The tensile strength of the medial patellofemoral ligament (MPFL), and of surgical procedures which reconstitute it, are unknown. Ten fresh cadaver knees were prepared by isolating the patella, leaving only the MPFL as its attachment to the medial femoral condyle. The MPFL was either repaired by using a Kessler suture or reconstructed using either bone anchors or one of two tendon grafting techniques. The tensile strength and the displacement to peak force of the MPFL were then measured using an Instron materials-testing machine. The MPFL was found to have a mean tensile strength of 208 N (SD 90) at 26 mm (SD 7) of displacement. The strengths of the other techniques were: sutures alone, 37 N (SD 27); bone anchors plus sutures, 142 N (SD 39); blind-tunnel tendon graft, 126 N (SD 21); and through-tunnel tendon graft, 195 N (SD 66). The last was not significantly weaker than the MPFL itself

Purpose The tensile strength of the isolated Medial Patellofemoral Ligament (MPFL) is unknown. The strength required of reparative or reconstructive procedures to re-constitute this major patella stabilising structure are therefore unknown. Method 10 fresh cadaveric right (6 female 4 male) knees, mean age 71.6 (SD 16.6) years, were prepared to isolate the MPFL between the patella and the Medial Femoral Condyle (MFC). The tensile strength and mode of failure were then determined. The ligament was then repaired using a suture and the tensile strength of this determined. The ligament was then reconstructed in three ways including: Biodegradable corkscrew anchors and two tendon techniques with interference screws. One method used a blind tunnel into the MFC, while the other passed through a tunnel in the femoral condyles. Both methods passed through tunnels in the patella. Results The mean ultimate tensile strength of the isolated MPFL was 207.9 (SD 90.1) Newtons. Seven specimens failed through a mid-substance tear while three pulled off the MFC. The mean strength of the suture repair was 36.7 (SD 26.5) Newton. The biodegradable bone anchor gave a mean strength of 142.3 (SD 38.5) Newton. The blind tunnel hamstring reconstruction’s had a mean strength of 126 (SD 20.8) Newton. The double tunnel hamstring reconstruction’s failed at a mean of 195.0 (SD 65.6) Newton. Conclusion The force required to rupture an isolated MPFL appears to be approximately 210 Newton. Suture repair is insufficient to reconstitute this. Reconstruction with bone anchors or hamstring tendon techniques come close to this

The purpose of this study was to clarify the effect of delay of the reattachment of the supraspinatus tendon into a bony trough to the strength of the repaired tendon-bone complex. The supraspinatus tendon of rabbits were transected and reattached into bony troughs at the greater tuberosity immediately and six weeks after transection. The tensile strength of the tendon-bone complex, harvested twelve weeks after reattachment, were measured. The tensile strength showed no difference between immediate and delayed reattached shoulders. Six weeks delay of supraspinatus tendon repair seems not to weaken the tensile strength of repaired tendon-bone complex. The purpose of this study was to clarify the effect of timing of surgery on the strength of the supraspinatus tendon-bone complex after the reimplantation of the tendon into a bony trough. In eight rabbits, the supraspinatus tendon was transected and reinserted into a bony trough at the greater tuberosity (early reattachment group). In seven rabbits, the supraspinatus tendon was reinserted six weeks after transection (delayed reattachment group). In both groups, the rabbits were sacrificed twelve weeks after reattachment, and the tensile strength of the tendon-bone complex was measured. The contralateral shoulders served as controls. None of the operated tendons failed at the site of reimplantation. The ratio of tensile strength of the operated tendon-bone complex to the controls showed no difference between two groups (Immediate reattachment group: 79.9± 1 S.E. 16.5%, delayed reattachment group: 80.4± 12.6%, P> 0.05). This is the first experimental study to compare the tensile strength of supraspinatus tendon-bone complex repaired after different time intervals. Stress-shielded tendon & bone tend to decrease their tensile strength. Given the six weeks duration of detachment, a weaker tensile strength of delayed reattachment group was expected than of the early reattachment group. The fact that both groups did not show a difference might be due to the recovery of tensile strength of tendon & bone in twelve weeks after reattachment. Six weeks delay of repair of supraspinatus tendon does not weaken the tensile strength of repaired tendon-bone complex. Fundings This study has been supported in part by a grant from the American Shoulder and Elbow Surgeons

Introduction. Demineralised Bone Matrix (DBM) is widely used in Orthopaedics and dentistry as a bone graft substitute and may be used to augment bone formation in load bearing applications. In this study we examine the effect of gamma irradiation and freeze drying on the tensile strength of Demineralised Cortical Bone (DCB). Methods. Tibias were harvested from mature ewes and cut into bony strips. Demineralisation was done using 0.6M HCL and confirmed by X-ray. Specimens were washed until a pH of 7.0 +/_ 0.2 was achieved in the washing solutions. Specimens were allocated into 4 groups; group (A) non freeze dried non gamma irradiated, group (B) freeze dried non gamma irradiated, group (C) non freeze dried gamma irradiated mention the level of gamma irradiation and group (D) freeze dried and gamma irradiated. The maximum tensile force and stress were measured. Statistical analysis using the Mann-Whitney U test was carried out. Results. The Median of maximum tensile force for group (A) was 218N, group (B) was 306N, group (C) was 263N and for group (D) was 676N. Group (D) results were statistically higher (p=< 0.05) compared to group (A) and (C), while there was no statistical significance compared to group (B). Conclusion. Previously published studies suggested the possibility of using DCB as ACL graft substitute. We examined the effect of gamma radiation as the most common sterilisation technique in medical field and the freeze drying as a possible technique for long term storage on the tensile strength of the DCB. Freeze drying significantly increases the tensile strength of the DCB while gamma irradiation has no significant effect. Our results indicate that freeze dried gamma irradiated DCB can be used as a ligament substitute

1. A series of experiments on the tensile strength of the anterior capsular mechanism have been performed. These show that in the young the weakest point is the glenoid labral attachment, whereas in the elderly calcification of tissues makes the capsule and subscapular tendon weaker. 2. It has been shown previously that glenoid labral detachment is the common injury in the young at the time of an acute dislocation, whereas capsular rupture and subscapularis tendon damage occur in the elderly. 3. These findings suggest that in an acute anterior dislocation of the shoulder the shoulder integuments give at their weakest point, and that it is the site of this weakest point and not the mechanism of injury which influences the liability to recurrence

Abstract

The April 2024 Research Roundup. 360. looks at: Prevalence and characteristics of benign cartilaginous tumours of the shoulder joint; Is total-body MRI useful as a screening tool to rule out malignant progression in patients with multiple osteochondromas?; Effects of vancomycin and tobramycin on compressive and tensile strengths of antibiotic bone cement: a biomechanical study; Biomarkers for early detection of Charcot arthropathy; Strong association between growth hormone therapy and proximal tibial physeal avulsion fractures in children and adolescents; UK pregnancy in orthopaedics (UK-POP): a cross-sectional study of UK female trauma and orthopaedic surgeons and their experiences of pregnancy; Does preoperative weight loss change the risk of adverse outcomes in total knee arthroplasty by initial BMI classification?

Purpose: Many different rotator cuff repairs have been advocated in previous publications without experimental evidence. Our aim was to mechanically test the static tensile properties and cyclical loading to failure of a single row lateral anchor repair and a double row medial and lateral anchor repair.

Method: Fresh frozen cadaveric shoulders were mounted on a rig and a mini-open deltoid split used to visualise the supraspinatus. A standardised full thickness incision of 2 cms was made with a scalpel across the supraspinatus tendon. After the deltoid was repaired and specimens randomised, an arthroscopic rotator cuff repair was performed by the two senior authors in which the medial border of the tear was apposed to the lateral border using either a double or single row technique with a ‘Twinfix AB’ suture anchor. Once the repair had been performed, the gross specimens were dissected down to the rotator cuff musculature and the repair inspected. Those with associated cuff pathology were excluded from the experiment. Specimens were then mounted on a custom made rig to statically load each tendon simulating physiological loading of a repaired cuff defect in a post-operative 300 abducted position. The increase in tear size was then measured against time for 1 hour or to a point at which the mean tendon gap formation exceeded 5mm. Each specimen was then transferred to an Instron tensile testing machine to cyclically load to failure the supraspinatus musculotendinous unit. Each specimen was freeze clamped proximally in a specially designed clamp, whilst the humeral shaft was mounted at an angle of 300 of abduction.

Results: The two groups had a distinct difference in tensile properties with the single row fixation developing a 5mm gap in under 30 minutes. After 1 hour, the gap formed in the double row specimens was less than 5mm. In cyclical loading, the single row failed at a lower load compared with the double row. In some double row specimens the tendon failed mid substance above 250N, rather than at the anchor-suture or suture-tendon interface.

Conclusions: Our results suggest that the double row mattress technique has superior loading properties when tested with a simulated physiological load comparative to the normal post-operative setting.

We examined macroscopically and microscopically 55 cadaver rotator-cuff tendons attached to their humeral heads to determine the distance between the edge of the articular cartilage and the tendon insertion of the supraspinatus (the width of the sulcus) and the score of regressive changes at the sulcus. In 33 specimens we measured the tensile strength. The width of the sulcus was correlated with the score of regressive changes and with the ultimate tensile strength of the supraspinatus tendon. The width of the sulcus correlated positively with the score of regressive changes (r = 0.66, p < 0.0001), but there was a negative correlation between the latter and the ultimate tensile strength (r = −0.81, p = 0.001) and between the width of the sulcus and the ultimate tensile strength (r = −0.74, p = 0.004). We believe that the width of the sulcus is a simple and useful clinical indicator of the integrity and the tensile strength of the supraspinatus tendon

This technique is a novel superior based muscle sparing approach. Acetabular reaming in all hip approaches requires femoral retraction. This technique is performed through a hole in the lateral femoral cortex without the need to retract the femur. A 5 mm hole is drilled in the lateral femur using a jig attached to the broach handle, similar to a femoral nail. Specialised instruments have been developed, including a broach with a hole going through it at the angle of the neck of the prosthesis, to allow the rotation of the reaming rod whilst protecting the femur. A special C-arm is used to push on the reaming basket. The angle of the acetabulum is directly related to the position of the broach inside the femoral canal and the position of the leg. A specialised instrument allows changing of offset and length without dislocating the hip during trialling. Some instrumentation has been used in surgery but ongoing cadaver work is being performed for proof of concept. The ability to ream through the femur has been proven during surgery. The potential risk to the bone has been assessed using finite analysis as minimal. The stress levels for any diameter maintained within a safety factor >4 compared to the ultimate tensile strength of cortical bone. The described technique allows for transfemoral acetabular reaming without retraction of the femur. It is minimally invasive and simple, requiring minimal assistance. We are incorporating use with a universal robot system as well as developing an electromagnetic navigation system. Assessment of the accuracy of these significantly cheaper systems is ongoing but promising. This approach is as minimally invasive as is possible, safe, requires minimal assistance and has a number of other potential advantages with addition of other new navigation and simple robotic attachments

Although autografts represent the gold standard for anterior cruciate ligament (ACL) reconstruction, tissue-engineered ACLs provide a prospect to minimize donor site morbidity and limited graft availability. This given study characterizes the ligamentogenesis in embroidered poly(L-lactide-co-ε-caprolactone) (P(LA-CL)) / polylactic acid (PLA) constructs using a dynamic nude mice xenograft model. (P(LA-CL))/PLA scaffolds remained either untreated (co) or were functionalized by gas fluorination (F), collagen foam cross-linked with hexamethylene diisocyanate (HMDI) (coll), or gas fluorination combined with the foam (F+coll). Cell free constructs or those seeded for 1 week with lapine ACL ligamentocytes were implanted into nude mice for 12 weeks. Following explantation, biomechanical properties, cell vitality and content, histopathology of scaffolds (including organs: liver, kidney, spleen), sulphated glycosaminoglycan (sGAG) contents and biomechanical properties were assessed. Implantation of the scaffolds did not negatively affect mice weight development and organs, indicating biocompatibility. All scaffolds maintained their size and shape for the duration of the implantation. A high cell viability was detected in the scaffolds prior to and following implantation. Coll or F+coll scaffolds seeded with cells yielded superior macroscopic properties when compared to the controls. Mild signs of inflammation (foreign-body giant cells, hyperemia) were limited to scaffolds without collagen. Microscopical score values and sGAG content did not differ significantly. Although remaining stable in vivo, elastic modulus, maximum force, tensile strength and strain at Fmax were significantly lower in the in vivo compared to the samples cultured 1 week in vitro, but did not differ between scaffold subtypes, except for a higher maximum force in F+coll compared with F samples (in vivo). Scaffold functionalization with fluorinated collagen foam provides a promising approach for ACL tissue engineering. (shared first authorship). Acknowledgement: The study was supported by DFG grants SCHU1979/9-1 and SCHU1979/14-1

Decellularised porcine superflexor tendon (pSFT) has been demonstrated to be a suitable scaffold for anterior cruciate ligament reconstruction[1]. While the role of collagen in tendons is well known, the mechanical role of glycosaminoglycans (GAGs) is less clear and may be altered by the decellularisation process. To determine the effects of decellularisation on pSFT GAG content and mechanical function and to investigate the consequences of GAG loss in tensile and compressive loading. pSFTs were decellularised following previous techniques [2]. For GAG removal, native pSFTs were treated with chondroitinase ABC (ChABC; 0.1U/mL, 72h). Cell and GAG removal was validated using histology and quantitative assays. Native, decellularised and ChABC treated groups (n=6) were biomechanically characterised. In tension, specimens underwent stress relaxation and strength testing using previous protocols [1]. Stress relaxation data was fitted to a modified Maxwell-Weichert model to determine time-dependent (E1 & E2) and time-independent moduli (E0). The toe and linear region moduli (Etoe, Elinear), in addition to tensile strength (UTS) and failure strain were determined from strength testing. In compression, specimens underwent confined loading conditions (ramp at 10 s-1 to 10% strain and hold). The aggregate modulus (HA) and zero-strain permeability (k0) were determined using previous techniques [3]. Data was analysed by one-way ANOVA with Tukey post-hoc test to determine significant differences between test groups (p<0.05). Quantitative assays showed no GAG reduction post-decellularisation, but a significant reduction after ChABC treatment. HA was only significantly reduced in the ChABC group. k0 was significantly higher for the ChABC group compared to decellularised. E0 was significantly reduced in the decellularised group compared to native and ChABC groups, while E1 and E2 were not different between groups. Etoe, Elinear, UTS and failure strain were not different between groups. Decellularisation does not affect GAG content or impair mechanical function in pSFT. GAG loss adversely affects pSFT compressive properties, revealing major mechanical contribution under compression, but no significant role under tension

Aims. This exploratory randomized controlled trial (RCT) aimed to determine the splint-related outcomes when using the novel biodegradable wood-composite splint (Woodcast) compared to standard synthetic fibreglass (Dynacast) for the immobilization of undisplaced upper limb fractures in children. Methods. An exploratory RCT was performed at a tertiary paediatric referral hospital between 1 June 2018 and 30 September 2019. The intention-to-treat population consisted of 170 patients (mean age 8.42 years (SD 3.42); Woodcast (WCG), n = 84, 57 male (67.9%); Dynacast (DNG), n = 86, 58 male (67.4%)). Patients with undisplaced upper limb fractures were randomly assigned to WCG or DNG treatment groups. Primary outcome was the stress stability of the splint material, defined as absence of any deformations or fractures within the splint during study period. Secondary outcomes included patient satisfaction and medical staff opinion. Additionally, biomechanical and chemical analysis of the splint samples was carried out. Results. Of the initial 170 patients, 168 (98.8%) completed at least one follow-up, and were included for analysis of the primary endpoint. Both treatment groups were well-matched regarding to age, sex, and type and localization of the fracture. Splint breakage occurred in three patients (3.6%; 95% confidence interval (CI), 0.007% to 0.102%) in the WCG and in three children (3.5%, 95% CI 0.007% to 0.09%) in the DNG (p > 0.99). The incidence of splint-related adverse events did not differ between the WCG (n = 21; 25.0%) and DNG (n = 24; 27.9%; p = 0.720). Under experimental conditions, the maximal tensile strength of Dynacast samples was higher than those deriving from Woodcast (mean 15.37 N/mm² (SD 1.37) vs 10.75 N/mm² (SD 1.20); p = 0.002). Chemical analysis revealed detection of polyisocyanate-prepolymer in Dynacast and polyester in Woodcast samples. Conclusion. Splint-related adverse events appear similar between WCG and DNG treatment groups during the treatment of undisplaced forearm fractures. Cite this article: Bone Joint J 2020;102-B(10):1405–1411

The suture properties associated with a successful tendon repair are: high tensile strength, little tissue response, good handling characteristics and minimal plastic deformation. Plastic deformation contributes to gap formation at a tendon repair site. Gaps greater than 4mm are prone to failing. This study investigates whether the plastic deformation demonstrated by two commonly used suture materials can be reduced by manual pre-tensioning. Twenty sutures of both Prolene 3/0 (Ethicon, UK) and Ethibond 3/0 (Excel, Johnson and Johnson, UK) were tested. Half of the sutures in each group were manually pre-tensioned prior to knot tying and half were knotted without pre-tensioning. All knots were standard surgical knots with six throws. The suture lengths were measured before and after a standardised cyclical loading regime on an Instron tensile tester. The regime was designed to represent the finger flexion forces produced in a typical rehabilitation programme. All sutures were subsequently tested to their ultimate tensile strength. After cyclical loading the pre-tensioned sutures demonstrated a mean increase in suture length of 0.7% (range 0.1-1.9%). The sutures not pre-tensioned showed a mean increase of 5.4% (range 3.3-7%). This equates to 87% less plastic deformation (p <0.05 Students' T-test) upon pre-tensioning. There were no differences with Ethibond. Pre-tensioning had no effect on ultimate tensile strength for either group. Manual pre-tensioning reduces plastic deformation in Prolene 3/0 sutures without affecting the ultimate tensile strength. This simple technique could theoretically diminish gap formation at the site of a tendon repair

Introduction. Successful tendon repairs are reliant on the suture material having high tensile strength, no or little tissue response, good handling characteristics and little elastic/plastic deformation. Plastic deformation contributes to gap formation at a tendon repair site. Previous research has shown a gap greater than 4mm is likely to fail. Pre-tensioning is a commonly used method to improve the handling properties of sutures. This study investigates whether the plastic deformation demonstrated by two suture materials used in flexor tendon repair is affected by manual pre-tensioning. Material/Methods. Twenty lengths of 3/0 Prolene (Ethicon, UK) and 3/0 Ethibond Excel (Ethicon, UK) were selected. Half of the sutures in each group were manually pre-tensioned (longitudinal stretch of 15N for 3s) prior to knot tying (standard surgical knot with six throws) and half were knotted without pre-tensioning. The suture lengths were measured before and after a standardised cyclical loading regime on a tensile tester. The regime was designed to represent the finger flexion forces produced in an active rehabilitation programme after tendon repair. All sutures were subsequently tested to their ultimate tensile strength. Results. After cyclical loading the Prolene sutures not pre-tensioned showed a mean increase in suture length of 5.4% (range 3.3-7%). The pre-tensioned Prolene sutures demonstrated a mean increase of 0.7% (range 0.1-1.9%). This equates to 87% less plastic deformation (p < 0.05 Students' T-test) with pre-tensioning. There were no differences with Ethibond. Pre-tensioning had no effect on ultimate tensile strength for either group. Conclusion. Manual pre-tensioning reduces plastic deformation in Prolene 3/0 sutures without affecting the ultimate tensile strength. This simple technique could theoretically diminish gap formation at the site of a tendon repair

Introduction: The suture properties associated with a successful tendon repair are: high tensile strength, little tissue response, good handling characteristics and minimal plastic deformation. Plastic deformation contributes to gap formation at a tendon repair site. Gaps greater than 4mm are likely to fail. This study investigates whether the plastic deformation demonstrated by two commonly used suture materials can be reduced by manual pre-tensioning. Methods: Twenty sutures of both Prolene 3/0 (Ethicon, UK) and Ethibond 3/0 (Excel, Johnson and Johnson, UK) were tested. Half of the sutures in each group were manually pre-tensioned prior to knot tying and half were knotted without pre-tensioning. All knots were standard surgical knots with six throws. The suture lengths were measured before and after a standardised cyclical loading regime on an Instron tensile tester. The regime was designed to represent the finger flexion forces produced in a typical rehabilitation programme. All sutures were subsequently tested to their ultimate tensile strength. Results: After cyclical loading the pre-tensioned sutures demonstrated a mean increase in suture length of 0.7% (range 0.1–1.9%). The sutures not pre-tensioned showed a mean increase of 5.4% (range 3.3–7%). This equates to 87% less plastic deformation (p < 0.05 Students’ T-test) upon pre-tensioning. There were no differences with Ethibond. Pre-tensioning had no effect on ultimate tensile strength for either group. Conclusions: Manual pre-tensioning reduces plastic deformation in Prolene 3/0 sutures without affecting the ultimate tensile strength. This simple technique could theoretically diminish gap formation at the site of a tendon repair

Summary Statement. A novel biomimetic polydioxanone tendon patch with woven and electrospun components is biocompatible, recapitulates native tendon architecture and creates a tissue-healing microenvironment directed by a subpopulation of regenerative macrophages. The woven component provides tensile strength while the tendon heals. Introduction. There is great interest in the use of biomimetic devices to augment tendon repairs. Ideally, implants improve healing without causing adverse local or systemic reactions. Biocompatibility remains a critical issue prior to implantation into humans, as some implants elicit a foreign body response (FBR) involving inflammation, poor wound healing and even fistulae formation. Additionally, the effect on articular cartilage locally or systemically with placement of a juxta-articular implant has not been examined. The purpose of this study is to test the in vivo biocompatibility of a novel hybrid woven and electrospun polydioxanone patch in a rat tendon transection model. Patients and Methods. Sixty Lewis rats were divided into 4 groups in which the infraspinatus was surgically transected 3 mm from its insertion. Tendons were repaired with a woven and electrospun polydioxanone patch (PDOe) and 5-0 Prolene sutures. Vicryl and Silk patches or a simple Prolene suture repair served as comparators. Animals were sacrificed at 1, 2, 4, 6 and 12 weeks to examine the biocompatibility of the implants. Immunohistochemistry was used to examine macrophage subpopulations and hematoxylin and eosin staining was used to assess foreign-body giant cells and both analyzed with a one-way ANOVA with significance set at p<.05. Articular cartilage was scrutinised with semi-quantitative analysis. Hind paw inflammatory indices were used to determine the systemic effects and biomechanical testing the tensile strength of the materials over time. Results. The PDOe patch remained grossly quiescent at all time-points. There was a severe inflammatory reaction to Vicryl at one and 2-week time-points with gross exudate. Silk patches were associated with larger fibrous capsules at each time point. There were no adverse systemic effects and articular cartilage remained normal with no differences between materials to controls. Immunohistochemistry showed a significantly higher ratio of regenerative to inflammatory macrophages for the PDOe patch compared to other constructs at each time-point and similar to controls. Silk and Vicryl patches had a greater than 10-fold increase in foreign-body giant cells compared to the PDOe patch and controls (p<.05) suggesting incorporation rather than rejection and walling off of the biomaterial. Tensile strength of the PDOe patch increased in the first 2 weeks to greater than 90 N and gradually declined to a mean of 22 N at 12 weeks. Discussion/Conclusion. The novel PDOe patch appears to be biocompatible and illicit very little FBR in this rat tendon injury model. Importantly, there was no joint reaction to the biomaterial which has not been addressed previously. We believe the electrospun component of the patch recapitulates native tendon architecture creating a tissue healing microenvironment directed by a regenerative macrophage subpopulation. These results corroborate earlier in vitro work that showed incorporation of tenocytes within the electrospun scaffold. The woven component of the scaffold provides tensile strength as the tendon heals and begins to degrade after healing is underway making it less likely to elicit a FBR. Based on these and earlier in vitro data we believe this implant shows excellent biocompatibility and is ready to proceed to human trials

Anterior cruciate ligament (ACL) reconstruction is the current standard of care for ACL tears. However, the results are not consistently successful, autografts or allografts have certain disadvantages, and synthetic grafts have had poor clinical results. The aim of this study was to determine the efficacy of tissue engineering decellularized tibialis tendons by recellularization and culture in a dynamic tissue bioreactor. To determine if recellularization of decellularized tendons combined with mechanical stimulation in a bioreactor could replicate the mechanical properties of the native ACL and be successfully used for ACL reconstruction in vivo. Porcine tibialis tendons were decellularized and then recellularized with human adult bone marrow-derived stem cells. Tendons were cultured in a tissue bioreactor that provided biaxial cyclic loading for up to 7 days. To reproduce mechanical stresses similar to hose experienced by the ACL within the knee joint, the tendons were subjected to simultaneous tension and torsion in the bioreactor. Expression of tendon-specific genes, and newly synthesized collagen and glycosaminoglycan (GAG) were used to quantify the efficacy of recellularization and dynamic bioreactor culture. The mechanical strength of recellularized constructs was measured after dynamic stimulation. Finally, the tissue-engineered tendons were used to reconstruct the ACL in mini-pigs and mechanical strength was assessed after three months. Dynamic bioreactor culture significantly increased the expression of tendon-specific genes, the quantity of newly synthesized collagen and GAG, and the tensile strength of recellularized tendons. After in vivo reconstruction, the tensile strength of the tissue-engineered tendons increased significantly up to 3 months after surgery and were within 80% of the native strength of the ACL. Our translational study indicates that the recellularization and dynamic mechanical stimuli can significantly enhance matrix synthesis and mechanical strength of decellularized porcine tibialis tendons. This approach to tissue engineering can be very useful for ACL reconstruction and may overcome some of the disadvantages of autografts and allografts

Abstract. Objectives. Direct ink writing (DIW) has gained considerable attention in production of personalized medical implants. Laponite nanoclay is added in polycaprolactone (PCL) to improve printability and bioactivity for bone implants. The 3D structure of DIW printed PCL/Laponite products was qualitatively evaluated using micro-CT. Methods. PCL/LP composite ink was formulated by dissolving 50% m/v PCL in dichloromethane with Laponite loading of up to 30%. The rheological properties of the inks were determined using Discovery HR-2 rheometer. A custom-made direct ink writer was used to fabricate both porous scaffold with 0°/90° lay-down pattern, and solid dumbbell-shaped specimens (ASTM D638 Type IV) with two printing orientations, 0° and 90° to the loading direction in tensile testing. The 3D structure of specimens was assessed using a micro-CT. Independent t-tests were performed with significance level at p<0.05. Results. The addition of Laponite in PCL ink has significantly enhanced viscosity for shape fidelity and shear-thinning property facilitating extrusion for DIW. Uniform distribution of Laponite was illustrated by micro-CT. For the 32-layer scaffold, interconnectivity of pores is observed at all 3 planes. The variation of height and width of layers is within 6% except the bottom 2 layers which are significantly lower and wider than other layers for mechanical support. For solid specimens, no ditches/interfaces between filaments are observed in 90° orientation while they are distinctive in 0° orientation because deposited filaments contact each other sooner in 90° orientation. 90° specimens also have lower air gap fraction (0.8 vs 5.4 %) and significantly higher Young's modulus (235 vs 195 MPa) and tensile strength (12.0 vs 9.5 MPa). Conclusions. The mechanical properties and printability of PCL/Laponite composites can be improved by controlling printing parameters; Micro-CT is an important tool to investigate the structure and properties of 3D printed products for bone tissue engineering