes. Herein, we aimed to emulate the natural bone healing cascades by coupling the processes of angiogenesis and osteogenesis with a hybrid dual growth factor delivery system to achieve vascularized bone formation. Basic fibroblast growth factor (bFGF) was loaded into methacrylate gelatin (GelMA) to mimic angiogenic signalling during the inflammation and soft callus phases of the bone healing process, while bone morphogenetic protein-2 (BMP-2) was bound onto mineral coated microparticles (MCM) to mimics osteogenic signalling in the hard callus and bone remodelling phases. An Initial high concentration of bFGF accompanied by a sustainable release of BMP-2 and inorganic ions was realized to orchestrate well-coupled osteogenic and angiogenic effects for bone regeneration. In vitro experiments indicated that the hybrid hydrogel markedly enhanced the formation of vasculature in human umbilical vein endothelial cells (HUVECs), as well as the osteogenic differentiation of mesenchymal stem cells (BMSCs). In vivo results confirmed the optimal osteogenic performance of our F/G-B/M hydrogel, which was primarily attributed to the FGF-induced vascularization. This research presents a facile and potent alternative for treating bone defects by emulating natural cascades of bone healing.Graphical

Controlled growth factor delivery system with osteogenic-angiogenic coupling effect for bone regeneration.

ObjectiveBone regeneration involves a coordinated cascade of events that are regulated by several cytokines and growth factors, among which bone morphogenic protein-2 (BMP-2), vascular endothelial growth factor (VEGF) and fibroblast growth factor-2 (FGF-2) play important roles. In this study, we investigated the effects of dual release of the three growth factors on bone regeneration in femur defects.MethodsA composite consisting of Gelatin microparticles loaded with VEGF/FGF-2 and poly(lactic-co-glycolic acid)-poly(ethylene glycol)-carboxyl (PLGA-PEG-COOH) microparticles loaded with BMP-2 encapsulated in a nano hydroxyapatite-poly actic-co-glycolic acid (nHA-PLGA) scaffold was prepared for the dual release of the growth factors.ResultsOn the 14th day, decreased release rate of BMP-2 compared with FGF-2 and VEGF was observed. However, after 14 days, compared to FGF-2 and VEGF, BMP-2 showed an increased release rate. Controlled dual release of BMP-2 and VEGF, FGF-2 resulted in a significant osteogenic differentiation of bone mesenchymal stem cells (BMSCs). Moreover, effects of the composite scaffold on functional connection of osteoblast-vascular cells during bone development were evaluated. The synergistic effects of dual delivery of growth factors were shown to promote the expression of VEGF in BMSCs. Increased secretion of VEGF from BMSCs promoted the proliferation and angiogenic differentiation of human umbilical vein endothelial cells (HUVECs) in the co-culture system. At 12 weeks after implantation, blood vessel and bone formation were analyzed by micro-CT and histology. The composite scaffold significantly promoted the formation of blood vessels and new bone in femur defects.ConclusionsThese findings demonstrate that dual delivery of angiogenic factors and osteogenic factors from Gelatin and PLGA-PEG-COOH microparticles-based composite scaffolds exerted an osteogenic-angiogenic coupling effect on bone regeneration. This approach will inform on the development of appropriate designs of high-performance bioscaffolds for bone tissue engineering.

Spatiotemporally controlled, aptamers-mediated growth factor release locally manipulates microvasculature formation within engineered tissues

Spatiotemporally controlled growth factor (GF) delivery is crucial for achieving functional vasculature within engineered tissues. However, conventional GF delivery systems show inability to recapitulate the dynamic and heterogeneous nature of developing tissue's biochemical microenvironment. Herein, an aptamer-based programmable GF delivery platform is described that harnesses dynamic affinity interactions for facilitating spatiotemporal control over vascular endothelial GF (VEGF165) bioavailability within gelatin methacryloyl matrices. The platform showcases localized VEGF165 sequestration from the culture medium (offering spatial-control) and leverages aptamer-complementary sequence (CS) hybridization for triggering VEGF165 release (offering temporal-control), without non-specific leakage. Furthermore, extensive 3D co-culture studies (human umbilical vein-derived endothelial cells & mesenchymal stromal cells), in bi-phasic hydrogel systems revealed its fundamentally novel capability to selectively guide cell responses and manipulate lumen-like microvascular networks via spatiotemporally controlling VEGF165 bioavailability within 3D microenvironment. This platform utilizes CS as an external biochemical trigger for guiding vascular morphogenesis which is suitable for creating dynamically controlled engineered tissues.

Release of basic fibroblast growth factor from acoustically-responsive scaffolds promotes therapeutic angiogenesis in the hind limb ischemia model

Pro-angiogenic growth factors have been studied as potential therapeutics for cardiovascular diseases like critical limb ischemia (CLI). However, the translation of these factors has remained a challenge, in part, due to problems associated with safe and effective delivery. Here, we describe a hydrogel-based delivery system for growth factors where release is modulated by focused ultrasound (FUS), specifically a mechanism termed acoustic droplet vaporization. With these fibrin-based, acoustically-responsive scaffolds (ARSs), release of a growth factor is non-invasively and spatiotemporally-controlled in an on-demand manner using non-thermal FUS. In vitro studies demonstrated sustained release of basic fibroblast growth factor (bFGF) from the ARSs using repeated applications of FUS. In in vivo studies, ARSs containing bFGF were implanted in mice following induction of hind limb ischemia, a preclinical model of CLI. During the 4-week study, mice in the ARS + FUS group longitudinally exhibited significantly more perfusion and less visible necrosis compared to other experimental groups. Additionally, significantly greater angiogenesis and less fibrosis were observed for the ARS + FUS group. Overall, these results highlight a promising, FUS-based method of delivering a pro-angiogenic growth factor for stimulating angiogenesis and reperfusion in a cardiovascular disease model. More broadly, these results could be used to personalize the delivery of therapeutics in different regenerative applications by actively controlling the release of a growth factor.

Engineering Bioactive Scaffolds for Skin Regeneration.

Large skin wounds pose a major clinical challenge. Scarcity of donor site and postsurgical scarring contribute to the incomplete or partial loss of function and aesthetic concerns in skin wound patients. Currently, a wide variety of skin grafts are being applied in clinical settings. Scaffolds are used to overcome the issues related to the misaligned architecture of the repaired skin tissues. The current review summarizes the contribution of biomaterials to wound healing and skin regeneration and addresses the existing limitations in skin grafting. Then, the clinically approved biologic and synthetic skin substitutes are extensively reviewed. Next, the techniques for modification of skin grafts aiming for enhanced tissue regeneration are outlined, and a summary of different growth factor delivery systems using biomaterials is presented. Considering the significant progress in biomaterial science and manufacturing technologies, the idea of biomaterial-based skin grafts with the ability for scarless wound healing and reconstructing full skin organ is more achievable than ever.

Development of Vancomycin Delivery Systems Based on Autologous 3D Platelet-Rich Fibrin Matrices for Bone Tissue Engineering.

Autologous platelet-rich fibrin (PRF) is derived from the blood and its use in the bone tissue engineering has emerged as an effective strategy for novel drug and growth factor delivery systems. Studies have approved that combined therapy with PRF ensures higher biological outcomes, but patients still undergo additional treatment with antibiotic drugs before, during, and even after the implantation of biomaterials with PRF. These systematically used drugs spread throughout the blood and lead not only to positive effects but may also induce adverse side effects on healthy tissues. Vancomycin hydrochloride (VANKA) is used to treat severe Staphylococcal infections but its absorption in the target tissue after oral administration is low; therefore, in this study, we have developed and analyzed two kinds of VANKA carriers—liposomes and microparticles in 3D PRF matrices. The adjustment, characterization, and analysis of VANKA carriers in 3D PRF scaffolds is carried out in terms of encapsulation efficiency, drug release kinetics and antibacterial activity; furthermore, we have studied the micro- and macrostructure of the scaffolds with microtomography.

Growth factor-loaded microspheres in mPEG-polypeptide hydrogel system for articular cartilage repair.

We developed an injectable hydrogel system with a sustained release of TGF-β3 through growth factor-loaded microsphere to mimic the cartilage-like microenvironment. Poly(lactic-co-glycolic acid) (PLGA) microspheres incorporated in three dimensional (3D) scaffolds were chosen because of its regulatory approval, good biodegradability, and acting as carriers with sustained release behavior. We evaluated sustained release of TGF-β3 by PLGA microspheres encapsulated in methoxy poly(ethylene glycol)-poly(alanine) (mPA) hydrogels and the resulting enhanced chondrogenic effects. We reported here the effect of the proposed system for sustained release of growth factors on chondrogenesis in cartilage regeneration. PLGA microspheres were used in our thermosensitive mPA hydrogel system with bovine serum albumin as a stabilizing and protecting agent for the emulsion and TGF-β3 enabling sustained release. Gelation, structural properties, and in-vitro release of this composite, that is, microspheres in hydrogel, system were investigated. Using PLGA microspheres to carry growth factors could complement the mPA hydrogel's ability to provide an excellent 3D microenvironment for the promotion of chondrogenic phenotype as compared the systems using mPA hydrogel or microspheres alone. Our study demonstrated that this synthesized composite hydrogel system is capable of modulating the biosynthetic and differentiation activities of chondrocytes. The sustained release of TGF-β3 in this novel hydrogel system could improve biomedical applicability of mPEG-polypeptide scaffolds. The distinctive local growth factor delivery system successfully combined the use of both polymers to be a suitable candidate for prolonged articular cartilage regeneration.

Green electrospinning for biomaterials and biofabrication

Green manufacturing has emerged across industries, propelled by a growing awareness of the negative environmental and health impacts associated with traditional practices. In the biomaterials industry, electrospinning is a ubiquitous fabrication method for producing nano- to micro-scale fibrous meshes that resemble native tissues, but this process traditionally utilizes solvents that are environmentally hazardous and pose a significant barrier to industrial scale-up and clinical translation. Applying sustainability principles to biomaterial production, we have developed a ‘green electrospinning’ process by systematically testing biologically benign solvents (U.S. Food and Drug Administration Q3C Class 3), and have identified acetic acid as a green solvent that exhibits low ecological impact (global warming potential (GWP) = 1.40 CO2 eq. kg/L) and supports a stable electrospinning jet under routine fabrication conditions. By tuning electrospinning parameters, such as needle-plate distance and flow rate, we updated the fabrication of widely utilized biomedical polymers (e.g. poly-α-hydroxyesters, collagen), polymer blends, polymer-ceramic composites, and growth factor delivery systems. Resulting ‘green’ fibers and composites are comparable to traditional meshes in terms of composition, chemistry, architecture, mechanical properties, and biocompatibility. Interestingly, material properties of green synthetic fibers are more biomimetic than those of traditionally electrospun fibers, doubling in ductility (91.86 ± 35.65 vs. 45 ± 15.07%, n = 10, p < 0.05) without compromising yield strength (1.32 ± 0.26 vs. 1.38 ± 0.32 MPa) or ultimate tensile strength (2.49 ± 0.55 vs. 2.36 ± 0.45 MPa). Most importantly, green electrospinning proves advantageous for biofabrication, rendering a greater protection of growth factors during fiber formation (72.30 ± 1.94 vs. 62.87 ± 2.49% alpha helical content, n = 3, p < 0.05) and recapitulating native ECM mechanics in the fabrication of biopolymer-based meshes (16.57 ± 3.92% ductility, 33.38 ± 30.26 MPa elastic modulus, 1.30 ± 0.19 MPa yield strength, and 2.13 ± 0.36 MPa ultimate tensile strength, n = 10). The eco-conscious approach demonstrated here represents a paradigm shift in biofabrication, and will accelerate the translation of scalable biomaterials and biomimetic scaffolds for tissue engineering and regenerative medicine.

One nanosystem with potent antibacterial and gene-delivery performances accelerates infected wound healing

Growth factor delivery has attracted high attention for the treatment of severe skin wounds, while it is still desirable to develop new delivery systems with superiority for both antibacterial and delivery performances. In this work, one bifunctional nanosystem (HPT-RP) was constructed for the anti-bacterial and gene-delivery (plasmid encoding epidermal growth factor (EGF)) treatment of infected wound through the one-pot dual conjugation of photosensitizer and bacterium/cell-affinity phenylboronic acid onto hyperbranched polyaminoglycosides. HPT-RP realized high anti-bacterial ability owing to the receptor-mediated photodynamic therapy. The nanoparticle morphology and phenylboronic acid conjugation endowed HPT-RP with high gene transfection. In a rat infected-skin-defect model, HPT-RP exhibited the remarkable performance of anti-infective/EGF-delivery and accelerated healing. More importantly, a new sight into rat-EGF production revealed the underlying mechanism of extraneous EGF delivery and endogenous EGF production. This work sheds light on the rational design of growth factor delivery systems for infected wound therapy.

Translational Studies on the Potential of a VEGF Nanoparticle-Loaded Hyaluronic Acid Hydrogel.

Heart failure has a five-year mortality rate approaching 50%. Inducing angiogenesis following a myocardial infarction is hypothesized to reduce cardiomyocyte death and tissue damage, thereby preventing heart failure. Herein, a novel nano-in-gel delivery system for vascular endothelial growth factor (VEGF), composed of star-shaped polyglutamic acid-VEGF nanoparticles in a tyramine-modified hyaluronic acid hydrogel (nano-VEGF-HA-TA), is investigated. The ability of the nano-VEGF-HA-TA system to induce angiogenesis is assessed in vivo using a chick chorioallantoic membrane model (CAM). The formulation is then integrated with a custom-made, clinically relevant catheter suitable for minimally invasive endocardial delivery and the effect of injection on hydrogel properties is examined. Nano-VEGF-HA-TA is biocompatible on a CAM assay and significantly improves blood vessel branching (p < 0.05) and number (p < 0.05) compared to a HA-TA hydrogel without VEGF. Nano-VEGF-HA-TA is successfully injected through a 1.2 m catheter, without blocking or breaking the catheter and releases VEGF for 42 days following injection in vitro. The released VEGF retains its bioactivity, significantly improving total tubule length on a Matrigel® assay and human umbilical vein endothelial cell migration on a Transwell® migration assay. This VEGF-nano in a HA-TA hydrogel delivery system is successfully integrated with an appropriate device for clinical use, demonstrates promising angiogenic properties in vivo and is suitable for further clinical translation.

A pilot study investigating a novel particle-based growth factor delivery system for preimplantation embryo culture.

Can vascular endothelial growth factor (VEGF)-loaded silica supraparticles (V-SPs) be used as a novel mode of delivering VEGF to the developing preimplantation embryo in vitro? Supplementation of embryo culture media with V-SPs promoted embryonic development in a manner equivalent to media supplemented with free VEGF. VEGF is a maternally derived growth factor that promotes preimplantation embryonic development in vitro. However, its use in clinical media has limitations due to its low stability in solution. This study was a laboratory-based analysis utilising a mouse model. V-SPs were prepared in vitro and supplemented to embryonic culture media. The bioactivity of V-SPs was determined by analysis of blastocyst developmental outcomes (blastocyst development rate and total cell number). SPs were loaded with fluorescently labelled VEGF and release kinetics were characterised. Bioactivity of unlabelled VEGF released from V-SPs was determined by analysis of embryo developmental outcomes (blastocyst developmental rate and total cell number) following individual mouse embryo culture in 20 µl of G1/G2 media at 5% oxygen, supplemented with 10 ng/ml recombinant mouse VEGF in solution or with V-SPs. The bioactivity of freeze-dried V-SPs was also assessed to determine the efficacy of cryostorage. VEGF release kinetics were characterised by an initial burst of VEGF from loaded spheres followed by a consistent lower level of VEGF release over 48 h. VEGF released from V-SPs resulted in significant increases in total blastocyst cell number relative to the control (P < 0.001), replicating the effects of medium freely supplemented with fresh VEGF (P < 0.001). Similarly, freeze dried V-SPs exerted comparable effects on embryonic development (P < 0.05). N/A. In this proof of principle study, the effects of V-SPs on embryonic development were only analysed in a mouse model. These findings suggest that SPs represent a novel method by which a targeted dose of therapeutic agents (e.g. bioactive VEGF) can be delivered to the developing in vitro embryo to promote embryonic development, an approach that negates the breakdown of VEGF associated with storage in solution. As such, V-SPs may be an alternative and effective method of delivering bioactive VEGF to the developing in vitro embryo; however, the potential use of V-SPs in clinical IVF requires further investigation. This work was funded by the University of Melbourne. The authors have no conflict of interest to declare.

The Role of Platelet-Rich Plasma in Reducing Pain, Pruritus, and Improving Wound Healing of Skin Graft Donor Site

Background: Wound healing is an intricate and interactive process. As a result, no single operator can efficiently and successfully help to resolve all attributes of healing process. The goal of the study that PRP was to systematically perceive the stimulatory effect at multiple stages during wound healing and trying to identify tissue repair mechanisms, lower pain, itching skin and healing time. Study design: This was a cross sectional study and carried out at plastic surgery department of Ghulam Muhammad Mahar Medical College Hospital, Sukkur for the duration of six months from June 2022 to December 2022. Methods: 120 participants which include male n=80 and female included n=40 who under the observation of split skin grafting due to reason of injuries, burning, accidents and traumas. These participants divide into two category of treatment for example, paraffin gauze dressing and platelet rich plasma (PRP). The age of participants between &gt;20 and &lt;50 years. To examine the preparation method of PRP, raw area dressing and clinical outcome for the assessment of pain, pruritus before and after comparison of gauze dressing and PRP. The data was analyzed by SPSS 21 version. Results: The total participants are 120 in this study and the age group between 20 and 50 with an average age was 35 years. The affected area was left leg was 25% and right leg 75%. The raw area in 54.1% participants was burn and 46% participants were by road accident. The dressing was changed alternate weeks. The treatment with PRP showed significant changing in the effective participants as compared to paraffin gauze dressing (p&lt;0.05). Conclusion: PRP serves as a delivery system for growth factors, making this blood product extremely useful for use in a variety of indications in plastic and reconstructive surgery. Intradermal injection of platelet rich plasma is a secure and efficient option for minimizing pain, adverse reactions, and ability to heal multiple injuries in patients with burns and radiation injuries. Keyword: Platelet rich plasma, wound healing, itching skin, growth factors

Injectable Glycosaminoglycan-Based Cryogels from Well-Defined Microscale Templates for Local Growth Factor Delivery.

Glycosaminoglycan-based hydrogels hold great potential for applications in tissue engineering and regenerative medicine. By mimicking the natural extracellular matrix processes of growth factor binding and release, such hydrogels can be used as a sustained delivery device for growth factors. Since neural networks commonly follow well-defined, high-aspect-ratio paths through the central and peripheral nervous system, we sought to create a fiber-like, elongated growth factor delivery system. Cryogels, with networks formed at subzero temperatures, are well-suited for the creation of high-aspect-ratio biomaterials, because they have a macroporous structure making them mechanically robust (for ease of handling) yet soft and highly compressible (for interfacing with brain tissue). Unlike hydrogels, cryogels can be synthesized in advance of their use, stored with ease, and rehydrated quickly to their original shape. Herein, we use solvent-assisted microcontact molding to form sacrificial templates, in which we produced highly porous cryogel microscale scaffolds with a well-defined elongated shape via the photopolymerization of poly(ethylene glycol) diacrylate and maleimide-functionalized heparin. Dissolution of the template yielded cryogels that could load nerve growth factor (NGF) and release it over a period of 2 weeks, causing neurite outgrowth in PC12 cell cultures. This microscale template-assisted synthesis technique allows tight control over the cryogel scaffold dimensions for high reproducibility and ease of injection through fine gauge needles.

Control Delivery of Multiple Growth Factors to Actively Steer Differentiation and Extracellular Matrix Protein Production.

In tissue engineering, biomaterials have been used to steer the host response. This determines the outcome of tissue regeneration, which is modulated by multiple growth factors (GFs). Hence, a sustainable delivery system for GFs is necessary to control tissue regeneration actively. A delivery technique of single and multiple GF combinations, using a layer-by-layer (LBL) procedure to improve tissue remodeling, is developed. TGF-β1, PDGF-ββ, and IGF-1 are incorporated on tailor-made polymeric rods, which could be used as a tool for potential tissue engineering applications, such as templates to induce the formation of in situ tissue engineered blood vessels (TEBVs). Cell response is analyzed in vitro using rat and human dermal fibroblasts for cellular proliferation, fibroblast differentiation, and extracellular matrix (ECM) protein synthesis. Results revealed a higher loading efficiency and control release of GFs incorporated on chloroform and oxygen plasma-activated (COX) rods. Single PDGF-ββ and IGF-1 release, and dual release with TGF-β1 from COX rods, showed higher cell proliferation when compared to COX rods alone. A substantial increase in α-smooth muscle actin (α-SMA) is also observed in GF releasing COX rods, with TGF-β1 COX rods providing the most pronounced differentiation. A significant increase in collagen and elastin synthesis is observed on all GF releasing COX rods compared to control, with COX rods releasing TGF-β1 and IGF-1 providing the highest secretion. TGF-β1 and IGF-1 releasing COX rods induced higher Glycosaminoglycan (GAG)/DNA amounts than the other GF releasing COX rods. As PDGF-ββ and TGF-β1/PDGF-ββ COX rods displayed the highest fibroblast attachment, these rods provided the highest total collagen and elastin production. The attractive results from efficiently incorporating single and multiple GFs on COX rods and their sustainable release to steer cellular behavior suggest a promising route to enrich the formation of in situ engineered tissues.

Hydroxyapatite sonosensitization of ultrasound-triggered, thermally responsive hydrogels: An on-demand delivery system for bone repair applications.

While bones have the innate capability to physiologically regenerate, in certain cases regeneration is suboptimal, too slow, or does not occur. Biomaterials-based growth factor delivery systems have shown potential for the treatment of challenging bone defects, however, achieving controlled growth factor release remains a challenge. The objective of this study was to develop a thermally responsive hydrogel for bone regeneration capable of ultrasound-triggered on-demand delivery of therapeutic agents. Furthermore, it was hypothesized that incorporation of hydroxyapatite (HA) into the hydrogel could increase sonosensitization, augmenting ultrasound sensitivity to enable controlled therapeutic release to the target tissue. Alginate thermally responsive P(Alg-g-NIPAAm) hydrogels were fabricated and varying quantities of HA (1, 3, 5, and 7% wt./vol.) incorporated. All hydrogels were highly injectable (maximum injection force below 6.5N) and rheological characterization demonstrated their ability to gel at body temperature. The study demonstrated the ultrasound-triggered release of sodium fluorescein (NaF), bovine serum albumin (BSA), and bone morphogenetic protein 2 (BMP-2) from the hydrogels. Release rates of BSA and BMP-2 were significantly enhanced in the HA containing hydrogels, confirming for the first time the role of HA as a son sensitizer. Together these results demonstrate the potential of these ultrasound-triggered thermally responsive hydrogels for on-demand delivery of therapeutic agents for bone regeneration.

Advances in Growth Factor Delivery for Bone Tissue Engineering.

Shortcomings related to the treatment of bone diseases and consequent tissue regeneration such as transplants have been addressed to some extent by tissue engineering and regenerative medicine. Tissue engineering has promoted structures that can simulate the extracellular matrix and are capable of guiding natural bone repair using signaling molecules to promote osteoinduction and angiogenesis essential in the formation of new bone tissues. Although recent studies on developing novel growth factor delivery systems for bone repair have attracted great attention, taking into account the complexity of the extracellular matrix, scaffolding and growth factors should not be explored independently. Consequently, systems that combine both concepts have great potential to promote the effectiveness of bone regeneration methods. In this review, recent developments in bone regeneration that simultaneously consider scaffolding and growth factors are covered in detail. The main emphasis in this overview is on delivery strategies that employ polymer-based scaffolds for spatiotemporal-controlled delivery of both single and multiple growth factors in bone-regeneration approaches. From clinical applications to creating alternative structural materials, bone tissue engineering has been advancing constantly, and it is relevant to regularly update related topics.