Next-Generation Biomaterials for Bone & Periodontal Regeneration

Richard J. Miron, Yufeng Zhang

• Publisher: Quintessence Publishing Co, Inc
• Year: 2019
• ISBN:
  9780867158359
• Topic: Medicina
• Subtopic: Odontología

New and innovative biomaterials are being discovered or created in laboratories at an unprecedented rate, but many of them remain entirely foreign to practicing clinicians. This book addresses this gap in knowledge by summarizing some of the groundbreaking research performed to date on this topic and providing case examples of these biomaterials at work. The book begins with a review of the biologic background and applications of bone grafting materials utilized in dentistry. The principles of guided tissue and bone regeneration are covered in detail, including many recent advancements in barrier membrane technologies as well as use of platelet-rich fibrin and various growth factors, and many next-generation materials that will optimize future bone and periodontal regeneration are presented. The final chapter is designed to help clinicians select appropriate biomaterials for each specific regenerative protocol. Much like one implant size and shape cannot be utilized for every indication in implant dentistry, one bone grafting material, barrier membrane, or growth factor cannot maximize regenerative outcomes in all clinical situations. This textbook teaches clinicians how to utilize biomaterials in an appropriate, predictable, and evidence-based manner. 384 pp; 960 illus; 2019

05

Next-Generation Natural Bovine Bone Mineral Grafting Material with Integrated Atelocollagen Type 1

Richard J. Miron / Mustafa Abd El Raouf / Yufeng Zhang / Andrea Grassi / Ferdinando D’Avenia

Summary

While typically all collagen and/or growth factors are removed during the processing of xenografts (commonly referred to as deproteinized), recently the development of a natural bone mineral containing atelocollagen type 1 has been proposed that utilizes atelopeptidation and lyophilization technologies. This processing technique modifies the collagen components within the bone structure to nonimmunogenic atelocollagen. Treatment therefore does not require heat (thermal) processing when manufactured, a process that has been shown to negatively impact the natural crystalline microstructure of hydroxyapatite, thereby causing ceramization and destruction of remaining collagenous and noncollagenous proteins. Thereafter, the lyophilization technique involves the evaporation of water contained in the graft by sublimation, in which a previously frozen material is placed in a vacuum that turns ice directly into vapor. These xenografts have been shown to preserve lyophilized collagen with lower humidity, making the bone matrix more hydrophilic. Following sterilization, they contain roughly 2% moisture, 65% to 75% hydroxyapatite, 25% to 35% atelocollagen, and up to 0.1% noncollagenous proteins. This chapter introduces atelocollagenized bovine bone mineral (ABBM) grafts, presents some preclinical data from in vitro cell studies as well as results from animal models, and demonstrates its favorable use in clinical practice.

FIG 5-1 (a and b) Processing steps from procollagen to atelocollagen. During the processing, N- and C-propeptides are cleaved by pepsin to become atelocollagen. This atelo-collagen is more immunogenic toward the human body.

While the role of bone grafting materials was initially described as a passive structural-support replacement material, more recently the aim has gradually evolved toward one that is better able to support more dynamic tissue interactions that favor tissue regeneration.¹ To that end, recently a new class of xenograft has been engineered with integrated atelocollagenized bovine bone mineral (ABBM). The processing techniques involved are more natural due to the use of atelopeptidation and lyophilization technologies that modify the immunocollagen components of the bone grafting material to nonimmunogenic atelocollagen. In summary, procollagen (standard type 1 collagen) presents with N-propeptides and C-propeptides that are immunogenic to the human body (Fig 5-1a). Processing xenografts utilizing these technologies using pepsin or carboxypeptidase pepsin can either partially or fully remove the immunogenic C- and N-propeptides found on collagen, thereby removing its antigenicity (Fig 5-1b). Therefore, atelocollagen bone grafting materials preserve the natural properties of collagen within a graft, with roughly 30% atelocollagen type 1 remaining within the xenograft. This chapter presents preclinical research investigating atelocollagen xenografts and compares their results with deproteinized bovine bone grafts. Thereafter, clinical cases utilizing ABBM are presented accordingly.

Biologic Background

Graft fabrication

ABBM scaffolds containing atelocollagen type 1 are processed utilizing atelopeptidation and lyophilization technologies that modify the collagen components within bone structure to nonimmunogenic atelocollagen (ImploBone, BioImplon). This technique does not use heat (thermal) processing when manufactured, which has been shown to negatively impact the natural crystalline microstructure of hydroxyapatite, causing ceramization and destroying collagen components. The lyophilization technique involves the evaporation of water contained in a product by sublimation, in which a previously frozen material is placed in a vacuum that turns ice directly into vapor. This process preserves lyophilized collagen with lower humidity, making the bone matrix hydrophilic. These bone grafts contain roughly 2% moisture, 65% to 75% hydroxyapatite, 25% to 35% atelocollagen content, and up to 0.1% noncollagenous proteins (proprietary information). This differs from previously utilized deproteinized xenografts in that collagenous proteins may be found on the material surface² (Fig 5-2). The surface morphology of deproteinized bovine bone mineral (DBBM) show a roughened 3D surface with many micro-topographies and nanotopographies.³ High-magnification images of DBBM scaffolds, however, demonstrate that this roughened surface is completely devoid of all extracellular matrix proteins (see Fig 5-2e). The changes in processing procedures for ABBM are shown to increase the number of collagen fibrils present on the bone particle surfaces even at low magnification (see Fig 5-2b). At higher magnification, a number of collagen fibrils can be seen on the material surface resembling native collagen (see Figs 5-2d and 5-2f).

Effect of atelocollagen incorporation into xenografts in vitro

A series of cell studies was performed to compare DBBM (without collagen) to ABBM (with atelocollagen). It was found that ABBM significantly increased osteoblast attachment when compared to DBBM (Fig 5-3a). More impressively, however, atelo-collagen xenografts induced over a 200% increase in osteoblast proliferation when compared to DBBM (Fig 5-3b). Osteoblast differentiation markers were also significantly upregulated in the ABBM group when compared to DBBM (Fig 5-3c) and induced over a fourfold increase in mineralization potential when compared to DBBM as assessed by alizarin red staining (Fig 5-3d).

FIG 5-2 Scanning electron microscopy (SEM) of DBBM scaffolds without collagen (a to c) and ABBM scaffolds with atelocollagen (d to f) at magnifications of ×100 (a and d), ×400 (b and e), and ×1,600 (c and f). Notice the collagen fibrils found on the high-magnification images of ABBM particles (f; arrow in d and e). (Reprinted with permission from Fujioka-Kobayashi et al.²)

FIG 5-3 Results from preclinical research on osteoblasts show that cells attach better on ABBM (a) and proliferate significantly faster when collagen is present within the graft (b). An asterisk denotes a significant difference (P < .05).

FIG 5-3 (cont) (c) Furthermore, osteoblast differentiation markers including Runx2, collagen-1 (COL1), and alkaline phosphatase (ALP) were all signi ficantly upregulated on ABBM scaffolds due to their incorporation of atelo-collagen within xenografts. (d) Alizarin red staining was utilized to investigate osteoblast mineralization. Once...