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1.
bioRxiv ; 2024 Apr 06.
Article in English | MEDLINE | ID: mdl-38617208

ABSTRACT

Compromised vascular supply and insufficient neovascularization impede bone repair, increasing risk of non-union. Cyr61, Cysteine-rich angiogenic inducer of 61kD (also known as CCN1), is a matricellular growth factor that is regulated by mechanical cues during fracture repair. Here, we map the distribution of endogenous Cyr61 during bone repair and evaluate the effects of recombinant Cyr61 delivery on vascularized bone regeneration. In vitro, Cyr61 treatment did not alter chondrogenesis or osteogenic gene expression, but significantly enhanced angiogenesis. In a mouse femoral fracture model, Cyr61 delivery did not alter cartilage or bone formation, but accelerated neovascularization during fracture repair. Early initiation of ambulatory mechanical loading disrupted Cyr61-induced neovascularization. Together, these data indicate that Cyr61 delivery can enhance angiogenesis during bone repair, particularly for fractures with stable fixation, and may have therapeutic potential for fractures with limited blood vessel supply.

2.
Biomed Mater Eng ; 32(3): 159-170, 2021.
Article in English | MEDLINE | ID: mdl-33780355

ABSTRACT

BACKGROUND: Implantable medical devices and hardware are prolific in medicine, but hardware associated infections remain a major issue. OBJECTIVE: To develop and evaluate a novel, biologic antimicrobial coating for medical implants. METHODS: Electrochemically compacted collagen sheets with and without crosslinked heparin were synthesized per a protocol developed by our group. Sheets were incubated in antibiotic solution (gentamicin or moxifloxacin) overnight, and in vitro activity was assessed with five-day diffusion assays against Pseudomonas aeruginosa. Antibiotic release over time from gentamicin-infused sheets was determined using in vitro elution and high performance liquid chromatography (HPLC). RESULTS: Collagen-heparin-antibiotic sheets demonstrated larger growth inhibition zones against P. aeruginosa compared to collagen-antibiotic alone sheets. This activity persisted for five days and was not impacted by rinsing sheets prior to evaluation. Rinsed collagen-antibiotic sheets did not produce any inhibition zones. Elution of gentamicin from collagen-heparin-gentamicin sheets was gradual and remained above the minimal inhibitory concentration for gentamicin-sensitive organisms for 29 days. Conversely, collagen-gentamicin sheets eluted their antibiotic load within 24 hours. Overall, heparin-associated sheets demonstrated larger inhibition zones against P. aeruginosa and prolonged elution profile via HPLC. CONCLUSION: We developed a novel, local antibiotic delivery system that could be used to coat medical implants/hardware in the future and reduce post-operative infections.


Subject(s)
Heparin , Anti-Bacterial Agents , Collagen , Gentamicins , Pseudomonas aeruginosa
3.
Mater Sci Eng C Mater Biol Appl ; 99: 96-102, 2019 Jun.
Article in English | MEDLINE | ID: mdl-30889771

ABSTRACT

Among a vast array of biomaterials investigated for tissue engineering applications, bacterial cellulose (BC) has not been evaluated in depth, despite the material's strong potential of applicability in the field of biotechnology. In this study we investigate the effect of sugar concentration and culture duration on physical and mechanical properties of BC. BC was grown in culture media with different glucose concentrations (weight percent) of 1.25%, 2.50%, 5.00%, 10.00%, 15.00% and also in media with fructose concentration of 5.00%. The swelling ratio of harvested BC sheets did not change significantly with concentration of glucose or the type of sugar (fructose vs glucose). Swelling ratio did not change significantly with culture duration either. Cellulose production rate was significantly higher (p < 0.05) at 5.00%wt. glucose concentration compared to other groups. Ultimate tensile strength (309.3 ±â€¯32.8 MPa) and Young's modulus (3.1 ±â€¯0.6 GPa) of BC sheets harvested from the medium with 5.00%wt. glucose concentration were the highest among all treatment groups. Bacterial removal process and testing condition (wet/dry) did not affect the mechanical performance of the bacterial cellulose significantly. X-ray diffraction data demonstrated higher crystallinity for samples cultured in media with 5.00%wt. glucose concentration. Viability/cytotoxicity, proliferation, and cells' metabolic activities demonstrated BC to be biocompatible. Cells attached, spread, and proliferated with time on bacterial cellulose. Results of this study showed 5.00 wt% glucose concentration is the optimum concentration of sugar in media to produce BC with highest strength and modulus compared to other concentration. High mechanical strength along with biocompatibility present bacterial cellulose as an invaluable material for use in tissue engineering of load bearing connective tissues such as tendons and ligaments.


Subject(s)
Bacteria/chemistry , Cellulose/pharmacology , Nanofibers/chemistry , Regeneration , Actin Cytoskeleton/metabolism , Cell Death/drug effects , Cellulose/ultrastructure , Elastic Modulus , Glucose/analysis , Humans , Mesenchymal Stem Cells/cytology , Mesenchymal Stem Cells/drug effects , Nanofibers/ultrastructure , Regeneration/drug effects , Tensile Strength , X-Ray Diffraction
4.
J Mech Behav Biomed Mater ; 90: 530-537, 2019 02.
Article in English | MEDLINE | ID: mdl-30469131

ABSTRACT

Effects of mercerization process on plant-based cellulose is well studied in the literature whereas the effects of mercerization on mechanical properties of bacterial cellulose is not investigated. In this work bacterial cellulose (BC) was mercerized in NaOH solution with different molar concentrations of 0, 1.50, 1.75, 2.00, 2.13, 2.25, 5.00, 7.00 and 10.00 M. The BC samples shrunk substantially with increasing NaOH concentration. At the same concentration, NaOH treatment resulted in significantly larger shrinkage than KOH treatment. Mercerization of BC samples in 7 M NaOH resulted in an order of magnitude increase in elongation from 5.4 ±â€¯1.6% to 50.8 ±â€¯5.7% along with about 30-fold reduction in Young's modulus. Mercerized samples in 4 M NaOH had maximum toughness among all groups at a value of 64.0 ±â€¯15.8 MJ m-3. Changes in BC crystalline structure from cellulose I to cellulose II were characterized and confirmed semiquantitatively by using X-ray diffraction (XRD) and Raman spectroscopy. Results of this work demonstrated mercerization as a method to tune the mechanical properties of BC precisely. Mercerized BC as a biocompatible material with tunable mechanical properties shows potential to be utilized in tissue engineering and regenerative medicine in the future.


Subject(s)
Cellulose/chemistry , Mechanical Phenomena , Probiotics/chemistry , Elastic Modulus , Materials Testing , Sodium Hydroxide/chemistry
5.
Acta Biomater ; 63: 200-209, 2017 11.
Article in English | MEDLINE | ID: mdl-28890257

ABSTRACT

Flexor tendon lacerations are traditionally repaired by using non-absorbable monofilament sutures. Recent investigations have explored to improve the healing process by growth factor delivery from the sutures. However, it is difficult to conjugate growth factors to nylon or other synthetic sutures. This study explores the performance of a novel electrochemically aligned collagen suture in a flexor tendon repair model with and without platelet derived growth factor following complete tendon laceration in vivo. Collagen suture was fabricated via electrochemical alignment process. Heparin was covalently bound to electrochemically aligned collagen sutures (ELAS) to facilitate affinity bound delivery of platelet-derived growth factor-BB (PDGF-BB). Complete laceration of the flexor digitorum profundus in the third digit of the foot was performed in 36 skeletally mature White Leghorn chickens. The left foot was used as the positive control. Animals were randomly divided into three groups: control specimens treated with standard nylon suture (n=12), specimens repaired with heparinated ELAS suture without PDGF-BB (n=12) and specimens repaired with heparinated ELAS suture with affinity bound PDGF-BB (n=12). Specimens were harvested at either 4weeks or 12weeks following tendon repair. Differences between groups were evaluated by the degree of gross tendon excursion, failure load/stress, stiffness/modulus, absorbed energy at failure, elongation/strain at failure. Quantitative histological scoring was performed to assess cellularity and vascularity. Closed flexion angle measurements demonstrated no significant differences in tendon excursion between the study groups at 4 or 12weeks. Biomechanical testing showed that the group treated with PDGF-BB bound heparinated ELAS suture had significantly higher stiffness and failure load (p<0.05) at 12-weeks relative to both heparinated ELAS suture and nylon suture. Similarly, the group treated with PDGF-BB bound suture had significantly higher ultimate tensile strength and Young's modulus (p<0.05) at 12-weeks relative to both ELAS suture and nylon suture. Compared to nylon controls, heparinized ELAS with PDGF-BB improved biomechanics and vascularity during tendon healing by 12-weeks following primary repair. The ability of ELAS to deliver PDGF-BB to the lacerated area of tendon presents investigators with a functional bioinductive platform to improve repair outcomes following flexor tendon repair. STATEMENT OF SIGNIFICANCE: A high strength aligned collagen suture was fabricated via linear electrocompaction and heparinized for prolonged delivery of PDFG-BB. When it was used to suture a complete lacerated flexor tendon in a chicken model controlled release of the PDGF-BB improved the strength of treated tendon after 12 weeks compared to tendon sutured with commercial nylon suture. Furthermore, Collagen suture with affinity bound PDGF-BB enhanced the vascularization and remodeling of lacerated tendon when it compare to synthetic nylon suture. Overall, electrocompacted collagen sutures holds potential to improve repair outcome in flexor tendon surgeries by improving repair strength and stiffness, vascularity, and remodeling via sustained delivery of the PDGF-BB. The bioinductive collagen suture introduces a platform for sustained delivery of other growth factors for a wide-array of applications.


Subject(s)
Collagen/chemistry , Drug Delivery Systems , Heparin/chemistry , Lacerations/drug therapy , Proto-Oncogene Proteins c-sis/therapeutic use , Sutures , Tendons/pathology , Animals , Becaplermin , Biomechanical Phenomena , Cattle , Chickens , Lacerations/pathology , Lacerations/physiopathology , Proto-Oncogene Proteins c-sis/pharmacology , Tendons/drug effects , Tendons/physiopathology , Wound Healing/drug effects
6.
Acta Biomater ; 58: 244-253, 2017 08.
Article in English | MEDLINE | ID: mdl-28602855

ABSTRACT

Extracellular matrix modulus plays an important role in regulating cell morphology, proliferation and differentiation during regular and diseased states. Although the effects of substrate topography and modulus on MSC differentiation are well known with respect to osteogenesis and adipogenesis, there has been relatively little investigation on the effects of this phenomenon on tenogenesis. Furthermore, relative roles of topographical factors (matrix alignment vs. matrix modulus) in inducing tenogenic differentiation is not well understood. In this study we investigated the effects of modulus and topographical alignment of type I collagen substrate on tendon differentiation. Type I collagen sheet substrates with random topographical alignment were fabricated with their moduli tuned in the range of 0.1, 1, 10 and 100MPa by using electrocompaction and controlled crosslinking. In one of the groups, topographical alignment was introduced at 10MPa stiffness, by controlled unidirectional stretching of the sheet. RT-PCR, immunohistochemistry and immunofluorescence results showed that mimicking the tendon topography, i.e. increasing the substrate modulus as well as alignment increased the tenogenic differentiation. Higher substrate modulus increased the expression of COLI, COLIII, COMP and TSP-4 about 2-3-fold and increased the production of COLI, COLIII and TSP-4 about 2-4-fold. Substrate alignment up regulated COLIII and COMP expression by 2-fold. Therefore, the tenoinductive collagen material model developed in this study can be used in the research and development of tissue engineering tendon repair constructs in future. STATEMENT OF SIGNIFICANCE: Although the effects of substrate topography and modulus on MSC differentiation are well known with respect to osteogenesis and adipogenesis, there has been relatively little investigation on the effects of this phenomenon on tenogenesis. Furthermore, a relative role of topographical factors (matrix alignment vs. matrix modulus) in inducing tenogenic differentiation is not well understood. We investigated the effects of modulus and topographical alignment of type I collagen substrate on tendon differentiation. This study showed mimicking the tendon topography, i.e. increasing the substrate modulus as well as alignment increased the tenogenic differentiation. Therefore, the tenoinductive collagen material model developed in this study can be used in the research and development of tissue engineering tendon repair constructs in future.


Subject(s)
Cell Differentiation , Collagen Type I , Extracellular Matrix/metabolism , Mesenchymal Stem Cells/metabolism , Tendons , Tissue Engineering , Collagen Type I/chemistry , Collagen Type I/metabolism , Humans , Mesenchymal Stem Cells/cytology
7.
Biomacromolecules ; 18(4): 1259-1267, 2017 04 10.
Article in English | MEDLINE | ID: mdl-28328202

ABSTRACT

An electrochemical process has been used to compact cellulose nanocrystals (CNC) and access aligned micron-sized CNC fibers. Placing a current across aqueous solutions of carboxylic acid functionalized CNCs (t-CNC-COOH) or carboxylic acid/primary amine functionalized CNCs (t-CNC-COOH-NH2) creates a pH gradient between the electrodes, which results in the migration and concentration of the CNC fibers at their isoelectric point. By matching the carboxylic acid/amine ratio of CNCs and collagen (ca. 30:70 carboxylic acid:amine ratio), it is possible to coelectrocompact both nanofibers and access aligned nanocomposite fibers. t-CNC-COOH-NH2/collagen fibers showed a maximum increase in mechanical properties at 5 wt % of t-CNC-COOH-NH2. Compared to collagen/CNC films which have no alignment in the plane of the films, the tensile properties of the aligned fibers show a significant enhancement in the wet mechanical properties (40 MPa vs 230 MPa) for the 5 wt % of t-CNC-COOH-NH2/collagen films and fiber, respectively.


Subject(s)
Cellulose/chemical synthesis , Collagen/chemical synthesis , Electrochemical Techniques/methods , Nanofibers/chemistry , Nanoparticles/chemistry , Cellulose/chemistry , Cellulose/ultrastructure , Collagen/chemistry , Collagen/ultrastructure , Mechanical Phenomena , Microscopy, Electron, Scanning , Nanofibers/ultrastructure , Nanoparticles/ultrastructure , Spectrum Analysis, Raman , Surface Properties , Tissue Engineering
9.
Ann Biomed Eng ; 45(1): 286-296, 2017 01.
Article in English | MEDLINE | ID: mdl-27164837

ABSTRACT

Extracellular matrix mimetic hydrogels which hybridize synthetic and natural polymers offer molecularly-tailored, bioactive properties and tunable mechanical strength. In addition, 3D bioprinting by stereolithography allows fabrication of internal pores and defined macroscopic shapes. In this study, we formulated a hybrid biocompatible resin using natural and synthetic polymers (chitosan and polyethylene glycol diacrylate (PEGDA), respectively) by controlling molecular weight of chitosan, feed-ratios, and photo-initiator concentration. Ear-shaped, hybrid scaffolds were fabricated by a stereolithographic method using a 405 nm laser. Hybrid hydrogel scaffolds of chitosan (50-190 kDa) and PEGDA (575 Da) were mixed at varying feed-ratios. Some of the cationic, amino groups of chitosan were neutralized by dialysis in acidic solution containing chitosan in excess of sodium acetate solution to inhibit quenching of newly formed photoradicals. A feed-ratio of 1:7.5 was found to be the most appropriate of the formulations considered in this study in terms of mechanical properties, cell adhesion, and printability. The biofabricated hybrid scaffold showed interconnected, homogeneous pores with a nominal pore size of 50 µm and an elastic modulus of ~400 kPa. Moreover, long-term cell viability and cell spreading was observed via actin filament staining. Printability of the biocompatible resin was confirmed by printing thresholded MR images of an ear and the feed ratio of 1:7.5 provided the most faithful reproduction of the shape. To the best of our knowledge, this is the first report of stereolithographic printing hybridizing cell-adhesive properties of chitosan with mechanical robustness of PEG in scaffolds suitable for repair of complex tissue geometries, such as those of the human ear.


Subject(s)
Chitosan , Hydrogels , Materials Testing , Mesenchymal Stem Cells/metabolism , Polyethylene Glycols , Printing, Three-Dimensional , Tissue Scaffolds/chemistry , Cells, Cultured , Chitosan/chemistry , Chitosan/pharmacology , Humans , Hydrogels/chemical synthesis , Hydrogels/chemistry , Hydrogels/pharmacology , Mesenchymal Stem Cells/cytology , Polyethylene Glycols/chemistry , Polyethylene Glycols/pharmacology
10.
Adv Healthc Mater ; 5(17): 2237-47, 2016 09.
Article in English | MEDLINE | ID: mdl-27377355

ABSTRACT

Rigidity of substrates plays an important role in stem cell fate. Studies are commonly carried out on isotropically stiff substrate or substrates with unidirectional stiffness gradients. However, many native tissues are anisotropically stiff and it is unknown whether controlled presentation of stiff and compliant material axes on the same substrate governs cytoskeletal and nuclear morphology, as well as stem cell differentiation. In this study, electrocompacted collagen sheets are stretched to varying degrees to tune the stiffness anisotropy (SA) in the range of 1 to 8, resulting in stiff and compliant material axes orthogonal to each other. The cytoskeletal aspect ratio increased with increasing SA by about fourfold. Such elongation was absent on cellulose acetate replicas of aligned collagen surfaces indicating that the elongation was not driven by surface topography. Mesenchymal stem cells (MSCs) seeded on varying anisotropy sheets displayed a dose-dependent upregulation of tendon-related markers such as Mohawk and Scleraxis. After 21 d of culture, highly anisotropic sheets induced greater levels of production of type-I, type-III collagen, and thrombospondin-4. Therefore, SA has direct effects on MSC differentiation. These findings may also have ramifications of stem cell fate on other anisotropically stiff tissues, such as skeletal/cardiac muscles, ligaments, and bone.


Subject(s)
Cell Differentiation , Cell Nucleus/metabolism , Collagen/chemistry , Cytoskeleton/metabolism , Mesenchymal Stem Cells/metabolism , Animals , Anisotropy , Cattle , Cell Shape , Humans , Mesenchymal Stem Cells/cytology
11.
Acta Biomater ; 41: 100-9, 2016 09 01.
Article in English | MEDLINE | ID: mdl-27240725

ABSTRACT

UNLABELLED: Suturing is the standard of repair for lacerated flexor tendons. Past studies focused on delivering growth factors to the repair site by incorporating growth factors to nylon sutures which are commonly used in the repair procedure. However, conjugation of growth factors to nylon or other synthetic sutures is not straightforward. Collagen holds promise as a suture material by way of providing chemical sites for conjugation of growth factors. On the other hand, collagen also needs to be reconstituted as a mechanically robust thread that can be sutured. In this study, we reconstituted collagen solutions as suturable collagen threads by using linear electrochemical compaction. Prolonged release of PDGF-BB (Platelet derived growth factor-BB) was achieved by covalent bonding of heparin to the collagen sutures. Tensile mechanical tests of collagen sutures before and after chemical modification indicated that the strength of sutures following chemical conjugation stages was not compromised. Strength of lacerated tendons sutured with epitendinous collagen sutures (11.2±0.7N) converged to that of the standard nylon suture (14.9±2.9N). Heparin conjugation of collagen sutures didn't affect viability and proliferation of tendon-derived cells and prolonged the PDGF-BB release up to 15days. Proliferation of cells seeded on PDGF-BB incorporated collagen sutures was about 50% greater than those seeded on plain collagen sutures. Collagen that is released to the media by the cells increased by 120% under the effects of PDGF-BB and collagen production by cells was detectable by histology as of day 21. Addition of PDGF-BB to collagen sutures resulted in a moderate decline in the expression of the tendon-associated markers scleraxis, collagen I, tenomodulin, and COMP; however, expression levels were still greater than the cells seeded on collagen gel. The data indicate that the effects of PDGF-BB on tendon-derived cells mainly occur through increased cell proliferation and that longer term studies are needed to confirm whether this proliferation is outweighs the moderate reduction in the expression of tendon-associated genes. STATEMENT OF SIGNIFICANCE: A mechanically robust pure collagen suture was fabricated via linear electrocompaction and conjugated with heparin for prolonged delivery of PDFG-BB. Sustained delivery of the PDGF-BB improved the proliferation of tendon derived cells substantially at the expense of a moderate downregulation of tenogenic markers. The collagen threads were functionally applicable as epitendinous sutures when applied to chicken flexor tendons in vitro. Overall, electrocompacted collagen sutures holds potential to improve repair outcome in flexor tendon surgeries by improving cellularity and collagen production through delivery of the PDGF-BB. The bioinductive suture concept can be applied to deliver other growth factors for a wide-array of applications.


Subject(s)
Collagen/pharmacology , Drug Delivery Systems/methods , Heparin/pharmacology , Proto-Oncogene Proteins c-sis/pharmacology , Sutures , Tendons/cytology , Animals , Becaplermin , Cattle , Cell Proliferation/drug effects , Cell Shape/drug effects , Chickens , Cross-Linking Reagents/pharmacology , Delayed-Action Preparations , Real-Time Polymerase Chain Reaction , Staining and Labeling , Tensile Strength
12.
Adv Healthc Mater ; 5(15): 1884-92, 2016 08.
Article in English | MEDLINE | ID: mdl-27191679

ABSTRACT

A microfabricated pillar substrate is developed to confine, align, and elongate cells, allowing decoupled analysis of stiffness and directionality in 3D. Mesenchymal stem cells and cardiomyocytes are successfully confined in a 3D environment with precisely tunable stiffness anisotropy. It is discovered that anisotropically stiff micropillar substrates provide cellular confinement in 3D, aligning cells in the stiffer direction with extraordinary elongation.


Subject(s)
Mesenchymal Stem Cells/metabolism , Myocytes, Cardiac/metabolism , Stem Cell Niche , Animals , Anisotropy , Cell Line , Humans , Mesenchymal Stem Cells/cytology , Mice , Myocytes, Cardiac/cytology
13.
Acta Biomater ; 30: 212-221, 2016 Jan.
Article in English | MEDLINE | ID: mdl-26602826

ABSTRACT

The unique arcade-like orientation of collagen fibers enables cartilage to bear mechanical loads. In this study continuous-length aligned collagen threads were woven to emulate the interdigitated arcade structure of the cartilage. The weaving pattern provided a macropore network within which micromass cell pellets were seeded to take advantage of mesenchymal condensation driven chondrogenesis. Compression tests showed that the baseline scaffold had a modulus of 0.83±0.39MPa at a porosity of 80%. The modulus of pellet seeded scaffolds increased by 60% to 1.33±0.37MPa after 28days of culture, converging to the modulus of the native cartilage. The scaffolds displayed duress under displacement controlled low-cycle fatigue at 15% strain amplitude such that load reduction stabilized at 8% after 4500 cycles of loading. The woven structure demonstrated a substantial elastic recoil where 40% mechanical strain was close to completely recovered following unloading. A robust chondrogenesis was observed as evidenced by positive staining for GAGs and type II collagen and aggrecan. Dimethyl methylene blue and sircol assays showed GAGs and collagen productions to increase from 3.36±1.24 and 31.46±3.22 at day 3 to 56.61±12.12 and 136.70±12.29µg/µg of DNA at day 28 of culture. This woven collagen scaffold holds a significant potential for cartilage regeneration with shorter in vitro culture periods due to functionally sufficient mechanical robustness at the baseline. In conclusion, the mimicry of cartilage's arcade architecture resulted in substantial improvement of mechanical function while enabling one of the first pellet delivery platforms enabled by a macroporous network. STATEMENT OF SIGNIFICANCE: Mesenchymal condensation is critical for driving chondrogenesis, making high density cell seeding a standard in cartilage tissue engineering. Efforts to date have utilized scaffold free delivery of MSCs in pellet form. This study developed a macroporous scaffold that is fabricated by weaving highly aligned collagen threads. The scaffold can deliver high density cell condensates while providing mechanical stiffness comparable to that of cartilage. The scaffold also mimicked the arcade-like orientation of collagen fibers in cartilage. A highly robust chondrogenesis was observed in this mesenchymal cell pellet delivery system. Baseline mechanical robustness of this scaffold system will enable delivery of cell pellets as early as three days.


Subject(s)
Biomimetic Materials/chemistry , Cartilage , Chondrogenesis , Mesenchymal Stem Cells/metabolism , Regeneration , Tissue Scaffolds/chemistry , Cells, Cultured , Humans , Mesenchymal Stem Cells/cytology , Weight-Bearing
14.
Biofabrication ; 7(3): 035005, 2015 Jul 22.
Article in English | MEDLINE | ID: mdl-26200002

ABSTRACT

Reconciliation of high strength and high porosity in pure collagen based structures is a major barrier in collagen's use in load-bearing applications. The current study developed a CAD/CAM based electrocompaction method to manufacture highly porous patterned scaffolds using pure collagen. Utilization of computerized scaffold design and fabrication allows the integration of mesh-scaffolds with controlled pore size, shape and spacing. Mechanical properties of fabricated collagen meshes were investigated as a function of number of patterned layers, and with different pore geometries. The tensile stiffness, tensile strength and modulus ranges from 10-50 N cm(-1), 1-6 MPa and 5-40 MPa respectively for all the scaffold groups. These results are within the range of practical usability of different tissue engineering application such as tendon, hernia, stress urinary incontinence or thoracic wall reconstruction. Moreover, 3-fold increase in the layer number resulted in more than 5-fold increases in failure load, toughness and stiffness which suggests that by changing the number of layers and shape of the structure, mechanical properties can be modulated for the aforementioned tissue engineering application. These patterned scaffolds offer a porosity ranging from 0.8 to 1.5 mm in size, a range that is commensurate with pore sizes of repair meshes in the market. The connected macroporosity of the scaffolds facilitated cell-seeding such that cells populated the entire scaffold at the time of seeding. After 3 d of culture, cell nuclei became elongated. These results indicate that the patterned electrochemical deposition method in this study was able to develop mechanically robust, highly porous collagen scaffolds with controlled porosity which not only tries to solve one of the major tissue engineering problems at a fundamental level but also has a significant potential to be used in different tissue engineering applications.


Subject(s)
Biocompatible Materials/chemistry , Biotechnology/methods , Collagen/chemistry , Computer-Aided Design , Tissue Scaffolds/chemistry , Animals , Cells, Cultured , Humans , Materials Testing , Mesenchymal Stem Cells , Porosity , Swine , Tensile Strength
15.
Biofabrication ; 7(3): 035001, 2015 Jun 12.
Article in English | MEDLINE | ID: mdl-26069162

ABSTRACT

Collagen solutions are phase-transformed to mechanically robust shell structures with curviplanar topographies using electrochemically-induced pH gradients. The process enables rapid layer-by-layer deposition of collagen-rich mixtures over the entire field simultaneously to obtain compositionally diverse multilayered structures. The in-plane tensile strength and modulus of the electrocompacted collagen sheet samples were 5200-fold and 2300-fold greater than those of the uncompacted collagen samples. Out-of-plane compression tests showed a 27-fold increase in compressive stress and a 46-fold increase in compressive modulus compared to uncompacted collagen sheets. Cells proliferated 4.9 times faster, and the cellular area spread was 2.7 times greater on compacted collagen sheets. Electrocompaction also resulted in a 2.9 times greater focal adhesion area than on regular collagen hydrogel. The reported improvements in the cell-matrix interactions with electrocompaction would serve to expedite the population of electrocompacted collagen scaffolds by cells. The capacity of the method to fabricate nonlinear curved topographies with compositional heterogeneous layers is demonstrated by sequential deposition of a collagen-hydroxyapatite layer over a collagen layer. The complex curved topography of the nasal structure is replicated by the electrochemical compaction method. The presented electrochemical compaction process is an enabling modality which holds significant promise for reconstruction of a wide spectrum of topographically complex systems such as joint surfaces, craniofacial defects, ears, nose, and urogenital forms.


Subject(s)
Biocompatible Materials/chemistry , Collagen/chemistry , Collagen/ultrastructure , Electrochemical Techniques/methods , Tissue Engineering/methods , Tissue Scaffolds/chemistry , Biocompatible Materials/pharmacology , Cell Adhesion/drug effects , Cells, Cultured , Collagen/pharmacology , Compressive Strength , Humans
16.
Clin Biomech (Bristol, Avon) ; 30(7): 669-75, 2015 Aug.
Article in English | MEDLINE | ID: mdl-26009492

ABSTRACT

BACKGROUND: Currently, there are no well-established suture protocols to attach fully load-bearing scaffolds which span tendon defects between bone and muscle for repair of critical sized tendon tears. Methods to attach load-bearing tissue repair scaffolds could enable functional repair of tendon injuries. METHODS: Sixteen rabbit shoulders were dissected (New Zealand white rabbits, 1yr. old, female) to isolate the humeral-infraspinatus muscle complex. A unique suture technique was developed to allow for a 5mm segmental defect in infraspinatus tendon to be replaced with a mechanically strong bioscaffold woven from pure collagen threads. The suturing pattern resulted in a fully load-bearing scaffold. The tensile stiffness and strength of scaffold repair were compared with intact infraspinatus and regular direct repair. FINDINGS: The failure load and displacement at failure of the scaffold repair group were 59.9N (standard deviation, SD=10.7) and 10.3mm (SD=2.9), respectively and matched those obtained by direct repair group which were 57.5N (SD=15.3) and 8.6mm (SD=1.5), (p>0.05). Failure load, displacement at failure and stiffness of both of the repair groups were half of the intact infraspinatus shoulder group. INTERPRETATION: With the developed suture technique, scaffold repair showed similar failure load, displacement at failure and stiffness to the direct repair. This novel suturing pattern and the mechanical robustness of the scaffold at time zero indicates that the proposed model is mechanically viable for future in vivo studies which has a higher potential to translate into clinical uses.


Subject(s)
Rotator Cuff/surgery , Suture Techniques , Tissue Scaffolds , Weight-Bearing/physiology , Animals , Biomechanical Phenomena , Collagen/therapeutic use , Disease Models, Animal , Female , Rabbits , Rotator Cuff Injuries , Tendon Injuries/surgery , Wound Healing/physiology
17.
Adv Funct Mater ; 24(36): 5762-5770, 2014 Sep 24.
Article in English | MEDLINE | ID: mdl-25750610

ABSTRACT

A novel biofabrication modality, electrophoretic compaction with macromolecular alignment, was utilized to make collagen threads that mimic the native tendon's structure and mechanical properties. A device with kinematic electrodes was designed to fabricate collagen threads in continuous length. For the first time, a 3D-biotextile was woven purely from collagen. Mechanical properties and load-displacement behavior of the biotextile mimicked those of the native tendon while presenting a porosity of 80%. The open pore network facilitated cell seeding across the continuum of the bioscaffold. Mesenchymal stem cells (MSCs) seeded in the woven scaffold underwent tenogenic differentiation in the absence of growth factors and synthesized a matrix that was positive for tenomodulin, COMP and type I collagen. Up-regulation of tenomodulin, a tendon specific marker, was 11.6 ± 3.5 fold, COMP was up-regulated 16.7 ± 5.5 fold, and Col I was up-regulated 6.9 ± 2.7 fold greater on ELAC threads when compared to randomly oriented collagen gels. These results demonstrate that a bioscaffold woven by using collagen threads with densely compacted and anisotropically aligned substrate texture stimulates tenogenesis topographically, rendering the electrochemically aligned collagen as a promising candidate for functional repair of tendons and ligaments.

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