Name: biological compatibility profile on biomaterials for bone regeneration
Uploaded: 2018-11-16T13:00:00
Description: Watch this Scientific Journal Video about Biological Compatibility Profile on Biomaterials for Bone Regeneration at JoVE.com

This research project has received funding from the European Union&#39;s Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 263363.

The procedures were done with BALB/c mice following all guidelines for the Care and Use of Laboratory Animals of the Austrian Ministry of Education, Science and Research and were approved by the Committee on the Ethics of the Austrian Ministry of Education, Science and Research.
1. Primary Mouse OB Culture
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	<li>OB isolation from neonatal mouse calvaria using enzymatic digestion
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		<li>Euthanize 1&#8211;2 day old neonatal pups (60 in total) by decapitation and place...

<ol>
	<li>Einhorn, T. A., Gerstenfeld, L. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fracture+healing:+mechanisms+and+interventions.">Fracture healing: mechanisms and interventions.</a> Nature Reviews Rheumatology. 11 (1), 45-54 (2015).</li><li>Marsell, R., Einhorn, T. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+biology+of+fracture+healing.">The biology of fracture healing.</a> Injury. 42 (6), 551-555 (2011).</li><li>Cooper, G. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Testing+the+critical+size+in+calvarial+bone+defects:+revisiting+the+concept+of+a+critical-size+defect.">Testing the critical size in calvarial bone defects: revisiting the concept of a critical-size defect.</a> Plastic and Reconstructive Surgery. 125 (6), 1685-1692 (2010).</li><li>O'Brien, F. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biomaterials+&amp;+scaffolds+for+tissue+engineering.">Biomaterials &amp; scaffolds for tissue engineering.</a> Materials Today. 14 (3), 88-95 (2011).</li><li>Stanovici, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bone+regeneration+strategies+with+bone+marrow+stromal+cells+in+orthopaedic+surgery.">Bone regeneration strategies with bone marrow stromal cells in orthopaedic surgery.</a> Current Research in Translational Medicine. 64 (2), 83-90 (2016).</li><li>Anderson, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Future+challenges+in+the+in+vitro+and+in+vivo+evaluation+of+biomaterial+biocompatibility.">Future challenges in the in vitro and in vivo evaluation of biomaterial biocompatibility.</a> Regenerative Biomaterials. 3 (2), 73-77 (2016).</li><li>Chen, Z., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Osteoimmunomodulation+for+the+development+of+advanced+bone+biomaterials.">Osteoimmunomodulation for the development of advanced bone biomaterials.</a> Materials Today. 19 (6), 304-321 (2016).</li><li>Ono, T., Takayanagi, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Osteoimmunology+in+bone+fracture+healing.">Osteoimmunology in bone fracture healing.</a> Current Osteoporosis Reports. 15 (4), 367-375 (2017).</li><li>Tsiridis, E., Upadhyay, N., Giannoudis, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+aspects+of+fracture+healing:+Which+are+the+important+molecules?.">Molecular aspects of fracture healing: Which are the important molecules?.</a> Injury. 38, S11-S25 (2007).</li><li>Velasco, M. A., Narvaez-Tovar, C. A., Garzon-Alvarado, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Design,+materials,+and+mechanobiology+of+biodegradable+scaffolds+for+bone+tissue+engineering.">Design, materials, and mechanobiology of biodegradable scaffolds for bone tissue engineering.</a> BioMed Research International. 2015, 729076 (2015).</li><li>Bastian, O., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Systemic+inflammation+and+fracture+healing.">Systemic inflammation and fracture healing.</a> Journal of Leukocyte Biology. 89 (5), 669-673 (2011).</li><li>El-Jawhari, J. J., Jones, E., Giannoudis, P. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+roles+of+immune+cells+in+bone+healing;+what+we+know,+do+not+know+and+future+perspectives.">The roles of immune cells in bone healing; what we know, do not know and future perspectives.</a> Injury. 47 (11), 2399-2406 (2016).</li><li>Changi, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biocompatibility+and+immunogenicity+of+elastin-like+recombinamer+biomaterials+in+mouse+models.">Biocompatibility and immunogenicity of elastin-like recombinamer biomaterials in mouse models.</a> Journal of Biomedical Materials Research. Part A. 106 (4), 924-934 (2018).</li><li>Laczko, J., Levai, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+simple+differential+staining+method+for+semi-thin+sections+of+ossifying+cartilage+and+bone+tissues+embedded+in+epoxy+resin.">A simple differential staining method for semi-thin sections of ossifying cartilage and bone tissues embedded in epoxy resin.</a> Mikroskopie. 31 (1-2), 1-4 (1975).</li><li>Nakayama, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Polarized+osteoclasts+put+marks+of+tartrate-resistant+acid+phosphatase+on+dentin+slices--a+simple+method+for+identifying+polarized+osteoclasts.">Polarized osteoclasts put marks of tartrate-resistant acid phosphatase on dentin slices--a simple method for identifying polarized osteoclasts.</a> Bone. 49 (6), 1331-1339 (2011).</li><li>Deguchi, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+model+of+bone+to+facilitate+measurement+of+adhesion+forces+and+super-resolution+imaging+of+osteoclasts.">In vitro model of bone to facilitate measurement of adhesion forces and super-resolution imaging of osteoclasts.</a> Scientific Reports. 6, 22585 (2016).</li><li>Epstein, N. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+analysis+of+noninstrumented+posterolateral+lumbar+fusions+performed+in+predominantly+geriatric+patients+using+lamina+autograft+and+beta+tricalcium+phosphate.">An analysis of noninstrumented posterolateral lumbar fusions performed in predominantly geriatric patients using lamina autograft and beta tricalcium phosphate.</a> Spine Journal. 8 (6), 882-887 (2008).</li><li>Epstein, N. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Beta+tricalcium+phosphate:+observation+of+use+in+100+posterolateral+lumbar+instrumented+fusions.">Beta tricalcium phosphate: observation of use in 100 posterolateral lumbar instrumented fusions.</a> Spine Journal. 9 (8), 630-638 (2009).</li><li>Kallai, I., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microcomputed+tomography-based+structural+analysis+of+various+bone+tissue+regeneration+models.">Microcomputed tomography-based structural analysis of various bone tissue regeneration models.</a> Nature Protocols. 6 (1), 105-110 (2011).</li><li>Lo, D. 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J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+matrix-induced+osteogenesis+in+rat+calvarial+bone+defects:+II.+Origins+of+bone-forming+cells.">Characterization of matrix-induced osteogenesis in rat calvarial bone defects: II. Origins of bone-forming cells.</a> Calcified Tissue International. 65 (6), 486-493 (1999).</li></ol>

Here, we show a multidisciplinary approach for the preclinical assessment of biocompatibility for representative biomaterials developed for bone regeneration and repair. We tested the responses of OBs, OCs, and the in vivo healing response in a critical bone defect model in mice as well as in vitro and in vivo immune responses. We aimed to demonstrate how the assays work and summarize the data and conclusions derived from the examination of the biomaterials. We show that our strategy generates ...

Bone repair is a complex process that begins with hematoma formation, inflammation, callus formation and then remodeling1,2. However, bone regeneration potential is limited to the size of the bone fracture1,3. For instance, large bone fractures caused by trauma, cancer or osteoporosis may not heal and are termed non-union bone fractures. These bone lesions often require treatment to promote healthy physiological bone repair and regeneration. Currently, autograft and allograft bone transplantation is the approach of choice4 with 2.2 million bone replacement procedures annually5. Though these procedures have a high success rate, there may be complications, for example, limited availability of bone, infection, donor site morbidity, and rejection4. New alternatives for bone tissue engineering are being sought to address these challenges.
The design of biomaterials based on natural or synthetic polymers, bioceramics or metals in combination with cells and bioactive molecules is on the rise6. Our current understanding of physiological bone healing and healing in the context of biomaterials depends on multiple factors such as mechanical properties and multiple local and systemic factors including cells from the circulation and fracture site7,8,9. Biomaterials for bone regeneration aim to promote osteogenicity and osseointegration10 and are ideally biocompatible, biodegradable, and porous (promoting cell migration, oxygen, and nutrients). They also need to be sufficiently strong to support the fracture site to relieve pain. Additionally, inflammatory factors are required to initiate the healing process. However, if the biomaterial induces excessive inflammation and allergic responses, this might limit or inhibit bone healing11,12. Thus, an interdisciplinary approach is necessary to evaluate biomaterials developed for bone repair.
In this study, we present a pre-clinical evaluation of representative materials, 1) Orthovita Vitoss foam which is a commercially available cancellous bone graft substitute consisting of tricalcium phosphate composed of nanometer-sized pure &#946;-tricalcium phosphate (&#946;-TCP) particles and Type 1 bovine collagen (C) (&#946;-TCP/C foam) and 2) &#946;-TCP disks. Here, we illustrate biocompatibility testing of these biomaterials using primary osteoblast (OB) and osteoclast (OC) assays, an in vivo model of bone repair, an immunological assessment comprising in vitro T lymphocyte proliferation and cytokine production, and in vivo immunogenicity and allergenicity, as previously reported13.

biological compatibility profile on biomaterials for bone regeneration

Large non-union bone fractures are a significant challenge in orthopedic surgery. Although auto- and allogeneic bone grafts are excellent for healing such lesions, there are potential complications with their use. Thus, material scientists are developing synthetic, biocompatible biomaterials to overcome these problems. In this study, we present a multidisciplinary platform for evaluating biomaterials for bone repair. We combined expertise from bone biology and immunology to develop a platform including in vitro osteoclast (OC) and osteoblast (OB) assays and in vivo mouse models of bone repair, immunogenicity, and allergenicity. We demonstrate how to perform the experiments, summarize the results, and report on biomaterial biocompatibility. In particular, we tested OB viability, differentiation, and mineralization and OC viability and differentiation in the context of &#946;-tricalcium phosphate (&#946;-TCP) disks. We also tested a &#946;-TCP/Collagen (&#946;-TCP/C) foam which is a commercially available material used clinically for bone repair in a critical-sized calvarial bone defect mouse model to determine the effects on the early phase of bone healing. In parallel experiments, we evaluated immune and allergic responses in mice. Our approach generates a biological compatibility profile of a bone biomaterial with a range of parameters necessary for predicting the biocompatibility of biomaterials used for bone healing and repair in patients.

To assess &#946;-TCP for its effectiveness as a biomaterial for bone repair, we used in vitro and in vivo screening methods. Firstly, we measured the OB responses to the &#946;-TCP disks compared with baseline medium alone controls. Figure 2 demonstrates the OB viability in response to &#946;-TCP disks at 7 and 14 days of culture. Cell viability measured from metabolically active cells in the culture wells was the same for OBs with medium in...

Watch this Scientific Journal Video about Biological Compatibility Profile on Biomaterials for Bone Regeneration at JoVE.com

Biological Compatibility Profile on Biomaterials for Bone Regeneration

The number of novel biomaterials engineered for repairing large bone lesions is continuously expanding with the aim to enhance bone healing and overcome the complications associated with bone transplantation. Here, we present a multidisciplinary strategy for pre-clinical biocompatibility testing of biomaterials for bone repair.

Large non-union bone fractures are a significant challenge in orthopedic surgery. Although auto- and allogeneic bone grafts are excellent for healing such ...

These methods can help answer the key questions in the field of biomaterials. Particularly for bone regeneration. They're used to evaluate the effectiveness of biomaterials and potential immune responses.The main advantage of this multidisciplinary platform is that it provides a range of parameters for predicting biocompatibility of biomaterials used for bone repair. The implications of these in vitro and in vivo bone techniques extend towards other bone disorders. Due to the need for preclinical screening of novel orthopedic biomaterials.The dermatological methodology can provide insights into biomaterials for bone healing, it can also be applied to biomaterial assessments for any other clinical indication. Aspirate culture medium from primary osteoblasts 14 days after the addition of osteogenic mineralization medium. Rinse twice with 0.5 milliliters of 1X PBS.Then fix the cells by adding 0.5 milliliters of 10%buffered formalin solution and incubating at room temperature for 10 minutes. After 10 minutes, aspirate the 10%buffered formalin with a single-use pipet and wash twice with 0.5 milliliters of ultrapure water. Then add 250 microliters of 40 millimolar Alizarin Red S staining solution to the fixed osteoblasts.And incubate the plate at room temperature for 10 minutes on a shaker at 100 shakes per minute. Following the incubation with staining solution, aspirate the staining solution with a single-use pipet and rinse with one milliliter of ultrapure water. Repeat this step five to 10 times until the rinsing solution comes off clear to remove nonspecific staining.After aspirating the final wash, add one milliliter of cold PBS. And incubate the plate at room temperature for 10 minutes on a shaker as before. Next, transfer the stained beta tricalcium phosphate discs to a new well and scan the plates with a flatbed scanner to record mineralization.After image capture, add 250 microliters of 10%cetylpyridinium chloride solution and shake for 15 minutes to extract the Alizarin Red S dye. Next, transfer the solution from the wells to individual 1.5 milliliters tubes and centrifuge at 17, 000 x g for five minutes at room temperature. Dilute the extract with 10%cetylpyridinium chloride solution at a dilution ration of 1:10 to 1:20 in a 1.5 milliliter tube.Then transfer 300 microliters of each diluted sample into the wells of the 96-well plate. Include two blank wells containing only 10%cetylpyridinium chloride. Next, prepare seven Alizarin Red S reference standards ranging from 4 400 micromolar by diluting 40 milliomolar Alizarin Red S staining solution with 10%cetylpyridinium chloride solution to generate a standard curve.Load 300 microliters of each standard into the plate. Lastly, read the absorbents of the samples, blanks, and reference standards at 520 nanometers. Isolate bone marrow osteoplast precursors from the femurs and tibiae of a euthanized mouse by using sterile scissors to remove the legs from the body at the hip joint.Cut the limbs at the knee and ankle joints and remove the soft tissue with sterile scalpel and forceps. Cut off the epiphyses. Insert a 27 gauge needle attached to a syringe filled with one milliliter of bone growth medium into the lumen and flush out the marrow into a six centimeter sterile Petri dish.After repeating this for all femurs and tibiae, transfer the cell suspension to a 50 milliliter conical tube. Wash the six centimeter Petri dish with five milliliters of bone growth medium and transfer it to the same 50 milliliter conical tube. Centrifuge at 350 x g at four degrees Celsius for five minutes.Following centrifugation re-suspend the cells in one milliliter per well of osteoclast differentiation medium. One BALB/c mouse provides sufficient numbers of osteoclast precursors for one 24-well culture plate. Add primary osteoblasts suspended in bone growth medium onto the biomaterial and the controls at 8.8*10^4 cells per square centimeter.Beta tricalcium phosphate discs, controlled bovine bone, and tissue culture plastic are used here. Incubate at 37 degrees celsius in five percent carbon dioxide for 24 hours. After 24 hours, add freshly isolated bone marrow osteoclast precursors and osteoclast differentiation medium to the cultured primary osteoblasts and return to the incubator for five days of culture at 37 degrees celsius at five percent carbon dioxide.Replace the medium with freshly-prepared osteoclast differentiation medium every other day. Then stain osteoclasts for tartrate resistant acid phosphatase to evaluate differentiation. Shave the scalp of an anesthetized eight-week-old BALB/c mouse and clean the surface with 7.5%povidone iodine solution and 70%ethanol.Cover the eyes with ophthalmic ointment to prevent drying during the procedure. Ensure an appropriate level of anesthesia by lack of a reaction to a toe and tail pinch. Then after making a midline sagittal incision remove the paracranium connective tissues above the right parietal bone by scraping it with a scalpel.Then use a sterile dental trephine with a diameter of four millimeters at 2000 rotations per minute to create a critical-sized defect in the right parietal bone. Constantly irrigate the region with sterile saline solution while notching the right parietal bone and cutting through the ectocortext and some endocortex. To prevent damage to the Dera Mater, use a small periosteal elevator to break through the remaining endocortex.Then use forceps to carefully lift the calvarial bone and remove it. The resulting defect should be circular and approximately 3.5 millimeters in diameter. Next, fill the calvarial defect with beta tricalcium phosphate collagen foam, presoaked in sterile PBS.To keep the biomaterial in place, apply 0.5 microliters of tissue adhesive at the end of the defect at two opposite points. Then close the skin with a nonabsorbable suture. Place an anesthetized mouse on its back, shave the abdominal fur and clean the shaved surface with 7.5%povidone iodine solution and 70%ethanol.After making an eight millimeter-long midline incision through the skin along the linea alba of the abdomen, implant PBS soaked biomaterial under the skin. Then suture the skin with a nonabsorbable suture. Eight weeks post-implantation, excise the implantation site with surrounding tissue from the euthanized mouse.This image demonstrates that growth on beta tricalcium phosphate discs shown in open bars does not affect osteoblast viability compared to growth on tissue culture plastic at seven and 14 days of culture. Cultured osteoblasts were stained with Alizarin Red S after 14 days. Mineralization was higher for mineralization medium controls compared to osteoblasts cultured in medium alone.And on beta tricalcium phosphate discs in suspension culture wells. When a surgically-induced critical-sized calvarial defect was left empty, a thin layer covering the entire defect was observed, but no significant bone formation was present at 12 weeks post-operation. In contrast, when the defect contained beta tricalcium phosphate collagen foam, foam remnants surrounded by dense fibrous tissue including some blood vessels and inflammatory cells bridged the defect area without evidence of bone formation.Following subcutaneous beta tricalcium phosphate collagen foam implantation, an inflammatory response with foreign body giant cells was observed on hematoxylin and Eosin-stained sections an evidence of fibrosis on Masson's trichrome stained sections at eight weeks. In contrast, the implantation site of the sham controls had minimal inflammation and no fibrosis. While attempting this procedure it's important to do precise and reproducible notching of the calvarium without hurting the animal.Following this procedure's other methods like osteoclast differentiations assays and high throughput into peritoneal immune models can be preformed in order to answer additional questions like osteoclast's response to biomaterials and type of immune response.

biological-compatibility-profile-on-biomaterials-for-bone-regeneration

Research

JoVE Journal

Bioengineering

Use of Human Perivascular Stem Cells for Bone Regeneration

Human perivascular stem cells (PSCs) can be isolated in sufficient numbers from multiple tissues for purposes of skeletal tissue engineering1-3. PSCs are a FACS-sorted population of 'pericytes' (CD146+CD34-CD45-) and 'adventitial cells' (CD146-CD34+CD45-), each of which we have previously reported to have properties of mesenchymal stem cells. PSCs, like MSCs, are able to undergo osteogenic differentiation, as well as secrete pro-osteogenic cytokines1,2. In the present protocol, we demonstrate the osteogenicity of PSCs in several animal models including a muscle pouch implantation in SCID (severe combined immunodeficient) mice, a SCID mouse calvarial defect and a femoral segmental defect (FSD) in athymic rats. The thigh muscle pouch model is used to assess ectopic bone formation. Calvarial defects are centered on the parietal bone and are standardly 4 mm in diameter (critically sized)8. FSDs are bicortical and are stabilized with a polyethylene bar and K-wires4. The FSD described is also a critical size defect, which does not significantly heal on its own4. In contrast, if stem cells or growth factors are added to the defect site, significant bone regeneration can be appreciated. The overall goal of PSC xenografting is to demonstrate the osteogenic capability of this cell type in both ectopic and orthotopic bone regeneration models.

Human perivascular stem cells (PSCs) are a novel stem cell class for skeletal tissue regeneration similar to mesenchymal stem cells (MSCs). PSCs can be isolated by FACS (fluorescence activated cell sorting) from adipose tissue procured during standard liposuction procedures, then combined with an osteoinductive scaffold to achieve bone formation in vivo.

Human perivascular stem cells (PSCs) can be isolated in sufficient numbers from multiple tissues for purposes of skeletal tissue engineering1-3. PSCs are ...

Polymer Microarrays for High Throughput Discovery of Biomaterials

The discovery of novel biomaterials that are optimized for a specific biological application is readily achieved using polymer microarrays, which allows a combinatorial library of materials to be screened in a parallel, high throughput format1. Herein is described the formation and characterization of a polymer microarray using an on-chip photopolymerization technique 2. This involves mixing monomers at varied ratios to produce a library of monomer solutions, transferring the solution to a glass slide format using a robotic printing device and curing with UV irradiation. This format is readily amenable to many biological assays, including stem cell attachment and proliferation, cell sorting and low bacterial adhesion, allowing the ready identification of 'hit' materials that fulfill a specific biological criterion3-5. Furthermore, the use of high throughput surface characterization (HTSC) allows the biological performance to be correlated with physio-chemical properties, hence elucidating the biological-material interaction6. HTSC makes use of water contact angle (WCA) measurements, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). In particular, ToF-SIMS provides a chemically rich analysis of the sample that can be used to correlate the cell response with a molecular moiety. In some cases, the biological performance can be predicted from the ToF-SIMS spectra, demonstrating the chemical dependence of a biological-material interaction, and informing the development of hit materials5,3.

A description of the formation of a polymer microarray using an on-chip photopolymerization technique. The high throughput surface characterization using atomic force microscopy, water contact angle measurements, X-ray photoelectron spectroscopy and time of flight secondary ion mass spectrometry and a cell attachment assay is also described.

The discovery of novel biomaterials that are optimized for a specific biological application is readily achieved using polymer microarrays, which allows a ...

Evaluation of Biomaterials for Bladder Augmentation using Cystometric Analyses in Various Rodent Models

Renal function and continence of urine are critically dependent on the proper function of the urinary bladder, which stores urine at low pressure and expels it with a precisely orchestrated contraction. A number of congenital and acquired urological anomalies including posterior urethral valves, benign prostatic hyperplasia, and neurogenic bladder secondary to spina bifida/spinal cord injury can result in pathologic tissue remodeling leading to impaired compliance and reduced capacity1. Functional or anatomical obstruction of the urinary tract is frequently associated with these conditions, and can lead to urinary incontinence and kidney damage from increased storage and voiding pressures2. Surgical implantation of gastrointestinal segments to expand organ capacity and reduce intravesical pressures represents the primary surgical treatment option for these disorders when medical management fails3. However, this approach is hampered by the limitation of available donor tissue, and is associated with significant complications including chronic urinary tract infection, metabolic perturbation, urinary stone formation, and secondary malignancy4,5.
Current research in bladder tissue engineering is heavily focused on identifying biomaterial configurations which can support regeneration of tissues at defect sites. Conventional 3-D scaffolds derived from natural and synthetic polymers such as small intestinal submucosa and poly-glycolic acid have shown some short-term success in supporting urothelial and smooth muscle regeneration as well as facilitating increased organ storage capacity in both animal models and in the clinic6,7. However, deficiencies in scaffold mechanical integrity and biocompatibility often result in deleterious fibrosis8, graft contracture9, and calcification10, thus increasing the risk of implant failure and need for secondary surgical procedures. In addition, restoration of normal voiding characteristics utilizing standard biomaterial constructs for augmentation cystoplasty has yet to be achieved, and therefore research and development of novel matrices which can fulfill this role is needed.
In order to successfully develop and evaluate optimal biomaterials for clinical bladder augmentation, efficacy research must first be performed in standardized animal models using detailed surgical methods and functional outcome assessments. We have previously reported the use of a bladder augmentation model in mice to determine the potential of silk fibroin-based scaffolds to mediate tissue regeneration and functional voiding characteristics.11,12 Cystometric analyses of this model have shown that variations in structural and mechanical implant properties can influence the resulting urodynamic features of the tissue engineered bladders11,12. Positive correlations between the degree of matrix-mediated tissue regeneration determined histologically and functional compliance and capacity evaluated by cystometry were demonstrated in this model11,12. These results therefore suggest that functional evaluations of biomaterial configurations in rodent bladder augmentation systems may be a useful format for assessing scaffold properties and establishing in vivo feasibility prior to large animal studies and clinical deployment. In the current study, we will present various surgical stages of bladder augmentation in both mice and rats using silk scaffolds and demonstrate techniques for awake and anesthetized cystometry.

Surgical stages of bladder augmentation are described using 3-D scaffolds in murine and rat models. To test the efficacy of biomaterial configurations for use in bladder augmentation, techniques for both awake and anesthetized cystometry are presented.

Renal function and continence of urine are critically dependent on the proper function of the urinary bladder, which stores urine at low pressure and ...

Micro-particle Image Velocimetry for Velocity Profile Measurements of Micro Blood Flows

Micro-particle image velocimetry (&mu;PIV) is used to visualize paired images of micro particles seeded in blood flows. The images are cross-correlated to give an accurate velocity profile. A protocol is presented for &mu;PIV measurements of blood flows in microchannels. At the scale of the microcirculation, blood cannot be considered a homogeneous fluid, as it is a suspension of flexible particles suspended in plasma, a Newtonian fluid. Shear rate, maximum velocity, velocity profile shape, and flow rate can be derived from these measurements. Several key parameters such as focal depth, particle concentration, and system compliance, are presented in order to ensure accurate, useful data along with examples and representative results for various hematocrits and flow conditions.

Micro-particle image velocimetry (&mu;PIV) is used to visualize paired images of micro particles seeded in blood flows which are cross-correlated to give an accurate velocity profile. Shear rate, maximum velocity, velocity profile shape, and flow rate, each of which has clinical applications, can be derived from these measurements.

Micro-particle image velocimetry (&mu;PIV) is used to visualize paired images of micro particles seeded in blood flows. The images are cross-correlated to ...

In situ Compressive Loading and Correlative Noninvasive Imaging of the Bone-periodontal Ligament-tooth Fibrous Joint

This study demonstrates a novel biomechanics testing protocol. The advantage of this protocol includes the use of an in situ loading device coupled to a high resolution X-ray microscope, thus enabling visualization of internal structural elements under simulated physiological loads and wet conditions. Experimental specimens will include intact bone-periodontal ligament (PDL)-tooth fibrous joints. Results will illustrate three important features of the protocol as they can be applied to organ level biomechanics: 1) reactionary force vs. displacement: tooth displacement within the alveolar socket and its reactionary response to loading, 2) three-dimensional (3D) spatial configuration and morphometrics: geometric relationship of the tooth with the alveolar socket, and 3) changes in readouts 1 and 2 due to a change in loading axis, i.e. from concentric to eccentric loads. Efficacy of the proposed protocol will be evaluated by coupling mechanical testing readouts to 3D morphometrics and overall biomechanics of the joint. In addition, this technique will emphasize on the need to equilibrate experimental conditions, specifically reactionary loads prior to acquiring tomograms of fibrous joints. It should be noted that the proposed protocol is limited to testing specimens under ex vivo conditions, and that use of contrast agents to visualize soft tissue mechanical response could lead to erroneous conclusions about tissue and organ-level biomechanics.

In situ Compressive Loading and Correlative Noninvasive Imaging of the Bone-periodontal Ligament-tooth Fibrous Joint

In this study, the use of an in situ loading device coupled with micro-X-ray computed tomography for fibrous joint biomechanics will be discussed. Experimental readouts identifiable with an overall change in joint biomechanics will include: 1) reactionary force vs. displacement, i.e. tooth displacement within the alveolar socket and its reactionary response to loading, 2) three-dimensional (3D) spatial configuration and morphometrics, i.e.&#160;geometric relationship of the tooth with the alveolar socket, and 3) changes in readouts 1 and 2 due to a change in loading axis, i.e. concentric or eccentric loads.

This study demonstrates a novel biomechanics testing protocol. The advantage of this protocol includes the use of an in situ loading device coupled to a ...

An Improved Mechanical Testing Method to Assess Bone-implant Anchorage

Recent advances in material science have led to a substantial increase in the topographical complexity of implant surfaces, both on a micro- and a nano-scale. As such, traditional methods of describing implant surfaces -&#160;namely numerical determinants of surface roughness -&#160;are inadequate for predicting in vivo performance. Biomechanical testing provides an accurate and comparative platform to analyze the performance of biomaterial surfaces. An improved mechanical testing method to test the anchorage of bone to candidate implant surfaces is presented. The method is applicable to both early and later stages of healing and can be employed for any range of chemically or mechanically modified surfaces -&#160;but not smooth surfaces. Custom rectangular implants are placed bilaterally in the distal femora of male Wistar rats and collected with the surrounding bone. Test specimens are prepared and potted using a novel breakaway mold and the disruption test is conducted using a mechanical testing machine. This method allows for alignment of the disruption force exactly perpendicular, or parallel, to the plane of the implant surface, and provides an accurate and reproducible means for isolating an exact peri-implant region for testing.

An improved method to mechanically test bone anchorage to candidate implant surfaces is presented. This method allows for alignment of the disruption force exactly perpendicular, or parallel, to the plane of the implant surface, and provides an accurate means to direct the disruption forces to an exact peri-implant region.

Recent advances in material science have led to a substantial increase in the topographical complexity of implant surfaces, both on a micro- and a ...

A Full Skin Defect Model to Evaluate Vascularization of Biomaterials In Vivo

Insufficient vascularization is considered to be one of the main factors limiting the clinical success of tissue-engineered constructs. In order to evaluate new strategies that aim at improving vascularization, reliable methods are required to make the in-growth of new blood vessels into bio-artificial scaffolds visible and quantify the results. Over the past couple of years, our group has introduced a full skin defect model that enables the direct visualization of blood vessels by transillumination and provides the possibility of quantification through digital segmentation. In this model, one surgically creates full skin defects in the back of mice and replaces them with the material tested. Molecules or cells of interest can also be incorporated in such materials to study their potential effect. After an observation time of one&#8217;s own choice, materials are explanted for evaluation. Bilateral wounds provide the possibility of making internal comparisons that minimize artifacts among individuals as well as of decreasing the number of animals needed for the study. In comparison to other approaches, our method offers a simple, reliable and cost effective analysis. We have implemented this model as a routine tool to perform high-resolution screening when testing vascularization of different biomaterials and bio-activation approaches.

A Full Skin Defect Model to Evaluate Vascularization of Biomaterials In Vivo

Vascularization is key to approaches in successful tissue engineering. Therefore, reliable technologies are required to evaluate the development of vascular networks in tissue-constructs. Here we present a simple and cost-effective method to visualize and quantify vascularization in vivo.

Insufficient vascularization is considered to be one of the main factors limiting the clinical success of tissue-engineered constructs. In order to ...

A Coupled Experiment-finite Element Modeling Methodology for Assessing High Strain Rate Mechanical Response of Soft Biomaterials

This study offers a combined experimental and finite element (FE) simulation approach for examining the mechanical behavior of soft biomaterials (e.g. brain, liver, tendon, fat, etc.) when exposed to high strain rates. This study utilized a Split-Hopkinson Pressure Bar (SHPB) to generate strain rates of 100-1,500 sec-1. The SHPB employed a striker bar consisting of a viscoelastic material (polycarbonate). A sample of the biomaterial was obtained shortly postmortem and prepared for SHPB testing. The specimen was interposed between the incident and transmitted bars, and the pneumatic components of the SHPB were activated to drive the striker bar toward the incident bar. The resulting impact generated a compressive stress wave (i.e. incident wave) that traveled through the incident bar. When the compressive stress wave reached the end of the incident bar, a portion continued forward through the sample and transmitted bar (i.e. transmitted wave) while another portion reversed through the incident bar as a tensile wave (i.e. reflected wave). These waves were measured using strain gages mounted on the incident and transmitted bars. The true stress-strain behavior of the sample was determined from equations based on wave propagation and dynamic force equilibrium. The experimental stress-strain response was three dimensional in nature because the specimen bulged. As such, the hydrostatic stress (first invariant) was used to generate the stress-strain response. In order to extract the uniaxial (one-dimensional) mechanical response of the tissue, an iterative coupled optimization was performed using experimental results and Finite Element Analysis (FEA), which contained an Internal State Variable (ISV) material model used for the tissue. The ISV material model used in the FE simulations of the experimental setup was iteratively calibrated (i.e. optimized) to the experimental data such that the experiment and FEA strain gage values and first invariant of stresses were in good agreement.

The current study prescribes a coupled experiment-finite element simulation methodology to obtain the uniaxial dynamic mechanical response of soft biomaterials (brain, liver, tendon, fat, etc.). The multiaxial experimental results that arose because of specimen bulging obtained from Split-Hopkinson Pressure Bar testing were rendered to a uniaxial true stress-strain behavior when simulated through iterative optimization of the finite element analysis of the biomaterial.

This study offers a combined experimental and finite element (FE) simulation approach for examining the mechanical behavior of soft biomaterials (e.g. ...

Engineering 3D Cellularized Collagen Gels for Vascular Tissue Regeneration

Synthetic materials are known to initiate clinical complications such as inflammation, stenosis, and infections when implanted as vascular substitutes. Collagen has been extensively used for a wide range of biomedical applications and is considered a valid alternative to synthetic materials due to its inherent biocompatibility (i.e., low antigenicity, inflammation, and cytotoxic responses). However, the limited mechanical properties and the related low hand-ability of collagen gels have hampered their use as scaffold materials for vascular tissue engineering. Therefore, the rationale behind this work was first to engineer cellularized collagen gels into a tubular-shaped geometry and second to enhance smooth muscle cells driven reorganization of collagen matrix to obtain tissues stiff enough to be handled.
The strategy described here is based on the direct assembling of collagen and smooth muscle cells (construct) in a 3D cylindrical geometry with the use of a molding technique. This process requires a maturation period, during which the constructs are cultured in a bioreactor under static conditions (without applied external dynamic mechanical constraints) for 1 or 2 weeks. The &#8220;static bioreactor&#8221; provides a monitored and controlled sterile environment (pH, temperature, gas exchange, nutrient supply and waste removal) to the constructs. During culture period, thickness measurements were performed to evaluate the cells-driven remodeling of the collagen matrix, and glucose consumption and lactate production rates were measured to monitor the cells metabolic activity. Finally, mechanical and viscoelastic properties were assessed for the resulting tubular constructs. To this end, specific protocols and a focused know-how (manipulation, gripping, working in hydrated environment, and so on) were developed to characterize the engineered tissues.

In this work, we present a technique for the rapid fabrication of living vascular tissues by direct culturing of collagen, smooth muscle cells and endothelial cells. In addition, a new protocol for the mechanical characterization of engineered vascular tissues is described.

Synthetic materials are known to initiate clinical complications such as inflammation, stenosis, and infections when implanted as vascular substitutes. ...

Sandwich-like Microenvironments to Harness Cell/Material Interactions

Cell culture has been traditionally carried out on bi-dimensional (2D) substrates where cells adhere using ventral receptors to the biomaterial surface. However in vivo, most of the cells are completely surrounded by the extracellular matrix (ECM), resulting in a three-dimensional (3D) distribution of receptors. This may trigger differences in the outside-in signaling pathways and thus in cell behavior.
This article shows that stimulating the dorsal receptors of cells already adhered to a 2D substrate by overlaying a film of a new material (a sandwich-like culture) triggers important changes with respect to standard 2D cultures. Furthermore, the simultaneous excitation of ventral and dorsal receptors shifts cell behavior closer to that found in 3D environments. Additionally, due to the nature of the system, a sandwich-like culture is a versatile tool that allows the study of different parameters in cell/material interactions, e.g., topography, stiffness and different protein coatings at both the ventral and dorsal sides. Finally, since sandwich-like cultures are based on 2D substrates, several analysis procedures already developed for standard 2D cultures can be used normally, overcoming more complex procedures needed for 3D systems.

The following protocol describes the procedure to assemble sandwich-like cultures to be used as an intermediate stage between bi-dimensional (2D) and three-dimensional (3D) cellular environments. The engineered systems can have applications in microscopy, biomechanics, biochemistry and cell biology assays.

Cell culture has been traditionally carried out on bi-dimensional (2D) substrates where cells adhere using ventral receptors to the biomaterial surface. ...