Hierarchically Assembled Nanofiber Scaffold Guides Long Bone Regeneration by Promoting Osteogenic/Chondrogenic Differentiation of Endogenous Mesenchymal Stem Cells.

Critical-sized segmental long bone defects represent a challenging clinical dilemma in the management of battlefield and trauma-related injuries. The residual bone marrow cavity of damaged long bones contains many bone marrow mesenchymal stem cells (BMSCs), which provide a substantial source of cells for bone repair. Thus, a three-dimensional (3D) vertically aligned nanofiber scaffold (VAS) is developed with long channels and large pore size. The pore of VAS toward the bone marrow cavity after transplantation, enables the scaffolds to recruit BMSCs from the bone marrow cavity to the defect area. In vivo, it is found that VAS can significantly shorten gap distance and promote new bone formation compared to the control and collagen groups after 4 and 8 weeks of implantation. The single-cell sequencing results discovered that the 3D nanotopography of VAS can promote BMSCs differentiation to chondrocytes and osteoblasts, and up-regulate related gene expression, resulting in enhancing the activities of bone regeneration, endochondral ossification, bone trabecula formation, bone mineralization, maturation, and remodeling. The Alcian blue and bone morphogenetic protein 2 (BMP-2) immunohistochemical staining verified significant cartilage formation and bone formation in the VAS group, corresponding to the single-cell sequencing results. The study can inspire the design of next-generation scaffolds for effective long-bone regeneration is expected by the authors.

Modifiable risk factors mediate the effect of gastroesophageal reflux disease on stroke and subtypes: A Mendelian randomization study.

OBJECTIVES: Previous observational studies have suggested that gastroesophageal reflux disease (GERD) increases the risk of stroke, but the specific underlying mechanisms are unclear. We investigated the causal associations of GERD with stroke and its subtypes using Mendelian randomization (MR), and evaluated the potential mediating effects of modifiable stroke risk factors in the causal pathway. METHODS: Genetic instrumental variables for GERD were extracted from the latest genome-wide association study (GWAS) summary level data. We initially performed two-sample MR to examine the association of GERD with stroke and its subtypes, including ischemic stroke, intracranial hemorrhage, and the major subtypes of ischemic stroke. Two-step MR was further employed to investigate the mediating effect of 15 risk factors in the causal pathway. RESULTS: We found significant causal associations of genetically predicted GERD with increased risk of stroke (OR: 1.22 95% CI: 1.126-1.322), ischemic stroke (OR: 1.19 95% CI: 1.098-1.299), and large-artery stroke (OR: 1.49 95% CI: 1.214-1.836). Replication and sensitivity analyses yielded consistent effect directions and similar estimates. Further mediation analyses indicated that hypertension (HTN), systolic blood pressure (SBP), and type 2 diabetes (T2D) mediated 36.0%, 9.0%, and 15.8% of the effect of GERD on stroke; 42.9%, 10.8%, and 21.4% for ischemic stroke, and 23.3%; 7.9%, and 18.7% for large-artery stroke, respectively. CONCLUSIONS: This study supports that GERD increases susceptibility to stroke, ischemic stroke, and large-artery stroke, and is partially mediated by HTN, SBP, and T2D.

gcaPDA: a haplotype-resolved diploid assembler.

BACKGROUND: Generating chromosome-scale haplotype resolved assembly is important for functional studies. However, current de novo assemblers are either haploid assemblers that discard allelic information, or diploid assemblers that can only tackle genomes of low complexity. RESULTS: Here, Using robust programs, we build a diploid genome assembly pipeline called gcaPDA (gamete cells assisted Phased Diploid Assembler), which exploits haploid gamete cells to assist in resolving haplotypes. We demonstrate the effectiveness of gcaPDA based on simulated HiFi reads of maize genome which is highly heterozygous and repetitive, and real data from rice. CONCLUSIONS: With applicability of coping with complex genomes and fewer restrictions on application than most of diploid assemblers, gcaPDA is likely to find broad applications in studies of eukaryotic genomes.

Ultra-absorptive Nanofiber Swabs for Improved Collection and Test Sensitivity of SARS-CoV-2 and other Biological Specimens.

Following the COVID-19 outbreak, swabs for biological specimen collection were thrust to the forefront of healthcare materials. Swab sample collection and recovery are vital for reducing false negative diagnostic tests, early detection of pathogens, and harvesting DNA from limited biological samples. In this study, we report a new class of nanofiber swabs tipped with hierarchical 3D nanofiber objects produced by expanding electrospun membranes with a solids-of-revolution-inspired gas foaming technique. Nanofiber swabs significantly improve absorption and release of proteins, cells, bacteria, DNA, and viruses from solutions and surfaces. Implementation of nanofiber swabs in SARS-CoV-2 detection reduces the false negative rates at two viral concentrations and identifies SARS-CoV-2 at a 10× lower viral concentration compared to flocked and cotton swabs. The nanofiber swabs show great promise in improving test sensitivity, potentially leading to timely and accurate diagnosis of many diseases.

Bioprinted Injectable Hierarchically Porous Gelatin Methacryloyl Hydrogel Constructs with Shape-Memory Properties.

Direct injection of cell-laden hydrogels shows high potentials in tissue regeneration for translational therapy. The traditional cell-laden hydrogels are often used as bulk space fillers to tissue defects after injection, likely limiting their structural controllability. On the other hand, patterned cell-laden hydrogel constructs often necessitate invasive surgical procedures. To overcome these problems, herein, we report a unique strategy for encapsulating living human cells in a pore-forming gelatin methacryloyl (GelMA)-based bioink to ultimately produce injectable hierarchically macro-micro-nanoporous cell-laden GelMA hydrogel constructs through three-dimensional (3D) extrusion bioprinting. The hydrogel constructs can be fabricated into various shapes and sizes that are defect-specific. Due to the hierarchically macro-micro-nanoporous structures, the cell-laden hydrogel constructs can readily recover to their original shapes, and sustain high cell viability, proliferation, spreading, and differentiation after compression and injection. Besides, in vivo studies further reveal that the hydrogel constructs can integrate well with the surrounding host tissues. These findings suggest that our unique 3D-bioprinted pore-forming GelMA hydrogel constructs are promising candidates for applications in minimally invasive tissue regeneration and cell therapy.

Engineering Biomimetic Nanofiber Microspheres with Tailored Size, Predesigned Structure, and Desired Composition via Gas Bubble-Mediated Coaxial Electrospray.

Minimally invasive therapies avoiding surgical complexities evoke great interest in developing injectable biomedical devices. Herein, a versatile approach is reported for engineering injectable and biomimetic nanofiber microspheres (NMs) with tunable sizes, predesigned structures, and desired compositions via gas bubble-mediated coaxial electrospraying. The sizes and structures of NMs are controlled by adjusting processing parameters including air flow rate, applied voltage, distance, and spinneret configuration in the coaxial setup. Importantly, unlike the self-assembly method, this technique can be used to fabricate NMs from any material feasible for electrospinning or other nanofiber fabrication techniques. To demonstrate the versatility, open porous NMs are successfully fabricated that consist of various short nanofibers made of poly(ε-caprolactone), poly(lactic-co-glycolic acid), gelatin, methacrylated gelatin, bioglass, and magneto-responsive polymer composites. Open porous NMs support human neural progenitor cell growth in 3D with a larger number and more neurites than nonporous NMs. Additionally, highly open porous NMs show faster cell infiltration and host tissue integration than nonporous NMs after subcutaneous injection to rats. Such a novel class of NMs holds great potential for many biomedical applications such as tissue filling, cell and drug delivery, and minimally invasive tissue regeneration.

Three-Dimensional Objects Consisting of Hierarchically Assembled Nanofibers with Controlled Alignments for Regenerative Medicine.

Assembling electrospun nanofibers with controlled alignment into three-dimensional (3D), complex, and predesigned shapes has proven to be a difficult task for regenerative medicine. Herein, we report a novel approach inspired by solids of revolution that transforms two-dimensional (2D) nanofiber mats of a controlled thickness into once-inaccessible 3D objects with predesigned shapes. The 3D objects are highly porous, consisting of layers of aligned nanofibers separated by gaps ranging from several micrometers to several millimeters. Upon compression, the objects are able to recover their original shapes. The porous objects can serve as scaffolds, guiding the organization of cells and producing highly ordered 3D tissue constructs. Additionally, subcutaneous implantation in rats demonstrates that the 3D objects enable rapid cell penetration, new blood vessel formation, and collagen matrix deposition. This new class of 3D hierarchical nanofiber architectures offers promising advancements in both in vitro engineering of complex 3D tissue constructs/models or organs and in vivo tissue repair and regeneration.

Tethering peptides onto biomimetic and injectable nanofiber microspheres to direct cellular response.

Biomimetic and injectable nanofiber microspheres (NMs) could be ideal candidate for minimally invasive tissue repair. Herein, we report a facile approach to fabricate peptide-tethered NMs by combining electrospinning, electrospraying, and surface conjugation techniques. The composition and size of NMs can be tuned by varying the processing parameters during the fabrication. Further, bone morphogenic protein-2 (BMP-2) and vascular endothelial growth factor (VEGF) mimicking peptides have been successfully tethered onto poly(ε-caprolactone) (PCL):gelatin:(gelatin-methacryloyl) (GelMA)(1:0.5:0.5) NMs through photocrosslinking of the methacrylic group in GelMA and octenyl alanine (OCTAL) in the modified peptides. The BMP-2-OCTAL peptide-tethered NMs significantly promote osteogenic differentiation of bone marrow-derived stem cells (BMSCs). Moreover, human umbilical vein endothelial cells (HUVECs) seeded on VEGF mimicking peptide QK-OCTAL-tethered NMs significantly up-regulated vascular-specific proteins, leading to microvascularization. The strategy developed in this work holds great potential in developing a biomimetic and injectable carrier to efficiently direct cellular response (Osteogenesis and Angiogenesis) for tissue repair.

Twisting electrospun nanofiber fine strips into functional sutures for sustained co-delivery of gentamicin and silver.

Surgical site infections (SSIs) represent the most common nosocomial infection among surgical patients. In order to prevent SSIs in a sustained manner and lessen side effects, we developed a twisting method for generation of nanofiber-based sutures capable of simultaneous delivery of silver and gentamicin. The prepared sutures are composed of core-sheath nanofibers with gentamicin/pluronic F127 in the core and silver/PCL in the sheath produced by co-axial electrospinning. The diameters of obtained sutures range from ~80 µm to ~1.2 mm. The in vitro release profiles of silver and gentamicin exhibit an initial burst followed by a sustained release over 5 weeks. The co-encapsulated sutures were able to kill bacteria much more effectively than gentamicin or silver alone loaded nanofiber sutures, without showing obvious impact on proliferation and migration of dermal fibroblasts and keratinocytes. The gentamicin and silver co-loaded PCL nanofiber sutures may hold great potential for prevention of SSIs.

Aligned cryogel fibers incorporated 3D printed scaffold effectively facilitates bone regeneration by enhancing cell recruitment and function.

Reconstructing extensive cranial defects represents a persistent clinical challenge. Here, we reported a hybrid three-dimensional (3D) printed scaffold with modification of QK peptide and KP peptide for effectively promoting endogenous cranial bone regeneration. The hybrid 3D printed scaffold consists of vertically aligned cryogel fibers that guide and promote cell penetration into the defect area in the early stages of bone repair. Then, the conjugated QK peptide and KP peptide further regulate the function of the recruited cells to promote vascularization and osteogenic differentiation in the defect area. The regenerated bone volume and surface coverage of the dual peptide-modified hybrid scaffold were significantly higher than the positive control group. In addition, the dual peptide-modified hybrid scaffold demonstrated sustained enhancement of bone regeneration and avoidance of bone resorption compared to the collagen sponge group. We expect that the design of dual peptide-modified hybrid scaffold will provide a promising strategy for bone regeneration.

Natural Polymers - Based Hydrogel Dressings for Wound Healing.

SIGNIFICANCE: Acute wounds such as severe burns and chronic wounds like diabetic ulcers present a significant threat to human health. Wound dressings made from natural polymers offer inherent properties that effectively enhance wound healing outcomes and reduce healing time. RECENT ADVANCES: Numerous innovative hydrogels are being developed and translated to the clinic to successfully treat various wound types. This underscores the substantial potential of hydrogels in the future wound care market. Economically, annual sales of wound care products are projected to reach $15-22 billion by 2024. CRITICAL ISSUES: While chitosan-, cellulose-, and collagen-based hydrogel dressings are currently commercially available, scaling up and manufacturing hydrogels for commercial products remains a challenging process. Additionally, ensuring the sterility and stability of the chemical or biological components comprising the hydrogel are critical considerations. FUTURE DIRECTIONS: In light of the persistent increase in wound fatalities and the resulting economic and social impacts, as well as the importance of educating the public about dietary health and disease, there should be increased investment in new wound care dressings, particularly hydrogels derived from natural products. With numerous researchers dedicated to advancing preclinical hydrogels, the future holds promise for more innovative and more personalized hydrogel wound dressings.

Dual effects of serum urate on stroke risk and prognosis: insights from Mendelian randomization.

Background: To investigate the causal associations of serum urate (SUA) with stroke risk and prognosis using Mendelian randomization (MR) and the potential mediating role of stroke risk factors in the causal pathways. Methods: We used the random-effects inverse variance weighting (IVW) as our primary method. We initially performed two-sample univariable MR (UVMR) to identify the causal associations of SUA (n = 437,354) with any stroke (AS, FinnGen: n = 311,635; MEGASTROKE: n = 446,696), ischemic stroke (IS, FinnGen: n = 212,774; MEGASTROKE: n = 440,328), intracranial hemorrhage (ICH, FinnGen: n = 343,663; ISGC: n = 3,026), functional outcome after ischemic stroke at 90d (n = 4,363), and motor recovery within 24 months after stroke (n = 488), and then multivariable MR (MVMR) to estimate the direct causal effects of SUA on these outcomes, adjusting for potential confounders. Finally, we further conducted a two-step MR to investigate the potential mediating role of body mass index (BMI), systolic blood pressure (SBP), diastolic blood pressure (DBP), and estimated glomerular filtration rate (eGFR) in the identified causal pathways. Results: Genetically predicted elevated SUA levels were significantly associated with increased risk of AS (meta-analysis: OR = 1.09, 95% CI [1.04-1.13], p = 3.69e-05) and IS (meta-analysis: OR = 1.10, 95% CI [1.01-1.19], p = 0.021) and with improved poor functional outcome after ischemic stroke at 90d (OR = 0.81, 95% CI [0.72-0.90], p = 1.79e-04) and motor recovery within 24 months after stroke (OR = 1.42, 95% CI [1.23-1.64], p = 2.15e-06). In MVMR, SBP and DBP significantly attenuated the causal effects of SUA on AS, IS, and functional outcome after ischemic stroke at 90d and motor recovery within 24 months after stroke. Further mediation analyses showed that SBP mediated 52.4 and 34.5% of the effects of SUA on AS and IS, while DBP mediated 28.5 and 23.4% of the causal effects, respectively. Conclusion: This study supports the dual role of genetically predicted SUA in increasing stroke risk, especially ischemic stroke risk, and in improving functional outcome and motor recovery. SBP and DBP are key mediators lying on the causal pathways of SUA with AS and IS.

Semi-supervised iterative adaptive network for low-dose CT sinogram recovery.

Background.Concern has been expressed regarding the risk of carcinogenesis from medical computed tomography (CT) radiation. Lowering radiation in CT without appropriate modifications often leads to severe noise-induced artifacts in the images. The utilization of deep learning (DL) techniques has achieved promising reconstruction performance in low-dose CT (LDCT) imaging. However, most DL-based algorithms require the pre-collection of a large set of image pairs (low-dose/standard-dose) and the training of networks in an end-to-end supervised manner. Meanwhile, securing such a large volume of paired, well-registered training data in clinical practice is challenging. Moreover, these algorithms often overlook the potential to utilize the abundant information in a large collection of LDCT-only images/sinograms.Methods.In this paper, we introduce a semi-supervised iterative adaptive network (SIA-Net) for LDCT imaging, utilizing both labeled and unlabeled sinograms in a cohesive network framework, integrating supervised and unsupervised learning processes. Specifically, the supervised process captures critical features (i.e. noise distribution and tissue characteristics) latent in the paired sinograms, while the unsupervised process effectively learns these features in the unlabeled low-dose sinograms, employing a conventional weighted least-squares model with a regularization term. Furthermore, the SIA-Net method is designed to adaptively transfer the learned feature distribution from the supervised to the unsupervised process, thereby obtaining a high-fidelity sinogram through iterative adaptive learning. Finally, high-quality CT images can be reconstructed from the refined sinogram using the filtered back-projection algorithm.Results.Experimental results on two clinical datasets indicate that the proposed SIA-Net method achieves competitive performance in terms of noise reduction and structure preservation in LDCT imaging, when compared to traditional supervised learning methods.

New dimensions of electrospun nanofiber material designs for biotechnological uses.

Electrospinning technology has garnered wide attention over the past few decades in various biomedical applications including drug delivery, cell therapy, and tissue engineering. This technology can create nanofibers with tunable fiber diameters and functionalities. However, the 2D membrane nature of the nanofibers, as well as the rigidity and low porosity of electrospun fibers, lower their efficacy in tissue repair and regeneration. Recently, new avenues have been explored to resolve the challenges associated with 2D electrospun nanofiber membranes. This review discusses recent trends in creating different electrospun nanofiber microstructures from 2D nanofiber membranes by using various post-processing methods, as well as their biotechnological applications.

Hierarchically Assembled Nanofiber Scaffolds with Dual Growth Factor Gradients Promote Skin Wound Healing Through Rapid Cell Recruitment.

To address current challenges in effectively treating large skin defects caused by trauma in clinical medicine, the fabrication, and evaluation of a novel radially aligned nanofiber scaffold (RAS) with dual growth factor gradients is presented. These aligned nanofibers and the scaffold's spatial design provide many all-around "highways" for cell migration from the edge of the wound to the center area. Besides, the chemotaxis induced by two growth factor gradients further promotes cell migration. Incorporating epidermal growth factor (EGF) aids in the proliferation and differentiation of basal layer cells in the epidermis, augmenting the scaffold's ability to promote epidermal regeneration. Concurrently, the scaffold-bound vascular endothelial growth factor (VEGF) recruits vascular endothelial cells at the wound's center, resulting in angiogenesis and improving blood supply and nutrient delivery, which is critical for granulation tissue regeneration. The RAS+EGF+VEGF group demonstrates superior performance in wound immune regulation, wound closure, hair follicle regeneration, and ECM deposition and remodeling compared to other groups. This study highlights the promising potential of hierarchically assembled nanofiber scaffolds with dual growth factor gradients for wound repair and tissue regeneration applications.

Orthogonally woven 3D nanofiber scaffolds promote rapid soft tissue regeneration by enhancing bidirectional cell migration.

Repairing large-area soft tissue defects caused by traumas is a major surgical challenge. Developing multifunctional scaffolds with suitable scalability and favorable cellular response is crucial for soft tissue regeneration. In this study, we developed an orthogonally woven three-dimensional (3D) nanofiber scaffold combining electrospinning, weaving, and modified gas-foaming technology. The developed orthogonally woven 3D nanofiber scaffold had a modular design and controlled fiber alignment. In vitro, the orthogonally woven 3D nanofiber scaffold exhibited adjustable mechanical properties, good cell compatibility, and easy drug loading. In vivo, for one thing, the implantation of an orthogonally woven 3D nanofiber scaffold in a full abdominal wall defect model demonstrated that extensive granulation tissue formation with enough mechanical strength could promote recovery of abdominal wall defects while reducing intestinal adhesion. Another result of diabetic wound repair experiments suggested that orthogonally woven 3D nanofiber scaffolds had a higher wound healing ratio, granulation tissue formation, collagen deposition, and re-epithelialization. Taken together, this novel orthogonally woven 3D nanofiber scaffold may provide a promising and effective approach for optimal soft tissue regeneration.

Carbonized Cellulose Aerogel Derived from Waste Pomelo Peel for Rapid Hemostasis of Trauma-Induced Bleeding.

Uncontrollable massive bleeding caused by trauma will cause the patient to lose a large amount of blood and drop body temperature quickly, resulting in hemorrhagic shock. This study aims to develop a hemostatic product for hemorrhage management. In this study, waste pomelo peel as raw material is chosen. It underwent processes of carbonization, purification, and freeze-drying. The obtained carbonized pomelo peel (CPP) is hydrophilic and exhibits a porous structure (nearly 80% porosity). The water/blood absorption ratio is significantly faster than the commercial Gelfoam and has a similar water/blood absorption capacity. In addition, the CPP showed a water-triggered shape-recoverable ability. Moreover, the CPP shows ideal cytocompatibility and blood compatibility in vitro and favorable tissue compatibility after long terms of subcutaneous implantation. Furthermore, CPP can absorb red blood cells and fibrin. It also can absorb platelets and activate platelets, and it is capable of achieving rapid hemostasis on the rat tail amputation and hepatectomized hemorrhage model. In addition, the CPP not only can quickly stop bleeding in the rat liver-perforation and rabbit heart uncontrolled hemorrhage models, but also promotes rat liver and rabbit heart tissue regeneration in situ. These results suggest the CPP has shown great potential for managing uncontrolled hemorrhage.

Anti-Inflammatory Peptide-Conjugated Silk Fibroin/Cryogel Hybrid Dual Fiber Scaffold with Hierarchical Structure Promotes Healing of Chronic Wounds.

Chronic wounds resulting from diabetes, pressure, radiation therapy, and other factors continue to pose significant challenges in wound healing. To address this, this study introduces a novel hybrid fibroin fibrous scaffold (FFS) comprising randomly arranged fibroin fibers and vertically aligned cryogel fibers (CFs). The fibroin scaffold is efficiently degummed at room temperature and simultaneously formed a porous structure. The aligned CFs are produced via directional freeze-drying, achieved by controlling solution concentration and freezing polymerization temperature. The incorporation of aligned CFs into the expanded fibroin fiber scaffold leads to enhanced cell infiltration both in vitro and in vivo, further elevating the hybrid scaffold's tissue compatibility. The anti-inflammatory peptide 1 (AP-1) is also conjugated to the hybrid fibrous scaffold, effectively transforming the inflammatory status of chronic wounds from pro-inflammatory to pro-reparative. Consequently, the FFS-AP1+CF group demonstrates superior granulation tissue formation, angiogenesis, collagen deposition, and re-epithelialization during the proliferative phase compared to the commercial product PELNAC. Moreover, the FFS-AP1+CF group displays epidermis thickness, number of regenerated hair follicles, and collagen density closer to normal skin tissue. These findings highlight the potential of random fibroin fibers/aligned CFs hybrid fibrous scaffold as a promising approach for skin tissue filling and tissue regeneration.

Activin B promotes initiation and development of hair follicles in mice.

Activin B has been reported to promote the regeneration of hair follicles during wound healing. However, its role in the development and life cycle of hair follicles has not been elucidated. In our study, the effect of activin B on mouse hair follicles of cultured and neonatal mouse skin was investigated. In these models, PBS or activin B (5, 10 or 50 ng/ml) was applied, and hair follicle development was monitored. Hair follicle initiation and development was examined using hematoxylin and eosin staining, alkaline phosphatase activity staining, Oil Red O+ staining, and the detection of TdT-mediated dUTP-biotin nick end-labeling cell apoptosis. Activin B was found to efficiently induce the initiation of hair follicles in the skin of both cultured and neonatal mice and to promote the development of hair follicles in neonatal mouse skin. Moreover, activin-B-treated hair follicles were observed to enter the anagen stage from the telogen stage and to remain in the anagen stage. These results demonstrate that activin B promotes the initiation and development of hair follicles in mice.

Weakly acidic microenvironment of the wound bed boosting the efficacy of acidic fibroblast growth factor to promote skin regeneration.

The pH value within the wound microenvironment influences indirectly and directly all biochemical reactions taking place in the process of skin wound healing. Currently, it is generally believed that a low pH value, such as it is found on normal skin, is favorable for wound regeneration, while some investigations have shown that in fact alkaline microenvironments are required for some healing processes. The role of growth factors in promoting wound healing requires a specific microenvironment. In wound microenvironments of different pH, growth factors with different isoelectric points may have different effects. To explore whether the application of FGF with different isoelectric points in wounds with different pH values interferes with the healing process to different degrees, GelMA hydrogels with different pH values were prepared to maintain the wounds microenvironment with the same pH values, in which aFGF and bFGF were loaded as well. The results show that GelMA hydrogels of different pH values maintained the same pH of the wound microenvironment sustainably on the 4th day. Moreover, aFGF and bFGF promoted skin wound healing to varying degrees in different pH wound microenvironments. In particular, aFGF significantly promoted wound re-epithelialization in a weak acidic microenvironment, while bFGF promoted collagen synthesis and deposition in the early stage of weak acid wounds. In addition, aFGF plays a superior role in inhibiting inflammation in weak acidic wounds.