PLLA-collagen and PLLA-gelatin hybrid scaffolds with funnel-like porous structure for skin tissue engineering

Polynucleotides in Aesthetic Medicine: A Review of Current Practices and Perceived Effectiveness

Polynucleotides, complex molecules composed of nucleotides, have gained attention in aesthetic medicine for their potential to regulate gene expression and promote tissue regeneration. This review aims to provide an overview of the current practices and perceived effectiveness of polynucleotides in aesthetic medicine. A comprehensive search of the literature was conducted using keywords related to polynucleotides, cosmetic application, and aesthetic application. Studies were selected based on their relevance to aesthetic medicine and the inclusion of human subjects. The review found that polynucleotides have been used to improve skin texture, reduce wrinkle depth, and enhance facial appearance. The studies reported varying degrees of efficacy and safety, with some studies demonstrating significant improvements in skin elasticity and hydration. However, others reported limited or no benefits. The review also highlighted the need for further research to establish the optimal use and efficacy of polynucleotides in aesthetic medicine. While the existing literature suggests that polynucleotides may have potential benefits in aesthetic medicine, more research is needed to fully understand their mechanisms of action and optimal use. Clinicians should be aware of the current limitations and potential risks associated with the use of polynucleotides in aesthetic medicine.

Effect of Gelatin Content on Degradation Behavior of PLLA/Gelatin Hybrid Membranes

BACKGROUND

Poly(L-lactic acid) (PLLA) is a biodegradable polymer (BP) that replaces conventional petroleum-based polymers.  The hydrophobicity of biodegradable PLLA periodontal barrier membrane in wet state can be solved by alloying it with natural polymers. Alloying PLLA with gelatin imparts wet mechanical properties, hydrophilicity, shrinkage, degradability and biocompatibility to the polymeric matrix.

METHODS

To investigate membrane performance in the wet state, PLLA/gelatin membranes were synthesized by varying the gelatin concentration from 0 to 80 wt%. The membrane was prepared by electrospinning.

RESULTS

At the macroscopic scale, PLLA containing gelatin can tune the wet mechanical properties, hydrophilicity, water uptake capacity (WUC), degradability and biocompatibility of PLLA/gelatin membranes. As the gelatin content increased from 0 to 80 wt%, the dry tensile strength of the membranes increased from 6.4 to 38.9 MPa and the dry strain at break decreased from 1.7 to 0.19. PLLA/gelatin membranes with a gelatin content exceeding 40% showed excellent biocompatibility and hydrophilicity. However, dimensional change (37.5% after 7 days of soaking), poor tensile stress  in wet state (3.48 MPa) and rapid degradation rate (73.7%) were observed. The highest WUC, hydrophilicity, porosity, suitable mechanical properties and biocompatibility were observed for the PLLA/40% gelatin membrane.

CONCLUSION

PLLA/gelatin membranes with gelatin content less than 40% are suitable as barrier membranes for absorbable periodontal tissue regeneration due to their tunable wet mechanical properties, degradability, biocompatibility and lack of dimensional changes.

Poly-l-lactic acid microspheres delay aging of epidermal stem cells in rat skin

Objective

Injectable skin fillers offer a wider range of options for cutaneous anti-aging and facial rejuvenation. PLLA microspheres are increasingly favored as degradable and long-lasting fillers. The present study focused solely on the effect of PLLA on dermal collagen, without investigating its impact on the epidermis. In this study, we investigated the effects of PLLA microspheres on epidermal stem cells (EpiSCs).

Methods

Different concentrations of PLLA microspheres on epidermal stem cells (EpiSCs) in vitro through culture, and identification of primary rat EpiSCs. CCK-8 detection, apoptosis staining, flow cytometry, Transwell assay, wound healing assay, q-PCR analysis, and immunofluorescence staining were used to detect the effects of PLLA on EpiSCs. Furthermore, we observed the effect on the epidermis by injecting PLLA into the dermis of the rat skin in vivo.

Results

PLLA microspheres promote cell proliferation and migration while delaying cell senescence and maintaining its stemness. In vitro, Intradermal injection of PLLA microspheres in the rat back skin resulted in delayed aging, as evidenced by histological and immunohistochemical staining of the skin at 2, 4, and 12 weeks of follow-up.

Conclusion

This study showed the positive effects of PLLA on rat epidermis and EpiSCs, while providing novel insights into the anti-aging mechanism of PLLA.

Gelatin Enhances the Wet Mechanical Properties of Poly(D,L-Lactic Acid) Membranes

Biodegradable (BP) poly(D,L-lactic acid) (PDLLA) membranes are widely used in tissue engineering. Here, we investigate the effects of varying concentrations of PDLLA/gelatin membranes electrospun in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP; C3H2F6O) solvent on their mechanical and physical properties as well as their biocompatibility. Regardless of the environmental conditions, increasing the gelatin content resulted in elevated stress and reduced strain at membrane failure. There was a remarkable difference in strain-to-failure between dry and wet PDLLA/gelatin membranes, with wet strains consistently higher than those of the dry membranes because of the hydrophilic nature of gelatin. A similar wet strain (εw = 2.7-3.0) was observed in PDLLA/gelatin membranes with a gelatin content between 10 and 40%. Both dry and wet stresses increased with increasing gelatin content. The dry stress on PDLLA/gelatin membranes (σd = 6.7-9.7 MPa) consistently exceeded the wet stress (σw = 4.5-8.6 MPa). The water uptake capacity (WUC) improved, increasing from 57% to 624% with the addition of 40% gelatin to PDLLA. PDLLA/gelatin hybrid membranes containing 10 to 20 wt% gelatin exhibited favorable wet mechanical properties (σw = 5.4-6.3 MPa; εw = 2.9-3.0); WUC (337-571%), degradability (11.4-20.2%), and excellent biocompatibility.

High-resolution 3-D scanning electron microscopy (SEM) images of DOTTM polynucleotides (PN): Unique scaffold characteristics and potential applications in biomedicine

INTRODUCTION

Polynucleotides (PN) are becoming more prominent in aesthetic medicine. However, the structural characteristics of PN have not been published and PN from different companies may have different structural characteristics. This study aimed to elucidate the structural attributes of DOT™ PN and distinguish differences with polydeoxyribonucleotides (PDRN) using high-resolution scanning electron microscopy (SEM) imaging.

MATERIALS AND METHODS

DOT™ PN was examined using a Quanta 3-D field emission gun (FEG) Scanning Electron Microscope (SEM). Sample preparation involved cryogenic cooling, cleavage, etching, and metal coating to facilitate high-resolution imaging. Cryo-FIB/SEM techniques were employed for in-depth structural analysis.

RESULTS

PDRN exhibited an amorphous structure without distinct features. In contrast, DOT™ PN displayed well-defined polyhedral shapes with smooth, uniformly thick walls. These cells were empty, with diameters ranging from 3 to 8 micrometers, forming a seamless tessellation pattern.

DISCUSSION

DOT™ PN's distinct geometric tessellation design conforms to the principles of biotensegrity, providing both structural reinforcement and integrity. The presence of delicate partitions and vacant compartments hints at possible uses in the field of pharmaceutical delivery systems. Within the realms of beauty enhancement and regenerative medicine, DOT™ PN's capacity to bolster cell growth and tissue mending could potentially transform approaches to rejuvenation treatments. Its adaptability becomes apparent when considering its contributions to drug administration and surgical procedures.

CONCLUSION

This study unveils the intricate structural scaffold features of DOT™ PN for the first time, setting it apart from PDRN and inspiring innovation in biomedicine and materials science. DOT™ PN's unique attributes open doors to potential applications across healthcare and beyond.

What are filling (volumizing) threads?

Facial aging prompts a shift in the demands for lifting procedures, transitioning from targeted improvements in younger individuals to overall facial contour enhancements as skin elasticity declines in later years. This paper examines the evolution of PDO volumizing threads, delineating their development from initial limitations to contemporary innovations aimed at addressing tissue deformation and maintaining thread integrity post-insertion. Categorizing these threads based on elasticity, shape, and functionality underscores their versatility and application nuances, catering to specific wrinkle correction, contour sculpting, and facial volume restoration. The discussion emphasizes the pivotal role of thread characteristics in achieving optimal outcomes while minimizing potential complications. By delving into historical contexts, mechanisms, effectiveness, and thread classification, this paper equips practitioners with a comprehensive understanding to make informed decisions in selecting threads for volumizing thread procedures. Recommendations for future research directions, including long-term safety assessments and patient-specific outcomes, seek to enhance the clinical utility and applicability of this analysis.

Electrospun Poly(L-Lactic Acid)/Gelatin Hybrid Polymer as a Barrier to Periodontal Tissue Regeneration

Poly(L-lactic acid) (PLLA) and PLLA/gelatin polymers were prepared via electrospinning to evaluate the effect of PLLA and gelatin content on the mechanical properties, water uptake capacity (WUC), water contact angle (WCA), degradation rate, cytotoxicity and cell proliferation of membranes. As the PLLA concentration increased from 1 wt% to 3 wt%, the tensile strength increased from 5.8 MPa to 9.1 MPa but decreased to 7.0 MPa with 4 wt% PLLA doping. The WUC decreased rapidly from 594% to 236% as the PLLA content increased from 1 to 4 wt% due to the increased hydrophobicity of PLLA. As the gelatin content was increased to 3 wt% PLLA, the strength, WUC and WCA of the PLLA/gelatin membrane changed from 9.1 ± 0.9 MPa to 13.3 ± 2.3 MPa, from 329% to 1248% and from 127 ± 1.2° to 0°, respectively, with increasing gelatin content from 0 to 40 wt%. However, the failure strain decreased from 3.0 to 0.5. The biodegradability of the PLLA/gelatin blend increased from 3 to 38% as the gelatin content increased to 40 wt%. The viability of L-929 and MG-63 cells in the PLLA/gelatin blend was over 95%, and the excellent cell proliferation and mechanical properties suggested that the tunable PLLA/gelatin barrier membrane was well suited for absorbable periodontal tissue regeneration.

Technological advances in ocular trabecular meshwork in vitro models for glaucoma research

Glaucoma is the leading cause of irreversible blindness worldwide and is characterized by the progressive degeneration of the optic nerve. Intraocular pressure (IOP), which is considered to be the main risk factor for glaucoma development, builds up in response to the resistance (resistance to what?) provided by the trabecular meshwork (TM) to aqueous humor (AH) outflow. Although the TM and its relationship to AH outflow have remained at the forefront of scientific interest, researchers remain uncertain regarding which mechanisms drive the deterioration of the TM. Current tissue-engineering fabrication techniques have come up with promising approaches to successfully recreate the TM. Nonetheless, more accurate models are needed to understand the factors that make glaucoma arise. In this review, we provide a chronological evaluation of the technological milestones that have taken place in the field of glaucoma research, and we conduct a comprehensive comparison of available TM fabrication technologies. Additionally, we also discuss AH perfusion platforms, since they are essential for the validation of these scaffolds, as well as pressure-outflow relationship studies and the discovery of new IOP-reduction therapies.

Surface Modification of Sponge-like Porous Poly(3-hydroxybutyrate-co-4-hydroxybutyrate)/Gelatine Blend Scaffolds for Potential Biomedical Applications

In this study, we described the preparation of sponge-like porous scaffolds that are feasible for medical applications. A porous structure provides a good microenvironment for cell attachment and proliferation. In this study, a biocompatible PHA, poly(3-hydroxybutyrate-co-4-hydroxybutyrate) was blended with gelatine to improve the copolymer’s hydrophilicity, while structural porosity was introduced into the scaffold via a combination of solvent casting and freeze-drying techniques. Scanning electron microscopy results revealed that the blended scaffolds exhibited higher porosity when the 4HB compositions of P(3HB-co-4HB) ranged from 27 mol% to 50 mol%, but porosity decreased with a high 4HB monomer composition of 82 mol%. The pore size, water absorption capacity, and cell proliferation assay results showed significant improvement after the final weight of blend scaffolds was reduced by half from the initial 0.79 g to 0.4 g. The pore size of 0.79g-(P27mol%G10) increased three-fold while the water absorption capacity of 0.4g-(P50mol%G10) increased to 325%. Meanwhile, the cell proliferation and attachment of 0.4g-(P50mol%G10) and 0.4g-(P82mol%G7.5) increased as compared to the initial seeding number. Based on the overall data obtained, we can conclude that the introduction of a small amount of gelatine into P(3HB-co-4HB) improved the physical and biological properties of blend scaffolds, and the 0.4g-(P50mol%G10) shows great potential for medical applications considering its unique structure and properties.

Poly-l-Lactic Acid (PLLA)-Based Biomaterials for Regenerative Medicine: A Review on Processing and Applications

Synthetic biopolymers are effective cues to replace damaged tissue in the tissue engineering (TE) field, both for in vitro and in vivo application. Among them, poly-l-lactic acid (PLLA) has been highlighted as a biomaterial with tunable mechanical properties and biodegradability that allows for the fabrication of porous scaffolds with different micro/nanostructures via various approaches. In this review, we discuss the structure of PLLA, its main properties, and the most recent advances in overcoming its hydrophobic, synthetic nature, which limits biological signaling and protein absorption. With this aim, PLLA-based scaffolds can be exposed to surface modification or combined with other biomaterials, such as natural or synthetic polymers and bioceramics. Further, various fabrication technologies, such as phase separation, electrospinning, and 3D printing, of PLLA-based scaffolds are scrutinized along with the in vitro and in vivo applications employed in various tissue repair strategies. Overall, this review focuses on the properties and applications of PLLA in the TE field, finally affording an insight into future directions and challenges to address an effective improvement of scaffold properties.

PLLA-gelatin composite fiber membranes incorporated with functionalized CeNPs as a sustainable wound dressing substitute promoting skin regeneration and scar remodelling

The need of wound dressing material that can accelerate wound healing is increasing and will last a long time. In this study, Cerium Oxide Nanoparticles (CeNPs) incorporated poly-L-lactic acid (PLLA)-gelatin...

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.

Preparation of PEG-modified wool keratin/sodium alginate porous scaffolds with elasticity recovery and good biocompatibility

To improve mechanical properties of keratin (KR) porous scaffolds, we prepared a PEGylated keratin through thiol-ene click reaction. Several porous scaffolds were prepared by blending PEGylated keratin with sodium alginate (SA). The surface morphology, mechanical properties, and porosity of scaffolds were detailed studied at different KR/SA proportions. The results showed the content of SA had an effect on pore formation and mechanical properties. When the mass ratio of KR to SA was 2:1, the stress of yield point of the keratin porous scaffold reached 1.24 MPa, and also showed good deformation recovery ability. The PEGylated keratin porous scaffold had a high porosity and great cytocompatibility. Its' porosity is up to 81.7% and the cell viability is about 117.78%. This allows it to absorb the simulated plasma quickly (9.20 ± 0.37 g/g). In addition, the structural stability and acid-base stability of the keratin porous scaffold were also improved after PEGylation. Overall, the PEGylated keratin porous scaffold will be promising in tissue materials due to its great physical, chemical, and biological properties.

3D Propolis-Sodium Alginate Scaffolds: Influence on Structural Parameters, Release Mechanisms, Cell Cytotoxicity and Antibacterial Activity

In this study, the main aim was to fabricate propolis (Ps)-containing wound dressing patches using 3D printing technology. Different combinations and structures of propolis (Ps)-incorporated sodium alginate (SA) scaffolds were developed. The morphological studies showed that the porosity of developed scaffolds was optimized when 20% (v/v) of Ps was added to the solution. The pore sizes decreased by increasing Ps concentration up to a certain level due to its adhesive properties. The mechanical, swelling-degradation (weight loss) behaviors, and Ps release kinetics were highlighted for the scaffold stability. An antimicrobial assay was employed to test and screen antimicrobial behavior of Ps against Escherichia coli and Staphylococcus aureus strains. The results show that the Ps-added scaffolds have an excellent antibacterial activity because of Ps compounds. An in vitro cytotoxicity test was also applied on the scaffold by using the extract method on the human dermal fibroblasts (HFFF2) cell line. The 3D-printed SA–Ps scaffolds are very useful structures for wound dressing applications.

A natural polymer-based porous sponge with capillary-mimicking microchannels for rapid hemostasis

Natural polymer materials have attracted great attention in the field of hemostasis because of their wide range of source, nontoxicity, hydrophilicity, and air permeability. In the present study, two natural polymers composed of carboxymethyl chitosan (CMCS) and sodium carboxymethylcellulose (CMCNa) plus γ-(2,3-epoxypropoxy) propytrimethoxysilane (KH560) that serves as a crosslinking agent were selected to synthesize a capillary-mimicking composite hemostatic (CCK) sponge with a low density, interconnected microchannel architecture, suitable mechanical strength, high resilience, and ultrastrong liquid absorption capacity. The introduction of a large number of hydrophilic carboxymethyl functional groups and the design of capillary-mimicking structures formed by the ice segregation-induced self-assembly (ISISA) process endowed the CCK sponges with an ultrastrong liquid absorption capacity, which significantly enhanced the hemostatic ability of the materials. Both in vivo and in vitro hemostatic experiments confirmed the potential of the CCK sponges to achieve rapid hemostasis. Additionally, cytotoxicity and hemolysis assays showed that the CCK sponges exhibited good biocompatibility and hemocompatibility. The possible hemostatic mechanism was also discussed in this study. In conclusion, the capillary-mimicking hemostatic sponge exhibits a high potential to induce rapid hemostasis in prehospital emergency and clinical settings. STATEMENT OF SIGNIFICANCE: In the present study, an oriented composite hemostatic (CCK) sponge with a capillary-mimicking structure formed by the ice segregation-induced self-assembly (ISISA) process was designed and used to achieve rapid hemostasis. The unique aligned microchannel structure of the sponge exhibited an ultrastrong capillary-mimicking action and endowed the prepared CCK hemostatic sponge with a strong liquid absorption capacity. By changing the proportion of raw materials, we could modify the unique capillary-mimicking structure with aligned microchannels. Two natural polymer-based materials with abundant hydrophilic groups were chosen to prepare the CCK sponge to fully utilize the characteristics of this structure. The oriented natural polymer-based porous sponge with capillary-mimicking microchannels exhibited a strong hemostatic ability in both in vivo and in vitro tests. The results showed that the CCK sponge with the capillary-mimicking structure has a high potential to achieve rapid hemostasis.

Fibro-porous PLLA/gelatin composite membrane doped with cerium oxide nanoparticles as bioactive scaffolds for future angiogenesis

Functionalized cerium oxide nanoparticle (CeNP)-loaded fibro-porous poly-l-lactic acid (PLLA)/gelatin composite membranes were prepared via an electrospinning technology. Considering the importance of such membrane scaffolds for promoting angiogenesis in tissue engineering and drug screening, a series of PLLA/gelatin composite fiber membranes loaded with different doses of CeNPs was prepared. The prepared composite membranes demonstrated hydrophilicity, water absorption, and improved mechanical properties compared to a PLLA and PLLA/gelatin membrane. Also, cell viability assay using somatic hybrid endothelial cells (EA.hy926) proved the biocompatible nature of the scaffolds. The biocompatibility was further supported by in vivo chick embryo angiogenesis assay using fertilized eggs. Our initial results support that these membrane scaffolds could be useful for angiogenesis-related disease treatment after further investigations.

PLA-Collagen Composite Scaffold Fabrication by Vacuum Pressure Impregnation

Composite scaffolds are made by various methods, such as copolymerization, freeze gelation, and thermally induced phase separation, which can compound materials with different properties using solvents and heat. However, it is difficult to compound solvents and heat-sensitive materials such as natural polymers. In this study, we investigated a vacuum pressure impregnation (VPI) method for creating a composite of natural polymers. A collagen solution could not be introduced into a poly (l-lactide) (PLA) porous material using an immersing treatment, but it is possible using the VPI method. The resulting PLA-collagen composite scaffold had greater water adsorption and degradation than a PLA scaffold. These results indicate that VPI may be a promising method for creating composites of natural materials. Impact Statement This is the development of a method for introducing cells into a completed porous material in a short time. This technology is expected to be applied to tissue regeneration and 3D culture.

Construction and application of textile-based tissue engineering scaffolds: a review

Tissue engineering (TE) provides a practicable method for tissue and organ repair or substitution. As the most important component of TE, a scaffold plays a critical role in providing a growing environment for cell proliferation and functional differentiation as well as good mechanical support. And the restorative effects are greatly dependent upon the nature of the scaffold including the composition, morphology, structure, and mechanical performance. Medical textiles have been widely employed in the clinic for a long time and are being extensively investigated as TE scaffolds. However, unfortunately, the advantages of textile technology cannot be fully exploited in tissue regeneration due to the ignoring of the diversity of fabric structures. Therefore, this review focuses on textile-based scaffolds, emphasizing the significance of the fabric design and the resultant characteristics of cell behavior and extracellular matrix reconstruction. The structure and mechanical behavior of the fabrics constructed by various textile techniques for different tissue repairs are summarized. Furthermore, the prospect of structural design in the TE scaffold preparation was anticipated, including profiled fibers and some unique and complex textile structures. Hopefully, the readers of this review would appreciate the importance of structural design of the scaffold and the usefulness of textile-based TE scaffolds in tissue regeneration.

A salt-based method to adapt stiffness and biodegradability of porous collagen scaffolds

Type I collagen scaffolds for tissue reconstruction often have impaired mechanical characteristics such as limited stiffness and lack of strength. In this study, a new technique is presented to fine-tune stiffness and biodegradability of collagen scaffolds by treatment with concentrated salt solutions. Collagen scaffolds were prepared by a casting, freezing and lyophilization process. Scaffolds were treated with 90% saturated salt solutions, the salts taken from the Hofmeister series, followed by chemical crosslinking. Treatment with salts consisting of a divalent cation in combination with a monovalent anion, e.g. CaCl₂, resulted in fast shrinkage of the scaffolds up to approximately 10% of the original surface area. Effective salts were mostly at the chaotropic end of the Hofmeister series. Shrunken scaffolds were more than 10 times stiffer than non-shrunken control scaffolds, and displayed reduced pore sizes and swollen, less organized collagen fibrils. The effect could be pinpointed to the level of individual collagen molecules and indicates the shrinking effect to be driven by disruption of stabilizing hydrogen bonds within the triple helix. No calcium deposits remained in CaCl₂ treated scaffolds. Subcutaneous implantation in rats showed similar biocompatibility compared to H₂O and NaCl treated scaffolds, but reduced cellular influx and increased structural integrity without signs of major degradation after 3 months. In conclusion, high concentrations of chaotropic salts can be used to adjust the mechanical characteristics of collagen scaffolds without affecting biocompatibility. This technique may be used in regenerative medicine to stiffen collagen scaffolds to better comply with the surrounding tissues, but may also be applied for e.g. slow release drug delivery systems.

Treatment of collagen scaffolds with salts taken from the Hofmeister series induce fast shrinkage and increased stiffness. Subcutaneous implantation in rats shows similar biocompatibility as control scaffolds, but reduced cellular influx and increased structural integrity.

PLGA–collagen–ECM hybrid scaffolds functionalized with biomimetic extracellular matrices secreted by mesenchymal stem cells during stepwise osteogenesis-co-adipogenesis

Development of an in vitro 3D model that reflects the dynamic remodeling of ECMs during simultaneous osteogenesis and adipogenesis of hMSCs.

Cellular and Molecular Interaction of Human Dermal Fibroblasts with Bacterial Nanocellulose Composite Hydrogel for Tissue Regeneration

The evaluation of the interaction of cells with biomaterials is fundamental to establish the suitability of the biomaterial for a specific application. In this study, the properties of bacterial nanocellulose/acrylic acid (BNC/AA) hydrogels fabricated with varying BNC to AA ratios and electron-beam irradiation doses were determined. The manner these hydrogel properties influence the behavior of human dermal fibroblasts (HDFs) at the cellular and molecular levels was also investigated, relating it to its application both as a cell carrier and wound dressing material. Swelling, hardness, adhesive force (wet), porosity, and hydrophilicity (dry) of the hydrogels were dependent on the degree of cross-linking and the amount of AA incorporated in the hydrogels. However, water vapor transmission rate, pore size, hydrophilicity (semidry), and topography were similar between all formulations, leading to a similar cell attachment and proliferation profile. At the cellular level, the hydrogel demonstrated rapid cell adhesion, maintained HDFs viability and morphology, restricted cellular migration, and facilitated fast transfer of cells. At the molecular level, the hydrogel affected nine wound-healing genes (IL6, IL10, MMP2, CTSK, FGF7, GM-CSF, TGFB1, COX2, and F3). The findings indicate that the BNC/AA hydrogel is a potential biomaterial that can be employed as a wound-dressing material to incorporate HDFs for the acceleration of wound healing.

Fabrication of Three-Dimensional Scaffolds Based on Nano-biomimetic Collagen Hybrid Constructs for Skin Tissue Engineering

Three-dimensional (3D) biodegradable and biomimetic porous scaffolds are ideal frameworks for skin tissue engineering. In this study, hybrid constructs of 3D scaffolds were successfully fabricated by the freeze-drying method from combinations of the type I collagen (Col) and synthetic poly(lactic acid) (PLLA) or polycaprolactone (PCL). Four different groups of 3D porous scaffolds including PCL, PCL-Col, PCL-PLLA, and PCL-PLLA-Col were fabricated and systematically characterized by hydrogen nuclear magnetic resonance, Fourier transform infrared spectroscopy, and scanning electron microscopy (SEM). Adipose tissue-derived mesenchymal stem cells (AT-MSCs) were seeded in all scaffolds, and the viability, proliferation, and adhesion of the cells were investigated using dimethylthiazol diphenyltetrazolium bromide assay and SEM. The results showed that scaffolds containing Col, particularly PCL-PLLA-Col scaffold, with pore sizes close to 400 nm and being sufficiently interconnected, have significantly greater potential (p < 0.01) for encouraging AT-MSCs adhesion and growth. The PCL-PLLA provided a mechanically stronger mesh support, and the type I Col microsponges encouraged excellent cell adhesion and tissue formation. The scaffold with the best properties could be an appropriate functional candidate for the preparation of artificial skin constructs.

Biomaterials for Skin Substitutes

Patients with extensive burns rely on the use of tissue engineered skin due to a lack of sufficient donor tissue, but it is a challenge to identify reliable and economical scaffold materials and donor cell sources for the generation of a functional skin substitute. The current review attempts to evaluate the performance of the wide range of biomaterials available for generating skin substitutes, including both natural biopolymers and synthetic polymers, in terms of tissue response and potential for use in the operating room. Natural biopolymers display an improved cell response, while synthetic polymers provide better control over chemical composition and mechanical properties. It is suggested that not one material meets all the requirements for a skin substitute. Rather, a composite scaffold fabricated from both natural and synthetic biomaterials may allow for the generation of skin substitutes that meet all clinical requirements including a tailored wound size and type, the degree of burn, the patient age, and the available preparation technique. This review aims to be a valuable directory for researchers in the field to find the optimal material or combination of materials based on their specific application.

Recent advances on biomedical applications of scaffolds in wound healing and dermal tissue engineering

The tissue engineering field has developed in response to the shortcomings related to the replacement of the tissues lost to disease or trauma: donor tissue rejection, chronic inflammation and donor tissue shortages. The driving force behind the tissue engineering is to avoid the mentioned issues by creating the biological substitutes capable of replacing the damaged tissue. This is done by combining the scaffolds, cells and signals in order to create the living, physiological, three-dimensional tissues. A wide variety of skin substitutes are used in the treatment of full-thickness injuries. Substitutes made from skin can harbour the latent viruses, and artificial skin grafts can heal with the extensive scarring, failing to regenerate structures such as glands, nerves and hair follicles. New and practical skin scaffold materials remain to be developed. The current article describes the important information about wound healing scaffolds. The scaffold types which were used in these fields were classified according to the accepted guideline of the biological medicine. Moreover, the present article gave the brief overview on the fundamentals of the tissue engineering, biodegradable polymer properties and their application in skin wound healing. Also, the present review discusses the type of the tissue engineered skin substitutes and modern wound dressings which promote the wound healing.

Combined chemical and structural signals of biomaterials synergistically activate cell-cell communications for improving tissue regeneration

Biomaterials are only used as carriers of cells in the conventional tissue engineering. Considering the multi-cell environment and active cell-biomaterial interactions in tissue regeneration process, in this study, structural signals of aligned electrospun nanofibers and chemical signals of bioglass (BG) ionic products in cell culture medium are simultaneously applied to activate fibroblast-endothelial co-cultured cells in order to obtain an improved skin tissue engineering construct. Results demonstrate that the combined biomaterial signals synergistically activate fibroblast-endothelial co-culture skin tissue engineering constructs through promotion of paracrine effects and stimulation of gap junctional communication between cells, which results in enhanced vascularization and extracellular matrix protein synthesis in the constructs. Structural signals of aligned electrospun nanofibers play an important role in stimulating both of paracrine and gap junctional communication while chemical signals of BG ionic products mainly enhance paracrine effects. In vivo experiments reveal that the activated skin tissue engineering constructs significantly enhance wound healing as compared to control. This study indicates the advantages of synergistic effects between different bioactive signals of biomaterials can be taken to activate communication between different types of cells for obtaining tissue engineering constructs with improved functions.

STATEMENT OF SIGNIFICANCE

Tissue engineering can regenerate or replace tissue or organs through combining cells, biomaterials and growth factors. Normally, for repairing a specific tissue, only one type of cells, one kind of biomaterials, and specific growth factors are used to support cell growth. In this study, we proposed a novel tissue engineering approach by simply using co-cultured cells and combined biomaterial signals. Using a skin tissue engineering model, we successfully proved that the combined biomaterial signals such as surface nanostructures and bioactive ions could synergistically stimulate the cell-cell communication in co-culture system through paracrine effects and gap junction activation, and regulated expression of growth factors and extracellular matrix proteins, resulting in an activated tissue engineering constructs that significantly enhanced skin regeneration.

Synthesis and characterization of PLGA/collagen composite scaffolds as skin substitute produced by electrospinning through two different approaches

Skin damage can occur for many reasons, including burns and injuries, which in extreme cases can even lead to death. Different methods such as electrospinning are used to produce scaffolds used in skin tissue engineering. Natural and synthetic polymers were used in this method. It was observed that the use of both natural and synthetic polymers gives better results for cell culturing rather than using of each material solely. In this study, scaffolds of poly(lactic-co-glycolic acid) and collagen were prepared using coating and common solvent methods. The characteristics of samples were evaluated through scanning electron microscopy, porosimetry, mechanical testing, degradation behavior, and in vitro assays. The mechanical and biocompatibility test results of the scaffold prepared by coating method were better than the other one. However, the degradation rate of the common solvent was nearly five times more than coating sample that leads to cytotoxicity in contact with the skin cells.

FABRICATION AND CHARACTERIZATION OF ELECTROSPUN PLLA/COLLAGEN NANOFIBROUS SCAFFOLD COATED WITH CHITOSAN TO SUSTAIN RELEASE OF ALOE VERA GEL FOR SKIN TISSUE ENGINEERING

Background and aim: Healing of fire-induced wounds has been still a challenge in clinical issues. The aim of this study was to fabricate a nanofibrous poly (L-lactic acid)/collagen (PLLA/COL) scaffold with sustained release of aloe vera (AV) gel using a chitosan (CT)-coated layer for skin tissue engineering applications. Material and methods: Morphology, porosity, tensile strength, hydrophilicity, degradation rate, water vapor permeability and water uptake ratio of the scaffold were characterized. The behaviors of mouse fibroblasts (L929) were evaluated on the scaffold. Results: We observed that although the porosity of the scaffold was decreased, other characteristics were enhanced by coating a CT layer. The scaffold supports attachment, viability and proliferation of mouse fibroblasts. Conclusion: Consequently, the PLLA/COL scaffold coated with CT for sustained release of AV gel can be considered as a desirable scaffold for skin tissue engineering.

Methodologies in creating skin substitutes

The creation of skin substitutes has significantly decreased morbidity and mortality of skin wounds. Although there are still a number of disadvantages of currently available skin substitutes, there has been a significant decline in research advances over the past several years in improving these skin substitutes. Clinically most skin substitutes used are acellular and do not use growth factors to assist wound healing, key areas of potential in this field of research. This article discusses the five necessary attributes of an ideal skin substitute. It comprehensively discusses the three major basic components of currently available skin substitutes: scaffold materials, growth factors, and cells, comparing and contrasting what has been used so far. It then examines a variety of techniques in how to incorporate these basic components together to act as a guide for further research in the field to create cellular skin substitutes with better clinical results.

Low-fouling electrospun PLLA films modified with zwitterionic poly(sulfobetaine methacrylate)-catechol conjugates

In this work, we modified a hydrophobic electrospun poly (l-lactic) acid (PLLA) film with poly (sulfobetaine methacrylate) (pSBMA)-catechol conjugates of different molecular weights to improve the biocompatibility of the film. These conjugates were synthesized via atom transfer radical polymerization. They consist of an ultra-low fouling pSBMA zwitterionic polymer with a surface-adhesive catechol moiety. X-ray photoelectron spectroscopy, contact angle and scanning electron microscopy experiments were performed to characterize films before and after modification with pSBMA-catechol conjugates. Enzyme-linked immunosorbent and fluorescently-labeled bovine serum albumin were used to study the interactions of proteins with these films. Results showed that low molecular weight zwitterionic pSBMA-catechol conjugates greatly discouraged protein adsorption as shown by use of single protein solutions on PLLA films when the modification was performed in ethanolic Tris-HCl solution. This work offers a convenient and effective method to modify electrospun PLLA films for biomedical applications.

STATEMENT OF SIGNIFICANCE

In this work, we report a convenient and effective method to modify electrospun PLLA films using pSBMA-catechol conjugates via "graft-to" for biomedical applications. After pSBMA modification, the PLLA surface becomes hydrophilic with low contact angle and protein adsorption. Results showed that lower molecular weight zwitterionic pSBMA-catechol conjugate led to lower contact angles and better nonfouling properties on PLLA films when the coating was performed in a solution containing ethanol.

Bilayer Cryogel Wound Dressing and Skin Regeneration Grafts for the Treatment of Acute Skin Wounds

In this study, the potential of cryogel bilayer wound dressing and skin regenerating graft for the treatment of surgically created full thickness wounds was evaluated. The top layer was composed of polyvinylpyrrolidone-iodine (PVP-I) cryogel and served as the antiseptic layer, while the bottom regenerative layer was made using gelatin cryogel. Both components of the bilayer showed typical features of a cryogel interconnected macropore network, rapid swelling, high water uptake capacity of about 90%. Both PVP and gelatin cryogel showed high tensile strength of 45 and 10 kPa, respectively. Gelatin cryogel sheets were essentially elastic and could be stretched without any visible deformation. The antiseptic PVP-I layer cryogel sheet showed sustained iodine release and suppressed microbial growth when tested with skin pathogens (zone of inhibition ∼2 cm for sheet of 0.9 cm diameter). The gelatin cryogel sheet degraded in vitro in weeks. The gelatin cryogel sheet supported cell infiltration, attachment, and proliferation of fibroblasts and keratinocytes. Microparticles loaded with bioactive molecules (mannose-6-phosphate and human fibrinogen) were also incorporated in the gelatin cryogel sheets for their role in enhancing skin regeneration and scar free wound healing. In vivo evaluation of healing capacity of the bilayer cryogel was checked in rabbits by creating full thickness wound defect (diameter 2 cm). Macroscopic and microscopic observation at regular time intervals for 4 weeks demonstrated better and faster skin regeneration in the wound treated with cryogel bilayer as compared to untreated defect and the repair was comparable to commercial skin regeneration scaffold Neuskin-F. Complete skin regeneration was observed after 4 weeks of implantation with no sign of inflammatory response. Defects implanted with cryogel having mannose-6-phosphate showed no scar formation, while the wound treated with bilayer incorporated with human fibrinogen microparticles showed early signs of skin regeneration; epidermis formation occurred at 2 weeks after implantation.

Growth of Self-Assembled Bio-Organic Nanomatrices for Skin Tissue Engineering — An in vitro Study

In this paper, we have developed self-assembled nanoscale assemblies that were prepared by conjugating furan-2-carboxylic acid-3-aminopropyl amide with the short peptide sequence Gly-His (abbreviated Gly-His-FCAP). To mimic the extracellular matrix of mammalian fibroblasts and keratinocytes, the assemblies were then conjugated with Type I collagen. We then integrated the collagen bound Gly-His-FCAP assemblies with a short peptide sequence derived from salamander skin into the nanoscale assemblies for the first time to impart regenerative and wound healing properties to the composites. The antioxidant, antimicrobial and biodegradable properties were examined and results indicate that the nanocomposites displayed antioxidant properties as displayed by 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. The biodegradability was found to be gradual. The nanocomposites were also found to inhibit the growth of the fungus Rhizopus sporangia over an 18[Formula: see text]h growth period. As proof of concept, to demonstrate the development of three-dimensional (3D) engineered skin in vitro, 3D printed PLA scaffolds of 2.5[Formula: see text]mm thickness were submerged in media containing nanocomposites and co-cultures of dermal fibroblasts with epidermal keratinocytes mimicking three dimensional skin substitute was examined. Our results indicated that the nanocomposites adhered to and supported cell proliferation and mimicked the components of skin and may have potential applications in skin tissue regeneration.

Extracellular Matrix-Based Biohybrid Materials for Engineering Compliant, Matrix-Dense Tissues

An ideal tissue engineering scaffold should not only promote, but take an active role in, constructive remodeling and formation of site appropriate tissue. Extracellular matrix (ECM)-derived proteins provide unmatched cellular recognition, and therefore influence cellular response towards predicted remodeling behaviors. Materials built with only these proteins, however, can degrade rapidly or begin too weak to substitute for compliant, matrix-dense tissues. The focus of this Progress Report is on biohybrid materials that incorporate polymer components with ECM-derived proteins, to produce a substrate with desired mechanical and degradation properties, as well as actively guide tissue remodeling. Materials are described through four fabrication methods: 1) polymer and ECM-protein fibers woven together, 2) polymer and ECM proteins combined in a bilayer, 3) cell-built ECM on polymer scaffold, and 4) ECM proteins and polymers combined in a single hydrogel. Scaffolds from each fabrication method can achieve characteristics suitable for different types of tissue. In vivo testing has shown progressive remodeling in injury models, and suggests ECM-based biohybrid materials promote a prohealing immune response over single component alternatives. The prohealing immune response is associated with lasting success and long term host maintenance of the implant.

Ultrastructural investigation on fibroblast interaction with collagen scaffold

Collagen-based scaffolds are used as temporary or permanent coverings to help wound healing. Under natural conditions, wound healing is affected by such factors as cell types, growth factors and several components of the extracellular matrix. Due to the complexity of the cell-to-matrix interaction, many cell based mechanisms regulating wound healing in vivo are not yet properly understood. However, the whole process can be partially simulated in vitro to determine how cells interact with the collagen scaffold in relation to such features as physico-chemical properties, matrix architecture and fiber stability. Under these conditions, cell migration into the collagen matrix can be easily assessed and causally correlated with these features. In this study, we aimed at providing a structural analysis of how NIH3T3 fibroblasts migrate and proliferate in vitro when seeded on a native type-I collagen scaffold. To this end, samples were collected at regular time intervals and analyzed by light microscopy (LM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Through this experimental approach we demonstrate that collagen is gradually frayed into progressively thinner fibrils as fibroblasts migrate into the matrix, embrace the collagen fibers with long filopodia and form large intracellular vacuoles. A key role in this process is also played by microvesicles shed from the fibroblast plasma membrane and spread over long distances inside the collagen matrix. These observations indicate that a native type-I equine collagen provides favorable conditions for simulating collagen processing in vitro and eventually for unraveling the mechanisms controlling cell uptake and intracellular degradation.

Biomaterials for in situ tissue regeneration: development and perspectives

Biomaterials are of fundamental importance to in situ tissue regeneration, which has emerged as a powerful method to treat tissue defects. The development and perspectives of biomaterials for in situ tissue regeneration were summarized.

Contribution of fibroblasts to the mechanical stability of in vitro engineered dermal-like tissue through extracellular matrix deposition

Tissue-engineered skin with mechanical and biological properties that match the native tissue could be a valuable graft to treat non-healing chronic wounds. Fibroblasts grown on a suitable biodegradable scaffold are a feasible strategy for the development of a dermal substitute above which epithelialization may occur naturally. Cell growth and phenotype maintenance are crucial to ensure the functional status of engineered tissue. In this study, an electrospun biodegradable polymer scaffold composed of a terpolymer PLGC [poly(lactide-glycolide-caprolactone)] with appropriate mechanical strength was used as a scaffold so that undesirable contraction of the wound could be prevented when it was implanted. To enhance cell growth, synthetic PLGC was incorporated with a fibrin-based biomimetic composite. The efficacy of the hybrid scaffold was evaluated by comparing it with bare PLGC in terms of fibroblast growth potential, extracellular matrix (ECM) deposition, polymer degradation, and mechanical strength. A significant increase was observed in fibroblast attachment, proliferation, and deposition of ECM proteins such as collagen and elastin in the hybrid scaffold. After growing fibroblasts for 20 d and 40 d, immunochemical staining of the decellularized scaffolds showed deposition of insoluble collagen and elastin on the hybrid scaffold but not on the bare scaffold. The loss of mechanical strength consequent to in vitro polymer degradation seemed to be balanced owing to the ECM deposition. Thus, tensile strength and elongation were better when cells were grown on the hybrid scaffold rather than the bare samples immersed in culture medium. Similar patterns of in vivo and in vitro degradation were observed during subcutaneous implantation and fibroblast culture, respectively. We therefore postulate that a hybrid scaffold comprising PLGC and fibrin is a potential candidate for the engineering of dermal tissue to be used in the regeneration of chronic wounds.

Electrospinning of gelatin for tissue engineering--molecular conformation as one of the overlooked problems

Gelatin is one of the most promising materials in tissue engineering as a scaffold component. This biopolymer indicates biocompatibility and bioactivity caused by the existence of specific amino acid sequences, being preferred sites for interactions with cells, with high similarity to natural extracellular matrix. The present paper does not aspire to be a full review of electrospinning of gelatin and gelatin containing nanofibers as scaffolds in tissue engineering. It is focused on the still open question of the role of the higher order structures of gelatin in scaffold's bioactivity/functionality. Gelatin molecules can adopt various conformations depending on temperature, solvent, pH, etc. Our review indicates the potential ways for formation of α-helix conformation during electrospinning and the methods of further structure stabilization. It is intuitively expected that the native α-helix conformation appearing as a result of partial renaturation of gelatin can be beneficial from the viewpoint of bioactivity of scaffolds, providing thus a much cheaper alternative approach as opposed to expensive electrospinning of native collagen.

Improved cellular response of chemically crosslinked collagen incorporated hydroxyethyl cellulose/poly(vinyl) alcohol nanofibers scaffold

The aim of this research is to develop biocompatible nanofibrous mats using hydroxyethyl cellulose with improved cellular adhesion profiles and stability and use these fibrous mats as potential scaffold for skin tissue engineering. Glutaraldehyde was used to treat the scaffolds water insoluble as well as improve their biostability for possible use in biomedical applications. Electrospinning of hydroxyethyl cellulose (5 wt%) with poly(vinyl alcohol) (15 wt%) incorporated with and without collagen was blended at (1:1:1) and (1:1) ratios, respectively, and was evaluated for optimal criteria as tissue engineering scaffolds. The nanofibrous mats were crosslinked and characterized by scanning electron microscope, Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. Scanning electron microscope images showed that the mean diameters of blend nanofibers were gradually increased after chemically crosslinking with glutaraldehyde. Fourier transform infrared spectroscopy was carried out to understand chemical interactions in the presence of aldehyde groups. Thermal characterization results showed that the stability of hydroxyethyl cellulose/poly(vinyl alcohol) and hydroxyethyl cellulose/poly(vinyl alcohol)/collagen nanofibers was increased with glutaraldehyde treatment. Studies on cell–scaffolds interaction were carried out by culturing human fibroblast (hFOB) cells on the nanofibers by assessing the growth, proliferation, and morphologies of cells. The scanning electron microscope results show that better cell proliferation and attachment appeared on hydroxyethyl cellulose/poly(vinyl alcohol)/collagen substrates after 7 days of culturing, thus, promoting the potential of electrospun scaffolds as a promising candidate for tissue engineering applications.

Collagen scaffolds with controlled insulin release and controlled pore structure for cartilage tissue engineering

Controlled and local release of growth factors and nutrients from porous scaffolds is important for maintenance of cell survival, proliferation, and promotion of tissue regeneration. The purpose of the present research was to design a controlled release porous collagen-microbead hybrid scaffold with controlled pore structure capable of releasing insulin for application to cartilage tissue regeneration. Collagen-microbead hybrid scaffold was prepared by hybridization of insulin loaded PLGA microbeads with collagen using a freeze-drying technique. The pore structure of the hybrid scaffold was controlled by using preprepared ice particulates having a diameter range of 150–250 μm. Hybrid scaffold had a controlled pore structure with pore size equivalent to ice particulates and good interconnection. The microbeads showed an even spatial distribution throughout the pore walls. In vitro insulin release profile from the hybrid scaffold exhibited a zero order release kinetics up to a period of 4 weeks without initial burst release. Culture of bovine articular chondrocytes in the hybrid scaffold demonstrated high bioactivity of the released insulin. The hybrid scaffold facilitated cell seeding and spatial cell distribution and promoted cell proliferation.

Preparation of collagen porous scaffolds with controlled and sustained release of bioactive insulin

Controlled and local release of bioactive growth factors from porous scaffolds can provide an efficient strategy to control the complex and dynamic regulation of cellular processes in a three-dimensional microenvironment. In this study, hybrid scaffolds of collagen and poly(lactic- co-glycolic acid) microbeads were prepared by introducing insulin-releasing poly(lactic- co-glycolic acid) microbeads into collagen porous scaffolds. Insulin-incorporated poly(lactic- co-glycolic acid) microbeads of two distinct sizes, 19.4 ± 1.6 and 4.4 ± 0.9 µm, were used to prepare the hybrid scaffolds. The scaffolds had controlled pore structure, and the poly(lactic- co-glycolic acid) microbeads were well distributed on the pore walls of the scaffolds. The scaffolds had a lower initial burst and a more stable insulin release than did the free microbeads. Culture of human dermal fibroblasts in the hybrid scaffolds were affected the bioactivity of released insulin. The hybrid scaffold prepared with 19.4 ± 1.6 µm microbeads had a more linear release of insulin and a higher promotion effect on cell proliferation than did the other hybrid group and control scaffolds. The hybrid scaffold should be useful for skin tissue engineering.