Considerations of growth factor and material use in bone tissue engineering using biodegradable scaffolds in vitro and in vivo

Bone tissue engineering aims to harness materials to develop functional bone tissue to heal 'critical-sized' bone defects. This study examined a robust, coated poly(caprolactone) trimethacrylate (PCL-TMA) 3D-printable scaffold designed to augment bone formation. Following optimisation of the coatings, three bioactive coatings were examined, i) elastin-like polypeptide (ELP), ii) poly(ethyl acrylate) (PEA), fibronectin (FN) and bone morphogenetic protein-2 (BMP-2) applied sequentially (PEA/FN/BMP-2) and iii) both ELP and PEA/FN/BMP-2 coatings applied concurrently. The scaffold material was robust and showed biodegradability. The coatings demonstrated a significant (p < 0.05) osteogenic response in vitro in alkaline phosphatase gene upregulation and alkaline phosphatase production. The PCL-TMA scaffold and coatings supported angiogenesis and displayed excellent biocompatibility following evaluation on the chorioallantoic membrane assay. No significant (p < 0.05) heterotopic bone formed on the scaffolds within a murine subcutaneous implantation model, compared to the positive control of BMP-2 loaded collagen sponge following examination by micro-computed tomography or histology. The current studies demonstrate a range of innovative coated scaffold constructs with in vitro efficacy and clearly illustrate the importance of an appropriate in vivo environment to validate in vitro functionality prior to scale up and preclinical application.

Successful centralisation technique for treatment of post-traumatic absence of the radial shaft in a dog

This report describes a centralisation procedure for the treatment of a radial non-union, characterised by extensive bone loss and an intact ulna, in an 18-month-old toy poodle. A lateral approach to the radius/ulna shafts was realised and, after debridement of the non-union site, an ulnar osteotomy was performed proximal to the styloid process of the ulna. Transposition of the distal fragment of the radius to the distal end of the osteotomised proximal segment of the ulna was performed and the stabilisation was obtained using a locking plate with proximal screws in the ulnar shaft and distal screws in the radius epiphysis. The patient achieved bone union in 10 weeks and the last evaluation, performed 112 weeks postoperatively, showed a full return to pre-injury function. Based on the results of this report, the centralisation was effective in the treatment of post-traumatic absence of the radial shaft in a dog.

Long-term outcomes of atrophic/oligotrophic non-unions in dogs and cats treated with autologous iliac corticocancellous bone graft and circular external skeletal fixation: 19 cases (2014-2021)

OBJECTIVES

To determine the short- and long-term outcomes and complications in dogs and cats undergoing surgical treatment for viable oligotrophic and nonviable atrophic non-unions using circular external skeletal fixation and autologous corticocancellous bone graft.

MATERIALS AND METHODS

In this case series, the medical records and radiographs of all dogs and cats with radius/ulna and tibia/fibula viable oligotrophic and nonviable atrophic non-unions treated with corticocancellous bone graft and circular external skeletal fixation at two referral veterinary hospitals between 2014 and 2021 were retrospectively reviewed. The long-term follow-up was 1 year or greater.

RESULTS

Thirteen dogs and six cats with 19 non-union fractures met the inclusion criteria for the study. Eighteen non-union fractures (94.7%) healed and one did not. Five patients (26%) had minor perioperative period complications (<3 months). The patient that did not achieve bone union underwent revision surgery with internal fixation (plate and screws) and autologous cancellous bone graft. Fifteen (78.9%) cases returned to full function and three (15.8%) cases returned to acceptable function in the long-term follow-up period.

CLINICAL SIGNIFICANCE

The use of circular external skeletal fixation associated with autologous corticocancellous bone graft for the treatment of radius/ulna and tibia/fibula atrophic/oligotrophic non-union fractures in dogs and cats was considered successful in the majority of patients and was free of major or catastrophic complications.

Long-Term Assessment of Bone Regeneration in Nonunion Fractures Treated with Compression-Resistant Matrix and Recombinant Human Bone Morphogenetic Protein-2 in Dogs

OBJECTIVE

 The aim of this study was to assess bone density, bone architecture and clinical function of canine nonunion distal appendicular long bone fractures with a defect treated with fixation, compression-resistant matrix and recombinant human bone morphogenetic protein-2 (rhBMP-2).

STUDY DESIGN

 Prospective cohort study with dogs at least 1-year post treatment. Computed tomography was performed and quantitative measurements from previous fracture sites were compared with measurements from contralateral limbs. Subjective evaluation included gait assessment and palpation.

RESULTS

 Six patients met the inclusion criteria. The rhBMP-2 treated bone exhibited higher density at the periphery and lower density in the centre, similar to the contralateral limb. All patients were weight bearing on the treated limb and all fractures were healed.

CONCLUSION

 The rhBMP-2-treated bone underwent restoration of normal architecture and density. Acceptable limb function was present in all patients. The results of this study can serve as a basis for long-term response in treating nonunion fractures in veterinary patients.

Case Report: Treatment of Femoral Non-union With Rib and Iliac Crest Autografts and rhBMP-2 in a Cat

A 5-year-old, intact male Bengal cat weighing 5.2 kg was referred for the fixation failure of a right femoral fracture. Multiple surgical revisions failed, and atrophic non-union was diagnosed. The cat was then admitted for a final revision surgery using locking plate fixation in conjunction with rib and iliac crest autografts and recombinant human bone morphogenetic protein 2 (rhBMP-2). The fracture site was debrided and stabilized before filling the defect with 1.8 cm of rib bone autograft. The residual space in the defect was then filled with an iliac crest autograft. Finally, a 3 ×5 cm absorbable collagen sponge soaked with 0.5 mL of 0.2 mg/mL rhBMP-2 solution was placed around the defect. No significant complications were noted postoperatively. Bone healing was noted 2 months postoperatively, and it continued for 12 months. Although mild lameness remained, the cat's ambulatory function and quality of life were good. To the authors' knowledge, this is the first case report of a clinical transplantation of a rib segment as an autograft in combination with rhBMP-2 in a cat with a large bone defect.

3D models of nonunion fractures in long bones as education tools

The appearance of fracture complications can present itself as a difficult scenario in a veterinarian's practice, and it can be difficult to diagnose and have a poor prognosis. The recognition of the different types of nonunion fractures can enable quick guidance on the best way to act, thus reducing the cost of treatment and the patient's suffering. The objective of this study was to create 3D models of nonunion fractures in long bones (3D NUFs). The study was carried out in three stages: 1) creating biscuit models from representations of nonunion fractures; 2) scanning the biscuit models of nonunion fractures and 3D modeling; and 3) printing and finishing the 3D models of nonunion fractures (hereafter, 3D NUFs). The creation of biscuit prototypes and the respective digitalization were decisive in producing 3D NUFs, which reproduced the main characteristics of each type of nonunion fracture classification described in the literature. It took 31.1 hours to create and print all 3D NUFs using 95.66 grams of filament (ABS) for a total cost of $3.73. The creation of 3D NUFs from the biscuit dough presented a new way of obtaining didactic models for the teaching of veterinary medicine. The 3D NUFs represent the different forms of low-cost manifestations that characterize this disease, which can be used as a possible teaching-learning tool for veterinary education.

Human placenta-derived matrix with cancellous autograft and demineralized bone matrix for large segmental long-bone defects in two dogs with septic nonunion

OBJECTIVE

To report the successful treatment of septic nonunion in two dogs with large segmental defects secondary to long-bone fractures by using a novel human placenta-derived matrix (hPM) as adjunct to fixation.

ANIMALS

One 3-kg 9-year-old neutered male Yorkshire terrier with a distal antebrachial fracture and one 6-kg 4-year-old spayed female miniature pinscher with a distal humeral fracture.

STUDY DESIGN

Short case series.

METHODS

Both dogs presented for septic nonunion after internal fixation of Gustilo type II open diaphyseal fractures from dog bite injuries. During revision, debridement of nonviable bone resulted in segmental defects of 32% and 20% of the bone length for the antebrachial and humeral fractures, respectively. The antebrachial fracture was stabilized with a circular external fixator, and the humeral fracture was stabilized with biaxial bone plating. The fracture sites were not collapsed, and full length was maintained with the fixation. Autogenous cancellous bone graft and canine demineralized bone allograft were packed into the defects, and hPM was injected into the graft sites after closure.

RESULTS

Radiographic union was documented at 8 weeks and 6 weeks for the antebrachial and humeral fractures, respectively. Both dogs became fully weight bearing on the affected limbs and returned to full activity.

CONCLUSION

Augmenting fixation with grafts and hPM led to a relatively rapid union in both dogs reported here.

Surgical Ectrodactyly Repair Using Limb-lengthening and Bone Tissue Engineering Techniques in a Toy Dog Breed

BACKGROUND/AIM

Bone tissue engineering is an emerging field of regenerative medicine that holds promise for the restoration of bones affected by trauma, neoplastic diseases, and congenital deformity. During the past decade, bone tissue engineering has evolved from the use of biomaterials that can only replace small areas of damaged bone, to the use of scaffolds in which grafts can be seeded before implantation. This case report proposes an alternative option for a veterinary patient suffering from ectrodactyly, which is one of several congenital deformities in dogs. A 2-month-old male toy poodle dog with ectrodactyly was treated using several stages of surgery involving pancarpal arthrodesis, limb lengthening, and bone tissue engineering techniques.

RESULTS AND CONCLUSION

Over a period of 2 years, the operated limb gained almost the same function as the contralateral limb. Bone tissue engineering techniques can be used for the treatment of congenital deformities in dogs.

Nanoscale Coatings for Ultralow Dose BMP-2-Driven Regeneration of Critical-Sized Bone Defects

While new biomaterials for regenerative therapies are being reported in the literature, clinical translation is slow. Some existing regenerative approaches rely on high doses of growth factors, such as bone morphogenetic protein-2 (BMP-2) in bone regeneration, which can cause serious side effects. An ultralow-dose growth factor technology is described yielding high bioactivity based on a simple polymer, poly(ethyl acrylate) (PEA), and mechanisms to drive stem cell differentiation and bone regeneration in a critical-sized murine defect model with translation to a clinical veterinary setting are reported. This material-based technology triggers spontaneous fibronectin organization and stimulates growth factor signalling, enabling synergistic integrin and BMP-2 receptor activation in mesenchymal stem cells. To translate this technology, plasma-polymerized PEA is used on 2D and 3D substrates to enhance cell signalling in vitro, showing the complete healing of a critical-sized bone injury in mice in vivo. Efficacy is demonstrated in a Münsterländer dog with a nonhealing humerus fracture, establishing the clinical translation of advanced ultralow-dose growth factor treatment.

Animal Models: New Biosensors and Technologies?Including Those for Bone Regrowth and Wound Healing?Advance Animal Health Care While Also Providing a Fertile Testing Ground for Human Health

Dogs have bad breath. But when Montana sheep rancher Katy Harjes noticed her collie, Hoshi, had particularly bad breath and facial swelling, she was concerned that the symptoms might be a sign of something serious. She was right; ten-year-old Hoshi had squamous cell carcinoma, a common type of oral tumor found in dogs. The cancer had not metastasized, but the damage was extensive enough that part of Hoshi's lower jaw needed to be removed. Luckily, Hoshi was a suitable candidate for a stateof-the-art bone regrowth procedure developed by Frank Verstraete, B.V.Sc, Dr.Med.Vet., M.Med.Vet., and Boaz Arzi, D.V.M., oral surgeons at the University of California (UC), Davis, School of Veterinary Medicine. Consequently, Katy and Hoshi embarked on a 15-hour road trip to California.