Antigenicity and immunogenicity of collagen

Effect of dentin depth on hybridization quality using different bonding tactics in vivo

OBJECTIVES

Incomplete resin infiltration and polymerization of adhesive contributed to nanoleakage formation. This study tested the null hypothesis that adoption of different bonding tactics and dentine depth will not affect hybridization quality in vivo.

METHODS

Class V cavities were prepared on the labial/buccal surface of monkey teeth. They were bonded by Single Bond (a two-step total-etch adhesive), Clearfil SE Bond (a two-step self-etch adhesive), or Clearfil S(3) Bond (an all-in-one self-etch adhesive). Combined nanoleakage analysis and quantitative immunolabeling evaluation were carried out in the hybrid layer formed in both cervical superficial and deep dentine.

RESULTS

Single Bond showed reticular and spotted nanoleakage while Clearfil SE Bond and Clearfil S(3) Bond presented only a spotted one. While Single Bond showed increased concentration of labeling of type I collagen within the deep part of the hybrid layer, two self-etch adhesives-Clearfil SE Bond and Clearfil S(3) Bond revealed a homogeneous labeling pattern, even if the latter presented a significantly increased labeling index in deep dentine.

CONCLUSIONS

Different bonding tactics showed different nanoleakage patterns and immunolabeling index, and was influenced by dentine depth at different levels in vivo.

Bespoke human hypertrophic chondrocytic cell lines provide the osteoinductive signals required for vascularized bone formation

Hypertrophic cartilage provides the morphological and biochemical template for orchestrating bone growth. To produce a bone-inductive material such as hypertrophic cartilage for clinical use, we have conditionally immortalized hypertrophic chondrocytic cells from human femur and expanded them in vitro through more than 145 divisions. The clonal cell lines generated by this process consistently express signals that induce both rat and human marrow cells to differentiate in vitro into osteoblastic cells. Further, implantation of the cell-free extracellular matrix from the immortalized chondrocytic cells causes vascularized bone to form in vivo in bony defects, but not in ectopic sites such as skeletal muscle. This study shows that molecular techniques can be used to generate bespoke human cell lines for bone tissue engineering. It also demonstrates that matrix material generated from human immortalized hypertrophic chondrocytic cells may provide an abundant, efficacious, and safer alternative to bone autograft--the currently preferred material for fracture repair.

Design and fabrication of sub-mm-sized modules containing encapsulated cells for modular tissue engineering

We have proposed modular tissue engineering as a strategy to construct vascularized tissues containing multiple cell types. To create a modular construct, instead of seeding a preformed scaffold, cells were encapsulated within sub-mm modules, and the outer surface of these modules was covered with a layer of endothelial cells. Modules were then added to a larger structure (here by filling a tube) to form the modular construct. Through a systematic process of materials selection, collagen, human umbilical vein endothelial cells (HUVECs), and HepG2 cells, a human hepatoma cell line, were identified as suitable components for module formation, at least for initial studies. A method, which involved cutting and shaping the modules within a tubular mold, was developed to fabricate sub-mm, cylindrical, collagen modules that contained viable, functioning HepG2 cells and that could be seeded with a surface layer of HUVECs. Module dimensions were reproducible and easily altered in a controlled fashion if desired. The module fabrication process developed here not only generated modules suitable for the assembly of a prototype modular construct, but also could potentially be used more generally for other applications for which the goal is to form submm-diameter cylinders from soft hydrogels.

Natural-origin polymers as carriers and scaffolds for biomolecules and cell delivery in tissue engineering applications

The present paper intends to overview a wide range of natural-origin polymers with special focus on proteins and polysaccharides (the systems more inspired on the extracellular matrix) that are being used in research, or might be potentially useful as carriers systems for active biomolecules or as cell carriers with application in the tissue engineering field targeting several biological tissues. The combination of both applications into a single material has proven to be very challenging though. The paper presents also some examples of commercially available natural-origin polymers with applications in research or in clinical use in several applications. As it is recognized, this class of polymers is being widely used due to their similarities with the extracellular matrix, high chemical versatility, typically good biological performance and inherent cellular interaction and, also very significant, the cell or enzyme-controlled degradability. These biocharacteristics classify the natural-origin polymers as one of the most attractive options to be used in the tissue engineering field and drug delivery applications.

Tissue Engineering Bone Formation in Novel Recombinant Human Bone Morphogenic Protein 2–Atelocollagen Composite Scaffolds

BACKGROUND

Bone morphogenic proteins (BMPs) are important bone-induction factors, and the development of a suitable carrier for BMPs is a critical step to achieve osteoinductive function. The aims of the present study were to evaluate, at the cellular and molecular levels, the feasibility of recombinant human BMP-2 (rhBMP-2)-collagen composite scaffold and its efficiency for carrying BMP-2 in ectopic bone formation in rats.

METHODS

Scaffolds with (test) or without rhBMP-2 (control) were made and implanted into the calf muscle of 16 5-week-old rats. The tissue responses to the scaffolds were examined by histology. Masson's trichrome and von Kossa stainings were performed to examine collagen matrix deposition and calcification at 3, 7, 10, and 14 days. Expressions of bone phenotypic markers, alkaline phosphatase, osteocalcin, osteopontin, and bone sialoprotein were detected by reverse transcription-polymerase chain reaction and immunohistochemistry.

RESULTS

No detectable adverse responses were noted around the implanted scaffolds, and the area of the resorbed scaffold had been replaced by young connective tissue by 3 to 7 days in both groups. In the rhBMP-2 composite scaffold, collagen matrix deposition was found in the implanted site on day 7 and initial signs of endochondral differentiation also appeared. Mineralization and the expressions of key bone proteins were demonstrated in chondroblasts and osteoblasts at 7 to 14 days. Molecular cascades of bone induction were not shown in control specimens.

CONCLUSION

The rhBMP-2-atelocollagen scaffold showed excellent biocompatibility and possessed a bone-inducing capacity in rat within 2 weeks, and, thus, may provide a potential application in tissue engineering of bone tissue.

Cell responses to biomimetic protein scaffolds used in tissue repair and engineering

Basic science research in tissue engineering and regenerative medicine aims to investigate and understand the deposition, growth, and remodeling of tissues by drawing together approaches from a range of disciplines. This review discusses approaches that use biomimetic proteins and cellular therapies, both in the development of clinical products and of model platforms for scientific investigation. Current clinical approaches to repairing skin, bone, nerve, heart valves, blood vessels, ligaments, and tendons are described and their limitations identified. Opportunities and key questions for achieving clinical goals are discussed through commonly used examples of biomimetic scaffolds: collagen, fibrin, fibronectin, and silk. The key questions addressed by three-dimensional culture models, biomimetic materials, surface chemistry, topography, and their interaction with cells in terms of durotaxis, mechano-regulation, and complex spatial cueing are reviewed to give context to future strategies for biomimetic technology.

Chondrogenesis of human periosteum-derived progenitor cells in atelocollagen

Periosteum-derived progenitor cells (PDPCs) could be differentiated into cartilage using atelocollagen as a carrier and in the presence of transforming growth factor-beta3 (TGF-beta3). Chondrogenesis was verified by RT-PCR and Western blotting. Expression of the type II collagen mRNA was found from the differentiated PDPCs in atelocollagen 3 weeks after chondrogenic induction. The chondrogenic potential of the PDPCs was also verified by histochemical staining for type II collagen protein. Increased production of glycosaminoglycan shows that the PDPCs in atelocollagen could differentiate into chondrocytes under a chondrogenic environment. PDPCs can therefore be used as a cell source for cell-based therapies targeted toward the articular cartilage of the knee.

Effects of citric acid and EDTA conditioning on exposed root dentin: An immunohistochemical analysis of collagen and proteoglycans

OBJECTIVE

Preservation of structural and biochemical properties of the root dentin matrix is crucial to favor healing and regenerative periodontal processes. Aim of this study was to evaluate the biochemical characteristics of collagen and chondroitin sulphate of root dentin surfaces exposed by periodontal disease after acid conditioning by means of an immunohistochemical technique.

DESIGN

Human teeth scheduled for extraction due to periodontal reason were submitted to: (A) scaling and root planning; (B) ultrasonic instrumentation; (C) no instrumentation. Teeth were then exposed to: (1) 10% citric acid; (2) 17% EDTA; (3) no etching. A double immunolabeling technique was performed to identify type-I collagen and proteoglycans and analyzed under FEI-SEM.

RESULTS

Use of 10% citric acid revealed intense labeling for collagen fibrils and proteoglycans; lower labeling was found after EDTA conditioning. Unetched specimens showed residual smear layer on the dentin surface resulting in no evident surface labeling.

CONCLUSIONS

This study supports the hypothesis that manual or ultrasonic instrumentation alone is not able to expose the sound dentin matrix, whereas a subsequent acidic conditioning exposes collagen fibrils and associated proteoglycans. The immunohistochemical technique revealed that despite their acidity, both citric acid and EDTA were able to preserve the structural and biochemical properties of the exposed dentin matrix.

Reduced antigenicity of type I collagen and proteoglycans in sclerotic dentin

Antigenic alterations to the dentin organic matrix may be detected by an immunohistochemical approach. We hypothesized that alterations in the antigenicity of type I collagen and proteoglycans occur in sclerotic dentin under caries lesions. Transverse sections were prepared from carious teeth in the sclerotic zone and normal hard dentin. A double-immunolabeling technique was performed on these sections, with anti-type I collagen and anti-chondroitin 4/6 sulfate monoclonal primary antibodies. We used gold-conjugated secondary antibodies to visualize the distribution of intact collagen fibrils and proteoglycans by high-resolution SEM. For sclerotic dentin, labeling densities were 19.57 +/- 3.01/microm2 for collagen and 9.84 +/- 2.62/microm2 for proteoglycans. For normal hard dentin, values were 35.20 +/- 2.73/microm2 and 17.03 +/- 1.98/microm2, respectively. Distribution of intact collagen fibrils and proteoglycans in sclerotic dentin was significantly lower than in normal hard dentin. Reductions in antigenicity from the organic matrix of sclerotic dentin under caries lesions raise concern about the potential of intrafibrillar remineralization.

Two Techniques for the Preparation of Cell-Scaffold Constructs Suitable for Sinus Augmentation: Steps into Clinical Application

The objective of this clinical trial was the analysis of 2 methods for engineering of autologous bone grafts for maxillary sinus augmentation with secondary implant placement. Group 1 (8 patients, 12 sinuses): cells of mandibular periosteum were cultured in a good manufacturing practice laboratory (2 weeks) with autologous serum and then transferred onto a collagen matrix. After another week, these composites were transplanted into the sinuses. In group 2A (2 patients, 3 sinuses), cells of maxillary bone were cultivated with autologous serum for 2 weeks, seeded onto natural bone mineral (NBM, diameter [Ø] = 8 mm) blocks, and cultivated for another 1.5 months. These composites were transplanted into the sinuses. Group 2B (control, 3 patients, 5 sinuses) received NBM blocks alone. In the course of implant placement 6 (group 1) and 8 (group 2) months later, core biopsy were taken. Clinical follow-up period was 1 to 2.5 years in group 1 and approximately 7 years in groups 2A and 2B. New vital bone was found in all cases at median densities of 38% (n = 12) in group 1, 32% in group 2A (n = 3), and 25% in group 2B (n = 5). Differences between group 1 and 2B as well as 2A and 2B were statistically significant ( p = 0.025). No adverse effects were seen. All methods described were capable of creating new bone tissue with sufficient stability for successful implant placement.

Collagen Scaffolds Reinforced with Biomimetic Composite Nano-Sized Carbonate-Substituted Hydroxyapatite Crystals and Shaped by Rapid Prototyping to Contain Internal Microchannels

The next generation of tissue engineering scaffolds will be made to accommodate blood vessels and nutrient channels to support cell survival deep in the interior of the scaffolds. To this end, we have developed a method that incorporates microchannels to permit the flow of nutrient-rich media through collagen-based scaffolds. The scaffold matrix comprises nano-sized carbonate-substituted hydroxyapatite (HA) crystals internally precipitated in collagen fibers. The scaffold therefore mimics many of the features found in bone. A biomimetic precipitation technique is used whereby a collagen membrane separates reservoirs of calcium and phosphate solutions. The collision of calcium and phosphate ions diffusing from opposite directions results in the precipitation of mineral within the collagen membrane. Transmission electron microscopy analysis showed the dimension of the mineral crystals to be approximately 180 x 80 x 20 nm, indicating that the crystals reside in the intermicrofibril gaps. Electron diffraction indicated that the mineral was in the HA phase, and infrared spectroscopy confirmed type A carbonate substitution. The collagen-HA membrane is then used to make 3-dimensional (3D) scaffolds: the membrane is shredded and mixed in an aqueous-based collagen dispersion and processed using the critical point drying method. Adjusting the pH of the dispersion to 5.0 before mixing the composite component preserved the nano-sized carbonate-substituted HA crystals. Branching and interconnecting microchannels in the interior of the scaffolds are made with a sacrificial mold manufactured by using a 3D wax printer. The 3D wax printer has been modified to print the mold from biocompatible materials. Appropriately sized microchannels within collagen-HA scaffolds brings us closer to fulfilling the mass transport requirements for osteogenic cells living deep within the scaffold.

Interventional Atrial Septal Defect Closure Using a Totally Bioresorbable Occluder Matrix

OBJECTIVES

We sought to test the hypothesis that interventional atrial septal defect (ASD) closure can be performed safely and effectively using a bioresorbable occluder matrix.

BACKGROUND

The ideal septal occluder scaffold should promote the healthiest and most complete healing response while eventually facilitating the full resorption of the material and leaving "native" tissue behind, thus minimizing the potential for future complications from chronic foreign body and maintaining the possibility for later unobstructed transseptal access to the left atrium.

METHODS

The STARFlex occluders (NMT Medical Inc., Boston, Massachusetts) were modified by substituting the conventional polyester fabric for a bioengineered, acellular type-I collagen matrix derived from porcine submucosa with a heparin-coated surface (BioSTAR occluder, NMT Medical Inc.). Comparative transcatheter closure of ASDs was performed in young sheep (n = 36). Gross pathology and histopathology were obtained after follow-up periods ranging from 7 days to 2 years.

RESULTS

The STARFlex (control) devices were encapsulated time-dependently by ingrown fibrous tissue. Histology showed a mild but chronically persisting foreign body reaction. By contrast, BioSTAR devices exhibited a mild-to-moderate transient cellular immune response. Heparin coating of the BioSTAR surface improved the biocompatibility of the device by reducing surface thrombogencity. A remodeling process of the collagen scaffold, starting after 30 days in vivo, resulted in the full replacement of the matrix by host tissue after 2 years of follow-up.

CONCLUSIONS

The BioSTAR device is the first septal occluder with a totally bioresorbable matrix that is fully replaced by host tissue during the healing process. The promising results of this study support testing of the BioSTAR device in clinical trials.

Self-assembly of synthetic collagen triple helices

Collagen is the most abundant protein in animals and the major component of connective tissues. Although collagen isolated from natural sources has long served as the basis for some biomaterials, natural collagen is difficult to modify and can engender pathogenic and immunological side effects. Collagen comprises a helix of three strands. Triple helices derived from synthetic peptides are much shorter (<10 nm) than natural collagen (approximately 300 nm), limiting their utility. Here, we describe the synthesis of short collagen fragments in which the three strands are held in a staggered array by disulfide bonds. Data from CD spectroscopy, dynamic light scattering, analytical ultracentrifugation, atomic force microscopy, and transmission electron microscopy indicate that these "sticky-ended" fragments self-assemble via intermolecular triple-helix formation. The resulting fibrils resemble natural collagen, and some are longer (>400 nm) than any known collagen. We anticipate that our self-assembly strategy can provide synthetic collagen-mimetic materials for a variety of applications.

Fibrillar assembly and stability of collagen coating on titanium for improved osteoblast responses

Collagen, as a major constituent of human connective tissues, has been regarded as one of the most important biomaterials. As a coating moiety on Ti hard-tissue implants, the collagen has recently attracted a great deal of attention. This article reports the effects of fibrillar assembly and crosslinking of collagen on its chemical stability and the subsequent osteoblastic responses. The fibrillar self-assembly of collagen was carried out by incubating acid-dissolved collagen in an ionic-buffered medium at 37 degrees C. The degree of assembly was varied with the incubation time and monitored by the turbidity change. The differently assembled collagen was coated on the Ti and crosslinked with a carbodiimide derivative. The partially assembled collagen contained fibrils with varying diameters as well as nonfibrillar aggregates. On the other hand, the fully assembled collagen showed the complete formation of fibrils with uniform diameters of approximately 100-200 nm with periodic stain patterns within the fibrils, which are typical of native collagen fibers. Through this fibrillar assembly, the collagen coating had significantly improved chemical stability in both the saline and collagenase media. The subsequent crosslinking step also improved the stability of the collagen coating, particularly in the unassembled collagen. The fibrillar assembly and the crosslinking of collagen significantly influenced the osteoblastic cell responses. Without the assembly, the collagen layer on Ti adversely affected the cell attachment and proliferation. However, those cellular responses were improved significantly when the collagen was assembled to fibrils and the assembly degree was increased. After crosslinking the collagen coating, these cellular responses were significantly enhanced in the case of the unassembled collagen but were not altered much in the assembled collagen. Based on these observations, it is suggested that the fibrillar assembly and the crosslinking of collagen require careful considerations in the collagen administration as a coating moiety.

Gene Therapy Progress and Prospects: In tissue engineering

Tissue engineering (TE) has existed for several years as an area spanning many disciplines, including medicine and engineering. The use of stem cells as a biological basis for TE coupled with advances in materials science has opened up an entirely new chapter in medicine and holds the promise of major contributions to the repair, replacement and regeneration of damaged tissues and organs. In this article, we review the spectrum of stem cells and scaffolds being investigated for their potential applications in medicine.

Regenerative effects of transplanting mesenchymal stem cells embedded in atelocollagen to the degenerated intervertebral disc

Intervertebral disc (IVD) degeneration, a common cause of low back pain in humans, is a relentlessly progressive phenomenon with no currently available effective treatment. In an attempt to solve this dilemma, we transplanted autologous mesenchymal stem cells (MSCs) from bone marrow into a rabbit model of disc degeneration to determine if stem cells could repair degenerated IVDs. LacZ expressing MSCs were transplanted to rabbit L2-L3, L3-L4 and L4-L5 IVDs 2 weeks after induction of degeneration. Changes in disc height by plain radiograph, T2-weighted signal intensity in magnetic resonance imaging (MRI), histology, immunohistochemistry and matrix associated gene expressions were evaluated between normal controls (NC) without operations, sham operated with only disc degeneration being induced, and MSC-transplanted animals for a 24-week period. Results showed that after 24 weeks post-MSC transplantation, degenerated discs of MSC-transplanted group animals regained a disc height value of about 91%, MRI signal intensity of about 81%, compared to NC group discs. On the other hand, sham-operated group discs demonstrated the disc height value of about 67% and MRI signal intensity of about 60%. Macroscopic and histological evaluations confirmed relatively preserved nucleus with circular annulus structure in MSC-transplanted discs compared to indistinct structure seen in sham. Restoration of proteoglycan accumulation in MSC-transplanted discs was suggested from immunohistochemistry and gene expression analysis. These data indicate that transplantation of MSCs effectively led to regeneration of IVDs in a rabbit model of disc degeneration as suggested in our previous pilot study. MSCs may serve as a valuable resource in cell transplantation therapy for degenerative disc disease.