Platelet-Rich Plasma-Loaded Poly(d,l-lactide)-Poly(ethylene glycol)-Poly(d,l-lactide) Hydrogel Dressing Promotes Full-Thickness Skin Wound Healing in a Rodent Model

Biopolymer hydrogels and synergistic blends for tailored wound healing

Biopolymers have a transformative role in wound repair due to their biocompatibility, ability to stimulate collagen production, and controlled drug and growth factor delivery. This article delves into the biological parameters critical to wound healing emphasizing how combinations of hydrogels with reparative properties can be strategically designed to create matrices that stimulate targeted cellular responses at the wound site to facilitate tissue repair and recovery. Beyond a detailed examination of various biopolymer types and their functionalities in wound dressings acknowledging that the optimal choice depends on the specific wound type and application, this evaluation provides concepts for developing synergistic biopolymer blends to create next-generation dressings with enhanced efficiencies. Furthermore, the incorporation of therapeutic agents such as medications and wound healing accelerators into dressings to enhance their efficacy is examined. These agents often possess desirable properties such as antibacterial activity, antioxidant effects, and the ability to promote collagen synthesis and tissue regeneration. Finally, recent advancements in conductive hydrogels are explored, highlighting their capabilities in treatment and real-time wound monitoring. This comprehensive resource emphasizes the importance of optimizing ingredient efficiency besides assisting researchers in selecting suitable materials for personalized wound dressings, ultimately leading to more sophisticated and effective wound management strategies.

Extracellular vesicles derived from "serum and glucose" deprived HUCMSCs promoted skin wound healing through enhanced angiogenesis

Extracellular vesicles (EVs) produced from MSCs were currently considered as a novel therapeutic agent for skin tissue regeneration and repair. Preconditioning stem cells may activate more molecular pathways and release more bioactive agents. In this study, we obtained EVs from normal (N-EVs) and serum- and glucose-deprived (SGD-EVs) human umbilical cord mesenchymal stem cells (HUCMSCs), and showed that SGD-EVs promoted the migration, proliferation, and tube formation of HUVECs in vitro. In vivo experiments utilizing a rat model show that both N-EVs and SGD-EVs boosted angiogenesis of skin defects and accelerated skin wound healing, while treating wounds with SGD-EVs led to faster skin healing and enhanced angiogenesis. miRNA sequencing showed that miR-29a-3p was abundant in SGD-EVs, and overexpressing miR-29a-3p enhanced the angiogenic ability of HUVECs, while inhibiting miR-29a-3p presented the opposite effect. Further studies demonstrated that miR-29a-3p directly targeted CTNNBIP1, which mediated angiogenesis of HUCMSCs-derived EVs through inhibiting CTNNBIP1 to activate Wnt/β-catenin signaling pathway. Taken together, these findings suggested that SGD-EVs promote angiogenesis via transferring miR-29a-3p, and activation of Wnt/β-catenin signaling pathway played a crucial role in SGD-EVs-induced VEGFA production during wound angiogenesis. Our results offered a new avenue for modifying EVs to enhance tissue angiogenesis and augment its role in skin repair.

Evolution of Hybrid Hydrogels: Next-Generation Biomaterials for Drug Delivery and Tissue Engineering

Hydrogels, being hydrophilic polymer networks capable of absorbing and retaining aqueous fluids, hold significant promise in biomedical applications owing to their high water content, permeability, and structural similarity to the extracellular matrix. Recent chemical advancements have bolstered their versatility, facilitating the integration of the molecules guiding cellular activities and enabling their controlled activation under time constraints. However, conventional synthetic hydrogels suffer from inherent weaknesses such as heterogeneity and network imperfections, which adversely affect their mechanical properties, diffusion rates, and biological activity. In response to these challenges, hybrid hydrogels have emerged, aiming to enhance their strength, drug release efficiency, and therapeutic effectiveness. These hybrid hydrogels, featuring improved formulations, are tailored for controlled drug release and tissue regeneration across both soft and hard tissues. The scientific community has increasingly recognized the versatile characteristics of hybrid hydrogels, particularly in the biomedical sector. This comprehensive review delves into recent advancements in hybrid hydrogel systems, covering the diverse types, modification strategies, and the integration of nano/microstructures. The discussion includes innovative fabrication techniques such as click reactions, 3D printing, and photopatterning alongside the elucidation of the release mechanisms of bioactive molecules. By addressing challenges, the review underscores diverse biomedical applications and envisages a promising future for hybrid hydrogels across various domains in the biomedical field.

Slow-sculpting graphene oxide/alginate gel loaded with platelet-rich plasma to promote wound healing in rats

Wounds, especially chronic wounds, have become an important problem that endangers human health. At present, there are many repair methods, and among them combines materials science and biology is one of the important repair methods. This study explored the preparation method, physicochemical properties, biological activity and safety of Platelet-Rich plasma (PRP)-loaded slow-sculpting graphene oxide (GO)/alginate gel, and applied it to acute full-thickness skin defect wounds in rats to observe its role in wound healing. The results show that the slow-sculpting GO/alginate gel has excellent plasticity and is suitable for a variety of irregularly shaped wounds. At the same time, its porous structure and water content can maintain the activity of platelets and their released growth factors in PRP, thereby promoting wound collagen synthesis and angiogenesis to accelerate wound healing. This indicates that the slow-sculpting GO/alginate gel is an excellent loading material for PRP, and the combination of the two may become one of the methods to promote wound repair.

Research progress related to thermosensitive hydrogel dressings in wound healing: a review

Wound healing is a dynamic and complex process in which the microenvironment at the wound site plays an important role. As a common material for wound healing, dressings accelerate wound healing and prevent external wound infections. Hydrogels have become a hot topic in wound-dressing research because of their high water content, good biocompatibility, and adjustable physical and chemical properties. Intelligent hydrogel dressings have attracted considerable attention because of their excellent environmental responsiveness. As smart polymer hydrogels, thermosensitive hydrogels can respond to small temperature changes in the environment, and their special properties make them superior to other hydrogels. This review mainly focuses on the research progress in thermosensitive intelligent hydrogel dressings for wound healing. Polymers suitable for hydrogel formation and the appropriate molecular design of the hydrogel network to achieve thermosensitive hydrogel properties are discussed, followed by the application of thermosensitive hydrogels as wound dressings. We also discuss the future perspectives of thermosensitive hydrogels as wound dressings and provide systematic theoretical support for wound healing.

Topical Synthetic Platelets Loaded With Gentamicin Decrease Bacteria in Deep Partial-Thickness Burns

INTRODUCTION

Prolonged inflammation and infection in burns may cause inadequate healing. Platelet granules contain anti-inflammatory mediators that impact wound healing. Synthetic platelets (SPs) avoid portability and storage difficulties of natural platelets and can be loaded with bioactive agents. We evaluated wound healing outcomes in deep partial-thickness (DPT) burns treated topically with SP loaded with antibiotics.

MATERIALS AND METHODS

Thirty DPT burns were created on the dorsum of two Red Duroc hybrid pigs. Six wounds were randomized into five groups: SP alone, SP loaded with gentamicin vesicles, SP with gentamicin mixture, vehicle control (saline), or dry gauze. Wounds were assessed from postburn days 3-90. Primary outcome was re-epithelialization percentage at postburn day 28. Secondary outcomes included wound contraction percentage, superficial blood flow relative to normal skin controls, and bacterial load score.

RESULTS

Results showed that re-epithelialization with the standard of care (SOC) was 98%, SP alone measured 100%, SP loaded with gentamicin vesicles was 100%, and SP with gentamicin mixture was 100%. Wound contraction was 5.7% in the SOC and was ∼10% in both the SP loaded with gentamicin vesicles and SP with gentamicin mixture groups. Superficial blood flow in the SOC was 102.5%, SP alone was 170%, the SP loaded was 155%, and gentamicin mixture 162.5%. Bacterial load score in the SOC was 2.2/5.0 and was significantly less at 0.8/5.0 in SP loaded with gentamicin vesicles (P > 0.05). SP and gentamicin mixture scored 2.7 and 2.3/5.0.

CONCLUSIONS

Topical SP treatment did not significantly improve outcomes. However, SP loaded with gentamicin-infused vesicles decreased bacterial load.

Enzymatically cross-linked hyaluronic acid hydrogels as in situ forming carriers of platelet-rich plasma: Mechanical properties and bioactivity levels evaluation

New studies have shown the great potential of the combination of in situ enzymatically cross-linked hydrogels based on tyramine derivative of hyaluronic acid (HA-TA) with platelet-rich plasma (PRP) and platelet lysate in regenerative medicine. This study describes how the presence of PRP and platelet lysate affects the kinetics of gelation, viscoelastic properties, swelling ratio, and the network structure of HA-TA hydrogels and how the encapsulation of PRP in hydrogels affects the bioactivity of released PRP determined as the ability to induce cell proliferation. The properties of hydrogels were tuned by a degree of substitution and concentration of HA-TA derivatives. The addition of platelet derivatives to the reaction mixture slowed down the cross-linking reaction and reduced elastic modulus (G') and thus cross-linking efficiency. However, low-swellable hydrogels (7-190%) suitable for soft tissue engineering with G' 200-1800 Pa were prepared with a gelation time within 1 min. It was confirmed that tested cross-linking reaction conditions are suitable for PRP incorporation because the total bioactivity level of PRP released from HA-TA hydrogels was ≥87% and HA-TA content in the hydrogels and thus mesh size (285-482 nm) has no significant effect on the bioactivity level of released PRP.

Structural and biological engineering of 3D hydrogels for wound healing

Chronic wounds have become one of the most important issues for healthcare systems and are a leading cause of death worldwide. Wound dressings are necessary to facilitate wound treatment. Engineering wound dressings may substantially reduce healing time, reduce the risk of recurrent infections, and reduce the disability and costs associated. In the path of engineering of an ideal wound dressing, hydrogels have played a leading role. Hydrogels are 3D hydrophilic polymeric structures that can provide a protective barrier, mimic the native extracellular matrix (ECM), and provide a humid environment. Due to their advantages, hydrogels (with different architectural, physical, mechanical, and biological properties) have been extensively explored as wound dressing platforms. Here we describe recent studies on hydrogels for wound healing applications with a strong focus on the interplay between the fabrication method used and the architectural, mechanical, and biological performance achieved. Moreover, we review different categories of additives which can enhance wound regeneration using 3D hydrogel dressings. Hydrogel engineering for wound healing applications promises the generation of smart solutions to solve this pressing problem, enabling key functionalities such as bacterial growth inhibition, enhanced re-epithelialization, vascularization, improved recovery of the tissue functionality, and overall, accelerated and effective wound healing.

Applications and perspectives of quaternized cellulose, chitin and chitosan: A review

Recently, increasing attention has been paid to natural polysaccharides for their low cost, biocompatibility and biodegradability. Quaternization is a modification method to improve the solubility and antibacterial ability of natural polysaccharides. Water-soluble derivatives of cellulose, chitin and chitosan offer the prospect of diverse applications in a wide range of fields, such as antibacterial products, drug delivery, wound healing, sewage treatment and ion exchange membranes. By combining the inherent properties of cellulose, chitin and chitosan with the inherent properties of the quaternary ammonium groups, new products with multiple functions and properties can be obtained. In this review, we summarized the research progress in the applications of quaternized cellulose, chitin and chitosan in recent five years. Moreover, ubiquitous challenges and personal perspectives on the further development of this promising field are also discussed.

VEGF-Encoding, Gene-Activated Collagen-Based Matrices Promote Blood Vessel Formation and Improved Wound Repair

Disruption in vascularization during wound repair can severely impair healing. Proangiogenic growth factor therapies have shown great healing potential; however, controlling growth factor activity and cellular behavior over desired healing time scales remains challenging. In this study, we evaluated collagen-mimetic peptide (CMP) tethers for their capacity to control growth factor gene transfer and growth factor activity using our recently developed gene-activated hyaluronic acid-collagen matrix (GAHCM). GAHCM was comprised of DNA/polyethyleneimine (PEI) polyplexes that were retained on hyaluronic acid (HA)-collagen hydrogels using CMPs. We hypothesized that using CMP-collagen tethers to control vascular endothelial growth factor-A (VEGF-A) gene delivery in fibroblasts would provide a powerful strategy to modulate the proangiogenic behaviors of endothelial cells (ECs) for blood vessel formation, resulting in enhanced wound repair. In co-culture experiments, we observed that CMP-modified GAHCM induced tunable gene delivery in fibroblasts as predicted, and correspondingly, VEGF-A produced by the fibroblasts led to increased growth and persistent migration of ECs for at least 7 days, as compared to non-CMP-modified GAHCM. Moreover, when ECs were exposed to fibroblast-containing VEGF-GAHCM with higher levels of CMP modification (50% CMP-PEI, or 50 CP), high CD31 expression was stimulated, resulting in the formation of an interconnected EC network with a significantly higher network volume and a larger diameter network structure than controls. Application of VEGF-GAHCM with 50 CP in murine splinted excisional wounds facilitated prolonged prohealing and proangiogenic responses resulting in increased blood vessel formation, improved granulation tissue formation, faster re-epithelialization, and overall enhanced repair. These findings suggest the benefits of CMP-collagen tethers as useful tools to control gene transfer and growth factor activity for improved treatment of wounds.

Applications and prospects of different functional hydrogels in meniscus repair

The meniscus is a kind of fibrous cartilage structure that serves as a cushion in the knee joint to alleviate the mechanical load. It is commonly injured, but it cannot heal spontaneously. Traditional meniscectomy is not currently recommended as this treatment tends to cause osteoarthritis. Due to their good biocompatibility and versatile regulation, hydrogels are emerging biomaterials in tissue engineering. Hydrogels are excellent candidates in meniscus rehabilitation and regeneration because they are fine-tunable, easily modified, and capable of delivering exogenous drugs, cells, proteins, and cytokines. Various hydrogels have been reported to work well in meniscus-damaged animals, but few hydrogels are effective in the clinic, indicating that hydrogels possess many overlooked problems. In this review, we summarize the applications and problems of hydrogels in extrinsic substance delivery, meniscus rehabilitation, and meniscus regeneration. This study will provide theoretical guidance for new therapeutic strategies for meniscus repair.

Tachyplesin I Analogue Peptide as an Effective Antimicrobial Agent against Candida albicans-Staphylococcus aureus Poly-Biofilm Formation and Mixed Infection

Microbial biofilms are difficult to tackle in many infectious diseases. Candida albicans and Staphylococcus aureus are prevalent symbiotic strains in polymicrobial biofilms, which showed enhanced antimicrobial resistance and made identifying effective treatment techniques more difficult. The antibiofilm abilities of tachplesin I analogue peptide (TP11A) and tachplesin I were investigated quantitatively in this study. Both inhibited C. albicans monomicrobial, S. aureus monomicrobial, and C. albicans-S. aureus polymicrobial biofilms quite well. TP11A suppressed the biofilm- and virulence-related genes of C. albicans (hwp 1) and S. aureus (ica A, fnb B, agr A, hla, nor A, and sig B) in the mixed biofilm, according to quantitative reverse transcription polymerase chain reaction analysis. We created an injectable thermosensitive in situ PLEL@TP11A gel system by simply adding TP11A into poly(d,l-lactide)-poly(ethylene glycol)-poly(d,l-lactide) (PLEL). Using C. albicans-S. aureus mixed infected wound models of mice, the in vivo therapeutic effect of TP11A and PLEL@TP11A in polymicrobial infections was investigated. The findings revealed that TP11A and PLEL@TP11A could efficiently reduce bacterial and fungal burden in wound infections, as well as accelerated wound healing. Based on above findings, TP11A might be an effective antimicrobial against C. albicans-S. aureus poly-biofilm formation and mixed infection.

Emerging Delivery Strategies of Platelet-Rich Plasma with Hydrogels for Wound Healing

Platelet-rich plasma (PRP), a platelet-rich plasma concentrate obtained from whole blood, has been widely used to treat wounds due to its high contents of growth factors that can not only play a role in the hemostasis, repair, and anti-infection of wounds but also promote cell proliferation, maturation, and angiogenesis. However, after PRP activation, its clinical effect was limited because of burst and uncontrolled release of growth factors and poor mechanical properties of PRP gels. In recent years, increasing attention has been moved to the loading and sustained release of growth factors in PRP by polymeric carriers. Hydrogels, as an interesting carrier, enable controlled delivery of growth factors by structural designs. Moreover, using hydrogels to encapsulate PRP is favorable to controlling the mechanical properties and water maintenance of PRP gels, which can provide a stable and moist wound repair environment to promote coordinated operations of skin tissue cells and cytokines as well as wound healing. In this review, the state of the art of hydrogels that have been used to load PRP for wound treatments is introduced, and further prospects in the research area are proposed.

Thermosensitive Hydrogel Incorporating Prussian Blue Nanoparticles Promotes Diabetic Wound Healing via ROS Scavenging and Mitochondrial Function Restoration

Diabetic foot ulcer is a serious complication in diabetes patients, imposing a serious physical and economic burden to patients and to the healthcare system as a whole. Oxidative stress is thought to be a key driver of the pathogenesis of such ulcers. However, no antioxidant drugs have received clinical approval to date, underscoring the need for the further development of such medications. Hydrogels can be applied directly to the wound site, wherein they function to prevent infection and maintain local moisture concentrations, in addition to serving as a reservoir for the delivery of a range of therapeutic compounds with the potential to expedite wound healing in a synergistic manner. Herein, we synthesized Prussian blue nanoparticles (PBNPs) capable of efficiently scavenging reactive oxygen species (ROS) owing to their ability to mimic the activity of catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD). In the context of in vitro oxidative stress, these PBNPs were able to protect against cytotoxicity, protect mitochondria from oxidative stress-related damage, and restore nuclear factor erythroid 2-related factor 2 (NRF2)/heme oxygenase-1 (HO-1) pathway activity. To expand on these results in an in vivo context, we prepared a thermosensitive poly (d,l-lactide)-poly(ethylene glycol)-poly(d,l-lactide) (PDLLA-PEG-PDLLA) hydrogel (PLEL)-based wound dressing in which PBNPs had been homogenously incorporated, and we then used this dressing as a platform for controlled PBNP release. The resultant PBNPs@PLEL wound dressing was able to improve diabetic wound healing, decrease ROS production, promote angiogenesis, and reduce pro-inflammatory interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) levels within diabetic wounds. Overall, our results suggest that this PBNPs@PLEL platform holds great promise as a treatment for diabetic foot ulcers.

Biomimetic Hydrogels to Promote Wound Healing

Wound healing is a common physiological process which consists of a sequence of molecular and cellular events that occur following the onset of a tissue lesion in order to reconstitute barrier between body and external environment. The inherent properties of hydrogels allow the damaged tissue to heal by supporting a hydrated environment which has long been explored in wound management to aid in autolytic debridement. However, chronic non-healing wounds require added therapeutic features that can be achieved by incorporation of biomolecules and supporting cells to promote faster and better healing outcomes. In recent decades, numerous hydrogels have been developed and modified to match the time scale for distinct stages of wound healing. This review will discuss the effects of various types of hydrogels on wound pathophysiology, as well as the ideal characteristics of hydrogels for wound healing, crosslinking mechanism, fabrication techniques and design considerations of hydrogel engineering. Finally, several challenges related to adopting hydrogels to promote wound healing and future perspectives are discussed.

PEG-based thermosensitive and biodegradable hydrogels

Injectable thermosensitive hydrogels are free-flowing polymer solutions at low or room temperature, making them easy to encapsulate the therapeutic payload or cells via simply mixing. Upon injection into the body, in situ forming hydrogels triggered by body temperature can act as drug-releasing reservoirs or cell-growing scaffolds. Finally, the hydrogels are eliminated from the administration sites after they accomplish their missions as depots or scaffolds. This review outlines the recent progress of poly(ethylene glycol) (PEG)-based biodegradable thermosensitive hydrogels, especially those composed of PEG-polyester copolymers, PEG-polypeptide copolymers and poly(organophosphazene)s. The material design, performance regulation, thermogelation and degradation mechanisms, and corresponding applications in the biomedical field are summarized and discussed. A perspective on the future thermosensitive hydrogels is also highlighted. STATEMENT OF SIGNIFICANCE: Thermosensitive hydrogels undergoing reversible sol-to-gel phase transitions in response to temperature variations are a class of promising biomaterials that can serve as minimally invasive injectable systems for various biomedical applications. Hydrophilic PEG is a main component in the design and fabrication of thermoresponsive hydrogels due to its excellent biocompatibility. By incorporating hydrophobic segments, such as polyesters and polypeptides, into PEG-based systems, biodegradable and thermosensitive hydrogels with adjustable properties in vitro and in vivo have been developed and have recently become a research hotspot of biomaterials. The summary and discussion on molecular design, performance regulation, thermogelation and degradation mechanisms, and biomedical applications of PEG-based thermosensitive hydrogels may offer a demonstration of blueprint for designing new thermogelling systems and expanding their application scope.

Small extracellular vesicles in combination with sleep-related circRNA3503: A targeted therapeutic agent with injectable thermosensitive hydrogel to prevent osteoarthritis

Osteoarthritis (OA), characterized by chondrocyte apoptosis and disturbance of the balance between catabolism and anabolism of the extracellular matrix (ECM), is the most common age-related degenerative joint disease worldwide. As sleep has been found to be beneficial for cartilage repair, and circular RNAs (circRNAs) have been demonstrated to be involved in the pathogenesis of OA, we performed RNA sequencing (RNA-seq), and found circRNA3503 was significantly increased after melatonin (MT)-induced cell sleep. Upregulation of circRNA3503 expression completely rescued the effects of interleukin-1β (IL-1β), which was used to simulate OA, on apoptosis, ECM degradation- and synthesis-related genes. Mechanistically, circRNA3503 acted as a sponge of hsa-miR-181c-3p and hsa-let-7b-3p. Moreover, as we previously showed that small extracellular vesicles (sEVs) derived from synovium mesenchymal stem cells (SMSCs) can not only successfully deliver nucleic acids to chondrocytes, but also effectively promote chondrocyte proliferation and migration, we assessed the feasibility of sEVs in combination with sleep-related circRNA3503 as an OA therapy. We successfully produced and isolated circRNA3503-loaded sEVs (circRNA3503-OE-sEVs) from SMSCs. Then, poly(D,l-lactide)-b-poly(ethylene glycol)-b-poly(D,l-lactide) (PDLLA-PEG-PDLLA, PLEL) triblock copolymer gels were used as carriers of sEVs. Through in vivo and in vitro experiments, PLEL@circRNA3503-OE-sEVs were shown to be a highly-effective therapeutic strategy to prevent OA progression. Through multiple pathways, circRNA3503-OE-sEVs alleviated inflammation-induced apoptosis and the imbalance between ECM synthesis and ECM degradation by acting as a sponge of hsa-miR-181c-3p and hsa-let-7b-3p. In addition, circRNA3503-OE-sEVs promoted chondrocyte renewal to alleviate the progressive loss of chondrocytes. Our results highlight the potential of PLEL@circRNA3503-OE-sEVs for preventing OA progression.

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CircRNA3503 alleviated apoptosis and the imbalance between ECM synthesis and ECM degradation.

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Wnt5a/b carried by sEVs promoted chondrocyte renewal to alleviate the progressive loss of chondrocytes.

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PDLLA-PEG-PDLLA (PLEL) triblock copolymer gels showed good performance in slow release of sEVs.

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PLEL@circRNA3503-OE-sEVs showed potential to prevent OA progression.

Wound dressings as growth factor delivery platforms for chronic wound healing

Introduction: Years of tissue engineering research have clearly demonstrated the potential of integrating growth factors (GFs) into scaffolds for tissue regeneration, a concept that has recently been applied to wound dressings. The old concept of wound dressings that only take a passive role in wound healing has now been overtaken, and advanced dressings which can take an active part in wound healing, are of current research interest.Areas covered: In this review we will focus on the recent strategies for the delivery of GFs to wound sites with an emphasis on the different approaches used to achieve fine tuning of spatial and temporal concentrations to achieve therapeutic efficacy.Expert opinion: The use of GFs to accelerate wound healing and reduce scar formation is now considered a feasible therapeutic approach in patients with a high risk of infections and complications. The integration of micro - and nanotechnologies into wound dressings could be the key to overcome the inherent instability of GFs and offer adequate control over the release rate. Many investigations have led to encouraging outcomes in various in vitro and in vivo wound models, and it is expected that some of these technologies will satisfy clinical needs and will enter commercialization.

Well-dispersed platelet lysate entrapped nanoparticles incorporate with injectable PDLLA-PEG-PDLLA triblock for preferable cartilage engineering application

Platelet lysate (PL) as a cost-effective cocktail of growth factors is an emerging ingredient in regenerative medicine, especially in cartilage tissue engineering. However, most studies fail to pay attention to PL's intrinsic characteristics and incorporate it directly with scaffolds or hydrogels by simple mixture. Currently, the particle size distribution of PL was determined to be scattered. Directly introducing PL into a thermosensitive poly(d,l-lactide)-poly(ethylene glycol)-poly(d,l-lactide) (PLEL) hydrogel disturbed its sol-gel transition. Electrostatic self-assembly heparin (Hep) and ε-poly-l-lysine (EPL) nanoparticles (NPs) were fabricated to improve the dispersity of PL. Such PL-NPs-incorporated PLEL gels retained the initial gelling capacity and showed a long-term PL-releasing ability. Moreover, the PL-loaded composite hydrogels inhibited the inflammatory response and dedifferentiation of IL-1β-induced chondrocytes. For in vivo applications, the PLEL@PL-NPs system ameliorated the early cartilage degeneration and promoted cartilage repair in the late stage of osteoarthritis. RNA sequencing analysis indicated that PL's protective effects might be associated with modulating hyaluronan synthase 1 (HAS-1) expression. Taken together, these results suggest that well-dispersed PL by Hep/EPL NPs is a preferable approach for its incorporation into hydrogels and the constructed PLEL@PL-NPs system is a promising cell-free and stepwise treatment option for cartilage tissue engineering.

Catechol modified quaternized chitosan enhanced wet adhesive and antibacterial properties of injectable thermo-sensitive hydrogel for wound healing

Wound dressings based on injectable thermo-sensitive hydrogel possess several advantages over preformed conventional dressings such as rapid reversible sol-gel transition behavior and the capacity of filling the irregular wound defect. Nevertheless, its clinical application is hindered by the weak tissue adhesiveness. Therefore, in this study, the catechol modified quaternized chitosan (QCS-C) was fabricated and incorporated into poly(d,l-lactide)-poly(ethylene glycol)-poly(d,l-lactide) (PLEL) hydrogel to develop an injectable hydrogel with the properties of thermo-sensitive, antibacterial and tissue adhesive. QCS-C could lower the LCST of hydrogel for easy gelation at physiological temperature, and significantly enhanced the tissue adhesion. For wound generation, nano-scaled bioactive glass (nBG：80 SiO₂, 16 CaO and 4 P₂O₅; mol%) was loaded into hydrogel to promote angiogenesis. The mice partial laceration experiment showed that PLEL-nBG-QCS-C hydrogel could effectively seal the ruptured skin and significantly accelerate wound healing. Thus, our findings established a new type of clinical treatment technology for complicated wounds.

Can hydrogel dressings reduce patients' discomfort and side effects of facial platelet-rich plasma injections?

The literature shows that facial injection of platelet-rich plasma (PRP) is a safe and effective treatment modality. Serious adverse effects have not been reported so far. Nevertheless, side effects such as redness, edema, bruising, pain, pruritus, and heat sensation have been reported. Our goal was to assess the potential effects of hydrogel dressing after injection of PRP. PRP was prepared using an ACP double-syringe system and applied on face by intradermal microdeposit injections. One half of the face was covered with a cooled (20°C) hydrogel dressing for 20 minutes before and after PRP injection. Patients rated the levels of pain separately for both sides. Physician and patient rated the overall appearance of the skin, redness, swelling, bruising, and number of bruises straight after the procedure. At 6-month follow-up, the physician rated the global aesthetic outcome. Needle prick-induced pain and edema were rated less on the hydrogel side. Our results demonstrate a significant reduction of patient's discomfort and side effects through application of hydrogel dressings. Recovery has been accelerated and the overall appearance of the skin straight after the procedure has been rated significantly better than without dressing application. At 6-month follow-up, the global aesthetic improvement was rated equally on both sides.

Functionalising Collagen-Based Scaffolds With Platelet-Rich Plasma for Enhanced Skin Wound Healing Potential

Porous collagen-glycosaminoglycan (collagen-GAG) scaffolds have shown promising clinical results for wound healing; however, these scaffolds do not replace the dermal and epidermal layer simultaneously and rely on local endogenous signaling to direct healing. Functionalizing collagen-GAG scaffolds with signaling factors, and/or additional matrix molecules, could help overcome these challenges. An ideal candidate for this is platelet-rich plasma (PRP) as it is a natural reservoir of growth factors, can be activated to form a fibrin gel, and is available intraoperatively. We tested the factors released from PRP (PRPr) and found that at specific concentrations, PRPr enhanced cell proliferation and migration and induced angiogenesis to a greater extent than fetal bovine serum (FBS) controls. This motivated us to develop a strategy to successfully incorporate PRP homogeneously within the pores of the collagen-GAG scaffolds. The composite scaffold released key growth factors for wound healing (FGF, TGFβ) and vascularization (VEGF, PDGF) for up to 14 days. In addition, the composite scaffold had enhanced mechanical properties (when compared to PRP gel alone), while providing a continuous upper surface of extracellular matrix (ECM) for keratinocyte seeding. The levels of the factors released from the composite scaffold were sufficient to sustain proliferation of key cells involved in wound healing, including human endothelial cells, mesenchymal stromal cells, fibroblasts, and keratinocytes; even in the absence of FBS supplementation. In functional in vitro and in vivo vascularization assays, our composite scaffold demonstrated increased angiogenic and vascularization potential, which is known to lead to enhanced wound healing. Upon pro-inflammatory induction, macrophages released lower levels of the pro-inflammatory marker MIP-1α when treated with PRPr; and released higher levels of the anti-inflammatory marker IL1-ra upon both pro- and anti-inflammatory induction when treated with the composite scaffold. Finally, our composite scaffold supported a co-culture system of human fibroblasts and keratinocytes that resulted in an epidermal-like layer, with keratinocytes constrained to the surface of the scaffold; by contrast, keratinocytes were observed infiltrating the PRP-free scaffold. This novel composite scaffold has the potential for rapid translation to the clinic by isolating PRP from a patient intraoperatively and combining it with regulatory approved scaffolds to enhance wound repair.

Hydrogel-Based Strategies to Advance Therapies for Chronic Skin Wounds

Chronic skin wounds are the leading cause of nontraumatic foot amputations worldwide and present a significant risk of morbidity and mortality due to the lack of efficient therapies. The intrinsic characteristics of hydrogels allow them to benefit cutaneous healing essentially by supporting a moist environment. This property has long been explored in wound management to aid in autolytic debridement. However, chronic wounds require additional therapeutic features that can be provided by a combination of hydrogels with biochemical mediators or cells, promoting faster and better healing. We survey hydrogel-based approaches with potential to improve the healing of chronic wounds by reviewing their effects as observed in preclinical models. Topics covered include strategies to ablate infection and resolve inflammation, the delivery of bioactive agents to accelerate healing, and tissue engineering approaches for skin regeneration. The article concludes by considering the relevance of treating chronic skin wounds using hydrogel-based strategies.

Acellular and cellular approaches to improve diabetic wound healing

Chronic diabetic wounds represent a huge socioeconomic burden for both affected individuals and the entire healthcare system. Although the number of available treatment options as well as our understanding of wound healing mechanisms associated with diabetes has vastly improved over the past decades, there still remains a great need for additional therapeutic options. Tissue engineering and regenerative medicine approaches provide great advantages over conventional treatment options, which are mainly aimed at wound closure rather than addressing the underlying pathophysiology of diabetic wounds. Recent advances in biomaterials and stem cell research presented in this review provide novel ways to tackle different molecular and cellular culprits responsible for chronic and nonhealing wounds by delivering therapeutic agents in direct or indirect ways. Careful integration of different approaches presented in the current article could lead to the development of new therapeutic platforms that can address multiple pathophysiologic abnormalities and facilitate wound healing in patients with diabetes.

Therapeutic strategies for enhancing angiogenesis in wound healing

The enhancement of wound healing has been a goal of medical practitioners for thousands of years. The development of chronic, non-healing wounds is a persistent medical problem that drives patient morbidity and increases healthcare costs. A key aspect of many non-healing wounds is the reduced presence of vessel growth through the process of angiogenesis. This review surveys the creation of new treatments for healing cutaneous wounds through therapeutic angiogenesis. In particular, we discuss the challenges and advancement that have been made in delivering biologic, pharmaceutical and cell-based therapies as enhancers of wound vascularity and healing.

An In Vitro Model of Angiogenesis during Wound Healing Provides Insights into the Complex Role of Cells and Factors in the Inflammatory and Proliferation Phase

Successful vascularization is essential in wound healing, the histo-integration of biomaterials, and other aspects of regenerative medicine. We developed a functional in vitro assay to dissect the complex processes directing angiogenesis during wound healing, whereby vascular cell spheroids were induced to sprout in the presence of classically (M1) or alternatively (M2) activated macrophages. This simulated a microenvironment, in which sprouting cells were exposed to the inflammatory or proliferation phases of wound healing, respectively. We showed that M1 macrophages induced single-cell migration of endothelial cells and pericytes. In contrast, M2 macrophages augmented endothelial sprouting, suggesting that vascular cells infiltrate the wound bed during the inflammatory phase and extensive angiogenesis is initiated upon a switch to a predominance of M2. Interestingly, M1 and M2 shared a pro-angiogenic secretome, whereas pro-inflammatory cytokines were solely secreted by M1. These results suggested that acute inflammatory factors act as key inducers of vascular cell infiltration and as key negative regulators of angiogenesis, whereas pro-angiogenic factors are present throughout early wound healing. This points to inflammatory factors as key targets to modulate angiogenesis. The here-established wound healing assay represents a useful tool to investigate the effect of biomaterials and factors on angiogenesis during wound healing.

Encapsulation of Biological Agents in Hydrogels for Therapeutic Applications

Hydrogels are materials specially suited for encapsulation of biological elements. Their large water content provides an environment compatible with most biological molecules. Their crosslinked nature also provides an ideal material for the protection of encapsulated biological elements against degradation and/or immune recognition. This makes them attractive not only for controlled drug delivery of proteins, but they can also be used to encapsulate cells that can have therapeutic applications. Thus, hydrogels can be used to create systems that will deliver required therapies in a controlled manner by either encapsulation of proteins or even cells that produce molecules that will be released from these systems. Here, an overview of hydrogel encapsulation strategies of biological elements ranging from molecules to cells is discussed, with special emphasis on therapeutic applications.

Delivery systems of current biologicals for the treatment of chronic cutaneous wounds and severe burns

While wound therapy remains a clinical challenge in current medical practice, much effort has focused on developing biological therapeutic approaches. This paper presents a comprehensive review of delivery systems for current biologicals for the treatment of chronic wounds and severe burns. The biologicals discussed here include proteins such as growth factors and gene modifying molecules, which may be delivered to wounds free, encapsulated, or released from living systems (cells, skin grafts or skin equivalents) or biomaterials. Advances in biomaterial science and technologies have enabled the synthesis of delivery systems such as scaffolds, hydrogels and nanoparticles, designed to not only allow spatially and temporally controlled release of biologicals, but to also emulate the natural extracellular matrix microenvironment. These technologies represent an attractive field for regenerative wound therapy, by offering more personalised and effective treatments.

In situ forming injectable hydrogels for drug delivery and wound repair

Hydrogels have been utilized in regenerative applications for many decades because of their biocompatibility and similarity in structure to the native extracellular matrix. Initially, these materials were formed outside of the patient and implanted using invasive surgical techniques. However, advances in synthetic chemistry and materials science have now provided researchers with a library of techniques whereby hydrogel formation can occur in situ upon delivery through standard needles. This provides an avenue to minimally invasively deliver therapeutic payloads, fill complex tissue defects, and induce the regeneration of damaged portions of the body. In this review, we highlight these injectable therapeutic hydrogel biomaterials in the context of drug delivery and tissue regeneration for skin wound repair.

A novel personalized 3D injectable protein scaffold for regenerative medicine

Biomaterials should be designed to closely resemble the characteristics and functions of the native extracellular matrix to provide mechanical support and signals to direct biological events. Here we have developed a novel injectable plasma rich in growth factors (PRGF-Endoret)-based formulation that combines a thermal-denaturation step of plasma with an autologous fibrin crosslinking. Rheological and mechanical properties were evaluated. Additionally, the microstructure and biological capacity of the biomaterial was also characterized. This novel formulation exhibited ideal mechanical properties and a gel-like behavior with the ability to progressively release its growth factor load over time. The results also suggested that the novel injectable formulation is non-cytotoxic, biocompatible and suitable for cell ingrowth as it is deduced from the fibroblast proliferation within the scaffold. Finally, stimulation of both cell proliferation and matrix proteins synthesis demonstrated the regenerative potential of this autologous protein based injectable scaffold.

Platelet-rich plasma ameliorates senescence-like phenotypes in a cellular photoaging model

Platelet-rich plasma (PRP) is a portion of blood plasma enriched with platelets widely investigated for accelerating bone and soft tissue healing.