Biodegradation of silk biomaterials

Effect of degumming condition on the solution properties and electrospinnablity of regenerated silk solution

The application of silk on tissue engineering scaffolds has been studied intensively because silk has an electrospinning technique using a good blood compatibility, excellent cytocompatibility and biodegradability. Silk consists of two polymers, fibroin and sericin. In spite of importance of sericin, most studies were focused on the fibroin only and the effect of residual sericin on the electrospinning performance of silk has not been considered. In this study, regenerated silk with different residual sericin contents was prepared by controlling the degumming conditions. The effects of the degumming conditions on the solution properties and electrospinning performance of silk were examined. The fast protein liquid chromatography (FPLC) measurements confirmed that the molecular weight of the regenerated silk decreased slightly with increasing residual sericin content. More molecular aggregation of silk occurred with increasing sericin content, resulting in an increase in the solution turbidity of formic acid. All silk formic acid solutions exhibited almost Newtonian fluid behavior and the viscosity increased with increasing sericin content. Interestingly, the dope solution viscosity of silk increased remarkably at sericin contents <1% (or degumming ratio >25%) leading to significant improvements in electrospinnability and an increase in the fiber diameter of the silk web.

High-throughput capillary electrophoresis-mass spectrometry: from analysis of amino acids to analysis of protein complexes

Recent advances in capillary electrophoresis-mass spectrometry (CE-MS) interfacing using porous tip is leading to commercialization of CE-MS with a sheathless interface for the first time. The new sheathless interface in conjunction with CE capillary coatings using self-coating background electrolytes (BGE) has significantly simplified CE-MS analysis of complex mixtures. CE-MS, with its high separation efficiency, compound identification capability, and ability to rapidly separate compounds with a wide range of mass and charge while consuming only nanoliters of samples, has become a valuable analytical technique for the analysis of complex biological mixtures. These advances have allowed a single capillary to analyze a range of compounds including amino acids, their D/L enantiomers, protein digests, intact proteins, and protein complexes. With these capabilities, CE-MS is poised to become the multipurpose tool of separation scientists. More recently, an eight-capillary CE in conjunction with an 8-inlet mass spectrometry has allowed 8 CE-MS analyses to be performed concurrently, significantly increasing throughput.

Preparation and in vivo degradation of controlled biodegradability of electrospun silk fibroin nanofiber mats

Controlled biodegradability of biomaterials is very important because different functionality and durability are required for various purposes and for specific tissues and organs. From this point of view, silk-based biomaterials have poor usability because of uncontrollable degradability, even though silk fibroin (SF) is highly biocompatible and a number of studies on silk biomaterials have been published to date. In this study, we prepared SF nanofiber mats that were recrystallized in different ways. These mats were fabricated by electrospinning with ethanol/propanol mixtures of various blend ratios, and their biodegradabilities in vitro and in vivo were evaluated using rats. As a result, we can suggest an established method to modulate the degradability of SF nanofibrous materials based on long-term (12 months) observations. In particular, we elucidated how the SF nanofibers are degraded and incorporated with surrounding tissue by observation of fluorescein isothiocyanate-labeled SF nanofiber in vivo. Our findings suggest a method for controlling the degradation rate of SF for medical applications.

Properties and biocompatibility of chitosan and silk fibroin blend films for application in skin tissue engineering

Chitosan/silk fibroin (CS/SF) blend films were prepared and evaluated for feasibility of using the films as biomaterial for skin tissue engineering application. Fourier transform infrared spectroscopy and differential scanning calorimetry analysis indicated chemical interaction between chitosan and fibroin. Chitosan enhanced β-sheet conformation of fibroin and resulted in shifting of thermal degradation of the films. Flexibility, swelling index, and enzyme degradation were also increased by the chitosan content of the blend films. Biocompatibility of the blend films was determined by cultivation with fibroblast cells. All films showed no cytotoxicity by XTT assay. Fibroblast cells spread on CS/SF films via dendritic extensions, and cell-cell interactions were noted. Cell proliferation on CS/SF films was also demonstrated, and their phenotype was examined by the expression of collagen type I gene. These results showed possibility of using the CS/SF films as a supporting material for further study on skin tissue engineering.

Blood compatibility of polymers derived from natural materials

Several polymers derived from natural materials are effective for tissue engineering or drug delivery applications, due to specific properties, such as biocompatibility, biodegradability, and structural activity. Their blood compatibility needs to be carefully evaluated to avoid thrombosis and other material-related adverse events in the hematic environment. We compared the surface properties and blood compatibility of protein and polysaccharide polymers, including fibroin, gelatin, and chitosan. Both fibroin and chitosan showed good hemocompatibility, with low platelet adhesion and spreading. Chitosan induced strong interactions with plasma proteins, especially with albumin. It was hypothesized that surface passivation by albumin inhibited the adsorption of other procoagulant and proadhesive proteins on chitosan and fibroin films, which limited platelet spreading. However, the significant and rapid polymer swelling encouraged protein entrapment within the soft, gelatin films, inducing higher platelet adhesion and activation. Thrombin generation assay confirmed the higher blood compatibility of chitosan and fibroin with regard to clotting.

Natural Products: A Minefield of Biomaterials

The development of natural biomaterials is not regarded as a new area of science, but has existed for centuries. The use of natural products as a biomaterial is currently undergoing a renaissance in the biomedical field. The major limitations of natural biomaterials are due to the immunogenic response that can occur following implantation and the lot-to-lot variability in molecular structure associated with animal sourcing. The chemical stability and biocompatibility of natural products in the body greatly accounts for their utilization in recent times. The paper succinctly defines biomaterials in terms of natural products and also that natural products as materials in biomedical fields are considerably versatile and promising. The various types of natural products and forms of biomaterials are highlighted. Three main areas of applications of natural products as materials in medicine are described, namely, wound management products, drug delivery systems, and tissue engineering. This paper presents a brief history of natural products as biomaterials, various types of natural biomaterials, properties, demand and economic importance, and the area of application of natural biomaterials in recent times.

Growth factor delivery systems and repair strategies for damaged peripheral nerves

Artificial nerve conduits (NCs) are, in certain cases, instrumental for repairing damaged peripheral nerves, although therapeutic efficacy remains often suboptimal. Considerable efforts have been made to improve the therapeutic performance of NCs. This article reviews recent developments in NC-technology for peripheral nerve regeneration with a main focus on growth factors delivery systems and repair strategies. Commonly used materials for NC fabrication include collagen, silk fibroin, and biodegradable aliphatic polyesters. The basic NC structure, i.e., a hollow tube, can be manufactured by diverse methods: spinning mandrel technology, sheet rolling, injection-molding, freeze-drying, and electro-spinning. Polymeric and cellular delivery systems for growth factors can be integrated in the NC wall or within luminal structures such as gels, fibers, or biological materials providing binding affinity for the bioactive compounds. NCs with sustained growth factor delivery generally improve significantly the axonal outgrowth in nerve defect models, although restoration of sensory and motor functions remains inferior to that achieved with autologous nerve grafts. To improve therapeutic outcomes, further biofunctionalization of NCs will be needed, i.e., adjusting degradation kinetics of NC scaffolding to be compatible with axonal regeneration; delivering multiple growth factors at individually optimized kinetics; incorporating modality specific glial cells and furnishing NCs with guiding nanostructures.

Fabrication of novel biofibers by coating silk fibroin with chitosan impregnated with silver nanoparticles

Nanoparticle based agents often applied as coatings on biomaterials have shown promise in delivering the improved sterility against variety of microbes. In the present study, silk fibers (SF) were coated with chitosan impregnated with silver nanoparticles (Ag-C-SF). These Ag-C-SF fibers were characterized using scanning electron microscopy (SEM) with energy dispersive X-ray analysis, atomic force microscopy (AFM), Infra Red spectroscopy, Thermogravimetric Analysis and Microbiological assay techniques. AFM studies have confirmed the nano sized silver particles in chitosan solution; SEM pictures have exhibited the coating of chitosan along with silver nanoparticles on the silk fibroin. The modified fibers have also shown anti-microbial activity and improved thermal stability. The Ag-C-SF fibers may be explored as wound dressing and tendon reconstruction material in future.

A novel marine silk

The discovery of a novel silk production system in a marine amphipod provides insights into the wider potential of natural silks. The tube-building corophioid amphipod Crassicorophium bonellii produces from its legs fibrous, adhesive underwater threads that combine barnacle cement biology with aspects of spider silk thread extrusion spinning. We characterised the filamentous silk as a mixture of mucopolysaccharides and protein deriving from glands representing two distinct types. The carbohydrate and protein silk secretion is dominated by complex β-sheet structures and a high content of charged amino acid residues. The filamentous secretion product exits the gland through a pore near the tip of the secretory leg after having moved through a duct, which subdivides into several small ductules all terminating in a spindle-shaped chamber. This chamber communicates with the exterior and may be considered the silk reservoir and processing/mixing space, in which the silk is mechanically and potentially chemically altered and becomes fibrous. We assert that further study of this probably independently evolved, marine arthropod silk processing and secretion system can provide not only important insights into the more complex arachnid and insect silks but also into crustacean adhesion cements.

Dating silk by capillary electrophoresis mass spectrometry

A new capillary electrophoresis mass spectrometry (CE-MS) technique is introduced for age estimation of silk textiles based on amino acid racemization rates. With an L to D conversion half-life of ~2500 years for silk (B. mori) aspartic acid, the technique is capable of dating silk textiles ranging in age from several decades to a few-thousand-years-old. Analysis required only ~100 μg or less of silk fiber. Except for a 2 h acid hydrolysis at 110 °C, no other sample preparation is required. The CE-MS analysis takes ~20 min, consumes only nanoliters of the amino acid mixture, and provides both amino acid composition profiles and D/L ratios for ~11 amino acids.

Artificial skin--culturing of different skin cell lines for generating an artificial skin substitute on cross-weaved spider silk fibres

Background

In the field of Plastic Reconstructive Surgery the development of new innovative matrices for skin repair is in urgent need. The ideal biomaterial should promote attachment, proliferation and growth of cells. Additionally, it should degrade in an appropriate time period without releasing harmful substances, but not exert a pathological immune response. Spider dragline silk from Nephila spp meets these demands to a large extent.

Methodology/Principal Findings

Native spider dragline silk, harvested directly out of Nephila spp spiders, was woven on steel frames. Constructs were sterilized and seeded with fibroblasts. After two weeks of cultivating single fibroblasts, keratinocytes were added to generate a bilayered skin model, consisting of dermis and epidermis equivalents. For the next three weeks, constructs in co-culture were lifted on an originally designed setup for air/liquid interface cultivation. After the culturing period, constructs were embedded in paraffin with an especially developed program for spidersilk to avoid supercontraction. Paraffin cross- sections were stained in Haematoxylin & Eosin (H&E) for microscopic analyses.

Conclusion/Significance

Native spider dragline silk woven on steel frames provides a suitable matrix for 3 dimensional skin cell culturing. Both fibroblasts and keratinocytes cell lines adhere to the spider silk fibres and proliferate. Guided by the spider silk fibres, they sprout into the meshes and reach confluence in at most one week. A well-balanced, bilayered cocultivation in two continuously separated strata can be achieved by serum reduction, changing the medium conditions and the cultivation period at the air/liquid interphase. Therefore spider silk appears to be a promising biomaterial for the enhancement of skin regeneration.

Safety evaluation of silk protein film (a novel wound healing agent) in terms of acute dermal toxicity, acute dermal irritation and skin sensitization

Acute dermal toxicity study was conducted in rats. The parameters studied were body weight, serum biochemistry and gross pathology. The animals were also observed for clinical signs and mortality after the application of test film. The dermal irritation potential of silk protein film was examined using Draize test. In the initial test, three test patches were applied sequentially for 3 min, 1 and 4 hours, respectively, and skin reaction was graded. The irritant or negative response was confirmed using two additional animals, each with one patch, for an exposure period of 4 hours. The responses were scored at 1, 24, 48 and 72 hours after the patch removal. Skin sensitization study was conducted according to Buehler test in guinea pigs, in which on day 0, 7 and 14, the animals were exposed to test material for 6 hours (Induction phase) and on day 28, the animals were exposed for a period of 24 hours (Challenge phase). The skin was observed and recorded at 24 and 48 hours after the patch removal. In acute dermal toxicity study, the rats dermally treated with silk film did not show any abnormal clinical signs and the body weight, biochemical parameters and gross pathological observations were not significantly different from the control group. In acute dermal irritation study, the treated rabbits showed no signs of erythema, edema and eschar, and the scoring was given as “0” for all time points of observations according to Draize scoring system. In skin sensitization study, there were no skin reactions 24 and 48 hours after the removal of challenge patch, which was scored “0” based on Magnusson/Kligman grading scale.

Effect of processing on silk-based biomaterials: reproducibility and biocompatibility

Silk fibroin has been successfully used as a biomaterial for tissue regeneration. To prepare silk fibroin biomaterials for human implantation a series of processing steps are required to purify the protein. Degumming to remove inflammatory sericin is a crucial step related to biocompatibility and variability in the material. Detailed characterization of silk fibroin degumming is reported. The degumming conditions significantly affected cell viability on the silk fibroin material and the ability to form three-dimensional porous scaffolds from the silk fibroin, but did not affect macrophage activation or β-sheet content in the materials formed. Methods are also provided to determine the content of residual sericin in silk fibroin solutions and to assess changes in silk fibroin molecular weight. Amino acid composition analysis was used to detect sericin residuals in silk solutions with a detection limit between 1.0 and 10% wt/wt, while fluorescence spectroscopy was used to reproducibly distinguish between silk samples with different molecular weights. Both methods are simple and require minimal sample volume, providing useful quality control tools for silk fibroin preparation processes.

Human dental pulp progenitor cell behavior on aqueous and hexafluoroisopropanol based silk scaffolds

Silk scaffolds have been successfully used for a variety of tissue engineering applications due to their biocompatibility, diverse physical characteristics, and ability to support cell attachment and proliferation. Our prior characterization of 4-day postnatal rat tooth bud cells grown on hexafluoro-2-propanol (HFIP) silk scaffolds showed that the silk scaffolds not only supported osteodentin formation, but also guided the size and shape of the formed osteodentin. In this study, interactions between human dental pulp cells and HFIP and aqueous based silk scaffolds were studied under both in vitro and in vivo conditions. Silk scaffold porosity and incorporation of RGD and DMP peptides were examined. We found that the degradation of aqueous based silk is much faster than HFIP based silk scaffolds. Also, HFIP based silk scaffolds supported the soft dental pulp formation better than the aqueous based silk scaffolds. No distinct hard tissue regeneration was found in any of the implants, with or without additional cells. We conclude that alternative silk scaffold materials, and hDSC pre-seeding cell treatments or sorting and enrichment methods, need to be considered for successful dental hard tissue regeneration.

Antimicrobial functionalized genetically engineered spider silk

Genetically engineered fusion proteins offer potential as multifunctional biomaterials for medical use. Fusion or chimeric proteins can be formed using recombinant DNA technology by combining nucleotide sequences encoding different peptides or proteins that are otherwise not found together in nature. In the present study, three new fusion proteins were designed, cloned and expressed and assessed for function, by combining the consensus sequence of dragline spider silk with three different antimicrobial peptides. The human antimicrobial peptides human neutrophil defensin 2 (HNP-2), human neutrophil defensins 4 (HNP-4) and hepcidin were fused to spider silk through bioengineering. The spider silk domain maintained its self-assembly features, a key aspect of these new polymeric protein biomaterials, allowing the formation of β-sheets to lock in structures via physical interactions without the need for chemical cross-linking. These new functional silk proteins were assessed for antimicrobial activity against Gram - Escherichia coli and Gram + Staphylococcus aureus and microbicidal activity was demonstrated. Dynamic light scattering was used to assess protein aggregation to clarify the antimicrobial patterns observed. Attenuated-total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and circular dichroism (CD) were used to assess the secondary structure of the new recombinant proteins. In vitro cell studies with a human osteosarcoma cell line (SaOs-2) demonstrated the compatibility of these new proteins with mammalian cells.

Biopolymer-based hydrogels as scaffolds for tissue engineering applications: a review

Hydrogels are physically or chemically cross-linked polymer networks that are able to absorb large amounts of water. They can be classified into different categories depending on various parameters including the preparation method, the charge, and the mechanical and structural characteristics. The present review aims to give an overview of hydrogels based on natural polymers and their various applications in the field of tissue engineering. In a first part, relevant parameters describing different hydrogel properties and the strategies applied to finetune these characteristics will be described. In a second part, an important class of biopolymers that possess thermosensitive properties (UCST or LCST behavior) will be discussed. Another part of the review will be devoted to the application of cryogels. Finally, the most relevant biopolymer-based hydrogel systems, the different methods of preparation, as well as an in depth overview of the applications in the field of tissue engineering will be given.

Modular elastic patches: mechanical and biological effects

A modular approach to engineering cross-linked elastic biomaterials is presented for fine-tuning of material mechanical and biological properties. The three components, soluble elastin, hyaluronic acid, and silk fibroin, contribute with different features to the overall properties of the final material system. The elastic biomaterial is chemically cross-linked via interaction between primary amine groups naturally present on the two proteins, silk and elastin, or chemically introduced on hyaluronan and N-succinimide functionalities of the cross-linker. The materials obtained by cross-linking the three components in different ratios have Young's moduli ranging from ∼ 100 to 230 kPa, strain to failure between ∼ 15-40% and ultimate tensile strengths of ∼ 30 kPa. The biological effects and enzymatic degradation rates of the different composites are also different based on material composition. These findings further underline the strength of modular, multicomponent systems in creating a range of biomaterials, targeted tissue engineering, and regenerative medicine applications, with application-tailored mechanical and biological properties.

Incorporation of proteinase inhibitors into silk-based delivery devices for enhanced control of degradation and drug release

Controlling the rate of silk degradation is critical to its potential use in biomedical applications, including drug delivery and tissue engineering. The effect of protease concentration on accelerating degradation, and the use of ethylenediamine tetraacetic acid (EDTA) on reducing rates of degradation and on drug release from silk-based drug carriers was studied. Increased rates of proteolysis resulted in increased dye release from silk carriers, while EDTA release from the silk carriers inhibited proteolysis. The sustained release of EDTA from silk carriers in combination with the release of the small molecule anti-convulsant adenosine was investigated in vitro. This combination of factors resulted in delayed release of adenosine by inhibiting proteolytic activity. These results introduce a promising strategy to control drug delivery through the regulation of silk degradation rate, achieved via manipulation of local proteolytic activity. This ability to modulate enzyme function could be applicable to a range of silk biomaterial formats as well as other biodegradable polymers where enzymatic functions control biomaterial degradation and drug release rates.

Quantifying osteogenic cell degradation of silk biomaterials

The degradation of silk protein films by human mesenchymal stem cells (hMSCs), osteoblasts and osteoclasts, cells involved in osteogenic functions in normal and diseased bone, was assessed in vitro. The involvement of specific matrix metalloproteinases (MMPs) and integrin signaling in the degradation process was determined. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to quantitatively compare degradation by the different cell types using surface patterned silk films. Osteoblasts and osteoclasts demonstrated significant degradation of the silk films in vitro in comparison to the hMSCs and the film controls without cells. The osteoclasts degraded the silk films the most and also generated the highest level of MMPs 1 and 2. The osteoblasts upregulated integrins α5 and β1, while the osteoclasts upregulated integrins α2 and β1. There was significant contrast in responses on the silk matrices between osteogenic cells versus undifferentiated hMSCs to illustrate in vitro the role of cell type on matrix remodeling. These are important issues in matching biomaterial matrix features and studies in vitro to remodeling in vivo, in both normal and disease tissue systems. Cell populations and niche factors impact tissue regeneration, wound healing, physiological state, and the ability to better understand the role of different cell types is critical to overall regenerative outcomes.

A transparent artificial dura mater made of silk fibroin as an inhibitor of inflammation in craniotomized rats

OBJECT

To improve the safety of dura repair in neurosurgical procedures, a new dural material derived from silk fibroin was evaluated in a rat model with a dura mater injury.

METHODS

The authors prepared new, transparent, artificial dura mater material using silk fibroin from the silkworm, Bombyx mori. The cytotoxic and antiinflammatory effects of the artificial dura mater were examined in vitro and in vivo by histological examination, western blotting, and reverse transcription polymerase chain reaction analyses.

RESULTS

The novel artificial dura mater was not cytotoxic. However, it efficiently reduced cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase expression as well as the expression of the proinflammatory cytokines IL-1β, IL-6, and tumor necrosis factor-α. Cerebrospinal fluid leakage did not occur after repair of the brain of craniotomized rats with the artificial dura mater material.

CONCLUSIONS

The new artificial dura mater described in this study appears to be safe for application in neurosurgical procedures and can efficiently inhibit inflammation without side effects or CSF leakage. Although the long-term effects of this artificial dura mater material need to be validated in larger animals, the results from this study indicate that it is suitable for application in neurosurgery.

Compliant electrospun silk fibroin tubes for small vessel bypass grafting

Processing silk fibroin (SF) by electrospinning offers a very attractive opportunity for producing three-dimensional nanofibrillar matrices in tubular form, which may be useful for a biomimetic approach to small calibre vessel regeneration. Bypass grafting of small calibre vessels, with a diameter less than 6mm, is performed mainly using autografts, like the saphenous vein or internal mammary artery. At present no polymeric grafts made of SF are commercially available, mainly due to inadequate properties (low compliance and lack of endothelium cells). The aim of this work was to electrospin SF into tubular structures (Ø=6mm) for small calibre vessel grafting, characterize the morphological, chemico-physical and mechanical properties of the electrospun SF structures and to validate their potential to interact with cells. The morphological properties of electrospun SF nanofibres were investigated by scanning electron microscopy. Chemico-physical analyses revealed an increase in the crystallinity of the structure of SF nanofibres on methanol treatment. Mechanical tests, i.e. compliance and burst pressure measurements, of the electrospun SF tubes showed that the inner pressure to radial deformation ratio was linear for elongation up to 15% and pressure up to 400 mm Hg. The mean compliance value between 80 and 120 mm Hg was higher than the values reported for both Goretex(R) and Dacron(R) grafts and for bovine heterografts, but still slightly lower than those of saphenous and umbilical vein, which nowadays represent the gold standard for the replacement of small calibre arteries. The electrospun tubes resisted up to 575+/-17 mmHg, which is more than four times the upper physiological pressure of 120 mmHg and more than twice the pathological upper pressures (range 180-220 mmHg). The in vitro tests showed a good cytocompatibility of the electrospun SF tubes. Therefore, the electrospun SF tubes developed within this work represent a suitable candidate for small calibre blood vessel replacement.

Restoration of peri-implant defects in immediate implant installations by Choukroun platelet-rich fibrin and silk fibroin powder combination graft

OBJECTIVE

The objective of this study was to determine the capability of silk fibroin powder as a biomaterial template for the restoration of peri-implant defects when mixed with Choukroun platelet-rich fibrin (PRF) in vivo.

STUDY DESIGN

Ten New Zealand white rabbits were used for this study. Using a trephine bur (diameter 7.0 mm), 2 monocortical defects were prepared. Subsequently, 2 dental implants were installed into the tibia (diameter 3.0 mm, length 10.0 mm). In the experimental group, the peri-implant defect was filled with a combination graft of silk fibroin powder and Choukroun PRF. The control was left in an unfilled state. The animals were killed at 8 weeks. Subsequently, a removal torque test and a histomorphometric analysis were done.

RESULTS

The removal torque for the experimental group was 30.34 +/- 5.06 N.cm, whereas it was 21.86 +/- 3.39 N.cm for the control. The difference between the 2 groups was statistically significant (P = .010). Mean new bone formation was 51.93 +/- 27.90% in the experimental group and 11.67 +/- 15.12% in the control (P = .003). Mean bone-to-implant contact was 43.07 +/- 21.96% in the experimental group and 15.37 +/- 23.84% in the control (P = .002).

CONCLUSION

A peri-implant defect can be successfully repaired by the application of Choukroun PRF and silk fibroin powder.

A combination graft of low-molecular-weight silk fibroin with Choukroun platelet-rich fibrin for rabbit calvarial defect

OBJECTIVE

The objective of this study was to determine the capabilities of silk fibroin as a biomaterial template for bone formation when mixed with Choukroun platelet-rich fibrin (PRF) in vivo.

STUDY DESIGN

Ten New Zealand white rabbits were used for this study and bilateral round shaped defects were formed in the parietal bone (diameter 9.0 mm). The silk fibroin was digested by acid and made into powder (molecular weight <1.0 kDa). The right side (experimental group) received the silk fibroin plus platelet-rich fibroin and the left side (control group) did not receive a graft. Animals were killed at 6 weeks and 12 weeks. The specimens were examined by microscopic computerized tomography (micro-CT). Subsequently, they underwent decalcification and were stained for histologic analysis.

RESULTS

There was no significant difference between groups at 6 weeks after operation. In the micro-CT results, however, tissue mineral content in the experimental group at 12 weeks after operation was 132.09 +/- 4.41 and that in the control group was 126.42 +/- 6.62 (P = .011). Tissue mineral density in the experimental group was 2,088.88 +/- 648.34, and that in the control group was 2,029.72 +/- 668.22 (P = .013). The results of the histomorphometric analysis were in accordance with the micro-CT results. The total new bone was 49.86 +/- 7.49% in the control group at 12 weeks after the operation and 59.83 +/- 10.92% in the experimental group (P = .021).

CONCLUSION

A combined application of Choukroun PRF with acid-digested silk fibroin showed more rapid bone healing than unfilled control.