Materials Science and Design Principles of Growth Factor Delivery Systems in Tissue Engineering and Regenerative Medicine

Immobilization of FGF on Poly(xylitol dodecanedioic Acid) Polymer for Tissue Regeneration

Fibroblast growth factor (FGF) plays a vital role in the repair and regeneration of most tissues. However, its low stability, short half-life, and rapid inactivation by enzymes in physiological conditions affect their clinical applications. Therefore, to increase the effectiveness of growth factors and to improve tissue regeneration, we developed an elastic polymeric material poly(xylitol dodecanedioic acid) (PXDDA) and loaded FGF on the PXDDA for sustained drug delivery. In this study, we used a simple dopamine coating method to load FGF on the surface of PXDDA polymeric films. The polydopamine-coated FGF-loaded PXDDA samples were then characterized using FTIR and XRD. The in vitro drug release profile of FGF from PXDDA film and cell growth behavior were measured. Results showed that the polydopamine layer coated on the surface of the PXDDA film enhanced the immobilization of FGF and controlled its sustained release. Human fibroblast cells attachment and proliferation on FGF-immobilized PXDDA films were much higher than the other groups without coatings or FGF loading. Based on our results, the surface modification procedure with immobilizing growth factors shows excellent application potential in tissue regeneration.

Electrical Stimulation Decreases Dental Pulp Stem Cell Osteo-/Odontogenic Differentiation

Dental pulp stem cells (DPSCs) have great potential for use in tissue engineering (TE)-based dental treatments. Electrical stimulation (EStim) has been shown to influence cellular functions that could play an important role in the success of TE treatments. Despite many recent studies focused on DPSCs, few have investigated the effect EStim has on these cells. The aim of this research was to investigate the effects of direct current (DC) EStim on osteo-/odontogenic differentiation of DPSCs. To do so cells were isolated from male Sprague Dawley rats (7-8 weeks old), and phenotype characterization and multilineage differentiation analysis were conducted to verify their "stemness." Different voltages of DC EStim were administrated 1 h/day for 7 days, and the effect of EStim on DPSC osteo-/odontogenic differentiation was assessed by measuring calcium and collagen deposition, alkaline phosphatase (ALP) activity, and expression of osteo- and odontogenic marker genes at days 7 and 14 of culture. We found that while 10 and 50 mV/mm of EStim had no effect on cell number or metabolic activity, 100 mV/mm caused a significant reduction in cell number, and 150 mV/mm resulted in cell death. Despite increased gene expression of osteo-/odontogenic gene markers, Osteocalcin, RunX2, BSP, and DMP1, at day 7 in EStim treated cells, 50 mV/mm of EStim decreased collagen deposition and ALP activity at both time points, and calcium deposition was found to be lower at day 14. In conclusion, under the conditions tested, EStim appears to impair DPSC osteo-/odontogenic differentiation. Additional studies are needed to further characterize and understand the mechanisms involved in DPSC response to EStim, with an eye toward its potential use in TE-based dental treatments.

Stimuli-Responsive Delivery of Growth Factors for Tissue Engineering

Growth factors (GFs) play a crucial role in directing stem cell behavior and transmitting information between different cell populations for tissue regeneration. However, their utility as therapeutics is limited by their short half-life within the physiological microenvironment and significant side effects caused by off-target effects or improper dosage. "Smart" materials that can not only sustain therapeutic delivery over a treatment period but also facilitate on-demand release upon activation are attracting significant interest in the field of GF delivery for tissue engineering. Three properties are essential in engineering these "smart" materials: 1) the cargo vehicle protects the encapsulated therapeutic; 2) release is targeted to the site of injury; 3) cargo release can be modulated by disease-specific stimuli. The aim of this review is to summarize the current research on stimuli-responsive materials as intelligent vehicles for controlled GF delivery; Five main subfields of tissue engineering are discussed: skin, bone and cartilage, muscle, blood vessel, and nerve. Challenges in achieving such "smart" materials and perspectives on future applications of stimuli-responsive GF delivery for tissue regeneration are also discussed.

Cell-modified bioprinted microspheres for vascular regeneration

Cell therapy is a promising strategy in which living cells or cellular materials are delivered to treat a variety of diseases. Here, we developed an electrospray bioprinting method to rapidly generate cell-laden hydrogel microspheres, which limit the migration of the captured cells and provide an immunologically privileged microenvironment for cell survival in vivo. Currently, therapeutic angiogenesis aims to induce collateral vessel formation after limb ischemia. However, the clinical application of gene and cell therapy has been impeded by concerns regarding its inefficacy, as well as the associated risk of immunogenicity and oncogenicity. In this study, hydrogel microspheres encapsulating VEGF-overexpressing HEK293T cells showed good safety via subcutaneously injecting into male C57BL/6 mice. In addition, these cell-modified microspheres effectively promoted angiogenesis in a mouse hind-limb ischemia model. Therefore, we demonstrated the great therapeutic potential of this approach to induce angiogenesis in limb ischemia, indicating that bioprinting has a bright future in cell therapy.

Combination of a biomolecule-aided biphasic cryogel scaffold with a barrier membrane adhering PDGF-encapsulated nanofibers to promote periodontal regeneration

OBJECTIVE AND BACKGROUND

To achieve periodontal regeneration, numerous investigations have concentrated on biomolecule supplement and optimization of bone substitute or barrier membrane. This study evaluated the benefit of combining these strategies for periodontal regeneration.

METHODS

Biphasic cryogel scaffold (BCS) composed of gelatin (ligament phase) and gelatin with beta-tricalcium phosphate/hydroxyapatite (BH) (bone phase) was designed as tested bone substitute, and both enamel matrix derivatives (EMD) and bone morphogenetic protein-2 (BMP-2) were applied to formulate a biomolecule-aided BCS (BBS). Functionally graded membrane (FGM) was designed as tested barrier membrane by adhering PDGF-encapsulated poly(L-lactide-co-D/L-lactide) nanofibers on the conventional membrane (CM). BBS and FGM were characterized and tested for biocompatibility in vitro. Thirty 4 × 4 × 5 mm³ periodontal intrabony defects were created on 6 Beagle dogs. Each defect was evenly assigned to one of the following treatments including BH-CM, BCS-CM, BBS-CM, BH-FGM, BCS-FGM, and BBS-FGM, for 12 weeks. The therapeutic efficiency was assessed by micro-CT and histology.

RESULTS

BCS and FGM sustained the release of biomolecules. The viability of MSCs was maintained in both phases of BCS and was promoted while seeding on the PDGF-encapsulated nanofibers. In CM-covered sites, BBS showed significantly greater osteogenesis (P < .01) and early defect fill (P < .05) relative to BH. FGM significantly promoted osteogenesis (P < .05) in BH-treated sites but showed limited benefit in BBS-treated sites. On denuded roots, cementum deposition was evident in BBS-treated sites.

CONCLUSIONS

PDGF-loaded FGM promoted periodontal osteogenesis, and BBS with EMD-BMP-2 had potential for reconstructing alveolar ridge, periodontal ligament, and cementum. FGM and BBS combination provided limited additional benefit.

Long noncoding RNA expression profiles during the NEL-like 1 protein-induced osteogenic differentiation

Long noncoding RNAs (lncRNAs) are important modulators of mesenchymal stem cells (MSCs) in cellular differentiation. However, the regulatory mechanisms of lncRNAs in NEL-like 1 (NELL-1)-induced osteogenic differentiation of human adipose-derived stem cells remain elusive. Expression profiles of lncRNAs and messenger RNAs during NELL-1-induced osteogenesis were obtained using high-throughput sequencing. Gene Ontology, Kyoto Encyclopedia of Genes and Genomes pathway analysis, and gene coexpression networks were performed. We identified 323 statistically differentially expressed lncRNAs during osteogenesis and NELL-1-induced osteogenesis, and three lncRNAs (ENST00000602964, ENST00000326734, and TCONS_00006792) were identified as core regulators. Hedgehog pathway markers, including IHH and GLI1, were downregulated, while the antagonists of this pathway (GLI3 and HHIP) were upregulated during NELL-1-induced osteogenesis. In this process, the antagonist of Wnt, SFRP1, was downregulated. According to the analysis, we speculated that lncRNAs played important roles in NELL-1-induced osteogenesis via the crosstalk between Hedgehog and Wnt pathways.

PEG grafted chitosan scaffold for dual growth factor delivery for enhanced wound healing

Application of growth factors at wound site has improved the efficiency and quality of healing. Basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) induce proliferation of various cells in wound healing. Delivery of growth factor from controlled release systems protect it from degradation and also result in sustained delivery of it at the site of injury. The goal of the study was to develop a Polyethylene glycol (PEG) cross-linked cotton-like chitosan scaffold (CS-PEG-H) by freeze-drying method and chemically conjugate heparin to the scaffold to which the growth factors can be electrostatically bound and evaluate its wound healing properties in vitro and in vivo. The growth factor containing scaffolds induced increased proliferation of HaCaT cells, increased neovascularization and collagen formation seen by H and E and Masson's trichrome staining. Immunohistochemistry was performed using the Ki67 marker which increased proliferation of cells in growth factor containing scaffold treated group. Frequent dressing changes are a major deterrent to proper wound healing. Our system was found to release both VEGF and bFGF in a continuous manner and attained stability after 7 days. Thus our system can maintain therapeutic levels of growth factor at the wound bed thereby avoiding the need for daily applications and frequent dressing changes. Thus, it can be a promising candidate for wound healing.

Modular Strategies to Build Cell-Free and Cell-Laden Scaffolds towards Bioengineered Tissues and Organs

Engineering three-dimensional (3D) scaffolds for functional tissue and organ regeneration is a major challenge of the tissue engineering (TE) community. Great progress has been made in developing scaffolds to support cells in 3D, and to date, several implantable scaffolds are available for treating damaged and dysfunctional tissues, such as bone, osteochondral, cardiac and nerve. However, recapitulating the complex extracellular matrix (ECM) functions of native tissues is far from being achieved in synthetic scaffolds. Modular TE is an intriguing approach that aims to design and fabricate ECM-mimicking scaffolds by the bottom-up assembly of building blocks with specific composition, morphology and structural properties. This review provides an overview of the main strategies to build synthetic TE scaffolds through bioactive modules assembly and classifies them into two distinct schemes based on microparticles (µPs) or patterned layers. The µPs-based processes section starts describing novel techniques for creating polymeric µPs with desired composition, morphology, size and shape. Later, the discussion focuses on µPs-based scaffolds design principles and processes. In particular, starting from random µPs assembly, we will move to advanced µPs structuring processes, focusing our attention on technological and engineering aspects related to cell-free and cell-laden strategies. The second part of this review article illustrates layer-by-layer modular scaffolds fabrication based on discontinuous, where layers' fabrication and assembly are split, and continuous processes.

Gelatin-based perfusable, endothelial carotid artery model for the study of atherosclerosis

BACKGROUND

Carotid artery geometry is important for recapitulating a pathophysiological microenvironment to study wall shear stress (WSS)-induced endothelial dysfunction in atherosclerosis. Endothelial cells (ECs) cultured with hydrogel have been shown to exhibit in vivo-like behaviours. However, to date, studies using hydrogel culture have not fully recapitulated the 3D geometry and blood flow patterns of real-life healthy or diseased carotid arteries. In this study, we developed a gelatin-patterned, endothelialized carotid artery model to study the endothelium response to WSS.

RESULTS

Two representative regions were selected based on the computational fluid dynamics on the TF-shaped carotid artery: Region ECA (external carotid artery) and Region CS (carotid sinus). Progressive elongation and alignment of the ECs in the flow direction were observed in Region ECA after 8, 16 and 24 h. However, the F-actin cytoskeleton remained disorganized in Region CS after 24 h. Further investigation revealed that expression of vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) was greatly increased in Region CS relative to that in Region ECA. The physiological WSS in the carotid artery system was found to stimulate nitric oxide (NO) and prostacyclin (PGI2) release and inhibit endothelin-1 (ET-1) release after 24-h perfusion experiments. The effective permeability (E.P) of fluorescein isothiocyanate (FITC)-dextran 40 kDa in Regions ECA and CS was monitored, and it was found that the turbulence WSS value (in Region CS) was less than 0.4 Pa, and there was a significant increase in the E.P relative to that in Region ECA, in which laminar WSS value was 1.56 Pa. The tight junction protein (ZO-1) production was shown that the low WSS in Region CS induced ZO-1-level downregulation compared with that in Region ECA.

CONCLUSIONS

The results suggested that the gelatin-based perfusable, endothelial carotid artery model can be effective for studying the pathogenesis of atherosclerosis by which flow dynamics control the endothelium layer function in vitro.

Multi-Functional Electrospun Nanofibers from Polymer Blends for Scaffold Tissue Engineering

Electrospinning and polymer blending have been the focus of research and the industry for their versatility, scalability, and potential applications across many different fields. In tissue engineering, nanofiber scaffolds composed of natural fibers, synthetic fibers, or a mixture of both have been reported. This review reports recent advances in polymer blended scaffolds for tissue engineering and the fabrication of functional scaffolds by electrospinning. A brief theory of electrospinning and the general setup as well as modifications used are presented. Polymer blends, including blends with natural polymers, synthetic polymers, mixture of natural and synthetic polymers, and nanofiller systems, are discussed in detail and reviewed.

The Clinical Use of Biologics in the Knee Lesions: Does the Patient Benefit?

PURPOSE OF REVIEW

Overview the outcomes of the latest use of platelet-rich plasma (PRP) for the treatment of knee lesions in the clinics and discuss the challenges and limitations.

RECENT FINDINGS

Recent clinical studies mainly indicate there may be benefit of PRP usage for the treatment of knee lesions. As an autologous source of bioactive components, PRP has been shown to be typically safe, free of major adverse outcomes. The use of PRP has been continuously increasing, and some well-designed, double-blinded, placebo-controlled clinical trials have been published. Clinical outcomes relating to PRP usage are multifactorial and depend on the severity of the lesion and patient characteristics. Although PRP is safe to use and it can be easily applied in the clinics, case-specific considerations are needed to determine whether PRP could be beneficial or not. If the use of PRP is favored, then, the configuration/optimization of the preparation and administration/delivery strategy with or without a concomitant treatment may further enhance the clinical outcomes and patients' experience.

Recent advances in cell sheet technology for bone and cartilage regeneration: from preparation to application

Bone defects caused by trauma, tumour resection, infection and congenital deformities, together with articular cartilage defects and cartilage-subchondral bone complex defects caused by trauma and degenerative diseases, remain great challenges for clinicians. Novel strategies utilising cell sheet technology to enhance bone and cartilage regeneration are being developed. The cell sheet technology has shown great clinical potential in regenerative medicine due to its effective preservation of cell-cell connections and extracellular matrix and its scaffold-free nature. This review will first introduce several widely used cell sheet preparation systems, including traditional approaches and recent improvements, as well as their advantages and shortcomings. Recent advances in utilising cell sheet technology to regenerate bone or cartilage defects and bone-cartilage complex defects will be reviewed. The key challenges and future research directions for the application of cell sheet technology in bone and cartilage regeneration will also be discussed.

Universal Biofactor-Releasing Scaffold Enabling in Vivo Reloading

The supply of growth factors to engineered tissues is essential for many physiological processes. These processes include the proper organization of the cells into functioning tissues, maintenance of their viability, vasculogenesis, proliferation, and differentiation. Systems to efficiently control the release of growth factors were previously incorporated into tissue engineering scaffolds to affect cells. However, because the initial concentration of the factors in these systems is finite, their ability to provide a long-term physiological effect is limited. Here, we report on a new reloadable system in which 3D fibrous scaffolds conjugated with an anti His-tag antibody enable the retention and controlled release of any His-tag-modified proteinaceous growth factor. The scaffolds can be reloaded in vitro or in vivo with any His-tagged biomolecule at any time according to the physiological need. We show the ability of the scaffolds to release angiogenic factors in a static cell culture or under flow in a microfluidics device and effect on endothelial cells. We also demonstrate the potential of the system to be sequentially reloaded in vivo with various factors, and as a proof of concept, we provide evidence for the efficient in vivo vascularization of scaffolds after reloading with tagged VEGF.