Immobilization of laminin peptide in molecularly aligned chitosan by covalent bonding

We developed a new biomaterial effective for nerve regeneration consisting of molecularly aligned chitosan with laminin peptides bonded covalently. Molecularly aligned chitosan was prepared from crab (Macrocheira kaempferi) tendons by ethanol treatment and 4 wt%-NaOH aqueous solutions to remove proteins and calcium phosphate, followed by deacetyl treatment using a 50 wt%-NaOH aqueous solution at 100 degrees C. Molecularly aligned tendon chitosan was chemically thiolated by reacting 4-thiobutyrolactone with the chitosan amino group. The introduction of thiol groups and their distribution to tendon chitosan and chitosan cast film were confirmed using ATR FT-IR, (1)H-NMR, and EDS. The 1.24 micromol/g of thiol groups introduced on the surface of tendon chitosan and the chitosan cast film was confirmed using ultraviolet (UV) spectra. Thiol groups of cysteine located at the end of synthetic laminin peptides were then reacted chemically with thiolated chitosan to form chitosan-S-S-laminin peptide. YIGSR estimated at 0.92 micromol/g and IKVAV estimated at 0.28 micromol/g on thiolated tendon chitosan were confirmed using UV spectra. YIGSR was estimated at 0.85 micromol/g and IKVAV was estimated at 0.34 micromol/g on the thiolated chitosan cast film.     

Calcium-deficient hydroxyapatite-PLGA composites: mechanical and microstructural investigation

The microstructural and mechanical properties of composites composed of calcium deficient hydroxyapatite (CDHAp) and poly(lactide-co-glycolide) (PLGA) have been investigated. The composites were formed by hydrolysis of alpha-tricalcium phosphate (alpha-TCP) to CDHAp in pressed precomposite compacts of alpha-TCP-PLGA-NaCl. The differences in hydrolysis of alpha-TCP-PLGA-NaCl for two compositions of 80:10:10 wt % and 60:20:20 wt %. were monitored by isothermal calorimetry and X-ray diffraction. The microstructural evolution and variance in final composite microstructure after hydrolysis at 37 degrees C, 45 degrees C, and 56 degrees C were examined by scanning electron microscopy. HAp-PLGA composite formed from the alpha-TCP-PLGA-NaCl (80:10:10) precomposites at 37 degrees C developed a tensile strength of 13.3 +/- 0.9 MPa, a flexural strength of 24.8 +/- 1.7 MPa, and Young's modulus of 2.8 +/- 0.3 GPa. These values were 12.00 +/- 0.2 MPa, 36.1 +/- 2.1 MPa, and 5.5 +/- 0.8 GPa for the precomposite composition 60:20:20. All these mechanical properties showed a variation with hydrolysis temperature and composition. The differences in mechanical properties were related to the final microstructures of the composites, which are governed by the morphological changes in the polymer structure at its glass transition temperature and the extent of cement-type formation of CDHAp by hydrolysis of alpha-TCP.     

The chitosan prepared from crab tendons: II. The chitosan/apatite composites and their application to nerve regeneration

The chitosan tubes derived from crab tendons form a hollow tube structure, which is useful for nerve regeneration. However, in order to use the chitosan tubes effectively for nerve regeneration, there remain two problems to be solved. First, the mechanical strength of the tubes is quite high along the longitudinal axis, but is somewhat low for a pressure from side. Second, the chitosan tube walls swell to reduce the inner space of the tubes in vivo. These two problems limit the clinical use of the chitosan tubes. In this study, to solve the problems, apatite was made to react with the chitosan tubes to enhance the mechanical strength of the tube walls. Transmission electron microscopy showed that apatite crystals were formed in the walls of the chitosan tubes. The c-axis of the crystals aligned well in parallel with chitosan molecules. These results indicate that the apatite crystals grow in the tubes starting from the nucleation sites of the chitosan molecules, probably by forming complexes with amino groups of chitosan and calcium ions. Further, the tubes were thermally annealed at 120 degrees C to prevent from swelling, and simultaneously formed into a triangular shape to enhance the stabilization of the tube structure. By these treatments, the hollow tubes could keep their shape even in vivo after implantation. Animal tests using SD rats further showed that the chitosan tubes effectively induced the regeneration of nerve tissue, and were gradually degraded and absorbed in vivo.     

Mechano-morphological studies of aligned nanofibrous scaffolds of polycaprolactone fabricated by electrospinning

Mechanical and morphological studies of aligned nanofibrous meshes of poly(epsilon-caprolactone) (PCL) fabricated by electrospinning at different collector rotation speeds (0, 3000 and 6000 rpm) for application as bone tissue scaffolds are reported. SEM, XRD and DSC analyses were used for the morphological characterization of the nanofibers. Scaffolds have a nanofibrous morphology with fibers (majority) having a diameter in the range of 550-350 nm (depending on fiber uptake rates) and an interconnected pore structure. With the increase of collector rotation speed, the nanofibers become more aligned and oriented perpendicular to the axis of rotation. Deposition of fibers at higher fiber collection speeds has a profound effect on the morphology and mechanical properties of individual fibers and also the bulk fibrous meshes. Nanoindentation was used for the measurement of nanoscopic mechanical properties of individual fibers of the scaffolds. The hardness and Young's modulus of aligned fibers measured by nanoindentation decreased with collector rotation speeds. This reveals the difference in the local microscopic structure of the fibers deposited at higher speeds. The sequence of nanoscopic mechanical properties (hardness and modulus) of three fibers is PCL at 0 rpm > PCL at 3000 rpm > PCL at 6000 rpm. This may be explained due to the decrease in crystallinity of fibers at higher uptake rates. However, uni-axial tensile properties of (bulk) scaffolds (tensile strength and modulus) increased with increasing collector rotation speed. The average ultimate tensile strength of scaffolds (along the fiber alignment) increased from 2.21 +/- 0.23 MPa for PCL at uptake rate of zero rpm, to a value of 4.21 +/- 0.35 MPa for PCL at uptake rate of 3000 rpm and finally to 9.58 +/- 0.71 MPa for PCL at 6000 rpm. Similarly, the tensile modulus increased gradually from 6.12 +/- 0.8 MPa for PCL at uptake rate of zero rpm, to 11.93 +/- 1.22 MPa for PCL at uptake rate of 3000 rpm and to 33.20 +/- 1.98 MPa for PCL at 6000 rpm. The sequence of macroscopic mechanical properties (tensile strength and modulus) of three fibers, from highest to lowest, is PCL at 0 rpm < PCL at 3000 rpm < PCL at 6000 rpm. This is attributed to the increased fiber alignment and packing and decrease in inter-fiber pore size at higher uptake rates.     

A composite polymer/tricalcium phosphate membrane for guided bone regeneration in maxillofacial surgery

The aim of the study was the development of a resorbable membrane for guided bone regeneration (GBR) with improved biocompatibility, which should be stiff enough to avoid membrane collapse during bone healing. Combining a bioactive ceramic with a resorbable polymer may improve the biocompatibility and osteoconductivity of resorbable devices. The present article describes the preparation, the mechanical properties, and the in vitro degradation characteristic of a composite membrane made of poly(L, DL-lactide) and alpha-tricalcium phosphate in comparison to a membrane made of pure poly(L, DL-lactide). The tensile strength and the elastic modulus as well as the molecular weight of the membranes were measured after in vitro degradation in buffer at 37 degrees C up to 28 weeks. The initial tensile strength of the composite and the polymer membrane was 37.3 +/- 2.4 MPa and 27.7 +/- 2.3 MPa and the elastic modulus 3106 +/- 108 MPa and 3101 +/- 104 MPa, respectively. The mechanical properties remained constant up to 8 weeks and then decreased slowly until week 28. The molecular weight of both membranes decreased steadily from 170,000 D to 30,000 D. It was concluded that the mechanical requirements for a membrane for GBR were fulfilled by the composite membrane.     

Evaluation of the mechanical properties of hot isostatically pressed titania and titania-calcium phosphate composites

A number of composites based on titania and calcium phosphates, hydroxyapatite, bone ash or beta-tricalcium phosphate, were sintered by glass-encapsulated hot isostatic pressing at 925 degrees C. The mechanical properties of the titania and titania-calcium phosphate composites--three-point bending strength, fracture toughness and Young's modulus--were 250-450 MPa, 2.5-2.9 MPa m1/2 and 230-270 GPa, respectively. Hardness and density were also measured. The results suggest that these composites have potential applications in medicine as implant materials.     

Mechanical and thermal properties of novel polymerized NDGA-gelatin hydrogels

Nordihydroguaiaretic acid (NDGA), an antioxidant with two functional ortho-catechols from the creosote bush, has been shown to increase the mechanical properties of synthetic collagen fibers, producing biologically based, biocompatible fibers with material properties in uniaxial tensile tests to failure that are comparable to those of native tendon (Koob and Hernandez, Biomaterials 23 (2002) 203; Koob et al., J Biomed Mater Res, 56 (2001) 31; 56 (2001) 40). The NDGA polymerization scheme was applied to gelatin hydrogels to determine whether it could provide a viable approach for producing gelatin based biological materials with advantageous mechanical and thermal properties. NDGA treatment eliminated gelatin solubilization from hydrogels in chaotropic agents and increased the thermal stability of gelatin hydrogels from less than 37 degrees C to over 80 degrees C. NDGA caused a dose dependent increase in the compressive stiffness and fracture load of gels ranging in concentration from 2.5% to 40% gelatin in uniaxial, unconfined compression tests to failure. Maximum fracture load averaged 0.5+/-0.1MPa and the compressive modulus averaged 4.4+/-1.4MPa for all gelatin concentrations, however, the concentration of NDGA that produced maximum strength and stiffness varied inversely with gelatin concentration. The compressive strength and stiffness of 5% gelatin hydrogels treated with NDGA were independent of temperature up to 52 degrees C. These results indicate that NDGA polymerization renders gelatin hydrogels thermally and mechanically stable and thereby potentially useful for surgical procedures that would benefit from biocompatible, stable and mechanically competent gelatin-based biomaterials.     

Effects of synergistic reinforcement and absorbable fiber strength on hydroxyapatite bone cement

Approximately a million bone grafts are performed each year in the United States, and this number is expected to increase rapidly as the population ages. Calcium phosphate cement (CPC) can intimately adapt to the bone cavity and harden to form resorbable hydroxyapatite with excellent osteoconductivity and bone-replacement capability. The objective of this study was to develop a strong CPC using synergistic reinforcement via suture fibers and chitosan, and to determine the fiber strength-CPC composite strength relationship. Biopolymer chitosan and cut suture filaments were randomly mixed into CPC. Both suture filaments and composite were immersed in a physiological solution. After 1-day immersion, cement flexural strengths (mean +/- SD; n = 6) were: (2.7 +/- 0.8) MPa for CPC control; (11.2 +/- 1.0) MPa for CPC-chitosan; (17.7 +/- 4.4) MPa for CPC-fiber composite; and (40.5 +/- 5.8) MPa for CPC-chitosan-fiber composite. They are significantly different from each other (Tukey's at 0.95). The strength increase from chitosan and fiber together in CPC was much more than that from either fiber or chitosan alone. The composite strength became (9.8 +/- 0.6) MPa at 35-day immersion and (4.2 +/- 0.7) MPa at 119 days, comparable to reported strengths for sintered porous hydroxyapatite implants and cancellous bone. After suture fiber dissolution, long macropore channels were formed in CPC suitable for cell migration and tissue ingrowth. A semiempirical relationship between suture fiber strength S(F) and composite strength S(C) were obtained: S(C) = 14.1 + 0.047 S(F), with R = 0.92. In summary, this study achieved substantial synergistic effects by combining random suture filaments and chitosan in CPC. This may help extend the use of the moldable, in situ hardening hydroxyapatite to moderate stress-bearing orthopedic applications. The long macropore channels in CPC should be advantageous for cell infiltration and bone ingrowth than conventional random pores and spherical pores.     

Natural origin scaffolds with in situ pore forming capability for bone tissue engineering applications

This work describes the development of a biodegradable matrix, based on chitosan and starch, with the ability to form a porous structure in situ due to the attack by specific enzymes present in the human body (alpha-amylase and lysozyme). Scaffolds with three different compositions were developed: chitosan (C100) and chitosan/starch (CS80-20, CS60-40). Compressive test results showed that these materials exhibit very promising mechanical properties, namely a high modulus in both the dry and wet states. The compressive modulus in the dry state for C100 was 580+/-33MPa, CS80-20 (402+/-62MPa) and CS60-40 (337+/-78MPa). Degradation studies were performed using alpha-amylase and/or lysozyme at concentrations similar to those found in human serum, at 37 degrees C for up to 90 days. Scanning electron micrographs showed that enzymatic degradation caused a porous structure to be formed, indicating the potential of this methodology to obtain in situ forming scaffolds. In order to evaluate the biocompatibility of the scaffolds, extracts and direct contact tests were performed. Results with the MTT test showed that the extracts of the materials were clearly non-toxic to L929 fibroblast cells. Analysis of cell adhesion and morphology of seeded osteoblastic-like cells in direct contact tests showed that at day 7 the number of cells on CS80-20 and CS60-40 was noticeably higher than that on C100, which suggests that starch containing materials may promote cell adhesion and proliferation. This combination of properties seems to be a very promising approach to obtain scaffolds with gradual in vivo pore forming capability for bone tissue engineering applications.     

Contribution of hydroxyapatite to the tensile strength of the isobutyl-2-cyanoacrylate-bone bond

The bonding strength between bone and alpha-2-cyanoacrylate polymers, with or without the addition of powdered hydroxyapatite, was determined. The tensile strength of a bone-cyanoacrylate bond was measured for each polymer: 4.31 +/- 0.88 MPa (methyl-), 5.74 +/- 0.62 MPa (ethyl-), and 8.33 +/- 0.41 MPa (isobutyl-). The tensile strength of the isobutyl-2-cyanoacrylate bond increased to 12.03 +/- 0.72 MPa with the addition of 10% (w/v) hydroxyapatite before decreasing to 7.89 +/- 0.58 MPa on addition of 15% (w/v) hydroxyapatite. An optimal concentration of hydroxyapatite significantly increased the tensile strength of a bone-cyanocacrylate bond in vitro in a manner comparable to reinforced bone replacement materials.     

Structure, metallurgy, and mechanical properties of a porous tantalum foam

This study evaluated a porous tantalum biomaterial (Hedrocel) designed to function as a scaffold for osseous ingrowth. Samples were characterized for structure, Vickers microhardness, compressive cantilever bending, and tensile properties, as well as compressive and cantilever bending fatigue. The structure consisted of regularly arranged cells having struts with a vitreous carbon core with layers of CVI deposited crystalline tantalum. Microhardness values ranged from 240-393, compressive strength was 60 +/- 18 MPa, tensile strength was 63 +/- 6 MPa, and bending strength was 110 +/- 14 MPa. The compressive fatigue endurance limit was 23 MPa at 5 x 10(6) cycles with samples exhibiting significant plastic deformation. SEM examination showed cracking at strut junctions 45 degrees to the axis of the applied load. The cantilever bending fatigue endurance limit was 35 MPa at 5 x 10(6) cycles, and SEM examination showed failure due to cracking of the struts on the tension side of the sample. While properties were variable due to morphology, results indicate that the material provides structural support while bone ingrowth is occurring. These findings, coupled with the superior biocompatibility of tantalum, makes the material a candidate for a number of clinical applications and warrants further and continued laboratory and clinical investigation.     

In vivo biocompatibility and mechanical properties of porous zein scaffolds

In our previous study, a three-dimensional zein porous scaffold with a compressive Young's modulus of up to 86.6+/-19.9 MPa and a compressive strength of up to 11.8+/-1.7 MPa was prepared, and was suitable for culture of mesenchymal stem cells (MSCs) in vitro. In this study, we examined its tissue compatibility in a rabbit subcutaneous implantation model; histological analysis revealed a good tissue response and degradability. To improve its mechanical property (especially the brittleness), the scaffolds were prepared using the club-shaped mannitol as the porogen, and stearic acid or oleic acid was added. The scaffolds obtained had an interconnected tubular pore structure, 100-380 microm in pore size, and about 80% porosity. The maximum values of the compressive strength and modulus, the tensile strength and modulus, and the flexural strength and modulus were obtained at the lowest porosity, reaching 51.81+/-8.70 and 563.8+/-23.4 MPa; 3.91+/-0.86 and 751.63+/-58.85 MPa; and 17.71+/-3.02 and 514.39+/-19.02 MPa, respectively. Addition of 15% stearic acid or 20% oleic acid did not affect the proliferation and osteogenic differentiation of MSCs, and a successful improvement of mechanical properties, especially the brittleness of the zein scaffold could be achieved.     

影响水溶性羧甲基壳聚糖稳定性的外界因素

以虾壳为原料,制备了水溶性羧甲基壳聚糖。通过对壳聚糖特性黏度的测定来表征其稳定性,具体研究了影响壳聚糖稳定性的因素温度、pH值、离子强度、紫外线和灭菌过程。结果表明溶液的酸碱度和离子强度对壳聚糖的特性黏度有很大的影响,在一定范围内,壳聚糖溶液的黏度随之变化敏感。紫外线照射和灭菌过程不但使特性黏度降低,更使壳聚糖的分子结构发生显著变化。特性黏度随时间而降低,在37℃时降低较快,在2℃～8℃冷藏条件下壳聚糖制品可保持一定的稳定性,为壳聚糖的存放条件提供了科学依据。     

Development of self-assembled, tissue-engineered ligament from bone marrow stromal cells

The human anterior cruciate ligament is ruptured 200,000 times per year in the United States, resulting in medical costs of $1 billion. The standard treatment is patellar tendon autograft, but this treatment is suboptimal because of lengthy recovery time, arthritis, donor site morbidity, and degenerative joint disease. This study aimed to engineer scaffold-free ligament analogs from a clinically relevant cell source and to examine mechanical and histological properties of the resulting engineered tissue. Porcine bone marrow stromal cells were seeded on laminin-coated substrates with silk suture segments as anchor points. Cells developed into monolayers that subsequently delaminated and self-organized into cohesive rod-like tissues that were held in tension above the substrate. After 14 days of maturation, scanning electron microscopy revealed a well-organized extracellular matrix, aligned collagen fibers, and a collagen fibril diameter of 51.1+/-77 nm. Histological evaluation showed that constructs were composed of approximately 60% collagen. During tensile tests to failure, constructs had a stress of 2.11 +/- 0.13 MPa, a strain of 28.8 +/- 0.95%, a force of 0.26 +/- 0.02 N, and a tangent modulus of 15.4+/-1.04 MPa. Mechanically and histologically, engineered ligament resembled native embryonic connective tissue and had an ultimate stress approximately 15% of native adult mouse tissue.     

Influence of matrix processing on the optical and biomechanical properties of a corneal stroma equivalent

Interest in developing tissue-engineered cornea has increased with the decrease in the supply of donor tissue; however, the high strength and transparency of the cornea present a challenge. Both the collagen processing and crosslinking methods were hypothesized to influence the optical and biomechanical properties of collagen matrices, while regular surface topography was hypothesized to align stromal fibroblasts. Improved transparency and strength were observed when soluble tropocollagen was added to the insoluble collagen and when glucose-mediated ultraviolet (UV) crosslinking as opposed to dehydrothermal crosslinking was used. The fraction of transmittance of the collagen films fabricated from insoluble collagen and soluble tropocollagen and glucose-mediated UV crosslinking was initially 0.91 +/- 0.02 and 0.98 +/- 0.01 for the smooth films and 0.90 +/- 0.02 and 0.97 +/- 0.02 for the microgrooved films at 400 and 700 nm and was comparable to that of the native cornea, while the relaxed modulus and ultimate tensile strength ranged from 0.9 to 9.4 MPa and from 0.7 to 4.1 MPa, respectively, over the 3 weeks of culture and were initially at or below the range of values for the native cornea. These collagen scaffolds were significantly stronger and more transparent than previous scaffolds, and aligned stromal fibroblasts were observed on microgrooved surfaces.     

Engineering of functional tendon

Surgical tendon repair is limited by the availability of viable tissue for transplantation. Because of its relatively avascular nature, tendon is a prime candidate for engineered tissue replacement. To address this problem, cells isolated from rat Achilles tendon were grown to confluence in culture and allowed to self-assemble into a cylinder between two anchor points. The resulting scaffold-free tissue was composed of aligned, small-diameter collagen fibrils, a large number of cells, and an excess of noncollagenous extracellular matrix; all characteristics of embryonic tendon. The stress-strain response of the constructs also resembles the nonlinear behavior of immature tendons, and the ultimate tensile strength is approximately equal to that of embryonic chick tendon, roughly 2 MPa. These physical and mechanical properties indicate that these constructs are the first viable tendons engineered in vitro, without the aid of artificial scaffolding.     

Microspheres of collagen/beta-TCP with an open network fibrillar structure strengthened by chitosan

A novel method of preparing collagen/beta-tricalcium phosphate microspheres with chitosan as the mechanical strength enhancer has been developed in this study. The process involved firstly droplet formation by discharging a mixture of collagen, beta-tricalcium phosphates and alginate into an aqueous solution of CaCl(2) by extruding through an air jet-syringe at 4 degrees C. The gel beads thus formed were collected and subsequently coated with chitosan to stabilize the surface of gel bead. Collagen within the gel beads was then reconstituted while the entrapped alginate was liquefied and drained by incubating in phosphate buffer at 37 degrees C. Microspheres comprised of fibrillar collagen and well-dispersed beta-tricalcium phosphate particulates were obtained by this process. And the mechanical strength of these microspheres was significantly enhanced by chitosan coating. These chitosan-coated collagen/beta-tricalcium phosphate microspheres have an open fibrillar network structure with a great potential for future application as biodegradable bone grafting materials.     

High-strength, in situ-setting calcium phosphate composite with protein release

The aim of this study was to develop a mechanically-strong calcium phosphate cement (CPC) with protein release. Chitosan was used to strengthen CPC and control protein release. Mass fraction of protein release = mass of released protein/mass of total protein incorporated into the specimen. Flexural strength (mean +/- sd; n = 6) of CPC containing 100 ng/mL of protein increased from 8.0 +/- 1.4 MPa with 0% chitosan, to 19.8 +/- 1.4 MPa with 15% chitosan (p < 0.05). The latter exceeded the reported strengths of sintered porous hydroxyapatite implants and cancellous bone. When the chitosan mass fraction was increased from 0% to 10% and 15%, protein release varied from 0.60 +/- 0.03 to 0.41 +/- 0.04, and to 0.23 +/- 0.07, respectively (p < 0.05). When powder:liquid ratio increased from 2:1 to 3:1 and 4:1, protein release changed from 0.89 +/- 0.10 to 0.41 +/- 0.04, and to 0.23 +/- 0.07, respectively p < 0.05. Therefore, chitosan content and powder:liquid ratio successfully controlled the protein release. The protein release mass fraction, M, was related to CPC porosity P by: M = 16.9 P(4.5). In summary, a mechanically-strong CPC with controlled protein release was formulated. Protein release was proportional to CPC porosity. The in situ-hardening, nano-apatite composite may have potential for bone tissue engineering, especially when both mechanical strength and controlled release of therapeutic/bioactive agents are needed.     

Successive epoxy and carbodiimide cross-linking of dermal sheep collagen.

Cross-linking of dermal sheep collagen (N-DSC, T(S) = 46 degrees C, number of amine groups = 31 (n/1000)) with 1,4-butanediol diglycidyl ether (BDDGE) at pH 9.0 resulted in a material (BD90) with a high T(S)(69 degrees C), a decreased number of amine groups of 15 (n/1000) and a high resistance towards collagenase and pronase degradation. Reaction of DSC with BDDGE at pH 4.5 yielded a material (BD45) with a T(S) of 64 degrees C, hardly any reduction in amine groups and a lower stability towards enzymatic degradation as compared to BD90. The tensile strength of BD45 (9.2 MPa) was substantially improved as compared to N-DSC (2.4 MPa), whereas the elongation at break was reduced from 210 to 140%. BD90 had a tensile strength of 2.6 MPa and an elongation at break of only 93%. To improve the resistance to enzymes and to retain the favorable tensile properties, BD45 was post-treated with 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC) in the presence of N-hydroxysuccinimide (NHS) to give BD45EN. Additional cross-linking via the formation of amide bonds took place as indicated by the T(S) of 81 degrees C and the residual number of amine groups of 19 (n/1000). BD45EN was stable during exposure to both collagenase and pronase solutions. The tensile properties (tensile strength 7.2 MPa, elongation at break 100%) were comparable to those of BD45 and glutaraldehyde treated controls (G-DSC). Acylation of the residual amine groups of BD45 with acetic acid N-hydroxysuccinimide ester (HAc-NHS) yielded BD45HAc with a large reduction in amine groups to 10 (n/1000) and a small reduction in T(S) to 62 degrees C. The stability towards enzymatic degradation was reduced, but the tensile properties were comparable to BD45.     

Glutaraldehyde Cross-Linking of Tendon—Mechanical Effects at the Level of the Tendon Fascicle and Fibril

Conclusive insight into the microscopic principles that govern the strength of tendon and related connective tissues is lacking and the importance of collagen cross-linking has not been firmly established. The combined application of whole-tissue mechanical testing and atomic force spectroscopy allowed for a detailed characterization of the effect of cross-linking in rat-tail tendon. The cross-link inducing agent glutaraldehyde augmented the tensile strength of tendon fascicles. Stress at failure increased from ～8 MPa to ～39 MPa. The mechanical effects of glutaraldehyde at the tendon fibril level were examined by atomic force microscopy. Peak forces increased from ～1379 to ～2622 pN while an extended Hertz fit of force-indentation data showed a ～24 fold increase in Young's modulus on indentation. The effect of glutaraldehyde cross-linking on the tensile properties of a single collagen fibril was investigated by a novel methodology based on atomic force spectroscopy. The Young's modulus of a secluded fibril increased from ～407 MPa to ～1.1 GPa with glutaraldehyde treatment. Collectively, the findings indicate that cross-linking at the level of the collagen fibril is of key importance for the mechanical strength of tendon tissue. However, when comparing the effects at the level of the tendon fascicle and fibril, respectively, further questions are prompted regarding the pathways of force through the tendon microstructure as fibril strength seems to surpass that of the tendon fascicle.